microphone circuit

Help Support GroupDIY:

Gus

Well-known member
Joined
Jun 3, 2004
Messages
4,893
Location
n
Easy this is gift of knowledge and learning not some blind hack at the circuit.
How many people own 2001s v67s and other microphones with circuits like this.  This is an easy inexpensive change to try.  One can then install other circuits if you don't like it.

Move the stock C1 .01uf to C6
add a 1meg
remove and install six other inexpensive parts
change one connection point
Leave the stock tants for now
I would use a film cap for C8

You might find the EQ and changed bias points useful.

Then if you like it, change caps to taste and match the 2.21Ks and 42.2ohms

 

dmp

Well-known member
Joined
Oct 28, 2009
Messages
3,098
Location
Madison, WI
Easy this is gift of knowledge and learning not some blind hack at the circuit.

If you are taking offense, perhaps you should read your own past posts in other people's threads. I don't see much of any gift.
A thread I started for a project I have been working on for weeks whenever I have the free time, and you post:
"You have some reading to do."
Arrogant and condescending comes to mind.
 

Gus

Well-known member
Joined
Jun 3, 2004
Messages
4,893
Location
n
Why does anyone care what I write? you don't need to listen.

The gift was meant as a gift this is a collection of things I learned over the years playing with microphones, a few adjustment to the circuit that some might find useful.  The web is limiting in conveying information you don't have the face to face interaction.

I have been told I am a minimalist.  A hint I like a few of William Carlos Williams poems.
 

mitsos

Well-known member
Joined
May 4, 2007
Messages
2,886
Gus said:
Why does anyone care what I write? you don't need to listen.
haha, nice. yeah, that goes for everyone here I guess.  Anyway, I wish we had more of these kinds of threads. A Mics 101 thread, like CJ's Electronics 101, would be cool to have.
 

hitchhiker

Well-known member
Joined
Jun 4, 2004
Messages
875
Location
vancouver island,bc,canada
William Carlos Williams poems are great to me!

Anyway,  if I had any of these budget mics around here I would most certainly welcome your offerings to tweak them at almost no expense. I hope you keep posting these offerings because there are too many mics out there in need of improvement that also for other reasons may not warrent the expense of upgrade transformers etc etc.

Cheers,
Lance
 

pyjaman

Well-known member
Joined
May 31, 2007
Messages
295
Location
Poitiers,France
Hi ! I can get everyone's point here . And I have to say I'm mostly in the dark regarding the different modifications Gus posted in this thread... I'd better just shut my... (but I'm a little bit drunk tonight, so...)
My point is: many discusion in this forum have been beyond my understanding, for years, and I LOVE when people take the time to answer my questions and/or explain things from the begining.
But sometimes discusions seems to be for the bigger boys...
And as I, and many others who are just amateurs with very few spare time, the more professional/experienced guys neither may have the time to start an "electronic 101" thread each time they post.
I Have learned A LOT from you, Gus, (mostly on microphone design), reading old posts, or from the answers you gave me to my few questions about the subject.
One day, in an uncertain future, I'll put my hand on one of those MXL mics, and I' get back to this thread.
When I'll be a bigger boy.
Thank you to all the guys I d'ont understand today. I'll still Have spare time when I can get what they're talking about.
Laurent.
 

Gus

Well-known member
Joined
Jun 3, 2004
Messages
4,893
Location
n
adjustedV67m.PNG


A screenshot of the LT Spice simulation of the circuit  2K load on the microphone note the roll offs.

Again I am not saying this is the best etc adjustment it is one of a few you can do with this type microphone circuit and the stock capsules and transformers. 

I am surprised at some of the posts in this thread.  I just gave away a nice low cost adjustment of a microphone circuit that can be found in a few different microphones.

tommypiper
note the part numbers in the first post look at the part numbers on the MXLV67 PCBs

link to a 2001 schematic  http://www.xaudia.com/omnip/Mics/MicSchLib/mxl2001.gif
 

bockaudio

Well-known member
Joined
May 30, 2008
Messages
244
Location
Los Angeles, CA
nicely done, Gus.
There really isn't anything here that hasn't been covered a thousand times, why the agita?
I also like that you didn't bother to include the optional HPF between the fet and the BJT, that capsule sure don't need it.
I recall when the Rode NT1 came out, around 16 years ago, before Chinese capsules were acceptable in the marketplace, and were decidedly thin sounding. The NT1 had a HPF. Why? There's no bass to cut!
 

Gus

Well-known member
Joined
Jun 3, 2004
Messages
4,893
Location
n
I see that a few people have viewed this thread.

I will try to answer some of the posts
The schematic in the first post is from a MXLV67 trace.  It is a screenshot of a LT spice sim.  The part numbers are the same as what is marked on the board I traced it from.  After I adjusted values in the sim I then changed some parts in a MXLV67.

Years ago I bought a number of MXLV67s with the painted grill.  I left the stock capsule and grill in most of them.
I thought it might be fun to see what I could do with the MXLV67 type circuit changing the smallest amount of parts and keeping the stock capsule and transformer.  This circuit is one of a few adjusted circuits in MXLV67 etc type microphones.

One of the links I posted in this thread seems to be broken.  It was a link to a post with the high-pass and low-pass -dB response of a U67 circuit.  Compare to the frequency response posted screenshot curve.

So the point of this thread is a simple adjustment to this type circuit.  It is a little different than what you find in forums for "mods" to this type microphone circuit.  The values of the components have been adjusted with LT spice to give an overall circuit response that might be useful.  If you look in a book like "The Art of Electronics" for the type of biasing used for the EF you should understand why I added one resistor, then there is the input resistance of the EF follower section and how it loads the jfet stage before it.

