I replaced r23 and r24 with 2k7 ohms and now I got the red leds to light up and adjusted for 3.8V across r12 and r13.
Between pd+ and pd- I measure 12.8v.
I tried to connect the ips to the ops still using the bulb limiter. The light bulb started glowing and the rails dropped to 24v.
I tried powering it up without the bulb limiter but the bias shot up to 150mv and could not be adjusted.
I tried to play some music through it (I don't have a scope) and it sounded very distorted, so I shut it down and plugged in the bulb limiter again for further testing.
Any ideas?
Between pd+ and pd- I measure 12.8v.
I tried to connect the ips to the ops still using the bulb limiter. The light bulb started glowing and the rails dropped to 24v.
I tried powering it up without the bulb limiter but the bias shot up to 150mv and could not be adjusted.
I tried to play some music through it (I don't have a scope) and it sounded very distorted, so I shut it down and plugged in the bulb limiter again for further testing.
Any ideas?
With the bias pot on maximum resistance and 15k resistors installed, the bulb gets a little bit brighter and the rail voltage falls to around 25v.
When I increase the bias, the bulb gets brighter and the bias adjustment seems to work fine.
I noticed that in the schematics Q105 should be mje340 and Q106 mje350. I populated these with 2sc3503 and 2sa1381 according to a BOM I found somewhere in this thread.
Should I replace these with MJE340 and 350?
When I increase the bias, the bulb gets brighter and the bias adjustment seems to work fine.
I noticed that in the schematics Q105 should be mje340 and Q106 mje350. I populated these with 2sc3503 and 2sa1381 according to a BOM I found somewhere in this thread.
Should I replace these with MJE340 and 350?
Either you are mistaken on which way maximum resistance is on the pot or Q103 and Q104 aren't doing their job. Raising the pot resistance should raise the current available to the bases of those two transistors, which should make them conduct more. The more they conduct, the less current there is available to the predrivers and the rest of the output stage.
You should verify you are correct on the bias pot adjustment. Put an ohm meter on the two pot leads that aren't shorted by the board trace. It should read 200 ohms. If you have 200 ohms there, power the board up again and measure the voltage between the base and emitter on both Q103 and Q104. If they are functioning properly there should be around .6 volts present.
You should verify you are correct on the bias pot adjustment. Put an ohm meter on the two pot leads that aren't shorted by the board trace. It should read 200 ohms. If you have 200 ohms there, power the board up again and measure the voltage between the base and emitter on both Q103 and Q104. If they are functioning properly there should be around .6 volts present.
With bias pot on 200r I measure 0.6v across base and emitter on q103 and q104. I have 0.6v between b and e on all transistors including outputs.
The rails are now 37v with 15k resistors from v- to ND and v+ to PD and the bias pot at 300r.
Voltage across one 0.22r resistor is 5-6mv.
When removing the resistors the rails increase to 53v and I get 0-0.1 mv across the 0.22r.
I'm using a 60w light bulb for testing, does it limit the current too much? 240v mains.
The rails are now 37v with 15k resistors from v- to ND and v+ to PD and the bias pot at 300r.
Voltage across one 0.22r resistor is 5-6mv.
When removing the resistors the rails increase to 53v and I get 0-0.1 mv across the 0.22r.
I'm using a 60w light bulb for testing, does it limit the current too much? 240v mains.
