John Curl's Blowtorch preamplifier part II - Page 3220 - diyAudio
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Old 3rd January 2013, 09:01 PM   #32191
gpapag is offline gpapag  Greece
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Quote:
Originally Posted by simon7000 View Post
Correct! Now who did it first?
According to the patent 4,555,751 (Nov 1985) it was Koga et al
Iíve traced patents with back to back diodes for noise reduction as far back as 1936


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Originally Posted by john curl View Post
Duh! '-)
In idiosyncratics this must mean ďI appreciate your inputĒ

George
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Old 3rd January 2013, 09:11 PM   #32192
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Quote:
Originally Posted by gpapag View Post
According to the patent 4,555,751 (Nov 1985) it was Koga et al
I’ve traced patents with back to back diodes for noise reduction as far back as 1936

George
Very interesting patent. They have the center tap inverse parallel diodes, but for a different reason! They want to keep the signal from going back into the transformer.

Yes diodes have been used as noise clippers for a very long time. (And you know that is not the same thing.)

Last edited by simon7000; 3rd January 2013 at 09:13 PM.
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Old 3rd January 2013, 10:27 PM   #32193
gpapag is offline gpapag  Greece
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Originally Posted by simon7000 View Post
Very interesting patent. They have the center tap inverse parallel diodes, but for a different reason! They want to keep the signal from going back into the transformer.
The center tap hosts a lot of traffic due to static and dynamic unbalanced currents. The back to back diodes reduces the nastiness of it.

With dual Ėand bifilar- split secondaries, each feeding itís own bridge, working conditions become more civilized.


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Originally Posted by simon7000 View Post
Yes diodes have been used as noise clippers for a very long time. (And you know that is not the same thing.)
I wish I was certain that itís not the same thing.

Strange. On this very topic, there was a paragraph in US patent 3,166,639 that caught my eye. I quote:

ďFor reasons not fully understood, the non-linear characteristic of the silicon rectifiers in the threshold region contributes to this noise reducing characteristic. Thus, the non-linear forward resistance of the rectifiers causes a distortion of the noise waveforms which appears to augment in a favorable manner the basic clipping action provided by the rectifierís unilateral characteristics. For these and other reasons, silicon diodes or semiconductors of comparable characteristics are preferred.Ē

I donít know if this was a misconception of the time (1965) but I am scratching my head realizing that I have never seen a back to back diode implemented with tubes.
Does anyone know anything on this?


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I am not big fan of inter-winding shielding as it does increase line coupling to the shield which creates the problem of where do you return those currents.
ES
I think that the proper think to do is to return these currents at the noise originatorís site.
True, we read conflicting implementations in the literature, as the writers can not be certain as to which ground point has the least impedance (this is also important). This is to be determined by the builder of the circuit.

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I prefer dual or split bobbin designs
I agree. For power transformers and less noise feedthrough, the less capacitive coupling btn prim and sec, the better. (*)
Additionally, increasing the primary inductance (more turns, lower Volts/turn) works for a smoother sinusoidal waveform.

George
(*) Inevitably this increases the leakage inductance (spreading of the magnetic field)
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Old 3rd January 2013, 10:46 PM   #32194
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I would give provisional first credit to Koga. I did it independently, a few years later. Still later, I went with dual bridges, with the Vendetta Research SCP-2A as a first effort in about 1989.
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Old 3rd January 2013, 11:04 PM   #32195
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I would give provisional first credit to Koga. I did it independently, a few years later. Still later, I went with dual bridges, with the Vendetta Research SCP-2A as a first effort in about 1989.
Thank you Mr. Curl

Can you give us YOUR reasoning for implementing center tap back to back diodes and YOUR reasoning for implementing dual rectifying bridges?

George
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Old 3rd January 2013, 11:38 PM   #32196
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I don't think that I can add to what Ed Simon has already offered, except that the dual bridge removes one potential ground loop. I saw this in the late 1980's when I upgraded the SCP-2 to the SCP-2A
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Old 3rd January 2013, 11:39 PM   #32197
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Splitt bobbin transformers, low C diodes, RC across the sec of the transformer, and an RC stage after the bridge to reduce the harmonics and RFI that is left. I like to keep the RF as low as possible before the DC voltage goes into the first PN junction in the regulator and starts mixing to produce IM products.
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Old 4th January 2013, 01:34 AM   #32198
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Don't forget Kelvin caps!
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Old 4th January 2013, 02:23 AM   #32199
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Well, some of us find that close attention to these relatively unused techniques do wonders for audio quality. It avoids the necessary use of batteries, which is a viable alternative to a good power supply. Unfortunately, batteries are even more expensive with medium current designs and wear out relatively quickly. That is why we try so hard to make the best power supplies that we can manage. Works for me (and my reputation).
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Old 4th January 2013, 05:23 AM   #32200
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As I found on the first batterry powered JC MC preamp... 1.5v batteries have a too high source Z and it just gets worse (higher) as they age and are drained. They also do not have a great transient energy - rise time. A very large cap across a battery is needed. So transformer c.t./grounding is one issue but then we get others. Regulated stable low Z vs freq is overall better sounding than batteries. So you are back to square one re. rect/xfmr/ct grnd. -Thx-RNMarsh

Last edited by RNMarsh; 4th January 2013 at 05:25 AM.
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