Wanted Gefell MV692 P48 conversion PCB's

[Murdock]

Hey folks,

I'm searching two of those small conversion PCB's for my Gefell MV692 mics. There was a seller on Ebay who offered these some time ago but he seems to have stopped selling.
Does anyone by chance have two of these?
I know Gefell and Thiersch offer conversion but I would like to do it myself is someone has those PCB's.
Even better if someone also have those XLR connector conversions too!

 

[SparkleBear]

Check this gear space thread... https://gearspace.com/board/high-end/354306-gefell-pm860-pm750-48v-phantom.html

I also have a source for those 48v boards if you want to just install inside rather than doing the in-the-cable solution that I posted below from the thread. PM me and ill give you his contact.

Im diving into my MV691s in a big way... two of them converted to km54 style circuits and two of them are going to stay stock. I hope I can learn the mods that make them better...

(older thread that talks about it -- bv130 specifications ? )

Cool to know more folks out there are getting into these... does not make it easier to find them though. lol

 

[Murdock]

Check this gear space thread... https://gearspace.com/board/high-end/354306-gefell-pm860-pm750-48v-phantom.html

I also have a source for those 48v boards if you want to just install inside rather than doing the in-the-cable solution that I posted below from the thread. PM me and ill give you his contact.

Im diving into my MV691s in a big way... two of them converted to km54 style circuits and two of them are going to stay stock. I hope I can learn the mods that make them better...

(older thread that talks about it -- bv130 specifications ? )

Cool to know more folks out there are getting into these... does not make it easier to find them though. lol

Thanks for your message! I'm interested in the contact for those 48V boards.
Send you a PM.

 

[zzzzz]

I know this is from almost two years ago buuuut.....

Laid out this PCB to be a copy of the factory conversion boards Microtech Gefell uses (used?) based on our own. Gerbers attached -- spec'ed out for JLCPCB, but other fabs should do the trick too. Very small (8.5mm x 11mm), all SMD parts.

Two versions of the gerbers:

• one uses a SMD tantalum cap like Gefell's own conversion boards and 0603 resistor footprints
  
  
• the other has a footprint for a thru-hole electrolytic cap and 0805 footprint resistors for easier hand-soldering.
  • (Nichicon used to have a line of "mini" 4mm diameter caps but they phased them out... Panasonic still makes some, I think, but I am unsure if they make a 22u/25v or 20v; might only have 16v which would work but isn't a lot of PHYSICAL wiggle room. otherwise, I think Panasonic has some fairly short 5mm diameter caps in the FC series)

The original used a SOT-123 package 12v Zener -- this one does not.

Instruction .pdf is attached from a different kit which isn't available anymore but basically same idea. Follow the schematic for wiring and component footprint sizes -- parts are very standard. "VT21" is a 60v NPN.

Also attached photos of one of the original MTG boards for reference. This would have come with an SMD tantalum 22u/20v cap, but they also included thru-holes on the footprint.

 

[bremusound]

Thank you very much!

 

[garp]

I have one of these populated boards in spare

 

[Khron]

Nichicon used to have a line of "mini" 4mm diameter caps but they phased them out... Panasonic still makes some, I think, but I am unsure if they make a 22u/25v or 20v; might only have 16v which would work but isn't a lot of wiggle room.

Well, you shouldn't need much "wiggle room", because whatever voltage is across that capacitor, is already clamped by the zener. Well, unless that NPN somehow gets zapped through, but then the capacitor's the least of your worries...

 

[zzzzz]

Well, you shouldn't need much "wiggle room", because whatever voltage is across that capacitor, is already clamped by the zener. Well, unless that NPN somehow gets zapped through, but then the capacitor's the least of your worries...

I meant physical wiggle room! For capacitor height.

 

[jp8]

I know this is from almost two years ago buuuut.....

