Humm - Vibro Champ

Fluddman
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« on: June 13, 2008, 05:08:29 AM »

I've got some unwanted hum on my recently built kit. Its not all that loud but still quite noticeable.

I think its power supply related as it continues even if I remove the preamp valves.

An amp tech told me that there is a simple fix (and that there is glaring problem with the ceriatone circuit)but I am determined to try and fix it myself rather than send it to him.

Anybody else have and solve this problem.

THanks


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cmoore
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Re: Humm - Vibro Champ

« Reply #1 on: June 13, 2008, 03:30:34 PM »

I would be very curious to know what the "glaring" problem is that your tech is referring to. I have a Ceriatone Vibro Champ in a head. There is absolutely no problems with any noise or oscillation. Who built your Champ?


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Fluddman
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Re: Humm - Vibro Champ

« Reply #2 on: June 14, 2008, 01:40:40 AM »

G'day Hired Hand - you sound a little defensive? Huh?

The tech doesn't like the way the heater circuit is balanced through the cathode resistor/capacitor. He reckons it should go straight to ground or better still to ground though another voltage divider circuit.

I've tried connecting it straight to ground but this is actually worse. I'll try the other circuit when I get a bit more time.

There is a bit if information at this site
http://www.netads.com/~meo/Guitar/Amps/Kalamazoo/Mods/hum.html

I made the amp myself - i have an electrical background but this is my first build. Everything else on the amp works great. The hum isn't major but it is annoying.

A few other owners have reported similar things.

Cheers


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cmoore
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Re: Humm - Vibro Champ

« Reply #3 on: June 14, 2008, 08:52:24 AM »

Defensive? I will rephrase. I will defer to your knowledge and the tech, as I was a painter and have absolutely no background in electronics or electricity. I can sort of follow along the website you linked to, but it really stretches my abilities with troubleshooting amplifiers. My limited knowledge of heaters and noise always makes me think of lead dress and not grounding. That is assuming you are working with a "proven circuit". And maybe the Ceriatone circuit is not "proven", I really do not know how closely it follows the Fender schematic. All I know is that my head is dead quiet and has bees in the studio a few times with no complaints. But maybe I got lucky. I am just one guy with one amp. Like you say, some other Ceriatone V-Champ owners have had the same problem. At any rate, it would be interesting to know the final outcome of your situation. I had a noisy TrainWreck clone, it is dead quiet now but it was almost responsible for a suicide.
Good Luck


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Fluddman
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Re: Humm - Vibro Champ

« Reply #4 on: June 14, 2008, 10:07:09 AM »

Hi again,

Thanks for your post. You raise some good points and really I think we are talking about the same thing. My limited understanding is that keeping the heater wiring twisted simply cancels out any electromagnetic fields that would otherwise be produced by the pulsating current flow.

For this to work properly the current needs to be equal in both wires. I think this more difficult on my ceriatone because it doesn't have a centre tapped winding for the heater supply (not sure if Fender does this too).

As for the circuits on the web page - I can follow the circuit (to create it) but I can't really explain how it works to reduce the hum. But I am hoping to find out.

I'll let you know how I get on. Cheers>


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Fluddman
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Re: Humm - Vibro Champ

« Reply #5 on: March 21, 2010, 08:31:18 AM »

Hey its been a while since i posted here and I thought I'd better give this some closure.

Turns out I had two main sources of hum and it had nothing to do with the heater circuit. A good way to eliminate problems in the heater circuit is to run them of a six volt battery - if the hums goes away there is a problem with the heater circuit (It didn't go away in my case).

Problem 1. insufficient filter caps - need to add an extra cap (I think this is now standard on the kits) - I've actually now have five 22mfd caps in my amp

Problem 2. there is a small hum created by the power transformer and output transformer being too close together. You can hear this hum as soon as the power is turned on (its created by the magnetic field from the power transformer cutting through the windings of the output transformer). Its noticeable but not too loud.


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