I built this amp about a month back and have been very impressed by its performance. I haven't however been able to listen to it as much as I'd like due to my main cans being away for repair. I've got them back now though and turned my amp on again today after a couple of weeks. While it's as good as I remember it (extremely good and perfect complement to my high distortion starving student variant), I still have a slight problem with the build and would like some advice.
My issue is with the time that the build takes to turn the relay on. It took 5.5 minutes with the standard configuration (I set my power supply up for +\-15V rails). My tests however show that offset is below 1mV within 10s of the amp turning on. the simulations I ran on the servo part of the amp indicated that the relay should have clicked in well under a minute (probably closer to 30s), but as this wasn't the case I decided to reduce C27 to 100uF today. Doing his has reduced turn on time to 4 minutes but I still feel that it's longer that necessary. So my question is, how long do your amps take to turn on and what can I do to speed mine up as I can easily measure that after 10-20s there's not going to be an offset issue. I was thinking of changing the resistor divider that biases C27, but would like advice before I do it as what's happening in reality doesn't quite add up to the sims and I didn't design the offset comparator (not quite sure what/if/whether the opamps are still configured as AND and if so what effect this has).
Thanks again for such a good design, it always amazes me the sound that comes out of such a small package.
(hope you're feeling at least a bit better by the time you read this waki).