Hi all,
Thanks for being so patient, this "quick test" turned into a bit of a marathon. Here are the results of my testing over the last few weeks.
Firstly, a description of the test equipment and set-up:
1. The split GK-1 boards were removed from their case as there wasn't enough room in the original case for experiments.
2. 2 x 6VA 15-0-15 potted transformers were used, which gave a slightly lower quality power supply than the usual GK-1 transformers.
3. Only the Solid-State section of the GK-1 was used for the test, output was taken to LF55s via a stepped attenuator with Vishays, later upgraded to TKD Stepped attenuator (tests were re-run after installation).
4. A daughter board was added above the GK-1 boards to hold the Caps on test and 2 multi-way switches to easily select which caps were in circuit.
5. C7 options:
a. Oscon SP 47uF + 0.22uF Evox SMR Bypass - The best I've heard until these tests
b. Wima MKS2-XL 22uF
c. Sonicap GenI 20uF + Sonicap GenII + 0.47uF Bypass
d. Solen 20uF 250V
e. Relcap AudioCap 40uF PPMF
6. C4 Options:
a. Black Gate N 47uF - The best I've heard until these tests
b. Wima MKS2-XL 22uF
c. Solen 20uF 250V
d. Sonicap GenI 20uF
e. Relcap AudioCap 40uF PPMF
7. T4 Options:
a. BC557 - Original
b. BC560 - Low noise replacement
8. T1+T2 Options:
a. BC557 - Original
b. BC560 - Low noise replacements
9. The last 3 caps were chosen for their physical size, as most people won't have loads of room in their GK-1 cases for anything much bigger than these.
The results:
I've based the Cap results on a standard score of 50%, which is the benchmark using the Oscons/Black Gates.
1. Wima MKS2-XL 22uF
Moving from the Oscon / Black Gates to the Wimas gave a useful improvement in detail and high frequencies, but these caps only gave around half the improvement to the soundstage of the physically bigger caps. 60%
2. Solen Fastcap 20uF 250V
Natural sounding mid-range, nice treble, accurate bass with punch. The soundstage really opened out with these. 75%
3. Sonicap GenI 20uF
With or witout bypass, the Sonicap was not a success at C7. It lost out on the start/stop of bass notes to the Solens, but still bests the Wimas. 70%
At C4 however, the Sonicap was marginally better than the Solens. There was slightly more high-frequency detail apparent. 78%
4. AudioCap PPMF 40uF
These caps extended the bass by easily half an octave or more. Maybe it was the value of 40uF, or maybe the construction. Sounded "right" and balanced from the word go. Alot like the solens, only a little bit more of everything: Sweeter treble, slightly more open mid-range, extended bass. Soundstage was as good if not slightly better than the Solens. 85%
One caveat with these: The Aksonic speakers I'm using in my system do not have the bass response of the V-Sonics which will replace them. There is the possibility of too much of a good thing here giving a hump in the bass response, in which case I'd go for the 40uF AudioCap at C7 and the 20uF Solen at C4.
5. Changing T4 from BC557 to BC560
There was a distinct lowering of noise by around 25% at full volume with shorted inputs when this transistor was swapped out. I couldn't detect any drawbacks in the sound. Worth doing.
6. Changing T1 and T2 from BC557 to BC560 (Matched)
I couldn't detect any improvement in noise performance with this change, but there was a slight "Mechanical" tinge to the sound with these in place. I was not able to source the same make of transistor that Hugh uses for these. Perhaps this is the reason for the slight degradation in the sound. For the record I used Fairchild transistors, maybe the On-semi version would be better?
Cheers,
Ron.
