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Post subject: Problem with my Fender Supersonic 100w twin -Mid & bass knob
Posted: Wed Feb 12, 2014 8:10 pm
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Problem here,

I purchased a Fender Supersonic Twin 100W almost 2 years ago and have been rocking day and night without any problem until today. While playing through the Vintage channel (Left set of knobs), I heard a subtle 'click' from the speakers that resulted in a marked change in the level of sound from my amp. (Note* No electrical modifications, pedals, switchboards are ever used with my amp.) After this, I noticed that both the Bass dial and the Mid dial no longer worked, while it appeared my treb dial turned into the Volume knob. I tried turning the dang thing off in hopes that it would reset the electrical system, or whatever, once i turn it back on. Turns out the problem is still there and it appears as if it is here to stay. What on earth happened to this amp? Could it be a Fuse, Resister, or a Capacitor problem? Would this be covered under fenders '5 year warranty'? Has anyone else experienced this problem?

Help,

A very sad fellow


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Post subject: Re: Problem with my Fender Supersonic 100w twin -Mid & bass
Posted: Wed Feb 12, 2014 9:50 pm
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Your warranty should cover any conceivable electrical problem aside from a defective tube (those are covered for 90 days only).

Arjay

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Post subject: Re: Problem with my Fender Supersonic 100w twin -Mid & bass
Posted: Wed Feb 12, 2014 9:58 pm
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The click you heard could have been one of the several relays in the amp switching modes. It could be caused by the relay power supply or a relay failing itself. Which one is impossible to tell without examining the amp. Looking at the schematic, I see no failure mode that would cause the vintage channel tone controls to act as you are describing. The burn channel controls might, but you said you were using the vintage channel. The only way to know if this would be covered under the warranty (my guess it that it will be) is be to take it to a Fender authorized amp tech. Good luck.

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Post subject: Re: Problem with my Fender Supersonic 100w twin -Mid & bass
Posted: Wed Feb 12, 2014 10:34 pm
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I would believe it to be a component failure judging by what you describe, and I would suspect it is covered under the Fender warranty. The only failure that I could see to cause this phenomenon would be the failure of C5 [250pF] capacitor in the vintage channel tone circuit by means of a short circuit. This would then offer no filtering for frequency separation and thus render the bass and mid useless and the trebble to act as a marginal volume control.

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Post subject: Re: Problem with my Fender Supersonic 100w twin -Mid & bass
Posted: Wed Feb 12, 2014 10:56 pm
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AaronK wrote:
I would believe it to be a component failure judging by what you describe, and I would suspect it is covered under the Fender warranty. The only failure that I could see to cause this phenomenon would be the failure of C5 [250pF] capacitor in the vintage channel tone circuit by means of a short circuit. This would then offer no filtering for frequency separation and thus render the bass and mid useless and the trebble to act as a marginal volume control.


Actually, a failure of C5 will not cause that problem. You can make the cap value infinitely small (approaching a short circuit) and all that happens is the highs are rolled off leaving only low midrange and bass (the opposite of the OP's issue). Making the cap infinitely large (approaching an open circuit) will eliminate the treble current loop entirely leaving only the bass and treble control functioning. The overall gain of the circuit will actually increase. You can use the Duncan tone stack calculator to demonstrate both effects.

http://www.duncanamps.com/tsc/index.html

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Post subject: Re: Problem with my Fender Supersonic 100w twin -Mid & bass
Posted: Wed Feb 12, 2014 11:20 pm
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To Retroverbial: All tubes appear lit, so I don't think it is a tube problem. Thanks.

To bluesky636: The problem seems to reside only within the Vintage channel. The burn channel, including all of the associated knobs seem to be working perfectly (I love this amp). I will bring the amp to an authorized tech soon. Thanks for your help.


To AaronK: A short circuit seems to be the most logical cause, but what do I know! I have never seen a schematic that looks so complex. It looks like it describes a freaking space shuttle! Thanks.

I will let everyone know what the tech finds.


