I think I had one channel go into oscillation after first connecting inputs and speakers. It had a bad 60hz buzz, then the protection board tripped from overcurrent.
I shorted the input to check it out and haven't had an issue since. New scope hopefully arrives tomorrow. I've purposely tried to induce noise into it. Very good rejection. It's silent. Time for a chassis and a test drive at home.
I shorted the input to check it out and haven't had an issue since. New scope hopefully arrives tomorrow. I've purposely tried to induce noise into it. Very good rejection. It's silent. Time for a chassis and a test drive at home.
I have some clip ons for them. Just need to figure out where I put them. Bias current keeps dropping on me. I need to get them warmed up properly and set them again. I think the driver heat sink may be too large. Too slow. Obviously I'm not driving them hard but the whole amp hardly warms up.
It's ok for this kind of design. My prototype fully settles in about 10 minutes.
Optimal quiescent current is around 35mA (rather low). After power-on it goes a bit higher and then comes back and settles. Distortion level is very low even during this process...
I found mine dropped but I don't think it ever really settled. It's under my fume extractor fan though so possibly that was cooling it excessively.
Measure a voltage drop on R26 from time zero (power on), no-signal warming up and later with 20 Vrms on the output. This will give you an impression of how VAS bias is fluctating regarding all possible conditions, you'll be amazed about the differences in response of VAS bias, caused by delta Vbe/temp of the input pair.
Measure a voltage drop on R26 from time zero (power on), no-signal warming up and later with 20 Vrms on the output. This will give you an impression of how VAS bias is fluctating regarding all possible conditions, you'll be amazed about the differences in response of VAS bias, caused by delta Vbe/temp of the input pair.
I'll try that next time I start it up.
I broke down and dragged this one home without a chassis for a test drive. Sounds excellent. It's very detailed even at low volume levels (this is the first amp I've ever found this). It's pretty particular about input cabling though. It will go into oscillation if everything isn't perfect. That probably goes along with being very detailed though. Now I just need to figure out how to keep my stupid cat from electrocuting itself.
). It's pretty particular about input cabling though. It will go into oscillation if everything isn't perfect. That probably goes along with being very detailed though. Now I just need to figure out how to keep my stupid cat from electrocuting itself.
Hi Jeff, interesting - I didn't notice this specialty with regards to input cabling. Maybe I just had the right cabling all the time - I don't know
For BJT outputs, you need:
Q18, Q22 = NJW1302
Q19, Q23 = NJW3281
R42, R43, R52, R53 = 100R
R44, R45, R54, R55 = 2.2R
No PCB changes required - which is pretty cool
For BJT outputs, you need:
Q18, Q22 = NJW1302
Q19, Q23 = NJW3281
R42, R43, R52, R53 = 100R
R44, R45, R54, R55 = 2.2R
No PCB changes required - which is pretty cool
I broke down and dragged this one home without a chassis for a test drive. Sounds excellent. It's very detailed even at low volume levels (this is the first amp I've ever found this
Yes, it's got excellent control over the speaker even at very low volume. Also - distortion level doesn't grow at low levels here.
Some time ago I had a cat, and at some point I caught him trying to byte the mains cable through
Hi Jeff, interesting - I didn't notice this specialty with regards to input cabling. Maybe I just had the right cabling all the time - I don't know
For BJT outputs, you need:
Q18, Q22 = NJW1302
Q19, Q23 = NJW3281
R42, R43, R52, R53 = 100R
R44, R45, R54, R55 = 2.2R
No PCB changes required - which is pretty cool
Is 1/4W still okay for R44, R45, R54, R55 base resistors of should they be higher power for BJTs?
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