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ART PRO MPAArt Pro MPA-II Professional Two Channel Tube Microphone Preamp
The new ART ProMPA II is the next generation in affordable high performance microphone preamp technology. Each microphone input circuit, with selectable 48v phantom power, features variable input impedance which can radically vary the overall performance of any high quality dynamic or ribbon microphone. The ProMPA II can be configured for dual mono or stereo operation with selectable mid/side mic support, summing the adjacent channel, to decode left/right signals.

Brand: ART
UPC: 840402018360
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ART Pro MPA II Studio 2 Channel Tube Preamp


User reviews and opinions

Comments to date: 12. Page 1 of 1. Average Rating:
P. S. Topp 4:45am on Tuesday, October 26th, 2010 
I love the pen pad the size takes abit of getting used as I used the extra large size at work for several years but the medium is the perfect size for... 12:07am on Sunday, September 26th, 2010 
If you like drawing or painting or editing photos like myself,This my friend is for you! Yes it is a bit steep in price.
gxxmxx 7:34am on Saturday, September 25th, 2010 
Amazing Simply put, this tablet is amazing. I went from using the Intuos2 to this tablet and I was blown away. Wacom Rocks I have had Wacom tablets for years. This product is great. The drivers are always the easiest to install. Intuos 2 pen The pen works fine. The only complaint I have is that the nib sometimes is too short.
Jairo Pereira 5:27pm on Friday, September 17th, 2010 
"very nice and responsive, only downfalls are small screen for the price... these tablet pads seem to be a little pricy for what they are i think... "Ok im only 13 but still I recomend this!
abc 4:25pm on Monday, August 30th, 2010 
I normally use a headphones when I want watch movies because I hate disturbing others when watching movies late night. So.
FSapp 12:07am on Monday, July 19th, 2010 
This device its about....10=15% better in feel than a tablet. It will not solve your inability to make quality marks. I am a college student that is heavily into graphic and web design. This is my first pen tablet and I am positive I have made the right decision!
Ion 6:49pm on Wednesday, July 14th, 2010 
Pros: I must have researched for days and could not pass this one by! Makes fine adjustments a snap. Upgraded from years of mousework and finally see what the big deal was! Good Control","Natural Feel
wombolombo 4:49am on Tuesday, July 6th, 2010 
I have been using an Intuos 2 tablet for the ...  Spring loaded tip for digital designers looking to reduce hard clicks. I have been using an Intuos 2 tablet for the past 8 years (yes they were sold in 2002). From experience.
fleenorcu 12:33pm on Sunday, June 27th, 2010 
Wonderful blue tooth headphones for the price. Great sound quality, keeps sound out and very comfortable Last only about one year if used every day
cpaeas 7:22am on Saturday, May 15th, 2010 
"Great size. Not too big and not too small of an area to work with. I use it for touching up photographs on the computer and painting.
Patrickske 2:08pm on Friday, April 9th, 2010 
As posted in the weakness column they should change this stand a little so you can tilt this all the way up to 90 degrees so you can use it as a regul... Absolutely brilliant. I am using the display under MacOSX. Setting it up was a breeze - plug it in and install the drivers.
akilee 11:21am on Wednesday, March 17th, 2010 
This is my first Wacom. It is much nicer than my off-market tablet, and rightfully so, but I suppose I expected more luxury out of the price.

Comments posted on are solely the views and opinions of the people posting them and do not necessarily reflect the views or opinions of us.





