Pronomic SCM-1

[Khron]

Those output transistors, have you replaced them? Or were they just hand-soldered (or hand-reworked) at the factory?

That source resistor on the edge of the board makes (more) sense,  since the bias varies with each individual JFET...

Received, inside photos.
I'll do better photos later with Nikon.

 

[JuanV]

I did not replace anything, it's stock photo after delivered to me.

 

[e.oelberg]

With a cutter you can remove the pronomic sign without scratches

 

[ln76d]

With a cutter you can remove the pronomic sign without scratches

Nitro solvent is much easier and safer to remove logo

 

[e.oelberg]

Nitro solvent is much easier and safer to remove logo

true

I did a couple of test with the mic but I didn't compare, usually i get annoyed of the sound of mics after a while. For instance  MBHO or Rode or Oktava or this very same mic with the old capsule. But with the new capsule I must admit, I like  them very much. They sound like no need for any eq to my ears.

 

[RuudNL]

I still want to measure and compare the Banzai "KM84" capsule and the Pronomic.
But busy, busy, busy...

 

[RuudNL]

I finally measured the "Banzai" capsule and the (new) Pronomic capsule.
The frequency response matched almost exactly! ( A centimeter difference in position can already make a difference.)
So I have the impression that they are made by the same manufacturer.

 

[JuanV]

So update pronomic mic with Banzai PCB (not available i guess) can do some improvements ?

 

[Icantthinkofaname]

So update pronomic mic with Banzai PCB (not available i guess) can do some improvements ?

I think the capsule is the important part. So buying a similar capsule to the Banzai one and installing it on an older Pronomic SCM-1 would be an improvement. The PCB would probably be less so because it seems that the capsule was the problem (or rather a bright installed in a circuit with no HF de-emphasis). Because the new SCM-1 is very balanced/neutral it's probably that the Banzai capsules are designed to be really flat sounding. Unless the new mics have a new circuit with HF de-emphasis but then why change the capsule?

 

[RuudNL]

Circuit of the "old" and "new" Pronomic microphones is (almost) the same.
The old ones had a trimpot to adjust the FET bias.
But both microphones are based on the "Schoeps" circuit, with a DC/DC converter for the polarisation voltage.
If Banzai is planning to sell the capsules separately (I think he mentioned this already), this capsule would be a great update for the "old" Pronomic or Takstar CM-60 microphones.

 

[JuanV]

I thought replace pronomic PCB with Banzai PCB with transformer - different circuit. Without changing capsule. But i do not know if banzai circuit is better than pronomic.

 

[RuudNL]

The Banzai circuit is the original Neumann KM84 circuit.
Personally I wouldn't go through all this trouble (expensive transformer!), because the stock Pronomic SCM-1 is good as it is.
(Anyway for me...  A transformer doesn't add quality, I prefer a transformerless circuit.)

 

[e.oelberg]

I agree with Ruud. The mic sounds just fine. Btw a Schoeps also sounds fine and  has no transformer. One of my mics needed a pcb wash and I will bias the FET if I have time. I guess  the Banzai capsule and the new pronomic are identical ...

 

[homero.leal]

The Banzai circuit is the original Neumann KM84 circuit.
Personally I wouldn't go through all this trouble (expensive transformer!), because the stock Pronomic SCM-1 is good as it is.
(Anyway for me...  A transformer doesn't add quality, I prefer a transformerless circuit.)

RuudNL,

Some time ago I published a Transformerless KM-84 schenmatic on the MicBuilders forum, if you want to give it a look.

https://groups.yahoo.com/neo/groups/micbuilders/files/Homero%20Leal%27s%20Files/Transformerless%20KM-84%20Refresh/


It works pretty well. I also have some PCBs left for BM-800/700 or MXL mic bodies,  if some want to try it.

Regards!

HL

 

[RuudNL]

Sorry, I can't find it.
It says:

"Oops!
You need to be a member to perform this action. "

Well, I am a member (and logged in), so I don't know what went wrong.

 

[homero.leal]

Ohh... that's strange... but anyway, i uploaded the schematic to my gdrive.

Try this link:

https://drive.google.com/file/d/10XbRknHqym6CZcVSylNRdk2m7URl4wEc/view?usp=sharing

For the actual build, I used:
- 39pF mica  cap for C14.
- 5k6 for R6.
- Jumper wire for R19.
- And 0.1uf film cap for C11.

Kind regards!

HL

 

[RuudNL]

Thanks.
Some remarks about a couple of  things that come to mind at first sight:

- I don't really see the point of using 3 resistors (R17, R18, R19). I suppose two 10 M.ohm resistors would do the same.
- The filtering for the polarisation voltage is a bit extreme.  0.1 uF + 1 G.ohm will cause a very long charge time!
(Something in the order of 100 seconds or more than 1.5 minute!)
- Personally, I don't like OpAmps in microphone circuits, but it has been done before, so it will probably work.

For the rest it is basically a KM84 circuit with an OpAmp buffer, so I don't expect real problems.
I suppose this will be a "high output" microphone, because in the KM84 a step down transformer is used, but in this design there is even 6 dB gain after the FET. But maybe this is already compensated by C14.

 

[Khron]

Just to chip in real quick, i'd personally lean towards using a dual opamp instead of two singles
Less board space, less traces to route, and potentially even lower current draw, as well as cost.

 

[homero.leal]

Yes Khron, I agree... originally, schematic had a dual unit OpAmp... but this design requires a very low quiescent current OpAmp.

I found the OPA145 that uses just 0.475mA per unit, but I could not find the dual version of it. So I had to stick with the single unit version.

To save space, I placed one OPA on the top, and the other at the bottom of the PCB.

I also considered OPA1692, but it's very tiny, may be for a next version.

If you have more options on low current Opas,  that could work, plz let me know!

Regards!

HL

 

[homero.leal]

- I don't really see the point of using 3 resistors (R17, R18, R19). I suppose two 10 M.ohm resistors would do the same.
- The filtering for the polarisation voltage is a bit extreme.  0.1 uF + 1 G.ohm will cause a very long charge time!
(Something in the order of 100 seconds or more than 1.5 minute!)

Yes RuudNL, you are right.

I suppose this will be a "high output" microphone, because in the KM84 a step down transformer is used, but in this design there is even 6 dB gain after the FET. But maybe this is already compensated by C14.

Yes, that's the reason C14 is 39p on my actual build.

Regards!