View Full Version : Transformer hum: how much is OK?


cchean
01-13-2012, 12:28 PM
OK, I just bought a Fisher Integrated tube amp and there's some hum coming from the main transformer. You don't really notice it when you are listening to music, but when it's dead quiet, you can notice its humming. Is that normal or should the transfromer be dead silent? The hum can be heard when putting the ear close to the transformer or, even from a couple of feet away. Can the transformer be "fixed" to eliminate the hum? All input appreciated. Thanks.

derekva
01-13-2012, 12:31 PM
Try tightening the nuts that hold the bells on the transfomers.

-D

gadget73
01-13-2012, 02:14 PM
+1 on trying to tweak the mounting hardware.

Also, has this amp been rebuilt? Excessive load caused by bad capacitors or improper adjustment will make it buzz.

cchean
01-17-2012, 01:06 AM
+1 on trying to tweak the mounting hardware.

Also, has this amp been rebuilt? Excessive load caused by bad capacitors or improper adjustment will make it buzz.

Not sure, but I'll guess it is still in stock form.

joel27
01-17-2012, 01:11 AM
From what I've read some hum seems to be normal on Fisher amps.

apurcell22
01-17-2012, 01:15 AM
It can also be tube related. If every thing is in probed working order (rebuilt, good tubes, etc..) and it still hums. Some times using rubber grommets between the transformer, and the chassis will minimize the issue.
Al

GreatTone
01-17-2012, 12:20 PM
The original Dynaco manual for my SCA-35 recommends taming power transformer hum by placing a wedge of wood between the xfmr and cage. The pressure on the xfmr can reduce hum. Worked on mine. Didn't cure it completely, but reduced it substantially.

derekva
01-17-2012, 01:30 PM
The original Dynaco manual for my SCA-35 recommends taming power transformer hum by placing a wedge of wood between the xfmr and cage. The pressure on the xfmr can reduce hum. Worked on mine. Didn't cure it completely, but reduced it substantially.

Yeah, that sounds like a Dynaco factory fix all right. :D

-D

audiodon
01-17-2012, 01:59 PM
You can tighten the end bells on the offending tranny and put isolation washers (try heavy duty plastic) on the bolts that hold it to the chassis, but that doesn't always fix it.

If it's not bad, put it in a case and try and not have the amp too close to your listening position.

Power tranny hum drives me to distraction.

NOSValves
01-17-2012, 03:59 PM
Masking the hum would not be my first recommendation. I would of course suggest tightening the transformer screws. But regardless if the transformer has started the physically hum its telling you one of two things...

1) It is being or has been stressed beyond its specification in the past.

2) Running a 50 year old tube based gear in original electrical condition is reckless and just plain asking for trouble. Most likely that is the what is/has caused the stress on the power transformer.

Get the amp completely rebuilt one way or the other if you truly like it.

No Fisher transformers do not hum if everything is right and it hasn't been over taxed beyond help.

Craig

BinaryMike
01-17-2012, 06:25 PM
Yeah, that sounds like a Dynaco factory fix all right.

That fix often works on other brands where there's very little clearance between the power xfmr core and a steel cabinet panel. Sometimes the noise is due to cabinet vibration, resulting from normal xfmr leakage flux.

rhing
01-17-2012, 08:13 PM
On my Dynakit Stereo 35, I use Silicone rubber washers underneath the power transformer, and I've tightened the mounting screws to the point where the hum is minimized. Silicone holds up to the heat pretty well and seems to absorb vibration from the hum. I've also tightened the screws and nuts that keep the transformer end bells together. Both of these measures have worked well.

audiodon
01-17-2012, 09:05 PM
Craig has it right. Additionally, putting two thermisters on the power supply primary windings as part of the restoration might drop the voltage enough to tame that hum.

rhing
01-18-2012, 05:22 AM
Craig has it right. Additionally, putting two thermisters on the power supply primary windings as part of the restoration might drop the voltage enough to tame that hum.

Ditto. Forgot to mention that I did that too--good point.

djnagle
01-18-2012, 02:14 PM
If you push on it with your finger, does it go away?

HiFiCanada
01-19-2012, 03:18 AM
Masking the hum would not be my first recommendation. I would of course suggest tightening the transformer screws. But regardless if the transformer has started the physically hum its telling you one of two things...

1) It is being or has been stressed beyond its specification in the past.

2) Running a 50 year old tube based gear in original electrical condition is reckless and just plain asking for trouble. Most likely that is the what is/has caused the stress on the power transformer.

Get the amp completely rebuilt one way or the other if you truly like it.

No Fisher transformers do not hum if everything is right and it hasn't been over taxed beyond help.

Craig
I agree, best to get it all checked over first, sounds like the transformer is working harder then it should, usually from a cap going bad in the power supply, could be drawing to much of a load on the transformer.
If you are hearing hum from a few feet away, that is a lot.