KMV254c: Gefell MV691 to KM54c modification.

[SparkleBear]

Hey!
Thanks for Your hard work!
I would like to buy 4 PCBs for the Mic Body and 2 PCBs for the Power Supply!
I have 3 691 amd one 750 which i like to convert!

Very nice project!

Bye Friedemann

That’s great! I’ll get those out to you when I’m back from tour at the end of April! I’m stoked you’re gonna get into this project.

The pm750 has a capsule with the same element as the m94 but it does not have the 10m dropper resistor so it is not swappable with the other capsules in the system. If you want to use the capsule with the KMV you will have to set the capsule voltage to 40v. The kmv has the 120v split in half by two 300k resistors. If you swap one of them for 600k (as in the the original km54 circuit) you will get the 40v you need. But make sure you swap the correct resistor because otherwise you’ll get 80v at the capsule and will likely cause collapse and damage due to arcing.
I’m working on making a mod for the capsule to turn it identical to the m94 by installing a precise ring to allow the 10m to join the circuit.

 

[adamasnan]

Just discovered this wonderful thread!

I would be interested in 2 mic PCBs and a PSU PCB please, am based in Berlin, Germany

Have DM'ed aswell

Thanks!

 

[SparkleBear]

DM'd In return

 

[el_rhodes]

DM'd In return

Hey man, I'd be very interested in buying a set of 4 pcbs for the mic bodies and psu. can you send me a DM? I cant as I'm still a "new member" here! Looking forward! Best! El

 

[madreza]

Hey man
Congrats for this project. Sounds awesome
Can’t wait to mod some and try
I d be interested in 4 mic pcb and 2 psu pcb pleaaaaaase

 

[donivan]

2 mic pcb 2 ps pcb
are they still available?

 

[Leo Schaal]

Hey Guys,
adamasnan told me about this project a while ago, I took a look at it and liked it very much. But I instantly had concerns about the use of the BV130 transformer in a cathode base tube setup. I have a vague feeling this transformer has a very low ratio, but do not remember exactly. I knew I have one of these lying around, but I have moved this summer and most of my stuff was still packed in boxes, so I did not find it and then forgot about it. But the use of 10µF and 22µF coupling cap in the MV692 and MV691 makes a low ratio quite probable. Also the circuit used in the MV691 mics has a very low output impedance. I think this might be a 2:1 to 4:1 transformer. Usually triode tube stages in microphone use 7:1 to 13:1 ratio. Too low ratios are like a short circuit for the sound, you loose a lot of level, deep and high frequencies.
It is possible to double the ratio by wiring the secondary transformer windings in parralel.
I will measure the impedances the next days and get back.
Greetings, Leo