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SUN SV 2A3 stereo SE amp .... MEASUREMENTS

76.4.177.203

Posted on March 30, 2015 at 14:49:09
drlowmu
Manufacturer

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Location: East of Kansas City
Joined: January 10, 2005
Hi,

I've recently worked from the schematics (on-line) of this cute amp, and developed two simple but seemingly-effective, conservative, circuit changes, that should equate to worthwhile performance improvements.

Is there anyone willing to make some voltage measurements of their amp, or even send it to me, so I can be sure I am modeling / simulating it all precisely, and not just depend on SUN's "limited-information" schematic.

I'd be happy to share my results, and give anyone who helps a preference on what I've developed and document. If you measure your amp at home, (which I would prefer), you (1) must have a multimeter and know how to measure Ohms, DC and AC volts and (2) know how to SAFELY measure below deck, amp ON, and not hurt yourself !

My email address is above.

'Have NO idea how many SV 2A3 SE'ers are out there. Its not a bad design to start with, BUT, two obvious areas just "BEG" for a reconfigure, to play better.

Jeff Medwin

 

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RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on March 30, 2015 at 18:15:26
Chip647
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I hope it is not converting it to a direct coupled single stage 12AX7.

Can you simply point to your insights on the above schematic?

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on March 30, 2015 at 19:29:11
drlowmu
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Location: East of Kansas City
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Hi Chip,

You obviously have never even HEARD the circuit you disparage, properly executed - that's OK, I forgive you.

NO, you can not Direct Couple the SUN amp with 290-0-290 VAC as the high voltage secondary. I ain't a one-trick pony either.

---------------------------------------------

So, you wanna pick my brain. Fine !

What that SUN SV 2A3 stereo amp DEARLY needs is - TWO things :

(1) A better power supply B+ filter, on several "levels" :

Change the stock B+ filter from a "super crude" C/L/C filter, ( with a NASTY "C" 47 uF ( ooochh, phooey ) ringing input filter and its stock L ( FAR too HIGH in DCR for a 2A3 ).

The SUN needs to use a refined-sounding L1/C1/L2/C2 B+ filter with modern film Cs and two Ls, both Ls small ( under 2 pounds). Ls each measuring under 10 Ohms in DCR... " ultra high fidelity ".

(2) The 2A3 is likely running stock at close to 100% of its 15 Watts plate dissipation, 250 VDC P-K at 60 ( too high ) milliamperes.

Use a more conservative 2A3 plate dissipation, closer to a "Golden Ratio" 62% proportion, The 2A3 will no longer be thermally stressed, and sound stressed. (As always IS the case, the way 90% of the people mis-run 2A3s.)

Hell, number (2)'s easy, changing the stock amp's self bias Rks to two Mills MRA-12s, in each channel.

With a SUN SV 2A3 however, both number (1) and (2) need to be done in conjunction with each other, to get within 5% of the new "optimized" B+ op points. I have figured out HOW to reasonably do that, as the result of many simulations.

Other than the above two changes, the rest of the amp is fine, "for a three stage amp". I have conservatively worked this modification out over the last few weeks. Just need to double check with someone - what the stock SUN amp measures, in four or five places at idle.

Jeff Medwin

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on March 30, 2015 at 23:11:14
Caucasian Blackplate
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No, he's going to convert it to nearly class B SET, probably raise the gain by using half a 6SL7 to drive each 2A3, and generally make it perform worse.

I just hope he does it to his own SV-2A3, and not someone else's.

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on March 31, 2015 at 05:56:06
Wojciech
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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"...

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on March 31, 2015 at 07:17:42
drlowmu
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Location: East of Kansas City
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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

 

RE: sell the Sun 2A3 amps ..., posted on March 31, 2015 at 08:05:26
deathtube 667
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Keep the Sun 2A3 stock and sell it on Ebay.

Use the money to build something that will perform closer to DF's standards if that is your goal.

BTW, what happened to the SS 2A3 clone project you were working on?

 

No No ....., posted on March 31, 2015 at 09:17:46
drlowmu
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Nope. Thats not my goal.

This exercise is to help others, who own and regularly use the SUN .

No one can possibly ever clone a Serious Stereo 2A3 !!

The DC 2A3 amp (for my use), using MOSTLY Dennis' ideas, takes time and lotsa $$$ . Relax some sir.

