JMP 50 Popping Sound

[Littlewyan]

Just to confirm, the problem disappears when you remove V3, what about if you remove V2? You said earlier the problem just gets quieter if you remove it, is that right?

[Riffmonster]

Just to confirm, the problem disappears when you remove V3, what about if you remove V2? You said earlier the problem just gets quieter if you remove it, is that right?

Yes that is correct.

What valve are you using for V2? As most russian valves can't handle the high heater to cathode voltage. I've had weird issues with this in the past. Once I had a problem where an amp would motorboat when I turned it off and it was the valve in V2.

I am using a JJ ECC83s and also tried a Tube Town branded 12ax7 (I guess Chinese?).

Unfortunately, I will be away from the amp for a whole now since I am traveling. I will get back to it as soon as possible and let you know. Thanks again for all the help. If someone has more ideas, please just let me know!

[Littlewyan]

When you get your hands on the amp again I would try grounding the PI input and seeing if the sound goes away.

Have fun travelling. Stay safe.

[ChloeFree]

The problem could be in Amp in Standby. I know that your one probably doesn't have the mode, but there can be something similar. I had the same problem with my sound bar. Here is what I found.
'When you switch on your amplifier, a continual source of voltage flows through it. When you place your amp in sleep mode, you are removing the high voltage part of the power supply. When connecting or removing high voltage, the voltage spike frequently produces a pop noise. The amount of "pop" produced depends on how the standby switch is built.
The good news is that you don't have to be concerned about that pop sound. It's perfectly natural. Also, bear in mind that you should only utilise standby mode when you initially switch on your amplifier. This is why: Guitar amplifiers employ high voltages to generate more watts, which can be taxing on the power supply circuit's capacitors. Standby switches were created to safeguard those capacitors. When you turn on your amp, set the standby switch to "Standby" to let the tubes to warm up before transferring full voltage to the power supply's capacitors. It takes a few seconds for the tubes to achieve operational temperature. The voltage on the capacitors might climb higher until the tubes can work, which is stressful for them. Once the tubes are heated, they reduce the power supply voltage to typical operating levels, allowing the capacitors to perform more effectively. In other words, as long as you don't utilise your Standby switch as a mute or kill switch, no one will hear the pop when you turn your amp on for the first time.'

[Riffmonster]

Thanks a lot for your help and input. Unfortunately, I had ruled out the standby switch earlier. The problem was still there after I removed the standby switch. Also, the pop appears randomly and not switching-related.

I am still away from the amp but I still hope I’ll be able to solve the problem with all your help here.

[Stephen1966]

Thanks a lot for your help and input. Unfortunately, I had ruled out the standby switch earlier. The problem was still there after I removed the standby switch. Also, the pop appears randomly and not switching-related.

I am still away from the amp but I still hope I’ll be able to solve the problem with all your help here.

Hey there! Just a thought, but could the intermittent pops be coming from other equipment on the same mains circuit? We were looking at a problem like this, here: https://ampgarage.com/forum/viewtopic.p ... 56#p441156

No experience with Marshall's unfortunately, but ruling out the environmental factors might help to dig down to the problem.

I have a spare scope for sale if you are in the EU. PM me.

Good luck!

Stephen

[Riffmonster]

[quote=Riffmonster post_id=442619 time=<a href="tel:1656935393">1656935393</a> user_id=18952]
Thanks a lot for your help and input. Unfortunately, I had ruled out the standby switch earlier. The problem was still there after I removed the standby switch. Also, the pop appears randomly and not switching-related.

I am still away from the amp but I still hope I’ll be able to solve the problem with all your help here.

Hey there! Just a thought, but could the intermittent pops be coming from other equipment on the same mains circuit? We were looking at a problem like this, here: https://ampgarage.com/forum/viewtopic.p ... 56#p441156

No experience with Marshall's unfortunately, but ruling out the environmental factors might help to dig down to the problem.

I have a spare scope for sale if you are in the EU. PM me.

Good luck!

Stephen
[/quote]

Hi Stephen,

Apologies for the late reply here. I was still away from the amp but I can finally start working on it again at the end of this week.

I ruled out interferences from other equipment on the same mains, in fact I tried the amp in several different rooms without any changes. The speaker, cables and guitars work fine on other amps.

I’ll send you a PM once I am back home regarding the scope, thanks a lot for the offer.

Cheers!

[Stephen1966]

Hi Stephen,

Apologies for the late reply here. I was still away from the amp but I can finally start working on it again at the end of this week.

I ruled out interferences from other equipment on the same mains, in fact I tried the amp in several different rooms without any changes. The speaker, cables and guitars work fine on other amps.

I’ll send you a PM once I am back home regarding the scope, thanks a lot for the offer.

Cheers!

Please do, it's sitting gathering dust in the basement

Stephen

[goldenGeek]

I dont know if its relatable, but I had a similar issue a while back that turned out to be a faulty output transformer. https://ampgarage.com/forum/viewtopic.php?f=6&t=33621

[Riffmonster]

Thanks for sharing this. I really hope it’s not the OT. It is brand new and I doubt that I cooked it somehow. But of course it could have been faulty when I received it…

I hope I can update you guys this weekend!

[Riffmonster]

So, I had the chance to have a quick look at amp again.

I made sure that no resistors on the board are touching each other as pointed out here before but this did not change anything. I also followed bepone‘s advise and bypassed the volume pot without success. I also changed the 100k resistor that sits on the V2 socket without success. Slowly running out of ideas now… could it be an arc from the mains switch and not the standby switch?

[neskor]

Once I had the same situation, it was loose connection on main power switch.
Try to move all mains wires with chopestick and listen.

[bepone]

Slowly running out of ideas now…

sorry to hear thatm but we need to work more.
also this is possible to try this. open yellow wire from V2 pin 8 socket and insert any film cap 0.022-0.1uF 400V in series with pin 8 and yellow wire and see is it changed something

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[sluckey]

also this is possible to try this. open yellow wire from V2 pin 8 socket and insert any film cap 0.022-0.1uF 400V in series with pin 8 and yellow wire and see is it changed something

That will totally kill the guitar signal.

[bepone]

it is not permanent , to everybody is clear. it is here to block DC from the cathode and see if the popping is from silver mica. after the wire will be returned back to pin 8.