RuudNL

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #20 on: August 04, 2019, 06:33:26 AM »
I don't think the AC126 is the best transistor for a microphone preamp...
There is a solution for every problem!

http://www.vansteenisaudio.nl


Re: Shure SM 57 Battery Mic Preamplifier
« Reply #21 on: August 04, 2019, 07:00:08 AM »
it intrigued me because it seems to be the schematic of an old low impedance commercial mic preamp

RuudNL

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #22 on: August 04, 2019, 09:22:14 AM »
An AC126 isn't exactly what we would call 'low noise' today!
There is a solution for every problem!

http://www.vansteenisaudio.nl

squarewave

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #23 on: August 04, 2019, 09:37:54 AM »
No. That has no gain.

The one posted by Strawtles is good. Try that one.

RuudNL

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #24 on: August 04, 2019, 10:19:12 AM »
Well, in fact it has gain. And noise. And distortion...
The Strawtles one is much better. And with modern components.
There is a solution for every problem!

http://www.vansteenisaudio.nl

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #25 on: August 04, 2019, 10:58:53 AM »
In the Strawtles circuit, what should be the value of Rf?

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #26 on: August 04, 2019, 12:16:31 PM »
Sorry I don't know. I have the schematic but I never built this preamplifier
I am sure someone can help you with this value  :)
« Last Edit: August 04, 2019, 12:29:22 PM by Strawtles »

radardoug

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #27 on: August 04, 2019, 05:39:52 PM »
Change Rf to change the gain. Put a pot in there and see what happens. And you still haven't told us why you cant use the mike preamp built into your device.

squarewave

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #28 on: August 04, 2019, 07:21:03 PM »
Well, in fact it has gain. And noise. And distortion...
Right sorry. The old upside-down PNP tricked me.

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #29 on: August 04, 2019, 08:47:55 PM »
What about a coin cell powered pre board that solders inside the body of the mic itself ,  could fit on a postage stamp  ,unscrew the mic body to change the batteries ,of course two 3 volt cells will limit output voltage , but if your well upto line level into 10 or 20 kohms it wouldnt matter much . Ive seen very high quality coin cell pre's made for acoustic guitars ,Fishman ones they work great ,tons of output level . Requirements for dynamic mic pre with balanced output are slightly different ,but might be do-able easily enough  . 


PRR

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #30 on: August 04, 2019, 09:11:43 PM »
The 200k 100k is an essential part of the DC stabilization.

(EDIT- fumble fingers)
« Last Edit: August 05, 2019, 11:30:38 PM by PRR »

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #31 on: August 04, 2019, 10:59:33 PM »
What value of potentiometer can I use?

It can be better to increase the value of input capacitor (C1) to 1uF ?

May help to reduce the R3 Value?

Consider I will use this preamp with a SM57

Thank you


radardoug:  the preamp in my device (M-Audio Microtrack) is noisy  :)
« Last Edit: August 05, 2019, 03:27:16 AM by Liutmod »

RuudNL

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #32 on: August 05, 2019, 04:27:48 AM »
What value of potentiometer can I use?
It can be better to increase the value of input capacitor (C1) to 1uF ?

The input impedance (R3 in parallel with the impedance on the base of the first transistor) is pretty high, so I suppose 0.1 uF is more than enough for a good frequency response. Changing R3 would also have some influence on the gain of the circuit.
I would start with a 100 K.ohm pot for Rf and see what happens.
There is a solution for every problem!

http://www.vansteenisaudio.nl

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #33 on: August 05, 2019, 06:09:03 AM »
Is it possible the 200k mentioned by PRR is for R3 value?

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #34 on: August 06, 2019, 03:38:50 AM »
No other suggestions to improve this circuit?

Khron

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #35 on: August 06, 2019, 06:41:09 AM »
Prototype it (on a breadboard, or even point-to-point if you're brave / adventurous), test it, THEN maybe see if it needs any tweaks.
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

RuudNL

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #36 on: August 06, 2019, 09:22:09 AM »
I get the impression that forum member Liutmod would like us to deliver him a finished and optimized design, and preferably build it for him...

But this is GroupDIY:P
There is a solution for every problem!

http://www.vansteenisaudio.nl

Khron

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #37 on: August 06, 2019, 10:17:48 AM »
No offense, but this forum is called "GroupDIY", not "Group-have-someone-else-do-it-for-you"... ;)


I get the impression that forum member Liutmod would like us to deliver him a finished and optimized design, and preferably build it for him...

But this is GroupDIY:P
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

mjrippe

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #38 on: August 06, 2019, 10:44:49 AM »
Just buy an RTS 1400.  Transformer in/out, gain control, switchable limiter, runs on 2x 9V.  On ebay for about $50 used.  Search this site for more info.

Re: Shure SM 57 Battery Mic Preamplifier
« Reply #39 on: August 06, 2019, 11:44:53 PM »
Beacuse at the momentI have not the time to try the many circuits on the net, in my first post I have written that I am searching for a battery preamplifier schematic optimized for Shure SM57
This means I need a schematic tested not that I want it realized for me  :)





 

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