Buzzing Hot Rod Deluxe.

[highlux]

Hello all.

I have a Hot rod Deluxe here. Buzzing when I play a low e. Noise comes through speaker. Does NOT do it if I bypass preamp and use only poweramp.

My Electronics skills are limited. I can listen and follow directions. I have a multi-meter. I have a soldering iron and know how to use it. I have worked on amps before,
and know how to keep from getting shocked, and I know how to drain a cap, or live test safely.

I am pretty sure...but not positive....that it does not do it on dirty channel...could be wrong here...

I have tested the tubes. (I have a B K tester) they are good.

Would love to learn to diagnose this. (Every screw on the amp is tight.)

Thanks in advance.

Dave

[nosaj]

On a whim I'd go get some chinese food with chopsticks of course. plug an mp3 player into the input don't overdrive the sound just have it playing then use a clean chopstick and prod the ribbon cables, some are known for being problematic.

nosaj

[g1]

Also tap on the preamp tubes, you may locate one that is microphonic. The tube tester does not test for this.

[highlux]

I should have mentioned...I had done that earlier...and one instance....v1 was micro phonic even switched tubes and it was v1 socket...that seemed to be micro-phonic. Then I turned on amp this morning...and could not get it to repeat symptoms or tap a tube and have it got micro-phonic. I will get a video of it buzzing up in the morning. Oh...and thank you for helping me...I honestly appreciate it.

I know its preamp. Seems to be only on clean. I do not have the Fender tube stabilizer foam on the preamp tubes. This alone would not do this...but I have ordered one for my friend...so that it can be ruled out...and I like stuff like that left on. Unless the general consensus is to remove. I have the fender schematics printed out. Should I post them here?

[g1]

As they seem to be up to re-issue III now, it's probably best if you post the exact version schematic for your amp.
Some of the power supply caps for the preamp in these models seem a bit more prone to problems, not sure if that would account for your symptoms.

[Mick Bailey]

I has a buzzing problem with one of these that drove me nuts - chopsticked the life out of it to no avail. It also buzzed through a remote speaker, yet it was clean on the scope. Clipped parallel caps to see if this eliminated the buzz, no change. Caps all tested fine and no leaks (they ooze a yellow crust around the + lead).

In the end it came down to a microscopic circular crack around one of the 22uf supply caps that only played up on the bottom E.

[highlux]

Wow....I will look into that....Im still getting the video today....I had a crazy busy day. 2 super sweet amps fell into my lap today to play with....and a scope!

[52 Bill]

Does this happen at low volume settings or only when played louder?

Have you actually ruled out the speaker itself? Loose mounting nuts, dirty extension speaker jack switch contacts, bad speaker cable?

[Drewline]

I'd add to what 52 Bill says above to check that the baffle board is tight. Here in Colorful Colorado they always seem to loosen up. Every one of the Hot Rod series amps that I serviced seemed to have loose baffle boards & loose speakers.

[nevetslab]

I agree with both 52 Bill and Drewline on the speaker/cabinet/mounting. I ran into that a lot as I began doing preventative maintenance on all our Fender combo amps, particularly the Hot Rod series. Getting at the top three baffle mounting screws is a pain...the middle one has the logo plate covering up the screw, so you can't prevent that screw from turning as you tighten the nut down

I've also run into some where speaker's voice coil adhesive bond began failing, so the speaker itself was buzzing. You can often stop it with your hand reaching inside the frame, putting finger pressure on the spider while the speaker is being driven separately by a tone generator/amp at an offending low frequency, and find certain places where your finger pressure will cause it to stop buzzing. Sometimes it's a tear that has occurred on the cone out at the edge, thru the surround to the gasket, or the surround itself now has a radial tear..If the tears aren't serious, you can repair them.

[Leo_Gnardo]

Yet another acoustic buzz source in this series of amps: output transformer. One of my crustomers took it upon himself to swap in a Scumback 12" speaker. Great speaker, luv the tone, but a lot more bass energy than the stock one. Low notes rattled like crazy & it turned out to be the OT and back of the chassis flapping in the wind so to speak. A wedge of wood about a quarter-inch thick, crammed between chassis & OT core fixed the problem cheap & fast. Worth a try on your HRD, highlux.

[Drewline]

I spaced that one out also. Loose transformers on the chassis.

[Leo_Gnardo]

I spaced that one out also. Loose transformers on the chassis.

Everything was bolted down snug as a bug in a rug. The clue was, buzz noise went away when I took the chassis out of the box. Sometimes you find a wood wedge in Mesa/Boogies and 60's Ampegs. Happened to have such a wedge ready to hand: "Hm... let's try this." Bingo! Buzz-B-Gone.

[52 Bill]

What a buzz kill!

[Chuck H]

To isolate it to a circuit problem or acoustic problem, plug the output into an external cabinet. This was hinted at in many of the posts above. I just thought I'd say it outright so it couldn't be missed