I've got a Rockford 4020DSM with one blown channel. The outputs are BUZ11A and IRF9530 with 10ohm gate resistors. Can I sub IRF540 and IRF9540?
Does anyone have the schematic for this? I'm also getting a little noise on the speaker negatives. Whole amp could likely use a recap...
Does anyone have the schematic for this? I'm also getting a little noise on the speaker negatives. Whole amp could likely use a recap...
The guts are considerably different looking between the 4020 and 4080, but besides that I don't know.
Perry,
I replaced the left rear blown outputs and some additional driver components that were damaged in that channel. Also recapped the entire amp except for the rail caps. Amp is working well, although I have some audible white noise coming through on both rear channels only when the input switch is on 4ch input and no RCA/source is hooked up to the rear RCAs. No audible noise if switched to 2ch input, regardless of RCA/source hooked up, although slightly higher noise when looking at it on the scope. I don't know if anything is wrong per se, but I just find it odd and I don't understand enough about the design (especially why there is additional input opamp circuitry on the rear channels when they are in 4ch input mode, but bypassed in 2ch input mode). Attached is the schematic PDF, and these are the pertinent sections of the front & rear left inputs.
Left front:
Left rear:
I replaced the left rear blown outputs and some additional driver components that were damaged in that channel. Also recapped the entire amp except for the rail caps. Amp is working well, although I have some audible white noise coming through on both rear channels only when the input switch is on 4ch input and no RCA/source is hooked up to the rear RCAs. No audible noise if switched to 2ch input, regardless of RCA/source hooked up, although slightly higher noise when looking at it on the scope. I don't know if anything is wrong per se, but I just find it odd and I don't understand enough about the design (especially why there is additional input opamp circuitry on the rear channels when they are in 4ch input mode, but bypassed in 2ch input mode). Attached is the schematic PDF, and these are the pertinent sections of the front & rear left inputs.
Left front:
Left rear:
It's common in other Rockford amps. It's not really a problem since you're unlikely to have the rear channels connected to speakers with no input.
I had a "noise" problem on a Rockford amp and found that the source resistors were out of tolerance. Also, re-adjusting the bias pots helped a ton.
I guess I'll let it ride then.
Another question I wasn't sure warranted a new thread - also repaired a 60dsm (leaky caps and overheated/ejected 150ohm 2w resistors on the speaker outputs). Amp works fine but bias pots ended up at about 10:00 and 12:00. Usually they are closer to the same position. Found that one 2k bias pot read 2120ohm and the other 1842ohm. Swapped the 1842ohm for one that was about 2150ohm with no real change in the resulting position.
Should I be concerned about the difference?
Another question I wasn't sure warranted a new thread - also repaired a 60dsm (leaky caps and overheated/ejected 150ohm 2w resistors on the speaker outputs). Amp works fine but bias pots ended up at about 10:00 and 12:00. Usually they are closer to the same position. Found that one 2k bias pot read 2120ohm and the other 1842ohm. Swapped the 1842ohm for one that was about 2150ohm with no real change in the resulting position.
Should I be concerned about the difference?