I hate my Champ: 40uF or 20uF first stage filtering?

efnikbug

Member
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631
I don't know where I got the notion, but when I recapped the amp some time ago, I recapped it with a 40-20-20 cap can. Now I look around, and all I see are schematics that say 20-20-20. Of all the things that can be contributing to what I consider bad tone, I'm caught up on the value of this first stage of filtering.

Everything else the same, what effects does a higher-value first stage filtering have?
 

wyatt

Member
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4,170
The 40uF cap it gives a more focused low-end it and every is tighter and punchier all around. How much more? I dunno. SF Champs/VC have 40uF stock, they also switched the cathode bypass cap on the 2nd gain stage — BF was 25uF, SF became 2uF. The 2UF only boosts top-end and upper mids instead of the whole signal, shaves off some of the lower end the 8" speaker seemed to struggle with. I think they are the reasons (especially the latter) why I greatly prefer SF Champs, they just seem much more lively with better cut than BF Champs to me.
 
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EFK

Member
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1,040
It could be you just don't like Champs ?
Not everyone does.
+1. It may be you don't like single ended amps, or small speakers, or both. I'm one of "those" people. They just don't do it for me - they all (little champs, supros, no-name brands w/. 8" speakers etc) have a weak, 'blatty' crappy tone to my ear.

Kind of like 80's onward Stevie Nicks voice.
 

efnikbug

Member
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631
It could be you just don't like Champs ?
Not everyone does.
Hmm . . . at the risk of sounding like a fool, you might be right.

Most of my amps are 2x6L6 amps too.

But so many people swear by them.

Sigh . . .

You're probably right. But I would have to play a few to really convince myself of this. I at least do not like mine.
 

Mattbedrock

Gold Supporting Member
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4,748
I went back and looked at the two champ style amps that I have built. On my BF Vibro Champ build, it appears I went 20/20/20.



You can see that tab "Y" is not connected (40). I built it with a 10" speaker and I like how it sounds. Use it for practice with my classic rock band. I think a 10" avoids some of the "blat", but it is a tiny amp in a tiny cab. Good for practice but not enough for gig volume.

My Brownface champ is wired 40/20/20.

It's in a head cab, so I use it with a variety of speakers, but usually a 2x10" Tremolux style cab. It also is setup for 6L6's and El34 style power tubes. It has plenty of oomph for a champ. I bring it to gigs as a backup amp in case my main rig goes down.
 

Steppin' Wolfe

Silver Supporting Member
Messages
5,059
Isn't a 40 mfd first stage of filtering a bit of a challenge for a 5Y3 rectifier, which has iirc a spec'd limit of 30mfd? IF I wanted to run 40mfd in the first stage, I might run a solid state rectifier. This will NOT affect the compression thing that a Champ does.
I find the OEM speakers in Champs....5F1, BF, Sf...to be weak. IF you ever find a Jensen P8RS speaker, grab it. You'll notice it by the size of the magnet. That speaker will open a Champ up...bigger bottom, more volume, better articulation....just a great speaker.
ONE wonders what this 'bad tone' is that you hear, efnikbug? I will also note that these amps are very sensitive to input level from the guitar. They don't like overly heavy pick attack....imho, no amp does. In this case, a little single ended amp like a champ can be a very instructive tool for a player who might be challenged regarding output levels form the guitar...whether that be from pick attack control or volume pot control.
Fwiw, I never find any reason at all to turn one of these amps down past 6 or 7 on the amp's volume control. OF course, this means one pays attention to the tone levels with the Bf/Sf Champs/Broncos/VC's.....again as with any other BF/SF Fender amp, ime, when the volume is pushed.
 

efnikbug

Member
Messages
631
ONE wonders what this 'bad tone' is that you hear, efnikbug?
Thanks for your post.

