Yamaha PM-180 Direct out info needed

[Ryan Anderson]

Hi, I have had this old pm180 for years and am finally thinking about adding some direct outs on it with some old output transformers from a PM700. I'm trying to figure out the best spot to tap into the circuit to make this happen. Thinking i may do the first 2 channels and leave 4 channels for sub mixing if needed. Here is a link to the service manual, https://audiocircuit.dk/downloads/yamaha/Yamaha-PM180-mix-sm.pdf
I think the schematics are on page 9 and page 16 has the board layout. I think just after the buffering amp right before the pan knob is the best spot? But I can not figure out where to tap into it. Any info is greatly appreciated. Thanks Ryan

 

[NOON]

Normally I'd tap it from the top of the fader but in this case there's no eq output buffer, so putting a variable load there might affect the eq response. You could put it post fader buffer, which gives you an output level control but also affects the mix. You might want to disconnect these channels from the mix bus if you're talking about using it as 2 preamps and a 4x2 mixer.
Alternatively you could add a high impedance buffer circuit to the feed from the top of the fader and use that to drive the transformer. A 5532 would do it or you could go fancier, I made an 8ch buffer board using THAT Corp balanced out chips for my PM700.

 

[Ryan Anderson]

Normally I'd tap it from the top of the fader but in this case there's no eq output buffer, so putting a variable load there might affect the eq response. You could put it post fader buffer, which gives you an output level control but also affects the mix. You might want to disconnect these channels from the mix bus if you're talking about using it as 2 preamps and a 4x2 mixer.
Alternatively you could add a high impedance buffer circuit to the feed from the top of the fader and use that to drive the transformer. A 5532 would do it or you could go fancier, I made an 8ch buffer board using THAT Corp balanced out chips for my PM700.

Thanks for the reply! I would for sure remove the 2 channels from the mix bus Post fader is most likely the easiest. R

 

[NOON]

If you want to get fussy about it, it looks like a passive mix bus rather than a virtual earth summer. This means removing channels can potentially change gain and noise on the mix bus. I've seen some good explanations on various sites, long time since I looked into the details. Might be as easy as grounding the mix resistor for each channel you remove to simulate the low output impedance of the buffer.

 

[NOON]

Actually, I think it was Douglas Self Small Signal Audio Design book that taught me the most about this when I needed it. A book well worth shelling out for, but also PDFs available in the usual suspect places.

 

[Ryan Anderson]

Actually, I think it was Douglas Self Small Signal Audio Design book that taught me the most about this when I needed it. A book well worth shelling out for, but also PDFs available in the usual suspect places.

I'm going to look into this! thanks, R