Hi people, I'm repurposing a GK BL112 power amp pcb into a DIY bass combo. Got the board cheap as a NOS spare part and it seems to fit my needs.
What pk-pk input voltage do these power amp boards expect from the preamp? I'm currently working on my diy preamp section and I have 4v pk-pk output to play with from its output. My initial plan would be to start at 0, then increase the preamp signal until the power amp output clips (with no load) then set the previous stage to never exceed this, but I'm not sure if the factory preamp's output would ever be this hot? Just afraid of blowing the whole thing up...
Also, could I place a 300ma load (tube heaters) on the LM78M15 regulator and not burn anything? I see the regulator inputs are fed through (each) a 15V zener diode and resistor in parallel, designed to power the preamp board which I assume won't pull 300ma... I've only got the power amp PCB to play with, no toroid for it yet either. I don't want to have a second toroid just for the heaters, so would like to tap off the (unused) regulators on board.
Finally, the spec calls for a 39v-0-39v transformer, I can only find 2x30v and 2x35v online. 2x35v is harder to find than 2x30v in the correct VA rating. Would a 2x30v transformer cause any problems for the power amp or just simply lower the output voltage at which it clips? I'm building this as a practice amp, 100w isn't enough to argue with a drummer anyway so that's out of the question. I'd happily run the amp 'cooler' and end up with 70w which is still more than required
Any guidance would be much appreciated! I have the service manual here but it doesn't tell everything.
Kind regards
What pk-pk input voltage do these power amp boards expect from the preamp? I'm currently working on my diy preamp section and I have 4v pk-pk output to play with from its output. My initial plan would be to start at 0, then increase the preamp signal until the power amp output clips (with no load) then set the previous stage to never exceed this, but I'm not sure if the factory preamp's output would ever be this hot? Just afraid of blowing the whole thing up...
Also, could I place a 300ma load (tube heaters) on the LM78M15 regulator and not burn anything? I see the regulator inputs are fed through (each) a 15V zener diode and resistor in parallel, designed to power the preamp board which I assume won't pull 300ma... I've only got the power amp PCB to play with, no toroid for it yet either. I don't want to have a second toroid just for the heaters, so would like to tap off the (unused) regulators on board.
Finally, the spec calls for a 39v-0-39v transformer, I can only find 2x30v and 2x35v online. 2x35v is harder to find than 2x30v in the correct VA rating. Would a 2x30v transformer cause any problems for the power amp or just simply lower the output voltage at which it clips? I'm building this as a practice amp, 100w isn't enough to argue with a drummer anyway so that's out of the question. I'd happily run the amp 'cooler' and end up with 70w which is still more than required
Any guidance would be much appreciated! I have the service manual here but it doesn't tell everything.
Kind regards