ART PRO MPA II Microphone Preamplifier


This symbol, wherever it appears, alerts you to the presence of uninsulated dangerous voltage inside the enclosure. Voltage that may be sufficient to constitute a risk of shock. This symbol, wherever it appears, alerts you to important operating and maintenance instructions in the accompanying literature. Please read manual.
Read instructions: Retain these safety and operating instructions for future reference. Heed all warnings printed here and on the equipment. Follow the operating instructions printed in this user guide. Do not open: Aside from two vacuum tubes, there are no user serviceable parts inside. Refer any service work to qualified technical personnel only. Power sources: Only connect the unit to mains power of the type marked on the rear panel. The power source must provide a good ground connection. Power cord: Use the power cord with the mains plug appropriate for your local mains supply as provided with the equipment. If the provided plug does not fit into your outlet consult your service agent. Route the power cord so that it is not likely to be walked on, stretched or pinched by items placed upon or against. Grounding: Do not defeat the grounding and polarization means of the power cord plug. Do not remove or tamper with the ground connection on the power cord. Ventilation: Do not position the unit where the air required for ventilation is impeded. If the unit is to be operated in a rack, case or other furniture, ensure that it is constructed to allow adequate ventilation. Moisture: To reduce the risk of fire or electrical shock do not expose the unit to rain, moisture or use in damp or wet conditions. Do not place a container of liquid on it, which may spill into any openings. Heat: Do not locate the unit in a place close to excessive heat or direct sunlight, as this could be a fire hazard. Locate the unit away from any equipment, which produces heat such as: power supplies, power amplifiers and heaters. Environment: Protect from excessive dirt, dust, heat, and vibration when operating and storing. Avoid tobacco ash, drink spillage and smoke, especially that associated with smoke machines. Handling: To prevent damage to the controls and cosmetics avoid rough handling and excessive vibration. Protect the controls from damage during transit. Use adequate padding if you need to ship the unit. To avoid injury to yourself or damage to the equipment take care when lifting, moving or carrying the unit. Servicing: Switch off the equipment and unplug the power cord immediately if it is exposed to moisture, spilled liquid, objects fallen into opening, or the power cord or plug becomes damaged during a lightning storm or if smoke odor or noise is noted. Refer servicing to qualified technical personnel only. Installation: Install the unit in accordance with the instructions printed in the user guide.
Input Gain control..... 3 Input Impedance control..... 4 Low Cut Filter control..... 4 Gain switch..... 4 Phantom switch..... 5 Phase switch..... 5 Plate Voltage switch.... 5 Mid/Side Matrix switch.... 6 Analog Output control.... 6 STEREO/Dual switch..... 6 +4/-10 switch (rear panel).... 7 Meter Trim.... 7
Front Panel connections.... 7

Instrument Inputs.... 7

Rear Panel connections.... 8
Balanced Inputs..... 8 Balanced Outputs..... 8

Obtaining the best noise performance with the PRO MPA II... 9 Adjusting the Input Impedance..... 9 Setting the Tube Plate Voltage.... 10 Using the Mid/Side mode.... 11
Limited Warranty..... 12 Exclusions..... 12
List of Figures Figure 1 Block Diagram.... 2 Figure 2 Front controls... 3 Figure 3 Rear connections.... 8 Figure 4 Mid/Side Mic alignment... 11
The ART PRO MPA II microphone preamplifier features a new low noise, high performance preamplification circuitry, designed for superior audio fidelity. Building upon the quality and success of great sounding products like the Pro MPA and MPA GOLD, ART engineers set out to develop the next generation of professional microphone preamplifier. PRO MPA II is the culmination of years of research and development, and sets a new standard for quality and value. Professional features and spectacular tone are what make the PRO MPA II a world-class microphone preamplifier. Its impressive feature set includes:
Variable input impedance for flexible microphone voicing (150 Ohms to 2400 Ohms). Selectable plate voltage Large VU meters Front accessible meter trim Discrete class A input microphone preamplifier Low noise at low gains Low THD Wide frequency response Front accessible Instrument Input Jack Very high input impedance Mid/Side micing support +4dBm/-10dBV output level selection Switch selectable Stereo/Dual operation of the output controls Automatically switches to the instrument input when you plug in
The signal path of PRO MPA II consists of a discrete class A microphone pre-amp followed by a Low Cut Filter, a balanced differential tube circuit with a 20dB Gain switch and then the phase switch. The Mid/Side Matrix switch sums the adjacent channel to decode left and right information following the gain switch function and before the output level control. The Tube Warmth display monitors the signal level before the output level control as well. The analog meter monitors the output level of the PRO MPA II before the +4/-10 switch but after the output level control. The PRO MPA II is an attractively styled processor, with a black anodized front panel and matching knobs. The switches on the PRO MPA II are backlit and illuminate when depressed.

Figure 1 Block Diagram


Figure 2 Front controls

Input Gain control This control optimizes the input signal level before the tube gain is applied. Both Microphone and Instrument input gains remain the same and are affected by this adjustment. Input gain can be adjusted from 0dB (for line level signals) to 40dB of gain.
The analog meters are used to see the effects of the input gain setting.
Additional gain is available via the Gain switch (+20dB) and the Analog Output control (+10dB) for a maximum of 70dB total.
The combination of these controls allows the user to adjust the signal level through the tube section, providing more or less tube sound as needed. To obtain more tube sound, increase input gain, use the +20dB Gain switch, normal plate voltage, and less Analog output gain.
Both the microphone and instrument inputs are optimized for their respective sources as far as signal levels and noise performance. Running most of the gain on the input generally provides the best performance of the PRO MPA II. Refer to the section titled Obtaining the best noise performance
with the PRO MPA II for more detailed instructions on setting the Input Gain control for the best results.
Input Impedance control This knob controls the Mic/line input amplifier impedance. This function allows variable voicing of any microphone.
Refer to the application section titled Adjusting the Input Impedance for more information on making the most of this function.
The instrument input is NOT affected by this control, and remains high (>1M Ohm) impedance.
Low Cut Filter control The Low Cut Filter is a single tuned High Pass Filter that is frequency tunable. The input signal can be filtered to remove pops or other extraneous low frequency information. This control moves the rolloff frequency from 10 Hz (fully CCW) to 200 Hz (fully CW). Since it is single tuned, it preserves some low frequency content so its use is less obtrusive. It is especially useful in close micd applications.
Gain switch The Gain switch is used in conjunction with the input gain control to adjust signal levels through the PRO MPA II. When depressed, the tube circuit provides 20dB more gain in the signal path. This also has the effect of driving the tube harder and making the tube the dominant source of gain and overload character.
Phantom switch Phantom power on the microphone input is turned on and off with this switch. Depressing the switch will power condenser microphones and other 48volt phantom powered devices. Phantom power is supplied to pins 2 and 3 of the input jack.
NOTE: 1) Dynamic microphones are NOT affected by Phantom power, although it should be turned off when using dynamic microphones or line level inputs.

