META - Microphone Preamplifiers

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Samuel Groner

Well-known member
Aug 19, 2004
Zürich, Switzerland
META - Microphone Preamplifiers

This is a meta-thread, made to allow you to keep track of the posts concerning this single issue. All should be contained in this first post - which is re-edited regularily. Everyone is welcome to reply with comments and pointers to things they consider relevant. This will be copy/pasted into the first post, if the meta-keeper finds it relevant. (We deeply dislike censorship, but here it seems necessary for the sake of overview). On a regular basis, a moderator will delete all posts but this first one, and bump the thread to the top.

Transformerless Input:

IC Based Designs:
INA 217 replacement -- with a good section on noise calculation.
Care to review an aplication-specific preamp design for me? -- preamplifier for a soundfield microphone.
B-Format buffer preamp, Mk.II -- follow-up to the above thread.
INA 163 low noise inputs -- discussion of the INA163 regarding noise and stability.
A Direct-Coupled Input-Capacitorless Active Mic Preamp -- using a THAT 1510/1512 IC without input coupling capacitors.
Small mic pre/mixer -- simple design based on a THAT1512.
IC micpre schematic check -- IC frontend an discrete OPA275-based output stage.
Portable Mic/Pre for field recording -- simple electret preamp.

Hybrid Transistor/IC Designs:
Millenia hv 3 -- short discussion of this design by John La Grou.
SM Pro PR8 Mic Preamps -- reverse engineering and modding the PR8.
AMEK 2500 mic pre: how does it work? -- discussion of the 2500 circuitry and similar designs.
Amek Neve 9098/9098i Query -- discussion of the 9098/9098i circuitry.
Matching Transistors for Valley People MicPre -- good information on how to match transistors for a low-noise frontend and discussion of the Trans Amp.
Preamp Project -- evolution of a transformerless microphone preamplifier project.
supergreen: I did it! -- slighty altered implementation of the 9098/9098i.
Qs for AES PrePrint 2106 (Cohen Transformerless Mic Pre) -- discussion of this famous design.
Double balanced microphone preamp project -- same topic as the above thread.
This Works -- simple design with a discrete frontend and an opamp-based second stage.
Valley People Op Amp -- documentation for these amplifiers.
N E V E 5 0 1 2 -- short and informal discussin of this rather new commercial design.
Mic Preamp Schematic Collection -- several design ideas. Good discussion of the famous "Cohen" transformerless topology.
Another hybrid mic preamp -- bipolar transistors and a dual opamp.
Benchmark Mic Pre Schematic from 1984 -- the name says it all.

Discrete Transistor Designs:
Discrete opamps in the instrumentation config. -- good discussion of typical transformerless preamplifier topologies.
why are there so few discrete transformerless mic preamps? -- discussion of some transformerless preamplifier topologies.
Transformerless discrete balanced micamp -- a few solutions to the discret transformerless preamplifier problem.
[DESIGN] Original(?) mike-amp design -- unfinished design, but a lot of good reading here on many issues with transformerless preamplifiers.
Different differential -- simple preamplifier.
Transformerless JFet mic preamp -- short discussion of the Borbely Audio preamplifier.
Simple Single Ended Mic Pre -- unbalanced preamplifier for a 5 V wall wart.
Exploring the monster (trafoless mic pre input) -- another possible topology.
INA134 instead of input transformer???? -- a simple discrete frontend.
Mic pre module thing -- a simple discrete frontend.
Altec 1578A octal mic-pre plug-in ** now with circuit ** -- the name says it all.

Tube Designs:
Transformerless tube mic preamp schem -- design with two ECC83/12AX7. Suggested improvements by knowledgable people.

Hybride Tube Designs:
FETCODED -- JFETs and tubes combined.
Hybrid As Always -- BJTs and tubes.
Another transformerless mic preamp -- again bipolar frontend and tubes.

Transformerbalanced Input:

