Help need speaker to match Threshold 4000 amp....

I'd say you're between a rock (Soderberg) and a mountain (Pass), both extremely knowledgeable about Threshold (understatement), but like Taam I'd have to give Nelson the nod. I was the one who sold the 4000 and posted the specs you linked, Nelson's answer matches the 75k in the manual (I have another 4000 for sale - rebuilt by Jon). 

During the almost 30 years I used the 4000 I paired it with an NS-10, an Amber Model 17, an ARC LS-1, and an ARC SP-16 (even a Dyna PAS3x for a little while ... Ha! PAS on Pass). I have fond memories of the NS-10, though I liked the SP16 best, that said there are a lot of good preamps out there, you'll get good advice here. 

As for speakers I had Tympani IIID's at first but Beveridge Model 3's most of the time - vertically bi-amped with 2 4000's for the last few years. In the end they were mated with Maggie 20.1R's. As noted they can drive about anything (the Bevs reportedly dropped below an ohm at the high end). 

So one mans pairings with a great amp, sorry to go a bit long winded, been a while since I've posted on the 'gone. 

05-19-11: Pescolar
Bombaywalla,

Any tube pre-amp recommendation mating my Threshold 4000.

How about Cary Slp-98 (output impedance 400 ohms)

Thanks.pescolar

looking at the specs only, the Cary SLP-98 looks like a good match. Anyway you can audition it/try it before buying?
Another person I know (who has a Threshold T series amp) uses a Music First Audio (MFA) passive TVC preamp & really likes what he hears.
An obvious match is what some others have already recommended - the Forte (down-market Threshold brand) & Threshold s.s. preamps such as Forte F-44, Model 2 OR Threshold FET-9, FET-10HL, T-2, T-3.

I wanted to clarify my post above. I contacted Nelson about my Stasis 2 and he informed me the following.

The input impedance is 75K. There is a 4.75K resistor and then a 10K resistor, the 10K has been bootstrapped to
a 70K value.

So the 75k reported looks to be the correct answer for both the 4000 and Stasis 2.

I have to agree that 75k input impedance is the right one.

-----Original Message-----
From: Nelson Pass
To: junpablo
Sent: Wed, May 25, 2011 5:32 pm
Subject: Re: Vintage Threshold 4000 Class A amp:/ Need specifications/ Input Impedance:

I looked at the schematic, and a quick calculation shows 75K. The 15K value is
in error - the 10K value he is looking at has been bootstrapped to a 70K value. and
is added to the 4.75K input resistor before it.
np

NOW IT'S TIME TO FIND A TUBE PRE-AMP THAT WILL SUITED IN MY BUDGET AND IN A TIMELY MANNER.THANKS TO ALL PESCOLAR.

Bombaywalla, recently sold all my tube gears including Cary SLP-98 for financial reasons and now I am starting to build a budgeted system.I am familiar with SLP-98 and actually I kept enough 6sn7 and extras...will be a little cheaper if i decide to slp-98...but dreaming to have ARC too.if i have extra dough then ill go to all Pass Labs gears.
SO MOST LIKELY MY PRE-AMP 'S CHOICE ....CARY SLP-98.