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Old 25th January 2014, 06:27 PM   #101
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Jason,

With VR2 in the orientation as in your photos, is max resistance fully clockwise or fully counterclockwise?
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Old 25th January 2014, 06:29 PM   #102
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Start fully clockwise (maximum resistance) and moving from there counter-clockwise will increase bias. It is counter intuitive and it is one thing I will consider revising.
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Old 25th January 2014, 07:12 PM   #103
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Quote:
Originally Posted by egra View Post
I think two questions arise about the ccs:

1. If we assume a really good PSU, does VSSA really need any kind of ccs to the optimal sonic performance? Shaan's answer is clear no. He used ccs in an experimental version of PeeCeeBee (not mentioned what type used) and the result described as "something strange" or "clinical" His opinion is that vssa sings perfect without ccs, and the music appears to be free of any limitation. Lazy Cat has totally opposite experience: the difference is like "day and night" benefit of ccs.

2. If yes it is not so clear to me, what is the correlation between the applied ccs and the sonic quality. Theoretically 2 Q's ccs is better than any other in respect of thermal stability, accuracy of FB, lower THD, etc.(see Rod Elliott's article e.g.) and very close the ideal constant current source though some builders found that bjt+led work better with this topology as ivanlukic mentioned above. How these collerate to the listening impressions. Has anyone experience with other type ccs, like TL431?

Thanks
egra
Hi egra

The question is who do you believe more.

1. My clear answer is the same as it was. There's not only one reason to go with CCS.

2. 2Q CCS is the worst among the others, again for more than one reason.

You're free to experiment, measure and listen, which is exactly what I did.
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Old 25th January 2014, 08:45 PM   #104
egra is offline egra  Hungary
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Hi Andrej!
Thank You for your answers. Finally I believe my ears of course, but the considerations of experienced designers are also important for me. Someone said that amplifier design isn't a rocket science, but seems it is more than engineering challenge, somewhere between art and science. I like the "avenue", where Jason is walking.

Cheers
egra
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Old 25th January 2014, 10:52 PM   #105
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Default Come on in! The water is fine...

OK folks, I just had a truly proper listen to my latest version of the VSSA and am quite pleased with it. I'd suggest that no one get stressed about the 2Q CCS, it sounds just fine. If a 1Q+LED CCS is truly superior then that can be left for a future revision. A pic attached of the stereo 'test rig'. It is just running on a CRC supply, not pictured.

For those with these boards my recommendation is just to build them to the published schematic that goes with this variant to ensure they work first shot. If you so desire, tweak them later. Hope to hear of a few more reaching their marks soon.
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Old 25th January 2014, 11:00 PM   #106
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If a 1Q+LED CCS is truly superior then that can be left for a future revision.
Jason, please do not understand me wrong, I never said 1Q+LED CCS is good, because it is not, especially for this purpose. VSSA and specifically First One has very different type of CCS.

Congratulations on a nice build. We should spread VSSA worldwide and promote this simple CFA wherever is possible.
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Old 25th January 2014, 11:12 PM   #107
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Looks good Jason. I'm just waiting on some caps and trimmers and mine will be done. Mounted them on a heatsink today. Looking forward to the listening test. In honor of this build I listened to both VSSA's today, yours and Pete's. They are virtuously identical in sound. They are both powered by identical power supplies. I'm planning to power this with a Connex SMPS to see if I can hear a difference. Can't wait.

Blessings, Terry
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Old 25th January 2014, 11:21 PM   #108
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Quote:
Originally Posted by Lazy Cat View Post
Jason, please do not understand me wrong, I never said 1Q+LED CCS is good, because it is not, especially for this purpose. VSSA and specifically First One has very different type of CCS.

Congratulations on a nice build. We should spread VSSA worldwide and promote this simple CFA wherever is possible.
Thanks LC.

I was not suggesting you said to use a specific CCS type, but others did. I simply chose what I thought would serve the purpose and be based on BJTs. I have little experience with JFETs as some like to use, so I tend to avoid them. And no, lack of experience isn't a valid reason the steer clear of FETs. Of the basic BJT CCS types the 2Q seemed to fit the bill so there it is.

Care to give a peek at what you feel is the most suitable CCS for the VSSA, assuming it isn't secret IP?
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Old 25th January 2014, 11:25 PM   #109
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Quote:
Originally Posted by still4given View Post
Looks good Jason. I'm just waiting on some caps and trimmers and mine will be done. Mounted them on a heatsink today. Looking forward to the listening test. In honor of this build I listened to both VSSA's today, yours and Pete's. They are virtuously identical in sound. They are both powered by identical power supplies. I'm planning to power this with a Connex SMPS to see if I can hear a difference. Can't wait.

Blessings, Terry
How did you find working with these boards? They seem to solder up nice and don't seem overly tight to me. I'll assume you got everything lined up fairly easily. Just looking even for some basic feedback on ease of construction for now.
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Old 25th January 2014, 11:57 PM   #110
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I think they are nice. The only thing I thought might be better would be larger solder pads for the FASTON connectors. Why is your input cap so big? Most of the other versions used a smallish electro.
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