2) Although the 48volt phantom power ramps up and down slowly it may still create a pop. Mute the output of the PRO MPA II when engaging or disengaging phantom power to prevent damage to equipment following the PRO MPA II.
Phase switch The Phase switch can invert the phase of the audio signal path in either channel. The Phase switch is located after the tube circuit in the signal path, so you can hear slight differences between different phase selections in the normal plate voltage mode near saturation. There are a number of reasons why adjusting the phase is needed these include, wiring errors and inversions in some audio equipment. Some microphones sound different depending on the phase chosen.
If two microphones are out of phase, they may cancel at various frequencies (depending on the distance between them). If this happens, try changing the phase of one of the microphones and see if there is an improvement.
Plate Voltage switch This switch sets both the tube bias point and the plate voltage level the balanced differential tube circuit runs at. The amount of headroom is adjusted by using the Gain switch and the input Gain control. The PRO MPA II takes about 10-30 seconds to smoothly transition from one mode to the other. There is a slight increase in gain in the High plate voltage mode.
In the normal (OUT) position, the tube distortion gradually rises until it smoothly clips. The tube is run almost completely open-loop in this mode, providing a musical tube crunch when overdriven with a natural recovery from clipping. The tube section can be more easily overdriven when the gain switch is in. This mode brings out the harmonics in the input sources, particularly stringed instruments.
The tube circuit runs extremely clean in the high (IN) position of the plate voltage switch. As signal levels rise distortion remains very low until within 6dB of clipping, where the overload characteristics smoothly limit the signal swing. There is increased bandwidth (>100KHz), and headroom in this mode as well.
Mid/Side Matrix switch The Mid/Side Matrix switch is used to decode Left/Right information when using two mics aligned for stereo recording. You can use either two figure-eight pattern mics or one omni-directional and one Figure-eight mic. Refer to the APPLICATIONS section titled Using the Mid/Side mode for more info on how to apply this function with your mics.
Analog Output control The output signal level at the rear output jacks is adjusted by this control. It can provide from +10dB of gain (fully clockwise) to completely muted. You can see the effects of this adjustment reflected in the analog meters.
STEREO/Dual switch The STEREO/Dual switch selects the operation of the output control knobs. Stereo mode gains and operation are marked with reversed out text.
In Stereo mode, CH1 output adjusts the output gain of both channels and CH2 output control acts as a power summed Balance control. There is a slight drop in output level in stereo mode when the Balance knob is centered vs. at one extreme or another.

When the switch is in the Dual position the output controls act on only their respective channels. +4/-10 switch (rear panel) The +4/-10 switch is used to set the output level of the PRO MPA II for the appropriate system levels. This feature allows you to match 0 VU on the meters of the PRO MPA II and your mixer or other equipment. When depressed, 0 VU on the output meter corresponds to +4dBu on the outputs. In 10 mode, the output level measures 10dBV. Meter Trim The Meter Trim is used to adjust the Meters 0 point when. This may change if the unit is NOT mounted with the front panel perpendicular to the floor. Using a small flat-blade screwdriver you can mechanically fine-tune the meter indicator position if, for example, it does not rest at the leftmost position when the unit is OFF. Adjustments for feedback readings, when the unit is in use, are internal and are not user serviceable.

Front Panel connections

Instrument Inputs The jacks on the front panel serve as an instrument input. The input impedance is always >1M Ohm and the gain can be adjusted by the Input gain control. The maximum input signal level is +17dBu (5V RMS) @ minimum input gain.
When you plug into this jack it DISABLES the balanced input on the rear of the unit. This feature allows you to keep the rear input patched in, and use the instrument input to switch to a different source. The instrument input allows the PRO MPA II to serve as a great DI device as well.

