You mean C2? I just double checked and I have an incorrect value there, I misread 4.5nF for 450pF (actually qnty 3 x 152 caps). That would explain it.
Ok, I will install maybe a 330pF and redo the sound clips.
Well, being an order of magnitude off would explain the discrepancy for sure! You had the -3dB set at about 22kHz. If you thought the amp lacked anything on the high end then you definitely need to correct the input filter and retry. Even going down to 100pF would be fine, just not larger than the 470pF. Wouldn't want anyone getting the idea that those little amps weren't any good
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JK VSSA Sound Clips (330pF filter)
Ok, my bad. That's the nice thing about the measurement - it turns up stuff like that we would probably not catch from a listening test. I removed the offending incorrect caps and replaced with the usual 330pF 1kV blue ceramic caps that are the staple here for RF suppression.
So here is the new frequency response, more in line with the other amps, but appears to have a little more bite in the higher registers - some would call "highly resolving"?
Here is the corresponding measured harmonic distortion:
Here is the corresponding measured impulse and step response:
And below are the new sound clips. Note the "b" filename to distinguish from previous set of files.
Ok, my bad. That's the nice thing about the measurement - it turns up stuff like that we would probably not catch from a listening test. I removed the offending incorrect caps and replaced with the usual 330pF 1kV blue ceramic caps that are the staple here for RF suppression.
So here is the new frequency response, more in line with the other amps, but appears to have a little more bite in the higher registers - some would call "highly resolving"?
Here is the corresponding measured harmonic distortion:
Here is the corresponding measured impulse and step response:
And below are the new sound clips. Note the "b" filename to distinguish from previous set of files.
Attachments
XRK, man, do you ever sleep? Seems like every time I'm reading a thread here that looks interesting, you are doing most of the legwork on it! Wish I had that energy.
Haha, you are right! I don't sleep enough but promised myself that I will get some catch up sleep tonight.
Many thanks. After comparing with the reference, now I'm clear why I don't like listening to the quasi amp... It is way off...
For easy listening, the circlo-phone is the best, very musical and pitch-natural. It has less impact and dynamics than other amps but does not lack of it. The hexfet dynamics is the highest but exaggerated, not better.
The circlo-phone seems to have high noise (white noise). Cymbals or HF decay sounds like noise, not as natural as the Quasi. May be can be improved in the design.
I'm very interested in improving the circlo-phone amplifier. Any link to the schematic?
Jay,
Glad you found Circlophone interesting enough to look into further. It was king of amps until Valery's Vhex+ came along
you can get more info on the Circlophone (inverted JFET variant) in its own build thread. Note how you liked it but say it lacked the dynamics of hexFET? Well a new version is being built by me with hexFET outputs. I have one channel completed and other is dogging me and refuses to work. Piersma sent me another PCB to start from scratch for I fear one of the traces is broken and I don't know where. It's indeed a fine amp and I should record it and add it to the group here. Interesting to compare BJT vs hexFET outputs on same amp. The schematic is in the link below - but beware, it's the most topologically complex amp and I cannot wrap my head around how the circuit works. It's got no less than 18 actives (if I counted correctly) and is a quasi output but seems to have no Vbe multiplier for tempco. It already has a servo's sliding bias so maybe that's already taken care of by drivers that are mounted on heatsink. http://www.diyaudio.com/forums/solid-state/294338-inverted-j-fet-circlophone-builders-thread.html
Can you comment on sound of JK's VSSA in relation to others?
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Listened carefully to the soundclips by headphones and must come the conclusion that all amps used in this setup by XRK sound very good. With the headphones I used differences were really hard to detect. My preference: Valery's VHex amp.
Hi Piersma,
Wow - Valery will be glad to hear it - and thanks for being honest. It takes real gusto to admit someone else's baby is more beautiful than your own
But Jay seems to also have very high regard for your Circlophone. I do too - it's the only amp that I have two sets of besides my FH9 and FH9HV. So indeed it's a special amp.
