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50w Single-Ended BAF2015 Schade Enabled
50w Single-Ended BAF2015 Schade Enabled
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Old 28th July 2017, 09:17 PM   #441
gior is offline gior  France
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Quote:
Originally Posted by Zen Mod View Post
with any signal xformer , I wouldn't go above 10 to 15mV max
two questions to be sure I understand correctly:
is that the potential between the two ends of each primary?
If so, can I then assume safely that I can put one of those ends at any voltage relatively to ground?
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Old 28th July 2017, 09:41 PM   #442
Zen Mod is offline Zen Mod  Serbia
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50w Single-Ended BAF2015 Schade Enabled
xformer is part which allows galvanic isolation ...... so , you can put primary and secondary on whole different potentials

however , that's common knowledge that signal xformers ( not made to have any significant DC flow through any of windings) are happy dealing only with AC through each/any winding
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Old 30th July 2017, 09:24 AM   #443
gior is offline gior  France
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Thanks a lot for your reply. Very clear
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Old 4th August 2017, 05:59 PM   #444
jamahamvui1978 is offline jamahamvui1978  Viet Nam
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Originally Posted by Michael Rothacher View Post
Can the Jensen tolerate DC in the primary?
Yes! F6, BAF2015 .... for examples.
all xtrans are still happy with some vdc bias or event 100-200vdc but depend on it's size and core they can not stand with some ma. Eg: fermalloy JS core will be saturated.
If xftrans must be stand some ma dc, do not use fermalloy core like Jensen xtrans. You could try some big trans have M6 core(Edcore) or amcc core(Lundahl)
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Old 12th August 2017, 02:10 PM   #445
jostwid is offline jostwid  Switzerland
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Originally Posted by Michael Rothacher View Post
Nothing new on my part. I was just going to lift Nelson's complementary JFET buffer and put it in there.

I'm interested in the opinion of the group though. Is it overkill?
YES AND NO
I am still using the scaled down version of the BAF Schade amp. But with regard to motorboating i think the problem remains the same for mine and the original version.
Currently i have put 10k from input to ground as suggested by Nelson. Most of the time this is working both with LuminAria and BA3 preamps. But sometimes one channel suddenly starts motorboating....especially on big changes in volume.

I find it a pity to have to add a buffer between these preamps and the BAF Schade. We should be able to control the problem without.

Nevertheless the buffer option should exist as many preamps simply would not cut it with regard to impedance.
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Old 12th August 2017, 06:38 PM   #446
ratbagp is online now ratbagp  United States
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I am puzzled by the discussion about DC flowing through the secondary of the input transformer. As far as I can see for this circuit there would only be 0.47 ma which is not exactly huge.

Am I missing something?

ray
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Old 12th August 2017, 07:19 PM   #447
Nelson Pass is offline Nelson Pass  United States
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.47 mA is pretty small. I wouldn't expect any issues.
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Old 12th August 2017, 08:46 PM   #448
vdi_nenna is offline vdi_nenna  United States
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Jostwid

What if you lowered the input resistor to 9k?
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Old 13th August 2017, 11:35 AM   #449
jostwid is offline jostwid  Switzerland
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Originally Posted by vdi_nenna View Post
Jostwid

What if you lowered the input resistor to 9k?
Since i have built versions with very different mosfets i came to the conclusion that the motorboating problem is more likely to occur with high transconductance devices. Maybe i am wrong...(and it was just coincidence)

But in any case it is probably advisable to build something that is stable, particularly if you build a 50 watt version...
When motorboating occurs this might damage your speakers. Even with my low power version that idles at only 1.2 amps the peerless woofer on the Boenicke W5 clones moves +- maximum (more than 1cm excursion).

Of course we can lower the resistor value but i do not feel totally at ease with it.
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Old 13th August 2017, 02:11 PM   #450
Michael Rothacher is offline Michael Rothacher  United States
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50w Single-Ended BAF2015 Schade Enabled
Quote:
Originally Posted by ratbagp View Post
I am puzzled by the discussion about DC flowing through the secondary of the input transformer. As far as I can see for this circuit there would only be 0.47 ma which is not exactly huge.

Am I missing something?

ray
Depends. What circuit are you talking about? If you're talking about the original unbuffered BAF amp, that's not why I asked the question.

And I was asking about the primary.
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Last edited by Michael Rothacher; 13th August 2017 at 02:15 PM.
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