API-553 Build 3 band with switchable frequencies

Perfect thank you Ian, I need to get these powered up first before any mods but as soon as I do I will try what you have said.

Don’t know if it’s possible or a stupid question but all the Psu schematics I’ve seen run off centre tapped txf.
I seem have a bit of confusion over this part of the circuit.
Is it possible to do a positive and negative feed Psu from just 2 X Ac feeds rather than centre tapped? (3 terminals)

Btw I have a 24vac toroidal and want to feed either LM317/337 or 7815/7915.

Also I’m using 5k pots rather than 10k, should this be an issue?

What current does each channel of these pull?

Right, finally had a bit of success with one pcb!
I’m getting good voltages and all pots work, even though they are 5k rather than 10k.
I’m going to try and connect these to the Neve 1290 and see how they sound.

This is the output waveform from the 553 being put just before the 1166 output txf in bypass.

This is with the 553 Engaged, you can see the waveform distorts.

success now, connected to P and L within Neve 1290 and get lovely waveform, circuit works!!!

Great work!! Any chance you might make the schematics/drawings available to the forum if u are successful?

Anyway will follow this build with great interest. Planning to design n build some stereo EQs with the option of both "modern" and "vintage" API sound in 19" format. Sort of what API done with the API 5500 but based on the 553 to lower the cost and make an easier build.

All the documents are on the first page, that’s what I used to do pcb.
I have made a few changes when looking at schematic, which is also there on the first page.
Still haven’t fully finished the faceplate for the 1073-553, but will do in a couple of weeks, busy time atm!!!

Spencerleehorton said:

All the documents are on the first page, that’s what I used to do pcb.
I have made a few changes when looking at schematic, which is also there on the first page.
Still haven’t fully finished the faceplate for the 1073-553, but will do in a couple of weeks, busy time atm!!!

Click to expand...

Haha sorry, for some reason (prob bad cellphone connection in the woods or a too tired brain) I did not see any attachment when I looked at the first posts the first time around. Now I clearly see them now.

And thx you for sharing this build with the rest of us

Spencerleehorton said:

All the documents are on the first page, that’s what I used to do pcb.
I have made a few changes when looking at schematic, which is also there on the first page.
Still haven’t fully finished the faceplate for the 1073-553, but will do in a couple of weeks, busy time atm!!!

Click to expand...

I'd be curious to look at your final schematics and build ! For some reason all the documents have vanished. I haven't pulled the trigger yet but I am thinking of a 553 clone with maybe two or three selectable frequency for the mid band. The high and low band are fine with stock frequencies, but some tweaks might be fun here too.

Thanks !