I got pops.

[warioblast]

I finished working on my amp a couple of weeks ago. I thought I was finally done. It turns out I'm not.

I started using pedals; lots of them have true-bypass; a few days ago and I noticed that they were popping.
My amp is based on a JCM800 2204 50W with an added clean channel, took from a Landry amp.  I have a single input.
I use a relay to switch between both channels. This clean channel uses a separate tube.
The amp is fairly quiet, and I have no pops when I'm switching channels.
The controls don't scratch.

The POPs appear on both channels.

I tried a using a couple of buffered pedals at the end of my chain, but my true-bypass pedals keep on popping.
I also noticed that when I'm using my Digitech DL-8 in buffered mode, my amp gets slightly quieter. 

When I insert a simple cable in my amp, I measure 0.25V DC between the tip and the sleeve of the loose end. It seems a bit high, doesn't it ?

I really don't know what to do from here :(


PS: please MOD, dont move this thread to the pedals forum. My pedals are fine.

[SILVERGUN]

Everything starts with a schematic

[vampwizzard]

Effects loop or front of amp? Schematic needed. Input resistor values? Theres a bunch that could go wrong here.

[warioblast]

There you go.

[SILVERGUN]

It is bad form to have one signal feeding both channels that are live and then just switching between the 2 pre PI.
To test:
Pull the first tube on either channel.
Or, just disconnect the grid of one channel from the input.
Still pop?

[warioblast]

Ok I have just pulled the first tube on either channel. It had no effects.
Still pop in both cases.

[DummyLoad]

have you tried adding an input coupling cap?


--pete

[terminalgs]

It is bad form to have one signal feeding both channels that are live and then just switching between the 2 pre PI.

silvergun: why do you say that? I don't think there is anything wrong with it. 


warioblast: Correct me if this is wrong: the popping occurs when you  turn pedals on/off, not when switching channels.

a high gain amp will amplify all AC waves coming into the input,  good signal as well as noise (pop). 

if signal is overdriving gain stages where the signal is clipped: crank up the first vol pots to 10.  say input to 2nd stage is 10V signal and 0.5V noise, the next stage Mu=30 but clips at ~40V..  signal becomes fuzzy and exits @ ~40V, noise exits @ 15V...  signal:noise ratio goes from 20:1 to 2.6:1  ( Mu & V's are examples, I didn't study your schematic values.. and I'm not an engineer but that's my limited understand based on looking at o-scopes).

[shooter]

was heading down that thought path! 

with NO pedals, amp pre cranked and guitar volume cranked NO pops?

as for SG suggestion, switching large signals is problematic, and that's the biggest signal point in the pre

[warioblast]

have you tried adding an input coupling cap?


--pete

No I haven't. I will try it. 

It is bad form to have one signal feeding both channels that are live and then just switching between the 2 pre PI.

silvergun: why do you say that? I don't think there is anything wrong with it. 


warioblast: Correct me if this is wrong: the popping occurs when you  turn pedals on/off, not when switching channels.

a high gain amp will amplify all AC waves coming into the input,  good signal as well as noise (pop). 

if signal is overdriving gain stages where the signal is clipped: crank up the first vol pots to 10.  say input to 2nd stage is 10V signal and 0.5V noise, the next stage Mu=30 but clips at ~40V..  signal becomes fuzzy and exits @ ~40V, noise exits @ 15V...  signal:noise ratio goes from 20:1 to 2.6:1  ( Mu & V's are examples, I didn't study your schematic values.. and I'm not an engineer but that's my limited understand based on looking at o-scopes).

was heading down that thought path! 

with NO pedals, amp pre cranked and guitar volume cranked NO pops?

as for SG suggestion, switching large signals is problematic, and that's the biggest signal point in the pre

I had not pushed the amp yet. I have just tried it.
With no pedals, amp pre cranked and guitar cranked, I do get pops when switching channels, but I have to turn the volume on 7 or 8 (/10, not o clock) to get audible pops.

What if I ground the unused preamp circuit ?

I guess I can try switching at the input too !?

[DummyLoad]

With no pedals, amp pre cranked and guitar cranked, I do get pops when switching channels, but I have to turn the volume on 7 or 8 (/10, not o clock) to get audible pops.

try connecting a 22MegΩ resistor between "R2" & "R3" relay contacts.

--pete

[warioblast]

 ^^ I will try it to.

[DummyLoad]

try using Vactrols for switching instead of relays - look at the soldano SLO schema for an example on how to. switching with relays at any grid circuit will pop. also, you can reduce pop noise with use of manual switches that have been constructed with make-before-break contacts.


--pete

[warioblast]

To be honest I could live with the the pops I have right now, switching channels. I never crank my amp that much.

But the pops I get with pedals, are noticeable at low levels. 

[shooter]

But the pops I get with pedals

that happens when you're NOT switching channels?

[warioblast]

Yes.

[tubeswell]

Your schematic shows a “1n” going from grid to ground at the input jack. There should also be a 470k- 1M grid leak resistor there. If you didn’t put that in, you’ll be getting a small amount of grid voltage there. (which would explain the pop)

[warioblast]

It is a 1M resistor. Sorry for the confusion. 

[vampwizzard]

Crazy question we haven't addressed yet: does the pop happen on other amps or just this one?

[warioblast]

I only have this one amp right now.
But I had those pedals for years, some over 2 decades. They worked fine on other amplifiers.

[warioblast]

Today I tried to add an input coupling cap. No changes.

I hardwired the amp as a single input plexi; no relay, no toggle switch. It stills pop.

