"DaviSecondSource" TB-12 MIC-ALL©™ Preamplifier
"On-Line Manual" - Applications Data
Copyright 2004 - 2007 © by DaviSound


The TB-12 is an idea that was initiated many months prior to its introduction in 2004 by inquirors requesting a smaller edition of the popular TB-6 specifically designed for the home project studio user.

The TB-12 offers some of the features of both the TB-6 and the TB-10 but it is a much more compact, simpler version of either previous unit.

For one obvious example, the TB-12 is a two channel, two circuit module, preamplifier; whereas, the TB-6 and the TB-10 each offer four discreet channels and circuit modules.


The microphone input in each channel offers a front panel XLR input connector (extra parallel rear panel connectors are available as a custom option for an extra fee) and the MIC-ALL active gain control.

The adjacent horizontal mounted mini toggle switch is the INPUT SELECT switch with left/right toggle operation. Left position, in the direction of the mic jack selects mic, while right toward the instrument jack selects that input.

The vertically mounted on/off switch located atop the gain control is the PHANTOM POWER on/off switch with up/down operation. An adjacent green LED indicates phantom power on/off.

A second horizontally operated toggle located below the active gain control is the phase reverse switch.

The left/right toggle handle position phase reverse action of the respective phase switches is all relative of course but the LEFT toggle position corresponds with input pins 2 & 3 to output pins 2 & 3, whereas the RIGHT position reverses the polarity of input pins 2 & 3.

Approximate gain control settings for the MIC-ALL microphone preamps, as determined by the white pointer position on the control knob, are as follows:

9 O'Clock = + 28 dB      12 O'Clock = + 48 dB     3 O'Clock = + 55 dB      Full CW = + 58 dB

The INSTRUMENT INPUTS offer approximately 18dB LESS GAIN at each similar position of their controls.

A very unique design for an instrument amp was incorporated into the TB-12!

Instead of the typical UNBALANCED instrument inputs found on most preamps, the TB-12 employs a special impedance/gain adjusted version of the MIC-ALL amplifier block in its DIFFERENTIAL configuration.

This arrangement offers the extremely large low frequency Common Mode Rejection Ratio inherent to the MIC-ALL amplifier design (around 100 dB) and this results in extremely quiet instrument input operation with extremely high immunity to hum pickup!

Since the TB-12 only utilizes a single MP-2 module per channel for all functions, special multi-way switching was devised to select between the front panel mic jacks and the instrument jacks and the latter's matching / support circuitry.

NOTE - The TRS "Instrument" inputs may also be used as balanced line inputs if a line level, universal booster amplifier or line driver application is ever desired from the TB-12!

This is possible because the medium/high impedance of these inputs is perfect for terminating, or bridging, all low impedance, line-level signal sources. And, since the first stage in this switched mode operates at unity gain, the following fully variable gain stage makes for a perfect, completely variable gain, matching buffer amplifier.

The REAR PANEL is as simple and uncluttered as it gets with a pair of XLR outputs for the two channels. Also, as mentioned, extra parallel mic input jacks may be ordered for the rear panel as a customer option at slight extra cost. In the case of utilizing parallel jacks, it is important to note that only either the front or rear jack may be used at any one time.

As of 2007, it was decided to begin adding remote DC power capabilities to certain, applicable Tool Box models. The new TB-12 is one of those models! To facillitate BATTERY OPERATION when required for remote, field use, THUMBSCREW TERMINALS coded red (+) and black (-) were added to the rear panel.

Note that the BLACK screw terminal could also serve as a supplemental direct ground terminal where desired in rack installations.

Any user supplied battery pack with a standard DC voltage of 12 volts to 44 volts may be utilized. Naturally, headroom and maximum output capabilities are closer to specifications with the higher supply voltages. However, professional results can easily be acheived with supplies of 18 to 36 volts and most traditional condenser mics function properly when phantom powered within this range as well.

While care should be taken when connecting a remote power supply since main on/off switching is by-passed in this mode, the TB-12 is internally protected against accidental power supply polarity reversal.

Please note that the front panel main on/off LED indicator (green) will light when the battery supply is connected. However, the main power switch (AC on/off) does not function when powered by remote. battery supply.

