Marshall JVM 215C Combo Fault ?

GrahamG

My JVM (Combo)is making a strange "sound" hard to explain,but i'll give it a go.:/ 
It's making a sort of "doubling or oscillating" souns/effect when I hit a note,most obvious when I hit a single note on the E 1st string.
If I plug the Amp head into a different cab it doesn't do it,which would suggest the speaker,but I've changes the standard speaker for an upgraded Celestion & it does the same thing,so i'm thinking it's a result of using it as a Combo.
Can anyone help ,(ICBM ?=) )

ICBM

Microphonic power valve.

If you want to know which one it is, try tapping on them with the amp running and nothing plugged in. Hold the other one with a cloth, they're usually sensitive enough that the vibration will travel via the chassis even if you're testing the other one.

Actually, having read that again it could be a preamp valve - if it's the top E rather than the bottom. Is it affected by any of the control settings? I know that might be hard to tell, if turning down stops it.

GrahamG

ICBM said:

Microphonic power valve.

If you want to know which one it is, try tapping on them with the amp running and nothing plugged in. Hold the other one with a cloth, they're usually sensitive enough that the vibration will travel via the chassis even if you're testing the other one.

Actually, having read that again it could be a preamp valve - if it's the top E rather than the bottom. Is it affected by any of the control settings? I know that might be hard to tell, if turning down stops it.

Thanks,ICBM.Just to make sure I understand correctly,if a valve is microphonic what would I expect to hear when I tap it ?,& if it is a valve,do I just replace it.

Sorry if this is a bit basic(but sadly I am) 

ICBM

GrahamG said:

Just to make sure I understand correctly,if a valve is microphonic what would I expect to hear when I tap it ?,& if it is a valve,do I just replace it.

Rattling or 'ringing' through the speaker - not from the valve itself. Yes, replace it.

If it's a power valve it's usually best to replace them as a pair, which is why it's worth identifying which one it is so you can keep the other as a spare... sorry, I should have said that . Preamp valves can be replaced individually.

Unfortunately there's no easy answer to 'how much is too much', other than replacing any suspect valve and seeing if the problem stops.

GrahamG

Thanks for the help,appreciated (a lot) 

GrahamG

ICBM said:

GrahamG said:

Just to make sure I understand correctly,if a valve is microphonic what would I expect to hear when I tap it ?,& if it is a valve,do I just replace it.

Rattling or 'ringing' through the speaker - not from the valve itself. Yes, replace it.

If it's a power valve it's usually best to replace them as a pair, which is why it's worth identifying which one it is so you can keep the other as a spare... sorry, I should have said that . Preamp valves can be replaced individually.

Unfortunately there's no easy answer to 'how much is too much', other than replacing any suspect valve and seeing if the problem stops.

Hi,ICBM,i have finally had the opportunity to check the valves & I think the small valve with the metal capping(ECC83)next to the transformer is making a much louder noise(thru the speaker)than the rest of the ECC83's,although a couple of them are making a slightly louder "ring" than the other 2,i have no way of knowing if any of this indicates a suspect valve/valves or is normal for the valve position,so once again i'm asking for your opinion .

Also the only valves I have as a substitute or replacement are the ECC83S valves which are in my Orange amps,would these be ok as a short term(tonight)substitute,if the existing valve/valves are suspect.?

Thanks,Graham.

ICBM

It's normal for that position - V1 - the reason for the cover is because it's also most prone to picking up electrical noise. It's at the start of the signal chain so any noise it produces is then amplified by everything else! The amount of noise should typically decrease as you go down the signal path towards the power valves.

Yes, the ECC83S is ideal for testing, and you should know they're OK if you purposely use the V1 valve from one of the Oranges, since you already know it's not overly noisy.

If you find any valve from the Marshall is too noisy, you could swap it for one of the other positions closer to the power amp which might not be as sensitive, without having to buy a new valve yet. I very often do this!

GrahamG

ICBM said:

It's normal for that position - V1 - the reason for the cover is because it's also most prone to picking up electrical noise. It's at the start of the signal chain so any noise it produces is then amplified by everything else! The amount of noise should typically decrease as you go down the signal path towards the power valves.

Yes, the ECC83S is ideal for testing, and you should know they're OK if you purposely use the V1 valve from one of the Oranges, since you already know it's not overly noisy.

If you find any valve from the Marshall is too noisy, you could swap it for one of the other positions closer to the power amp which might not be as sensitive, without having to buy a new valve yet. I very often do this!

