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Old 11th March 2012, 02:22 PM   #3231
Pano is offline Pano  United States
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Originally Posted by janneman View Post
Pano, DON'T measure the resistance of a transformer with a multimeter. Indeed, sending DC through the coil (as the multimeter will) may magnetize it and that will increase distortion and decrease induction.
Thanks Jan. It may be too late for some of my transfos. Do you really think the tiny current (microamps) of the DVM will hurt it?

As for DC imbalance, I was going to measure DC flow thru the primary with the DC powered on, but no signal. By measuring a few different chips, I hoped to find an average value.

When I've had Bud Purvine make transformers for me he has said that they can stand a little DC current without trouble. How much, I don't remember - because I wasn't planning to run DC thru them. I'm interested to know how much is too much. And if there is anywhere near that much imbalance on typical DAC chips.
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Old 11th March 2012, 02:26 PM   #3232
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Not wild speculation.
All audio transformer manufacturers, that I am aware of, warn of the risks of allowing DC into the transformer.
Right, I understand that and agree. I just find it hard to believe that there is enough current DC offset on the pins of the DAC to cause significant current flow. That's the speculation I was talking about. I thought maybe you had some actual numbers or experience with it. Seems not.

It's a good point, but I wonder how much it matter in reality. Some measurements might tell me.
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Old 11th March 2012, 02:35 PM   #3233
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Originally Posted by Pano View Post
Thanks Jan. It may be too late for some of my transfos. Do you really think the tiny current (microamps) of the DVM will hurt it?
I think this was more of an issue in the days of 20,000 ohm/volt VOMs. Remember, Jan is even older than I.
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Old 11th March 2012, 02:58 PM   #3234
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Which is saying something!!

If they did get magnetized by the VOM's DC - would they get demagnetized by the AC of the audio signal? This is worth a thread on its own.
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Old 11th March 2012, 04:58 PM   #3235
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[snip] Remember, Jan is even older than I.
Only on my passport
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Old 11th March 2012, 05:01 PM   #3236
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Originally Posted by Pano View Post
Right, I understand that and agree. I just find it hard to believe that there is enough current DC offset on the pins of the DAC to cause significant current flow. That's the speculation I was talking about. I thought maybe you had some actual numbers or experience with it. Seems not.

It's a good point, but I wonder how much it matter in reality. Some measurements might tell me.
My experience with the DCX2496 has never shown any offset differences on the DAC outputs, so I agree that would be a non-issue. Although if you look look close enough you'll find some uV probably.

As to measuring the DC resistance, yeah it may not be an issue with modern very low current multimeters. I can't find the data right now but I think that even 1mA DC might be harmfull for low-level input xformers.

jan
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Old 11th March 2012, 05:09 PM   #3237
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.......... I think that even 1mA DC might be harmfull for low-level input xformers.
that's why the manufacturers specify the distortion of high level low frequency as being much worse than low level higher frequencies.

The short term effect of sustained one way current due to big bass signals distorts the output.
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Old 11th March 2012, 05:32 PM   #3238
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Quote:
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that's why the manufacturers specify the distortion of high level low frequency as being much worse than low level higher frequencies.

The short term effect of sustained one way current due to big bass signals distorts the output.
I think it has more to do with the B-H curve of the core material. At low levels or high frequencies you are on the linear portion of the curve, so distortion is at a minimum. When the frequency is decreased to the sub-20Hz region and signal level is sufficiently high, you start to flat top on the curve, leading to distortion.

There is no one-way current of bass signals in music; they have the same area above and below the curve, though they may look much different above and below the zero axis.

You can have pretty good results demagnetizing your transformers by running them at 10 Hz for a period of time with a strong signal (even into saturation), then slowly reduce level and/or increase frequency. Resets the net flux to near the origin of the B-H curve. On a practical level, even minor offset on the B-H curve is still in a linear region on a well-designed xfmr that is not run near its limits, so you end up with good performance.
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Old 11th March 2012, 06:19 PM   #3239
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Originally Posted by zigzagflux View Post
I think it has more to do with the B-H curve of the core material.
Agreed.
Quote:
At low levels or high frequencies you are on the linear portion of the curve, so distortion is at a minimum. When the frequency is decreased to the sub-20Hz region and signal level is sufficiently high, you start to flat top on the curve,
Agreed
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leading to distortion.
Why? I think because the "flat top" as you put it, is the direct equivalent to adding a DC current to a smaller AC current in that "half" of the waveform. i.e. the flat top whether due to DC saturation or due to extended period of long wavelength music signal sounds the same. The core has become saturated.

Quote:
There is no one-way current of bass signals in music;
If I consider the "half waveform" and make it of long duration, then it is a one way current for the period that the waveform is all to one side of the zero current axis.
Quote:
they have the same area above and below the curve,
Almost agreed. There can be a small area offset from second to second. Most of the time these small offsets cancel out to leave a net near zero offset in the long term.
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Last edited by AndrewT; 11th March 2012 at 06:22 PM.
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Old 19th March 2012, 05:56 AM   #3240
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Default Improvements to the 'Pilgham Audio' Upgrades?

Hi There,

I have, for some time now, the full compliment of upgrades offered by Pilgham Audio installed in my DCX..

I'm just wondering if I could improve its performance further with the following change:

-Replacing the LM4562's on the 'Jan Didden' i/o board with Burson Discrete op-amp modules? Would they work as a direct drop in replacement?

I know the actual Burson modules are a direct replacment for LM-4562's in general, but is there anything special or different about the Jan Didden active i/o that would prevent them from being a drop in replacment?? (not including physical space for the modules)

Thanks!
CM
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