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Old 24th June 2008, 03:09 AM   #11
Zap is offline Zap  United States
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Just as an update, the KT88's seem to have a lot more of the glow as of late since I have been using the amplifier a lot more often. I'm not sure if they had not stabilized yet or what. I still can't get over the way it sounds and I'm hoping to build a set of speakers that will properly go with it.
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Old 24th June 2008, 12:07 PM   #12
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Quote:
Originally posted by Zap
...I'm running an Edcor power transformer, so I don't know how they compare to the Hammonds. The buzz is still present, but the actual speakers are whisper quiet without any input...
Is that the Edcor XPWR033 by any chance? I'm disappointed to hear a report that it might generate mechanical noise. I was considering using that transformer for a Simple SE myself.
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Old 25th June 2008, 05:25 AM   #13
Zap is offline Zap  United States
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Yes, I am running the XPWR033 transformer. I was a bit disappointed by the fact that there is a hum that comes from it. With music playing it is completely inaudible, but at idle it can be heard.

I was going to install a DC blocker, but haven't gotten around to it yet so I can report if that helps any when I get the parts for it. I'm gathering that none of the power transformers are gapped to eliminate the effects of DC, though.

If anyone has any tips for finding the source of the hum, I'd be all ears. I'm gathering that it is the HV taps producing the hum - however the Edcor has a higher current rating than the Hammond / Allied that is normally called for, so I would think that it isn't being run too hard. I guess it could simply be due to different construction? Maybe it is my particular transformer?

It would be nice to know, as the Edcor transformers do look nice as a set and the shipping cost is less from one source.
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Old 26th June 2008, 12:48 AM   #14
kevinkr is offline kevinkr  United States
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Some power transformers buzz, I find this to be particularly the case with new vendors and ones not really accustomed to making transformers for audio applications. (Goes without saying that cheapies usually scrimp on the techniques required to control noise.) My old vendor had to be "trained" to make quiet transformers, but ultimately they got pretty good at it.

Frequently the chassis is a sounding board that amplifies and transmits the buzz to the surrounding air. Sometimes rubber isolation bushings between the offending transformer and chassis can help in this regard. Do a search on the subject here - it's been discussed recently. McMaster Carr has suitable items for this task.

IMO I am not too enthusiastic about mains dc blocking. (Safety concerns mainly - most topologies use low voltage electrolytics which can fail spectacularly if not chosen to handle large ac currents) I would try to locate sources of dc and get rid of them if possible or at least make sure that they are off when listening to music.
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Old 26th June 2008, 12:53 AM   #15
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Kevin,

Would you be able to recommend a couple manufacturers that make power transformers with a known reputation for being silent? So far, all I know is:

Edcor XPWR - one report of buzzing
Hammond 200 series - several reports of buzzing
Hammond 300 series - reputed to be fairly quiet (?)
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Old 26th June 2008, 01:02 AM   #16
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I dunno bout the Edcore XPowers. I just ordered three of thier
CXPP's. Two of the hundred watters, and an unlisted 10 watter
to fit my Heathkit A7... Remains to be seen if I ordered the right
thing yet or not.
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Old 26th June 2008, 01:04 AM   #17
kevinkr is offline kevinkr  United States
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Unfortunately I have very limited experience with current production items, I am still mostly running off of my remaining stock of custom ACR transformers. (They are out of business unfortunately.)

I have used a number of Hammond 300 series stuff and that has been very quiet.

Hashimoto, Iso-Tango, Tamura - all encountered types have been dead silent, and rather expensive, getting 120V versions can sometimes be a problem.

I also have a surprising number of old utc, triad/utrad, stancor labelled stuff that is very quiet. eBay might be a good source, and I will say that the Magnequest and Electra- Print make quiet power transformers in my limited encounters with them.

All old potted US milspec is quiet. Look for those on eBay..
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Old 26th June 2008, 01:53 AM   #18
AJT is offline AJT  Philippines
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Quote:
There is a faint buzz that seems to come from the power transformer.
what you can do is the remove the end bells of the bussing traffo and shim the center legs, a small wooden wedge should do it.....
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Old 26th June 2008, 06:47 PM   #19
Zap is offline Zap  United States
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I've received some tips and have spoken with Edcor now - I'll keep everyone posted if I eliminate the hum. Seeing as this is my first amplifier, I would suspect myself first before the transformer.
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Old 27th June 2008, 07:04 PM   #20
Zap is offline Zap  United States
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Kevin,

Would choosing caps with a higher voltage rating make the DC blocker less of a safety concern? I was surprised that the voltage ratings were so low on something being used for AC service.
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