SV20H hissing like crazy!

[nemo_kost]

Hi folks, I'd like to report something is happening to my SV20H, maybe someone could point me in the right direction.

Last couple of gigs I noticed a loud hiss coming from the speaker, just after turning the amp on an putting it from standby to running mode (nothing plugged in front). The hissing is more evident in 20W mode, but is there in 5W mode too, just quiter.
I also noticed this did not happened every time, so I discovered that with a little "bump" given to the head, the hiss can go away!!! Probably it did not happen every time because this thing started during trasportation, at least this is my guess...
Anyway, I already tried:
-Changing the cab.
-Changing ALL the tubes (PRE and POWER).
-Changing ALL the cables involved (AC cord, speacker cable, patching/no patching...).
Nothing solved the problem, so is probably something inside.
The inside looks fine to me, but I'm no tech, so it's just a speculation based just looking at it and not finding anything "burned" or similar, and it was never touch before, as far as I know (I bought it new from Thomann on march 2023).
I recorded a video showing the problem.
Marshall SV20H Hissing

Any idea?
Thanks for your help!

 

[Creach]

Hello nemo_kost,

Not easy to see on the photo but you can you take a closer look at R18, I think it should be 220K.

 

[nemo_kost]

...take a closer look at R18, I think it should be 220K

Thanks for the reply.
You're right about the R18 value, the schematic says 220K.
Actually I cannot see the R18 colors too from the pic, they don't look like 220K code, but maybe it's just bad lighting, I'll need to check again.

Beside that, the head was bought new from Thomann and never been serviced by me, nobody opened it up before my pic, so I think no components have been changed. The board look untuched, normally you see some "marks" if someone changed components. I know it would better to look on the other side too, but from above it looks fine.
Do you think R18 could be the culprit of the hissing?

I failed to mention earlier the head worked perfectly for 16 months and more than 30 2-hours-gigs prior to the last coulple of live shows.
I used to carry it around in my car on soft surface and firmly stored between other stuff, of course it gets some bumps from the trips, but nothing serious (and I have other older amps that got carried around the same way and never had this problem).

 

[Creach]

From the photo it seems to me that the resistor is slightly fried but it can be just from the photo, or just lighter green color when they made the resistor.
And a color band looks almost gone (even if it was for example a yellow it seems so light color).

So it is worth a closer photo or a value reading from a multimeter. In case it is not 220K you can simply compare it with the same resistor of the second el34.

 

[nemo_kost]

From the photo it seems to me...

OK thanks. Probably it's just the light, but I'll have another look.

 

[marshallmellowed]

Try removing all cables from the inputs, then plugging your guitar into each input, one at a time, while the hissing is present. What do you hear? (post video if possible)

 

[nemo_kost]

Try removing all cables from the inputs, then plugging your guitar into each input, one at a time, while the hissing is present. What do you hear?

Good tip, I'll try that! Thanks.

 

[nemo_kost]

Try removing all cables from the inputs...

I tried marshalmellowed suggestion and these are the results.
Funny thing is the haed did not leave my house in a while, so no transportation involved. Every time I switch her on the problem is present (and goes away with the usual "bump"), so it looks like is something connected with the "resting" of the head, I don't know if you guys understand what I mean... Almost like some component runs into the problem everytime the head cools down completely.

Marshall SV20H Hissing - Part 2

 

[marshallmellowed]

I tried marshalmellowed suggestion and these are the results.
Funny thing is the haed did not leave my house in a while, so no transportation involved. Every time I switch her on the problem is present (and goes away with the usual "bump"), so it looks like is something connected with the "resting" of the head, I don't know if you guys understand what I mean... Almost like some component runs into the problem everytime the head cools down completely.

Marshall SV20H Hissing - Part 2

Hey there. Thanks for taking the time to do that video. Have you considered just returning the amp, since it should still be under warranty? You shouldn't be having to troubleshoot an amp under warranty. If you're wanting to continue with troubleshooting, and since your problem obviously seems to be mechanical in nature, I'd try these next steps.

While the hissing is present...

1. Try placing a jumper cable between the Send and Return jacks of the loop.
2. With the volume set low, very lightly wiggle each tube to see if the hissing changes (use a cloth if the tubes are hot).
3. Remove the chassis from the amp and with the speaker connected, power the amp on.
4. While the hiss is present, use a chopstick, or other non-conductive object to lightly press on the cable connectors (keep your hands out of the amp).
5. While the hiss is present, use the same (chopstick...) to lightly press on each component on the circuit board.

Let us know if any of these steps cause the hissing to stop.

 

[nemo_kost]

Hey there. Thanks for taking the time to do that video...

Hi marshallmellowed, no problem at all, thanks to you for the suggestions!
Yesterday I opened a support ticket with Thomann, they opened an RMA and already sent me a return label.
I asked you guys first cause maybe someone had the same problem and it was something stupid, like a cable touching a component, easily solvable without sending tha amp away, but probably this is not the case...

