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

Showing 5 responses by dsper

Hi All,

Thanks for the responses.

I have a CJ 17LS2 that bumps up close to the 10X rule with the DNA-500 and I can hear the LF rolloff compared to other preamps.

Knowing that AR really wants 20K, I will look elsewhere.

Dsper




Well now.

I like the sound of the CJ pre except for the slight LF rolloff due to the impedance issue.

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

Or look into the ET5 which has a lower out impedance. 

Thanks for listening,

Dsper
georgehifi,

"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."

georgehifi, You certainly have given me some discussion points with CJ and what is possible to accomplish. Thank you!

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?

Or could this possibly change/degrade the overall sound of the preamp?

I assume my last question may illustrate how little I know about this technical stuff so any additional comments would be greatly appreciated!

Thanks for listening,

Dsper
Atmosphere,

" But obviously the Aesthetix faces the same issue of what is the lowest impedance it can actually drive actually; this information does not show up in their specs or operating manual."

I do not understand technically why a particular preamp may have a greater capability to drive a low impedance amplifier.

While, I try to follow these types of discussions, something basic is lacking in my current understanding as well as how it impacts how it sounds..

Could you perhaps elaborate further or direct me to another thread where I am sure that this has been covered before?

Thanks for listening!

Dsper
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