This would also be an opportune place to mention that the Main power indicator LED, on most Tool Boxes including the TB- 12, does NOT turn off instantly when power is removed! There will be a decay, typically, of around thirty seconds or so. We mention this here since some users have actually thought something was "wrong" with their units because of this. Quite the contrary! This "hold function" delay is simply an indication of the superior filtering capacity of the on-board power supply filter capacitors!

It is advisable to have the detachable AC power cord REMOVED whenever remote DC power is connected to the thumbscrew terminals since AC power should not be applied simultaneously with remote DC battery supplies connected to the unit!

As with all DaviSound Tool Boxes, the AC power cord IEC EMI FILTER RECEPTACLE and FUSE HOLDER are at the far left of the panel. .

The XLR outputs are grouped to the right of the panel.

As of 2006, the rear output jacks are arranged left to right, with channel 1 on the left and channel 2 on the right as you face (look at) the rear panel. Originally, these were just the opposite with the outputs directly adjacent, behind their respective front panel controls as with most other units. This was recently changed on the simpler, two jack TB-12 since it presents no internal problems and makes for logical, left/right identification.

The output impedance is 100 ohms "quasi-balanced" as per DaviSound Tool Box standards with PIN 2 HI and PIN 3 LO. Shields are, of course, GROUND.

For unbalanced operation from the XLR outputs, use only PIN 2 for signal (IGNORE PIN 3) and the shield as ground.

For more information and tips on special grounding considerations for difficult installations, please see the "Tool Box Top Tips" printed information included in the paperwork shipped with your unit.

Instrument/Line inputs utilize T-R-S jacks to offer additional instrument cable wiring options when mating with the differential inputs.

The TB-12 front panel was redesigned in 2006 with slightly enlarged control spacing as shown in the photos on this page and the one below ...
this one showing Front Panel Name Plate in place.

Also please note that the photos on this page show "clone" units with a special, custom "Antique Mahogany" cabinet finish.
Standard Models utilize our traditional American Red Oak cabinetry unless special ordered otherwise.

Performance "DaviSpecs" Specifications

Unless specifically stated otherwise in individual descriptions ...
and for all Tool Boxes which employ our "MP-2 MasterPiece" circuit module, which is nicknamed the "Mic-All", for the complete signal chain gain block, the electrical specifications are as follows:

    ALL amplifiers feature ruler flat frequency response ...
    with -3dB points at 1.6 HZ and 35 KHz (maximum gain). There is a slightly variable HF bandwidth increase as gain is actively decreased to unity or below
    (flat to 70KHz at unity).

    This is because an active filtering configuration is employed to intentionally rolloff extreme high frequency response to minimize RF / EMI out of band interference, noise contribution, and intermodulation distortions.

    Combined distortions specifications are where the DaviSound "MIC-ALL" amplifiers REALLY outperform most all others anywhere! There is virtually NO measurable distortion at any level or frequency until maximum gain settings are utilized. Even then, the measurements are near the residuals of the test instruments and barely detectable at the frequency extremes- (.008% at 20 KHZ, +55dB gain)!

    Under more reallistic gain settings, amplifier distortion is even lower (example: typically .001%, 1KHZ, 40dB gain ... immeasurable at gain settings below 40 db [theoretically, mathematically indicated better than .0008%] )!

    This performance characteristic is responsible for claim after claim from virtually ALL awe inspired users that our amp is the "cleanest" they have ever heard!

    One of the most crucial parameters in microphone signal handling is HEADROOM. The MIC-ALL amps are relatively unsurpassed in this regard with signal handling capability right up near +32 dBU before clipping! We acheive this with our House IC and thermal protection which allows a much higher power supply voltage than most conventional designs. This provides a full 8 to 10 dB more headroom than many other professional designs on the market today!

    Keep in mind, that output level offered by an output boosted stage does NOT always correspond to system headroom throughout! Some other units boast an output of +36 dB, or more, that do NOT offer that headroom throughout their chain. DaviSound specs are through chain, input to output.

  • NOISE -
    EIN Unweighted -122dB 100 ohms
    Noise 20Hz to 20KHz Unweighted - 98dB

    Actual internal impedance is 2KOhms, differentially balanced for optimum voltage transfer of all low impedance professional microphones from 50 ohms impedance to 600 ohms impedance.

