16-01-2021, 09:37 PM
You won't need more drive - the load impedance at the far end is only 20k. Just alter those resistors according to how much extra level you need, and take cold to ground via whatever Zout results.
Looking at the schematics of the 33, as Zout appears to vary according to user controls, it's not an obvious candidate for a simple impedance-balanced mod. Of course, an NE5532 could be hidden inside, though looking at the PSU, the extra 8mA of current draw might need consideration if you run if from the same 12V rail that's feeding the rest of it - I'd just take it from the first cap. It doesn't look like it would be easy physically, unless you didn't care about neatness.
Personally, I'd just use the 33 as an outboard phono pre, and feed it into one of the inputs of the 34. Of course, there's nothing stopping you use the other inputs of the 33 too, should you need to accommodate more sources. Cascading the 33 and 34 together might cause some initial operational confusion for non-technical folk, but aside from that, it seems like a perfectly viable solution IMHO. And the least amount of effort too.
Looking at the schematics of the 33, as Zout appears to vary according to user controls, it's not an obvious candidate for a simple impedance-balanced mod. Of course, an NE5532 could be hidden inside, though looking at the PSU, the extra 8mA of current draw might need consideration if you run if from the same 12V rail that's feeding the rest of it - I'd just take it from the first cap. It doesn't look like it would be easy physically, unless you didn't care about neatness.
Personally, I'd just use the 33 as an outboard phono pre, and feed it into one of the inputs of the 34. Of course, there's nothing stopping you use the other inputs of the 33 too, should you need to accommodate more sources. Cascading the 33 and 34 together might cause some initial operational confusion for non-technical folk, but aside from that, it seems like a perfectly viable solution IMHO. And the least amount of effort too.
