JMP1 crackling noise and loud pops

[SideWindeR [00]]

Hi everybody,
I have found your forum searching for a solution about a problem I'm experiencing with a JMP1.

Since a couple of days ago my JMP1 started to make crackling noises when playing on the low strings. I can emphasize the problem by turning on the bass shift or adding some basses to the eq.

Moreover, whenever I turn the preamp on or off, I can hear a loud pop coming from the speaker. It started to do this about a month ago.

Do you have any idea of what the problem could be?

I have changed the valves on the preamp about 4 months ago. Now it has 2 12AX7B. I have tried swapping back the original ECC83 valves but the problem persists.

Any idea or suggestion is more than welcome!

Thanks!
Guido

 

[impetus maximus]

WELCOME TO THE FORUMS!

i'm no Tech but crackling and pops sound like Power Tubes are going.
take it to a tech to get it checked out. i wouldn't use it till you do just to be safe.

 

[phiit]

WELCOME TO THE FORUMS!

i'm no Tech but crackling and pops sound like Power Tubes are going.
take it to a tech to get it checked out. i wouldn't use it till you do just to be safe.

JMP-1 is a preamp with 2 ECC83 tubes.. I had JMP-1 years ago, very nice preamp, sometimes I wish I hadn't sold it

 

[Hollowbody]

I remember when those came out and I almost bought one. Wish I had.

 

[impetus maximus]

JMP-1 is a preamp with 2 ECC83 tubes.. I had JMP-1 years ago, very nice preamp, sometimes I wish I hadn't sold it

ahh, i see. what is he plugging it into? dirty tube sockets? capacitors going?

 

[Georgiatec]

Tap the tubes with a pencil while the amp is on....if you get the pops and crackles it's more than likely the tube socket (since you said the tubes are only a couple of months old, it's unlikely to be the tubes themselves). You can try spraying contact cleaner onto the tube pins and then working them in and out of the sockets a few times to clear any crap. If this doesn't work it's install a new socket time. If tapping the tube doesn't cause the noise then sorry, I can't help you. I'm sure one of the tech guys will chime in if the problem persists.

 

[gjohnson]

I'd take it in. Could be a leaking battery. That can cause all kinds of problems. You shouldnt get a pop if you turn your power amp off first.

 

[Kunnz]

I'm figuring a cap job on your PSU and valve driver section.

Also, that pre amp produces its distortion from diode clipping and not the valves themselves which is a bit of a let down IMO, so it would be best anyway to re-cap as it probably needs it anyhow then take it from there.

 

[Hollowbody]

The OP is getting some very diverse responses.

And with all the discussion on the forum about diode clipping someone might get on here and argue with Kunnz statement.

 

[SideWindeR [00]]

Hi guys,
first of all thanks for your suggestions.

I'm shure it's not the battery. Didn't see any leak when I opened the unit, and I've never had a problem with the patch memory so far.

I'll first try with the tube sockets.
I'll keep you posted

Ciao

 

[MKB]

I'm figuring a cap job on your PSU and valve driver section.

Also, that pre amp produces its distortion from diode clipping and not the valves themselves which is a bit of a let down IMO, so it would be best anyway to re-cap as it probably needs it anyhow then take it from there.

This is a true statement, but do NOT remove the clipping diodes!! The gain channel depends on these diodes to limit the signal level to IC's further down the signal path; you could damage those IC's if the diodes are removed.

To the OP's question; it would be best to have a tech look over the preamp for cold solder joints, especially with the jacks and the tube PCB. Also, check all of your cables for intermittent connections.

 

[SideWindeR [00]]

Hi guys,
the filter caps were the culprit.

After changing the psu electrolytic caps everything went back to normal.
Tone and bass response have improved too.

 

[Kunnz]

Sweet!