Jeff

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on March 31, 2015 at 10:16:58
Caucasian Blackplate
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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)

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on March 31, 2015 at 10:24:16
drlowmu
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Location: East of Kansas City
Joined: January 10, 2005
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

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on March 31, 2015 at 10:40:10
Caucasian Blackplate
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Thank you, you proved my point.

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on March 31, 2015 at 14:05:27
drlowmu
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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

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on March 31, 2015 at 15:10:58
elblanco
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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.

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 1, 2015 at 07:43:39
FenderLover
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" Use a more conservative 2A3 plate dissipation, closer to a "Golden Ratio" 62% proportion. "

Sorry, kinda new at these SET amps. How do you get a single-ended amp's output tube to run at 62%?

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 1, 2015 at 09:08:13
drlowmu
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First, you figure out what 62% is, in terms of Watts of plate dissipation. Maximum dissipation of a 2A3 plate is 15 Watts. Sixty two percent is 9.3 Watts of continuous dissipation.

I envision tubes as "voltage swing" devices, so I maintain the usual voltage, typically 250 VDC P-K, and REDUCE THE CURRENT draw such that voltage times current equals "about" 9.3 Watts. 9.3 Watts divided by 250 VDC is 0.0372 A., or 37.2 mA.

In actual practice, audio people I trust the most ( Dennis Fraker and Jac of Jac Music) privately say that their favorite 2A3 op point is 42 or 43 mA. at 250 P-K , or 10.5 to 10.75 Watts plate dissipation, so THAT is what "I" will shoot for in my amps.

The 2A3 WILL sound more relaxed, less stressed sounding, BETTER, at this "loaf mode" op point, unless your amp is so poorly designed with a typical crummy power supply , and insufficient wiring ( transfer efficiency in both cases) such that you need to HOTROD the tube to get the amp to play effortlessly and "dynamically".

The difference in lifespan of a 2A3 run at maximum dissipation ( 250 VDC P-K at 60 mA.) and at 42 mA. might be 10,000 hours at 60 mA. versus PERHAPS 50,000 hours useful life at 42 mA.

So, the wonderful thing is, IF the amp is well executed, the 2A3 lasts five times longer and SOUNDS BETTER at 42 mA. all the while !! That is smart audio design, conservative. You can easily justify to yourself to buy the better sounding and better made 2A3s, like the current EMLs, and be ahead in TWO ways, quality of musical performance and far longer lifespan.

For a Type 45, I'd use ABOUT 250 VDC P-K and about 27 mA., where 25 mA. equals 62.5 percent of 10 Watts maximum rated dissipation.

The Golden Ratio is just a CONCEPT that applies to design, and many many other things in our lives. Hope this helps. Have fun. I sure do !!

Jeff Medwin

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 1, 2015 at 09:35:04
FenderLover
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So the amp is running in Class "A" at 62% max dissipation?

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 1, 2015 at 09:52:46
drlowmu
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Hi,

I don't know the Class designation for sure.

I have asked EE Paul Joppa, a educated guy, above in this thread, lets see where that goes !!

I am not sure it matters. Because ................

What does matter is that I run the tubes where they sound the best, less thermally STRESSED SOUNDING, and they have long life.

Jeff Medwin

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 1, 2015 at 10:01:07
drlowmu
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Thank you, very much, for responding in a clear and concise way.

Very good. Keep it up.

Jeff Medwin

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 1, 2015 at 10:05:20
drlowmu
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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

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 1, 2015 at 10:58:33
elblanco
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Do you have a load line drawn for this op point?

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 1, 2015 at 17:02:25
Caucasian Blackplate
Industry Professional

Posts: 6675
Location: Seattle
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That might be too technical for Jeff. (The middle red dot is the quiescent operating point)

Making these changes, you can expect less power and higher THD. I'd expect just over a Watt RMS before things fall apart. Jeff likes to talk about overload recovery, but when you stress an amp like this (which will happen on GPA-604's), you will drive the amp to the point where the 2A3 will be off on one side of the waveform.

Heading in this direction brings you to class B amplification, which is useless without some feedback to keep the distortion under control at useful power.

(yes, I have heard these amps)

 

he's on the right path...., posted on April 1, 2015 at 17:26:09
PakProtector
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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.

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 1, 2015 at 18:17:07
elblanco
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Yes. I plotted it earlier and things got wierd. I dont own a curves stretcher.

