Help with homebrew mic preamp please!!!

[mwmitchell]

Hi everyone,

I have been messing around with a balanced preamp for a low impedance dynamic microphone (like a shure sm-57). Problem is I don't know much about this stuff and have no software to help build it. So, I have been tweaking wires and values to get good results, mainly using potentiometers in place of the cathode and plate resistors. I have attached my circuit and was wondering if I could get some comments on it, or maybe even have someone build it in software and test it!! That would be most appreciated.

I know that mic preamps really benefit from a transformer or solid state input for hi gain and low noise, but I just want to try something different here. C

ould anyone suggest a good output stage for this thing?

Is it un-common to have a balanced, low signal pentode input stage?

What exatly do you do with the screens grids in this situation?

Thanks for any help at all. The circuit is attached below...

-Matt Mitchell

 

[phil]

Have a look at this, it may help or give you some ideas.
http://laplaza.taos.nm.us/~fvuotto/micpre.html

 

[dice45]

Matt,
dynamic microphones are like moving coil cartridges in output level and source impedance.

Methinks, pentodes are too noisy for that.

A circuit you could try : look at Allen Wright's differntial preamp RTP3 or RTP5. His website is www.vacuumstate.com . TMK, this preamp also was used as professional µphone preamp. Without phono EQ of course.

The thing uses cascodes for the input stage, the lower system being a 2SK147 FET and the upper one an ECC88 triode section. This preamp has no noise problems and is ultra-neutral; detail resolution is top-notch.

 

[DrExotica]

ISO MC pre-amp design

On the topic of moving coil cartridges, is anyone aware of a reasonable pre-amp design that can handle one? Most of the designs that I have seen are for moving magnet. I have a Linn Troika on an LP12 that I'd love to be able to send through a tube pre-amp and amp.

Thanks for any ideas.

 

[fdegrove]

Erik,


Take a look at the thread Marjan posted for 6922 in the directory of this section.
Several circuits were suggested there.

Rgds,

Frank.

 

[fdegrove]

MIC PREAMP

Hi Matt,

Check out this link for inspiration on yr. project:

http://www.gyraf.dk/gyraf2/gy_pd/g7/gic.htm

Rgds,

 

[Brett]

Re: ISO MC pre-amp design

On the topic of moving coil cartridges, is anyone aware of a reasonable pre-amp design that can handle one? Most of the designs that I have seen are for moving magnet. I have a Linn Troika on an LP12 that I'd love to be able to send through a tube pre-amp and amp.

Thanks for any ideas.

Erik,

If you want a single ended design, look at www.vacuumstate.com for the FVP5.

Cheers
Brett