Rear Panel connections

Figure 3 Rear connections
Balanced Inputs The PRO MPA II s XLR connectors follow the AES standard of Pin 1 = Ground, Pin 2 = Hot (+), Pin 3 = Cold (-). The Balanced inputs have an input impedance that is variable from 150 to 3K Ohms via the front panel control. The Maximum input level is +19dBu balanced and +17dBu unbalanced.
Balanced Outputs The PRO MPA II s flexible active balanced outputs are available on both and cannon connectors. They offer low impedance for driving long cable runs and are intelligent enough to maintain the same output level weather it is balanced or unbalanced.
The PRO MPA II s XLR connectors follow the AES standard of Pin 1= Ground, Pin 2= Hot (+), Pin 3= Cold (-). The balanced phone jacks are typical Tip = Hot (+), Ring = Cold (-), Sleeve = Ground Maximum output level is +27 balanced and +20 unbalanced.

Obtaining the best noise performance with the PRO MPA II
Start by turning down the Input Gain knob and centering the Analog Output knob. Use the analog meter to view the operating level by depressing the switch under the center of the analog meter. The meter will now indicate how much tube headroom there is. Set the +20dB switch to the out position.
Increase the Input Level knob until the meter reads above 10dB.
If you have turned the input knob fully clockwise and the indicated level is still below 10dB on the meter, center the input knob and depress the Gain switch. Increase the Input Gain until there is sufficient level. This procedure optimizes the gain elements to provide the widest dynamic range possible.
Adjusting the Input Impedance
The same microphone can sound different on various pre-amps. One reason is that every pre-amp presents a different load to on its input, some even change as gain is changed! Our third generation discrete front end was designed to be absolutely transparent. Every nuance of the microphone is maintained providing detail masked by inferior pre-amps. The Input Impedance control is one key element in providing new versatility in voicing microphones.
NOTE: the Input impedance control only affects the cannon connector inputs. The instrument input on the front panel is NOT affected by this control in any way. The instrument input impedance is ALWAYS >1M Ohm.
Dynamic microphones are affected as much as phantom powered units.
We provide a continuously variable impedance control to allow you to fine-tune the voicing, finding the perfect interaction between microphone and pre-amp.
Start by setting the centering the Input Impedance knob. This provides a 600-Ohm load.
Lower impedance loads will reject more noise picked up by cabling, and dampen microphone resonance.
Higher impedance settings provide a more open sound. Lower impedances tend to focus the sound more.
Setting the Tube Plate Voltage The PRO MPA II allows the user select between one of two vastly different tube bias and power supply levels. The transition between either setting is smooth and quiet and the gain variation is minimal.
NOTE: It takes 15-30 seconds for the tube circuit to fully transition between either mode. During this time, the unit passes a signal and the only noticeable change is a slight increase in level in the HIGH setting.
The Warm setting produces a smooth transition from very clean low levels up to a round saturated clipping on peaks. This setting is reminiscent of old tube gear, and used to get the most tube-like sound out of the unit. Common uses include tracking with instruments.
The High setting of the plate voltage switch has increased bandwidth and headroom, very low distortion and runs extremely clean until it reaches a point of saturated clipping. The clipping is well controlled and still sounds natural. This setting is incredible on vocals.

Using the Mid/Side mode The PRO MPA II is designed for stereo operation using the Mid/Side switch and two microphones. One of the mics needs to have a figure-8 pickup pattern. Start by aligning two mics 90 degrees apart. Connect the mic facing front (with an omni-directional or cardiod pickup pattern) to CH1. Face the front of the figure-8 pickup mic to the left side and connect it to the CH2 input. Depress the Mid/Side Matrix switch and center both of the Output Gain controls. Adjust the Input gain controls to such that both meters show the same level with a sound source at least two feet in front of the forward mic. The CH1 output is now the Left channel and the CH2 output is now the Right channel. Adjust the Output gain controls as needed for your system level.
Figure 4 Mid/Side Mic alignment


Limited Warranty
Applied Research and Technology will provide warranty and service for this unit in accordance with the following warrants: Applied Research and Technology (A R T) warrants to the original purchaser that this product and the components thereof will be free from defects in workmanship and materials for a period of three years from the date of purchase. Applied Research and Technology will, without charge, repair or replace, at its option, defective product or component parts upon prepaid delivery to the factory service department or authorized service center, accompanied by proof of purchase date in the form of a valid sales receipt.
Exclusions This warranty does not apply in the event of misuse or abuse of the product or as a result of unauthorized alterations or repairs. This warranty is void if the serial number is altered, defaced, or removed. A R T reserves the right to make changes in design or make additions to or improvements upon this product without any obligation to install the same on products previously manufactured. A R T shall not be liable for any consequential damages, including without limitation damages resulting from loss of use. Some states do not allow limitations of incidental or consequential damages, so the above limitation or exclusion may not apply to you. This warranty gives you specific rights and you may have other rights, which vary from state to state. For units purchased outside the United States, an authorized distributor of Applied Research and Technology will provide service.


