Primrose(SumR Audio) Toroid GB - Page 57 - diyAudio
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Old 31st October 2013, 12:38 AM   #561
PMI is offline PMI  United States
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Quote:
Originally Posted by goober5 View Post
... Also I'm wondering whether anyone other than those with 800VA having this problem?
It is not the VA rating. Mine is 400VA. That is actually why I was surprised. In general, I believe it is more common the bigger the transformers.
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Old 31st October 2013, 01:17 AM   #562
labjr is offline labjr  United States
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Quote:
Originally Posted by PMI View Post
It is not the VA rating. Mine is 400VA. That is actually why I was surprised. In general, I believe it is more common the bigger the transformers.
I have four 400VA transformers two 18v and two 24V. Anyone know how I should test them?
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Old 31st October 2013, 03:45 AM   #563
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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
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Old 31st October 2013, 08:43 AM   #564
RKH is offline RKH  United States
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Default clarification

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

Quote:
Originally Posted by PMI View Post
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.
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Lighten up while you still can ...
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Old 31st October 2013, 07:35 PM   #565
PMI is offline PMI  United States
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Quote:
Originally Posted by RKH View Post
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.
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Old 31st October 2013, 08:39 PM   #566
labjr is offline labjr  United States
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Quote:
Originally Posted by PMI View Post

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.
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Old 31st October 2013, 10:49 PM   #567
PMI is offline PMI  United States
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Quote:
Originally Posted by labjr View Post
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.

Quote:
Originally Posted by labjr View Post
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.

Quote:
Originally Posted by labjr View Post
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... should we ask how the toast turned out?
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Old 25th December 2013, 07:47 PM   #568
sibbeli is offline sibbeli  Sweden
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is this GB over?!

please tell me it's not..
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Old 21st January 2014, 05:03 AM   #569
BDP is offline BDP  United States
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Default 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
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Old 21st January 2014, 05:13 AM   #570
emyeuoi is offline emyeuoi  Italy
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I was part of the GB with two trafo 600VA 24V and they are buzzing too much.
I have already substitute them with two new trafos ordered in Italy
Enrico
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