"DaviSuper" TB-10 Preamplifier
"On-Line Manual" - Applications Data
As of 2008, we decided to veer from our present course of utilizing larger 3RU cabinetry for most multiple channel Tool Boxes and design a new TB-10 package in compact, 2 RU cabinetry. This edition was created to feature, and introduce, our new, standard SiFam "Retro" styled VU meters in the smaller 2 1/2" square package. The inaugural edition of this new model is pictured above housed in contrasting "aged" Oak cabinetry with Purpleheart faceplate.
To make this unique, "compactness" possible, we also designed an all new MP-TB10 "MasterPiece" circuit module which houses ALL of the circuitry for one channel of the TB-10, including the dual "Mic-All" amplifiers and the precision VU meter driver amp. Therefore, only two of these modules are required on board for ALL of the circuit functions of the TB-10.
More photos of the new, inaugural TB-10 can be viewed at this link ...
NEW TB-10 - 2008 Edition
This dual preamplifier package is, in reallity a FOUR CHANNEL unit offering TWO DaviSound "MIC-ALL" microphone amplifiers and TWO instrument preamps. The layout is grouped in pairs with the channel one mic and instrument amp to the left side of the unit with a second identical pair on the right side. The left and right VU meters may be switch selected to monitor the output of either respective amplifier.
The individually isolated and buffered VU meters are independently selectable to monitor either the mic channels or the instrument channels and are trim adjustable to calibrate over a 20 dB range.
The VU Meters employ a mini-toggle switch located directly to the right of the meter face. This switch, mounted horizontially selects either the INSTRUMENT signal when switched toward the left of the panel in the direction of the instrument inputs, or when switched to the right position, the MICROPHONE signal level is monitored.
The gain trim control is located directly below the select switch to allow easy, front panel precision trim and alignment calibration of the meter drive amplifiers. CAUTION: Care should be taken whenever setting up the TB-10 to be sure that the gain trim controls are both turned fully off (CCW) to avoid pegging the meters with excessive input signal prior to calibration.
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 PHASE REVERSE switch with left/right toggle operation, and the vertically mounted on/off switch below it is the PHANTOM POWER on/off switch with up/down operation. A green LED indicates phantom power on/off.
Precision adjustment can be obtained by injecting an accurate, oscillator signal to the input and monitoring the output voltage on a digital, AC voltmeter. The gain trims can then be adjusted for "zero VU" at the desired output signal level. Close approximation for "zero VU = +4 dBU" can be obtained by setting the trim knob pointers at their 9 O'Clock positions.
The left/right 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:
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-10!
Due to the rather crowded conditions of four front panel inputs along with the proximity of the higher impedance instrument inputs to the VU meters and their corresponding susceptibility to hum pickup, instead of the typical UNBALANCED instrument inputs found on most preamps, the TB-10 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!
The TB-10 employs four, separate MP-2 modules for all functions thereby allowing the four channels to all be used simultaneously.
As can be seen, the REAR PANEL is as simple as it gets with a pair of outputs for each channel.
The lower level jacks are Mic Channel outputs and the upper level jacks are Instrument outputs.
These jack pairs are orriented in actual left to right fashion with the first pair for the left channel as you face the rear panel.
The AC power cord IEC EMI FILTER RECEPTACLE and FUSE HOLDER are at the far left of the panel.
The single, black, thumbscrew terminal, banana jack post, is an optional, utility grounding connection.
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The XLR outputs are 100 ohms "quasi-balanced" as per DaviSound Tool Box standards with PIN 2 HI and PIN 3 LO. For balanced operation, shields are ground and, for optimum RF rejection, it is good engineering practice for cable shields to be connected to ground at ONE END only. This practice assumes, of course, a good single ground connection between components such as one complete cable shield or a separate wire to the utiility ground post from main system ground.
For unbalanced operation from the XLR outputs, use only PIN 2 (IGNORE PIN 3) and the shield which, for unbalanced use, should be connected to connectors at both ends of the cable.
Inputs now utilize T-R-S jacks to offer additional instrument cable wiring options when mating with the differential inputs.
PERFORMANCE -
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.
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!
ELECTRICAL SPECIFICATIONS FOR DAVISOUND HOUSE IC USED IN "MIC-ALL" MP-2 "MasterPiece" Modules |
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-TB10 circuit 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 dissipated in the thermally conductive epoxy encasement 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.
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NOTE:
While the MIC-ALL AMP in the TB-10 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 in order to avoid clipping at LINE INPUT LEVEL!
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-10, 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!
GENERAL -
The rack cabinet itself is made from hand sculptured SOLID OAK, natural wood. As of spring 2001, we have opted for lustrous, hard penetrating oil finishes for the cabinetry as this provides added protection for the wood and, unlike other oil finishes, it is relatively maintenance free. Simply wipe it with a soft dry cloth to restore lustre. The front and rear panels are treated with extra coatings of acrylics for added protection.
WG Models, such as the TB-10, 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 as well!
Keep in mind that as part of this wood "character" it is impossible to find/utilize a "PERFECT" piece of wood. This means there may be slight imperfections, or variations, in terms of grain pattern, color uniformity, and skew. However, any such natural variations in our selected pieces are very minor and are the very thing that gives wood its charm and "character" appeal!
There are NO user servicable parts inside. DaviSound Tool Boxes are fashioned from our "Master Pieces" modules which employ hand-laid circuitry, epoxy 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).
Be advised that ANY internal tampering or unauthorized repair or modification attempts void all warranties!
Do NOT REMOVE The Top Cover! Potentially LETHAL VOLTAGES may be exposed internally. Any attempt to remove the front, bottom or rear panels will result in permanent damage to the unit!
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 make the semiconductors and we don't wind the AC 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!
THANK YOU and GOOD LUCK!