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Proprius Amp tweaking......

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Graham Slee View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jul 2022 at 8:09am
Originally posted by Mikeh Mikeh wrote:

I recently watched this Alan Shaw (Harbeth) video on YouTube which demonstrates how different types of music (I.e. dynamic electronic vs mellow classic) can create vastly different demand on amplifier output, for the same sound level....

Has anyone measured the the Peak or Transient output of the Proprius? I read Bruce's (BAK) comments that into 8ohm load this could be approx. 50 to 75 W resp. It just seems that the Proprius design with it's 25 (Yorkshire ) W has plenty of capacity to handle the most onerous speaker loads and music demands, so I'd be interested to understand more.

It's an academic  question for my listening, where in a small room with nearfield positioning I can't be using 1W output for my little Harbeths to be singing.

If the r.m.s. voltage just prior to clipping is 14.14 volts, and the load resistance is 8 ohms, then the current is

14.14 / 8 = 1.77 amps (r.m.s.)

14.4 volts r.m.s. * 1.77 amps r.m.s. = 25.5 watts

Tell me how it can do 50 or 75 watts?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mikeh Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jul 2022 at 8:36am
Originally posted by Graham Slee Graham Slee wrote:

Originally posted by Mikeh Mikeh wrote:

I recently watched this Alan Shaw (Harbeth) video on YouTube which demonstrates how different types of music (I.e. dynamic electronic vs mellow classic) can create vastly different demand on amplifier output, for the same sound level....

Has anyone measured the the Peak or Transient output of the Proprius? I read Bruce's (BAK) comments that into 8ohm load this could be approx. 50 to 75 W resp. It just seems that the Proprius design with it's 25 (Yorkshire ) W has plenty of capacity to handle the most onerous speaker loads and music demands, so I'd be interested to understand more.

It's an academic  question for my listening, where in a small room with nearfield positioning I can't be using 1W output for my little Harbeths to be singing.

If the r.m.s. voltage just prior to clipping is 14.14 volts, and the load resistance is 8 ohms, then the current is

14.14 / 8 = 1.77 amps (r.m.s.)

14.4 volts r.m.s. * 1.77 amps r.m.s. = 25.5 watts

Tell me how it can do 50 or 75 watts?


Graham, having asked if anyone has measured the Peak and Transient output of the Proprius, I was simply (mis) quoting BAK's earlier estimate of Peak and Transient output...
"The Proprius amplifiers can produce 26 watts rms driving into an 8 ohm speaker load... rms = rout-mean-square (another mathematical term for average power).
 That same rms power can be as much as 52 watts peak power, or more, even 70 watts instantaneous. That is the solid state circuit doing it's best into 8 ohms.
When driving into 4 ohms it will be almost 2 X as much!"
Mike

Technics sl1210g with Victor U-2
Accession MM, Majestic + Proprius, Solo ULDE
Cambridge Audio CXC CD player
Lindemann Limetree Bridge streamer
Harbeth P3ESR XD paired with 2x REL t5x
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jul 2022 at 9:33am
Originally posted by Ash Ash wrote:

Graham, could you remind me again why you don't strive to make your amp stages totally silent in terms of background noise? I always remember you saying something like "cut it too much and you've killed it". You have to juggle many parameters simultaneously and rely on 'sensible use' of the product. Basically, dead quiet amps are boring to listen to, yeah?

The formula for slew-rate in V/s is

S.R. = 2π * ƒc * Vpk

(ƒc is the corner or cut frequency)

Divide answer by 1,000,000 to obtain V/us

All amplifying devices (valves, FETs, BJTs...) have parasitic capacitance which limits the extent of ƒc and therefore limits slew-rate.

Poor slew rate results in high frequency distortion, felt especially on transients.

Slew rate can be increased using brute force or by more natural means.

The brute force method always threatens stability, and so sounds artificial, but is low noise.

The natural method works with stability, and sounds natural too, but results in higher noise by comparison, due to the resistive "degeneration" required, and all resistors have a noise voltage.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jul 2022 at 10:24am
Originally posted by Mikeh Mikeh wrote:

Graham, having asked if anyone has measured the Peak and Transient output of the Proprius, I was simply (mis) quoting BAK's earlier estimate of Peak and Transient output...

