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Post subject: Hot Rod Deluxe buzzing problem
Posted: Sun Feb 23, 2014 12:43 am
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I have a Hot Rod Deluxe which is making a very odd electrical hum. It's particularly stonger in the upper right (as illustrated in the image).

Image

You can hear a samaple of the noise at http://soundcloud.com/user485777105/hot-rod-buzz-clip

Any ideas what could be causing it?


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Post subject: Re: Hot Rod Deluxe buzzing problem
Posted: Sun Feb 23, 2014 2:14 am
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Look at the back , is the Power Transformer is there ? I guess so . Put your hand on , do feel the buzz ? How to fix ???? If it is not loose screws ....

Is it a new amp on waranty ? Can you bring it back to the store


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Post subject: Re: Hot Rod Deluxe buzzing problem
Posted: Sun Feb 23, 2014 2:30 am
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stratele52 wrote:
Look at the back , is the Power Transformer is there ? I guess so . Put your hand on , do feel the buzz ? How to fix ???? If it is not loose screws ....


Indeed. That is the general area of the power tranny. As well, the power tubes are very close to that vicinity. My first thought was a blown speaker but I'm doubtful about that since the offending noise is localized near the chassis.

If the tranny's windings are coming unraveled there's not much to be done save for outright replacement. OTOH, a microphonic or rattling tube is more easily (and cheaply) addressed. It's worth checking all chassis screws for sufficient snugness first though.

Arjay

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Post subject: Re: Hot Rod Deluxe buzzing problem
Posted: Sun Feb 23, 2014 2:37 am
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+1 Retroverbial :)


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Post subject: Re: Hot Rod Deluxe buzzing problem
Posted: Sun Feb 23, 2014 2:55 am
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I couldn't get the soundcloud file to work, so is the noise any louder than the normal hum from the transformer? Being as how you have to get practically right next to the speaker to hear it, I'm guessing that this is normal, and nothing to worry about.

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Post subject: Re: Hot Rod Deluxe buzzing problem
Posted: Sun Feb 23, 2014 8:36 am
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I can hear the noise; a loud, raspy buzz. Sounds like when you plug a guitar cable into an amp and touch the tip of the cord. Is the sound coming from the speaker or the power tranny itself? What I can't tell is the relative loudness of the noise. In isolation, as in the recording, it sounds quite nasty. Can it be heard when a guitar is actually being played through the amp?

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Post subject: Re: Hot Rod Deluxe buzzing problem
Posted: Sun Feb 23, 2014 11:31 am
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Nice slapback echo EFX.

http://soundcloud.com/user485777105/hot-rod-buzz-clip

http://www.webphix.com/schematic%20heav ... deluxe.pdf

First rule-out all external problems (guitar, EFX pedals, etc). Then, the tubes and trannies.

The hum sounds 120Hz to me. Mechanical power tranny buzz tends to be 60Hz in nature. IME, 99% of tranny hum issues have been due to the power tranny.

But first... have you modded the amp?. If you have, and the buzz started after the modification --- you must carefully inspect the work done. Reverse the mod to original, if possible. Rule out anything done to amp, after you bought it.

Do you get this buzz with no EFX or guitar plugged-in? Like Bluesky said, it sounds like ground loop buzz created when the guitar is picking up RF noise. Best way to rule-out guitar induced noise --- does the hum change when you touch the bridge? The control knobs on the guitar? Change character when you spin the guitar controls? If it's the guitar, pups, EFX boxes, etc --- you need to fix that first.


If it isn't the guitar, suspect the input section of the amp. If you pull only V1, does the noise change? If no change, then pull V2 (so both V1 and V2 are pulled). Noise change? Keep pulling each tube in order (next V3). See if the hum goes away with a specific tube pulled. Finally, pull all tubes (V4 and V5, 6L6GC). If hum is still present, look at the trannies. There is very little chance the noise is coming from the speaker, if all the tubes are pulled. If the noise is related to one tube pulled, replace that tube with a known good one. Did the noise change wih new tube? If not, move on. Though, the problem could lie within the cirucitry related to that tube.

Tighten the tranny hold-down screws, LIGHTLY & EVENLY. First, back off the four hold-down screws, on each tranny, until they are slightly loose. Then, cross-torque them evenly, like torque-ing a clutch pressure plate onto the car's flywheel. A few inch-pounds are needed. DON'T OVER-TIGHTEN!!!

If you still get noise, the issue prolly inside the circuitry. A bad or loose grounding point. Bad filter cap. Some kind of lead dress issue.

We can address those issues, once the above potential problems are ruled-out.


Good luck! :mrgreen: :D :mrgreen:


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Post subject: Re: Hot Rod Deluxe buzzing problem
Posted: Tue Jun 28, 2016 3:21 am
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I never did fix this problem... haven't really been using the amp but recently I noticed that the noise is greatly reduced on drive channel. Any ideas why the clean channel would buzz/hiss more?


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Post subject: Re: Hot Rod Deluxe buzzing problem
Posted: Tue Jun 28, 2016 6:18 am
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WAG... I'd suspect something in the switching portion (Clean/OD) of the circuit. A ground loop, bad chip, or LED. Could be a board that needs the grounding resoldered.

The power supply and output section seems to be the same, whether clean or OD. So, I don't think these parts of the amp are the issue. How often do you use the Clean versus OD in the amp? May not be worth the trouble if you rarely use the Clean --- to diagnose and fix the issue.

BTW... thanks, for reposting. Nice to hear about amp updates. Fixes or fixes that didn't work. :D

http://bmamps.com/Schematics/fender/Hot ... _Rev-B.pdf


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Post subject: Re: Hot Rod Deluxe buzzing problem
Posted: Tue Jun 28, 2016 3:22 pm
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Thanks. I really only ever use it on the clean channel so I'd love to solve it, especially as it's been there for so long.

I'll check the gnd solder but I'm not sure that will solve the problem as you can hear an audible buzz from the back if you put your ears close to the cab - somewhere at the top.


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Post subject: Re: Hot Rod Deluxe buzzing problem
Posted: Wed Jun 29, 2016 7:45 am
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You've tried new set of output tubes? If this didn't help... you should try to locate the buzz. This would require pulling the amp and bench testing. Prolly, best thing for you or tech to do --- before hit-&-miss fix attempts.

Could be the PSU caps, grounding, transformer buzz, burnt leads on board. I've even had amps with bad power supply rectifier diodes cause a buzzing noise --- maybe as a result of improper low B+ causing excessive current draw by the output stage). Anyhow, good luck with the search.

If you decide to bench test it. Be sure amp is secure. Watch out for high voltages (450-500VDC).

Good luck!


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