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Hoffman Amps Forum image Author Topic: Single Input JCM 800 2204 clone  (Read 3706 times)

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Offline MikePR

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Single Input JCM 800 2204 clone
« on: June 05, 2020, 04:09:55 pm »
Just finished a Mojotone 2204 clone without the Low input jack but it seems I wired something wrong on the cliff jack. Here are some pics. Any idea was wrong? It sounds but with no Gain.

Thx


Offline sluckey

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Re: Single Input JCM 800 2204 clone
« Reply #1 on: June 05, 2020, 04:54:17 pm »
Make the corrections shown in red...
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline MikePR

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Re: Single Input JCM 800 2204 clone
« Reply #2 on: June 05, 2020, 07:08:25 pm »
Thx!! That worked. Another question. I want to remove the Presence knob. Could I connect the 4.7k to ground and remove the 22k pot plus the cap? Any recomendation?

Thx
« Last Edit: June 05, 2020, 07:16:29 pm by MikePR »

Offline sluckey

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Re: Single Input JCM 800 2204 clone
« Reply #3 on: June 05, 2020, 07:32:34 pm »
Thx!! That worked. Another question. I want to remove the Presence knob. Could I connect the 4.7k to ground and remove the 22k pot plus the cap? Any recomendation?
That'll work. You must keep the 4.7K.

Here's another way to do the same thing. Might be a bit neater...
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline MikePR

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Re: Single Input JCM 800 2204 clone
« Reply #4 on: June 06, 2020, 04:00:31 pm »
Well that one did not worked. There is loud squeal coming from the amp. If i put a 25k pot with the .1 uf cap and 4.7k resistor the squeal only goes away when the pot is full.  :dontknow:

Offline sluckey

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Re: Single Input JCM 800 2204 clone
« Reply #5 on: June 06, 2020, 05:13:47 pm »
Well that one did not worked. There is loud squeal coming from the amp. If i put a 25k pot with the .1 uf cap and 4.7k resistor the squeal only goes away when the pot is full.  :dontknow:
Yes it did, but it reveals that you have the NFB phase wrong. Swap the OT plate leads to correct.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline MikePR

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Re: Single Input JCM 800 2204 clone
« Reply #6 on: June 06, 2020, 06:30:05 pm »
Thx again! Did worked but had to change the OT pin 3 wires to each other and now is silent.

Offline sluckey

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Re: Single Input JCM 800 2204 clone
« Reply #7 on: June 06, 2020, 07:02:45 pm »
Quote
now is silent
Is that good or bad?
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline MikePR

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Re: Single Input JCM 800 2204 clone
« Reply #8 on: June 07, 2020, 03:03:08 am »
Great!!!! 800 Growl. Thx again.

Offline MikePR

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Re: Single Input JCM 800 2204 clone
« Reply #9 on: June 11, 2020, 08:24:06 am »
The pilot light flickers every time i turn the amp out of stand by. Meaning on. Is there anything wrong? Do i need to add a cap between pilot light and switch so it does not do it?

 


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