The following information is provided in the unlikely event that your unit requires service. 1) Be sure that the unit is the cause of the problem. Check to make sure the unit has power, all cables are connected correctly, and the cables themselves are in working condition. You may want to consult with your dealer for assistance in troubleshooting or testing your particular configuration. 2) If you believe the ART unit is at fault, go to You may contact Customer Service for more assistance, or directly request a Return Authorization for service in the resources area of the website. 3) If you are returning the unit for service, pack the unit in its original carton or a reasonable substitute. The original packaging may not be suitable as a shipping carton, so consider putting the packaged unit in another box for shipping. Print the RA number clearly on the outside of the shipping box. 4) Include, with your unit, a note with the RA number and your contact information including a daytime phone number, preferably attached to the top of the unit.
Frequency Response.. 15Hz to 48 kHz (+0, -1dB) @ normal plate voltage 15Hz to 120 kHz (+0, -1dB) @ high plate voltage Dynamic range:.. >110dB (A weighted) CMRR:.. >90dB THD:... <0.005% (typical) Equivalent Input Noise:.. -129dBu (XLR, A weighted) Maximum Input Level:.. +19dBu (cannon) Maximum Instrument Input:. +17dBu Input Impedance.. 150-3000 Ohms adjustable (XLR) >800K Ohms (Instrument) Maximum Output Level.. +27dBu (XLR) Output Impedance:. < 47 Ohms (XLR) Maximum Gain.. 70dB
Meter Calibration.. 0 VU = +4dBu output (+4dB mode) 0 VU = -10dBV output (-10dB mode)
High Pass Filter.. single pole, 10-200 Hz adjustable
Power Requirements:.. USA 105 to 125 VAC / 60 Hz Export units configured for country of destination.
Dimensions:.. 3.50 H x 19.0 W x 8.75 D Weight:.. 10.5 Lb.

NOTES: E-mail:
PRO MPA II Microphone Preamplifier



Thank you for purchasing the Vinktronic Labs ART Pro MPA Tube Microphone Preamplifier. I have been studying tube design and theory for 25 years. This piece is the result of many years spent modifying, altering, studying and tweaking different pieces of new and vintage tube equipment. I have designed this piece to be user adjustable when creating the subtle harmonic distortion characteristics that many listeners and recordists find desirable. It emulates many of the different vintage tube processors of the early days of music recording. This machine however, allows you to adjust the harmonic distortion, dynamic equalization and non linear gain limiting by use of 2 stages of tube preamp redesigned with a unique circuit using constantly variable controls to carefully tweak the sound character. It has also has improved signal to noise ratio that modern recording studios require for microphone or line level preamping (the unit has been converted to be used at line level for audiophiles and final mixing in a studio). Please take a minute to read through this manual before using the preamp so you can get the best use out of this piece. I will also explain a little theory of harmonic enhancement and dynamic equalization as it applies to affecting the tonal quality of musical signals when the total audio volume is changing. As an overview, I will admit the preamp has been voiced for semi-professional home recording studios, where the musician is using a stereo pair of quality microphones, small or large diaphragm condensers with wide bandwidth and expecting to capture a very analogue sound field. The device can also be used as a single channel preamp, but its capability in offering 2 well matched channels of vintage character can create a remarkable stereo recording. The preamp is not flat in frequency response or super low distortion. It is attempting to mimic a vintage sound the ear likes to hear, but also creating a slight characteristic of dynamic sound equalization for mechanical transducers when capturing the sound waves. As an anecdotal point, microphone capsules shouldnt necessarily be round, or square, but perhaps oval-like in shape to accommodate hearing patterns and to reduce foil plate resonances within the diaphragm itself. Such a microphone would probably have a slight natural equalization of audio which accommodated the fact that it is a mechanical transducer. Specifically, good microphones should have no narrow pass band resonances (peaks in the response), but in many cases (especially near field micing) it is acceptable for the mic to have slight bass or presence enhancement. Infact many microphones do, and the equalization/harmonic switches attempt to accommodate many microphones.


