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Hoffman Amps Forum image Author Topic: Help with JCM800 BASS STD 1992  (Read 3399 times)

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Offline Travis8

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Help with JCM800 BASS STD 1992
« on: April 27, 2021, 09:45:46 am »
Hi everyone!!!

It makes this sound without any pedal or guitar connected.

Some recommendation?

https://drive.google.com/file/d/1147T6ck39eDy0_sVYTSBnaZ0Q55VFPg5/view?usp=sharing
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Offline sluckey

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Re: Help with JCM800 BASS STD 1992
« Reply #1 on: April 27, 2021, 09:49:30 am »
Is that the only sound it makes? No music at all?
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Offline Travis8

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Re: Help with JCM800 BASS STD 1992
« Reply #2 on: April 27, 2021, 09:51:27 am »
I can play with it, but sometimes Itīs makes that noise in background
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Offline Travis8

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Re: Help with JCM800 BASS STD 1992
« Reply #3 on: April 27, 2021, 09:52:35 am »
I try to touch with a pencil all valves but didnīt changue the problem, Iīm sure valves are not the problem (I think)


The noise come and goes randomly
« Last Edit: April 27, 2021, 09:54:58 am by RCZ »
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Offline Travis8

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Re: Help with JCM800 BASS STD 1992
« Reply #4 on: April 27, 2021, 10:04:23 am »
The noise also sound with de D.I output of the amp
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Offline Travis8

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Re: Help with JCM800 BASS STD 1992
« Reply #5 on: April 27, 2021, 10:26:33 am »
With a pencil I detect maybe the problem is V2 of preamp, I swap witht the other preamps tubes but the problem is always V2
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Offline Travis8

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Re: Help with JCM800 BASS STD 1992
« Reply #6 on: May 04, 2021, 10:45:07 am »
I swap preamp tubes and the problem still there.


Some help please?
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Offline SILVERGUN

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Re: Help with JCM800 BASS STD 1992
« Reply #7 on: May 04, 2021, 01:07:16 pm »
could be RF interference from you phone


the way it starts and stops kinda reminds me of when I have my phone in my pocket and it bleeds through my guitar

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Offline sluckey

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Re: Help with JCM800 BASS STD 1992
« Reply #8 on: May 04, 2021, 02:05:48 pm »
Pull V1 and V2. Does the noise go away?
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A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline Travis8

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Re: Help with JCM800 BASS STD 1992
« Reply #9 on: May 05, 2021, 03:59:27 am »
Quote from: sluckey on May 04, 2021, 02:05:48 pm
Pull V1 and V2. Does the noise go away?

The noise dissapear
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Offline Travis8

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Re: Help with JCM800 BASS STD 1992
« Reply #10 on: May 05, 2021, 04:00:44 am »
Quote from: sluckey on May 04, 2021, 02:05:48 pm
Pull V1 and V2. Does the noise go away?

The noise only dissapear without V1 and V2 and without power tubes
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Offline Travis8

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Re: Help with JCM800 BASS STD 1992
« Reply #11 on: May 05, 2021, 04:02:13 am »
Quote from: RCZ on May 05, 2021, 04:00:44 am
Quote from: sluckey on May 04, 2021, 02:05:48 pm
Pull V1 and V2. Does the noise go away?

The noise only dissapear without V1 and V2 and without power tubes

The noise dissapear if I remove only V1
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Offline pdf64

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Re: Help with JCM800 BASS STD 1992
« Reply #12 on: May 05, 2021, 05:06:00 am »
The noise suggests to me a bad valve / bad anode load resistor / bad connection between valve pin and socket contact / failing solder joint (probably in anode circuit) / coupling cap from anode leaking DC.
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Offline Travis8

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Re: Help with JCM800 BASS STD 1992
« Reply #13 on: May 05, 2021, 05:07:17 am »
Quote from: pdf64 on May 05, 2021, 05:06:00 am
The noise suggests to me a bad anode load resistor / bad connection between valve pin and socket contact / failing solder joint in anode circuit / coupling cap from anode leaking DC.

Could be a good idea resolder this?
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Offline pdf64

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Re: Help with JCM800 BASS STD 1992
« Reply #14 on: May 05, 2021, 01:43:37 pm »
Quote from: RCZ on May 05, 2021, 05:07:17 am
Quote from: pdf64 on May 05, 2021, 05:06:00 am
The noise suggests to me a bad anode load resistor / bad connection between valve pin and socket contact / failing solder joint in anode circuit / coupling cap from anode leaking DC.

Could be a good idea resolder this?
Got to start somewhere  :icon_biggrin:
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Offline Travis8

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Re: Help with JCM800 BASS STD 1992
« Reply #15 on: May 06, 2021, 04:20:46 am »
this is the amp
« Last Edit: May 06, 2021, 04:34:26 am by sluckey »
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Offline Travis8

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Re: Help with JCM800 BASS STD 1992
« Reply #16 on: May 06, 2021, 04:38:42 am »
The noise also come out from D.I out
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