Capacitance multiplier: which Darlington to choose?

[thor.zmt]

Gents, could this be one of the first cap multipliers /choke emulators? IRT V81 from 1964.
View attachment 109693

Not sure about "first", but definitely

Thank you. TF80/60 had a Beta of approx. 50 in this circuit, think thats enough for good filtering of the push pull output stage of this 10W power amp.

PP Outputstages have quite high PSRR. At least while operating in Class A.

Is there something better available today with bipolar transistors?

MJE350 would drop in and is available.

This isn't a high voltage type, but it's employed in a high voltage PSU. Has this been achieved because it's placed in the negative part of the PSU?

No. I suspect that when circuit starts up the 5k/50u = 250milliSec causes a quick voltage rise. Plus other than charging the capacitors via large value resistors there is no current flow (heaters are still cold).

So with nowhere for current to flow, even if the transistor goes into "avalanche", without current flow this is largely inconsequential and by the time tubes conduct the transistor will be back in normal operation.

It is a way that nowadays is generally avoided, as suitable alternative parts exist that do not need to be operated under conditions exceeding limits.

I could imagine when someone is "pumping" a breaker with this circuit attached the transistor may very well pop.

Can someone use a modern type of PNP low voltage transistor and replicate this PSU for a tube amp easily?

Probably yes, with all the caveats applying to the original version. It is considered poor design practice.

Does this type of transistor in general eliminate the need for a high voltage bipolar transistor in tube amp PSU? It would have been a clever idea.

No, because it still operates under conditions that have the potential to be destructive, just not under normal careful operation.

Thor

 

[thor.zmt]

I met several who were liabilities. I remember one army cook who couldn't spell his own name, but it was a difficult name.

Tell me about it. Some included officers.

He wouldn't have washed out, just repeated the training course until he passed. FWIW I never had to use my training in anger.

It is best that way.

Business is right, its all about the Benjamins, don't look now but China is on the move (and India has expanded their navy).

Let's not talk geopolitics here. We can on Quora. This is about Boyz Toyz.

Thor

 

[thor.zmt]

One problem is that measurement doesn't always translate to good sound, or even accurate measurements.

Indeed, from instrument Ghosts and Gremlins to metrics that are no congruent with real world sound quality, "Houston, we have a problem!"...

If you don't properly test what happens when you overdrive the circuit, you are a useless fool as an engineer of audio products, or your customers don't care about high quality sound reproduction
I find that many engineers who worked in audio prior to the 80s and were taught "feedback fixes everything" still don't get it.

I had two very graphic illustrations of what happens when feedback goes off track. One involved a missile and the other a crane with a 140 Ton's liquid steel in a "pan" load. Both most impressive illustrations.

I've recently changed my longstanding belief about the HP 330 series of distortion analyzer. It's a good tool for checking the quality of sine waves produced by HP analog oscillators. Just garbage for testing amplifiers.

Well, it is a tool to answer a specific and very limited question with accurate data.

Data itself is not information, it is just data. The Engineer with his/her experience and understanding provides the context that turns data into information. Wrong context = GIGO.

High quality sound doesn't necessarily translate into sales.

The correct objective correlation of sales is with marketing. Spend very little on the product, a lot on marketing, branding (and lawyers) and you have a successful audio company. Just ask Amar.

Thor

 

[ruffrecords]

Did anyone ever see one? Is there a photo or schematic?

I have not found either on line but I have a whole bunch of actual Wireless World magazines from the 1940s. I will check them out.

Williamson was not a commercial product claiming low HD for marketing.

It was presented as "high fidelity" design and used a test of jangling keys in front of a microphone and played back via the Amplifier (amongst other tests such as pipe organ music) to validate fidelity.

I agree. It simply illustrates that the aim of 0.1% distortion was not an uncommon hi-fi target ten years before Leak marketed point one and furthermore that it was achieved using the same tube complement that Leak was using at the time. In other words Leak was making 0.1% capable amps ten years before you claim he simply copied Mullard circuits. In addition the Williamson published objective distortion versus output level curves as well as making objective tests like jangling keys. And the original Leak/Williamson topology was copied by Mullard not the other way round.

So it did. And?

So your claim 0.1% was achieved simply by lowering the rated output is incorrect

It does not change that low distortion as measure of fidelity as actual marketing macguffin goes back to Leak and was done using generic circuits that were simply rated at a lower power output than the competition, who rated power ay 3% or 10% which remained common practice for decades longer, into the solid state era where 3% or 10% THD at rated power were no longer appropriate.

I agree Leak was the one who first successfully marketed 0.1% distortion but it was not achieved originally by simple derating.

Cheers

Ian

 

[thor.zmt]

So your claim 0.1% was achieved simply by lowering the rated output is incorrect

Incorrect. Example TL12+ vs. Mullard 5-10 - both are identical (with very minor variations), one has a
higher rated output and distortion.