Egra,
I might have mentioned this - but FAST 2 way with a full range cone for mid/tweet is not the best for complex music like symphonies. For that, I am building my new 3 way transient perfect speaker with B&O hole filler XO with a real soft dome tweeter. I could play and record some complex stuff on current speakers for you. Let's see what it sounds like.
I might have mentioned this - but FAST 2 way with a full range cone for mid/tweet is not the best for complex music like symphonies. For that, I am building my new 3 way transient perfect speaker with B&O hole filler XO with a real soft dome tweeter. I could play and record some complex stuff on current speakers for you. Let's see what it sounds like.
Ok, your choice:
Confutatis Islandsmoen Requiem
or
Britten Simple Symphony Opus 4?
or
Zimmer's The Might of Rome?
Is there a specific 45 sec passage you want me to concentrate on? I can't put all 6 amps through this as it's a lot of work but say Quasi, FH9, Vhex, FX8? Doesn't seem fair not to run all amps through this though.
Confutatis Islandsmoen Requiem
or
Britten Simple Symphony Opus 4?
or
Zimmer's The Might of Rome?
Is there a specific 45 sec passage you want me to concentrate on? I can't put all 6 amps through this as it's a lot of work but say Quasi, FH9, Vhex, FX8? Doesn't seem fair not to run all amps through this though.
After listening the circlophone quite long enough during work today, I was sure that I have never enjoyed class-B amp like that before, and I was sure that I wanted the amp...
Later after reading the first post of the link you gave (thanks) I found out that it is "semi class-A". Hmmm.....
It was king of amps until Valery's Vhex+ came along
For a low biased hexfet amp, the VHEX is indeed very good. But from what I heard, there is unnaturalness and I suspect that in the long run it might get less appreciation.
The dynamics of a hexfet came with a price. For me, it is okay having less dynamics (above minimum threshold), but the price]trade-off is usually not okay.
The circlo-phone has a CFP output. It seems to be a perfected design. I don't think it will be the same when a hexfet is used at the output. But I think I have heard some musical character of a JFET (and the noise character) in the sound clip. Who knows it would become a good match for the hexfet.
I only heard several minutes (for all the 3 clips) and didn't compare with the other amps in an ABX. But I could hear what I have heard before: (1) The highs is better, but the difference is not too important (2) I like the vocal very much (3) The low frequencies is "thin", otherwise it is an easy amp to listen to (4) The bass is typical, as if the damping is low. Sometimes I (and I think others too) wonder if it is what the bass is supposed to sound, but no, comparing with the reference, the bass should sound like the circlo-phone.
Jay, are you saying that because it is semi-class A you lose interest in it? FYI, it's quiescent current is only in the 200mA range - no where near the typical 1.5 to 2 amp (or more) range of of typical class A's. If you look at my photos, the typical small heatsink I use for 50w amps is perfectly sufficient.
I meant, no wonder I liked to listen to it in a long listening session. It is then less of a surprise... But BTW, if only 200mA, that's not "semi class-A"
I will build it but will not be fast... Need to redesign with different JFET... And PCB design...
200mA is the starting bias current - it's a sliding bias that is servo controlled, so I assume it may go up a bit higher depending on the need. I have no idea how that is accomplished.
I have some single can LSK389 that may work well for the inputs and can try out to see if makes a difference. Although, aren't 2SK170's one of the lowest noise transistors around? Originally designed for phono cartridge pickup preamps.
Piersma has PCBs available now - you can save some time by starting with that.
I have some single can LSK389 that may work well for the inputs and can try out to see if makes a difference. Although, aren't 2SK170's one of the lowest noise transistors around? Originally designed for phono cartridge pickup preamps.
Piersma has PCBs available now - you can save some time by starting with that.
Thank you X! I know the setup is very time-consuming so leave it for now. I can wait for the right time and more optimal conditions. Thanks again.
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