strange problem with 5e3 build

[jazzycian]

Hey all, I hope some of you could shed some light on this for me.

I built a 5e3 a good while ago.sounds really good.Hammond transformers, sozo caps, sprague atom filter caps. Electro harmonix 12ax7's, tung sol 6v6gt's and a nos sylvania 5y3gta. I had it hooked into a 30w weber alnico speaker, the ones that are jensen copies. But I think it blew the speaker because I was getting this nasty buzz along with anything you played- -kinda the same frequency as what you were playing and then faded out in the background. Sounded to me like voice coil rub so I presume the speaker needs to be reconed. So I plugged it into a mesa boogie one speaker cab with a celestion black shadow in it (90w) it's much much better but still on low sustained notes I can hear a buzz, not as bad but it's still there. Now maybe this speaker is on the way out too.

But the strangest part of this is when I play the open a string and the 6th fret on the d string together (g#) and let them ring together it kinda oscillates...like a tremolo effect. A fairly strong pulsing.

Can anyone shed any light on my problems?

Thanks

[Viejo]

I notice you are plugged into what in standard Fender style output jack wiring would be the external speaker jack. Is the amp wired like a Fender with a shorting jack as the internal speaker jack?

[jazzycian]

I have two cliff shorting Jack's and they are both joined together so it doesn't matter what Jack the speaker is plugged into.

[jazzycian]

Anyone???

[andyfromdenver]

Re: The a and g# thing, can you post a clip cause they're a half step apart (as you know) and your saying it really strongly emphasizes that discordant nature?
Maybe also try shaking your tubes close to your ears and listen for any loose parts etc? Maybe your getting a microphonic rattle? Have you swapped tubes? I've definitely heard the bad speaker sound you did in the beginning, but this seems like maybe something else as you suspect.
Hope that helps a little!

[jazzycian]

I haven't swapped tubes yet but I do have some spare 12ax7s and a 5y3 lying around. Don't think I have 6v6s though. I don't think it's microphonics because I just disconnected the speaker in the combo and ran a lead to another speaker cab I have. So the combo itself isn't getting vibrated by the speaker. I don't really have anything to record the sound with though. It's pretty much like a pulsing tremolo effect when those two notes are allowed ring together. It just doesn't sound right. I wonder has anyone else experienced this? I doubt it's normal??

[Viejo]

jazzycian ,I remembered Gerald Weber talking about a problem in 5E3's with a parasitic oscillation that sounds like a blown speaker and is worse on certain notes. I looked it up in his book and he says it is caused by the proximity of the .1 cap connected to pin 6 of V2 to the instrument channel input jacks.Using Cliff jacks instead of Switchcraft jacks probably puts the jacks even closer to that .1 cap. Gerald recommends rotating that cap 90 degrees to cure the problem.

[hackworth1]

Any cold solder joint can cause this problem, when the frequency of the note is sympathetic with the bad joint. Look for any potentially poor joints. Shorten some wires where you can. Avoid looping of wires, over and under weaving wire paths and flying suspended leads. Make crossings at 90 degrees. Put a little bend where necessary to mae a 90 degree crossing, while making wire runs as short as is practical.

Spread your caps and resistors apart from each other and give them a little breathing space. They should not be snuggling together.

[jazzycian]

Thanks for the replies guys,
Much appreciated. This was in fact the first amp I built about two years ago so the lead dress isn't the neatest and perhaps I should explore the cold joint thing. And that .1cap is quite close to that Jack so I will try rotate it 90 degrees. I will let you guys know how I get on. Also I will plug the amp into another set of speakers that I know are fine just to rule speakers out altogether

[Keyser Soze]

Does the amp exhibit this same phenomenon with multiple guitars, or just one?

How about when you play the same note combination on different strings (e.g. 6th string 5th fret and 5th string 11th fret)?

[jazzycian]

I only have one guitar at the moment with a pair of HumBuckers in it so I can't really check if it's the same with other guitars but I will check if the same note combinations on other frets still does the same thing. I'm putting together a champ at the moment so I can check that through the speakers I have to rule out rubbing voice coils. I should have it built today to check.

[Mightyaxeman]

I had a similar problem with my weber 5e3. My baffle was slightly loose and caused some weird distorted noises with certain notes. Make sure your baffle and speaker are fairly tight.

[muchxs]

Go with the Weber tip and consider this: You might want to go bigger on the filter caps. 50hz power, right? The lower the frequency on the mains, the bigger you want to go on your filter caps.

I'd go 40/20/20 (uf) and swap to a different rectifier. A 5Y3 isn't supposed to play nice with a 40uf filter cap. Fender did exactly that in the Vibro Champs, though.

[CA_Dan]

My guess is either a rattle from your speaker or baffle, or oscillation. Try poking around with a chopstick and see if you can get the oscillation to go away. If that doesn't do it I would start playing with adding a 470 pF cap somewhere to kill the oscillation.