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Old 28th December 2002, 10:33 PM   #1
dhaen is offline dhaen  Europe
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Default Is PSE is a poor relation?

Below is an edited version of a post I made to another thread. It wasnft followed up with any vigor then, possibly because it was a side issue. So Ifve started this thread to try and explore it better.
Well, here goes:

Is PSE is a poor relation?
It reportedly suffers from some lack of clearness, or blurring due possibly, to differences in valve characteristics.

I contend that PSE = PP in terms of valve matching weaknesses.

I want to take the thought path to it's logical conclusions:

If the parallel valves had a single load (as normal), it's true that they might share the current with varying fairness.

If 2 primaries were wound, on the same transformer, and one supplied each anode, there would be more chance of independent operation. But, if the coupling was tight, and R was low; ie a good transformer, then there would be no performance difference between this and a single winding.

Now the leap:

Disconnect the each end of the second primary winding and reconnect it reversed.
Of course there will be no sound because each primary will cancel the other.
So, invert the phase of the signal fed to one valve.

Apart from the DC cancellation, the circuit should act the same...... or will it?
We now have a Push Pull circuit running in class A.

Does this mean that all class class A PP circuits suffer from the blurring, which is claimed as the downfall of PSE?
Or is blurring a myth?
Or are there factors I haven't considered?
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Old 28th December 2002, 11:40 PM   #2
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Default TRICK QUESTION.

Hi,

Quote:
Is PSE is a poor relation?
Not necessarilly...but perfectly matched valves are a big help.
All in all not such a good idea.
No two or more valves ever ages the same way.

Hang in there there are more surprises.


Quote:
I contend that PSE = PP in terms of valve matching weaknesses.
Same as above but different...in a PP arrangement the OPT plays a big role as well.
I may have said this before:in PP arrangement you need to take inbalances in the OPT into account as well.
Bias accordingly and all is bliss.
That's one of the best kept secrets John, so now you know...

Quote:
If 2 primaries were wound, on the same transformer, and one supplied each anode, there would be more chance of independent operation. But, if the coupling was tight, and R was low; ie a good transformer, then there would be no performance difference between this and a single winding.
Better to use independant OPTs (at least on the primary side),capacitive coupling you know...
Funny you mention it though...been thinking along the same lines.

Quote:
Of course there will be no sound because each primary will cancel the other.
Good thinking....and it proves my point.
If there is a sound,it would prove an inbalance anyway.

Quote:
Or are there factors I haven't considered?
You pretty much covered it....we just can't control all the elements
can we?

Surprised to see it still sounds as good?

Quote:
Or are there factors I haven't considered?
Yes John,there are.How do // valves behave according to Ohm's law?
Gm?

Do I need to remind anyone of my reservations towards using series caps in a PSU?
There are //s,you know.

Cherio,
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Old 29th December 2002, 11:29 AM   #3
dhaen is offline dhaen  Europe
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Quote:
Bias accordingly and all is bliss.
So PSE with individual bias is OK?
[In my book, it takes at least 3 points of tracking to "fit" 2 unequal curves.
And PP without is no better (in terms of clarity) than PSE?
[I'm ignoring the hum rejection, and harmonic mix-ups in PP]..


Quote:
Do I need to remind anyone of my reservations towards using series caps in a PSU?
Do remind me.
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Old 29th December 2002, 03:49 PM   #4
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Default PSE PPP AND ALL THINGS //.

Hi,


Quote:
So PSE with individual bias is OK?
Surely better than common,shared bias.

Quote:
In my book, it takes at least 3 points of tracking to "fit" 2 unequal curves.
I agree,if you can afford the royal road.
See my remarks on voltage regulation elsewhere.

Quote:
And PP without is no better (in terms of clarity) than PSE?
In a single pair PP arrangement things are different but matched valves and individual bias is still an asset.
I once suggested individual cathode resistors to Joel but he didn't see the benefit.
I haven't insisted since....

Ah...series caps!

Well,you face the same problems as with // valves.
The entire circuit never finds a stable working point and the weakest link always takes the heat.

Only way I know to combat this is once again individual rail regulation.
Not exactly cheap,I know.

Once you have all these parameters under control you will have very audible benefits in that the whole presentation of the music will be far more relaxed and natural.
Subjectively you'll also have the impression of a little bit more headroom.

Actually it is measurable as well..the circuit take longer before going into clipping and has less distortion.

To me it is comparable to a Class A design and a Class AB1...once you hear the difference there just is no going back.

Cheers,
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Old 29th December 2002, 05:41 PM   #5
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Subjectively parallel anything doesn't sound good to me. Whether it's input valves/fets/bipolars or outputs there is always blurring. I may accept a compromise sometimes as the paralleled devices also offer more solidity to the sound and generally better bass, but all my attempts with paralleling SE valves have been disastrous. Otoh i don't have the same subjective problem with PP stages (as long as they're not paralleled).

cheers

peter
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Old 30th December 2002, 05:21 PM   #6
dhaen is offline dhaen  Europe
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Frank said,
Quote:
In a single pair PP arrangement things are different
(to PSE)..

I had attempted to show that there is no difference.
Which difference are you talking of?
Why should 2 tubes "blur" when they're in phase, but not when operated out of phase?

In other words:
We seem to agree that 2 tube curves are difficult to fit. But why should it be different in PP to PSE?

In fact in the PP case, we're trying to match different parts of the curve together, so even perfectly matched (if that's possible) tubes will not fit. Hence increased odd order distortion.

Is the problem with PSE, that the closer we match the tubes, (unless the fit is perfect), the worse it will sound?
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