Which is better and why- The outward speaker-cone excursion driven by the triode going toward saturation or by the triode going toward cutoff?
Presume the signal can be inverted at the input, so reversing the leads at the speaker would restore correct polarity. But unlike doing this with a push-pull design, the asymmetic linearity (even-order harmonic distortion) of the SET would make the resultant signal *different*, even though the absolute polarity at the speakers is "positive" in both cases. (A sine wave would be "flattened" at the top in one case, at the bottom in the other.)
Since the response is asymmetrical, one would presume one of the above-mentioned setups would be more-ideal than the other.
Todd, you are on the right track. There will be a 'BEST' configuration with a speaker (especially horns) and a SET combination. This combination should NOT be changed.
Think it through: The speaker (horn especially) has lots of 2'nd harmonic. The amp, being SET , etc has lots of 2'nd harmonic. If you get them out of phase (the 2'nd harmonic), then they should cancel. What a deal! Free distortion cancellation.
Is this practical? Sometimes.
Absolute polarity, like what Clark is referring to, is a different problem entirely.
You either got it right, or you don't!
A SE circuit is asymmetrical. Even if you have the absolute polarity right, the circuit could be configured in 2 different orientations.
Sounds like a classic case of "try it both ways and report back"
...no such thing as negative Absolute Polarity.
> Which is better
> and why-
Because some Speakers distort more on the "out" stroke while others distort more on the "in" stroke. HOWEVER, due to the magnet geometry in most Drivers (from the cheapest dreck to really expensive boutiqe drivers) it is often the "out" stroke that is a little compressed compared to the "in" stroke
> The outward speaker-cone excursion driven by the triode
> going toward saturation or by the triode going toward cutoff?
From the Above, the outward stroke should be driven by the triode going to cutoff. However there is no simple "cut & dried" rule. The best methode to find the correct polarity is by keeping the system polarity the same (polarity switch on Preamp - what do you mean yous doesn't have a polarity switch?) while changing the polarity of the speaker wrt the amp. Using distortion meansurements is the scientific methode. I found that "by ear" I routinely prefer the lower distortion connection.
in other tube applications, such as my old Millenium preamp, the inversion switch introduces another tube stage. Since most tube units invert anyway, the best way to play this unit was to invert at the speakers and never use the invert switch.
Either way you'll be right only half the time, so what's the diff?
One thing that is nice about the Meitner is that it has a invert switch. Now if only it did not depend on this crappy Phillips 1000.
The only one I can think of is the Golden Tube Audio SEP-1, but it is not in the form of a switch, but in the form of "inverted output" jacks.
All of my best preamps for more than the last 20 years have polarity inversion switches. It is necessary for a complete preamp. Unfortunately we don't now have a mono switch, but I could consider it important in some situations.
"It is necessary for a complete preamp".
Hopefully, "complete" doesn't mean its panel all covered with
knobs & switches. I agree old timers all got many knobs, & buttons, including the then "must" knobs - bass & treble controls. For 60-80s vintage gears, it was a fashion & win-win sales features to put knobs & buttons all over the front panel.
But who needs them nowadays? With the era of straight-line concept,
enchanced by direct-coupling design topology, even with one-century-
young valves already gone OTL & OCL commercially, redundant knobs & buttons (hence redundant internal wiring), should be done away with.
With the reproduction-chain getting so effective todate, we can even detect subjectively the tonal signatures of coupling caps & filter caps of different designs (say, oil or polypropylene, etc.), these
vintage panel features should only be our sweet memory of the past.
Surely, it is not "necesssary" any more today.
My DIY phono+line preamp, pure DC (battery) powered, got only one knob
for line output level control & a toggle selector switch for phone/line input. Simple nothing is always better than indequate
As for phase checking, I always play a monoral signal, say, an AM
radio broadcast with voice only programmes. It should sound like at the dead centre of the soundstage.
A good rig should be able to reproduce a stereo recording of a singer's voice at the dead centre of the soundstage, even without the use of any 'mono' switch. Mine always does.
Listening is believing.
Aug 20, 2003.
Better do a search on "phase" and "polarity"--they're not the same thing. You need a polarity switch on your preamp because records, CDs, and other recorded media come both ways. One way sounds better; hence John's remark about "complete" preamp.
You need a mono switch if you ever listen to mono records with a stereo cartridge. Cancels out much noise. Handy for system de-bugging, too.
If you have ported speakers and listen to LPs, an infrasonic filter can really clean up the sound. Added to the signal path: one cap, one resistor, one switch.
I for one miss several of those knobs and switches (not all of them, obviously)--they were useful. And now that we know much more about the sound of caps, switches, etc., I'm sure they could be made much more transparent than they were.
I'd like to have a preamp with those switches and connections for two-way tape/CD dubbing--I need it for my work. Not gonna find one in the high-end these days.