Thanks,AGAIN).I should have said the noisiest was valve next to the Smaller transformer near the output sockets.

I hate doing stuff with amps in the House,because I normally only use an Amp at stage volumes(loud),but because everybody's out I whacked up the volume to test before & after with the different valves & I've realised that the "noise" only develops after the Amps been on for about 15 mins,it really is a strange noise almost like the notes on tremolo.

ICBM

GrahamG said:

I should have said the noisiest was valve next to the Smaller transformer near the output sockets.

I hate doing stuff with amps in the House,because I normally only use an Amp at stage volumes(loud),but because everybody's out I whacked up the volume to test before & after with the different valves & I've realised that the "noise" only develops after the Amps been on for about 15 mins,it really is a strange noise almost like the notes on tremolo.

It could still be a valve, as they get hot then they can develop issues they don't have when cooler.

Basically with any valve amp, unless you have a strong indication or experience otherwise, it's always worth eliminating the valves as the cause first - in most cases you can do that without getting into the chassis. It can be time-consuming to change one at a time if the problem takes a while to show itself - although you can shorten the process somewhat by only putting the amp on standby rather than fully off, if you're careful - don't burn yourself on the hot valves!

(There are a very few amps where this isn't entirely safe, but all Marshalls I can think of other than those with valve rectifiers fully turn off the high voltage when on standby, so are safe to do this with.)

I can't remember which valve the one closest to the output sockets is - probably phase inverter, or maybe after the FX loop - but that sounds like a possible candidate since it should be at a relatively late stage in the circuit. Try changing that one first.

GrahamG

ICBM said:

GrahamG said:

I should have said the noisiest was valve next to the Smaller transformer near the output sockets.

I hate doing stuff with amps in the House,because I normally only use an Amp at stage volumes(loud),but because everybody's out I whacked up the volume to test before & after with the different valves & I've realised that the "noise" only develops after the Amps been on for about 15 mins,it really is a strange noise almost like the notes on tremolo.

I can't remember which valve the one closest to the output sockets is - probably phase inverter, or maybe after the FX loop - but that sounds like a possible candidate since it should be at a relatively late stage in the circuit. Try changing that one first.

I'm not sure where to start with this answer,but I hope i'm not imagining things.
I swapped out the 3 of the ECC83(with ECC83S) valves,starting with what you described as V1 & the following seems to have happened.
On switch on the noise level of the Amp is greatly reduced(in standby),the Amp has always had what I thought was a "noisy" transformer,so even when it was in standby it emitted a sort of hard buzzing sound,like a mechanically noisy transformer, clearly audible on stage & really loud in the house,this has virtually stopped.  
Out of standby the Amps has always sounded "noisy" & just generally buzzy,with a lot of background hum & buzz,this too has almost stopped.
1st impressions(in the house) are that the EQ is different, a lot less treble & the gain seems less edgy sort of more rounded ?,it feels like I want to turn everything up instead of down,always a good thing .
The "tremolo" noise is just about gone,maybe just a very slight hint when the pickup is full on,but this is in the house,with no stage racket(Drums).
An obvious question I suppose is,are the ECC83S valves lower gain,to account for all this,i suspect not,but they could be I suppose,oh & I wonder has someone else been chasing this noise,the 83 in V1 looked like a different age to the other 83's with red block writing instead of the white scroll writing of the other 2(all still Marshall valves.)
Edit:just read the writing,the 2 valves with white writing WK 23/09 & the Red says 12/16,i'm taking this to be dates,so year 09'&16' years?but the amp was bought new in August 17',maybe the plot thickens,or maybe I should go & have a lie down.
the other thing that bothers me is why have I not heard this tremolo effect when using my EV speaker ?
Anyway ICBM,many thanks for all your help & knowledge,we'll see what it's like at the gig tonight.

ICBM

GrahamG said:

I swapped out the 3 of the ECC83(with ECC83S) valves,starting with what you described as V1 & the following seems to have happened.

All at the same time? Generally you shouldn't do that since you don't know which one was the problem.

GrahamG said:

On switch on the noise level of the Amp is greatly reduced(in standby),the Amp has always had what I thought was a "noisy" transformer,so even when it was in standby it emitted a sort of hard buzzing sound,like a mechanically noisy transformer, clearly audible on stage & really loud in the house,this has virtually stopped.

That can't be anything to do with the valves, but it could be that when you changed them you disturbed the circuit board enough to move it and reduce a physical vibration between the transformer and the rest of the amp.

