Convert MXL3000 to 84 type, could it be this easy?

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Dec 13, 2017
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I've got an MXL 3000 that is very easy to work on, but I've found it captures too much above 10k. It might even be noise, I'm not sure.
The circuit is almost exactly a V67 except the input stage is direct from capsule to fet. I know this circuit has been a target of modding to an 84 type by removing the transistor follower and replacing it with a higher ration transformer. I've replaced the transformer. My question to you all is can I simply cut the traces at the 2 'x' marks and connect the the 'A''s together?

2nd question is - would a C12 type capsule work better with these changes than say, an 47 or the existing 67?
 

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I would increase C3 to something in order of 600pF without thinking or hearing stock mic. It would get the response of the mic close to u87. You might try even with 800pF, or even a switch between values to get Warbler thing going on.

I wouldn't go with k47 as this circuit has de-emphasis network, so it would be too dark.

As I have a similar mic with 797 audio k67 I couldn't recommend it more for this type of schematic. Try to get hold of one, or just buy older used Behringer  B1. Very easy to get spot on u87 sound with these and increased C3 cap. You will get better low end, and smoother HF curve compared to stock.

OEM C12 type capsule has less dips in high end and overall smoother HF response. This one will work great too. But you won't get c12 style mic, as a matter of fact it will sound even closer to u87 than some k67 copies.

As for the noise it will go down with increased C3. Try to clean HiZ parts, and try with Teflon wire from capsule to FET.

I cant answer conversion question, but I guess it will bring more or less low end harmonics depending on the transformer used. You would have to measure that though, and see if the 84 ''upgrade'' does anything. I don't think it would do much for vocals and guitars, but might be audible on bass heavy high SPL sources like kick drum, bass amp...
 
kingkorg said:
I would increase C3 to something in order of 600pF without thinking or hearing stock mic. It would get the response of the mic close to u87. You might try even with 800pF, or even a switch between values to get Warbler thing going on.
Will do. The MXL 3000 that is my current victim has 260pf C3, and I will try various values up to 800.
I wouldn't go with k47 as this circuit has de-emphasis network, so it would be too dark.

As I have a similar mic with 797 audio k67 I couldn't recommend it more for this type of schematic. Try to get hold of one, or just buy older used Behringer  B1. Very easy to get spot on u87 sound with these and increased C3 cap. You will get better low end, and smoother HF curve compared to stock.

OEM C12 type capsule has less dips in high end and overall smoother HF response. This one will work great too. But you won't get c12 style mic, as a matter of fact it will sound even closer to u87 than some k67 copies.
I have one of the RayKing C12's that you talked about in another thread. I'll probably want to try that once I've got the conversion working.
As for the noise it will go down with increased C3. Try to clean HiZ parts, and try with Teflon wire from capsule to FET.

I cant answer conversion question, but I guess it will bring more or less low end harmonics depending on the transformer used. You would have to measure that though, and see if the 84 ''upgrade'' does anything. I don't think it would do much for vocals and guitars, but might be audible on bass heavy high SPL sources like kick drum, bass amp...
I've got the 3U Audio GZT-47 installed. I'm still wondering if it's ok to leave the emitter follower circuit almost completely intact, sucking power, except that I've cut it out of the signal path (I think).
 
The short-circuit current for phantom-power is about 14mA (which would be "burnt off" in the 6.8k resistors inside the preamp), soooo... i wouldn't sweat it ;)

12strings2hands said:
I've got the 3U Audio GZT-47 installed. I'm still wondering if it's ok to leave the emitter follower circuit almost completely intact, sucking power, except that I've cut it out of the signal path (I think).
 
12strings2hands said:
The circuit is almost exactly a V67 except the input stage is direct from capsule to fet. I know this circuit has been a target of modding to an 84 type by removing the transistor follower and replacing it with a higher ration transformer.
All you can expect by doing that is increase low-frequency distortion.
 
Khron said:
The short-circuit current for phantom-power is about 14mA (which would be "burnt off" in the 6.8k resistors inside the preamp), soooo... i wouldn't sweat it ;)
You are right.  I cut out the emitter follower in 2 places:
C6 closest to FET was unsoldered.
C8 and the larger cap (on the MXL 3000 there is a huge capacitor in parallel  to C8) was unsoldered.
I  jumpered these two points.
It works. Sounds nice. Next up are the capsule replacements and doing something with C3 per KingKorg ( bridged an additional cap to C3, upping it to 340. KingKorg's idea about variable caps for C3 has got me thinking of how to the mechanics.
 
Perhaps a small multi-position rotary switch? Screwdriver-access-hole-in-the-body optional :p

That'd probably work best with a new / "custom-made" PCB though... Or if not "best", at least "cleanest", anyway :)

12strings2hands said:
KingKorg's idea about variable caps for C3 has got me thinking of how to the mechanics.
 

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