Anyway, I'll let Thomann having a look at it, hopefully they'll repair it under warranty...
I don't know how their after sale support works, never needed before, I'm scared they'll finally say it's a problem caused by the use, but frankly I'm no pro musician who travels the world and just used it in the "proper way", not abusing it at all (never run it past noon live), always stored it properly and with a dust cover etcetera, etcetera. I've other older amps and never had this kind of problem and the funny thing is the SV20H is my first amp bought new!

I'll let you know how it goes, thanks again.

 

[marshallmellowed]

Hi marshallmellowed, no problem at all, thanks to you for the suggestions!
Yesterday I opened a support ticket with Thomann, they opened an RMA and already sent me a return label.
I asked you guys first cause maybe someone had the same problem and it was something stupid, like a cable touching a component, easily solvable without sending tha amp away, but probably this is not the case...

Anyway, I'll let Thomann having a look at it, hopefully they'll repair it under warranty...
I don't know how their after sale support works, never needed before, I'm scared they'll finally say it's a problem caused by the use, but frankly I'm no pro musician who travels the world and just used it in the "proper way", not abusing it at all (never run it past noon live), always stored it properly and with a dust cover etcetera, etcetera. I've other older amps and never had this kind of problem and the funny thing is the SV20H is my first amp bought new!

I'll let you know how it goes, thanks again.

Good deal, and no problem. Never dealt with Thomann, but hopefully they'll get you taken care of.

 

[goldtop0]

A few of us on here changed the bight cap to a 100pf and that solved the hiss problem.

 

[marshallmellowed]

A few of us on here changed the bight cap to a 100pf and that solved the hiss problem.

If you read his initial post, his was an intermittent hissing, a defect.

 

[nemo_kost]

...intermittent hissing, a defect.

Unfortunately, yes!

...changed the bight cap...

Thanks for the reply. If you take a look at the first video you could understand better the situation.
Not a normal "amp hissing" at all, probably not connected with the bright cap.

Amp is on its way back to Thomann, let's hope for the best!

 

[PelliX]

Sounds to me like a warranty issue. After you've checked your cables, swapped valves done a basic optical inspection, it's warranty time. That's what warranty is for.

Now, I'd probably rip it open and start chopsticking the resistors - chances are one is damaged and the heating/cooling is causing it to intermittently produce self-noise. The fact that the old percussive maintenance trick (aka "The Slap") changes the issue means it's mechanical in essence. If you swap the resistor, you void your warranty at the same time, of course. Handy to keep in the back of your mind for whenever you're dealing with an amp that's not covered.

 

[nemo_kost]

Sounds to me like a warranty issue...

Thanks for your reply.
Yes, "the slap" is indeed curing the problem...
If it wasn't covered by the warranty, it'd been opened by my tech, he was already aware of the situation. But... using the warranty seems to be better in this situation, let's see how it goes!

 

[nemo_kost]

HI everybody,
on the 17th of september I got the SV back from Thomann. All in all it stayd there 10 days and got back "cured". The hissing is gone, I played it live last saturday and it seems fine (it was a small gig and I couldn't push it as I wanted, but there was no noise).

Just to let you know, a couple of minor issues with Thomann support:
1) During the opening of the RMA we exchanged frequent emails with no problem. After the SV arrived at their repair center I didn't get anything at all for ten days, no updates or similar. I discovered "something" was coming my way from a whatsapp message from DHL, I had to assume it was the SV coming back to me. So, I didn't know what happened, if they found the issue, solved it and than sent the SV back untill I got the delivery.

2) With the head I got a report saying:
"Checked for specified errors. Cable break identified and eliminated. All tube tested, no errors found. The functional test and the VDE test were succesfully carried out."
So, I asked if they could be more specific regarding the break, also because the warranty is going to be over soon, but they replied "they cannot say" what's been repaired...

Anyway, I'm happy everything went OK with Thomann, a little bit of more information from their side would've been better.

Thanks for listening!

 

[ByrdmanFL]

Cable break identified and eliminated.

That sounds like a wire or wire connector/plug that was grounding out or not making proper connection or not crimped properly.

Glad it was not anything major and you are fixed!

 

[PelliX]

1) During the opening of the RMA we exchanged frequent emails with no problem. After the SV arrived at their repair center I didn't get anything at all for ten days, no updates or similar. I discovered "something" was coming my way from a whatsapp message from DHL, I had to assume it was the SV coming back to me. So, I didn't know what happened, if they found the issue, solved it and than sent the SV back untill I got the delivery.

That's a bit poor, indeed. I've had good experience with their CS, though I've never actually returned anything for repair. I guess they might be outsourcing that to an 'authorized service partner' who is not that good at providing updates. It's bad enough that companies now provide "whatsapp" as a means of contact *instead* of a telephone number or at least an email address. Glad to hear it's resolved and fingers crossed it doesn't do it again!

 

[nemo_kost]

Glad it was not anything major and you are fixed!

Yeah, probably my tech would had spotted that too in a few sec, luckily it was "nothing".
But it'd be nice to get more info from them, you know something like "pay attention to this and that" or "this particular cable/connection was broken since it came out from the factory, now it's rock solid".

...they might be outsourcing...

I thought that too and maybe this is the reason why. But I found it strange anyway, cause i guess the outsurcer need to contact Thomann in any case, updating about the problem status...
Anyway, nothing big at all, just a bit annoying.