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Old 12th June 2003, 11:34 PM   #1
jonk is offline jonk  Canada
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Default Threshold sl-10?

Iím looking for a decent MC phono stage to get me by while I slowly work away on my DIY unit. I seen a Threshold sl-10 for sale (which I understand NP designed) and was wondering how this unit stands up today. I remember dreaming of having one twenty or so years ago and at the time thought it sounded (and looked) incredible. I remember they were dead quite and well built but havenít heard one in 20+ years. Could I make this unit sing or have things changed with SS too much in the last couple decades? Any comments/opinions/mods/ideas would be appreciated.
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Old 13th June 2003, 06:11 PM   #2
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It holds up pretty well. The gain stages are cascoded
matched Fets driving a PNP whose Collector is biased
by a constant current source and which drives a complementary
pair of followers. Very standard stuff, even today.

The MC input is still unique, consisting of parallel low noise
bipolars operated in Common Base mode, where the input
is into the Emitters and the output comes from the collectors.
No feedback, very quiet, sounds great. Why nobody else
seems to have caught on to this approach is beyond me.

I would replace all the electrolytic caps, which will have gotten
old by now.
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Old 13th June 2003, 07:20 PM   #3
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Quote:
Originally posted by Nelson Pass

The MC input is still unique, consisting of parallel low noise
bipolars operated in Common Base mode, where the input
is into the Emitters and the output comes from the collectors.
No feedback, very quiet, sounds great. Why nobody else
seems to have caught on to this approach is beyond me.

I build this MC input. It is similar approach ,not as quiet as the aleph phono MC input but I can report it sound GREAT.

I ask if is it possible parallel the bipolars the same way Passlabs does with Jfets.

Thanks.
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Old 14th June 2003, 12:36 PM   #4
djk is offline djk
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"Why nobody else
seems to have caught on to this approach is beyond me."

I built a couple of common base MC head-amps about 20 years ago, they sounded great!

http://users.ece.gatech.edu/~mleach/headamp/
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Old 14th June 2003, 02:51 PM   #5
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Quote:
No feedback, very quiet, sounds great. Why nobody else
seems to have caught on to this approach is beyond me.
Hallo Mr. Pass,

I was wondering if you can tell us/me where we/I can find the schematic of this nice and quiet MC amp?
I want to build a nice and simple MC amp and this one maybe the one for me and perhaps for other DIYers.

Thanks in advance,

Audiofanatic
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Old 16th June 2003, 06:16 PM   #6
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Quote:
Originally posted by djk
[BI built a couple of common base MC head-amps about 20 years ago, they sounded great! http://users.ece.gatech.edu/~mleach/headamp/ [/B]
This would be a complementary version. The Threshold M1 dates
back to about 1976, was single-ended and used about 8
parallel devices. I don't seem to be able to find the schematic,
but I'll see about recreating it from memory.
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Old 16th June 2003, 07:36 PM   #7
jonk is offline jonk  Canada
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Thanks for the replies.
Was the fet 10pc a similar design? It can be found used for just a couple hundred more (worthwhile?). I understand its not a full function pre but I really only need the phono.
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Old 18th June 2003, 02:57 PM   #8
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Default Thresold SL-10

I was using the SL-10 for many years.
Stunning looks (have you seen the knobs?) and incredible midrange.
Very few of today's solid state preamps can come up against it.
After I sold it to get a VTL ULTIMATE I couldn't find an MC prepre as good as the one built into the SL-10.
So I built the SL-10 MC stage (actually I built 2 of them).
Each was powered by 2 9V batteries in series which lasted for about 4 months of heavy use.
It is very easy to build, if you cannot find the original japanese bipolar transistors you can use BC550C (7 per chanel but all fourteen very well matched).
If that means anything, I stopped using these MC stages last year when I built my Aleph Ono/L preamp.

Nick
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Old 19th June 2003, 04:18 PM   #9
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The original used MPS6571's, but MPSA18's or similar low noise
NPN's will work fine.

I'm still working on sketching up the schematic.
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Old 19th June 2003, 05:13 PM   #10
arg_ is offline arg_  Greece
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Is it possible that the circuit in question is the one below?
I built it some ten years ago, using low noise SSM2210, and it works like a charm ever since
Thank you Nelson !!!
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File Type: jpg mc_pre.jpg (51.4 KB, 1414 views)
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