Buzz in power supply

[bal704]

I'm starting a Hot Cat 30 build based on the Ceriatone Stray Cat 30 layout:

http://ceriatone.com/images/layoutPic/m ... iatone.jpg

I'm putting a couple of twist on it, but I'm just at the stage of laying in my power circuit. I'm adding a third EF86 channel, and adding a VVM type circuit using the IRFPE50 transistor. The VVM circuit I've used in other builds with success, and it appears to be working on this one.

I've currently got the PT,OT and Choke bolted on the chassis, the heaters wired and the power caps and VVM circuit installed. I only have the PT and Choke wired up, no OT hookups yet. Powers up just fine, VVM appears to be working fine. However, when I kick the power on, I hear a faint buzz. The buzz goes away when I kill the power. The OT is not hooked up, so this buzz is something I hear with my ear (the room is very quiet).

I assume this buzz is coming from the PT or the IRFPE50, since I've never heard of a cap or resistor audibly buzzing. Is this something normal that won't affect the build, or is this something a defect I need to fix?

[martin manning]

Power transformers can make an audible buzz if there are loose laminations or windings. If the transformer is mounted in such a way that you can increase the clamping force on the lam stack you could give that a try, but don't over tighten the bolts or you may break them. If the buzz is only noticable in a quiet room, then I'd say don't wory about it.

[bal704]

Thanks. I placed the OT using the headphone method, and I don't remember the PT buzzing then. However, the room may not have been as quiet.

I'm pretty sure the OT has been placed so that it's as quiet as it will get. I just didn't want there to be another issue I'd have to deal with.

[martin manning]

When you placed the OT, did you have any load on the PT? That could be the difference.

[bal704]

No load. Just hooked the Input side up to 120, left the output side dangling. I was under the impression that was how you were supposed to do the headphone method.

[xtian]

No load. Just hooked the Input side up to 120, left the output side dangling. I was under the impression that was how you were supposed to do the headphone method.

Right. So are you saying you hear the hum with no speaker attached?

[bal704]

OT isn't hooked up, so no speaker attached. Just the PT and Choke hooked into the power circuit.

[martin manning]

I assumed that you had no load on it when you placed the OT, but when you heard the hum was there any load on it? I think so since you had a voltage regulator powered up.

[bal704]

I hear the hum when the filter caps and VVM circuit are hooked up. It may have been there when I placed the OT, but I didn't notice it.