IC Based Designs:
Captain Kraplin Mic Pre-amp -- a battery-powered design based on a Sowter input transformer and an OP27. Good information on zobel networks for input transformers as well.
Any one know the Focusrite mic pre topology? -- good information on the ISA110.
my new mic pre-comments please -- simple design based on a Neutrik NTM4 and OPA604.
Constructing A Klein + Hummel Mic Preamp - Can Anyone Help? -- how to use a Beyerdynamic TR/BV35806 input transformer.
Can Someone Check This Mic Pre Schematic Please? -- follow-up to the above thread.
Preamp Project: Samuel Groner's Shared Gain Preamp -- follow-up to the above thread.
Solving Oscillation In An Opamp-based Mic Pre....??? -- follow-up to the above thread.
Opamp Mic Pre Design (Transformer In/Out) -- simple design with an OPA604 gain stage.
Jung mic pre - anyone tried it? -- discussion of the Jung design which uses a Jensen JT-16-A/B, a LT1115 and a LT1010. ICs are biased into class A.
St*der D19 Mic Pre -- discussion of an interesting topology which includes the input transformer in the feedback network for reduced distortion.
fully differential transformer balanced mic pre? -- evolution of a design which started with two OPA2604s and ended with one of them. Good information on balanced transformer loading by Bill Whitlock.
Low-noise opamp for battery-powered preamp. -- battery powered two-stage design.
MCI mic pre -- Jensen input transformer and one high-voltage IC.
Sad Mike Amp /Xformer balanced in/out DC servo -- input transformer, SSM2019 and an OPA275.
OPA2228 Based MicPre -- how to use an OPA2228 for a microphone preamplifier.
Mic Preamp Schematic Collection -- several design ideas.

Hybrid Transistor/IC Designs:
Mic Preamp Schematic Collection -- several design ideas.

Discrete Transistor Designs:
992 opamps application, doubt -- design based on a Jensen JT-16-B and a JFET-992.
Melcor AML-27 Preamp questions -- some info on the Melcor AML-27.
So I've got these 990s.... -- excellent information on how to build a Twin Servo preamplifier and on the 990C.
high microphone level output, microphone preamp -- about as simple as it gets.
My first schematic. -- based on a JH-990C discrete opamp and a Cinemag CMMI-8-PCA.
Great River OpAmp -- discussion of the MP-2/MP-4 circuitry.
Beyer micpre - circuit analysis & sims -- short discussion of a three-transistor preamplifier.
Darlington spinoff: bcarso's preamp circuits -- interesting design with JFET-frontend.
TZ81 Transistor -- schematics for the Altec 1588B microphone preamplifier.
fet boy -- microphone preamplifier based on Hamptone JFP gain modules.
anyone got a schemo for this pre and or EQ -- some info on the Avalon M3.
Calrec1061 PREAMP redesign schematic - thoughts? -- interesting redesign.
v72t -- schematic for this early transistorised preamplifier.
Bryston BMP-2 Mic Preamp -- some info on this preamp.
characteristics input trafo -- simple two-transistor design.
312 preamp in my way -- a variation of this most famous preamplifier.
Studer mic preamp - modified diy -- simple discrete design.
Racking Spectra Sonics 101 -- how to use these cards.

Tube Designs:
Another tube preamp/lineamp circuit -- preamplifier with a 12AV7 and a 12BH7A.
Collins 6q-1 mic preamp pics and schemo -- two tubes per channel.
Let's try this again - Al's Mic Pre... -- another tube design with something to learn from.
High-Gain Amplifier Circuit -- high gain with three dual tubes.
Very simple tube preamp -- one 12AX7 does it!
Single-tube preamp revisited -- follow-up to the above thread.
One-Bottle Preamp -- follow-up to the above two threads.
R*E*D Forty Seven -- some info on this famous tube preamplifier.
Extra simple valve preamp with a good sound? -- follow-up to the above three threads.
ef 86 / ecc 81 mic pre -- a pentode and a dual triode to be found here.
second mic pre finished *pics* -- follow-up to the above thread.
mic-pre #3 -- one with an EF83, an EF11 and a ECC82.
io micpre #4 -- another tube preamp.
Simple tube Mic preamp help -- how to design a tube pre as simple as possible.
Western Electric 417A Tube Preamp -- design with one bottle.
6SN7 / 6CG7 preamp -- design with three triodes.
micpre#5 -- three pentodes in it.
Microphone preamp idea -- simple tube preamp ideas.
Slow Blow pre? -- another tube preamplifier.
Aikido microphone preamp -- tube preamp with four bottles.
mic pre #7 -- three tubes here.
6EM7 Mic Preamp -- design with two tubes.
One Tube Pre -- another one with two tubes.
WE 407A Push-Pull Mic Preamp -- oh hell, tubes as well!
mic pre with feedback limiter. -- simple microphone preamplifier with built-in limiter.
V76 Hack !!! -- simplified V76.
Pre/DI -- a tube operation amplifier used as microphone preamplifier.
A Pre for your Ribbons -- a design with a lot of gain.
WE417A / 12B4A mic pre schematics -- big case here...
micpre#9 -- tubes without feedback.
R*E*D*D*ish mic preamp -- more tubes!
Tube Decibel Meter into Mic Preamp -- converting a level meter into a microphone preamplifier.
Another interesting mic preamp -- fully balanced and with interstage iron.
My new tube mic pre... and... I´m out for getting married! -- tubes and a 1:18 input transformer!
Nuke-'Em E2 Octal Tube Mic Pre -- another tube amplifier circuit.
tube mic pre with small-ratio input transformer -- looking for a circuit to use a 1:3 transformer.
Interesting schematic -- transformer feedback with tubes.