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 1, 2015 at 18:51:24
drlowmu
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CB,

(1) "That might be too technical for Jeff."

YOU asked for it !!!!!

FYI, I mastered graphic load line analysis in 1982, taught by the late Bob Goodman of Texas. .............Were you even born then ??

(2) You don't like "competition" I can see. That is OK. I understand.

(3) Your own graph is laughable - INCORRECT in two or three ways :

(a) You don't know the STARTING B+ level, because you don't KNOW what FILTER I am using and its effect upon B+ ( VDC level ) on the 2A3's plate.

(b) Nor do you know how much the power transformer will unload, raising B+, with my unknown but lower current load.

(c) You don't know what op point I decided to use, as a best compromise in this amplifier.

(d) The 2A3 quiescent point you have denoted is well above 50 mA. and is of course, totally WRONG.

If you were intelligent, you would NOT have drawn that and then quoted textbook baloney as to distortion and swing, that even a well trained parrot could recite.

Well, maybe you can do better the next time you RUSH to attempt to discredit me C.B. You will have to THINK before you post though.

What does the "P" after your moniker stand for...Industry Professional. OMG. Save us amateur DIYers !!

Until someone offers to make a few measurements on a SV 2A3, I am done with this thread totally - and outta here.

Bye all !!! Have fun.

Jeff Medwin


 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 1, 2015 at 19:43:16
Caucasian Blackplate
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Since you were too lazy to read my post, which indicated that the center dot was the quiescent operating point, I've added a blue box to help you.

You suggested to Fenderlover an operating point of 37ma/250V. I drew the load line assuming a 2.5K output transformer.

B+ is irrelevant with respect to the operating point. The same operating point could have a B+ of 600V or 275V.

It is easy enough to look at the load line and tell when the tube stops conducting. There's no negative axis for current for a reason...

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 1, 2015 at 19:45:42
Caucasian Blackplate
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Yeah, when you look at what's actually going on in this "de-stressed" 2A3 amplifier, lack of stress isn't actually an inaccurate way of describing things. When you push the output stage, the 2A3 just shuts off for part of the waveform, and gets to take a little break during playback.

Most of us who build single ended amps consider this bad design (or maybe just sloppy design). It isn't that hard to imagine one or two people out there who really like the sound of that much asymmetrical THD.

 

whoa!..what just happened, posted on April 2, 2015 at 06:17:49
elblanco
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Walk us through it , please.

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 2, 2015 at 10:42:50
I believe the whole idea is to give the amplifier a certain 'flavour' . Not only does the inadequately filtered , higher impedence supply give it's own heavy footprint but also the driver . The driver usually being a flimsy device with inadequate current to drive the output stage anywhere near 0 grid volts so the asymmetric clipping not that much of an 'issue' . You get the bandwidth back with the wiring , or so I'm told...

Tons of distortion , rolled off due to the driver and much lower power . May as well use a type 45/4P1L and a higher ratio OPTX IMO for the same output power . If people like the sound of such amplifiers , good on them but I usually prefer in the amplifier as a whole , the output transformer to be the limiting factor

Al

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 2, 2015 at 11:08:49
drlowmu
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Hiah Al,

See this, he is LOCAL to you. Visit him one day.

His first build ever !!

Jeff Medwin

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 2, 2015 at 13:57:08
Not local at all , it's a nasty 40 mile drive to the other side of town through some of the worst traffic you could possibly imagine . That amp you mention uses a 5k optx strapped on the 8 ohm tap with 16 ohm speakers , if I remember correctly . So his loading is totally different to what you advocate and he also has an active sub for bass .

Al

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 2, 2015 at 14:22:51
drlowmu
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Excuses, excuses, excuses Al.

Jeff

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 2, 2015 at 16:04:05
Have you heard this amp ?

Al

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 2, 2015 at 17:15:17
drlowmu
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No, but I designed it for him. He is more than 40 miles travel distance for me Al.

His FIRST audio build, which I think is unusual and interesting as a DIY start place !!

Nice guy, awfully nice person.

Jeff Medwin

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 2, 2015 at 18:49:52
Paul Joppa
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I did not locate Jeff's question to me, but having been invited here I'll take this opportunity to give my thoughts. (I'm an engineer, but not specifically electrical - worked mostly in acoustical engineering FWIW.)

