Gus

interesting microphone circuit
« on: March 10, 2019, 04:37:52 PM »
Traced a microphone I bought for the body it turned out to be interesting.


analogguru

Re: interesting microphone circuit
« Reply #1 on: March 10, 2019, 06:04:54 PM »
Is this a Samson microphone ?

gyraf

Re: interesting microphone circuit
« Reply #2 on: March 11, 2019, 03:34:33 AM »
..rotated for readability..
..note to self: don't let Harman run your company..

RuudNL

Re: interesting microphone circuit
« Reply #3 on: March 11, 2019, 04:24:20 AM »
Personally I am not a big fan of adding resistors (in this case 2 x 100 ohm) in series with the output, because it increases noise.
(I do understand why they do this, but I would prefer a lower value.)
There is a solution for every problem!

http://www.vansteenisaudio.nl

Gus

Re: interesting microphone circuit
« Reply #4 on: March 11, 2019, 05:43:21 AM »
MXL 190

Bought a few on sale for the body and grill thinking 49, 50 like.

I don't know why 100 ohms were used could be due to the opamp drive or something(s) else.

Microphone has two Nichicon 100uf electrolytics and a few film caps I did not pull the SMD ceramics to measure them.

The use of the 6241 is what I find interesting.

Something different than a Schoeps like circuit.

RuudNL

Re: interesting microphone circuit
« Reply #5 on: March 12, 2019, 12:57:52 PM »
It seems the only reason for using a dual-OpAmp is the high pass filter, since there isn't any gain in the circuit.
I will take a closer look at the specifications of the OpAmp.
In the past most OpAmps were simply too noisy to use in an application like this.
Behringer used a TL07x OpAmp in their C3 microphone...
That is probably the reason that this microphone is even too noisy to record hardrock!
There is a solution for every problem!

http://www.vansteenisaudio.nl

RPC360

Re: interesting microphone circuit
« Reply #6 on: March 12, 2019, 03:36:58 PM »
So the LTC6241HV has a noise spec of 7nV/rtHz typical, 10 max. Two in series would give you about 10 typical/14 max, discounting any additional noise from the output stage. This would be about 6dB more noise than a JFET such as a J201. You also get a low impedance output stage for "free." As RuudNL says, not the way I'd have done it, but functional. You could maybe drop in e.g. an OPA1642 and get 3dB less noise.

analogguru

Re: interesting microphone circuit
« Reply #7 on: March 12, 2019, 03:40:03 PM »
Samson uses a TL072 too in their C03 (they appear very similar).  10nV/V-Hz for the 6241 is not amazing.  In the Samson Meteor they use a MAX4475.  Rode has a discrete Buffer stage in the M2 (M3?) which is followed by an OP184.  All these mics have electret capsules....

Gus

Re: interesting microphone circuit
« Reply #8 on: March 15, 2019, 06:02:52 AM »
As I said I found this interesting.
 
Something instead of a Schoeps based transformerless.

Mix of leaded and SMD parts.

The 100 Ohms can be lowered if you want they are leaded parts.

Seems to have lower noise than the TL07x based microphones I have heard.

Something I am thinking about testing is the 6241HV noise with 1Gig at the input and then with lower values.

The input resistor load is a  that I have not measured I took a guess that it is 1gig.

Why are most of the post negative? I did read the spec sheet on the 6241. I did not post anything more than it was interesting to see something different.

The capsule mount and grill are different than the bodies you find used on a lot of microphones.

 

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