Could use some help with a tough match

I currently have a pair of Threshold SA 1's which have been completely rebuilt. My challenge is to find a preamp to create the right synergy with my Sonus Faber Amati's. I would like to try a tube preamp but the Threshold's input impedence (75k) and its unbalanced inputs are making it very difficult to find a match. Has anyone out there had any success running the SA 1's with a tube preamp ?
I ran a Threshold S/300 series 2 with the Thor T1000 linestage with no problems at all......Used also a Phono Audio Rsearch PH3 ..Also no problems.....
Though I have no first hand expereince with them; Audio Research and Sonic Frontiers are reputed to work well with Threshold. Again, I don't have first hand experience, but, I suspect some lower impedance output conrad-johnson pre's would work, and you wouldn't be paying extra for unused balanced circuitry with c-j.
Whats bad about Threshold's input impedence (75k ???
Thats very high, and should work with basically any preamp.. Now if it was VERY low like 10k input than you would have a problem.. Just about any tube pre should match very well as most tube amps are an input of between 40k and 100k normally, so you have a very nice solid state load I believe.. Maybe I am wrong but I don't think so.
I agree with Undertow, 75K input impedence should not be an issue at all for any preamp that I'm aware of.
You might want to look at the Blue Circle preamplifiers. They all have adjustable gain to match your amplifier and preamplifier.
Second (or third) that 75K input impedence would not be a problem for a tube pre-amp.
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Thank you for all of your great feedback. What started this thread is I was looking at a BAT VAT 51se so called BAT and Threshold directly to discuss compatability. What prompted the call was the Stereophile review of the BAT which cautioned against matching low inpedence input on some amps with the BAT's 410 ohm balanced output. BAT said that it should be ok but running a balanced unit into unbalanced amps would certainly would not allow me to get the maximum performance the preamp is capable of. Threshold told me I would not have close to the 10x ratio that is the general rule of thumb for a good match. Also that a lot of tube gear had high output impedence. I must admit that the feedback I am receiving from each of you is different so I am a little confused. I really appeciate the input because I need to narrow the field a bit before I can shop for the appropriate preamp. My SA 1's have always served me well ( Maggie's, Thiel's) which is why I really wanted to match them up. I currently have 2 Threshold pre's but time to upgrade to current technology (a remote control :}
Well Threshold is right, you will not have close to a 10X ratio. You have a 183X ratio (75000/410). What they didn't tell you is that 10X is the MINIMUM recommended ratio. The higher the better. 183 is much better than 10, so no worries.
Obviously BAT gear was designed to run balanced. You can run it unbalanced, but you will not get optimum performance. This has nothing to do with the impedance matching though.

If I understand the conversation correctly with Threshold if I installed balanced inputs it is not a matter of straight math. The input impedence of the Threshold's would be approximately 600 ohms balanced. That was the issue. Certainly not an engineer but that's the feedback I received.
I'm sorry, I must have missed the earlier post where you stated the 600 ohms balanced, not recommended with a tube preamp. So obviously you can only run SS preamps balanced. If you want a tube preamp you will need to run it unbalanced, obviously.

Really sorry if I came across poorly. I certainly did not mean to come across negatively and truly appreciate and welcome your suggestions and feedback. This is my first time posting here because I am trying to learn ( at least a little... In all these years I have never owned a tube preamp, or a remote control :) on my systems so I am really venturing into new territory . My general principle has been simplicity of design (less parts, loops and interfaces) = less noise and better sound. I think the challenge for me is the number of quality components that are going to all balanced inputs and outputs with some making a concession to RCA outputs and inputs for convenience. ie in Stereophile measurements of the ARC reference 3 it was pretty obvious that measurements were better in balanced mode. I know measurements don't always tell the story but it's a start.
So thanks again for your feedback it really is greatly appreciated !

All my best,
Hi Don,

No need for apologies, I'm just trying to figure out where you want to go here. It seems like you want a tube balanced preamp, am I wrong? Obviously your amp is a poor match for this, so you will need to either change amps, go balanced SS or single-ended if you want tubes.

FWIW, when you talk about simplicity of design, a single ended circuit is much simipler to implement than a balanced circuit, with approximately half the parts. So maybe it sounds like a single ended tube preamp is for you. There are many good single ended tube preamps out there, Shindo, Doshi, CAT, Joule, among many others. In fact, your choices amongst single ended tube preamps is far greater than your choices amongst fully balanced tube preamps.

If you wish you certainly could try a balanced tube preamp with your Threshold, nothing will blow up. The impedance matching is just to help the sound. With an impedance mismatch like you would be likely to have, would just make the sound rolled off at the frequency extremes.

IMHO you would be better served trying a nice single ended tube preamp with your amp.


BTW, I currently own a ARC Ref 3, great preamp. I can't say that I have compared the SE to the BAL though, as I've only run balanced. My amp has a 200K balanced input impedance though.
Thanks John,
The driver behind my change is I am in the process of upgrading. From what I have learned the general concensus is that a tube preamp is a better match for my Sonus Faber Amati's. So if I am going to change I might as well explore the world of tubes.
FYI (and to the best of my knowledge), the earlier single ended Threshold amps are cap coupled. The later e series fully balanced Threshold amps are DC coupled. Some earler Threshold amps were upgraded to "e" series with balanced inputs, but are still cap coupled. Most tube pres are not DC coupled (the only ones I'm aware of are Atmasphere and Sonic Frontiers). Adding balanced inputs to your Threshold amps might help with long cable runs, but will other wise just add needless complexity. You might have more (though not necessarily better) tube pre options sticking with your single ended Threshold amp. On the other hand upgrading to newer fully balanced Threshold amps might offer better tube pre options, albeit at a cost. My previous recommendations for Audio Research and Sonic Frontiers comes from an ex Threshold tech with lots of expereince and feed back from Threshold customers. The c-j thought just seems to make sense. Why pay for expensive fully balanced operation if you won't use it. The really high end c-j pres output impedance might be cause for concern though.
Thank you Unsound. Excellent post, you have helped me crystalize my way forward. I will leave the Thresholds unbalanced because frankly I firmly believe they match up well with my speakers so will look for a single ended ARC, Sonic Frontiers or c-j preamp but welcome other suggestions. I looked at the ARC 3 but once again would be paying for technology ( balanced operations) I won't use. Any recommendations on a good ARC, Sonic Frontiers, or c-j models? I don't mind if its a few years old but I really want a quality unit. It will be the heart of my system so a class A component is essential ( quiet, big soundstage and dynamics ). I will start researching again but if anyone has a slam dunk recommendation I would appreciate your input.
Don, if you are looking for a great single-ended preamp, I suggest that you do some research on this Shindo Monbrisson. They are a rare find on the used market.

FWIW, I have no connection with the seller.

I have use a few different preamps from Space Tech Labs with S series Threshold and Fote #4 + #6 amps with very good results. Custom built to match the rest of your gear.