At the operating point mentioned in this thread and shown in the curves provided by Caucasian Blackplate (250v/37mA/2500 ohms) the tube is operating at about 11% second harmonic distortion. As long as the reflected speaker impedance is greater than the nominal, distortion may be high but technically it is Class A - the tube is never cut off. But it is at the edge - if the impedance of the speaker dips below nominal (they all do!) then the operation will be Class AB, with the tube cut off for a portion of the cycle but less than 50% of the cycle.

The interesting thing to me is that the output power is 2.9 watts at the edge of grid current, whereas if it were really linear then 37mA would produce at most 1.7 watts. In addition to the extra power, the high second harmonic gives a psychoacoustic effect of greater loudness, often described as "more dynamic". The price paid is masking of the music by the distortion products. With enough distortion at full power, the distortion of real overload clipping is probably less obvious.

The average current at full power is nearly 50mA, 35% more than the 37mA at no signal. This is a reasonable explanation of the need for a tightly regulated and fast power supply - to control envelope modulation. Rapid power supply recovery is much less important when the tube is operated as RCA suggests, where the variation of average current is less than 10%.

At smaller signals, the distortion can be reduced by using a driver stage with similarly high levels of second harmonic, which is what you will get from a notoriously nonlinear tube like the 12AX7, with a resistor plate load. Of course, this distortion cancellation actually increases the higher harmonic distortion products.

Using direct coupling eliminates blocking from grid current into the coupling capacitor, but blocking from the cathode bypass capacitor is still present, and is increased by the large variation in average current. Balancing the blocking against the power supply regulation is a complex challenge, since the time scales are psychoacoustically important as well.

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 3, 2015 at 07:59:22
drlowmu
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Hi Paul,

You show a fine understanding of electronics and you write clearly. I respect that, and do not have that attribute.

The 37 mA. at 250 VDC P-K ( 9.3 Watts dissipation) was simply the Golden Ratio ( 62% ) of 15 Watts, with 15 Watts being the maximum 2A3 plate dissipation rating. I mentioned that low current number to Fender Lover only as an example, but it is NOT at all what I have ever used.

Caucasion Blackplate, in his rush to try to discredit me ANY way he can, seized upon the "lowest" number mentioned, ( and inadvertently perhaps,... so have YOU ! ) without figuring-out what I really liked to employ.

The favored op point of mine was in my description to Fender Lover. In practice, I typically will use 42 mA. on a 2A3, when given free reign to pick the spot.

At 250 VDC P-K, 42 mA. is 10.5 Watts of plate dissipation, or 70 percent of maximum. It is dissipating 8% over the Golden Ratio of 62%. It certainly is NOT operating at 95 to 100% of maximum ( 60 mA. times 250 is 15 Watts, 100% ). The stock SUN SV 2A3, and MOST 2A3 amps running 60 mA. and 250 VDC P-K exhibit a negative-to-my-ear STRESSED SOUND trait, due to thermal issues.

The other thing, ( which I think is totally hilarious ), is that you and Caucasion Blackplate, and MOST other EEs TOTALLY FAIL to ever consider in your analysis is this :

WHERE does the tube operate, on its load line, 90% or more ( 99% ?? ) of the time??

At RMAF shows, LOUDLY playing demanding music (Symphonic Orchestra with Organ), we may reach 3/4s of one Watt. In my home's listening room, ditto, 1/4 of a Watt to 3/4s of a Watt.

CB's graphical load line analysis, and your analysis, is quoting distortion figures at FULL SWING and maximum possible power.

THAT is what BOTH of your analysis' is "all about". Max swing.

I question you two guys, and you TRADITIONAL way of "looking" at audio design. Almost ALL of the time, I am swinging at LESS than full power out, in the linear mid-point on the load line, and at LOW distortion.... BUT..... 42 mA. does NOT sonically exhibit the thermally-stressed "thumbprint" of a 60 mA. bias.

Simply put, my load line SOUNDS NICER, more RELAXED, at normal listening levels we would employ.

If everyone else wants to conventionally design and listen to 2A3 amps with a STRESSED presentation, and burn up the output tubes doing so, so be it. I just simply LAUGH at that !!!