Many manufacturers rated amplifiers that COULD have been rated as 0.1% THD at "clipping" (3/10% THD) and quoted higher power, for essentially identical product.

What made Leak's "Point One" products unique was not the electronic design, but simply the way it was measured and marketed and as such was the beginning of the "THD race" that promoted low THD as a figure of merit, without there being any scientific evidence that low THD correlates with high sound quality or audible transparency.

I agree Leak was the one who first successfully marketed 0.1% distortion but it was not achieved originally by simple derating.

BUT IT WAS achieved ONLY by derating. The same Amplifier could have been rated at much higher power had it been rated at 3% or 10% THD.

In other words, Leak rated power at 0.1% THD while others rated power at 10% THD but produced the same power at 0.1% THD. Leaks marketing implied their product was less distorted than the competition, which at least as far as "standard designs" were concerned was not the case, under identical conditions.

Thor

 

[thor.zmt]

In other words Leak was making 0.1% capable amps ten years before you claim he simply copied Mullard circuits.

Leak CLAIMED that this was the case.

Others had also produced amplifiers with 0.1% THD at a given output.

Making a tube amplifier with 0.1% THD at 400Hz and at some power level is trivial. Actually ALL Tube Amplifiers not hard Class B PP will fulfil that, even old transformer coupled non-feedback WE Cinema Amplifiers from the 1930's (e.g. Type 86) will show 0.1% THD at some power level.

Thor

 

[ruffrecords]

Incorrect. Example TL12+ vs. Mullard 5-10 - both are identical (with very minor variations), one has a
higher rated output and distortion.

Demonstrably untrue. The 5-10 was rated at 10W and their own article shows it has 0.3% distortion at 10W rising to 1% at 14W. Nobody thinks of this as anything other than a 10W amplifier

Many manufacturers rated amplifiers that COULD have been rated as 0.1% THD at "clipping" (3/10% THD) and quoted higher power, for essentially identical product.

Examples please

What made Leak's "Point One" products unique was not the electronic design, but simply the way it was measured and marketed and as such was the beginning of the "THD race" that promoted low THD as a figure of merit, without there being any scientific evidence that low THD correlates with high sound quality or audible transparency.

I agree Leak was an excellent marketer but the ).1% race began more than 10 years earlier as I have already demonstrated.

BUT IT WAS achieved ONLY by derating. The same Amplifier could have been rated at much higher power had it been rated at 3% or 10% THD.

Not true - see Mullard 5-10

In other words, Leak rated power at 0.1% THD while others rated power at 10% THD but produced the same power at 0.1% THD. Leaks marketing implied their product was less distorted than the competition, which at least as far as "standard designs" were concerned was not the case, under identical conditions.

Thor

As I have said, I agree Leak was a better marketer.
Cheers

Ian

 

[Walter66]

Maybe the hazardous V81 design let them choose a 3A type germanium transistor. This is massive oversized.

A THD of 1% means damping of unwanted distortions at a rate of 40dB, 0.1% means damping with 60dB.

German studio tube power amps were designed to produce less than 1% THD at full rated power (TAB V81, V69), the best studio tube preamp, V76, rated as low as 0.1% THD in some of it's amplifier modes. Technical designers always need measurements to meet design goals, objectives count.

Some people like Telefunken V69, for me it's too sterile sounding. Had a Klangfilm KLV502, which is EL34 pp design, it was more romantic sounding, but still good specs. So it's always a choice to go the studio route or walk on the sound creator path.

WE 41/42/43, their first cinema amp system, sounded excellent, despite the technical standard of that time, their lack of transformer wide frequency range (WE was always very concervative with stated measurements). To me, it showed many qualities for ultra high end tube gear, even at the High End fair 2023 this wouldn't have to hide and could outperform many modern transistor amps in combination with LOUD speakers. It's audio realism, true to life performance and lifelike sound is remarkable. There are so many things in audio which can't be described with measurements.

 

[ruffrecords]

Leak CLAIMED that this was the case.

Others had also produced amplifiers with 0.1% THD at a given output.

Making a tube amplifier with 0.1% THD at 400Hz and at some power level is trivial. Actually ALL Tube Amplifiers not hard Class B PP will fulfil that, even old transformer coupled non-feedback WE Cinema Amplifiers from the 1930's (e.g. Type 86) will show 0.1% THD at some power level.

Thor

OK, let us put this to bed once and for all. Here is a Leak advert from February 1946 Wireless World advertising the point one series of amplifiers. This is a year before Williamson published his amplifier and a decade before the Mullard 5-10. The advert clearly states the distortion at 15 watts and 1KHz is 0.1% and even shows that at 60Hz it is still only 0.2%.

