17-01-2021, 07:45 AM
(This post was last modified: 17-01-2021, 07:51 AM by ppppenguin.)
I was being a bit thick about the output drive needed from the TL071 on the 34. Lowering the series resistor values (R117, 118 on left channel) doesn't increase the load on the opamp except for R119 which can be raised as you said.
Looking back at the 33, I'd forgotten just how weedy the PSU is. The things people did to get nice smooth 12V before we had single chip regulators. I'd also forgotten about lack of output buffering. I suppose it was OK when you knew you were feeding a 303 (or, later, a 405) via a short cable. Schematic fragment attached.
I'm forming a sort of idea. Small diecast box with 5532, 2x XLR output, 1x 4 pin DIN input. Pin 4 of the DIN has a power feed from a separate rectifier that may have been used for some obscure purpose in the distant past. Could use that to power the 5532 if there's enough voltage and current. Or perhaps just connect pin 4 to the main rectified power. Minimal mods to the 33, easy to fit XLRs. I think it ticks all the boxes. Simple, easy to build, XLR outputs, keeps the 33, minimal mods to the 33.
Further thought. Make the audio/power input to the diecast box something totally non-standard so no possible confusion of cables. Like a 5 pin 240 degree DIN or a 6 pin DIN. Or even a 4 pin XLR. Pretty sure I've got all of those in the stores.
Thanks for the idea of using the 33 as an outboard phono amp.
Looking back at the 33, I'd forgotten just how weedy the PSU is. The things people did to get nice smooth 12V before we had single chip regulators. I'd also forgotten about lack of output buffering. I suppose it was OK when you knew you were feeding a 303 (or, later, a 405) via a short cable. Schematic fragment attached.
I'm forming a sort of idea. Small diecast box with 5532, 2x XLR output, 1x 4 pin DIN input. Pin 4 of the DIN has a power feed from a separate rectifier that may have been used for some obscure purpose in the distant past. Could use that to power the 5532 if there's enough voltage and current. Or perhaps just connect pin 4 to the main rectified power. Minimal mods to the 33, easy to fit XLRs. I think it ticks all the boxes. Simple, easy to build, XLR outputs, keeps the 33, minimal mods to the 33.
Further thought. Make the audio/power input to the diecast box something totally non-standard so no possible confusion of cables. Like a 5 pin 240 degree DIN or a 6 pin DIN. Or even a 4 pin XLR. Pretty sure I've got all of those in the stores.
Thanks for the idea of using the 33 as an outboard phono amp.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
