5F1 With Noise I Just Can't Isolate

[rp]

When playing, and only when playing, I get a 'snare drum rattling in the room' sound coming out the speaker, a hashy paper ripping rattle, sounds like a bad speaker with a rubbing voice coil or tear but it's absolutely not. It rattles over the lowest notes only, and rides the signal but does not get louder or snowball, it just stays in the back-ground over the low notes. It's a non-harmonic rattle, more tearing paper, frying bacon. It's gets worse as the amp is turned up but doesn't really get louder - ie it's not like an oscillation, it doesn't build.

Otherwise it's a great 5F1, it's the most quiet Champ I ever heard and sounds perfect across the board: Dead silent at idle, volume progression is perfect, voltages perfect. Clean to mean perfect. You can ignore the rattle and it sounds fantastic, which is what I've been doing, and when cranked and I'm flailing away the sound overwhelms the rattle. When you ease up the rattle becomes apparent and annoying. So when the s/n ratio is low, like when you play bass runs with palm muting, it's really apparent.

Here's my troubleshooting:

- does it with different speakers in that combo cab, ergo - Not the speaker.
- plugging the champ into an external cab sounds fine - Not the speaker or head.
- plugging an other head into the champ speaker it's fine - Not the speaker, cab or loose hardware.
- pulled the head out and ran it back to the cab - All fine, no rattle.

Conclusion: It's the head and the speaker together in the cab, and the speaker must be inducing a mechanical vibration into the electronics of the Champ and it's coming out the speaker as electronic noise. Am I right so far?

- tried reflowing the solder joints I could get to easily - no change.
- tried different coupling caps, new 150s and PS6s - no change.
- tried different power tube and rectifier - nada.
- tried different v1 - nada.
- re-tensioned the sockets (I was sure this was it) - nope

Could a defective filter cap do this? There's not a hint of hum. A cold solder joint I didn't hit? Bad cc resistor? Bad pot? Bad socket?

As you can see from the pic it's not exactly something I want to go shot-gunning any more than I have to. This one's a real bear to work on. Any ideas what stage to concentrate on, not that there are many? BTW that's a boost switch with 2 cathode caps (1 & 25mf) on V1 but the problem was there before that was added.

I've been fighting this one since I built it, just hoping it goes away by itself, but it hasn't. Wasn't too bad with the muddier 8" MOD but it seems worse with the brighter more sensitive Blue Pup. I'm stumped, how many times can one go through a Champ? So far I've put as much time into troubleshooting as I did building it. Arrrgh!

BTW/FYI the 8" Blue Pup is awright - still a touch dark but nicer all around than the Mod 8. Rich crisp distortion. The 8F125 wouldn't fit.

http://picasaweb.google.com/ardpan/5F1T ... directlink

[xtian]

I'd like to see one more test: remove the chassis from the cab and play. That is, play the existing speaker, mounted in the cab, with the existing amp, just with the amp NOT mounted in the cab.

You describe the rattle as "snare drum" which to me means filaments rattling inside a bottle.

Another test for this is to get the rattle going (best to use a fixed sound source like an oscillator) and grab each tube with an oven mitt to see if you can quiet the rattling.

[rp]

Another test for this is to get the rattle going (best to use a fixed sound source like an oscillator) and grab each tube with an oven mitt to see if you can quiet the rattling.

hey xtian, ahead of you, fourth one down: - pulled the head out and ran it back to the cab - All fine, no rattle.

let me try one more 6V6, though I've done and redone this. Is it possible this thing is put together in such a way that whatever tubes are in it the filaments get shaken? Sure hope not.

I don't have a signal generator. I'll try the oven mitt as soon as I get a buddy over.

[rp]

SOB. I went to pull the 6v6 out and one of the pins pulled out of the tube! Never seen that. I guess the socket pins are nice and tight now! Was a nice black plate thin base Sylvania too. Might have to replace that socket. Modern crap, never had problems till my NOS sockets ran out.

[Structo]

Yeah that is one of the reasons I got away from combo amps.

I used the O rings with some success on a EL84 amp.
In fact, that was the nice thing about that amp was the tubes were all the same diameter.

