A quick update on the HPA1. I have placed a 0.8 uH inductor in parallel with the 3.3 ohm output series resistor. The amplifier remains stable into all the capacitive loads used on the original test.
Some folks like to drive their headphones from a very low Zsource, so this will be of interest to them. I’m off to Scotland at the end of the week with some visitors here this week, so when I’m back in late April, I will post up the results.
Some folks like to drive their headphones from a very low Zsource, so this will be of interest to them. I’m off to Scotland at the end of the week with some visitors here this week, so when I’m back in late April, I will post up the results.
oh, that's a good news. I calculated 15.62 turns on a 8mm air core, with 1mm diameter bare copper wire. 8mm is the size of a pencil, so it could be wound easily using just a pencil and some 1mm wire.
You have a big loop area between your power ground and the input signal ground. Run the input signal ground round towards the front and then down the middle of the board to the power connector 0V and connect it star-ground. Keep the signal ground and the power ground as close as possible to each other until you join them back at the main incoming power ground.
Each transistor will dissipate about 1.5W on +-15V rails, so my suggestion is that you put the transistors under the board with the leads bent upwards so they are pressing on a heatsink, or, you bolt them to the bottom plate of the amp assuming the chassis is aluminium 3mm thick minimum.
I can't see where C214/215 are, but they must be as close to the opamps as possible - especially if you are using the LM4562 which have c. 55MHz GBW.
Note, I also built and measured this with the OPA1642 - I think its a bit better sounding with that opamp, but to be honest the measurements were almost exactly the same as the LM4562. Make sure you can get the opamps you are going to use in the DIP8 package otherwise its mostly SO8 nowadays.
Otherwise, layout looks good - nice and compact!
Each transistor will dissipate about 1.5W on +-15V rails, so my suggestion is that you put the transistors under the board with the leads bent upwards so they are pressing on a heatsink, or, you bolt them to the bottom plate of the amp assuming the chassis is aluminium 3mm thick minimum.
I can't see where C214/215 are, but they must be as close to the opamps as possible - especially if you are using the LM4562 which have c. 55MHz GBW.
Note, I also built and measured this with the OPA1642 - I think its a bit better sounding with that opamp, but to be honest the measurements were almost exactly the same as the LM4562. Make sure you can get the opamps you are going to use in the DIP8 package otherwise its mostly SO8 nowadays.
Otherwise, layout looks good - nice and compact!