newbie builds ioaudio MK47 microphone

[innercityman]

Hi, I posted this message on the official MK47 building thread but no answer or interest so I hope I'll have a better chance around here...

I started to build this mic and it's been my first DIY microphone project build so any advices would be welcome. I have few questions though.

- I read the topic from the beginning an even if I still have a lot of pages left to read, I'd like to understand what to do with the 1.5K ciment resistor that came with the kit. It seems that it's a heater resistor and needs to be close to the mic body and not soldered directly on the PCB right ? But does it do the trick or do I need to replace it by a chassis resistor ?

- For the PSU I'm using the Zayance MKPSU pcb. I saw on a lot of pictures that the choke resistor was missing. Does it means that if using the choke (like I will do), I have to leave the location empty ?

- And finally, I bought the components referring to the bom from Chunger but I read that if using a 200V transformer, one of the 1K 10W resistor needs to be changed by one 680R and one 330R, also the pot needs to be changed to a 500R 5W. I bought the power transformer which is recommended on the bom which is a 200V and 6.3V secondary.

Here's the link : https://www.tube-town.net/ttstore/toroidal-30va-8808.html

So could someone tell me if I understood everything...

 

[reginator]

Hi, I posted this message on the official MK47 building thread but no answer or interest so I hope I'll have a better chance around here...

I started to build this mic and it's been my first DIY microphone project build so any advices would be welcome. I have few questions though.

- I read the topic from the beginning an even if I still have a lot of pages left to read, I'd like to understand what to do with the 1.5K ciment resistor that came with the kit. It seems that it's a heater resistor and needs to be close to the mic body and not soldered directly on the PCB right ? But does it do the trick or do I need to replace it by a chassis resistor ?

- For the PSU I'm using the Zayance MKPSU pcb. I saw on a lot of pictures that the choke resistor was missing. Does it means that if using the choke (like I will do), I have to leave the location empty ?

- And finally, I bought the components referring to the bom from Chunger but I read that if using a 200V transformer, one of the 1K 10W resistor needs to be changed by one 680R and one 330R, also the pot needs to be changed to a 500R 5W. I bought the power transformer which is recommended on the bom which is a 200V and 6.3V secondary.

Here's the link : https://www.tube-town.net/ttstore/toroidal-30va-8808.html

So could someone tell me if I understood everything...

Sorry you're not have much luck with your build.

I built my MK47 and PSU around six years ago and followed Chunger's build guide explicitly. I installed a BeesNeez M7 capsule in the mic and Western Electric tubes during the build, but I eventually switched to GE tubes because the noise floor became too loud over time to record vocals. The MK47 has been in nonstop service since then and has given me no trouble at all.

I found everything I needed to build the MK47 in this thread and the original MK47 thread, including the schematics. If you build it like Chunger (which is what I did) you'll need to drill a small hole in the mic base and install a "chassis-mount type 1.5K resistor".

It's been a long time and I don't remember much about the PSU transformer wiring. I haven't opened up the PSU in years but I built an exact replica of Chunger's PSU. Hopefully another member can offer some insight.

 

[innercityman]

Thanks for your answer reginator.

I've just ordered a pair of Western Electric NOS tubes. Hope they will last a bit. The problem on the MK47 official thread is that the links for the pictures of the build are dead, I don't know how to connect the capsule wires, and it seems that Chunger forgot to explain this build stage. Even if I'm not a newbie to DIY audio gear, I'm new to HT Tube circuits so I hope I'll get some advices and help if troubleshoots.

 

[reginator]

Hey innercityman,

I wish I had taken a snapshot of my capsule hookup and I don't really remember how I did it.

I'll study Chunger's posts again to see if it jogs my memory.

As an FYI, my MK47 really does sound like Telefunken U47 when comparing it to audio clips I found on the internet. I record vocals and sound effects in a dry environment. Most of the clips I've heard have a bit of studio ambiance giving them livelier sound. If I add a hint of LX480 ambiance to anything recorded on the MK47 it sounds like a U47 recording.

 

[reginator]

Thanks for your answer reginator.

I've just ordered a pair of Western Electric NOS tubes. Hope they will last a bit. The problem on the MK47 official thread is that the links for the pictures of the build are dead, I don't know how to connect the capsule wires, and it seems that Chunger forgot to explain this build stage. Even if I'm not a newbie to DIY audio gear, I'm new to HT Tube circuits so I hope I'll get some advices and help if troubleshoots.

I just looked at Chunger's photos and you can see how the capsule is wired. On the half-moon pcb where the tubes are installed you can see the words "front", "back-plate" and "rear" by the glass feedthroughs. That's where the front & rear capsule diaphragm wires are soldered. The third wire from the capsule mounts to the "back-plate".

 

[innercityman]

Hi guys,

I finished my mic and power supply. PSU tested with load resistor and I get my 105V. When testing continuity between PSU connections and mic wires, I found that I had continuity between A+ and A- solder pads on the mic's PCB. Is that ok or is there's a short somewhere ?

 

[innercityman]

Project finished and mic perfectly working at first fire up !

After one hour powered up, the mic doesn't get hot as I was afraid off. Very funny build.

Some pictures in case there is still some interest in this project...

 

[innercityman]

Calibrating with mic load on...

 

[innercityman]

Got the 105V needed...

 

[innercityman]

Audio tests...

 

[innercityman]

What a sound !!!

 

[innercityman]

Hi,

after few months I decided to check the PSU B+ voltage and I've measured 96V so I let the mic warming up for about half an hour and tried to adjust the potentiometer to get 105V, but the maximum I can get with the pot fully counterclockwise is 104,5V. Do you guys think it's ok ? Or should I replace the potentiometer with one with other value ? Don't remember which value is the adjustment potentiometer.

 

[Delta Sigma]

Do you have a power supply schematic? If you can't adjust higher, changing the pot value won't help; it's maxed out to a short.

 

[innercityman]

You are everywhere... Haha !

I used the Zayance MK-47 PSU pcb for the power supply, and yes I have the schematic, here it is...

 

[innercityman]

when searching for the schematic on the PSU docs, I found this info ont the doc attached, but what does "bridge a resistor" mean ? Put two in parallel... ?

 

[TillM]

Just change the resistors to 500ohm, you don’t have to bridge them.
You can first try only change one resistor from 1k to 500ohm.

 

[Delta Sigma]

What value did you use for R4? 680R parallel with 330R?

 

[innercityman]

What value did you use for R4? 680R parallel with 330R?

Nope, only 680R. Maybe I should start doing this... Here's a picture of my PSU...

 

[innercityman]

So I did that... Put 330R and 680R in parallel and it works like a charm ! I've been able to calibrate to 105V, far from fully pot.

Thanks again Delta Sigma, you're the best !!!

 

[Delta Sigma]

You may have been fine with just the 330R. Make sure you measure the drop and calculate power. Gotta make sure you're decently lower than the rating of the resistor.