Hybride Tube Designs:
Simple Pre -- iron, vacuum and silicone.

Microphone Splitter:
Active Mic Splitter Ideas -- collecting mic splitter ideas.
Mic Splitter with Haufe RK284 transformers -- passive splitter design.

General Design Discussions:

BigMicPreThread - from the old place [on it's way]
Interviews with some of the best designers -- thread with links to interviews with well-known designers.
mic pre concepts -- a lot to read on microphone preamplifier design.
trafoless microphone preamp wish list -- many design ideas, nothing finished!

Phantom Power:
slow rise phantom power schem -- collecting ideas on how to implement a slow-rise phantom power circuit.
Why 48V for phantom power? Who started this convention? -- the name says it all.
slow ramp 48v phantom -- discussion of a specific slow-rise phantom power circuit.
Barry Porter phantom powering schem -- discussion of a specific slow-rise phantom power circuit by Barry Porter.
48v power supply -- the name says it all.
What's the deal with phantom power and patchbays? -- the name says it all.
Phantom resistor buffer -- resistor value for phantom power and a little reading on forming voltage for electrolytic caps.
DC on mic-input transformer primaries -- issues with phantom power and input transformers.
Phantom powering: history, specs, and pitfalls -- good article on phantom power.
Phantom Powered Mic Box?? -- good links on phantom powering.
Phantom power and transformer - how does that work? -- phantom power trough center tap.
6AL5 for Slow Start Phantom -- a tube abused for a slow start phantom power supply.
Phantom Blocking Caps -- value of input coupling caps.
Phantom pwr from a DC to DC converter? -- the name says it all.
Some Quick Mic Pre Input Transformer Questions -- why (not) to feed phantom power through a center tab.
48v slow regulator question... -- another go on the slow rise phantom power topic.
+48 volt phantom supply -- clear but dangerous idea.
Phanthom from B+ ? -- how to get 48 V from a high voltage supply (and why not to do so).
Phantom power from battery -- get 48 V from 1.5 V.
Phantom LED indicator -- make a LED indicating phantom power.
TL783 Bypass Reference Pin Or Not -- the name says it all.
pm1000 phantom problem -- troubleshooting phantom power.
9 V To 48 V DC-DC Converter Design -- two different DC-DC converter design for getting phantom power from either +9 V or +15 V.
Phantom power voltage -- general discussion on phantom power voltage.
Phantom current -- how much current can a mic draw?
Noisy phantom rail...? -- LM317 stability problems in a phantom power supply.
Ramped phantom power project -- the name says it all.

Microphone Input Transformers:
Captain Kraplin Mic Pre-amp -- a battery-powered design based on a Sowter input transformer and an OP27. Good information on zobel networks for input transformers as well.
OEP transformer measurements -- some measurements on the A262A2E.
Microphone Input Transformer Characteristics -- what makes a good input transformer and how to use a power transformer for audio.
Zobel network for OEP mic transformer -- best zobel network for the A3E.
DC on mic-input transformer primaries -- issues with phantom power and input transformers.
Mic TX winding variations -- what about bifilar windings on mic input transformers?
high-gain tube mic pres -- good discussion on input transformers for tube preamplifiers.
Correct output transformer termination for LL1517? -- the importance of zobel networks.

Input Impedance Of Microphone Preamplifiers:
Variable Impedence Mic Input -- some reading on microphone input transformers for variable input impedance.
Mic transformer load question -- how does transformer loading affect input impedance?
Looking for a variable impedance transformer. -- some ideas for a variable input impedance input transformer.
Microphone Impedance Matching -- discussion on microphone loading.

