Fender Silverface Champ questions

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Matt C.
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Fender Silverface Champ questions

Post by Matt C. » Mon Jan 03, 2011 12:58 pm

I just bought a 1979 Silverface Fender Champ on a whim and i'm having a bit of buyer's remorse. i wanted something for that "tiny tube amp cranked to 10" sound, but the distortion i'm getting out of this thing is pretty unpleasant.

i know this a subjective issue, but what are my options as far as trying to change this tone? change tubes? change the speaker? open it up and modify the circuit or replace the caps? i'm new to DIY stuff and haven't worked on tube amps before, but i hear this amp is a good place to start.

thanks!

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Post by ShinyBox » Mon Jan 03, 2011 1:33 pm

First up, do you know that the amp is functioning properly now? If it isn't, that could be part of your problem. Either have someone check it out, or try to find another champ (local store, local musician) that you can play so you can determine this.

If it's working properly, and it's not your thing, I would sell it and find what your thing is, rather than Frankensteining a perfectly good amp, especially if you have zero experience with amp modifications.

$.02

Regards

Jon

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Post by Matt C. » Mon Jan 03, 2011 1:38 pm

as far as i can tell it's working properly, but i don't really know for sure. the clean tone at lower volumes is great, there's no buzzing or hissing or anything like that.

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Post by ??????? » Mon Jan 03, 2011 2:45 pm

mattcastore wrote:Ibut what are my options as far as trying to change this tone? change tubes? change the speaker?
change amps.


...seriously, not being snide-- if the amp isn't giving you what you want, and you're sure it's working properly, you will lose more money (and get more frustrated) trying to make it into something it's not.

That amp is so simple that it "is what it is." You can modify it and effect some superficial changes, but if it fundamentally doesn't give you what you want, trying to make it into something else is a losing battle.
Last edited by ??????? on Sat Jan 20, 2018 6:18 am, edited 2 times in total.

unchartedthickets
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Post by unchartedthickets » Mon Jan 03, 2011 3:03 pm

i'd agree that getting a new/old amp is better than modding. you could also use
a distortion pedal with it. what is your idea of good distortion? my 74' Champ
has some good breakup but i also run it with a pedal to take it over into stupidville.
I like the amp for the cleans and bluesy breakup it has at ten. I also like overdriving the hell out of it with a tubescreamer, rat, big muff, boss OD 2 etc....

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Post by ??????? » Mon Jan 03, 2011 3:05 pm

this line...
i wanted something for that "tiny tube amp cranked to 10" sound
makes me wonder: what first formed your opinion of what a "tiny tube amp cranked to 10" sounds like? If you can remember, you should probably seek out that amp, as it's probably what shaped your taste on the matter.

The subject of distortion in a guitar amp can be a deep subject, because the distortion itself can come from at least ten or more different mechanisms, in varying proportions, and can be colored/shaped by a near-infinite number of other variables. If you're seeking to get a particular type of sound, it pays to know a little more about this. It can help you ascertain what types of distortion you're hearing, and help you predict what characteristics in an amp will offer that.

Here are some things that can cause distortion in a (small) tube amp:
  • 1) slamming the front end of the first triode of the first preamp tube with a booster or hot pickups, causing this small-signal tube to clip
    2) Turning the amp up so that the first half of the first small-signal tube slams the second half of that tube, and any subsequent tubes, including the output tube. A very different flavor of distortion.
    3) power supply compression or "sag" due to underfiltering, interelectrode resistance in a rectifier tube, or core saturation in a power transformer.
    4) Intermodulation of the audio signal with 50/60Hz ripple from insufficient power supply filtering or aging filter caps, giving complex, non-harmonically-related distortion sounds
    5) Output transformer core saturation as a result of an under spec'd or too small output transformer
    6) Second harmonic distortion resultant from voltage coefficients of resistance of carbon composition resistors-- a property exclusive to these resistors wherein resistance changes as a function of voltage applied.
    7) Gentle compression due to flux loss with voice coil movement in AlNiCo magnet speakers
    8 ) distortion from a speaker cone flexing
    9) distortion from a speaker voice coil reaching the end of its voice coil gap and 'brick-walling'
    10) "edge yowl" or "cone cry" resulting from the edges of a speaker cone resonating at a particular frequency or set of frequencies.
...there are probably more that aren't coming immediately to mind right this second.

Here are some other factors that can shape the timbre of distortion in a guitar amp:
  • 1) voice of the speaker(s) used, including size, make, model, magnet, cone material, dust cap material, flux density in the voice coil gap....
    2) resonance or inertia of a cabinet material
    2a) size and tuning of cabinet
    3) amount of negative feedback (or lack thereof) in an amplifier design
    4) inherent timbre and construction of the output transformer.
    5) values of coupling and bypass capacitors
    6) style of tone stack, or lack thereof
    7) input impedance
etc etc etc.

Here's the deal with silverface Champs, and blackface/silverface amps in general: they were designed with headroom in mind. Even the tiny Champ was designed to be as clean as possible for its size.

Consequently, many of the factors above were selected for minimum distortion.

The notable exception is the stock speaker, which can REALLY misbehave. Punishing this speaker doesn't always sound too good. A really distort-y speaker can work great in the context of a bunch of other distortion all happening at once, but doesn't always work so hot on its own.

Something like a Tweed Champ, for instance, has a whole bunch of other factors that result in comparatively HIGH amounts of distortion, all throughout the amp. So when the speaker acts up, it fits right in.

This is just food for thought. You really don't have to think about any of this stuff if you don't want to-- you could always just go try a bunch of amps and see which one gives the sound you like.