    Actual output impedance is 100 ohms (47 ohms unbalanced) and the high current "Mic-All" output stages will drive virtually any line load from 600 ohms to high impedance bridging with no increase in distortion or any other loading effect!


    Frequency response, (as-is, un-compensated, unity gain, .777 V RMS input ) ... flat to 10 MHZ
    Input Noise Voltage at 1KHZ - less than 4 nanovolts per stage
    Typical Supply current - 11 mA (maximum- at full gain- full load)
    THD plus noise at unity gain, per inverter stage less than .0002%
    Slew Rate 12 V/uS
    Maximum Supply Voltage + 48 volts
    Lifespan- unknown - absolute minimum expected performance ...
    under less than ideal thermal conditions - 20 years ...
    Typical expected performance under average operating conditions - 100 plus years ...
    Theoretical performance under ideal conditions - 1,000 years!

    The inherent specifications of the House IC itself are actually further enhanced in our actual audio application by our circuit design techniques within the
    MP-2 module!

    One such technique ... which we believe has so much to do with the exceptional, noticable "accuracy of detail" comment that we hear so often from users in regard to the performance of our amplifiers ... is a unique inter-stage direct coupling/biasing scheme which forces the amplifier into near full Class-A operation. Any extra heat generated in this process is harmlessly dissapated in the thermally conductive epoxy ecasement of the sealed MP-2 module!

    This, combined with the, overload proof, fully variable, active gain technique, produces results as close as you can get to a truly "distortionless" amplifier!

    Generally speaking, in regard to most performance specifications, DaviSound Tool Boxes perform better than any of the state-of-the-art equipment that is currently available to test them! This is why we say they offer the quality reference by which to judge all others.


    The fully ACTIVE, contnuously variable gain control of the "Mic-All" Circuitry design allows you to DIAL IN exactly the right amount of amp gain for a given application. Often this will be +20 to 30dB and seldom more than 40 to 50 dB as will be noted!

    Now, consider that when any amplfier operates with GAIN ...its NOISE GAIN also increases! SO, the actual NOISE contribution of a MIC-ALL amp or any other variable gain amp, is also VARIABLE depending on the actual active gain settings! This means, that you have a MUCH superior noise specification and actual performance with an ACTIVE gain control set for, say, 30dB of needed gain as opposed to a fixed gain amplifier of, say 40 dB of fixed gain with a simple PASSIVE attenuator added to reduce level!


    "Wide-Open" on a volume control in front of a fixed 40dB gain stage is NOT the same thing as "wide open" on a variable gain control offering 58dB of gain - by FAR not the same thing! That is the whole POINT of and the whole beauty of operation with a VARIABLE gain control! ON the "Brand X" amp, with the "noise gain" always fixed ... all the "control" does is passively attenuate the signal! - (ORANGES!)

    Alternately, with our FULLY VARIABLE ACTIVE control, the amplifier GAIN STRUCTURE is fully variable from 0 dB to +58 dB based on the control setting whereby if, say, only 20dB of gain is needed on the mic amp, then as it turns out, the user would actually have about a 30dB lower noise floor, in that case, all other factors equal, than with "brand-X"! See the BEAUTY? - (APPLES!)

    While the TB-12 offers up to near 60 dB of gain, keep in mind, as can be seen from the chart below, that such extreme settings are very seldom needed! Typical maximum studio mic preamp gain requirements are around 40 dB or less on the average.

    Some interesting observations in regard to actual microphone output levels and, thus, resulting amplification requirements -

    Here is an enlightening study, done some time ago, and published in Audio Amateur Magazine on several occasions (original- Russell Hamm - JAES 21:4 [May, 1973] ) in regard to audio signal levels measured direct FROM MICROPHONES.

    Please note that the measured levels we are talking about here are STRAIGHT out of the microphones themselves with NO additional amplification!

    This will surprise most all but the most experienced, veteran recording engineers since, in some cases as will be shown, you would not only NOT need ANY mic preamplification but might even need gain reduction!

