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Post subject: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 1:34 pm
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Hello,

I have a Fender Champion 600 that I am in the process of modding. This is a nice little amp with a lot of potential. Have already swapped the tubes, speaker and grill cloth. The first circuit mod :oops: was to remove the Negative Feedback Loop by lifting R7 (2.2k). I could stop here because the amp really comes alive now! Great amp for my '60 Les Paul Jr w/P90!

The next baby step is to replace R7 with a 22k but want to be able to bypass R7 altogether or have R7 in the circuit. This seems simple enough but I cannot find how to wire this properly. I've researched but couldn't find any resource that showed how this is done.

Would someone please show me how to do the wiring? You can start off with which end of R7 do you lift for the wiring? The DPDT switch is a simple On-Off with 6 poles for the wiring. I would like the On position to be up with the NFL engage.

Any help would be most appreciatiated!


regards,
Robert


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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 2:09 pm
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sanctuary wrote:
Hello,

The first circuit mod :oops: was to remove the Negative Feedback Loop by lifting R7 (2.2k). I could stop here because the amp really comes alive now! Great amp for my '60 Les Paul Jr w/P90!

The next baby step is to replace R7 with a 22k but want to be able to bypass R7 altogether or have R7 in the circuit. This seems simple enough but I cannot find how to wire this properly. I've researched but couldn't find any resource that showed how this is done.
regards,
Robert


I try to understand , first you remove R 7 by lifting and you like the sound.

Second, you want to install a switch to bypass R7 . For your information , a bypass is shorting R 7 , shorting R 7 is not a good idea. You want also to put a 22 k in place of R 7 and you want also to put R 7 in circuit . This mod with one switch yes ?

What about disconnect R 7 wich make the amp come alive ?


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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 2:25 pm
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sanctuary wrote:
Hello,

I have a Fender Champion 600 that I am in the process of modding. This is a nice little amp with a lot of potential. Have already swapped the tubes, speaker and grill cloth. The first circuit mod :oops: was to remove the Negative Feedback Loop by lifting R7 (2.2k). I could stop here because the amp really comes alive now! Great amp for my '60 Les Paul Jr w/P90!

The next baby step is to replace R7 with a 22k but want to be able to bypass R7 altogether or have R7 in the circuit. This seems simple enough but I cannot find how to wire this properly. I've researched but couldn't find any resource that showed how this is done.

Would someone please show me how to do the wiring? You can start off with which end of R7 do you lift for the wiring? The DPDT switch is a simple On-Off with 6 poles for the wiring. I would like the On position to be up with the NFL engage.

Any help would be most appreciatiated!


regards,
Robert


Lifting R7 and taking it out of the circuit is ok. You have reduced the feedback to zero. Changing R7 to a 22K ohm resistor will require you to modify the cathode circuit (R3, R23, C10) of V2-B to get the proper amount of feedback. Bypassing (shorting out) R7 is not a good idea as that drastically changes the feedback loop. You need some resistance in there. If you really meant to say that you just want to switch R7 in and out of the circuit, then all you need is an SPST switch wired in series with R7.

See my thread for mods that I did to my Champ 600 to convert it to a 5F1 Champ configuration.

viewtopic.php?f=13&t=63259

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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 3:01 pm
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first my obligatory statement:
Ok, I'm an idiot. I simply need a SPST switch and that I can figure out. Actually, I'm understanding the DPST switch now.

stratele52:
The most obvious change with removing R7 or the Negative Feedback Loop was an increase in gain. The amp is more responsive and breaks up rather nicely now. I put the volume on the 600 to 12 and let the guitar control the tone!

bluesky636:
I have read that thread regarding your mods to the 600. That is where I got the idea for the 22k mod R7. So if I understand you correctly, the 22k mod for R7 should be done during the cathode circuit mod? Would the SPST switch for R7 be practical in that config too?