Is is worth the hassle to try another grounding schematic ? Right now I have a single ground connection near the power transformer.

What else can I try ?

[shooter]

POP is the breaking/making of the signal path.  when that happens, depending on "where" in the path, a transient spike happens, then gets amplified, then get sent to the speaker to be heard

[warioblast]

Are you saying it's not related to ground.

Since it happened on both channels. It was either at the very beginning (the input jack ?) or after the PI connection !?
Besides reflowing my solderings around that area, I don't know what to do. I don't have a scope, but I could borrow one to a friend if need be.

[sluckey]

Show us some high rez gut shot pics of your amp. There may be a clue in hiding.

[shooter]

I could borrow one to a friend if need be.

perfect tool for the job
set it up at the Common relay terminal, feed a signal, when you're happy, start switching the relay, look for transients, guessing you might have some close to signal size, they will be way higher frequency, so might have to mess with trigger.

once you find 'em kill 'em 

[SILVERGUN]

I started questioning if cheap patch cables would have an effect and I came across this video. I'm not saying that this is the solution, I'm just posting this as a public service announcement.
Right around 22:15 he switches a pedal on while doing a db test for noise and you can see the pop on the bar meter.
https://www.youtube.com/watch?time_continue=1300&v=u530vUk6mmE&feature=emb_logo


Test each pedal and cable individually to try and weed out the potential offender.

[warioblast]

I'm ashamed to post those pics.
I started this project in 2016. The amp was a DSL50. I swear it looked nice on my first build (JTM50). But since, it had other lifes. (1987, 2204, shiva, landry...).

I rewired the amp. Changed the input jack.
I tried to use different instruments cables, speaker cables.
I tried different tubes.
I tried to plug my amp directly into the wall plug.

Even when the gain is set low, it pops.
I tried using a single pedal. (so patch cables are not my problem).
I tried different power supply. Though I have never had problems with the Voodoo Lab PP2+.
No matter how many times I stomp on a pedal. The pops are always there. It doesnt fade away.

I tried putting a buffered pedal at the end of my "chain".
I tried putting my DIY 6G15 in between too.

Anyways. It goes the horror show.

[warioblast]

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[vampwizzard]

Im looking at your input ground.. where does that ground bus that goes across the pots hit ground?

Also: other than being unnecessarily cramped that looks pretty good!

[SILVERGUN]

1) I can't see how your input jack wiring matches your schematic. I can see where the wire goes to the grid stopper and into one stage but the other connection is unclear.
 

[warioblast]

Like I said earlier, I got rid of the relay and toggle switch. It's more or less the high input channel of the 1987 / 1959. With an added master volume.

The ground bus above the pots is connected to the input, which is connected by a black wire (highlighted in blue) that goes to the 0.68 uf cap. Which is the beginning of the ground bus that is next to the tags strip.

[shooter]

is there a ground wire from the black cap on left going to the PT ground?  in other words 2 points of ground on same buss?

[warioblast]

There is a wire connected to the dual 33uf black cap, but it's the only wire from the ground busses (yellow) that is connected to the chassis.
Earth in green. Speaker jacks are grounded near the output tube.
All the rest is grounded to the same spot as the ground busses.

[shooter]

guessing the input jack is an isolated jack?

the big black cap "feeds" the Pre section?

if so to ?'s above;
this is typically how I would do it;
put a ground screw in the hole I indicated near the input and cut the black wire going back to the PS.  IF everything on those 2 busses are PRE amp stuff, no PI, no PA

[warioblast]

I will give it a try. I appreciate all the support guys.

[warioblast]

Ok, so I tried it. The amp became noisy, and the pops were still there.

[shooter]

thanks for trying;

you can see the pop on the bar meter.

you're at the bar meter point 
If you can hear it you can "see" it, start at the speaker, voltmeter, scope, mic into audio software, once you see it, you can track it.

[warioblast]

Now that I think about it, before I dismantled the amp; the DSL 50; pops started to happen a short time ago.
It was a very quiet amp when I got it, I didn't have any pops at all. For years, I have used many of the pedals you have seen on my pedalboard without problems.

But in its last days, I started to have pops with pedals, and also, my pedals became noisy. The DSL also had bias drift.

The only parts remaining from the DSL50 are the chassis, switches and PT & OT transformers.
Could those pops come from a faulty / damaged OT transformer ?

[Ed_Chambley]

Doesn't the Filaments running under the pots and all close to preamp tubes cause noise?   This is a High Gain, Cold Clipper Amp, Right?  I know Builders, Mike Soldano who align preamp tubes offset from Power amp tubes, but not that close.

[warioblast]

It's not high gain anymore, it's just a plexi.

The amp is fairly quiet, as far as operating noise level goes. It is a bit sensitive to guitar proximity though.
At one point I had the filaments with straight wires like the SLO, and also away from the front pannel; with the preamp tubes closer to the power tubes.
It sounded as quiet as it does now. But then again I didn't tried to use pedals at that time, and I don't remember about the proximity sensitivity.

I can try to move the filaments arouund one more time. 

[vampwizzard]

Hard to tell from the pics.. did you use shielded cable off the input? Is the shield wire pulled back far enough that it doesn’t make contact with the conductor?

[warioblast]

I did use shielded cable for the input and a couple of other connections.
I thought I did it right, but I'm getting some weird readings with the multimeter continuity test.

[vampwizzard]

how so? could be a few reasons for it. What I do is take the shield and peel it back and twist into a second wire pointed the opposite direction from the conductor. I solder a ground wire to that shield and then heat shrink that connection. Its important that the shield doesnt overlap the conductor at all.