[aphex944]

After listening and comparing the amp for several hours last night, I'm not very satisfied. Even with the BJTs, it still has a strained character to it.

I used my Chesky "Ultimate Demonstration Disc" reference CD with my DT 880s. On a Sara K track, her voice was edgy, and the background noise was "wispy" and unnatural sounding. By far though the biggest issue is with the lower midrange. There is no body to the music, and this leaves a lot to be desired in drums, but especially voices.

It is finely detailed, and very quiet(black background), but it's just too unbalanced for my tastes. Compared directly to my MOSFET amp on the same source, there's more naturalness, and music seems to flow much easier than on the CK2III.

I'll be bringing this amp to the upcoming NC meet on the 23rd, so I'm very curious to see what everyone thinks(especially in comparison with my other amp). Eventually I plan on reinstalling the JFETs, and assembling the board completely to spec before putting it up for sale.

 

[MisterX]

Using the suggested BD139/BD140 output transistors?
If so I think you will like the MJE243/MJE253 better.

 

[cotdt]

What!? no wai man! the stock CKKIII build sounds not harsh and gritty at all. i think you must have gone wrong somewhere... what you hear must be very high levels of distortion, which means something is wrong.

 

[aphex944]

See above cotdt, we measured the amp using test equipment. Besides being thermally unstable and oscillating with a capacitive load, all was well. I'd like to clarify my use of the word "gritty." Perhaps it was the wrong adjective to use, but I was trying to convey that it is an edgy, dirty sound. Also, I did not find it to be bright or harsh, but simply strained. I think this is mainly due to the lack of body and presence in the lower midrange.

And to be honest, the sound is exactly what I've experienced with JFETs. Just last night some friends and I were playing around with my Music Hall CD25.2 player. We compared some BB JFET opamps with LME49710 & LM4562s and immediately noticed the dirty, unbalanced sound of the BB opamps. I'm not sure why, but that's been the track record so far

Quote:

Originally Posted by MisterX Using the suggested BD139/BD140 output transistors? If so I think you will like the MJE243/MJE253 better.

Hm.. I'll definitely look into it

 

[i has a can]

Choice of headphones may have played a part.

 

[LostOne.TR]

roughly how much does this amp cost in parts for the stock version?

 

[MisterX]

Very roughly $150.

http://www.amb.org/audio/ck2/

 

[majkel]

OPA275 has got hybrid JFET/BJT input, called Burton differential amplifier.

Regarding oscillations on the output - connect the heaphone jack channel pins to the amplifier via choke inductors, start from 2.2uH, it should work and have no impact on the sound (I've never realized any).