I also must seriously question your impartiality when you describe a 12AX7 as being a non linear tube. If one looks at the characteristic curves, it certainly looks MOST linear to me! Furthermore, it has a RICH proven history of being used in audio devices with State of the Art performance level, for decades in our lifetimes. Think of the ARC SP-3 and SP3A-1, when we were younger, or the highly regarded ARC SP-8.

Now Paul, ALL OF THE ABOVE, ....ALL OF IT...., is just hypothetical engineering gobble-de-gook to me !!!

The proof of the pudding is in the eating. I live in Missouri Paul, the "Show Me" state. "Don't tell me about the pregnancy, just SHOW ME the baby".

Are you coming this year to RMAF 2015, October 2-4 ? If so, look me up and you can HEAR precisely what I am talking about !! Its superb, and beautifully honest to the recorded music. If it sounds good, and is reliable, it IS good !!

Regards and best wishes,

Jeff Medwin , DIY audio amateur .... mostly

 

De gustibus non est disputandum (nt), posted on April 3, 2015 at 10:24:39
Paul Joppa
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nt

 

RE: De gustibus non est disputandum (nt), posted on April 3, 2015 at 10:39:49
drlowmu
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From Wikipedia, the free encyclopedia

De gustibus non est disputandum is a Latin maxim meaning "In matters of taste, there can be no disputes" (literally "about tastes, it must not be disputed/discussed").[1][2] The implication is that everyone's personal preferences are merely subjective opinions that cannot be right or wrong, so they should never be argued about as if they were.

 

RE: De gustibus non est disputandum (nt), posted on April 3, 2015 at 10:41:24
Tre'
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I just posted this to dadbar in a thread below.

dadbar had said,

"The point I was making is that I don't really care about what the music should "really" sound like as long as I am totally enjoying what I hear out of my own system."

My response to him was,

"That is the way most people feel about the subject but the original goal of the hobby, Hi-Fi, was to reproduce as accurately as possible the sound of the original event.

Since we can't control the recording process, reproducing the recording as accurately as possible is all we can do.

There is nothing wrong with having a different goal but having a different goal means that it's a different hobby.

I call it [the] "Happy, Happy sound machine" [hobby] with no real disrespect intended."

Tre'

Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 3, 2015 at 11:49:42
Caucasian Blackplate
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Location: Seattle
Joined: June 18, 2004
Yeah, I mean, such an amp will sound very different than most others, it's just whether you like or your system needs those limitations imposed on it.

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 4, 2015 at 05:51:23
coolhand
Audiophile

Posts: 537
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Ohh..! the pain Doctor Smith, the pain.. !!

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 11, 2015 at 02:47:20
rage
Audiophile

Posts: 495
Joined: December 17, 2010
Class B SE. Thats a new one.

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 11, 2015 at 03:12:45
rage
Audiophile

Posts: 495
Joined: December 17, 2010



here's my most recent measurement after I got up and running again.

I"m a bit off from Jeff's ideal... i'll adjust later... 270v @ 46ma

12ax7 driver, 285k plate loads, this measurement was with a 30uf cathode bypass cap on the 2a3. have not measured since going to 10uf dc-link.

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 11, 2015 at 03:15:08
rage
Audiophile

Posts: 495
Joined: December 17, 2010



both measurents at 1 watt.

class b, doesn't work, horribly distorted.. blah blah blah

the cree schotky diodes are keepers too, although jeff wouldn't agree!

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 11, 2015 at 10:08:07
drlowmu
Manufacturer

Posts: 9704
Location: East of Kansas City
Joined: January 10, 2005
Thank you for measuring and posting this Rage !!

We "all" KNOW that a 12AX7 at .0006 A. can't drive a 2A3's Miller capacitance, in this Direct Coupled amp of yours. Some "theoreticians" who never heard our amps have REPEATEDLY told us that up here.

Surprise surprise when you measure it.... or HEAR it, .....and its way cool.

Thanks again, nice work. Crees will be low Z, but then there is long term start-up considerations with a solid state rectifier in a tube amp, unless you switch filaments "on" first, and delay the B+ high voltage.

Have fun, I sure am !!

