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Question About Audio Research Preamp Specs

Hi,

I am trying to understand Audio Research terminology while looking at their product specs.

For example, for the LS28 OUTPUT IMPEDANCE, it reads "600 ohms Balanced, 300 ohms SE Main (2), 20K ohms minimum load and 2000pF maximum capacitance..."

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

I am running a McCormack DNA-500 and it has an input impedance of 10K Ohms. It would seem that the amp would be compatible with this preamp based on the 10X/15X minimum rule of thumb. 

My concern is that the AR spec is telling me use amps with input impedance of 20K ohms and the DNA would not work well.

Thanks for listening,

Dsper
dsper
dsper OP
663 posts
 
Hi All,

For those that might care, I followed up with Conrad Johnson regarding adjusting the output capacitors in my 17LS2 preamp. 

The technical person I spoke to understood immediately what I was requesting. Unfortunately, they explained that there is no room under the hood to replace the existing capacitors with larger ones.

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

I took a look myself and it would seem to my unpracticed eye that there is no space. The inside is chock full of large white "CJ" capacitors already!

In the meantime, I will explore different 6922 tubes that might help to mask the LF roll-off. Not sure if that makes any sense...

Otherwise, it seems like I may want to replace the 17LS2.

Thanks for listening,

Dsper
georgehifi's avatar
georgehifi
10,312 posts
 
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
atmasphere's avatar
atmasphere
11,804 posts
 
@dsper 

In the meantime, I will explore different 6922 tubes that might help to mask the LF roll-off. Not sure if that makes any sense...
It doesn't. Changing the tube won't affect the frequency response.


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