Need help on P27
I've build the P27 (P27) on the PCB made by me. First I must say that the preamp sounds greate. I tried it with TL 072 and then I put inside the OPA 2134 - resoult dead quiet. For testing I connected the preamp on my P3A - PCB made by me - cool combinatin with nice sound. Then I connected the preamp with proper amp and there was a problem. If I put all the commands to max (gain, volume, ....) there is a strange noise from the speaker - like strange oscilation but not in the HF (this doesn't happend with the P3A). Then I've tried to disconect the feedback from -spk throu the R23 and it was much better, but not OK. Now I'm a bit puzzled. Strange thing is that the drivers Q7 and Q6 are getting too hot (cca. 65°C). I've measured the voltage drop trough the R14 and R15 and the resoult was 11V drop. 11V means that there is a current flow of 19,6 mA. Is this OK ? The PCB is not the first I made - all double checked (layout and components placing and components values also) from me and another two friends of mine.
I must ask - is the +/- 23V OK for this amp ? The mentioned +/- 23V are from the power supply from amp I actualy use (toroidal transformer 2x17V 60VA, 20A rectifier, 2x4700mF/50V capacitors, 2x100nF blocking capacitors) and I want to use it for P27 (because I only need 30W amp). If you have some idea what could be wrong, please help me !
Thanks in advance !
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