Jeff Medwin

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 11, 2015 at 21:06:24
dave slagle
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Posts: 4754
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Is it really -5dB or so at 20Khz?

dave

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 11, 2015 at 21:44:58
elblanco
Audiophile

Posts: 2320
Joined: August 20, 2004
Then walk us through it ...because what I built from you posts sounds like a dynamic expander with a healthy dose of distortion.is it inviting ear candy?, yes..is it true to the source, NO. Its OK if you like that, no problem, but its not music. Its Dr. Seuss hifi, like Sakuma san, its a SOUND. Ting tinglers and bong bonglers. I visited him once years ago and for the music he listened to it worked, FOR HIM.

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 12, 2015 at 08:00:07
Tre'
Industry Professional

Posts: 12028
Location: So. Cal.
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Rage, thanks for posting the measurements.

That's quite a bit of HF roll off. It seems to me that would be audible in a way that would have a negative impact on the sound.

My educated guess as to the cause of the roll off would be the inability of the driver stage to properly drive the Miller capacitance of the 2a3.

Isn't there a driver tube that can give you the gain you require, while at the same time be able to fully drive the Miller?

From a technical POV, I would think that would give a "truer" sound.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 13, 2015 at 06:18:42
-5dB down at 20kHz ? Not hifi , not even midfi but I suppose some may like this sort of thing . Either this is deliberately poorly-engineered amp or you are using crap output transformers . I can't think of any such causes in a properly engineered design , it certainly should not be the driver stage causing this rolloff...

I think it's time for you to find your own way and put this Lowmu/Dennis crap behind you .

Al

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 14, 2015 at 14:41:08
rage
Audiophile

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let me dig up the measurements with 6ej7... hf rolloff wasn't that much better, but maybe I read it wrong.

both measurements with ds-025 outputs so yes definitelty circuit specific rolloff.

we'll see how I like the other extreme as I"m building the KT120 PP amp with Hammond 1650R outputs right now... in a 12u rack chassis on casters. :)

 

RE: 40 mile drive ..., posted on April 16, 2015 at 06:39:41
deathtube 667
Audiophile

Posts: 1278
Joined: November 25, 2010
Al,

40 miles is nothing.

I used to drive a 400 mile truck route every night for years and often in horrible winter weather.

Get up early before the traffic gets too bad.

It is your chance to listen to a JM designed amplifier in a good system.

How can you pass up this opportunity?

Don't you want to hear it for yourself?


DT 667

 

RE: 40 mile drive ..., posted on April 16, 2015 at 07:06:50
I'll be perfectly frank with you : I have no time and no interest...

If it's so good , why don't you jump on a plane and hear it yourself ?


Al

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 17, 2015 at 13:28:27
rage
Audiophile

Posts: 495
Joined: December 17, 2010
I thought the distortion measurement I made was moderately low for an SE amplifier without feedback.

did you measure this amp that was a dynamics expander?

I won't deny some possible enhancement in dynamics.. I am OK with Tre's happy music machine reference in this case.

I don't hear past 15k. I realize the biggest potential issue here is phase shift given the high -3db points and lack of current to drive miller capacitance.

I'm a little familiar with audio processing and I don't hear the familier increase in density from compression and limiting. I do hear what I would call "soft clippinbg", and I think in the case of the dc2a3 that Jeff passionately presses that the compromises of the amplifier are mainly for the purpose of good sounding "clipping behavior."

a little clipping and distortion is pleasing to the ear for many, who just like their shit loud anyhow.

Still, my prefernece is studio monitors and flat response. I'd argue this amplififer is more accurate then most might assume.


 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 19, 2015 at 23:51:51
hennfarm
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Performing your option #2 would lighten the load on the power supply and b+ would climb, all the op points would have to be fiddled with, and I mean fiddled:-) JH

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 21, 2015 at 09:57:57
drlowmu
Manufacturer

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Not hard to do. I have quite good ideas on where the 2A3 should operate, versus stock. One can use resistive values to return B+ to the front end 6SN7s, so that they are essentially equal to stock amp's quiescent operating points.

Jeff

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 21, 2015 at 16:38:27
drlowmu
Manufacturer

Posts: 9704
Location: East of Kansas City
Joined: January 10, 2005
Hi Rage,

You have not executed this amp quite as I suggested. You need to fully bypass the Rk of the 12AX7 driver, to extend the amp's overall band width.

A single 20 uF film Rk cap, and a 0.68 across it, will roll off the top end. You could easily pick up four more db at 20 KHZ, if you would have done a complete and linear bypassing of the 12AX7's Rk as I detailed to you in numerous emails. Its important to do.