GrahamG said:

On switch on the noise level of the Amp is greatly reduced(in standby),the Amp has always had what I thought was a "noisy" transformer,so even when it was in standby it emitted a sort of hard buzzing sound,like a mechanically noisy transformer, clearly audible on stage & really loud in the house,this has virtually stopped.  
Out of standby the Amps has always sounded "noisy" & just generally buzzy,with a lot of background hum & buzz,this too has almost stopped.
1st impressions(in the house) are that the EQ is different, a lot less treble & the gain seems less edgy sort of more rounded ?,it feels like I want to turn everything up instead of down,always a good thing .
The "tremolo" noise is just about gone,maybe just a very slight hint when the pickup is full on,but this is in the house,with no stage racket(Drums).
An obvious question I suppose is,are the ECC83S valves lower gain,to account for all this,i suspect not,but they could be I suppose,oh & I wonder has someone else been chasing this noise,the 83 in V1 looked like a different age to the other 83's with red block writing instead of the white scroll writing of the other 2(all still Marshall valves.)

This all sounds like valves. The ECC83S are most likely JJs, which are well known as a darker-sounding valve. Marshall have used different types of valves in the amps, a red ink one I think is specially selected for low noise so they put those in V1. Do the other valves have a double chrome strip inside on each side of the valve? Those are Chinese and are brighter-sounding.

GrahamG said:

the other thing that bothers me is why have I not heard this tremolo effect when using my EV speaker ?

In a different cab, or in the combo? If in a different cab, because it isn't vibrating the valve that was causing the trouble. If in the combo, just because it sounds different so may not have had as much of the particular troublesome frequency.

GrahamG

ICBM said:

GrahamG said:

I swapped out the 3 of the ECC83(with ECC83S) valves,starting with what you described as V1 & the following seems to have happened.

All at the same time? Generally you shouldn't do that since you don't know which one was the problem.

GrahamG said:

On switch on the noise level of the Amp is greatly reduced(in standby),the Amp has always had what I thought was a "noisy" transformer,so even when it was in standby it emitted a sort of hard buzzing sound,like a mechanically noisy transformer, clearly audible on stage & really loud in the house,this has virtually stopped.

That can't be anything to do with the valves, but it could be that when you changed them you disturbed the circuit board enough to move it and reduce a physical vibration between the transformer and the rest of the amp.

GrahamG said:

On switch on the noise level of the Amp is greatly reduced(in standby),the Amp has always had what I thought was a "noisy" transformer,so even when it was in standby it emitted a sort of hard buzzing sound,like a mechanically noisy transformer, clearly audible on stage & really loud in the house,this has virtually stopped.  
Out of standby the Amps has always sounded "noisy" & just generally buzzy,with a lot of background hum & buzz,this too has almost stopped.
1st impressions(in the house) are that the EQ is different, a lot less treble & the gain seems less edgy sort of more rounded ?,it feels like I want to turn everything up instead of down,always a good thing .
The "tremolo" noise is just about gone,maybe just a very slight hint when the pickup is full on,but this is in the house,with no stage racket(Drums).
An obvious question I suppose is,are the ECC83S valves lower gain,to account for all this,i suspect not,but they could be I suppose,oh & I wonder has someone else been chasing this noise,the 83 in V1 looked like a different age to the other 83's with red block writing instead of the white scroll writing of the other 2(all still Marshall valves.)

This all sounds like valves. The ECC83S are most likely JJs, which are well known as a darker-sounding valve. Marshall have used different types of valves in the amps, a red ink one I think is specially selected for low noise so they put those in V1. Do the other valves have a double chrome strip inside on each side of the valve? Those are Chinese and are brighter-sounding.

GrahamG said:

the other thing that bothers me is why have I not heard this tremolo effect when using my EV speaker ?

In a different cab, or in the combo? If in a different cab, because it isn't vibrating the valve that was causing the trouble. If in the combo, just because it sounds different so may not have had as much of the particular troublesome frequency.

Yes I did change all 3 at the same time & as you suggested the ECC83S,did make the amp sound different,maybe it lost a bit of it's "sparkle" or "dulled a bit"

The "noise level of the Amp has definitely dropped"

Yes the EV is loaded in a separate Mesa cab.

At the gig on Saturday after about 30mins,the Amp started making the weird sound again & only stopped when I plugged into the Mesa cab,i'm going to have to find a good tech & try to get it sorted out,i'll also take my Rocker 30(which is also faulty).
ICBM I really appreciate your help with this, now the trick is finding a tech who can sort both Amps out,then i'm really thinking about selling them & going back to some sort of S/S or digital solution.