Threshold sl-10?

[jonk]

I’m 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 haven’t 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.
Thanks

 

[Nelson Pass]

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.

 

[stefanobilliani]

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.

 

[djk]

"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/

 

[Audiofanatic]

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 😉

 

[Nelson Pass]

[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.

 

[jonk]

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.
Thanks

 

[Nickolas K.]

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

 

[Nelson Pass]

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.

 

[arg_]

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 !!!

 

[Nickolas K.]

Yes, that's it.
If someone chooses to use 18V batteries, R17 has to be 1KOhm.

Nick

 

[Nelson Pass]

Is it possible that the circuit in question is the one below?

Close enough, and batteries are a great way to go with it.

 

[Notorious]

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.

I have SME 30/2 turntable, fitted with Ortofon Jubilee cartridge and using Ortofon T 20 MK II moving coil step up transformer on my Audio Research SP10 MK II.
Well what can I tell you? Sounds like dream and I just can't get enough listening my huge record collection..
Time ago I could buy SL10 from a guy in Amsterdam but I had to go on business trip next day so I asked him to keep it for me till I get back. He probably thought I was kidding and sold it.
Anyway.. I was talking to mr. Tiefenbrun (Linn's father) one day, and he told me that any step up transformer beat transistor based head amps hands down..
Since you are Treshold founder and designer of SL 10 I am really interested to hear your opinion on this.. 🙂

 

[analog_sa]

Just a casual opinion 🙂

The Ortofon T20 falls way below the level of your front end. Many active devices, both tube and SS will certainly sound better. It took me, in fact years to find a step-up transformer that sounds decent and actually better than an active step-up.

Not so sure about most common base circuits as they typically require a large electrolytic coupling cap in a very sensitive position.

 

[vendetta]

jonk
here's the SL-10 schematic.