Amp Camp Amp - ACA

Replacing LSK170 with Toshiba 2SK170 JFETs

Hello Everyone.

I wonder if any of the ACA builders have any experience replacing LSK170 with Toshiba 2SK170 JFETs.

Does it make a noticable difference in sound quality?

Also, does anyone know what grade of LSK170 comes with the ACA kit?
I am asking in reference to the Idss matching.

Any feedback would be very appreciated.
Thank you.

Kris
 
I energized my small room heater.

I finally built my kit! I am listening to it right now through my DH1A's. It sounds pretty good even without any burn in. Here is a photo of the first time I powered it up and set the Bias, Im super happy. :)
 

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So I've been spending some time listening to the ACA#1. Iv'e even swapped a few system components like op-amps and interconnects, but I just can't loose the fatiguing top end. The cymbals just wear me out after 10 minutes or so.
I am wondering what components I should try changing to calm the top end?
 
I am using 4 MyRef FE's (BOM spec with Russian K caps) with Marchand xm44 active crossovers . The DH1A is extremely efficient and has a reasonably flat frequency response with a 5000k/6db boost. I am very familiar with my system and have enjoyed it daily for over a year now, tweaking things here and there. I was hoping that a capacitor or resistor may be causing the slight fatiguing issue with the ACA#1.

Has anyone's else had any success with a compression driver and ACA?

At 6W it has huge potential with these extremely efficient speakers. I love how quite the noise floor is with this ACA#1. My loudest component is the toroids. :)

If the issue is not within the ACA#1 than it would be hidden by the Russin K capacitor rolling off the highs in the MyRef FE. Perhaps I should try replacing them with the Audyne Plus that I have collecting dust.

Bob, you have both of these amps. How are you finding the top end in comparison?
 
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Has anyone's else had any success with a compression driver and ACA?

Yes, I am using 4 x ACA's kits to drive 8 ohm Selenium D405 midrange and BMS 4540 high frequency compression drivers in a Digital XO tri-amp set up. The only mod is the higher bias. I am using Solen caps in series with the compression drivers for protection (turn off thumps).

I am impressed with the sound quality - highly detailed, yet smooth and sweet.

Have you applied the bias mod?
 
I agree the top end of the FE is brighter and more delicate than the ACA. However I attribute much of that to the Class A nature and Pass approach inherent in discrete amps. I'm convinced absolute direct comparisons can't be made between the two families. In both cases the amps designers had a "signature" in mind. I feel comfortable respecting both. Right now I'm listening to Rachmaninov Sym #2. on the FE betas. Very nice and dynamic, but know I would get more of a "concert" image with any of the Pass style set. Program material, system components and personal preference always seem to rule.

I'm also interested in hearing from ACA builders with VoM/Altec high efficiency speakers. I'm getting good (for me) SPL now with the new O2 pre on both the ACA and the F5, but I know that's a bit out of the standard combination. I was actually looking around the Google this weekend at the type of speakers you have - just from the efficience aspect.
 
I found a good comparison playing Hootie & the Blowfish - Time. With the MyRef the Tambourine sounds correct. The ACA#1 makes the Tambourine have a ringing effect.

I applied the bias mod when I assembled the kit and have not listened to it without.

I really like the sound of the ACA#1 and am looking forward to helping it evolve.

The big question is what can cause this kind of ringing effect in a Mosfet amplifier? Could it be the supply or just a simple capacitor type?