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Old 24th July 2008, 01:01 AM   #531
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You are wiring the 15V secondary of the second transformer ACROSS the 270EX 5V winding - I guess you'd call this "parallel".

Cheers,
Ian
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Old 30th July 2008, 11:40 AM   #532
jkeny is offline jkeny  Ireland
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Hi Ian,
In the original ECL86 Baby Huey, is it possible to make it accept a balanced input? I wish to front end it with a BDT preamp which puts out balanced signal!

Thanks
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Old 30th July 2008, 05:53 PM   #533
jkeny is offline jkeny  Ireland
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I searched through the thread and found the answer - if global feedback is dispensed with then differential input can be used - is this correct?
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Old 30th July 2008, 11:41 PM   #534
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Yes thats right. You may well be able to treat the -ve input to the diffamp as a summing junction and still keep global feedback if you want/need it but I haven't tried that.

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Ian
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Old 31st July 2008, 08:14 PM   #535
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Default snubber caps across rectifier diodes

Ian: What function do the 10nf 3000v caps provide across the rectifier diodes? Are these to tame transient spikes into the diodes?

Is ceramic the cap of choice in this application or will 2000v PP's also work?

Do all SS rectifier diodes stand to benefit from these bypass caps?
(FREDs, 5YVXXX, 1n4007, etc.)

Sorry if these are newb questions but searching and reading Morgan Jones hasn't enlightened me...

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Old 31st July 2008, 11:37 PM   #536
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These caps are as you suggest to tame diode switching noise.
They should be high voltage ceramic but 2kV rated is fine.
2KV rated Polypropylene would certainly work but might be a bit "over the top", save them for use in the audio path.

If using standard diodes (1N4007 etc) they are essential.
If using Ultrafast Soft Recovery types (what I mainly use) they still help.

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Ian
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Old 31st July 2008, 11:47 PM   #537
anatech is offline anatech  Canada
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Hi boywonder,
I'm in agreement with Ian here, he is giving you wise advice.

I only disagree in rectifiers and find that standard ones are the best. Just don't use too much capacitance. A capacitor that is high in capacitance for the job will only increase diode switching noise and ringing. Also, this will cause the transformer to run warmer in extreme cases.

Hi Ian,
I have not had any bad behavior with standard rectifier diodes. The ones made for switching supplies do cause trouble. Fast rectifiers work best with switching power supplies, the reason they were created in the first place. I accept that a soft recovery type may have less noise, but the noise levels created with standard diodes is easy to deal with. I am open to your experiences. Am I way off base here?

-Chris
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Old 31st July 2008, 11:57 PM   #538
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Chris,
I don't believe you are "way off base".

I have found that the caps worked well to suppress switching noise with standard diodes.
I also found that when I changed standard diodes to fast soft recovery types that I could hear the improvement - so these days I do both, use the fast soft recovery diodes and fit the suppression caps.

I admit I have'nt investigated this in depth with the oscilloscope.

Cheers,
Ian.
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Old 20th August 2008, 07:55 PM   #539
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Hi everyone,

I was playing with the shunt feedback resistors for a while.
The difference on the performance is quite obvious and I would like to have a changeable setup. I used a potentiometer for the global feedback at the beginning and the effect was very nice, but since I liked the sound with no gNFB best I omitted that later.

Now I am wondering if a similar setup would be possible for the shunt feedback. Obviously the power requirements make it impossible to use a potentiometer (would have to be stereo).
Ideally I would like to have a setup that I can switch while playing.

I was thinking about a 2W resistor that is paralleled with a rotary switch to dial in different parallel resistors. This way there is always at least one resistor (the one with the most feedback) in the path.
Would the sudden change in feedback level that happens when switching "live" be a problem, though?
Do I have to expect a loud "pop" and dead speakers?
Has anyone thought about that earlier or implemented something similar?

It would make the setup easier, less prone to placebo effects and I could use different feedback settings in the final version for different type of music (eventually I might reduce that to two different values - high and low feedback).
Any input is welcome!

Thanks,
Martin
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Old 20th August 2008, 08:26 PM   #540
Yvesm is offline Yvesm  France
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Quote:
Originally posted by bayermar
Hi everyone,

I was playing with the shunt feedback resistors for a while.
The difference on the performance is quite obvious and I would like to have a changeable setup. I used a potentiometer for the global feedback at the beginning and the effect was very nice, but since I liked the sound with no gNFB best I omitted that later.

Now I am wondering if a similar setup would be possible for the shunt feedback. Obviously the power requirements make it impossible to use a potentiometer (would have to be stereo).
Ideally I would like to have a setup that I can switch while playing.

I was thinking about a 2W resistor that is paralleled with a rotary switch to dial in different parallel resistors. This way there is always at least one resistor (the one with the most feedback) in the path.
Would the sudden change in feedback level that happens when switching "live" be a problem, though?
Do I have to expect a loud "pop" and dead speakers?
Has anyone thought about that earlier or implemented something similar?

It would make the setup easier, less prone to placebo effects and I could use different feedback settings in the final version for different type of music (eventually I might reduce that to two different values - high and low feedback).
Any input is welcome!

Thanks,
Martin
Hi Martin,

You need to change ONLY ONE resistor, R12 in this version.

Click the image to open in full size.

There is no DC voltage accross it (although it is at near the B+), only
AC.
If shorted: no more shunt feedback.
I suppose that an 1W potentiometer can do the job.

Yves.
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