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Post subject: Re: Problem with my Fender Supersonic 100w twin -Mid & bass
Posted: Wed Feb 12, 2014 11:29 pm
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bluesky636 wrote:
AaronK wrote:
I would believe it to be a component failure judging by what you describe, and I would suspect it is covered under the Fender warranty. The only failure that I could see to cause this phenomenon would be the failure of C5 [250pF] capacitor in the vintage channel tone circuit by means of a short circuit. This would then offer no filtering for frequency separation and thus render the bass and mid useless and the trebble to act as a marginal volume control.


Actually, a failure of C5 will not cause that problem. You can make the cap value infinitely small (approaching a short circuit) and all that happens is the highs are rolled off leaving only low midrange and bass (the opposite of the OP's issue). Making the cap infinitely large (approaching an open circuit) will eliminate the treble current loop entirely leaving only the bass and treble control functioning. The overall gain of the circuit will actually increase. You can use the Duncan tone stack calculator to demonstrate both effects.

http://www.duncanamps.com/tsc/index.html


Bluesky, does this hold true if C5 was short circuit (meaning no capacitance), as your explination still assumes some capacitance no matter how infinately small. My reasoning was based on short circuit scenario, as if a hypthetical link was soldered across the capacitor C5's legs.

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Post subject: Re: Problem with my Fender Supersonic 100w twin -Mid & bass
Posted: Wed Feb 12, 2014 11:32 pm
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AaronK wrote:
bluesky636 wrote:
AaronK wrote:
I would believe it to be a component failure judging by what you describe, and I would suspect it is covered under the Fender warranty. The only failure that I could see to cause this phenomenon would be the failure of C5 [250pF] capacitor in the vintage channel tone circuit by means of a short circuit. This would then offer no filtering for frequency separation and thus render the bass and mid useless and the trebble to act as a marginal volume control.


Actually, a failure of C5 will not cause that problem. You can make the cap value infinitely small (approaching a short circuit) and all that happens is the highs are rolled off leaving only low midrange and bass (the opposite of the OP's issue). Making the cap infinitely large (approaching an open circuit) will eliminate the treble current loop entirely leaving only the bass and treble control functioning. The overall gain of the circuit will actually increase. You can use the Duncan tone stack calculator to demonstrate both effects.

http://www.duncanamps.com/tsc/index.html


Bluesky, does this hold true if C5 was short circuit (meaning no capacitance), as your explination still assumes some capacitance no matter how infinately small. My reasoning was based on short circuit scenario, as if a hypthetical link was soldered across the capacitor C5's legs.


I believe it does. Try the calculator yourself. Put in the smallest cap you can (I entered 1xe-17p) and see what happens.

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Post subject: Re: Problem with my Fender Supersonic 100w twin -Mid & bass
Posted: Wed Feb 12, 2014 11:46 pm
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Thanks, Bluesky, that's a nifty tool. But the tool does not allow one to select 0f like I was suggesting for C5 as if it was short, bypassing any capacitance value for C5. My assumptions were based on no capacitance for C5 (i.e dead short - 0f). Infinitely small capacitance would squeeze the treble down to almost nothing, as you suggested, but no capacitance would allow all frequencies to pass as well as DC voltage.

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Post subject: Re: Problem with my Fender Supersonic 100w twin -Mid & bass
Posted: Thu Feb 13, 2014 7:15 am
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AaronK wrote:
Thanks, Bluesky, that's a nifty tool. But the tool does not allow one to select 0f like I was suggesting for C5 as if it was short, bypassing any capacitance value for C5. My assumptions were based on no capacitance for C5 (i.e dead short - 0f). Infinitely small capacitance would squeeze the treble down to almost nothing, as you suggested, but no capacitance would allow all frequencies to pass as well as DC voltage.


I understand what you are saying, but not sure I agree without further analysis. You have to consider that the tone stack contains three current loops whose performance is affected not only by the value of the tone caps but also by the settings of the tone pots themselves. Of course, one could just place a jumper across the treble cap to test this, but I'm not inclined to take an amp apart to do so. :lol: :lol: :lol:

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