So this thread is about some part changes to this type microphone circuit that people might learn from.  It is a few resistor and caps changes, one cap needs to have one connection point changed and you add R100.  Also I find LT spice useful in adjusting and designing solid state, solid state and tube and tube microphone circuits.

It is a set of compromises keeping most of the stock parts and circuit.  Note the stock circuit does not have a voltage regulator like a u87 km84 etc circuit does.

I might install a  k67 capsule in the microphone I adjusted as test.

EDIT I should add I would not build this from parts it is more of an adjustment of the MXLV67 type circuit that some might find useful keeping most of the stock parts.  I would build different solid state circuits with regulated supplies and greater capsule voltage etc.

I have a number of microphone circuits designed/simmed some built.  Been running sims/thinking about phantom power designs since people seem not to want to have an external power solid state microphone.
 

tchgtr

Well-known member
Joined
Feb 25, 2009
Messages
467
Location
Los Angeles
Thanks for this Gus.
I, for one, appreciate your input in this area, but have yet to try this out, as other projects have intervened. It's simple, so I will get to it, and I also have a few of these capsules lying around left over from some other projects.
This might get seen more if it gets to the new "microphone" listings...can anyone do that?
 

leswatts

Well-known member
Joined
Apr 29, 2009
Messages
269
Location
Tiger, Ga USA
Hi Gus.

I use a somewhat similar circuit in a production mic.

So for this I see a fairly high gain common source with partially bypassed degeneration. I also see gate feedback.

I don't use extensive LF rolloff in the tronics. I do this by reducing capsule acoustic damping and raising resonance...for the small capsules I use
there is noise advantage.

I do use a slight HF shelving before the EF.

And I use 60V polarization via the typical Hartley circuit. It's a "Hot diaphragm" which eliminates the coupling cap to gate and allows atten pad
by pol voltage change rather than distortion inducing shunt capacitance.

So in general I use much less first stage gain and higher pol voltage. But mine is optimised for very small diaphragm.

Those are my comments FWIW.

Les
L M Watts Technology
 

bockaudio

Well-known member
Joined
May 30, 2008
Messages
244
Location
Los Angeles, CA
leswatts said:
And I use 60V polarization via the typical Hartley circuit. It's a "Hot diaphragm" which eliminates the coupling cap to gate and allows atten pad
by pol voltage change rather than distortion inducing shunt capacitance.


Les
L M Watts Technology
how does the shunt capacitance induce distortion?
 

leswatts

Well-known member
Joined
Apr 29, 2009
Messages
269
Location
Tiger, Ga USA
If one separates active and stray capacitance Ca and Cp (where Ca is delta pressure dependent) the output with a voltage amplifier
at constant charge is  Q/Ca+Cp. Then expand into a power series.

All explained well here.

orbit.dtu.dk/getResource?recordId=249608&objectId=1...1

There are some B&K papers on it as well...where they use a negative capacitance input impedance stage to eliminate it.

It of course also causes capacitive voltage division...attenuation.

We have to take great pains to minimise it in mems designs.

Les
L M Watts Technology
 

dai h.

Member
Joined
Oct 9, 2009
Messages
17
(looks like this one--I hope this is correct)

"Modelling distortion in condenser microphones"

http://orbit.dtu.dk/getResource?recordId=249608&objectId=1&versionId=1
 

leswatts

Well-known member
Joined
Apr 29, 2009
Messages
269
Location
Tiger, Ga USA
Thanks for correcting the link Dai.

Any stray capacitance from dead areas of diaphragms, wiring, and amp input capacitance induce this distortion with constant charge systems.

To keep this on topic I suspect the 2SK170 is not the best device choice for this circuit. While very low noise it has HUGE input capacitance
that would be multiplied much further (Crss*-Av) by miller effect in the common source configuration shown.

I suspect the capsule acoustic resistance noise would much bigger than the 2SK170.

Consider something with lower capacitance like a selected J201, 2N4416, or LS846.

Les
 

bockaudio

Well-known member
Joined
May 30, 2008
Messages
244
Location
Los Angeles, CA
excellent link, thank you. Will read this week.
Interesting I know more than one older, geniusier EE/eletroacoustic transducer designer mfg's who would argue capacitive pads do NOT induce distortion, theoretically, including the designers at Neumann (past).
I can see that the stray cap issue is of more concern to small D mics. I wonder, for those who are changing polarzation voltage is if they have accounted for the change in frequency response, which becomes more dramatic as the membrane size decreases, or it doesn't matter-whatever?
In the Soundelux U195 I did this (non-capacative pad) in 1995, and wonder if it had been done before. My argument against capacitive pads was from the music engineer's view, as I and every other engineer I knew felt the cap pads altered the sound too much, not from a pure EE point of view.
 

ricardo

Well-known member
Joined
Apr 28, 2011
Messages
1,431
bockaudio said:
I wonder, for those who are changing polarzation voltage is if they have accounted for the change in frequency response, which becomes more dramatic as the membrane size decreases, or it doesn't matter-whatever?
In the Soundelux U195 I did this (non-capacative pad) in 1995, and wonder if it had been done before. My argument against capacitive pads was from the music engineer's view, as I and every other engineer I knew felt the cap pads altered the sound too much, not from a pure EE point of view.
I did the pad with reduced Vp on the Calrec Soundfield Mk4 circa 1980(?).

I'm not sure either method changes the frequency response enough in the audio range that it matters.  I've never designed a mike with a cap pad so can't claim to have done extensive listening tests.  There is more distortion but again I'm not sure enough to matter unless you were interested in specs rather than sound.
 
Top