Bringing this amp back to stock form, I would like to rewire the impedance switch back to stock, removing the 2x3300pf caps connected between the NFB purple wire and the 4 ohm yellow tap wire (bass boost/resonance mod?).
I'm confused how this switch would have been wired originally. Being a...
So I brought the amp home and it sounds great. Looked at the inside closely today and all looks in order, minus the cap on the mid tone pot being removed and a cap across pins 6 and 8 on V1.
I know this is to help with oscillations, but what impact does it have on tone? Is it safe to remove...
These 2 resistors and orange caps seems upgraded (red arrows, bottom of board). Any idea what the resistors are for and if the new orange caps are good?
Thinking about acquiring this Canadian vertical input 4010 but I noticed some.work on the bias resistor and elsewhere. Can someone help me understand what has been modded and whether or not this is one to get? Thanks in advance!
I didn't do anything to the presence control. I understand it's function is impacted (full on) at low master volume due to the NFB being reduced in this setup, but it hasn't really bothered me at this point. Do you have a recommendation to address this? I have read about installing another...
My issue was that the original pre-PI master volume did not have shielded wire. I left the pot in the same location for the new PPIMV, beside the standby switch, and used shielded wire with a PEC dual gang pot (LarMar type). No noise whatsoever. With shielded wire, the pot is fine beside the...
Here's an update.
I pulled out the pre-PI master volume and brought the amp back to stock. Whisper quiet and no issues. I then installed a LarMar PPIMV and rebiased the tubes to 65% and voila, it is working great! Lack of presence control at low volumes, but that is a known tradeoff. The...
From the effects loop card - W4 connects to the middle terminal on the treble pot. W3 connects to BN4 on the PCB which has a trace to C11.
I'm not sure where W1(red) and W2(green) go at this point.
I dug up this old thread where this "fix" was discussed, connecting the resistors to W1 then W2 and W3. Is this the same as mine?
http://www.marshallforum.com/threads/what-is-this-hum-balance-pot-on-my-1987x.97032/
I'm not following how W3 is connected between the hum balance area on the PCB and the effects loop card. The schematic shows a closed loop for the hum balance.
I see that they used W2 and W3 on the PCB for the new led installed when the original indicator lamp was removed and replaced with the mv pot. Could this led be the culprit, feeding noise into the signal path?
This is based on your assumption that W3 on the effects card is the same as W3 on the PCB, correct? I don't think they are related as BN4 from the PCB connects to the W3 post on the effects card. I could be wrong. Additionally, R31's trace underneath the PCB goes to W3 with the other end...
I've decided to pull this master volume out and replace it with a Lar/Mar PPIMV using a dual gang PEC pot in the same location. I'll reconnect W3 to BN4 using the stock brown 22awg wire and be sure to use sheilded wire on the PPIMV.
Since I bypassed the FX and am still getting the noise, doesn't that eliminated the FX loop jacks as the culprit? My understanding is the FX loop jacks are only in the signal chain when the FX loop is activated.
I'm wrong, W3 at the FX loop card is the input into the PI after the FX loop, so this master is after the tone stack and FX loop, right before the PI.
W4 is the input into the FX loop from the tone stack.
Bad pot or lack of shielding at the pot?