Gefell MV692+M93 nickel SD head - building a M582 out of it

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Thanks! Modified!  8)

Why G7?
You can even make U47 - what for?
If you will use different tube for any of these circuits, you will have to change most of the circuit, so still it wouldn't be G7 or U47.
Most of these circuits are plate followers - nothing magic in it.
You need to set plate resistance, cathode resistance for choosed transformer and best performance.
Here's example of my tube SDC (still not finished):
http://groupdiy.com/index.php?topic=63436.msg803459#msg803459

Don't rewind original transformer, it wouldn't be usefull for this project, but maybe for any different - if you don't need it, i can exchange for some other transformer.
You can also make cathode follower circuit which utilise usual 2:1, 3:1 ratio transformers.
If you will be interested, measure first ratio of it.

Hmm, the M93 capsule is an omni one with a goldsputtered diaphragm, no nickel here!
Did you mean the M94 capsule?

The MV692 produces about 60V polarisation voltage and the M94 capsule has an internal resistor to get down to about 40V.
The other capsules in the SMS70 series (M70, M71, UM70, M93, M58 etc) are working with 60V.

Sredna said:

Hmm, the M93 capsule is an omni one with a goldsputtered diaphragm, no nickel here!
Did you mean the M94 capsule?

The MV692 produces about 60V polarisation voltage and the M94 capsule has an internal resistor to get down to about 40V.
The other capsules in the SMS70 series (M70, M71, UM70, M93, M58 etc) are working with 60V.

Click to expand...

Thanks for the correction, indeed it is the M93, I was under the wrong impression there's nickel in there.  :

ln76d said:

Why G7?
You can even make U47 - what for?
If you will use different tube for any of these circuits, you will have to change most of the circuit, so still it wouldn't be G7 or U47.

Click to expand...

No particular lust over G7, it's just a documented project and I could use some help ha ha.

Don't rewind original transformer, it wouldn't be usefull for this project, but maybe for any different - if you don't need it, i can exchange for some other transformer.
You can also make cathode follower circuit which utilise usual 2:1, 3:1 ratio transformers.
If you will be interested, measure first ratio of it.

Click to expand...

You're right, I'll settle for a transformer first. Just saw your SDC build. Nice idea!

Now that I'm thinking with a more clear head, I've decided to build an M582 in the 692 body. I already have a factory serviced M582 (with an alteration so it can accommodate the UM70 head for cardioid only) for reference so I think it's worth a shot. Maybe I'll tinker with the circuit a bit. If anyone care to offer any advice I'm all ears!! I intend to use it with my m70 and m93 capsules and will probably have to re-skin an old neumann-logo m94 capsule too ha ha.

Btw, since I'm keeping the mv692 body but won't be using the pad and low-cut switches, now there are two nice ventilation slots on the body  8). I'll test various components and will take photos so it will be a nice thread I hope.

P.S: I was thinking if it is feasible to place the output transformer in the PSU. Will the particular circuit be able to drive 3ft of cable to the PSU without many losses/sideeffects?

Oh, I forgot to say that the MV692 isn´t the best choice (of the SMS70 bodies) for modifications in my opinion.
The MV692 has the thread for the capsule on the body tube and the (electrical) connector for the capsule is a part of the inner (very brittle) plastic structure.  The plastic structure takes up a lot of space and you would certainly not be able to fit an EC92 inside. (Maybe a 5840)
MV690, MV691 and PM750 would be much more suitable as they all have sturdy flat metal rods  between the cable connector and the capsule connector. Much easier to build up something new on that basis.

For reskinning the M94 I´d recommend Thiersch, fast, good and reasonable priced.

I dont know if the M582 circuit allows you to have a 3ft cable between the tube and transformer, I only know that the transistor based MV710 (similar to MV690) uses no tranformer but has an unbalanced cable of about 3-4 ft.

Thanks for replying, appreciate it!

Well, I like both my 691 and 690, both serviced at MG so unless I find another one for cheap I'll stick with messing with the 692. I'm gonna keep as little of the plastic thingie as possible - I've already disassembled it.

Btw, what's up with the 6-pin connector I see on some 582s? The August 1973 schematic shows a 5-pin output connector. Is any pin not connected?

The middle pin (pin 6)  is not connected, for the UM57 it´s used for the pattern voltage. They probably used 6 pin connector because they were out of the 5 pin ones.

Ok, 5-pin it will be then. I'm building the PSU from scratch so no problem there.

I'm using the August 1973 RFT schematic and so the parts list is as follows:

R1 - 4,7K 0.125W 5%
R2 - 56K 0.125W 5%
R3, R4 - 10M 10%
C1 - 4700pf Rohrkondensator (meaning axial I presume?) no voltage rating
C2 - 330pf 500V scheibenkondensator ( disc capacitor)
C3 - 1uf 150V electrolytic
C4-C7 - 15000pF axial no voltage rating
transformer
EC92 tube


Any particular suggestions for C1 and C4-C7? I can exchange the MV692 transformer for a couple tested EC92s if anyone's interested (or whatever swap you love).

Also can anyone suggest a solid PSU schematic for this mic?

Any more opinions on whether the M582 circuit can drive a few ft of cable so I can put a larger transformer in the power supply?

Since you're building your own power supply, consider UC92 with 9V heater instead of the expensive EC92 with 6V heater. Same tube otherwise. UC92's are cheap and plentiful. Be prepared to go through a few of whichever tube variant you choose to find a quiet, low microphonic one. That's where the low cost of the UC92 helps. I have found one out of two is my average.

Oh yeah, you can use a modified Alctron PSU for this mic. No need to reinvent the wheel.

AusTex64 said:

Since you're building your own power supply, consider UC92 with 9V heater instead of the expensive EC92 with 6V heater. Same tube otherwise. UC92's are cheap and plentiful. Be prepared to go through a few of whichever tube variant you choose to find a quiet, low microphonic one. That's where the low cost of the UC92 helps. I have found one out of two is my average.

Oh yeah, you can use a modified Alctron PSU for this mic. No need to reinvent the wheel.

Click to expand...

Hey, thanks for taking the time to reply. I broke my index finger and type a bit slower these days haha.

Do you mean the alctron psu for the bv563 mic or any alctron tube mic psu?