    Peak Mic levels 0dB ref to 0dBu=.775 volts
    INSTRUMENT        Distance in inches    Neumann U-87               RCA-77DX           EV-666   
                                                             (Typical condenser)           (Ribbon)            (Dynamic)
     Bass Drum                     6                         0                                 -9                      -4
     Large Tom Tom              12                       -1                                 -9                      -5
     Small Tom Tom              12                       -1                                 -7                      -1
     Piano (single note)           6                       -25                               -38                    -32
    Cow Bell                         12                      -10                               -29                    -15
    Loud Yell                         4                         0                            Not Tested             -10

    Notice that a loud yell (or similar loud vocal musical note!) into a typical condenser mic can produce an unamplified output of 0 dBU which is .775 volts RMS or about 2.2 volts peak to peak!

    On the other hand, it is not uncommon to encounter, say with a "whispery" female vocalist into a ribbon mic, even as close as three inches, signals as low as -50 dBU or about 7 millivolts!

    So, a microphone preamp has to, quite literally, deal with one extreme to another.

    The MIC-ALL preamp can, as structured in the TB-6, typically output +28 dBu with some headroom.

    However, if set for a gain of, say, 40 dB...it can be seem from the above examples that it would easily overload and distort with many of the microphone signals shown!

    At that setting, a loud yell or vocal extreme into a condenser mic at about six inches could cause the amp to try and pass a +40dBu signal ...obviously at LEAST 12 db past the clipping point! Obviously, the higher you raise your "0 VU" operating level, the LOWER your headroom before the clipping stage!

    That is the point of the INFINITELY VARIABLE GAIN CONTROL that allows you to continually "dial-in" just the right amount of gain for your incoming microphone signal!

    The rack cabinet itself is made from hand sculptured SOLID OAK, natural wood, or other exotic woods by special order. As of spring 2001, we have opted for lustrous, hard penetrating oil finishes for the cabinetry as this provides added protection for the wood. Unlike other oil finishes, it is relatively maintenance free. Simply wipe it with a soft dry cloth to restore lustre.

    WG Models, such as the TB-12, are entirely made of wood! The front panel as well as the rest of the cabinet are ALL solid oak (unless other exotic woods have been utilized by client arrangement/preferance). Like all natural things, every piece of wood has its own, distinct character and "personality". This makes EACH AND EVERY "WG" model unique unto itself which enhances the aesthetic value of the piece and the actual appreciative monetary value, over time, as well!

    There are NO user servicable parts inside. DaviSound Tool Boxes are fashioned from our "Master Pieces" modules which employ hand-laid circuitry, silicon embedded into plastic cased modules. In the unlikely event that service should ever be required, simply contact us for return authorization and we will replace the defective module(s).

    While never having been enforced, it has always been original DaviSound policy to void warranties if the cover is removed! However, certainly be advised that ANY internal tampering or unauthorized repair or modification attempts void all warranties!


    DaviSound products are carefully assembled BY HAND, one piece at a time from start to finish, in prototype assembly fashion, with extreme care and attention. They are designed to perform from now on with no trouble.

    However, there are always "real world" imperfections that can not be anticipated or accounted for no matter HOW careful one might be in fabrication. For example, we don't wind the power supply transformers and these things can fail at times. Ours seldom do, due to extensive testing and pre shipment "burn-in" periods, but if you should ever have a problem, you are protected for as long as you own the equipment, as the original owner.

    Simply carefully repack the unit in the original packing, ship it back to us (after notification) to
    DaviSound, 1504 Sunset Ave., Newberry, SC 29108 803-276-0639
    and we will repair and reship at no charge to you whatever!

    Thank you for your purchase and use of a DaviSound Tool Box!

    And, we also thank you for allowing us to go these "extra lengths" within YOUR operating manual to elaborate in accordance with our "mission" in publishing these on-line manuals. It is all part of an ongoing effort to provide as much educational material as possible from this website in the sincere belief that ...

    The more one truly KNOWS about audio electronics, the more one can truly appreciate the DaviSound methods!

    We thank all of you who ALREADY know all of this covered herein for your indulgence as we present it for those who do not!

    Please let us hear from you regarding your application of our unit and feel free to contact us with any questions or comments throughout the future!

    We also hope that you will consider ALL of the DaviSound Tool Box models for your rack!


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