So, you still listen to mono records! You must be some connoisseurs who still backtrack music of the good old days. No wonder you like to have a preamp with a mono switch, or even hi-cut & lo-cut switches
to remove the noise of the old old recordings. Very hard, if not impossible to get such 'obsolete' features in 'modern' amps these days, unless you go for amps of vintage years back to 60s. But then, there will be some dramatic trade-offs sonically. I won't touch those old timers without major DIY overhauling.
One solution is to simply add a DP/ST toggle switch, at the back of
your existing pre-amp, to bridge up the L/R channels for playing those old recordings, be them monaural LPs or tapes. No big deal.
In fact, I still listen a lot to some good AM broadcasts of oldie music, & taped them off on stereo cassette tapes. I don't need any mono switch as I have no problems with those 'modern' recordings.
My LPs collection (not many, quite a few hundreds only)_are ALL stereo format. To me, only stereo recordings, not monaural nor 5.1/multi-channel digital formats, can satisfy me with the closer-to-real sonic perspectives I pursue.
Like my antique radios, I also collect historic stereo LPs. Mind you, those oldies sound pretty good, recorded back in the tubes-only analogue era with the traditional two-microphone technique. That's why.
Here, I want my readers tour back 50 years with me, through the historic LP, packed in an entirely golden coloured sleeve, which I picked up quite unexpectedly, from a local Goodwill store two years ago. I think it could be a very first stereo LP in the market:
a "Spectrum Stereophonic Recording" label, released in New York in 1958. It was recorded by a then revolutionary "authentiphonic Stereo Process" under the engineering auspices of some big-shot, Dr. Harlow White, who pioneered the "independent impulse stereo record cutting" technology in 1936. He reportedly developed this record cutting know-how after A.D. Blumlein, who publicly demonstrated his world's first stereophonic record in 1933.
Some stereo record history flashback! Sound interesting? The music is one of my favourite classical piece: "Tchaikovsky Piano Concerto in B Flat Minor", performed by The Royal Farnworth Orchestra, conducted by Warren Edward Vincent, & soloist: Jean Bargy.
The sound? Pretty good. The background is surprisingly quiet (master tape hiss & vinyl noise are not noticeable). Airy & dynamic. What impresses me most is the effortless rich bass that I can't find in many modern LP recordings. I paid only 50 cents for it!
It again, confirms my impression that a lot of old recordings sound
better than today's LPs digitally recorded.
Back to my less-is-better straight-line concept. Surely I won't recommend you to enjoy music using a pre-amp loaded with knobs & buttons, however functional they may be for your work. I would use
a 'straight-line' pre-amp strictly for music listening, & acquire a features-loaded vintage amp, after major sonic upgrading, for dubbing work.
"Simple nothing is always better than inadequate something".
To me, 'phase' & 'polarity' is terminlogy difference in its practical sense.
According Rob Karsten, designer of Atma-Sphere Music Systems, the 'inverse' switch on the front panels of its MP-1 MK2 & MP-3
pre-amp, is to ensure "absolute system phase" is in line with the
correct phase in which the music was recorded.
Unfortunately, many music performances were unintentionally recorded out of phase or wrong polarity, thanks to those recording engineers' 'great' job. This inversed polarity or phase sonic effect
will render individual instruments sound 'tarnished' & lack of 'attacks' or 'bites'.
However, such inverse sonic effect will not be so noticeable unless the recordings are acoustical performances, e.g. classical, jazz &
non-electronic-type music, & were recorded with basically, two microphones, where reversed phase or polarity is crucial.
For thode modern music, heavily electronic & recorded in muli-miking & multi-tracking format, the sonic importance of polarity or phasing
is out of consideration. One just can't detect the difference.
To ensure the rig is reproducing music recordings of the correct polarity or phasing, one can always reverse the polarity of speaker terminals, of BOTH channels, i.e. (+) switched to (-), according to
Rob Karsten. Then, listen to any sonic improvement. If it does sound better, it means the rig is now in "absoluate system phase". Otherwsie, undo what one just did.
However, it will surely be a pain if for every recording one got to carry out testing by reversing speaker terminals, in order to get the best sound effect. Here comes the 'inverse' switch, so that such hassle can be eliminated for good.
However, there is one technically issue here. To reverse the phase
of the amp circuit, it needs a phase or polariity inverter. An active
one, usually with some gain, will introduce unwanted distortion.
The better topology is to employ differential input circuitry, so that
the signal can be directed to other reversed phase input with a simple
passive switching method, without adding unwanted distorition.
Some hi-end amp with differential input driving stages will do polarity or phase reversing properly, e.g. Atma-Sphere.
More on this issue next time.
Both the Spectral and the Bryston have it. So does my Levinson 390S cd player...it can get confusing at times!
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