I really like this amp now. It has potential for even better tones and with various pups. This will be a Frankenstein amp of EVH proportions! :wink: So switchable tone options are being considered.


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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 3:11 pm
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stratele52 wrote:


What about disconnect R 7 wich make the amp come alive ?


I just ask why you don't ask how to disconnect R 7 with the switch if you like the sound


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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 3:20 pm
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sanctuary wrote:
stratele52:The most obvious change with removing R7 or the Negative Feedback Loop was an increase in gain. The amp is more responsive and breaks up rather nicely now. I put the volume on the 600 to 12 and let the guitar control the tone!


FWIW, I did not like the sound of the amp with the feedback loop disconnected.

sanctuary wrote:
bluesky636:I have read that thread regarding your mods to the 600. That is where I got the idea for the 22k mod R7. So if I understand you correctly, the 22k mod for R7 should be done during the cathode circuit mod? Would the SPST switch for R7 be practical in that config too?


Yes and yes.

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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 3:43 pm
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stratele52 wrote:
stratele52 wrote:


What about disconnect R 7 wich make the amp come alive ?


I just ask why you don't ask how to disconnect R 7 with the switch if you like the sound


I want tonal options so would like to be able to turn the NFL On or Off.


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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 3:49 pm
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bluesky636 wrote:
sanctuary wrote:
stratele52:The most obvious change with removing R7 or the Negative Feedback Loop was an increase in gain. The amp is more responsive and breaks up rather nicely now. I put the volume on the 600 to 12 and let the guitar control the tone!


FWIW, I did not like the sound of the amp with the feedback loop disconnected.

sanctuary wrote:
bluesky636:I have read that thread regarding your mods to the 600. That is where I got the idea for the 22k mod R7. So if I understand you correctly, the 22k mod for R7 should be done during the cathode circuit mod? Would the SPST switch for R7 be practical in that config too?


Yes and yes.


Maybe it's the old P90 pup in my LP Jr or these ears but like where this amp is going after that R7 mod. Ordering parts shortly to continue the quest.

thank you!


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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 3:52 pm
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Just how old is that P90 pickup, sanctuary?

Arjay

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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 4:27 pm
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I am a proud owner of a '60 Les Paul Jr double-cutaway. My first electric guitar that I have enjoyed for over 35 years, beautiful! I recently sold my amp ('66 SuperReverb) because that beast Ampzilla was just too much and more then I needed or could really enjoy. Into small watt amps now like the 600, Vox AC4TVH (nice!) and the Orange Crush 12L for just plain distortion.

Robert


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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 4:39 pm
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Any pics?

I have a sunburst '57 that I periodically use for slide work -- perfect for that fat "Animal Trainer And The Toad" vibe.

Arjay

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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 4:39 pm
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sanctuary wrote:
thank you!


You're welcome. :D

After you finish modding it, play it through a separate cab with a 12" speaker and stand back. :shock:

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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 4:45 pm
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bluesky636 wrote:
After you finish modding it, play it through a separate cab with a 12" speaker and stand back. :shock:


+1000!

It should sound positively monstrous.

8)

Arjay

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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 5:48 pm
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Retroverbial wrote:
bluesky636 wrote:
After you finish modding it, play it through a separate cab with a 12" speaker and stand back. :shock:


+1000!

It should sound positively monstrous.

8)

Arjay


I have a 12" cab that currently holds a stock BluesJr speaker!


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Post subject: Re: How to wire a DPDT switch to bypass the NFB resistor
Posted: Tue May 22, 2012 6:06 pm
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sanctuary wrote:
Retroverbial wrote:
bluesky636 wrote:
After you finish modding it, play it through a separate cab with a 12" speaker and stand back. :shock:


+1000!

It should sound positively monstrous.

8)

Arjay


I have a 12" cab that currently holds a stock BluesJr speaker!


Give it a try. I run mine through a Raven cab with a 12", 8-ohm Celestion. I'll have to make a recording of it.

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