Laid out this PCB to be a copy of the factory conversion boards Microtech Gefell uses (used?) based on our own. Gerbers attached -- spec'ed out for JLCPCB, but other fabs should do the trick too. Very small (8.5mm x 11mm), all SMD parts.

Two versions of the gerbers:

• one uses a SMD tantalum cap like Gefell's own conversion boards and 0603 resistor footprints
  
  
• the other has a footprint for a thru-hole electrolytic cap and 0805 footprint resistors for easier hand-soldering.
  • (Nichicon used to have a line of "mini" 4mm diameter caps but they phased them out... Panasonic still makes some, I think, but I am unsure if they make a 22u/25v or 20v; might only have 16v which would work but isn't a lot of PHYSICAL wiggle room. otherwise, I think Panasonic has some fairly short 5mm diameter caps in the FC series)

The original used a SOT-123 package 12v Zener -- this one does not.

Instruction .pdf is attached from a different kit which isn't available anymore but basically same idea. Follow the schematic for wiring and component footprint sizes -- parts are very standard. "VT21" is a 60v NPN.

Also attached photos of one of the original MTG boards for reference. This would have come with an SMD tantalum 22u/20v cap, but they also included thru-holes on the footprint.

View attachment 132452

For my MV692, I made this circuit with a BC850C BJT. It's a 50V device, but max Vce in the circuit equals 54 -12 = 42 V. For more safety, consider BC846C. This transistor has a high gain, so I increased R22 to 10k and reduced C27 to 2.2uF for more or less same amount of capacitance multiplication by the BJT and zener noise filtering. Instead of a 12V zener, I took a 13V type. The circuit requires 12V, so I assumed VD21 in the original Gefell circuit would also be 13V instead of 12V. But maybe I'm wrong here. I replaced C4 and C5 on the main PCB with 10uF, which lowered the noise floor.

Some suggestions for the PCB layout: if you place the SMTs on both sides, the three connections to the main PCBA can be aligned like pictured below, which makes assembly on the main PCBA a bit easier, while still being a tiny 7 x 10mm board. The PCBA on the picture is not the final circuit that I ended up using, btw. For the final version, I used the same PCB, but assembled the same circuit on it as yours, with the exceptions mentioned above (C27 is on the backside of the PCB).

I got XLR tail-parts from Gefell via someone in Germany. AFAIK, they do not sell more than two per mail address. After two years, they are still waiting to be used .

Jan

 

[zzzzz]

For my MV692, I made this circuit with a BC850C BJT. It's a 50V device, but max Vce in the circuit equals 54 -12 = 42 V. For more safety, consider BC846C. This transistor has a high gain, so I increased R22 to 10k and reduced C27 to 2.2uF for more or less same amount of capacitance multiplication by the BJT and zener noise filtering. Instead of a 12V zener, I took a 13V type. The circuit requires 12V, so I assumed VD21 in the original Gefell circuit would also be 13V instead of 12V. But maybe I'm wrong here. I replaced C4 and C5 on the main PCB with 10uF, which lowered the noise floor.

Some suggestions for the PCB layout: if you place the SMTs on both sides, the three connections to the main PCBA can be aligned like pictured below, which makes assembly on the main PCBA a bit easier, while still being a tiny 7 x 10mm board. The PCBA on the picture is not the final circuit that I ended up using, btw. For the final version, I used the same PCB, but assembled the same circuit on it as yours, with the exceptions mentioned above (C27 is on the backside of the PCB).

I got XLR tail-parts from Gefell via someone in Germany. AFAIK, they do not sell more than two per mail address. After two years, they are still waiting to be used .

Jan

View attachment 132589

good call Jan, I can change that and upload another layout for sure with footprints on both sides (which is what MTG did for the tantalum cap, anyway).

originally, I just did single-sided for PCBA services rather than hand-soldering in mind.

 

[jp8]

Don't know which service you had in mind, but double sided SMT placement is not an uncommon process. It will only add costs, of course.

Jan