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Primrose(SumR Audio) Toroid GB

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I purchased a large transformer from Primrose/Richard and had the same issue, my suspicion is it is mechanical noise. When I received my transformer it has taken quite a beating due to not being sufficiently packed. Richard offered to take it back and examine it. I did not follow up due shipping cost, Oddly enough in time it quieted down. Maybe in the heating and cooling cycle the glue in the laminations stuck back together.

Bill
 
clarification

Are you suggesting two 250W bulbs in series on a single secondary of the transformer or one 250W bulb per secondary?
Thanks,
Ryan

No, it is a mechanical issue. I tested with purely resistive loads, and Lamp loads with no rectifier/filter supply connected. All you need to verify is a couple 250~300W light bulbs, and some sockets w. holders from Home Depot.
 
Are you suggesting two 250W bulbs in series on a single secondary of the transformer or one 250W bulb per secondary?
Thanks,
Ryan
I assume you meant to say "parallel", or one per secondary winding. (two in series would be a smaller load than one).

In my case, I used one 250W lamp load (light bulb), per 35V secondary. This was for a 400VA transformer, and after warming up, the bulbs generate a bit under a 1 amp load.

If your secondary voltage is lower, or your transformer higher power, you may have to use two in parallel per secondary winding, to produce the same effect. 1 amp is not a lot, the buzz gets progressively louder as the load increases.

I first noticed it when I tested with the power supply and a DC load, and I naturally assumed that the current spikes from the rectifier were causing it. So then I tried just the bulbs as a cleaner load, connected to the secondary winding through a screw terminal strip. So then I found the buzz is related to just load - not type of load.

It is a simple test, all anyone needs is some high-wattage light bulbs, some sockets, and a terminal strip or wire nuts. The bulbs will get hot, but not as much as you might think, because you are running them at ~1/3 rated voltage.

I can post more information, but a couple transformers out of a 100+ is a non-issue, at least until a few other people try it.
 
If your secondary voltage is lower, or your transformer higher power, you may have to use two in parallel per secondary winding, to produce the same effect. 1 amp is not a lot, the buzz gets progressively louder as the load increases.


Are you saying the load increases as the bulb warms up? 1 Amp is enough to make a 400VA transformer start buzzing?

I have a bunch of 50 watt 6 Ohm resistors. I guess I could series parallel them to make the proper load. I'm thinking it's not good to jolt the transformers with a big load instantly when you plug them in.

BTW I've used a 2 slice toaster to load test large like 500-1000 watt PA power amps when repairing.
 
Are you saying the load increases as the bulb warms up? 1 Amp is enough to make a 400VA transformer start buzzing?
Resistance increases as the filament heats up. 1 A is enough to make my particular 400VA transformer buzz, yes.
Not most 400VA transformers in general, no.
Other 400VA transformers, in this Group Buy, unknown.
At 2A, which is ~1/3 nominal load, in a quiet room you can hear it 9~10 feet away.

I have a bunch of 50 watt 6 Ohm resistors. I guess I could series parallel them to make the proper load. I'm thinking it's not good to jolt the transformers with a big load instantly when you plug them in.
Exactly what we do when we turn on an amp with a big capacitor array. Even with a thermistor, or some kind of other soft start circuit, the inrush is considerable.

BTW I've used a 2 slice toaster to load test large like 500-1000 watt PA power amps when repairing.
That is a fantastic idea... :D should we ask how the toast turned out? :clown:
 
Transformer buzz

I finally installed the SumR transformer as part of the group buy (400VA, 22VAC) and it mechanically buzzes badly, not usable for my standards.

While I was waiting for the SumR transformer I was testing a single channel F4 with a 120VA, 22VAC Plitron and it was dead silent at full bias.

I would suggest everyone involved in the group buy test their transformers before too much time passes.

BDP
 
I finally installed the SumR transformer as part of the group buy (400VA, 22VAC) and it mechanically buzzes badly, not usable for my standards.

While I was waiting for the SumR transformer I was testing a single channel F4 with a 120VA, 22VAC Plitron and it was dead silent at full bias.

I would suggest everyone involved in the group buy test their transformers before too much time passes.

BDP

This sucks, I have four transformers I haven't unpacked yet. I'm afraid to try them. What are we supposed to do about it if they do buzz? Ship them back to Toronto? Shipping cost would be too high. Sumr should know better. They market and sell to audio people all the time.
 
It has not happened in all cases that I am aware of. I am a bit surprised as well. EUVL used these with great success in his F5T builds. It seems to be some issue with this group. Why I cannot say. Richard has assured me he we resolve any issues. I would not assume it to be an issue until it is.
 
He has not expressed a specific opinion. Possibility of loose winding's is what i have surmised, but i cannot say for sure. I do not want to speculate as I am not a transformer guy. Most important part is that he is serious about making it right. As I said, the problem has not been universal.
 
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