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Hoffman Amps Forum image Author Topic: Input Stage Comparison  (Read 1857 times)

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Offline mwelch55

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Input Stage Comparison
« on: June 27, 2019, 10:00:39 am »
I noticed that the input stage for Epiphone Valve Junior is done slightly different than the input stage of a Fender Champ.  I was wondering about the 1M resistor.  On the Epiphone, the resistor is attached from the grid to ground, and the fender has the resistor attached before the 68K grid stopper resistor.

What is the advantage of one vs the other?  Why would you want to place the 1M resistor directly from the grid to ground instead of the way Fender does it?  How will it affect tone?

Offline sluckey

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Re: Input Stage Comparison
« Reply #1 on: June 27, 2019, 10:23:58 am »
I think it's just a matter of choice. Either will work just fine. The Epiphone will have slightly less signal applied to the grid. I would not expect any difference in tone.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline mwelch55

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Re: Input Stage Comparison
« Reply #2 on: June 27, 2019, 10:32:59 am »
Thanks for the reply.  I have seen other amps that have that resistor from grid to ground.  I wasn't sure if one had an advantage over the other.

Offline PRR

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Re: Input Stage Comparison
« Reply #3 on: June 27, 2019, 06:34:59 pm »
68k (should be 34k) in front cuts signal a half dB, not enough to care.

 


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