I think there is a lot of confusion because of the writings in sales blurbs and due to the ignorance of the non-technical hi-fi press.

There is force, in that voltage is an electromotive force (E.M.F.).

However, current is not a force but a product of an E.M.F. across a resistance. Thus satisfying Ohm's law.

For wattage to increase, either the E.M.F. must increase, or the resistance must be lowered.

A modern speaker is a combination of capacitive reactance and inductive reluctance, with resistance thrown in.

Reactance and/or reluctance create impedance vectors, that might still be 8 ohms (or whatever the nominal impedance is), but at a different phase angle - hence me calling them vectors.

If these are parallel to the speaker resistance, then the load becomes greater than the nominal impedance, e.g.,

at the ƒc of the reactance or reluctance, the phase lags or leads by 45 degrees, and becomes 1/√2 * Rnom ≈ 0.707 * Rnom.

If it were to appear in parallel, then first 1/√2 * 8 ohms ≈ 5.6 ohms, then in parallel with 8 ohms, is 3.3 ohms.

To drive 3.3 ohms at maximum voltage (14.14) delivers 60.6 watts (14.14^2 / 3.3).

This has to come from somewhere, and that is the power supply, which for the Proprius is 120 watts.

However, circuit resistance due to the load, will drop the E.M.F., making it somewhat short of 60.6 watts.

Much of this, as you commented, is academic, in that to wholly accommodate the transients, the average or "base" "listening power" can only be the fraction demanded by those transients.

For example, if all the transients were being reproduced via the vinyl medium, then groove breakover limits them to +14dB, and within 500 to 2500 Hz.

Firstly, +14dB in power terms is 25 times the "base", so that's at 1 watt.

Secondly, between 500 and 2500 Hz, it might be less likely to encounter such a harsh amount of reactance or reluctance.

Thirdly, I doubt if in domestic listening the "base" power is remotely near 1 watt -- probably more likely nearer 1/3rd of a watt.

Now, in sound reinforcement, which is a different kettle of fish, then "difficult to drive speakers" would have consequences for the amplifier. But then, due to the non-linearity of our hearing, we would not be concentrating on the beautiful subtleties of a "holographic" stereo image. Instead, our hearing and emotions would be being overtaken by the beat. Then you need the watts!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jul 2022 at 11:16am
Something else might be responsible for the "Yorkshire Watts".

There is roughly 0.1 coulombs of charge in the output capacitor...

(hey, this guy uses output capacitors?

yes, and I'm not ashamed to admit it!)

So, although it would clip on positive excursions, the negative excursions have their own power supply sufficient to do approximately 200 amps...

But for only one half cycle at 1kHz...

Confused?

(to understand more about amplifiers, buy my book, that I'm still writing...) Embarrassed

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Post Options Post Options   Thanks (0) Thanks(0)   Quote goldiver Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jul 2022 at 10:34am
What a wonderful forum—it's a pleasure to read informed, educational responses and speculation, not to mention your Electronics 909 submissions Graham!

Leaving the Proprius pot meters on max seems to aid dynamics and energy in music reproduction, to my ear, even though there may be some hiss up close to low-impedance speakers.



Edited by goldiver - 07 Jul 2022 at 2:09pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ash Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jul 2022 at 2:07pm
I will have to experiment further with them and see if I can hear any difference. Geek I might have to compromise on noise somewhere in the middle.

I used to use AKG K1000 (74dB/mW sensitivity and 120 Ohm nominal load) with the Proprius and could turn the dials to 3 o'clock without any hiss then used the Majestic pot at a lower level. Then I tried 12 o'clock on the Proprius and set the Majestic higher. I don't recall being able to hear any difference but headphones are spatially constricted binaurally so I will have to judge it again with two different speaker drivers, where much more spatial depth will be possible.


Edited by Ash - 07 Jul 2022 at 2:21pm
We do not see things as they are. We see things as we are.
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