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Post subject: Frontman 25R unusual ground problem
Posted: Tue Sep 12, 2017 3:24 am
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Hi Everyone. I believe this is the 3rd time I've ever posted to a forum on the internet so please bear with me. I have a Frontman 25r that I don't really use much. I bought it on the cheap and noodled with the insides for fun (I will put the details of that below). But the actual issue is this: With the guitar plugged it, I get a hideous ground hum and some distortion at certain frequencies which go away when I touch one of the top screws which mount the amp chassis to the cabinet. With no guitar or just the cable plugged in, its quite silent. Also, when the amp chassis is out of the cabinet, the problem is gone and everything works as expected. My only thought is the shielding tape inside might be to blame, but I'm unclear on what to do about that. Any help would be appreciated.

What I did to it:
1. I tried to replace the tl074s with opa2134s but ended up switching them back, but installed some IC sockets in case I wanted to switch them back again.
2. I switched two of the pots inside (I believe the reverb and the clean volume) to be able to make "1" useful on the volume knob
3. Swapped out the speaker for a Warehouse G10C

Thanks again!


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Post subject: Re: Frontman 25R unusual ground problem
Posted: Thu Sep 14, 2017 10:11 pm
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Silent with no guitar ; check guitar, it is not the amp.


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Post subject: Re: Frontman 25R unusual ground problem
Posted: Fri Sep 15, 2017 5:09 pm
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I was annoyed I hadn't thought of that so I tried a second guitar. No problem. Plugged in the first guitar and again no problem. Maybe it's a bad solder joint somewhere on the amp? The problem seems to come and go


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Post subject: Re: Frontman 25R unusual ground problem
Posted: Fri Sep 15, 2017 10:32 pm
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Bad guitar cable


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Post subject: Re: Frontman 25R unusual ground problem
Posted: Sat Sep 16, 2017 1:16 am
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No. Its not the cable unfortunately. Thanks though


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Post subject: Re: Frontman 25R unusual ground problem
Posted: Sat Sep 16, 2017 6:28 am
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Power ON the amp alone, no guitar no cable nothing plug at the input.
Wait longtime to hear if amp do noise.
If the issue is the amp, you will hear the hum
Report


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Post subject: Re: Frontman 25R unusual ground problem
Posted: Mon Sep 18, 2017 1:07 pm
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stratele52 wrote:
Power ON the amp alone, no guitar no cable nothing plug at the input.
Wait longtime to hear if amp do noise.
If the issue is the amp, you will hear the hum
Report


+1

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Post subject: Re: Frontman 25R unusual ground problem
Posted: Mon Sep 18, 2017 1:46 pm
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Hi guys. I appreciate the responses. But allow me to be clear. Across 3 guitars, the problem is consistent, regardless of which cable I use. However the problem randomly goes away. The amp is the source of the problem. Does anyone have any thoughts on what part of the amp might cause what i described?


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Post subject: Re: Frontman 25R unusual ground problem
Posted: Mon Sep 18, 2017 4:05 pm
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Intermittent problems can usually be traced to broken solder connections. I'm gonna bet on the input jack soldering. Otherwise it would hum with the cable plugged in.
These may not be visible cracks, but a complete resoldering of the circuit board usually takes care of it and problems that are about to happen.


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Post subject: Re: Frontman 25R unusual ground problem
Posted: Mon Sep 18, 2017 4:12 pm
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Good stuff. Thank you. Ill start with the input and pots and see where that gets me. Much appreciated


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