Thoughts on Audio Research D70

Johnsonwu, i am following this thread with interest. I have has several ARC amps and preamps modded by GNSC )Steve Huntley) over the last 10 years.

I still own a pair of Classic 120's which i hope to put head to head with a REF150 soon. I also have a REF3 LE and REF Phono 2 both modded by Steve.

The only thing that Steve did not replace in the critical signal path are the interstage coupling caps (4 in each unit). He felt that the stock caps were good enough and need not be replaced. What ARC use in their SE upgrades for the REF5 and REF2's are teflon 150 vdc 10.0uf =/- 10%.
What similar caps would you recommend as replacement (Vcaps?). I doubt that ARC would release those proprietary caps for installation in the field. Any recommendations much appreciated. Thanks again.

@Smoffat: The reason why I sold my CL120 (and CL150 of course) was the solid state input and gain stages.
I believe in the Counterpoint (Michael Elliot) philosophy of getting the small signal stage as tubey and transparent as possible and use whatever as the output stage as it has the least influence to the sound.

The 10uF caps had to be output caps (from pre to power) or from phono to pre. Upgrading those to any exotic brand like Duelund or Mundorf or VCap would be cost/size prohibitive.

The coupling caps within each device had to be 2uF or under I imagine. But until I get to see the schematic I cant comment.

Anyway, upgrading the small signal coupling caps would have a more noticeable benefit than the output caps.

JohnsonWu, I just don't agree with your assessment of the sound that the older ARC amps exhibit. My D70Mk2 has wowed all of the a'phile group that has heard it in my system. So much so, that one of the group traded a BAT VK75SE for a pair of M100's ( with the same wonder caps) and never looked back after he heard my ARC/CAT set up.
I'm sure you are aware that ceramic tweeters will exhibit glare and hardness with aplomb. The same can be said, to a slightly lesser extent, for the beryllium tweeters in your Utopia's. A hard dome can be bright and exhibit glare IF any of the upstream components are at all bright...speaker cables, preamp, front end, amp etc.
I believe and i think many others are beginning to believe also, that a silk dome or a ribbon is far less likely to exhibit this behavior than a hard ceramic or metal dome. Which, if I'm not mistaken is one of the reasons that Dave Wilson chose a silk dome for his top of the line speaker, the Alexandria XLF. I guess when it comes to this discussion, YMMV.

@DaveyF: It's AOK... to each his own.

I am writing this echoing my opinion which concur with that of many others, esp on the more DIY oriented forums.
Perhaps too many people who posted similar opinions have metal dome or ribbon tweeters that need some balance.

BTW I didnt come up with the idea of replacing the Rel+Wonder combo with Inifinicaps. It was a suggestion by none other than Leonard @ Audio Research.

I have some 1mfd@600V teflon caps if you are interested...