Add Neve BA283 outputs+transformer to buffer & balance Yamaha PM-700 direct outs

[Urskov]

Hi there

Right now I'm modding a Yamaha PM-700 - working on recapping, upgrading op-amps and possibly input transformers and adding direct outs for every channel.

I know I've got PLENTY of work cut out for me here... but as I'm waiting for my parts, I'm already thinking about the next possible step that could be balancing the outputs.
I know that it technically isn't required so long as avoid long cable runs, but I thought it'd be great to find a way to give each channel output transformers as well - instead of just using something like an easier-to-implement THAT-chip-circuit.

I read somewhere in another post - I've been unable to find it since - someone suggesting using the BA283 output amp+transformer to buffer and balance the direct outs (edited) and, just as important, add flavor.

If it's possible to implement, I'd do it in a stand-alone box with it's own power supply seeing how the Yamaha's stock power supply won't be able to handle it - not to mention space inside is limited.

I know, I know - lipstick on a pig and all that, but if it's possible, it's a project I'd have fun undertaking while getting a fully transformed coupled stack of pres in the process.

What do you think?

 

[noizetoys]

Do you mean "using the BA283 output amp to BUFFER the direct outs."? The 283 won't balance it, you'll need a transformer for that, it's just a couple of amplifiers.

You might be better off using something like a 553x to drive a transformer on the direct out.

If you wanted to electronically balance the direct out, without a transformer, you might want to reconsider using the THAT chips.

Just my $0.02.

 

[NOON]

I am currently modding a PM700. A previous owner changed the input TXs for some nice Beyers and added a more advanced monitor section. I am adding DB25 inputs and an input switch so I can switch between mic inputs and a line level mixdown. I've added a THAT-based 8ch direct out to DB25 board, I figure the other 4 channels can go out via the main mix buses. Speaking of which, I've converted the parallel of the main outs which go via another set of DOAs into another mix bus and added output TXs. I've also added a switch to each channel to change the mid EQ point. Still a lot of wiring to go before I get to test everything together but I expect this thing to be a very versatile late-70s-sounding lump.

 

[Urskov]

Do you mean "using the BA283 output amp to BUFFER the direct outs."? The 283 won't balance it, you'll need a transformer for that, it's just a couple of amplifiers.

You might be better off using something like a 553x to drive a transformer on the direct out.

If you wanted to electronically balance the direct out, without a transformer, you might want to reconsider using the THAT chips.

Just my $0.02.

Oh, I know - that's why I wrote "find a way to give each channel output transformers as well - instead of just using something like an easier-to-implement THAT-chip-circuit."
Basically I want maximum mojo, and I thought some discrete components+output transformer could add something extra.

I am currently modding a PM700. A previous owner changed the input TXs for some nice Beyers and added a more advanced monitor section. I am adding DB25 inputs and an input switch so I can switch between mic inputs and a line level mixdown. I've added a THAT-based 8ch direct out to DB25 board, I figure the other 4 channels can go out via the main mix buses. Speaking of which, I've converted the parallel of the main outs which go via another set of DOAs into another mix bus and added output TXs. I've also added a switch to each channel to change the mid EQ point. Still a lot of wiring to go before I get to test everything together but I expect this thing to be a very versatile late-70s-sounding lump.

That sounds awesome! That's gonna be a great board.

I'm basically only gonna use them as preamps to add some color to my dull Focusrite interface, so a lot of your mods probably won't be relevant for me.
But I'm interested in the EQ mod!
Also te direct outs DB25 board - how have you implemented that more specifically? Is the board in the chassis or in a seperate box? With separate power supply or can the Yamaha's power supply handle the extra circuitry?

 

[NOON]

I have a little pcb I designed for another project that has 8 x THAT chips and mounts directly onto a db25. I've done db25 cutouts on the back of the mixer for extra I/O. I don't expect the THAT board will add enough extra load to stress the power supply, unlike adding class A circuits. The mid shift is literally just mounting an extra switch on the front panel between channels that switches extra caps in parallel with the mid cap. Can't remember what values I ended up with, it's been a while.

 

[Urskov]

I have a little pcb I designed for another project that has 8 x THAT chips and mounts directly onto a db25. I've done db25 cutouts on the back of the mixer for extra I/O. I don't expect the THAT board will add enough extra load to stress the power supply, unlike adding class A circuits. The mid shift is literally just mounting an extra switch on the front panel between channels that switches extra caps in parallel with the mid cap. Can't remember what values I ended up with, it's been a while.

Great. I'm gonna try that once I get there. Even if you can't remember the values.. can you recall the ballpark? Or recommend the resource to calculate the values?

I hear there's not too many issues with unbalanced direct outs as long as the cable run is short. So I'm pretty dead set on the BA283 in a separate box /w it's own power supply, IF it's possible, for more gain and output transformer vibes. Especially now that UTM sells some very reasonable Neve-style ones. It would really make the "Japaneve"-nickname that people have given to the big brother consoles, PM-1000 and PM-2000, very literal, haha.

The kind soul @rsasgtr has also provided an Eagle layout for cheap ordering of the stand-alone boards (Neve BA283 Eagle)

 

[jaywilliamhenderson]

Did anyone ever figure out a transformer out mod for the pm700? I have one that has all the eq’s modded with switchable frequencies and an unbalanced direct out for all the channels. I would love to balance the outputs. Also has anyone experimented with different inductors for the eqs?