Grant Handley, aka GSH and Satin Patiently made the same exact error. Do that, and re measure and you will see, and you will hear it also !!

Cheers,

Jeff Medwin

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 22, 2015 at 13:31:39
dave slagle
Manufacturer

Posts: 4754
Location: NYC
Joined: April 27, 2001
If the circuit is -4dB @ 20Khz and the 12AX7 has a 20uf film Rk, there is no way any additional bypassing will miraculously give you that 4dB back.

Historically, Kondo used a very small bypass cap in the driver for the ongaku to gain back some HF lost by the output but that is doing just the opposite of what you suggest.

dave

 

RE: perhaps RMAF ..., posted on April 25, 2015 at 08:02:46
deathtube 667
Audiophile

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RMAF in Denver would be more likely since DF & JM would be there and I could hear the legendary SS product line.

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 25, 2015 at 15:49:12
drlowmu
Manufacturer

Posts: 9704
Location: East of Kansas City
Joined: January 10, 2005
His circuit is -5 dB at 20K with his not-to-my-specified bypassing.

I contend, with a DC two stage amp, it is possible to get 4 dB back Dave !!!

Careful Rk multiple film cap bypassing, of not only the 12AX7 half, but also the Rk for the 2A3. NEITHER stage's Rk was built by him as was suggested, and one can not leave this out.

Allow rage to do that and re-measure his frequency response for us all.

Jeff Medwin

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 26, 2015 at 09:08:54
rage
Audiophile

Posts: 495
Joined: December 17, 2010
I'll do that Jeff.

I'll be wrapping up latest build in next few weeks then can put the 2a3 amp back on the bench.

I'll also vefify my measuring setup!

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 28, 2015 at 07:55:25
dave slagle
Manufacturer

Posts: 4754
Location: NYC
Joined: April 27, 2001
I'll give you that the multiple bypass can sound different/better but on the test bench I can see no possible way that anything other than absolute value can effect a 4dB change at 20Khz. Furthermore, given the nature of capacitors, (lower impedance as frequency goes up) I see no possible way that a capacitor change can actually cause an increase in output at 20Khz compared to a normalized 1K output. What can happen by using an overly small bypass is nearly full bypassing at high frequencies transitioning to partial bypassing at lower frequencies causing what appears to be a rise in high frequency response but is actually a reduction of lower frequency output level. (Kondo-san did this on the ongaku driver to make up for loss of HF response in the OT)

In any case I'll await the bench tests....


dave

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 29, 2015 at 17:07:01
Mr_Steady
Audiophile

Posts: 904
Location: North Florida
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With your bench tests. Do you find frequency response and phase to be strongly correlated?


-----------------------------------------------------
Big speakers and little amps blew my mind!

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 29, 2015 at 18:26:12
Tre'
Industry Professional

Posts: 12028
Location: So. Cal.
Joined: February 9, 2002
I didn't think the two could be separated.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on April 29, 2015 at 18:54:02
Mr_Steady
Audiophile

Posts: 904
Location: North Florida
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Gotcha.

--------------------------------------------------
Big speakers and little amps blew my mind!

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on May 6, 2015 at 01:49:34
rage
Audiophile

Posts: 495
Joined: December 17, 2010
I think my Lynx one audio card is ready for the trash. Its from ~ 1999.. I see electrolytic caps I assume are on the output stage. I"m betting its responsible for some of the top end rolloff.


I've got a spare Audiosciecne PCI card at work to borrow, 96khz and fairly new.. I'll run new measurements very soon.

I am in agreement with Dave in that I don't believe the bypass caps will cause that much boost up to 20khz....and also hoping I've got quesitonable measurements. Definitely up for following Jeffs outline for educational purposes. If he's wrong I can always sell some caps or put them to use in other projects.

The sound is not an issue to me, although I do realize that there is a great deal of bias since I built the amp!

In watching a few posters on here I"ve somewhat deduced that low frequency phase response from the low current 12ax7 might be less an issue than its made to be...given the lack of global feedback.. (althouigh there is some degenerative feedback I think from smaller cathode bypass caps)

 

RE: SUN SV 2A3 stereo SE amp .... MEASUREMENTS , posted on February 6, 2017 at 10:06:30
used-hifi
Audiophile

Posts: 475
Location: portage IN
Joined: March 18, 2003
Updates?

 

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