[Solved]Looking for Peluso 2247LE schematic / help

[kilmister]

Hi!

Got this mic on my bench and looking for schematic for it. I've wrote to Peluso Labs allready but haven't got any reply yet.

The mic has very annoying high frequency noise. Haven't recorded a sample yet but I would describe noise as "chirping" and it's around 10K.
My first thought was noise is coming from filament rails LM7806 regulator (which is lifted about 0,5V from ground via 1n4004) so I built one RC filter more but it didn't change a thing. Mic has spare tube which I tested but nothing happend. HT rail seems to be clean for me, I didn't find any ripple from there. I've also cleaned high-Z parts without success.

Ideas?

Thanks in advance,
Paavo

 

[HellfireStudios]

I can't be sure, as I don't have one to open up, but those mics could very well be a modified Apex 460 style circuit. A lot of mics with that 9 polar pattern power supply use a variation of that circuit. The values of the resistors and capacitors as well as the EF14 tube pinout will be different, but it should be easy enough to trace out.

-James-

 

[kilmister]

Thanks for your input.

Yes, it's not too complicated, just thought if anyone has schema laying around to save tracing time (read: I'm a bit lazy  )

Cheers,
Paavo

 

[kilmister]

Ok, PSU it was.

I gave a try to LM7809 and bigger voltage drop resistor but it didn't change a thing.
Hate to say, but I don't like Pelusos PSU board layout. Allmost all filtering caps are far far away from the electric route. Therefore I decided to build a new board and made sure all the caps are on the route. I got rid of zener diodes from the end of HT rail and changed filament regulator to LM317 with RC filter after it.
Noise gone.

-Paavo

 

[benqbasic]

Interesting information. Do you have any pictures of the internals?

 

[HellfireStudios]

I definitely want to see some internal pics. New and old PCB please...

-James-

 

[kilmister]

Here's some shots. Click for hi-rez.
At the time of picture I've allready slightly modified the old PSU. All components on solder side are extra as well 3watt resistor above FL00571 text.

Old board from top:


Old board bottom:


And bottom with symbols to get an idea of electric route:


Then my home brew from top:


And bottom:


I also took sound samples from slightly modified old psu and the new one. Samples are recorded in our live room with full gain of SSL 4K. No processing execpt digital gain around +20dB. Files are around 4Mb and 45sec wav.
http://www.5by5.fi/diy/peluso2247le/peluso2247le_psu_old.wav
http://www.5by5.fi/diy/peluso2247le/peluso2247le_psu_new.wav

-Paavo

edit: typos

 

[kilmister]

Bumping...
I would like to hear some opinions about Peluso's pcb.

Cheers,
Paavo