Bored with all the common microphone circuits?

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Gus

Well-known member
Joined
Jun 3, 2004
Messages
5,249
Location
n
Bored with all the common microphone circuits?

External powered solid state idea(not built)

Positive ground. Like some Rode transformerless microphones so you can use electrolytic caps at the output with or without phantom on. Noticed this when I traced a NTK/K2 microphone some years ago

Differential input (issue differential input has more noise than single input)

Followers like used in some Sony microphones

Some parts should be matched.

Can add matched CCs in the follower source/emitter leg in place of the resistors.

Resistor and caps values can be changed in some places for input resistance and capsule loading

Will it do anything much different or "better"? I don't know I have not built it yet  Right now it is just something different.

Sometimes I draw up different ways to build a microphone circuit trying to do things a little different. This does not mean they are any better than what has been done just different.

Discuss
 

Attachments

  • posgnddiff.png
    posgnddiff.png
    85.2 KB · Views: 141
Gus said:
Positive ground. Like some Rode transformerless microphones so you can use electrolytic caps at the output with or without phantom on.
If it was a real concern I would use NP caps, but it's not since modern lytic caps tolerate reverse voltage reasonably well.


Differential input (issue differential input has more noise than single input)
Since acoustic radiation noise and QTC noise are dominant, that shouldn't be a problem.

Followers like used in some Sony microphones
I believe there is potential improvement (THD, headroom) in choosing complementary pairs (Szlikai-ish) and/or full NFB with opamps in the loop.

Will it do anything much different or "better"? I don't know I have not built it yet  Right now it is just something different.
That may well be the final answer...
After all, the big question is what needs to be improved in microphones today?
 
Thanks for the reply.

I did not say this was a good design just different than most.

I agree with your posts about adding EQ after the microphone.

The post was about having some fun with a different take on a microphone circuit.

I don't have any issues with opamps in microphones, some people do that is why the simple followers

I did not post an AKG EB like with bootstrapped drain or the better AKG, Neumann style. Look at a TLM170 or AKG 3000 follower etc for examples.

Build the 3000 type circuit without the top boost add a good capsule and grill environment. Someone posted about this on the forum in the past

It is funny to me with all the builds using China capsules and tiny T14 size lams without Is


Another thing you kind of brought up
Why are Schoep type circuits missing Darlington or Sziklai outputs?

https://sound-au.com/articles/cmpd-vs-darl.htm

 
I haven't analyzed your circuit Gus, but appreciate the desire to encourage folks to not just build one of the usual circuits out there, also that you post ideas here for discussion.
Even without doing analysis, I'm sure what you did post is a perfectly good circuit.

The only problems I've found with CFP/Sziklai pairs is possible instability when it's part of a global feedback loop. 
In a microphone where you'd probably be running it naked (or at least not part of a high OLG amp), then I see it as a good thing to consider using.
Having a discrete power supply too rather than running off phantom opens up all sorts of possibilities.

Years ago, I was testing one of the Cinemag replacement mic transformers that are typically driven from an anode or drain.
As one would expect, driving the transformer from a low source Z follower reduced transformer distortion on the bottom end.   
Is that a good thing?  I suppose it depends what the user wants.  I'd certainly think about adding a follower to a transformer coupled gain stage myself.

Diff-amp - yep we have around 3dB more noise.  Will it matter?  I dunno.
I suppose you could double up on the J-Fets if the capacitance isn't too high and you need it to be about the same noise figure as without the diff-amp.
Cascode them if that's your thing.

What's QTC noise that Abbey mentioned? 




 
So hows about some gain ?
Let's say between 0 and 40 db ?
Running from 9V - 52V phantom power with a current consumption of < 2,5mA ?
And the noise specs from below ?

index.php


 

Attachments

  • the-gain-mic-by-analogguru-snr.gif
    the-gain-mic-by-analogguru-snr.gif
    5.1 KB · Views: 372
Very good impedance converter. Flat from 10Hz and beyond 10Mhz. Unity gain when the differential is recombined. So 1V in nets you .5V +/-
 
micc.png

Now it's swinging +/- 3.5V. No need for a pre? Anyway it's bedtime I'm not at my brightest right now!
 
Gus said:
Bored with all the common microphone circuits?.....
I must admit I've been a bit disappointed that some of the more experienced experimenters on this board didn't find the RF project we discussed here: https://groupdiy.com/index.php?topic=71586.0  interesting enough to take any further?
 