1 - Plug in the microphone. It will be positioned when everything set up to be at a distance from the instruments of which the gain and level controls are somewhat at way to way up to produce a professional 0 dbm signal level out, as shown by the MPA
meter. Be aware the output signal level of the MPA may be too high the expected signal level input of many semi pro processor devices such as reverbs or equalizers. Their input levels may require to be turned down. I have not encountered a situation yet where real pro equipment cannot take the true 0dbm level output with peaks of dynamics at +14db (the unit intentionally limits more excessive signals above +6db mostly though only on complex signal or severe transients). 2 - Let the unit warm up at least 5 -10 minutes. 3 - Switch on the 48 volt phantom if required by the microphone. Also 5 minute warmup. 4 - Microphones can be placed a little further back than typical as the preamp has a different way it preamplifies and slightly gain rides the signal with harmonic and equalization enhancement. Close micing is acceptable though as there is plenty of dynamic headroom available. In my preamp circuit it is virtually impossible to overload the gain stages unless the LED or meters are totally continually maxed out. This situation will nonetheless create a usable soft overdriven tube sound which some original owners of prototypes liked for certain effects, such as stressing a sense of sonic urgency on vocals or bass, so this effect is left in but lessened on this newer audiophile version. In general however omni-directional mics work better for close field micing (6 to 3) picking up sound all around the instrument and cardiods work better 2 to 6 feet away, as they focus on musical sounds which are mostly in front of the mic capsule.


1 - Set the INPUT GAIN as high as possible to affect the tube LEDs to run near the red when playing an instrument at the loudest volume. a- When the LEDs are running in the red, you will get more tube saturation/ analogue tape character, as the tube circuit now truly allows a soft symmetrical tube limiting of strong dynamics and peaks. Very few tube circuits actually do this. Most designs clip somewhat asymmetrically and impart a sonic fussy grit to the signal. With my unit, more desirable 2nd and less 3rd harmonics are created, but this is gain limited so as not to cause an obvious fuzzy tube distortion when excessive signal is present. Again I feel it is better to create a little soft limiting of dynamics rather than soon clip the audio at a higher level. b- When the LEDs are running under the red, the circuit will produce more 2nd harmonic presence which is adjustable in phase and equalization by the tube cathode bias control (adjustment will be explained later). c- When the LEDs are running low (in the green/orange area), it will give a more clean sound with virtually no 3rd harmonics added to the music. In general, the distortion now is mostly predominated by 2nd and 4th harmonics, but as will be discussed later, this is adjustable as in phase or out of phase harmonics of the original audio signal. These preferred harmonics at lower level are gain ridden up to provide a more obvious tube thickness and presence depending upon use of cathode bias and equalizer controls. This is the subtle but important sonic effect which can be heard by listeners as the tubes are warm yet detailed sound but now at low signal levels far away
from the overdriven tube effect creating a sonic texture very much more euphonic on a wide range of recording situations. This is a crucial design criteria which sets my unit apart from most modern units. Some vintage preamps and compressors were able to achieve this but did not have enough adjustment versatility. As an anecdotal point, Ive encountered too many modern designs which are inconsistent to deliver this effect. The same model will seldom create this effect consistently or at all (especially with aging use), hence the wide range of users opinion of what they hear. This is due to subtle differences in aging circuits, power supplies and especially tube selection as it applies to a particular circuit design. It is important to note here and break the myth that certain name tubes are better or worse, but really from an engineering standpoint it is the actual circuit design which will determine the tubes performance to create the euphonic second harmonic trick. There are good and bad tubes past and present. People should not be so compulsive about a brand name, especially now that some modern 12AX7 are so good. My circuit is designed to be capable to adapt a part or two and then accommodate a wide range of tubes if necessary, more manufacturers should do this. From a personal perspective, Ive seen countless expensive tube designs which were running really poor but the user thought it was great, until I fixed it correctly and then was told, Wow I didnt know it was supposed to sound this (better) way!.


1 - Set the output control so the VU meters hit or go above the 0db mark. 2 - When the OUTPUT CONTROL is set higher and the meter is reading into the +0 to +3 region (it is OK to pin the meters occasionally) a slight volume leveling will start to occur. This gives instruments a fuller, more forward sound, although slightly compressed, the deep bass impulses and high frequency transient peaks will not be reduced as much or lose clarity. More high frequency harmonics are added and the middle range will be more controlled, slightly veiled with presence. This is not a simple compressor. It is a subtle logarithmic level reduction of volume of sonics, as well a slight gain riding of lower level signals keeping the tube sonic effect present. It also does not compress the lows and highs as much as the midrange, trying to approximate the loudness equalization that a human ear/brain perceives. The meter circuit electronics and needle movement calibration are part of the tube harmonic gain riding effect and actually forcing the tube to maintain 2nd harmonics from the tube at -20db and less at 0db level. This is the most important trick my MPA does. Again it is important to note my design forces the tube to create a truly pleasant tube 2nd harmonic distortion at lower levels (-20db) as opposed to most circuits whereby the tube must be driven to near clipping to get a tube stressed character. Use of the cathode bias control forces the tube to create in phase harmonics and warming up the sound character or adjusting out of phase harmonics from the tube will affect a slight presence or sparkle to the detail of music. No need to overdrive the tube. More control to enhance low level signals which create a bigger, richer sonic image to the ear.


