Converting Yamaha PM2000 to API (kind of) using CAPI 2S-LA cards.

[JW]

Okay,

I think this pdf is downloadable and one can zoom in/out. Pardon my chicken scratch. I've taken parts of your (Boji's) schematic and Yamaha and put them together. The arrows are the in/out at the interstage which is normalled to the eq switch I have drawn into the schematic. This assumes, though I haven't annotated it, that all four bands of eq are hard-wired "on." but fully bypassable with my placement of the simpler eq switch.

After IC6 on the Yammy schematic,  if eq is engaged, it's then routed to the channel "on/off" switch of the API schematic, then to the fader.

(FYI, I don't have the pre and post echo switching on there, so to make the schematic a little less complicated looking. Also, ignore the polarity switch where it is on the API schematic as I'll just have it on the input where Yamaha has it wired already. And finally, might be obvious, but ignore any "mic" part of the circuit on the input as I'm going for line only)

 

[boji]

Hope other yamaha desk owners will disagree with me, but looking at the bigger picture plans, I think you're potentially eliminating the soul of this api-type upgrade, which is 2520's interacting with 2623's/2503's.  Without the tx's, a desk running discrete yam opa's with 24v bipolar supply is going to provide headroom.  Adding discrete opa's to some sections will color/drive them a little more effortlessly, but as they say- 'The sound is in the iron'.

Don't at all mean to dissuade you from your upgrade project of course! Btw, when's the last time the desk got a full recap?

I'd like to experiment with a channel or two, copying the API line amp.

IMO, biggest upgrade bang-for-buck might be to replace mixbus section(s) with something like CAPI's ACA/Bo. This provides some of the sought-after vintage console sound without the expense of having to add dozens of tx's across channels. A few others around here upgraded their old desks in this way and were pleased with the results.

 

[JW]

Thanks Boji,

I've actually installed an ACA bus in the past. At some point I realized that it wasn't up enough in gain and was causing me to push my channels too hard. Unfortunately I didn't know enough at the time (or was too impatient) that simply adjusting the opamp gain of the ACA was all I needed. And I pulled it and went back to the Yamaha's summing, which isn't bad.

But never the less. What I actually have in there now is a 1272 summing bus, which I like very much. So I'm not going for api exactly, just utilizing it's short, simple circuit. I'm not quite satisfied with the Yamaha channels. It's not just one channel of course, it's all of them together. It's good. Don't get me wrong. Better than a good many boards, but I hear something pokey in the high mids at times, but simultaneously a bit of muffled hi hi's, and a low end that is big and bloomy, but also has a tendency to get lost. I know these are all very subjective descriptions, but I like what I'm hearing so far with the channel I've wired up as an API circuit. (without eq, mind you)

I got plenty of 2520's in racked API ish preamps. They're great. But so are others. I'm really liking Pier Paulo's APP992.

Seems like I hear different opinions simultaneously about API console. First is that the short path out of the first opamp in microphone mode is often used for a clean representation upon recording, and one time through the console is a great sound. But multiple times and the amount of opamps and transformers start to add up and darken the sound. Still, many folks say you can't just record with the preamps, you have to go through multiple stages transformers, 2520's, the eq stage too of course, and then two transformers in the bus. And then you have the sound.  So, how many stages is too many? Hah. I'm happy to go through no transformers, but discrete API line circuit using opamps I like, and then have 1272 on the back end, with a final Sowter transformer. Can't wait, actually to hear multiple channels of the API modification

Do you have your incredible rig up and running yet?

 

[JW]

A couple questions.

For the input protection diodes, are 1N4004 okay? I have a ton of them.

Second question. Can someone help me calculate a rough estimate of the total load on the last DOA in the PM2000 circuit? I want to try to compare with what the 2520 is driving with regard to API input channel? Trying to see if they are roughly similar. I know both 2520 and 80100 have a lot of power and very low impedance but I definitely see differences in places like the pan pot, which is dual 2K in Yamaha's case. But we're talking about the total load right? So, all those 33K summing resistors and see all the 10K pots on the echos and foldbacks? So does the load of the pan pot become slightly irrelavent in the context of the total load?