Input attenuator help -- how to design a variable input pad.
Your mic preamp philosophy -- open discussion about microphone preamplifiers.
SSL 9k - background -- good info from the designer itself.
How to do a pre shootout, need advice. -- the name says it all.
EMI/RFI with Mic preamps (Inductors, Common Mode, etc.) -- how to do RFI protection with transformerless preamplifiers.
Question about multistage preamps -- how to distribute gain amongst two stages.
AMEK2500 preamp Troubles -- how to measure noise of a microphone preamplifier.
Mic Pre Workshopping... -- hints for a microphone preamplifier workshop.
Mic Switcher w/48V -- transformer balanced mic switcher.
990 noise measurement -- about noise measurement and optimum source impedance.
John Hardy 990 vs. 2520: color or no color? -- why do they sound different?
Consider the mic amp -- a discussion by Ted Fletcher.
Hum madness, driving me wild... how do you fair? -- ideas for reducing hum in a microphone preamplifier.
Line into mic pre - how is it designed? -- adding a line input to a microphone preamplifier.
DPA HV Microphone (discrete) Power Supply -- how to build a high voltage supply.
Mic Pre Front-End PCB -- EMI filter, phantom power, PAD, polarity and high pass filter.
using plastic for a chasis to hold a mic pre -- the name says it all.
Software audio analyzer to mic pre... impedance issues? -- on measuring microphone preamplifiers.
Proper Way to Measure Preamp Gain -- the name says it all.

Related METAs:
META - Discrete Opamps
META - Schematic collection links
META-Power Supplies
META - Green Pre
META - SSL 9K Preamp
META - G9 Tube Micpre

Commercial Inside Views:
Pics of that high woltage opamp... -- SPL Gainstation 1.
Gear Pr0n !!! pics inside -- Millennia HV-3D.
Avalon 747sp inside pics posted -- the name says it all.
Avalon M5 Pics -- the name says it all.
INSIDE a Red8 -- the name says it all.
Inside the Groove Tubes BRICK -- the name says it all.
ua l*a* 6 1 0 inside pics -- the name says it all.
Sytek? What's inside? -- the name says it all.
SSL XLogic Channel -- the name says it all.

External Links: -- design philosophy of Michael Grace. -- how to evaluate microphone preamplifiers, by John Hardy. -- John Hardy on preamplifier design. -- interview with John Hardy on different design aspects. -- The Design of Microphone Preamplifiers, by John La Grou.

Listening Comparisons:
3D Audio -- a well made microphone preamplifier comparison CD ready to order.
The Listening Sessions -- a ton of mp3s to download.


Books that cover microphone preamplifier design directly:
Audio IC Op-Amp Applications
Walter G. Jung
Howard W. Sams & Co., 3rd edition, 1986
ISBN: 0-672-22452-6

Microphone Engineering Handbook
Michael Gayford
Focal Press, 1994
ISBN: 0-7506-1199-5
Chapter 8 (Microphone amplifiers and transformers)

Handbook For Sound Engineers
Glen M. Ballou
Focal Press, 3rd edition, 2002
ISBN: 0-240-80454-6
Chapters 11 (Audio transformer basics), 21 (Preamplifiers and mixers) and 25 (Consoles and computers).

Op Amp Applications Handbook
Walter G. Jung
Newnes, 2005
ISBN: 0-7506-7844-5

Books with related information, mostly on low-noise design:
Low-Noise Electronic Design
C. D. Motchenbacher and F. C. Fitchen
John Wiley & Sons, 1973
ISBN: 0-471-61950-7

IC Op-Amp Cookbook
Walter G. Jung
Howard W. Sams & Co., 3rd edition, 1987
ISBN: 0-672-22453-4
Part I (Introducing the IC Op Amp) and Part II, Chapter 7 (Amplifier Techniques)

Low-Noise Electronic System Design
C. D. Motchenbacher and J. A. Connelly
John Wiley & Sons, 1993
ISBN: 0-471-57742-1

Audio Electronics
John Linsley Hood
Newnes, 2nd edition, 1999
ISBN: 0-7506-4332-3
Chapter 3 (Preamplifiers and input signals)

Self On Audio
Douglas Self
Elsevier, 2000
ISBN: 0-7506-4765-5
Chapter 10 (Design of moving-coil head amplifiers)

Application notes:
High-Performance Audio Applications of The LM833
Section 4 (Transformerless Microphone Preamplifiers)

Microphone Preamp using a THAT 120 Transistor Array

Configuring gain with the THAT 1510 and 1512
I have an Excel chart designed to be used for calculating the feedback resistor values in a 12 step switched op amp based mic preamp. For download at the top of the page: Direct link:
Apologies if im posting in the wrong place, first post on this forum.

Quick question, if anyone can help. I am putting together a G9 and found a Transformer with a 15V 1A winding on it. I intend to use this for the phantom power. Does anyone have a problem with this? Is 1A overkill?


1A is way overkill for PP. But also, 15V won't get you to 48V even with a tripler, not even accounting losses from regulation, etc.

The Lab forum is actually the more appropriate place for questions like this. This thread is meant to serve as a convenient aggregation of mic preamp threads, it does not technically function as a thread itself.