Thoughts on Audio Research D70

@Sbrown: Check VHAudio V-cap's web page on sizing coupling caps. The -3dB rolloff point is lower than audible. Plus there is hardly over 2 inches of traces from plate to grid for each coupling stage.

Also even in the 90s when I used to call Leonard at Audio Research to get suggestions on how to upgrade the Classic 120s he's recommend 0.47 or 0.68uF Infinicaps (Dynamicaps werent available yet) to replace the paralleled 1uF Rel 0.01 Wondercaps.

Larger caps were used in the 70s and 80s to add a thicker sonic signature to mask the mid high glare.

@Hifigeek1: Those huge lytics are Sprague and Mallory and hard to find in-stock @ Digikey or Allied. The cap plugs are impossible to buy in qty < 1000.

Thanks for the tip the V-cap's website. Do you think that the mid high glare you refer to is from the Rel/Wondercaps??

My experience with stock vintage Audio Research gear is that all of them distort/smears quite early with complex passages esp. chorale and loud piano chords.
I also have a problem with constantly trying to adjust the volume when listening to music. To low and I miss resolution, too loud and the glare is mighty annoying.
Not sure if the Relcap/Wondercaps are not aging well which contribute to that or not.

Everytime after I re-cap these amps with any new caps I often find they get more headroom before they start smearing and exhibit glare.

I have tried Infinicap, Dynamicap, Obligato, and Auricap on my previously owned Audio Research amps with varying levels of success. Each has their strengths and weaknesses. All of them, while better than the Rel/Wonder combo, still exhibit glare IMO.

My old Counterpoints (except for the NPs) all use Wondercap. All have benefitted from changing to oil or Teflon caps.

However, I have not tried the state of the art caps like Mundorf SGO or Vcap or even Jensens on my previous Audio Research Power amps ($$$, number of caps involved) like i have on other gear but based on my experience with the k40y9s on other gear and on this D115Mkii I am confident that this amp can even be further improved with the class AA+ caps. (Audio Research uses Teflon nowadays, wonder who makes them?)

Also regarding the size of the caps, look at what other manufacturers use these days for similar circuits. Very few of them use 1uF or larger anymore. Preamp output caps are a different story.

This is only the first step in modding this unit. I am still trying to find a way to install fast recovery diodes and am considering upgrading the high voltage bypass as well. Not now but later.

Johnsonwu,

Thanks for your input. I think the current ARC cap is the TRT Stealth cap. No outside reviews that I've been able to find. I do know that Aesthetix also uses these in their Eclipse series. From what I've read, I'm not sure these are teflon - they sound simular to the Clarity MR's if you read the write up. If you look closely at ARCDB for the Ref 110, there's a side photo that shows the gold & red Stealth cap with a small silver cap which looks to bypass the Stealth. I would venture a guess that the small silver cap is teflon.

Another interesting cap is the duelund Alexander's. In the smaller size range, they are not nearly as expensive as the teflon caps.