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In Reply to: RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS posted by drlowmu on March 30, 2015 at 19:29:11
I built Sun 2a3 kit for my friend years ago substituting 2a3 with VT52 which he had in his tube stash. It was my first encounter with VT52 and it's a truly lovely tube. For whatever reason , (actually ever since I owned once Audio Note Quests ) I like plain vanilla 6SN7 cascade driver.I heard many supposedly more refined , better designs but still fond of that "pedestrian" design .
Here is what Zoran from Belgrade wrote regarding SUN 2A3 amp (courtesy of Diyaudio.com , and I hope he doesn't mind"..
..."sorry but that from sun audio is not good at all
first, the value of pot 100k is too high for the 6sn7
right value if pot required is 25K...
next the values of Rload at anodes of 6sn7
are too high value.
The load line will be almost horizontal.
and the drop of voltage is probably large,
so the resulting Va will bi lower voltage,
against higher voltage that
should be like Va when we talk about the 6sn7...
next, the device will have more than sufficiant gain,
like common fassion in that design, so the pot most
of the time will be at lower positions causing loss of highs.
*
that is from the first sight cheers"...
Follow Ups:
The 25k volume pot is a good idea IFF the linestage is capable. As you have seen once or twice, the linestage job is to grab the amp, and feed it signal no matter what silliness happens with the wire, or solder, or rca jacks...such a linestage makes it rather difficult to pick out the 'good' patch cords...LOL
At one point I dropped the input grid resistors in my 1619 E-Linear amp to 10k...it was entertaining to use it for linestage comparisons. Only a truly meaty one had the stones to drive it.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
My dear friend,I would NOT pay much attention to what "Zorin from Belgrade" wrote at all!! Whos he, what are his qualifications ? A 25K pot on the input will short out the signal to ground, destroying what micro-detailing the amp has. Heck, I'd like the 100K to become 250K !!
I would trust NOT what you read, but TRUST what you personally HEARD and said you liked about the SUN 2A3 amp.
Changing to a VT-52 is ONLY hearing the difference between tubes !!
Its like a pretty gal changing from a brunette hair coloring to a bleached blond, while all along, she is a hunchback.
The amp itself only requires the two mods I suggest, to immediately gain about 25% in performance improvement, fun, and all-around listenability .
Its truly a Fool's Game to be listening to 2A3s with a high DCR choke and a ringing ( .47 uF. / . L . / .47 uF. ) B+ supply.
I have not had a chance yet to be given the extra measurements I need, but above PSUD 2 simulation is just a guess - judging on the posted 10 VDC drop across the schematic's stock B+ Finals filter.
Imagine how it will play music, when the dreaded and unwanted series resistances in the B+ Finals filter gets comprehensively and thoughtfully reduced by a factor of TEN, and the 2A3 tube's dissipation gets optimized.
There are many many things anyone can "change" inside an amp, but understanding the one or two most important things to optimize, IS a horse of a different color. Fun.
Jeff Medwin
Edits: 03/31/15 03/31/15 03/31/15
Why do your models assume insufficient inductance in the output transformer?Or are you simulating for grid current? (an AX7/SN7 couldn't cope with that anyway)
Edits: 03/31/15
Goodness, CB,
What in THIS world are you talking about??
PSUD2 has no output transformer function I know of. Its for power supply filters !!!
I addressed the two things that need fixing the most - to run a 2A3.
Jeff Medwin
Thank you, you proved my point.
In plain English, WHAT point are you trying to make ??
Explain what you are trying to communicate to ALL of us, very clearly, so we ALL on this Forum can understand you.
No riddles please, we have others who do that !! How well can you communicate with your fellow human beings?
Thanks,
Jeff Medwin
I think what he is trying to say, or ask you to think about is what is average constant current draw of class A amp, and what is the job of inductance versus what you modeled.
Thank you, very much, for responding in a clear and concise way.
Very good. Keep it up.
Jeff Medwin
I think, ( am not sure ) that C.B's point, has very little to do with my overall goal - of changing the SUN SV 2A3 to easily play music better-than-stock.In the end, "we all listen to a modulated power supply". How good is the stock SUN supply ?? Mediocre. It BEGS for "help" IMHO, to get the most from the 2A3 - and one's listening experience with any SUN amp.
NOTE : If someone who has a SUN SV 2A3 amp can contact me, I can detail about four things that need to be easily measured, and complete this documentation/project to help others.
Jeff Medwin
Edits: 04/01/15 04/01/15 04/01/15
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