JVM410HJS no sounds properly

[Kuga]

Hi
My JVM410HJS sounds bad. It sounds so darker every day. It's goes worse when you turn up gain pot at 5 to 10. I tryed with new tubes ( preamp and power valves) no differences. It sounds dark without clarity.
If I use a Guv'nor clone pedal in front looks like It regains its shine and definition.
Any Input are welcome.
I used long time ago a 5751 tubes on V6(V101) and V7(V102) (first two preamp valves). Maybe It has a faulty component.

On the other hand
C144 & C147 on the JVMHJS are not fitted.
Are this caps to get more brighter sounds?
Are C44 & C41 ones from JVM410 same as C144 & C147 from JVM410HJS?

Thanks.

 

[Tatzmann]

Maybe a good idea to check the preamp heater voltages first. They are probably partly rectified, maybe a problem with the rectifier.

"C144 & C147 on the JVMHJS are not fitted.
Are this caps to get more brighter sounds?"

A cap from cathode to plate suppresses highs.

 

[Kuga]

Maybe a good idea to check the preamp heater voltages first. They are probably partly rectified, maybe a problem with the rectifier.

"C144 & C147 on the JVMHJS are not fitted.
Are this caps to get more brighter sounds?"

A cap from cathode to plate suppresses highs.

Thanks you. I will take a look on heater voltages. I will report results here.
Also I will check noise gates althrough I never use them.

 

[Crikey]

Hi
My JVM410HJS sounds bad. It sounds so darker every day. It's goes worse when you turn up gain pot at 5 to 10. I tryed with new tubes ( preamp and power valves) no differences. It sounds dark without clarity.
If I use a Guv'nor clone pedal in front looks like It regains its shine and definition.
Any Input are welcome.
I used long time ago a 5751 tubes on V6(V101) and V7(V102) (first two preamp valves). Maybe It has a faulty component.

On the other hand
C144 & C147 on the JVMHJS are not fitted.
Are this caps to get more brighter sounds?
Are C44 & C41 ones from JVM410 same as C144 & C147 from JVM410HJS?

Thanks.

View attachment 155357
View attachment 155355View attachment 155356

What speaker cabinet are you using?

 

[Kuga]

What speaker cabinet are you using?

Today I was using a regular 1960A cab with G12-75T spks. Rythm parts sounds better with 75T speakers but it still sounds dark with. It get worse If I use a 1960AHW. I tryed It with other guitars as well. I love high output ceramic magnets pickups and I know this pickups are not very good with this amp. Low output pickups are better with a JVM410HJS.

A low voltage on heaters has sense with this issue. Also I checked It with different wall voltage. In the morning at 245Vca sounded better than in the night at 229 Vca when all people are using his A/A. Here we have really hot wheather on summer. 41°C today.

 

[Kuga]

At 231,6 Vca on the wall socket.
Heater voltages with power switch on

Preamp valves
V6 11,87 Vdc
V7 11,69 Vdc
V8 3,09 & 3,09 Vca
V9 3,07 & 3,07 Vca

Phase inverter valve
V5 3,05 & 3,05 Vca

Power valves
V4 3,06 & 3,05 Vca
V3 3,06 & 3,07
V2 3,06 & 3,06
V1 3,05 & 3,07

Heater voltages with amp turned on

Preamp valves
V6 11,13 Vdc
V7 10,89 Vdc
V8 3,01 & 3,01 Vca
V9 3,00 & 2,99 Vca

Phase inverter valve
V5 2,98 & 2,98 Vca

Power valves
V4 3,00 & 3,02 Vca
V3 3,03 & 3,01
V2 3,04 & 3,01
V1 3,00 & 3,02

What do you think about It? Are they correct?

 

[Tatzmann]

Looks like the voltages one would expect, so yes, nothing far out of the ordinary there.

Even though, they are a little low throughout, especially v6 and v7, but i don't think this is the source of the problem.

 

[Kuga]

Update.
Today at 225Vca on the wall socket It sounded properly. It sounded like should be.

The good news. I think it's not a failty component. Should be a poor connection or bad solder. When it sounds bad it's in any mode of the 4 channels.

It will be really difficult find where it's wrong but I hope find It. First a clean guitar tone recorded in a loop pedal then I'll connect It in front of the amp. Let's see If I find what it's happening.

