Question About Audio Research Preamp Specs

dsper OP
Unfortunately, they explained that there is no room under the hood to replace the existing capacitors with larger ones.

This Dsper is BS sorry to say, they either don’t want to do it or have other things in mind, go to a tech that will do it.

At least they know that the caps are too small as i first said to you.

The person did comment that their latest redesigns addressed this and the output impedance has been reduced.

Sure they can’t be put "maybe where the existing ones are, but there are other places they can go.
(PS: you can even add (parallel) more of the same type to make what’s there larger no need to get rid of the existing ones)

Here in this shot circled in green is the output rca’s of your preamp. Circled in red right next to them is 2 massive amount of spaces that you can put more new caps than you need, take it to someone who knows. https://ibb.co/r4LBDcc

Price should be around $40 for two good quality caps, and about a hour labour from what I see. This is a great preamp just needs those larger caps so it can show it’s greatness to you with your amp.


Cheers George

Not that it matters over 1:10 I and many say.
But if you want high ratio go Krell preamp at 1ohm and Rogue Audio poweramp 1meg ohm!!!!! that’s an output to input ratio of 1:1000000 !!!

Cheers George

Why would CJ not have done this in the first place? Maybe a cost/benefits decision considering how relatively few amps have 10K ohm impedance?

It wasn't common to have such low 10k input impedance poweramps in the past, as the loosely based standard was 47k or 50k and many especially tube were 100k.
  
Ever since Class-D has reared it's ugly head has 10kohm become more apparent, which means it's not suited to many tube preamps and also many passives.

I believe there should be one standard and that's 100kohm then anything can drive it, hell Rogue Audio use 1megohm on their poweramps and they don't have any problems at all.

Cheers George 

Maybe I should call CJ and ask them if they can adjust the caps on the 17LS2.

Great idea, tell them you want the "uF" of coupling cap increased so you can have "little or no" rolloff above 20hz into your amps 10kohm input impedance.
This is around $20 for the caps, and a 1hr labour.

My calculation for 17ls2’s new coupling caps into the 10kohm of the amp. Any/All are fine.
4.7uf will be -3db at 3hz
6.8uf will be -3db at 2.3hz
10uf will be -3db at 1.6hz

Cheers George

The reason ARC didn't do this initially was simply because the larger you make a coupling cap the more coloration no matter what type of construction.

Take that with a grain of salt. I do prefer direct coupling (no cap), best cap is no cap mentality. 

But dsper OP one of the best tube preamps hailed even by many tube and solid state preamp manufactures as being the best tube preamp ever made is the  Aesthetix Calypso preamp, and it has massive output coupling caps, as shown in this pic circled in red.
https://ibb.co/4Jb0bSV

Cheers George

    

dsper
What does the "20K ohms minimum load" tell me?

As mzkmxcv stated 8 x output to input ratio is even fine.

But in this case the AR preamp would be capacitor coupled output, and the roll off in the low frequency could be too high if the partnering power amp is less than 20kohm input, with the size of the AR’s coupling cap. And so you may miss out on the low frequencies.

There are two way this can be fixed, don't get fooled into needing another preamp.  
dsper
1: If you own the AR pre, tell me the size (uF) of the output coupling cap, (it will be the big ones near each output) and what the poweramp input impedance is you want to use it with, and i’ll calculate at what low frequency it’s at -3db for you.
It’s a simple to correct if too small, with a $20 larger coupling cap, don’t go buying another preamp because of it.

2: Or you can go the other way and get the input impedance resistor (20cents) raised to 50kohm on the poweramp, if it’s fet input no problem, even a 100kohm

Cheers George

audioconnection
 George
Makes great sense here.
easy to have a tech make the resistor changes on the power amp
.sometimes I wonder if guys like Rowland and McCormick make amps input Imp so low that only their own preamps have an advantage even over great pre amps.

That’s more truth than fiction, we have a very good power amp maker here that has 1kohm input, and yes his preamp is 10ohms, so any other preamp sounds like **** into it but his doesn’t.
But the 1k input resistor on the amp is socketed and if removed the input becomes 68kohms, but he doesn’t advertise this, and any preamp/tube ss/or passive will drive it then.

Cheers George