Writing up my Parasound comments, since it is so lengthy.
Stock – JC1 has a very refined sound, midrange is very smooth and refined. Emphasis is tilted slightly towards the upper midrange which causes the audio to sound just a little bit thin in the midbass area. Sound is soft. Overall, sound to me is just a little bit low fidelity. It’s very smooth and refined, but just doesn’t sing or have that effect of sounding real.
Main A/C fuse (on back panel) replaced with Furutech 15A – This significantly improved things. The attack and resolution is much better and tonal qualities are much more real. Instruments and vocals ring out with more truth. Sound is no longer tilted so much towards the upper mids and it is fuller sounding. The high frequencies are just a little bit jangly sounding (best I can describe), but overall a significant improvement. Bass is a significant improvement. It is still somewhat soft sounding.
All internal fuses replaced with Furutech (there are 6 fuses inside each JC1 that affect audio) – This is the best and most natural sounding result so far. There is no grain or jangly resonance heard in any of the frequencies. Bass is just absolutely amazing – oh my god! I cannot stress how much tight deep and strong bass you get with this particular configuration. It’s a serious “punch you in the chest” type of bass – hits really hard, but sounds natural and deep. Resolution and attack are still soft here. I think the soft attack also extends into some of the high frequencies as well.
In actuality, I discovered my Emotiva XPR-1 amps (also loaded with Furutech fuses) just beat the crap out of the JC1 with regards to resolution and detail. However, the Emotiva is not the cleanest sounding amp and I can definitely hear a slight element of grain in the sound.
So what’s really going on here? I think it’s a combination of things. I have listened very closely this weekend and I think the main thing I am hearing is that the Parasound amps have a very soft attack on midrange and early high frequencies. I believe this is mostly due to the Class A biasing. Even though JC1 is not a pure Class A amp, it is still Class A biased into 10 watts (at low bias setting). This is still enough Class A biasing to soften the attack on the midrange waveforms by smoothing out the response to the waveforms themselves. Class A circuits will tend to have a very gradual curved response when it receives a waveform spike on the input. This is less sensitive with analog preamp circuits, but when you are working with speaker level voltage, the response curve is much more gradual (based on slew rate response). This has a result of making angular waveforms (like a snare hit) more rounded or curved. Again, it depends on the engineering of the Class A circuit and how it responds to spikes on the input.
A comment on the high bias (25 watt) configuration of the JC1. The only time in my system that the 25 watt high bias Class A setting sounded good was with the stock fuses. The High Bias actually provided a more engaging sound. However, with Furutech fuses, it just made things too slow and mushy.
Another possible reason is my speakers, which are B&W 805 D3 diamonds. They are not a very fast responding speaker (they are actually hard to drive from an amp standpoint), but they are very natural sounding (the reason I went with them). So the combination of a neutral responding speed and the difficulty of pushing the drivers and magnet engines could contribute to the slow attack on the midrange and highs.
Finally, it can also be from having too many Class A stages. I have found through extensive testing with DAC/preamp stages that if you have too many Class A stages in a row, the sound becomes too slow and soft. So, my configuration:
HT Processor – Krell S1200U discrete Class A analog stage
JC1 – discrete JFET Class A input stage, MOSFET driver stage
JC1 – high biased Class A output stage
In my case, I think all of the above items contribute to a soft attack on the mids/highs. It does sound very nice and pleasant. Music is nice and pleasant (such as with a tube amp), but just doesn’t have that extra bit of attack and resolution to make things stand out. For home theater purposes, I just don’t have enough attack/detail to make movies exciting and engaging. It’s definitely not an optimum amp choice for my system.
I think the Parasound amps would work very well with speakers that are extremely fast responding and no decay. The Martin Logan panels are one example as they definitely have a tendency to sound bright/thin/harsh. They require the waveforms to be further smoothed so that it fills out the sound. Other speakers that might excel are the Monitor Audio Platinums (with the very fast ribbon tweeters) or maybe the Focals with their extremely light and fast responding midrange/woofers. Or add a JC1 if you have a very thin/bright sounding preamp/source.
@bigddesign3 – this could also be the reason that the Krell Class A works so well with your Martin Logan panels. If you read Whitecamaross’s amp thread, he states that the JC1 does everything right from top to bottom. Reading further, he found that the huge Pass Labs 200 watt full Class A monoblocks were the best sound he heard (though I am suspicious of his continued “this is the best” posts). He also was listening with high end Martin Logan Panels with those two amps.