[xtian]

hey xtian, ahead of you, fourth one down: - pulled the head out and ran it back to the cab - All fine, no rattle

OK, that supports my theory.

Sorry about your tube!

[rp]

OK, that supports my theory.

but it did it with other 6v6s not just that one. That was the best sounding one and it was a solo unmatched one I had too. Getting pin out of the socket's gonna keep me busy. Rats!

[rp]

Pin 6! tube's still good! Looks like the tube gods are f'ing with me today.

Now I got the head out again I tested it once again as xtian requested: head out back to cab. Sounds perfect - no rattle. Noise is only with the head in the cab.

This was my first and only combo - not gonna do that again, at least after the Harvard's done. Gotta give big credit to people like Leo Fender, cranking out thousands of combos without vibration issues. And mostly hand work back then too, no robots, no CAD, no lasers.

BTW Here's a pic of me being too clever for my own good. This is how the head goes in and what I have to go through every time I pull it. I didn't want bolts showing on the top. But to be fair to myself I wasn't on planning on pulling it out 4 times a day.

Ok, back to the original problem. Where's the dang noise coming from?

[Structo]

You should be able to solder that pin back on the tube if it still has it's vacuum.

[Richie]

Vibration problems usually take 2 people. Get someone to play the note that causes the problem. Then use a non conductive piece of wood dowel or similar. Touch componets like signal caps. make sure you have good connection to the controls. Sometimes a little wire wiggle will find the problem.
When you use the dowel, you want to use it to hold a componet to see if it stops or makes the problem less. Sometimes it can be more than one causing it. Although this may not be your problem,i'll add it for others. Look for other things, such as a loose cab handle, and things like that. They can buzz and rattle on certain frequencies.
You can also turn the amp on, and tap around on the chassis,and board. The closer you get to whats causing the problem, the more effect it will have,or sound stronger. If you find a cap, or whatever,you can straighten it,or move it to the side,can sometimes cure it,or a little goop.

[xtian]

I didn't guess you were new to combos! Welcome! Now run like hell.

I've never owned a combo that hasn't had some tube rattle. It's part of the charm, right? Some tubes are better than others. There's plenty of after-market rubber bands and other stabilizers for solving this problem, and they work to varying degrees. This kind of noise is only a problem when you're playing by yourself, because when you get rockin' with a band, you'll not notice it any more.

There's two kinds of tube noise to watch out for. The sympathetic mechanical vibration (snare drum sizzle) can usually be mitigated partially by pressure (finger, dowel, rubber band, etc.) and is not a big problem, other than it can bother you if you want a pristine GUITAR ONLY sound!

Then there's microphonic noise, where the mechanical vibration gets AMPLIFIED by the amp, and can feed back on itself! Very ugly, I understand, though I've never had this problem.

[rp]

I didn't guess you were new to combos! Welcome! Now run like hell.

No, not new to combos, just new to homebrew idiot-savant ones. I was aware of the problems and always did heads but who wants a Champ 2 piece? Good learning experience, like avoid alu Bud boxes for the chassis. I always build solid but you must cover ALL the bases with combos it seems. Gotta give the mass producers credit, especially Leo.

Anyway, turns out it was multiple things causing the rattle.

-Flimsy Alu chassis and my terminal strip ptp style with all the parts floating. Solved by shoving rubber grommets under stuff. The thin alu itself rattled like a snare once I started tapping, wedging the grommets helped here too. I hate kludges, but sometimes that's all you got.

-Put two cleats on the sides of the chassis btwn the cab and head and screwed in here too. So now it's braced on 3 sides and doesn't just hang down where it would rake and flex. Ran some thin weather strip btwn the edge and the back plate. This however breaks the contact with the shielding I had on the back but I cut a notch on the chassis edge and bent the 'finger' up above the foam to make a springy contact. Looks clever, intentional, and purposeful.

-Installed a STR417. More hard rock, sounds bit less wild then the plain '60s 6V6, I will have to try others. There are no more STR417 in the world.

Killed 98% of it. Lotsa time consumed, but I'm digging my 5F1. Now here comes the Harvard built into a shit Marshall Lead 12 combo.... fingers crossed.

[kevmin]

Make sure the preamp tube is not the problem first, but I have experienced similar wacky noises with a loose turret strip.