I enjoyed doing the experiments that ended up as my version of the idea: http://www.amx.jp137.com  which of course included a lot of input from other posters on this board, but no one else seems to have wanted to take the idea any further.  Perhaps using SDC capsules for example?..

Looking at the posts on this board over the last year or so, and it seems that there is LOTS of interest in various versions of old tube mic 'clone' projects .. which do tend to be about the same old circuits, IMHO... 

I would have thought the comparative rarity of  RF mic circuits might have stimulated some interest from experienced experimenters here, looking for something a bit different as a hobby mic project?   

Apparently not, it would seem?....
 
abbey road d enfer said:
West-East collaboration, Darlington + Szlikai !

Not something seen in mics that I'm aware of, but certainly a combo used elsewhere. 
Thanks gus, abbey, analogguru, analag, and rogs :)   
 
rogs said:
I must admit I've been a bit disappointed that some of the more experienced experimenters on this board didn't find the RF project we discussed here: https://groupdiy.com/index.php?topic=71586.0  interesting enough to take any further?
 
I enjoyed doing the experiments that ended up as my version of the idea: http://www.amx.jp137.com  which of course included a lot of input from other posters on this board, but no one else seems to have wanted to take the idea any further.  Perhaps using SDC capsules for example?..

Looking at the posts on this board over the last year or so, and it seems that there is LOTS of interest in various versions of old tube mic 'clone' projects .. which do tend to be about the same old circuits, IMHO... 

I would have thought the comparative rarity of  RF mic circuits might have stimulated some interest from experienced experimenters here, looking for something a bit different as a hobby mic project?   

Apparently not, it would seem?....

Your RF circuit is in the list of things to build. I followed the thread I did not post because I had nothing to add.

 
analag said:
micc.png

Now it's swinging +/- 3.5V. No need for a pre? Anyway it's bedtime I'm not at my brightest right now!

Looks like a fun build.
The next step I was going to maybe post was a dual matched CCs for the follower resistors.
 
I am a little bored with tube to transformer out microphone circuits they are kind of easy to build and often work. So I built a few solid state tube voltage transformer out circuits for fun. I would not call them a tube replacement more of what is "good" about solid state and tubes in a transformer out microphone.

I have been finding transformerless circuits more interesting Things like Neumann, TLM170, TLM67(I asked a member about pictures of the PCBs and they sent some to me. I have to admit I was defeated by the epoxy? coating when trying to trace it) I was wondering what the tube sound circuit(if it has one) was that looks like it is under the epoxy. The output looks like it might be a rail to rail op amp impedance balanced and I would guess the input is nicely design input follower.

This thread is interesting I like the circuit design(without the boost)
https://groupdiy.com/index.php?topic=67911.0

The MXL CR89, 890, and two more models have a nice circuit design. This surprised me I bought a few for the bodies and left them stock. I cleaned up the flux saw a few things I would change however, the circuit sounds good stock.

The bootstrapped drain in one of the akg 414 first stages is interesting for an older design. I have not seen this copied in a clone.

I am not a fan of the charge amp with a limited openloop gain stage. I could be fooling myself but it sounds a little odd to me.




 
mikk.png

Here is the schematic of two of my working solid state mikes. One is edge terminate and the other is center terminated capsule. C2 is the capsule, R13 is omitted.
 
Pretty sure C12 is unnecessary there. And/or R7.

Well, that's unless you enjoy the 8-9 minutes of "warm-up time" that the circuitry would need, for the capsule bias voltage to reach maximum... ::)

(1 gig and 100nF give a time constant of 100 seconds to reach 63%, and about 5 times as long to reach maximum. And that's not even counting the time constant of the filtering before that...)


analag said:
mikk.png

Here is the schematic of two of my working solid state mikes. One is edge terminate and the other is center terminated capsule. C2 is the capsule, R13 is omitted.
 
analag said:
mikk.png

Here is the schematic of two of my working solid state mikes. One is edge terminate and the other is center terminated capsule. C2 is the capsule, R13 is omitted.

FWIW if I traced the Phantom C from pictures correctly(2004) it uses a source follower output I am guessing for a little higher output resistance than a emitter follower.
Some Sterling/groove tubes solid state microphone use a 200 ohm series resistor after an emitter follower before the transformer.


 
Back
Top