To SET or not to SET

[NOSValves]

Hwatkins,

very well said no bunk there.

Craig

[Deang]

Hey, I just thought of something: Drivers are push-pull -- so there!

[rloggie]

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On 6/28/2004 3:34:42 PM popbumper wrote:

Henry:

If it helps clarify at all (noise floor), I believe he is referring to the direct or indirect causes of extraneous noise in the room which contribute to the overall "ambient sound". You probably realize this already, so let me address your question of "is 55dB typical"?

My "listening room" (I use this term loosely) is upstairs, above the garage. This is no "special" room, in that it has no acoustic treatments, and is non-isolated from the house (in that it has an attached stairwell, as well as a pair of windows looking out over the driveway.

During the time I was setting up my equipment and doing calibrations, without effort I was immediately confronted with the sound of the overhead fan (which is precisely over the seats), and I was able to capture this "noise" on my sound meter - a whopping 70dB!!!

My best time to listen in this rom is after 10PM, when most of the neighborhood noise is quelled, and the wife/kid have gone to bed. Interestingly, here is what I have noticed:

a) The fan sound is the most predominant. If it is NOT really hot in the room (upstairs, Texas, Summer time), I turn it off.

The AC outlets (on the ceiling), contribute quite a bit of noise, though certainly not at the level of the fan.

c) The computer at the back of the room has some nice fan noise as well.

d) With heavy drapes, and at night, the outside noise is pretty low.

I was actually surprised at what these all contribute to the noise floor. My conclusion is that 55dB would not be atypical, but it really depends on the room location/environment and what is in it.

Popbumper

When I lived in Nevada, I'd turn off the refridgerator (No compressor cycling), and the air conditioner during the summer to get the quietest room. Stereo sounded better and cold beer kept me air-conditioned.

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[mike stehr]

"Problem with push-pull amplifier designs associated with crossover distortion have been discussed elsewhere at length, and one of the primary results is non-monotonicity. Class B and many AB designs have distortion products which dramatically inclease with decreasing signal. This is reduced greatly by Class A mode, but crossover distortion remains as a lower order discontinuity in the transfer curve.

For reproducing music as naturally as possible, push-pull symmetric operation is not the best approach. Air is not symmetric and does not have a push-pull characteristic. Sound in air is a pertubation around a positive pressure point. There is only positive pressure, more positive pressure and less positive pressure.

Descriptions of push-pull often illustrate this type of operation with a picture of two men sawing a tree by hand, one on each side of the saw. Certainly this is an efficient way to cut down trees, but can you imagine two men playing violin?

By contrast, push pull Class A circuits have two opposing gain devices producing the output signal, and though it is industrially effective and efficient, it is not the most delicate way to amplify the signal. Push-pull circuits give rise to odd ordered harmonics, where the phase alignment reflects compression at both positive and negative peaks and crossover nonlinearity near the zero point."

If this was written by Nelson Pass, then this paragraph is probably refering to solid state class A amplifiers.

[Deang]

It does -- but it also applies to tube amps. Still, SE is his thing, so naturally he has to give the reasons why he prefers it as both a designer, and listener. With tube amps, matched tubes, or being able to individually bias the tubes, keeps crossover distortion to the a minimum.

I don't know why, but I haven't heard a Class A amp that sounds better than the last two I've had. It seems like if things get too smooth, I start noticing the system behind the music more. I guess I just like a little bit of edge to the music -- it sounds more real to me.

I had to edit the above, which originally said, "...I haven't been too thrilled with the Class A amps I've heard in the past." -- which isn't true. I liked the sound of the AE-25 and the Canary both.

[jt1stcav]

Ditto to what hwatkins said. I'll probably never experience SET anyway since my 300B hasn't arrived yet...But I've got this trusty 2 WPC class-A SE EL84 power amp that probably sounds very close to SET IMO (or maybe not?). With my 98.5dB Cornwalls, I ain't complainin'!

[jt1stcav]

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On 6/28/2004 7:45:41 PM AK-4 wrote:

..."I don't know why, but I haven't been to thrilled with the Class A amps I've heard in the past. When things get too smooth, I start noticing the system behind the music more. I guess I like a bit of an edge to things, it just sounds more real to me."

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And that's what makes our hobby so great. There are so many choices out there, each topology different from the other that attracts so many listeners to a particular design, with one ultimate goal...whatever sounds the most "real" to each listener. That's why I have no problems with either SET or PP, tube or SS. A different flavor for everyone!

[tubelover]

Nvermind, I will bite my tongue.

[Deang]

So what are you trying to say exactly, that SE pentode is the best or something? I'm not stupid, I can read between the lines, and I see exactly where you're going with this thing.

[jt1stcav]

Hell yeah, 'cause I own it and I say so!

[3dzapper]

Dean, Don't your Quads play in class A at low wattage such as that used by Klipschorns and then go over to class AB at higher wattage? Unless they are biased like Macs,or you don't have any windows left, you have probably never heard them in PP.

Rick

[mike stehr]

My RCA SEP amp is non-ultralinear with no feedback.

It rocked, but it would grate on ya after awhile.

The mid and highs were nothing special, and it seemed like too much gain, coming unglued once you turned it up a bit.

We attempted a UL connection, but without a choke and some power supply work, there was just too much noise.

(I still need to try the UL connection, it was a still ongoing experiment.)

So I tried a really easy thing to do, lift the screen supply and put a couple of 100 ohm resistors from pin 7 to 9 on the 6BQ5's, and strapped them in triode.

Tried it, tons of hum. The RCA SEP amp has 80 uf right off the 5Y3 rectifier, a little too much I guess, but 5Y3's were cheap in those days.