When this switch is pushed in it will boost the overall gain throughout the unit, giving a more forward, thicker powerful sound. When the switch is out, a gain matching and equalization circuit is turned on. This will give the impression that the mics have been moved farther away from the instruments and the gain has been automatically turned down. This circuit also attempts to phase correct and equalize the mic signal tonal quality to be more distant but still big sounding. Admittedly this is my perception of what sounds good to me, when using wide bandwidth microphones placed in an intimate (2 to 6 ft. mic position) set up or remixing an audio track which seems too forward. The sonic picture will be more laid back. An anecdotal point here to make is that many older mics (well respected and much recommended but not necessarily the most honest sounding) will not have the true wide bandwidth which I feel is important to create a natural soundscape. Many of these older mics were design for close field recording and even the most famous names do not have bass bandwidth down to 30-60 cycles or past 12-14 kHz. Sorry to say many of the new generation of an Asian made mics are remarkable in dynamic range and audio bandwidth. When older mics are placed close the bass predominance effect and treble clarity will be more apparent. This was part of their design criteria. They can take high signal levels and the mic elements have clarity a high SPL. Where as the more modern efficient mics with wider band width and dynamic range appear to blur up a little at close micing but sound incredibly clean at a little more distance. Actually some of this mic distortion is really the mic preamps within the mic itself slew limiting or clipping. I admit I prefer to get the microphone a little further away now that the mic can hear more completely the whole instrument. I have tried to allow controls to adjust for either use. This is a sonically dryer and thicker sound and will sound excellent when processed through a good reverb. Move the input or output controls to make up gain if necessary.


The Harmonics equalization switch is a 3-position toggle switch. Each position affects the general tonal balance and somewhat the tube compression of sound. Each position will alter the compressor tracking and affect a slight timbre change of the music. a- The up position is good for close micing with older warm sounding mics. It gives the impression of the mics being moved back but keeping brightness or detail. If the mic or instrument is too fat this will balance out the tone quality and lessen mic predominance effects of reducing the bass, accenting the high frequency content. Especially use full equalization for ribbon microphones. b- The middle position is good for lead instruments or vocals. The harmonic equalization circuit keeps the sonic information strong and forward and the most natural setting, flat frequency response, less gain riding of high and low sonics. This is probably the best setting for ensemble instrument recording or remix of stereo program (I use an MPA on my CD player). c- The down position is good for near field mics which are too noisy or have too much presence (close micing of piano, acoustic guitar and other acoustic 4
instruments). It allows the low and midrange harmonics to dominate but still keeps detail in the high frequencies. This is the warmer setting of the preamp. Very useful on microphoning with bright mics or music which is too edgy or strident. It is also my opinion of the warm tube sound and works best when recording in bright rooms or instruments which are naturally too bright. Drums, reed instruments, voice and 12 string guitar can now sound very rich in harmonics with out the edgy or strident quality.


This control affects the bias and gain of the tubes and creates the harmonic distortion being introduced into the signal path by adjusting the DC cathode bias and gain of the two stages of tubes. aStart with the bias control in the middle position. This gives a fairly neutral tube character to the sound, only a slight amount of tube character with typical gain a tube would want. Probably preferable when complex or harmonically already rich musical information is passing through. bTurning the control to the right (clockwise) will add more in phase 2nd harmonics. This will give a velvety, slightly veiled sound character ideal for use on bright mics, guitars, pianos and vocals. Creating about 2% 2nd harmonic distortion with the control at the maximum setting. Sometimes perceived as a dryer sound. aTurning the control to the left (counter-clockwise) will add more out of phase 2nd harmonics. This will thicken the bass and midrange with more edge to the sound character or presence to guitars and voice. This effect will be subtle, the more complex the overtones the more obvious the effect will be. The control will create up to 2% harmonics at extremes of knob position. No other device I know of allows the user to vary the strength of harmonic enhancement, to be in phase or out of phase, with attendant equalization, and a subtle gain riding of those harmonics. Remember too the harmonics are naturally part of and created only from the original musical signal passing through the circuit. If the signal level becomes louder, the ratio of harmonic in my circuit design will stay about the same, as opposed to other designs where louder signals get the tube to sound dirtier or be missing at low signal levels.

