Peavey 5150 and Classic 50 Footswitch LED's

[bobloblaws]

I added a couple of LED's to the footswitch for my Peavey Classic 50 to indicate reverb and channel status. A single LED for 2 channels isn't ideal, but better than nothing. Both the ring and the tip are at approximately -25V when the respective stomp switches are open. I simply wired LED and resistor pairs in series with the lines connected to the tip and ring and terminated at the respective switch. When the channel switch is closed the ring still has -12V, the LED is illuminated, and the Normal channel is operational. So far, so good. Then I tried the same thing with the footswitch for my 5150. In this case it is problematic. As with the Classic 50 Normal channel, when the channel select switch is open the Rhythm channel is operational. With a stock footswitch closing the switch grounds the ring portion of the jack and the Lead channel becomes operational. But with the LED and and resistor added something strange happens. When I first step on the switch the green Rhythm indicator on the panel lights up faintly for a split second and then it's back to the red Lead indicator being lit up. The controls for the Rhythm channel are operational (Pre, Post, Bright, Crunch) and the Pre and Post for the Lead channel are completely out of the circuit. However, there is increased volume and gain compared to the Rhythm channel engaged with stock footswitch (or sans footswitch). Unfortunately the schematic has not been helpful to me yet, I can't make heads or tails of the relay switching scheme as drawn. Is it possible its a non-starter with the 5150 and I just got lucky with the Classic 50?

peavey_5150_combo.pdfPeavey-Classic50-Schematic.pdf

[Enzo]

You put up the drawing for 5150 Combo, but you refer in your text to 5150. Those are two very different amps. WHich one do you actually have?

Assuming the combo, With switch open, Relays K1,K2 are off and the amp is in NORMAL. WHen you turn on the switch, those relays energize to switch to LEAD. Note the voltage at the unenergized relays is full 23v, and that turns on Q8 to energize relay K3 and lights the green LED. When you add an LED in the footswitch, the voltage at the bottom of the K1,2 is now a couple volts higher. And I suspect that upsets the circuit for Q8, K3. SO the K3 functions don't track.

[bobloblaws]

You put up the drawing for 5150 Combo, but you refer in your text to 5150. Those are two very different amps. WHich one do you actually have?

Assuming the combo, With switch open, Relays K1,K2 are off and the amp is in NORMAL. WHen you turn on the switch, those relays energize to switch to LEAD. Note the voltage at the unenergized relays is full 23v, and that turns on Q8 to energize relay K3 and lights the green LED. When you add an LED in the footswitch, the voltage at the bottom of the K1,2 is now a couple volts higher. And I suspect that upsets the circuit for Q8, K3. SO the K3 functions don't track.

I have the combo.

Ok, the schematic/switching etc. makes a bit more sense to me now. I wasn't cluing in that S1 is the channel switch in the panel. But are S1 and S2 on the same physical switch? What does the "SUZZPP" label mean? I also can't suss out where the "Crunch" switch is.

Is only the the coil portion of K3 utilized?

To be clear, the Rhythm mode (footswitch open) is OK. The problem occurs when engaging the footswitch (switch closed) which switches the amp to Lead mode, just as you said, only in this case the gain and volume are still affected by the Rhythm channel Pre and Post controls instead of the Lead channel Pre and Post. The red LED does come on. I think I misspoke when I said "the green Rhythm indicator on the panel lights up faintly for a split second and then it's back to the red Lead indicator being lit up" and possibly confused the issue. I was probably recalling some other scenario.

So in any event, my resistor and LED are on the ground side of the switch so with the switch open there should be no effect on Q8 etc. So I'm going to venture a guess and say the voltage drop from the LED and resistor when the switch is closed are actually leaving K1 and K2 under powered?

[Enzo]

The PP means push-push type switch. SU, I THINK means standup. meaning the switch sticks straight up from the board, contrast with some panel switches which mount parallel to the board. I don't know offhand what the Z is for.

S1,2,3 are three separate push switches. The three on your control panel. Each switch has two sections though, that is why S1a controls those relays, and S1b is not used - it is drawn as not connected nearby. a and b are just the two halves of the switch. S3 is the bright switch, and only half of it is used. S2 is the crunch switch, right next to the bright switch. Both halves of that are used.

Lead and normal channels are switched by relay. Crunch is not really another channel, it is just some gain and tone adjustments to the normal channel.

The coils are drawn alone for the relays and the relay switch contacts are up in the audio circuitry. This is done for the same reason as the build. The coil drive circuit is electrically separate from the signal/audio path, so why draw them together? Building an amp, the idea of a relay is to have some circuit switching near the audio path, while the control of the relay is remote - ie someplace else on the board. SO ALL of K3 is used. The coil that activates it is in the footswitch circuit, the contacts are in the audio. K3a switches in/out some local feedback in V5b. K3b is by the LEAD tone stack and does some level changing.