I went back and played it with the intentions of answering your question. I'm embarrassed to say, with a different attitude, I guess it doesn't sound so bad? I always thought it sounded too tight and sterile, and I think it still does at low volume. Today, I had it on 10 and messed with the volume of my Strat and another bridge-humbucker-only Strat. I was getting what I perceived as the slow grinding overdriven sound that I like, however bright and fuzzy it was on the top.

I think I was the fool for comparing my Champ with my older Fender 2x6L6 heads. I like their sound when cranked.

I think I have to question my own judgement of everything now.
 

enorbet

Member
Messages
46
Single Ended Class A power sections do have some advantages that allow for some tonal explorations and with very little work. The initial stage of such exploration must be recognized as a tad short of ideal but will tell you if it is worth fine tuning. I'm referring to the fact that most such amps use Fixed Bias which means instead of a B- supply they have a Cathode resistor which, based on the current draw of the specific tube, creates a positive voltage on the Cathode making the grid relatively negative by that amount. This means virtually any power pentode with he same pinout can simply be plugged in, substituted for the 6L6 to get an idea of dynamic tonal changes possible.

The only concern occurs if you wish to try EL34s/6Ca7s because unlike most other power tubes Pin 1 and Pin 8 are NOT connected internally
in EL34s. For this reason it is essential to connect the socket's Pin 1 and 8 EXTERNALLY often meaning Pin 1 of the socket has been used as a convenient soldering lug since it is not used at all in tubes like 6L6s (see below). If this is so in your amp, any component soldered to the Pin 1 lug must be disconnected from that lug so it is safe to connect Pin 1 lug to Pin 8 (Ground for Push-Pull AB Class) or the Cathode resistor for Single-Ended Fixed Bias Class A amps. You can easily see internal connections below.

If you find you prefer the characteristics of a different tube, calculate a precise Cathode Resistor value to bring bias voltage to ideal conditions for best results. It will, I assure you, work without harm with stock value since each tube will alter the implied bias voltage by how much current it draws.

Also if your version has a negative feedback resistor you can add a 10K pot to see if you like it a little less suppressed. If you do that it is also wise to diminish highs with some manner of High Cut capacitor whether a properly designed "Snubber" or a bypass cap on the driver's plate resistor. This would have the added benefit of reducing high overtones which apparently offend you some.


 

Steppin' Wolfe

Silver Supporting Member
Messages
5,059
enorbet wrote: "Single Ended Class A power sections do have some advantages that allow for some tonal explorations and with very little work. The initial stage of such exploration must be recognized as a tad short of ideal but will tell you if it is worth fine tuning. I'm referring to the fact that most such amps use Fixed Bias which means instead of a B- supply they have a Cathode resistor which, based on the current draw of the specific tube, creates a positive voltage on the Cathode making the grid relatively negative by that amount."

enorbet, I think perhaps you meant to write 'self-biasing' or 'cathode biased' when you typed in 'fixed bias', didn't you? A cathode biased amp such as this single ended amp here does NOT have fixed bias. It does have a fixed value resistor there, but the bias is not fixed in that the signal coming to the control grid swings the biasing...therefore being 'not fixed'. IN a fixed bias circuit, that biasing is fixed by the voltage applied to the control grid by the bias circuit....the negativity of the control grid is constant with regard to the cathode which is at ground.


efminkbug, your description of the sonics makes me want to suggest that one needs to know what the current draw and plate dissipation is in that output section. It may be a bit to the cool side. You need to know that plate voltage, the cathode voltage, the cathode resistance, and the maximum plate dissipation factor of the tube being used. OR....if you can measure the current draw, all you need is the plate voltage, that draw figure and the tube's specs. IMe, a 'stiff' filtering stage will not cause an amp to yield harsh, cold sonics.....but rather simply firm low end will be attained. Cold biasing will yield an amp that I personally do not want to hear. A good champ circuit at 10 on the volume should yield very smooth distortion, ime.....unless the biasing is to the cold side.
 




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