Do not be afraid to experiment with different settings. All the controls on the front of the faceplate are always live. Try different combinations of control settings. Combinations of mics, placement and instrument will create a myriad of different sonic characters.
Example: The harmonics switch in the up position and the bias control turned to the left (clockwise) will give an edgy or sparkling sound. Very desirable on voice and acoustic guitar, especially to push them forward in the mix. Do not be afraid to run the meters hot. At +1db/+3db meter swing is typical of peak signals. Again the unit will self limit to reduce overloading of the next device (mixer, reverb) connected to the MPA output. The logarithmic compressor, dynamic equalizer is designed to be only slightly obvious, but admittedly I have voiced it to work well with large plate diaphragm mics at midfield placement. 1 to 3 feet away from guitars voice, maybe 3 to 6 feet away from piano or drums. The compressor is similar in some ways to an RCA BA6 (Teletronics) design and attempts to slew limit the audio signal so as not to cause digital conversion distortion (slew rate limiting) problems. All digital converters regardless of price or manufacturers claims slew limit above 4kHz. 96kHz sample rate improves the slew rate whereby slew limiting starts to occur at 8kHz to 12kHz. Oddly most speakers or people truly cannot hear this problem but reverbs algorithms suffer obviously, if you listen very carefully. Another unique feature on the modified MPA is the variable predominance filter. This circuit has been altered to be more phase correct and truly filters bass dominating the sound when using mics placed close to instruments. My circuit maintains a more phase correct bass even when attenuating, dipping out the bass muddiness, and less extreme deep bass, and pluck is also not lost. To be honest, Im surprised more designers have not figured out this trick. Its effect is very obvious to a trained ear with true wide band speaker monitors. Since this unit is voiced to be used with a good large plate condenser microphone which have a wide dynamic range. The LED meter can often run into the red for most recording purposes. Constantly red LED meter will affect the tube to symmetrically soft clip causing an aggressive overloading of tape sonic character or overdriven guitar amp effect when totally red. Be careful this overdrive tube character is best used only on individual instruments or simple instrumental passages. Although original engineering samples of the modified MPA were used by hard rock and roll types who liked this subtle tube grunge, especially as a final mix effect. I left its capability in but now gain limit a little more for the audiophile recordist. Also, I will admit there is a design of the tube circuit to intentionally plump the sound. Its a slight tube kick (really a DC bias shift) which is inherent even in well done designs. This sound effect is for some people one of the most desirable effects, either you like it or you dont. By keeping the meters and LEDs out of the red it will be little noticed. The design attempts to gain ride just enough so as not to allow slew limiting affects to occur in digital converter which will probably be in the next device, reverb, eq, computer recording etc. This is a subject which will need more space to explain clearly, but simply put digital has great signal to noise but no dynamic head room at all. Most sample rates will still create slew limiting problems in the audio typically audible to the trained ear a

slight stridency of high frequencies. This may not be too noticeable on most speaker monitors presently used. (Most tweeters have such poor high frequency response and horrible dynamic linearity that this speaker effect actually dominates, but I am predicting a truly great improvement in the next generations of studio monitors. Another anecdotal point, after 20 years of actually measuring so many professional speakers - I will tell you honestly Ive seen very few tweeters which could do more than 30 to 50 db worth of dynamic range and get frequency response out to 20 kHz. Think about how often a true test report graph of such parameters presented to the purchaser of speakers. A good look at most of these pro speaker show them to be cheap Asian parts, or just simple archaic designs with fancy cabinets and trim on them. Sorry, Im not impressed. However, high quality headphones can be far more revealing. The best ones are phase coherent and very linear in frequency response, but unfortunately subject to ear/phone cup coupling problems. In closing I will be clear that this is not the perfect preamp. It wasnt intended to be. It is a great preamp with some novel user adjustable function which allows it so sound like many fancy priced items. It does have an excellent mic preamp front end which can adapt to any mic impedance, high or low, by use of well done multi parallel transistor input true low impedance stage with 3 stages of RFI filter (modified) to keep out as best possible all that crazy radio noise (kudos to ART). It also uses the tube for the best advantage of harmonic character (too bad they didnt use my idea). The output stage can drive any combination of balanced, faked balance line, reverse balanced line with any problem. ART did it right. Some very fancy units will blow the output amp if not in only 1 way. My metering attempts to truly show the dynamics and volume level of the musical sonics. This device can be used as a final mix processor, by use of the phone plug ins. This is my swan song for the music business, my friends, and for my own music. I give much credit to ART who supplied me willingly with schematics, parts, some advice and especially for designing a very clever preamp which was just the right thing for me to rev up. The quality of parts and honesty to put a real design into a box instead of an op amp in a box with a pretty face plate and marketing hype was refreshing. Most sound engineers will never really get it. A fancy name will attract more attention, but some musicians can be slowly persuaded once they try a new thing.



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