If not, I'm thinking travel to Milton Keynes. I don't trust any tech service from my area. This amp deserve It.

 

[Tatzmann]

Idk, travelling from Croatia? to England over a dizzy JVM seems rather excerbate to me.

I guess they would send you new pcboards, but they will be as pricy as a whole used JVM in Europe.

Not worth it.

 

[Kuga]

Idk, travelling from Croatia? to England over a dizzy JVM seems rather excerbate to me.

I guess they would send you new pcboards, but they will be as pricy as a whole used JVM in Europe.

Not worth it.

I'm from Catalonia (Spain). Near France and near Andorra. Just 15H drive to Milton Keynes.

 

[PelliX]

My JVM410HJS sounds bad. It sounds so darker every day.

Something's drifting then. I agree with Tatz that the heater voltages are a bit low, but not entirely out of range.

V8 3,09 & 3,09 Vca

AC is expressed as VAC not Vca, which would be a voltage controlled amplifier - just sayin'. You got the VDC right (though it would typically be in all caps). Vxx with the latter letters in lower case typically refers to the voltage at a specific point in a circuit or for a specific purpose.

The good news. I think it's not a failty component. Should be a poor connection or bad solder. When it sounds bad it's in any mode of the 4 channels.

So you're saying just 6VAC less from the wall is causing the amp to sound correct again? That's dropping the heater voltages even further...

How old is this amp and have you done a basic visual inspection? I'm vaguely guesstimating an issue in the power supply/smoothing somewhere.

 

[Kuga]

The amp it's from 2017. Today morning at 235Vac. It sounded good wile I check all connectors, solder joins. Putting pressure on the boards. Putting pressure on preamp valves. All this with a litle wood stick. I doing It with a lot of care. It doesn't fails. Two days ago It sounded really bad. It's a really mistery thing.

 

[PelliX]

Check your capacitors.

 

[Kuga]

I tested some caps as PelliX sugest. I guess the problem it's on V101, V102. I check C145, C153, C154, C146, C132, C131. C146 (680nF) seems out of Range with 710nF because this I chech C149 too (680nF) but It tested same value. Yes I took out V103 socket to do It. Even I tryed them (C146 & C149) with a paper oil caps. No differences.
I reinstalled stock caps. Yes I took out V103 socket again to do It.
The amp works great, no static noises. I use proper tools to do this job. It sounds with extra bass sound again but If you use a tubescreamer or a Guv'nor pedal in front It sounds great.
I will check C155 & C180.

 

[PelliX]

I check C145, C153, C154, C146, C132, C131. C146 (680nF) seems out of Range with 710nF because this I chech C149 too (680nF) but It tested same value. Yes I took out V103 socket to do It.

That's a little off, but unlikely to have any *significant* tonal impact. Depending on what you're measuring with, a little deviance in very low capacitance caps can be attributed to the meter/leads. I would say that part is fine. Do you have an insulation tester or other method to check for breakdown at high(er) voltages? Caps can misbehave at higher voltage and leak, while showing perfectly acceptable values at low voltage tests. An insulation tester like a Megger or similar is a great tool for determining this and can be got fairly cheap if you so desire. I snagged a UNI-T 511 with hardcase and probes for a few tenners, still had the clingfilm on the display.

Even I tryed them (C146 & C149) with a paper oil caps. No differences.

Wax/paper caps are not the best, I'd avoid using them for these purposes, but for a quick A/B test, sure.

Do you have a scope, so that you can maybe quantify the issue at all, presuming you can get it into the 'fault condition' again? Maybe a can of freeze spray to help narrow down a dodgy part?

 

[Kuga]

I don't own a osciloscope and a megger too.

Update
Today It sounded fantastic again. When It sounds good It sounds good all the time. When It sounds bad It sounds bad all the time. You can shake It and look it inside and use a small wooden stick to check If It has a bad or poor connection. No differences. When It sounds good or when It sounds bad.
After a 100Km travel It sounded great. 15 days ago I did same thing. I did 100Km travel and I used It in the same place. It sounded really bad. When It sounds good If you use a tubescreamer in front (No drive, gain/drive at 0) you can hear a small differences on the sound. When It sounds bad If you use a tubescreamer in front (No drive, gain/drive at 0) you can hear a Big differences on the sound.

Here a video I did two days ago when It sounded bad but using a tubescreamer to get a properly sound from It.