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Old 11th March 2008, 09:25 PM   #1
wicked1 is offline wicked1  United States
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Default Does size really matter - SE Output

I've read a lot of posts about the importance of size in a single ended output transformer.
When I was choosing mine, after a lot of reading I decided to go w/ one of the smaller "build to order" (tho mine was a stock product) transformer companies, which is sometimes recommended here.
A friend of mine has the Hammond 16**sea series.
I paid about 1.75 times what he did, and my transformers are about 1/3 the size and weight.

My amp isn't finished yet, so we haven't been able to do any comparisons. His amp is also a completely different design (although both se 300b). I don't think a direct comparison will be fair when I do finish my amp.

It's only human nature to place importance on size, and I'm starting to feel a little inadequate here .

So, is size really that important, or should I keep a positive outlook until the sound test.
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Old 11th March 2008, 09:31 PM   #2
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Important is the bandwidth of the transformer at the rated power. So I would say you either have lower wattage tranny (or you friend has more wattage) or your tranny hasnt got the same bandwidth as your friends.
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Old 11th March 2008, 10:57 PM   #3
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I agree with kacernator that either power or bandwidth is reduced with the smaller transformer. Compared to a similar size P-P xfmr, the SE one only gets to use 1/2 the flux swing, this translates into 1/4 the power rating, unless the low frequency rating is compromised instead (which is the easy way out since the air gap reduces the inductance).
But there does seem to also be a limit to how big one can make a SE transformer before other factors kill the high frequency end. Hammond's big 75W one, 1642SE, is likely pushing the envelope for conventional audio SE xfmr design.

Hey, St Louis huh
I used to live in Brentwood, a long time ago.

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Old 12th March 2008, 12:08 AM   #4
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Default Re: Does size really matter - SE Output

Quote:
Originally posted by wicked1
clip

... or should I keep a positive outlook until the sound test.
I would keep that positive outlook until you hear what they sound like. I, too, look for big transformers and often overdo a bit when I'm buying for a project, but several times in the past I've built amplifiers with what appeared smaller than optimum transformers (because I already had them on hand) and the resulting sound was far better than I expected.

I'm not trying to suggest that there is some way around the physics, just that the bandwidth may be just fine once you listen to them. If not, you know what you'll have to do.

Kind regards, Wade
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Old 12th March 2008, 12:31 AM   #5
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There is another engineering compromise that can be made to keep bandwidth up and sorta keep power up with a smaller xfmr. That is to use smaller diameter wire. Then they can put sufficient turns on the smaller xfmr to get the inductance needed for the same low frequency response. SE xfmrs aren't limited by wire resistance heating like power xfmrs, so the high power spec can still be met with some increased coil heating.

But the increased primary resistance will cause the speaker damping factor to degrade some, since the wire resistance is in series with the load Z. Silver wire, with its lower resistance, could counter this effect some.

Also, a toroidal SE xfmr would come out a bit smaller than EI for the same power, but not much since the air gap is what sets the permeability of the core.

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Old 12th March 2008, 01:10 AM   #6
flg is offline flg  United States
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Well, if we were talking about a Para-Feed topology. I beleive the Xfmr could be much smaller than one that also carries the DC.
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Old 12th March 2008, 02:28 AM   #7
wicked1 is offline wicked1  United States
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It's not parafeed. It's the onetics level one. weighs in at 3lbs 12oz versus the 11lbs of the hammond.
I've not read any bad reviews on them, so I'm keeping my hopes up. Unfortunately for this situation, bass is very important to me.
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Old 12th March 2008, 03:11 AM   #8
zelgall is offline zelgall  Canada
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A Hammond 1627 which may be appropriate for a 300B at certain operating points has a max current rating of 160mA. The size is required to avoid saturation.
A typical optimized 300b transformer would have a max current around 80mA.
The high Frequencies may be better in a smaller transformer... or not.
You have more versatility with a higher current rating - later you can satisfy your urge to try KT88's with 250V @ 140mA which I think sounds pretty good.
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Old 12th March 2008, 05:03 AM   #9
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In my 300B SE Amp, I am currently using Tango XE-60-3.5-S, which is each rated for 30W, 180mA. They sound absolutely good, and they look beautiful too. I tend to agree that as long as the transformer has good bandwidth and has been built with good quality material, 30W is more than enough for an SE-amp which can only put out no more 9W per channel. I am using a pair of ProAC 2.5 clone (sensitivity = 85dB/W/m, I think) with this Amp and the bass output is comparable to an good qaulity 100-150W solid-state design, and even better than my friend's one which is also using the same transformer and connected to the same loudspeakers. My point is that output transformer is very important components in any Amp but it is not as important as the driver-stage.
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Old 12th March 2008, 05:18 AM   #10
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Quote:
Originally posted by wicked1
It's the onetics level one.
I bet it spanks the Hammond. We have a set of those in an amp under development.

dave
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