Adcom GFA-5200 transformer replacement

[tanelpld]

Hey!

Got myself the Adcom GFA-5200. Sounds really nice. It's a bit noisy in speakers, not terrible but will recap it first and replace the 4 x 6800/50 bank with 10000/63 while doing it.

Anyway, bigger issue is the is mechanical hum from the transformer - too much, can hear it from couple of meters on quiet listening volumes. Seems like something to fix with the replacement as it's not bad mounting or anything but internal noise of the toroid. It's hard to find a 350VA / 32V replacement that the original is. Most 500VA are too big to fit.

Now, would going down to 300VA make much difference unless running on absolute max levels?
99% of time this amp will be serving quieter volumes in my small living room into Beovox s45-2 speakers.

What do you think?

 

[RVT1K]

An interesting question. My gut tells me that as long as the voltages are the same, it should be ok until, like you mentioned, trying to get max power from it.

How much is the replacement that you're thinking of? Maybe look for a non-functioning donor unit? I imagine one would be pretty cheep.

 

[wdecho]

The amp is not class A so 300VA should be fine if not pushed. Try replacing the filter capacitors first though. Might solve the trans buzz. Transformers buzz when working hard. I do not believe they start buzzing just because of age. Something is causing it to work too hard my first thought.

Check dimensions of the trans below to se if it will fit if you decide to replace.

AS-4432 - 400VA 32V Transformer

Toroidal transformers and power supplies

www.antekinc.com

 

[wdecho]

Check the bias. Bias out of whack would cause buzzing. Are the heat sinks getting hot at idle no signal?

 

[whoaru99]

Have you looked at AnTek?

They have 300VA and 400VA. They are 50/60 Hz trafos and they say are good up to 20% over rating when used on 60Hz.

IMO, if you are not needing full rated output at the lowest rated impedance, you'd be unlikely to notice difference with 300VA.

 

[tanelpld]

Thanks for the input, everybody!

Yeah, checked out the Antek, too thick—the box is about 68mm high inside, rather slim.

I'll definitely do the recap and all the basic service before going for the tranny change, to see if anything changes. But for now it seems to run pretty fine, just warm at idle, bias seems healthy, transformer is not warm. But haven't dug deep yet.
Other amps from the same power source run nicely.With a couple of different amps/pres I've had similar problems with, the only real help was the change. It would go unnoticed in a garage or something, but during quiet evening listening, it's annoying enough.

Found this available from the EU, seems doable and a nice price too: Lumonic Toroidal transformer 300VA | Primary 230V AC | Secondary 2x 30V AC or 1x 60V AC | Humming arm | Transformer for HiFi audio amplifiers

I'll wait for the service parts and see where it takes things.

 

[whoaru99]

Do you have any other amps with toroidal transformer?

Asking because toroidal trafos are more sensitive to something like DC on the mains. If it's something like that it might not be the trafo itself.

Article on Rod Elliott's ESP site could be of interest before just replacing the trafo.

"Blocking Mains DC Offset From Transformers"​

 

[tanelpld]

Yes indeed I have couple with toroidal. Got a Bomaster 1900-2, dead quiet, only if pressing my ear to the chassis can hear it deep in there.
Nad 114 preamp had a buzzing EI-core, changed it to a toroid, became dead quiet not possible to hear it in any way.