I finally just threw a small choke between the 35 mic section and the 80 mic section of the PS cap, that helped quite a bit. Still some hum when the VC is cranked, but tolerable until I figure it out.

First thing I noticed is the midrange really opens up, seems to sound a little cleaner, probably not.

Probably would look like hell on a scope, but the RCA pentode connected stock with no feedback looked like hell on the scope.

The bass is a little soft, but it was pretty soft pentode connected.

I have a pair of Amperex SE OPT's for EL-84's out of a tape recorder(Ebay). They are a little larger and appear to be more tightly wound, and measured better on the bench the the stock RCA OPT's. They'll swap right in...

Triode strapping this amp doesn't seem too bad, and I still have enough gain to rock a bit. (More than I ever thought I would.)

[Deang]

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On 6/28/2004 8:47:27 PM 3dzapper wrote:

Dean, Don't your Quads play in class A at low wattage such as that used by Klipschorns and then go over to class AB at higher wattage? Unless they are biased like Macs,or you don't have any windows left, you have probably never heard them in PP.

Rick----------------

Push-pulls are always in "push pull". The class of operation just determines the amount of overlap between half cycles at hand off.

http://www.anthemav.com/OldSitev1/pdf/taste.pdfhttp://www.anthemav.com/OldSitev1/pdf/tot3.pdf' target=_blank>

[edwinr]

Thanks for your interesting dissertation Neo. Certainly SET is a very attractive option and

I have been surprised during recent listening experiences what 3 to 5 well designed watts will do with sensitive loudspeakers. I won't say I'm a convert yet, but I have a more open mind. I don't know whether you are familiar with Loth-X. This company is based in Singapore and promotes a design philosophy featuring a single paper coned 'Stamm' driver in a folded horn enclosure. The company believes that using a single crossoverless driver promotes a coherency not apparent in other more complicated or multi driver designs. Like any speaker system designs, there are compromises. Most Loth-X enclosures make the Klipschorn look like a book shelf model. I also think power handling, absolute loudness, and a wide frequency response are all issues in many Loth-X designs - there's only so much you can do with a single driver.

[3dzapper]

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On 6/28/2004 10:06:24 PM AK-4 wrote:

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On 6/28/2004 8:47:27 PM 3dzapper wrote:

Dean, Don't your Quads play in class A at low wattage such as that used by Klipschorns and then go over to class AB at higher wattage? Unless they are biased like Macs,or you don't have any windows left, you have probably never heard them in PP.

http://forums.klipsch.com/idealbb/images/smilies/2.gif">

Rick----------------

Push-pulls are always in "push pull". The class of operation just determines the amount of overlap between half cycles at hand off.

http://www.anthemav.com/OldSitev1/pdf/taste.pdf

http://www.anthemav.com/OldSitev1/pdf/tot3.pdf"'

target=_blank>

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Yes your reference proves my point:

"A push pull amplifier may be operated in class A, B, or AB.

The class of operation is determined by the amount of

overlap between the half cycles at the hand-off."

(In other words the bias point)

Ref:http://www.anthemav.com/OldSitev1/pdf/taste.pdf page 40 of the PDF file, page 35 of the document.

Rick

[Deang]

You're looking at it from the point of view that while in Class A, both tubes are always "on", and one doesn't go "off" after the transition. Is that it?

[3dzapper]

Correct until the negative part of the waveform shuts off one tube and that part of the waveform is taken up by the other tube.

Mark gave me a drubbing on this once 'cause I didn't realize that Mac's run in true class B all the time. (I do now )

Rick

[maxg]

I am not at all sure about this class A / Class A/B option at all. My Ultra Linear amps switch from one to another at a certain point - which is largely controllable by setting the bias. If I set the mV indicator for bias to a higher level the crossover point between class A and class A/B rises and conversely for a lower mV rating.

When I was supplied the amp Odyseus set it up for maximum class A operation. I think that this meant that the amp would play in class A operation upto something around 30 wpc at which point it would switch to A/B.

The funny thing is that this wasnt right for me. I have re-set the bias level to switch from A to A/B at a much lower level. This is because, to my ears, class A operation lacked impact in comparison to A/B.

With my current setup I listen to classical at low levels (during the evening) in what I assume to be pure class A. At weekends - with wife and baby out - I crank up the volume and listen to Rock. This, I assume, is in class A/B operation which impacts the presence of the Bass, positiviely, more than anything. The side effect of playing at higher levels it the loss of some of the sweetness to the sound. In other words playing, for example, Beethoven's Violin Concerto, at higher volumes does not sound as good to me as it does at lower volumes whilst the reverse is true for DSOTM, where sweetness is not such a desireable feature.

My, untested, fear would be that a class A, low power triode, might well match or even surpass my current low level listening experience (although even there there is a question over the bass reproduction) but it would lose out for my higher level listening lacking the punch for rock.

Just as an aside - I guess I am lucky with my background noise levels. Most of the time the RS meter shows less than 50 dB (its minimum measurement).

To summarise all of the above. I feel that there are probably swings and roundabouts here - gains and losses if you will. I will accept that for low level listening the SET option may be better (although that is not my experience to date with the single SET amp I have tried) but I would be surprised to find it holds up quite so well at higher listening levels.

Isnt this what Kelly always said? He was/is a huge fan of SET amps - but he also kept and used PP amps when the going got loud.

[Deang]

He only started saying that after I got done brainwashing him.

[edwinr]

The Audio Space AS300B has just become available in Australia. About $3,800 in $A or only a few hundred dollars more than a Nain Nait 5. Chinese made. 8 watts SET per channel. Two pairs of RCA inputs, one set rear and one pair at the front switchable between integrated operation or power amp operation. Is this the start of the SET revolution vis a vis affordable 300B SET in Australia? I wonder what the entry level for SET is in the U.S.?