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Re: Fender Silverface Champ questions

Post by Nick Sevilla » Mon Jan 03, 2011 3:10 pm

mattcastore wrote:I just bought a 1979 Silverface Fender Champ on a whim and i'm having a bit of buyer's remorse. i wanted something for that "tiny tube amp cranked to 10" sound, but the distortion i'm getting out of this thing is pretty unpleasant.

i know this a subjective issue, but what are my options as far as trying to change this tone? change tubes? change the speaker? open it up and modify the circuit or replace the caps? i'm new to DIY stuff and haven't worked on tube amps before, but i hear this amp is a good place to start.

thanks!
Let me get this straight...

You bought this on a whim, and now you are disappointed? Really...

Buy a different amplifier. You will never get a sound you like out of a whisical purchase. Seriously.
A friend of mine modified his Fender amplifier thinking he could "make it better".
He still cries at what he did. It USED to work great. Now it is a wounded piece of crap that will never sound good again.

Cheers
Howling at the neighbors. Hoping they have more mic cables.

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Re: Fender Silverface Champ questions

Post by ??????? » Mon Jan 03, 2011 3:35 pm

Nick Sevilla wrote: A friend of mine modified his Fender amplifier thinking he could "make it better".
He still cries at what he did. It USED to work great. Now it is a wounded piece of crap that will never sound good again.
I'd be really curious as to what kind of number he did on it.

I've never met a vintage Fender amp that couldn't be rescued. The circuits are simple, and VERY GOOD replacement parts-- sometimes in many boutique-y flavors-- are available for pretty much every single part in the amp.

Consequently, your friend should cheer up. Find someone moderately knowledgeable, and that amp can most likely be made to sound very good indeed-- maybe not exactly iike his memory of it, but certainly very good.

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Post by KennyLusk » Mon Jan 03, 2011 3:50 pm

??????? wrote:this line...
i wanted something for that "tiny tube amp cranked to 10" sound
makes me wonder: what first formed your opinion of what a "tiny tube amp cranked to 10" sounds like? If you can remember, you should probably seek out that amp, as it's probably what shaped your taste on the matter.
Total wisdom there.

Also, unless you're certain the amp doesn't need to be re-biased I would check that (or have it checked).
"The mushroom states its own position very clearly. It says, "I require the nervous system of a mammal. Do you have one handy?" Terrence McKenna

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Post by ??????? » Mon Jan 03, 2011 4:18 pm

The Champ is a cathode-biased design, which means its bias is self-adjusting.

However the bias range offered by the stock 470 ohm cathode resistor does put the stock 6V6 in a slightly "weird" place. If you wanted, you could change this resistor to 1k (I'd also change the bypass cap from 25?f to 50?f at the same time). Actually, a more optimal thing "on paper" would be to "split the difference" somewhat (800 ohm bypassed by 33?f, or another common/close value).

But this is 'fine tuning' to get the tube closer to where it wants to theoretically operate 'on paper,' and I doubt it would do worlds of good for changing the timbre of the distortion.

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Post by Matt C. » Mon Jan 03, 2011 4:23 pm

point taken (and thank you for the information about amp distortion, even though it is well over my head). i'll keep looking for something else. maybe i'll keep this one around for the day i decide to learn about how tube amps work.

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Re: Fender Silverface Champ questions

Post by Nick Sevilla » Mon Jan 03, 2011 4:55 pm

??????? wrote:
Nick Sevilla wrote: A friend of mine modified his Fender amplifier thinking he could "make it better".
He still cries at what he did. It USED to work great. Now it is a wounded piece of crap that will never sound good again.
I'd be really curious as to what kind of number he did on it.

I've never met a vintage Fender amp that couldn't be rescued. The circuits are simple, and VERY GOOD replacement parts-- sometimes in many boutique-y flavors-- are available for pretty much every single part in the amp.

Consequently, your friend should cheer up. Find someone moderately knowledgeable, and that amp can most likely be made to sound very good indeed-- maybe not exactly iike his memory of it, but certainly very good.
I have told him at least 6 or 7 times to restore it to original specs.
But... I guess he likes being depressed all the time, so this amp plays right into his mood swings.

Cheers
Howling at the neighbors. Hoping they have more mic cables.

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Post by unchartedthickets » Mon Jan 03, 2011 5:14 pm

i would also keep the Champ for when your taste changes ( and it will) and you really want that little tube amp sound with a little raunch at 10.

my experience with playing guitar and using classic tube amps (with a strat or tele especially) is that you need to hone your skill as a player. this setup has revealed
things I'm surprised hasn't made me quit yet. today, i really like the classic small watt tube amps. A 58' Tweed Champ, 64' Supro Vibra-Verb and a 61' Ampeg Reverberorocket are some beautiful examples of amps i've been lucky to play through
and they sure beat the Crate i bought in 89'.

if you're not strapped for cash, just keep the Champ and have it checked by a good amp tech. that's what i'd do.

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Post by Matt C. » Mon Jan 03, 2011 5:33 pm

unchartedthickets wrote:little tube amp sound with a little raunch at 10.
yeah i guess part of this is just me complaining about the never-ending quest for the "right" kind of raunch.

for clean stuff this amp suits me just fine, but that comprises about 1% of all the guitar playing i do, so i'm easy to please in that department.

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Post by ??????? » Mon Jan 03, 2011 5:35 pm

Champs have been going up in value lately, too, so keeping it is hardly a losing proposition. Either you decide you like it later, or you sell it later for a modest return on investment... probably beating the interest in a saving's account or even a CD these days.

Does it have the original speaker? Does it have nice, original-ish old-stock tubes, or new "former communist bloc" type of tubes?

One thing to remember-- in such a simple amp, each and every part becomes more important. If an amp has just a handful of components, each one of those components is proportionally a bigger part of the amp's sound.

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