Looking for the schematic for the IOAudio MK7

[neowalla]

Hello friends, I bought the MK7 kit from member desol on the black market and I'm trying to find the schematics. The thread for the build is from 2010 and all the links with schematics and build photos are long dead. I spoke with Derrick (desol) and he suggested posting here as he knows at least a couple folks here have built this mic.

To clarify, this is the single tube circuit, akin to Poctop's DEF47 not to be confused with the dual parallel pentode circuit, the MK 47, which is akin to Poctops D47.

 

[Accelerator]

See at the attached file the MK7 Microphone Schematic with the EF/PF 86 tube…

 

[neowalla]

Thank you!!

You wouldn't happen to also have the power supply schematic?

 

[Accelerator]

You Welcome neowalla!...

Till this time I haven’t find any specific P.S.U. schematic for the IOAudio MK7 microphone, so I suspect that the t.bone PSU Retro Tube II will be a good starting point as a donor P.S.U. to start your modifications to it and get the 150 DC Volts Vb…

I hope this will helps you to your task…

 

[neowalla]

I have a PSU from a DEF47 build I did last year. I just want to finish the power supply for this MK7 kit since it came with the PCB, transformers, and case.

 

[Accelerator]

Your D-EF47 P.S.U. will work your with your IOAudio MK7 microphone if you change the whole circuit of your IOAudio MK7 microphone to something very similar to the Oliver Archut U47 Alternative Tube schematic with Remote Polarity Switch on Power Supply Unit or to the Oliver Archut UM75 - 92 - 92.1 Mod Schematic…

In both of these cases you have to look around for something that will deliver HT: 120 DC Volts Vb and LT: 6 DC volts…

 

[DFischer]

Power supply schematics attached.

 

[neowalla]

Referring to LM317 on the schematic, there is no voltage regulator in this circuit. No place for one on the PCB. After the bridge rectifiers are the filter caps and a choke.

 

[DFischer]

It's been a long time since I built mine, but I think that the second schematic was given as an aid to modify a generic PSU with an LM317 to work with the MK7. The first schematic doesn't contain any voltage regulators and does have a choke on the heater supply. Does this not match the board you have?

 

[neowalla]

It's been a long time since I built mine, but I think that the second schematic was given as an aid to modify a generic PSU with an LM317 to work with the MK7. The first schematic doesn't contain any voltage regulators and does have a choke on the heater supply. Does this not match the board you have?

I don't know how I missed that. Yes the first schematic matches. The one with the choke. Whew!

 

[Accelerator]

@neowalla​

I have a PSU from a DEF47 build I did last year. I just want to finish the power supply for this MK7 kit since it came with the PCB, transformers, and case.

Referring to LM317 on the schematic, there is no voltage regulator in this circuit. No place for one on the PCB. After the bridge rectifiers are the filter caps and a choke.

The IOAudio MK7 uses either the EF86 or the PF86 tube so in a clear new build you can use any proper voltage regulator that you like for getting regulated the L.T. 6,3 Volts heater voltage for heating the EF86 tube…

If the PSU from a D-EF47 build that you did last year doesn’t have the LM-317 or any other voltage regulator, you can use zener diodes (with some extra filtering capacitors) to regulate the L.T. 6,3 Volts heater voltage, and keep down the zener diodes hum, or even better to re-build a new P.S.U. dedicated to the IOAudio MK7 microphone, or as I wrote you above to use the t.bone PSU Retro Tube II that will be a good starting point as a donor P.S.U. to start your modifications to it and get the H.T 150 DC Volts Vb / L.T. 6,3 Volts heater voltage …

If the H.T 150 DC Volts Vb / L.T. 6,3 Volts heater voltage it is not a matter for you and you can re-build your IOAudio MK7 microphone to work at a lower H.T. 120 Volts / L.T. 6,3 Volts heater voltage more like a Gefell UM75, Gefell UM92 and UM92.1. microphones, you have in this case more options like the Mic&Mod Premium Vintage Hammered Tube Microphone Transformer PSU at 64 Euros or the Mic&Mod Premium Tube Microphone Transformer PSU at 90 Euros…

 

[DFischer]

I don't know how I missed that. Yes the first schematic matches. The one with the choke. Whew!

I figured that was the one you were looking for. I included the other one for completeness. Someone might be searching this thread later for power supply info.