Champ noise

[stax]

I built a Champ 5f1 a couple of years ago, which I love but as I plan to use it in the studio soon I could do with quietening it down a bit.
Thinking of adding a choke, any opinions on this or any other noise reducing tips much appreciated.
Stax

[Wally]

What kind of noise does the amp create? How did you wire the heater filaments?

[JohnnyCrash]

Is it high frequency hiss, or low frequency hum?

A choke and/or larger filter caps likely won't be the solution.

[Tele-Dave]

I always put Metal Film resistors on plate supply and cathode bias for the preamp tube.
Seems to help some.

[DH82c]

I understood that because the current draw is low on a champ, adding a choke has little effect.

[Wally]

Stax, are you there? What kind of noise? 60-cycle hum? Hi freq hiss?

[stax]

Definitely hum not hiss,I could put up with it but I’m thinking it would be a good idea to lose it if possible as I’m recording in July and would like to use it on a couple of tracks.
Had it all to bits today and did the chopsticks thing to no avail, the heaters were a pair of wires twisted nice and tight and routed above the rest of the wiring.
Mojotone transformers, metal film resistors, good quality filter caps and orange drops elsewhere.
Also found inside a date Aug 2006, it was the last of four amps I built and in less than three years I seem to of forgotten anything I learned.
Stax

[Wally]

Stax, is the heater filament center tapped? If not, did you go to ground with 100ohm balancing resistors? AND...if it is center tapped, do the 100 ojm resistors over there at the pilot llight....take both wires to ground from those contacts with one resistor per leg of the filament wiring.

[stax]

Had a look again and there are two 100-ohm resistors from the heater wires going to ground.
The only other thing I could think of was the proximity and orientation of the two transformers but I don’t fancy mucking about with that.
Looking on youtube it seems a common prob for small single ended amps so perhaps I’m being over fussy.
Stax

[Wally]

Those trannies should be a right angles to each other, IIRC.

[metropolis74]

Might just be the nature of the single-ended beast. I got my first Champ style amp a couple of months ago and it has some 60 cycle hum so I kind of freaked out about it until I compared it to a few other Champs both new and vintage. They all hummed a bit. The hum is present with nothing plugged in and is at a constant level regardless of where the volume is set. I read somewhere that Fender issued a service bulletin to repair locations back in the 50's or 60's that stated all Champs will have some hum and don't bother trying to fix them. I'm still deciding if can live with the hum.

Originally Posted by Wally

Those trannies should be a right angles to each other, IIRC.

Yep. Here's some other tips to reducing hum in a Champ. It includes the virtual center tap mod that Wally described above.

I'm curious if anyone has any other suggestions because I also would be more than happy to have a quiter Champ to record with.

[Wally]

I guess I just love the little buggers so much that I don't notice whatever inbred hum there is. Plug a single coil..tele?...into a Champ, and the guitar's hum is louder than any hum that the amp creates on its own, ime. Plug a humbucker in, and maybe it would bother someone. I just play so loud that I don't notice some little hum....keep hitting notes so you don't notice the hum. hahaha
HUm? I don't hear no stinkin' hum! LOL
I have heard some noisy vintage Champs, but after they were recapped adn properly serviced, things seemed normal/natural and quiet to me.

[Wally]

And....I am going to have to listen to 'Layla' again to see if there is any obnoxiously loud Champ humming on that album.

[stax]

A couple of pics of the Champ in question


[IMG]

I moved one of the transformers through 90 degrees and it made no difference, gonna try some additional shielded wire as recommended in link section 2.

Section 3 goes on to say
“Since the stock filtering values were selected when the standard line voltage was 105-110VAC, it is now commonly believed that the tweed era amps and some Blackface models are under filtered. We now enjoy AC line supplies of 120VAC in some areas in can actually be closer to 130VAC. In some, but not all cases, the stock filtering is not strong enough and results in an unacceptable level of 60 cycle hum.”

But us Champ users in the U.K. are on 230-240 ac; I wonder what the effect of that is??
Would be nice to sort out cos we’re in the studio soon and will be recording rhythm tracks live, with the Champ I can get the perfect sound without spilling over too much.
Stax

[Wally]

The 964 schematic shows 20mfds straight across. 20mfd is the max for a 5Y3, isn't it? It wouldn't hurt to try to bump up the filtering if you used 16, 8 and 8 in your build.
Sharp looking amp. What are those switches between the jack and the volume control?

[stax]

One switches in a treble bleed cap on the volume pot, the next is negative feedback on or off and the third switches in a 25uf cathode cap that’s in the 5E1 but not the 5F1.
Stax

[muchxs]

Originally Posted by metropolis74

Might just be the nature of the single-ended beast.

No, it isn't.

I've built a ton of these and I've managed to eliminate the hum. Mine are dead quiet. They're also aggressively obnoxiously gainy (as gainy as an amp with three tubes can be) and I've mangaed to elminate the noisy artifacts you might expect. I use carbon comps everywhere aside from the dropping string.

Originally Posted by stax

One switches in a treble bleed cap on the volume pot, the next is negative feedback on or off and the third switches in a 25uf cathode cap that’s in the 5E1 but not the 5F1.
Stax

I'd like ot see a gut shot of that thing.

I build mine on repro 5F1 chassis. On the minus side it's tight in there. On the plus side it's tight in there, that keeps the signal path short. That's one of my Rules to Live By... keep it short and sweet. Figure out what it has to be and hardwire it. Excess wire is just a bunch of little antennas (antennae?! ) and the excess wire can pick up hum. Keep the signal path short, keep the ground path short then use shielding sparingly to eliminate any residual hum and crosstalk.

Check your filament voltage. Should ideally be 6.3. The more you increase filament voltage above 6.3 volts the more the amp will hum. I like to keep my filaments at around 3 volts on either side of ground. DC filaments increase parts count and they're unnecessary.

[JohnnyCrash]

Also, check the wires on your switches. With multiple switches comes wires running over noisey areas. You may need to reroute and clean up your lead dress there.

I agree... I've built TONS of Champ and similar 5w SE circuits. Noise isn't part of the package. Try a AX84.com HO or Lead amp - high gain JCM800 style preamps with 5w SE Champ style power sections. I've built a few of those and even had no noise issues.

Check the usual suspects (grounding, heater voltage, lead dress, etc) as muchxs says, but be aware of those extra switches and how they may introduce noise if the lead dress to-&-from them isn't so good.

[stax]

Funny but yesterday I thought the same thing myself about the switches, so I cut a new front panel did away with the treble bleed switch (left the cap on) and run the other two to the back panel.
I was just about to shield up the wires to the volume when (embarrassing bit) I realised I’d used carbon comp resistors nearly everywhere on the board, can’t believe I didn’t notice that straight away.
I must have done this deliberately for some reason at the time but I’ll swap them over with the metals when I get some, redo the shielded bits and see what happens.
Thanks everyone for input.
Stax

[metropolis74]

Hey Stax, any update on your humming Champ? I'm always on the lookout for new mods to make my Champ quieter. Any info you can share would be great.