ST-70 Power Transformer Buzz

A few months after re-doing the power supply on my ST-70 using the Triode Electronics upgrade tranny, it has developed a loud mechanical buzz from the transformer. I have tried re-tightening the mounting bolts, sandwiching strips of sorbothane between the transformer and chassis, changing the rectifier and output tubes, etc. This has reduced it quite a bit, but it is still audible from the listening chair. I've noticed that it's worse when using KT-77's instead of EL-34's, I assume because of the higher filament current.
I'm also using about 300uF of capacitance in the B+ supply, with some film by-pass caps, but only 40uF in the first section before the choke.
It's livable now, but I'd like to get it quieter. Any suggestions would be appreciated.

Thanks

Griff

Griff,

Is your amplifier on a wooden shelf, and if so, is it well isolated from the shelf. I once had a single-ended amplifier with a slight PT buzz that was being exacerbated by the shelf acting as a soundboard of sorts. When I better isolated the amplifier from the shelf the buzz became nearly inaudible up close and certainly inaudible from a couple of feet or more away.

Charlie

Thanks Charlie, but it is pretty well isolated from the shelf on four rubber feet, plus I put a sheet of sorbothane inside the bottom cover. It's really coming from the unit itself.

Spudnik wrote:Thanks Charlie, but it is pretty well isolated from the shelf on four rubber feet, plus I put a sheet of sorbothane inside the bottom cover. It's really coming from the unit itself.

I was afraid that might be the case. Unfortunately, it is probably a problem within the transformer, itself. Have you spoken to anyone at Triode Electronics? Hopefully, they will resolve the problem for you.

Charlie

I was going to leave that as a last resort, but it looks like I'm there now. I'll drop Triode a line and see what they say.

Thanks

Griff

No reply from Triode on this after a week.

Spudnik wrote:No reply from Triode on this after a week.

Griff,

Who knows, maybe they don't keep up with their emails. If it were me, I would phone them next week. Just in case you need this, here is their phone info:

Phone Tech Support & Customer Service 4 Days per week
Tech support/Customer Service Phone Hours are: 10:30 AM to 5 PM on Monday, Tue, Thurs, & Friday
773-427-8823 (773HASTUBE)

Best Regards,
Charlie

Good point Charlie, I'll do that. Thanks for the 411.

I finally got around to calling Triode elect. on this, and they are sending me out a replacement power tranny at no charge. If only every company's customer service was this hassle-free!

I'll post the results when I get the new one installed.

Thanks for the help Charlie!

Griff

Well, that is true Bob. I actually never did get a reply from a couple of e-mails. Sometimes it is just more expedient to get someone on the horn. Triode's site doesn't actually say that they have e-mail tech support or customer service, just a phone number. Now I understand why.

Anyway, it's good to know that a replacement's on the way. That buzz is getting annoying!

Well, I take back my comment on this being hassle free. A month after being told a replacement was on the way, I still have not seen my new tranny. I have called Triode repeatedly over the past two weeks without anyone answering the phone, and have had no call back after several messages. I'm starting to wonder if anyone's home at Triode!

My ST-70 is now so noisy it is unusable. I had to pull my old NAD 3020 out of the bedroom system to use as the power amp. I am an unhappy camper.

If I don't get satisfaction soon, I'll just have to bite the bullet and buy a replacement from Bob, who I assume uses a different supplier.

Whooo hoooo! My replacement transformer has FINALLY arrived from Triode! Now I have something to do tomorrow as the coming snowstorm howls. I'll post the results of the heart transplant once it's up and running.

Well, the old ST-70 is up and running again, but there's still some transformer humm.
It's MUCH quieter, but the hum is still audible from the listening chair, which I don't find acceptable. It's only a mechanical humm, it's DEAD quiet through the speakers, you can only hear a slight tube rush if you have your ear right up to the tweets. I'll see if it gets quieter later at night when the AC is better.
It's still good to have it working again. It's sooo much sweeter than the Adcom GFA535II that I picked up as a temporary replacement, it's silly.

I still can't get rid of this hum, and it's too distracting to use the amp for any serious listening. Any suggestions would be appreciated. I'd like to get this back in operation, since it sounds great otherwise. Thanks!