Cheers

Ian

 

[Walter66]

" POINT ONE "* is the Trade Mark of H. J. Leak & Co., Ltd. It was originally applied to the first power amplifiers having a total distortion as low as point one of one per cent, when in June, 1945 H. J. Leak, M.Brit.I.R.E., revolutionised the performance standards for audio amplifiers by designing the original "POINT ONE" series.
Leak Point One Amplifiers

A Leak 3-stage triple loop feedback circuit, the main loop applying 26db of negative voltage feedback over the complete amplifier from input to output terminals. The output stage uses two 25 Watt triode-connected valves in push-pull with 400V on the anodes.
A discussion about those pp feedback designs can be viewed on this forum:
feedback in Shindo pushpull amp

 

[thor.zmt]

The advert clearly states the distortion at 15 watts and 1KHz is 0.1% and even shows that at 60Hz it is still only 0.2%.

So, again, it illustrates my point of Leak making low THD a "Thing" to sell amplifiers that are technically indistinct from competitors products.

And funnily enough, the "point one" amplifier is actually a "point two" (and probably "point four" at 30Hz).

And the "triple feedback" thing... I still want to see a schematic, which is not in any of your links, TL/12 is single loop feedback.

Lloks to me still like zero engineering (even less than "Madman" Muntz) and 500 Million % marketing.

Without the shuckster HJL was, who knows if THD would have been a figure of merit, as opposed to Olson's or D.E.L. Shorter distortion metric.

The whole course of the way audio electronics developed, including digital audio decades later might have been different (and arguably better).

ThanX HJL!

Thor

 

[JohnRoberts]

I can't point to a date on the calendar when small differences in performance metrics came to dominate merchandising. This was a sign that the audio paths were so good that the specifications were less meaningful. The success of such marketing efforts ultimately put pressure on engineering to improve high profile metrics. Kind of the tail wagging the dog but that happens in competitive product categories.

For several decades typical path performance has been better than needed for most tasks. Engineers to amuse themselves will sometimes over shoot performance targets. For example an amplifier company like Crown manages to deliver a silly high damping factor (DF). DF used to be a useful figure of merit back in the days of transformer output (tube) power amplifiers with relative high source impedance. A marketing guy picked up on that numerically much better specification, and blew it up in advertising to create a perceived difference between otherwise similar amplifiers. Competing amplifier designers responded to the point of sale comparisons when pressured by marketing pukes.

Similar marketing driven faux benefits have been assigned to other characteristics like "slew rate", "frequency response" , etc. I apologize if this triggers anecdotal reports from people who hear these benefits.

JR

 

[thor.zmt]

Similar marketing driven faux benefits have been assigned to other characteristics

And crucially without any evidence that "better numbers = reduced fidelity impairment".

This is not scientific, it is not evidence based. It's simple BS.

I apologize if this triggers anecdotal reports from people who hear these benefits.

Fun thing, I had the chance to do fairly large scale blind testing in product development.

In one case it was two versions of the same circuit, one agressively optimised for low THD (-130dB H2 @ 50% output) and another without such optimisation (-110dB H2 @ 50% output).

The difference between the two circuits according to AP2 was exactly that, 20dB difference of H2 at @ below 18bit dynamic limits.

Now, the difference between the two circuits was heard clearly in blind testing.

But that would not make me conclude that the difference between -110dB and -130dB H2 is audible with music
We know it is not.

So often I suspect people hear differences, between devices, but what they hear is not the difference in the advertised figure of merit.

Thor

 

[JohnRoberts]

And crucially without any evidence that "better numbers = reduced fidelity impairment".

This is not scientific, it is not evidence based. It's simple BS.



Fun thing, I had the chance to do fairly large scale blind testing in product development.

In one case it was two versions of the same circuit, one agressively optimised for low THD (-130dB H2 @ 50% output) and another without such optimisation (-110dB H2 @ 50% output).

The difference between the two circuits according to AP2 was exactly that, 20dB difference of H2 at @ below 18bit dynamic limits.

Now, the difference between the two circuits was heard clearly in blind testing.

Small distortion differences can be heard on pure tones while they are generally masked by complex music.

I recall when designing the sine wave generator inside my TS-1 audio test set, I could hear distortion differences on the order of 0.1% THD when alternating A/B between the extra distortion, or not. I'm not sure I could identify that low level of distortion from a cold start.

JR

But that would not make me conclude that the difference between -110dB and -130dB H2 is audible with music
We know it is not.

So often I suspect people hear differences, between devices, but what they hear is not the difference in the advertised figure of merit.

Thor

 

[Walter66]

Just for curiosity, will TIP 150 Darlington be suitable for a high voltage cap multiplier circuit? 300-400V possible.

"The TIP150, TIP151, and TIP152 are silicon NPN power Darlington transistors in a TO−220 type
package designed for use in automotive ignition, switching, and motor control applications."