I am ssorry I said bottom of the relay, that is just shop slang here. By bottom, I meant the low voltage end, the end that gets grounded. Look at K1, K2 in the footswitch. The righthand end is connected to +23v and should always have that voltage. The left end is the end that gets switched to ground. If you ground that end, the 23v drops across the two coils, about 12v apiece, and current flows through them and they energize. Now S3 does this grounding by way of the footswitch jack. But it draws that current through the LED CR5. Now LEDs have a voltage drop across them. Depending on color, that voltage can be anything from 1.2v to 4v, maybe more. SO when you close S3, the left end of the relay coils does not go all the way to ground, there is a couple volts lost through the LED. Now if you add an LED in your pedal, that is in series with the existing LED in the amp. SO now you have doubled the voltage lost to LEDs. That means instead of 23v across the relays less 2v for CR5, 21v, we now have 2 more volts lost so we wind up with 19v. SO that means we have about 4v on the left end of the coils, versus 2v before. If it were just the two relays, that probably wouldn't matter.

But we still have that pesky Q8, CR10, K3 circuit. And that draws a control voltage from the left end of those relay coils, and a 2v difference CAN be enough to affect operation.

[bobloblaws]

Thanks Enzo, that is a boatload of valuable info. I fear we might have got crossed up because I went and edited my last post and the time stamp shows a later time than your reply, I guess I assumed you wouldn't have responded already at that late hour. In any case your assessment is probably still relevant, but just to clarify, are you suggesting that Q8, etc. could have an adverse effect when in switch closed/Lead mode? Because as I attempted to clarify with my edit, the issue I'm having is when the stomp switch is closed and the red panel LED is lit and the green panel is unlit (therefore no voltage drop from the green LED I presume) and I might have led you to believe the problem is occurring with the opposite scenario, that being with the stomp switch open/Rhythm mode. Rhythm mode is working OK. Is the Q8 control voltage still a factor when in the Lead scenario, or does CR6 come into play and negate it somehow? Sorry for the snafu.

[Enzo]

I am not a go back and edit fan. it gets confusing when we write something, then someone responds, and the the OP goes back and changes what they wrote before.

Q8 is controlled by the voltage at its base. That voltage changes from about +23v in one state, and about +2v in the other. BY adding LEDs in the FS, we change that to +23v and +4v. That COULD affect operation of Q8. That extra couple volts MIGHT cause Q8 not to turn fully off.

When the switch is open, the relay coil voltage is up to +23, so Q8 should be turned on, lighting CR10 and energizing K3. Close the switch and the voltage to Q8 drops, hopefully enough, so Q8 turns off. K3 drops out and K1,2 pull in. If Q8 only marginally can turn off, you might get a sluggish K3 action, a flickering or dimmer CR10 LED, and so on.

If the amp works fine without the FS, and has the weird symptom with the FS, then we have to look at what changes were made to the FS, the diode being pretty much all it was.

[bobloblaws]

I am not a go back and edit fan. it gets confusing when we write something, then someone responds, and the the OP goes back and changes what they wrote before.

Q8 is controlled by the voltage at its base. That voltage changes from about +23v in one state, and about +2v in the other. BY adding LEDs in the FS, we change that to +23v and +4v. That COULD affect operation of Q8. That extra couple volts MIGHT cause Q8 not to turn fully off.

When the switch is open, the relay coil voltage is up to +23, so Q8 should be turned on, lighting CR10 and energizing K3. Close the switch and the voltage to Q8 drops, hopefully enough, so Q8 turns off. K3 drops out and K1,2 pull in. If Q8 only marginally can turn off, you might get a sluggish K3 action, a flickering or dimmer CR10 LED, and so on.

If the amp works fine without the FS, and has the weird symptom with the FS, then we have to look at what changes were made to the FS, the diode being pretty much all it was.

Yes, I apologize again, I shouldn't have assumed I was the only one burning the midnight oil.

Anyway, thanks for indulging me on this. Of course the amp itself can't be blamed. In fact I should have listed the thread under the mods category, not the repairs category. Force of habit.

I had been hoping there was some way to tweak the footswitch as a workaround. I suppose I could put in a DPDT switch and add a 9V battery to power my LED. It might seem like overkill but there are times at band practise in the middle of a tune where I'm not sure which channel I'm on.

Anyway, thanks again, Enzo.

[bobloblaws]

I'm happy with the solution I came up with. Replaced the stock switch with a DPDT and use 9V battery to power green and red LED's corresponding to the panel LED's. One side of the switch is the original circuit and the other side toggles between the two LED's. I added a mini toggle as well to disengage the battery when not in use. Adding the resistor and purple LED to the tip/sleeve circuit for reverb switching worked from the start.

[Enzo]

I am glad you worked it out.