Circuit Explanation / Part Recommendations.

Note - Most parts are equivalent to Tangents’, his explanations are excellent, check em out.

 

Similarities with PPA -

 

Rail isolated opamp rails - JFETs beneath the board, they isolate the opamps

 

3 channel differential topology - Sinks and sources current well.

 

Dissimilarities

 

Unified opamp rails - all 3 opamps have a single rail, instead of 3 for PPA, less current draw, more channel crosstalk.

 

Class-A - Not done by cascades, but by a single CRD.

 

Rail caps - Less rail capacitance .. about 1/3rd.

 

Battery powered - .. duh.

 

Less current draw - On a low current mode, 20mA maximum, 10 hours of play time.

 

Part Recommendations..

 

JFET - the 4 JFETS on the main rail act as current sources using JFETs, they output constant IdSS, if you don’t know what this means, just use the default value, SST310. If you want more / less draw, you can get tricky and use ones with lower IdSS (or higher, for better opamp slew).

 

R6 - This determines the bandwith of the L/R channel, lessen the resistor if your amp oscillates. Should fix it.

 

Buffer - Ground channel MUST use open-loop ground, if you don’t know what that means, get a BUF634 / LM6321, its really not worth it to get anything else, it’ll oscillate like hell. The other 2 buffers will work with closed-loop buffers given that your bandwith is not too mismatched.. (rule of thumb, gain stage bandwith < buffer bandwith)

 

Jumper - If one puts a jumper across the jumper pads (beneath the pot, left of the buffer) it’ll put the BUF634 into wide-band mode. Putting a controlled resistance will put it somewhere between quiescent mode and wide band mode, wide band sounds better, but basically draws 4x more current..

 

Class-A - Pads DG DR DL which use the SST502 for biasing..

 

LED - should be high brightness, or the 10k resistor will overwhelm the LED.