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Old 28th February 2007, 10:10 PM   #21
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Quote:
did not see where anyone had given an explanation as to why one might want to choose a balanced preamp even if they intend to use only single-ended signals.
Nelson mentioned that balanced inputs are especially benefical when there is noise injected into the signal. Maybe from radio or emf interference. I guess longer cable runs are possible with balanced. Theat's one reason in the Pro arena. So, if you are using a balance preamp with unbalanced source, you can expect to have the sound be about the same.
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Old 1st March 2007, 05:15 AM   #22
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Quote:
Originally posted by GRollins
I glanced at previous posts and at the links to other threads given above and did not see where anyone had given an explanation as to why one might want to choose a balanced preamp even if they intend to use only single-ended signals.
The answer lies in the fact that a differential tends to cancel even order harmonics. As such, it lowers distortion in much the same way that a push-pull output stage does. The closer the match between the two devices making up the differential, the better the cancellation.
Many people automatically tend towards circuits with lower distortion. I would suggest that you approach the question by deciding whether you think you'd be happier with the single-ended circuit's relatively higher even order harmonics, or the differential's tendency towards odd order harmonics.
As with everything else about this hobby, there are choices to be made. The answers are not necessarily as obvious as they might first appear.

You are right - they aren't as obvious. Aside from any personal
observations about performance, the popularity of the
Aleph P type circuit over the Aleph L, coupled with the popularity
of the First Watt F1 over the F2 tells a story.

Tradition has it that people prefer 2nd harmonic over 3rd
characteristic, but the 2nd harmonic product usually has more
measured distortion because of the cancellation available in
balanced topologies.

Does this mean that the preference for lower distortion is more
important than the preference for 2nd over 3rd harmonic?
Not necessarily. Quite a few people seem to like 3rd harmonic
anyway.

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Old 1st March 2007, 06:10 AM   #23
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Drinking dry red wine with a Cohiba on the mouth under the dim
light in mood, I like Aleph L


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Old 2nd March 2007, 03:23 AM   #24
traw is offline traw  United States
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hmmm, considering making the p1.0 as bit simpler than the p17 (which i still need to repair one i made). so, looking at serv manual, the REF A. it looks like a tap of 18 volts or so from the power supply. I was hoping to use my p17 power supply board (veteran boards). Am i correct about REF A being a tap after the lowest 2 zeners in the reg supply?

Irfp240 suitable in place of irf244 i assume after some thread search/reading.

Also... can i still just put a 10k pot up front for volume control? Planning on unbalanced in only but both (xor) balanced or unbalanced. When, or if, using unbalanced out, do i need to ground out-?
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Old 2nd March 2007, 07:56 AM   #25
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Quote:
Originally posted by traw
hmmm, considering making the p1.0 as bit simpler than the p17 (which i still need to repair one i made).

Me too. Didn't like the sound of the 1.7 that much and would be happy to cut down on coupling caps.


Quote:
Am i correct about REF A being a tap after the lowest 2 zeners in the reg supply?
Yes.

Quote:
Irfp240 suitable in place of irf244 i assume after some thread search/reading.
That's my intention too.



Quote:
can i still just put a 10k pot up front for volume control?


Can see no reason why not.


Quote:
When, or if, using unbalanced out, do i need to ground out-?

No. Both outputs are produced at all times. Grounding one will probably affect the balance by changing the gain and probably have a negative effect on distortion. Just take an output between gnd and either + or -. If single ended input is used ground the unused one.
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Old 2nd March 2007, 07:56 PM   #26
traw is offline traw  United States
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thanks for the info.

would it be feasible to just use 2 additional 9.1v zeners and a 3k or so to tap off the 60v coming to the amp board to provide REF A ? Could i further imply that REF A is +18v, 20 mA? Not know enough of circuit, wonder how critical it is, like tolerance acceptable. Just curious as have an alternative regulated 60v supply that could use but need to reproduce that point.
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Old 2nd March 2007, 08:57 PM   #27
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I don't think a very accurate value is critical at all. Your suggestion to tap from a regulated supply will certainly work. Btw, where do you get those 20mA from? Surely the current through the gate is negligible.

I'd certanly make sure that the filtering cap for the bias voltage is as nice as possible and experiment with bypassing.
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Old 6th March 2007, 03:19 AM   #28
traw is offline traw  United States
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etched myself a board to stuff the p1.0 into... gutted my p1.7 construction. put the p1.0 in it... tapped the p1.7 power supply for 18 volts. works well....sounds nice. have to listen to more. just so happy to finally have a working pre again.
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Old 6th March 2007, 12:05 PM   #29
Vix is offline Vix  Yugoslavia
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Looking at the Aleph p 1.0, I can't resist not to make a question that has most probably been answered before:

How can an IRFP240 sucessfully work there? Doesn't it have a high input capacitance?

I'd be thankful if someone can answer to this, or at least point me to the appropriate thread.

Second dumb question: Can two 9v alkaline batteries in series serve as the 18V reference voltage? If yes, how often will they need a replacement?

Thank you very much,

Vix
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Old 13th March 2007, 02:40 AM   #30
bou is offline bou  Canada
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Default Aleph L service manual

I would like to have the service manual for the Aleph L. If someone could send it to me it would be greatly appreciated.

I want to build one of those and a Aleph X.

Thank you
Bou
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