 

[ruffrecords]

So, again, it illustrates my point of Leak making low THD a "Thing" to sell amplifiers that are technically indistinct from competitors products.

I don't know what your problem is with that. Just after WW2 negative feedback was barely 10 years old. Lots of companies had explored it in detail as part of their war work and the literature is littered with articles about its application to sound reproduction in order to lower distortion. All Leak did was apply that experience. He didn't make a thing about low distortion it was already a thing.

And funnily enough, the "point one" amplifier is actually a "point two" (and probably "point four" at 30Hz).

Funnily enough so did every other tube power amp using negative feedback where the low frequency open loop bandwidth was limited. Not many manufacturers were brave enough to quote it though

And the "triple feedback" thing... I still want to see a schematic, which is not in any of your links, TL/12 is single loop feedback.

Not it isn't. It has a global feedback loop and local feedback too.

Lloks to me still like zero engineering (even less than "Madman" Muntz) and 500 Million % marketing.

Applying that degree of negative feedback to a tube amplifier in the mid 1940s was no mean feat given the components they had available. And once again I agree Leak was an excellent marketer just like all the other hi-fi brigade. Don't forget vinyl records with their extended frequency response only became commonplace after the war.

Leak Point One Amplifiers

Without the shuckster HJL was, who knows if THD would have been a figure of merit, as opposed to Olson's or D.E.L. Shorter distortion metric.

THD was already an established figure of merit when Leak released his point one range. He didn't invent it. There was a huge sea change in fidelity as a whole post WW2 and Leak played a part in it but by no means did he have the degree of influence you seem to imagine.

Cheers

Ian

 

[thor.zmt]

Just for curiosity, will TIP 150 Darlington be suitable for a high voltage cap multiplier circuit? 300-400V possible.

This part was EOL'ed a while ago.

If you want to, you can use TIP122(127) for the job, just add suitable protection against possible problems, or evaluate everything to the point where you are sure that no issues will make themselves felt in practice.

I fail to understand why you must have this exact circuit, one resistor, one cap, one transistor. Adding protection circuits doesn't change the way it sounds.

Insisting on using poorer grade parts where superior alternatives exist.

Just because "X" did it this way doesn't mean you have to. Who knows, maybe "X" had a fee boxes of the exact part in the warehouse and decided to use them up.

Thor

 

[thor.zmt]

I don't know what your problem is with that.

By promoting THD as figure of merit in advertising, LEAK bears a large responsibility for the direction audio developed.

Had (say) the same THD (& N) meter included a 12dB /8ve emphasis for higher order distortion products and this distortion audibility index been promoted instead, a lot of things would have developed differently.

As if is, 70 years after HJL foisted THD as figure of merit onto the audio world, we are still stuck with it.

Thor

 

[Walter66]

I fail to understand why you must have this exact circuit, one resistor, one cap, one transistor. Adding protection circuits doesn't change the way it sounds.

Insisting on using poorer grade parts where superior alternatives exist.

Just because "X" did it this way doesn't mean you have to. Who knows, maybe "X" had a fee boxes of the exact part in the warehouse and decided to use them up.

Thor

Thanks for your comment, Thor.

Please let me explain my intentions on audio design.

It's all about learning and improving on the best. That's asian philosophy. If you know the best, only then your competent to improve on it. If one doesn't know what others have achieved and how they managed to do so, then improving is much more difficult.

This is the normal way of studying topics. One makes himself knowledgeable which methods and circuits others have applied for a given problem, then testing and comparing them (sonically and technically) and choose the best for yourself or modify, improve on this. Shindo has done it exactly the same way, he started with copies and modded famous tube audio gear, which even had the nomenclatura of old gear in its name, and sold it in an own housing and a little improved. Then slowly applying his own circuits, up to the point now, five decades later, where he completely do his own thing in terms of circuit design, choice of parts and sonic results. One who thinks he can climb the highest mountain and don't have advise from others which already made it will not succeed.

I want to learn how to choose parts for a given task (in this subject: choose the right IC), apply it on the task in the correct manner and listen to the different sonic results different parts produce. You can be sure, if it don't give successfull sonic results, I will not copy anything. My own desings are either heavily modded or completely self designed.

 

[JohnRoberts]

By promoting THD as figure of merit in advertising, LEAK bears a large responsibility for the direction audio developed.

Had (say) the same THD (& N) meter included a 12dB /8ve emphasis for higher order distortion products and this distortion audibility index been promoted instead, a lot of things would have developed differently.

As if is, 70 years after HJL foisted THD as figure of merit onto the audio world, we are still stuck with it.

Thor

The customers who rewarded advertisers who hyped performance specifications by buying their SKUs deserve the blame/credit for how the industry evolved.

JR