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Hoffman Amps Forum image Author Topic: Yet another JCM 800 Mod: Good or bad design?  (Read 3192 times)

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Offline tmknight

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Yet another JCM 800 Mod: Good or bad design?
« on: November 14, 2021, 12:05:45 pm »
OK, this is more of a question of "how" to implement rather than "should I".  I've already arrived at what I'm changing and what values will be applied.  My plan is where I'm looking for some constructive feedback.  My approach is to put it on a perf-board so I could completely switch-off the circuit(s) as desired. 

Update:
Implemented and safely working as designed.  You may wish to consider an electrolytic for the C2 (layout) bypass cap.
« Last Edit: November 27, 2021, 03:01:41 pm by tmknight »

Offline sluckey

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Re: Yet another JCM 800 Mod: Good or bad design?
« Reply #1 on: November 14, 2021, 12:17:07 pm »
A schematic would be much easier to understand.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline shooter

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Re: Yet another JCM 800 Mod: Good or bad design?
« Reply #2 on: November 14, 2021, 12:47:10 pm »
Quote
but rather is it safe?
with a schematic it'll be easy to see if you're switching HighVolts DC and signal or just signal
Went Class C for efficiency

Offline tmknight

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Re: Yet another JCM 800 Mod: Good or bad design?
« Reply #3 on: November 14, 2021, 02:22:49 pm »
Thanks, gents.  From the "standard" 2204 schematic, splitting the "straight line" V2b cathode to tone stack and inserting the clipping circuit.  So, my thinking is that it is "pure" signal, albeit with quite a bit of DC.  This is a well-known/proven mod in and of itself, just haven't seen it switched in this same way...most leave in the res/cap and "eat" the signal loss.

Thanks, you've given me the pointer that helped me think through it...

Cheers!

Offline thetragichero

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Re: Yet another JCM 800 Mod: Good or bad design?
« Reply #4 on: November 14, 2021, 04:07:18 pm »
a picture is worth a thousand words, even when it comes to a relatively common design. it's not so much pedantry but accuracy: we wanna make sure your thing works when you're done!

Offline tmknight

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Re: Yet another JCM 800 Mod: Good or bad design?
« Reply #5 on: November 25, 2021, 10:36:38 am »
 :thumbs:
« Last Edit: November 26, 2021, 02:44:54 pm by tmknight »

Offline sluckey

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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 66Strat

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Re: Yet another JCM 800 Mod: Good or bad design?
« Reply #7 on: November 27, 2021, 09:55:32 am »
Are there posts missing from this thread? I seem to recall at least one post with the layout for this mod that appears to be missing.
Regards,
JT

Offline sluckey

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Re: Yet another JCM 800 Mod: Good or bad design?
« Reply #8 on: November 27, 2021, 10:47:25 am »
The layout was in the original post but he removed it yesterday.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline 66Strat

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Re: Yet another JCM 800 Mod: Good or bad design?
« Reply #9 on: November 27, 2021, 11:01:56 am »
So much for information sharing.
Regards,
JT

Offline tmknight

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Re: Yet another JCM 800 Mod: Good or bad design?
« Reply #10 on: November 27, 2021, 02:51:07 pm »
Updated

 


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