Blown Amp/Mixer

[Trinite]

Re: Blown Amp/Mixer

Here is a diagram of the circuit that provides the +60V to the phantom power reg.

Note: Ground reference is provided by the transformer center tap and is not referenced to the -20VDC output.

[Trinite]

Re: Blown Amp/Mixer

Been busy lately, but finally got around to fixing this unit. Replaced 2 op-amps, 2 burned out resistors, added a bleed resistor on the high voltage section and added a ground-lift switch.

Ended up learning quite a bit about audio systems in the process as well.

[Agent24]

Re: Blown Amp/Mixer

Nice job!

[Trinite]

Re: Blown Amp/Mixer

Also replaced all the non-name caps in the amp section, which got rid of a lot of the AC hum, along with grounding it. Actually sounds quite decent now. In any case, it's a much nicer unit than when I first started.

Just for laughs, I uploaded a pic of the warning label to show the quality of the "Engrish" used, which also implies the original build quality of the unit.

[hardwareguy]

Re: Blown Amp/Mixer

Those crooked heatsinks need to be set so they cannot touch...those are NOT isolated TO220 devices on those heatsinks. You have a short circuit hazard.

[Trinite]

Re: Blown Amp/Mixer

Those crooked heatsinks need to be set so they cannot touch...those are NOT isolated TO220 devices on those heatsinks. You have a short circuit hazard.

I checked. Both heatsinks are grounded, so them touching is not an issue. The 7815 and 7812 regs each are grounded through the center leg, so their contact with the heatsink again poses no issue. Otherwise, I would have straightened them out; but in this case, the work was unnecessary and a posed a risk of PCB damage, so I left them as is.

[Agent24]

Re: Blown Amp/Mixer

I had a feeling that would probably be the case...