Push-Pull Basics.

[IslandPink]

Gary would have used whatever was handy, from memory I think the amp ( he showed it to me ) used a mix of the battery-bias CCS and the self-bias CCS's :
http://www.pimmlabs.com/web/Battery_biased_ccs.htm
http://www.pimmlabs.com/web/self_bias.htm
Gary used to sell the PCB's and a few components like the LND150's, at a nominal cost, but isn't doing this at the moment, as far as I am aware .

[Cressy Snr]

Here is another circuit.


It is my existing amp but converted to run balanced feedback, (Jones - Valve Amplifiers 4th ed ) from the OPT secondary.

Not that I'm about to try it, just a discussion exercise really.
For a start I, probably would hate the sound of a pentode driving a pentode output stage that actually acts like a pentode. IYKWIM.

[Alex Kitic]

Are we talking differences in micro-dynamics, or bass dynamics ? Most PP amps seem superior in bass dynamics to SE amps unless the SE amp has a shunt-regulated supply . In microdynamics it can be the other way round . On the other hand the Aurora that I built , and Gary P's 47 PP amp were as dynamic as anything I've heard.

This is really difficult to resist, sometimes it is like waving a red scarf in front of a bull's head.

Most PP amps seem superior in bass dynamics to SE amps unless the SE amp has a shunt-regulated supply.

I can hardly believe what I am reading?!
1) SE amps have a rather steady current draw and if the power supply has enough power reserves (in Joules) there should be no problem whatsoever in operation: thus a shunt regulated supply is totally superfluous, in particular for the task above mentioned.
2) It is actually the PP amp that might have (if AB) rather large variations in current draw, and would benefit from a shunt regulated power supply (i.e. all the contrary from what stated).
3) Since none of the RH amps has a shunt regulated power supply, they should be rather deficient in the bass department - but on the contrary, those who have built any RH amp, even the lowly ones (RH84) know what is the real situation with bass.

In microdynamics it can be the other way round.

Really? And why would that be? Maybe this time shunt regulated has nothing to do with reproduction? How do you define "microdynamics"? Is it just a nice word for defining natural instrument timbre reproduction?

On the other hand the Aurora that I built, and Gary P's 47 PP amp were as dynamic as anything I've heard.

I like the "as dynamic as anything". This probably means "just as good as anything else"... and yes, I know you built the Aurora - but you never built any of the RH amps (or heard any), so you don't know the difference. I guess they were not complicated enough for your taste, or maybe the designer is not a nice guy and certainly not a hero...

[Alex Kitic]

How stupid I was... it took me years and years to get to the truth!

1) People know little or nothing, while I imagine they do know something and start by giving them credit for what they are not.

2) I come late, so people are already fascinated by what they have been told previously. Thus their opinion is already formed. Lacking knowledge, they continue to believe in what they "already know".

3) Stakeholders will defend their turf (yes, I already knew that: what I did not know is how important the stakes and the turf are to them).

The result is an unnecessary loss of energy and nerves trying to explain stuff to people who either know better than to acknowledge it, or know little or nothing so they cannot acknowledge it.

This is a revelation to me, at last. The uselessness of such discourse. The walls are better interlocutors: at least they don't echo the words of others.

[Nick]

I like the "as dynamic as anything". This probably means "just as good as anything else"... and yes, I know you built the Aurora - but you never built any of the RH amps (or heard any), so you don't know the difference. I guess they were not complicated enough for your taste, or maybe the designer is not a nice guy and certainly not a hero...

And you built the Aurora?

Come on Alex, tone it down a bit maybe? I refuse to micromanage this place, but your level of anger against the rest of the world and self promotion is getting a bit tedious. Play nice with the other inmates please.

[Alex Kitic]

No Nick, I did not build the Aurora. And I do not intend to.

I did not get the "self promotion" part, but it does not matter.

And you don't have to worry about me, I can manage myself quite well... as my post above points out, I don't intend to waste time in pointless discourse.

[Nick]

No Nick, I did not build the Aurora. And I do not intend to.

It was a rhetorical question

I did not get the "self promotion" part, but it does not matter.

No? must be me then. Maybe I should alter my sig to point to my own opinions.

And you don't have to worry about me, I can manage myself quite well... as my post above points out, I don't intend to waste time in pointless discourse.

I don't, I am just looking for a pleasant life. My original request stands. Tone it down a bit please. If you want to express negative options about other people, do it somewhere else.

[Alex Kitic]

I did not get the "self promotion" part, but it does not matter.

No? must be me then. Maybe I should alter my sig to point to my own opinions.

I would like to stress the fact that my signature links to my design work and not my opinions.

I seldom post opinions, I prefer stressing out facts. Others, on the opposite, post their opinions that get disguised as facts.

In most cases, I find it difficult to accept opinions being presented as facts, and therefore I react. But that is my problem and I have to deal with that. If I cannot keep my mouth shut ("my pencil put"), it's best that I refrain from posting at all.

[steve s]

What speakers do you use alex to assess your amplifiers.?

[Alex Kitic]

What speakers do you use alex to assess your amplifiers.?

At home, Heybrook Sextets (SEAS woofer and mid with Tonegen ribbon tweeter). The speakers are between 88 and 90 dB/W/m efficiency.

I have made recently slight modifications to the crossovers, as explained in more detail in this thread:
http://www.world-designs.co.uk/forum/sh ... php?t=1318
If you are not too familiar with this Heybrook model, you should try reading the thread since a lot of interesting details will emerge, both about the (in)consistency of manufacture and the "liberty" one may or may not have in tweaking those.

I consider the speakers to be "nothing special", and as such they give a good approximation of the "voicing" of the amplifier projects in a normal home with normal speakers. Those with more efficient, possibly horn speakers will obviously enjoy more loudness than is available to me, but should be more susceptible to discovering eventual tonal defects (horns tend to be more troublesome than "standard" speakers): since no such problems have been pointed out so far, I guess the "etalon" I use is just fine.

Of course, the speakers are just one link (the last one) in the audio chain. In may case, there is a preamplifier (RPA: http://www.tubeaudio.8m.com/Rpa/rpa.html) which is important in complementing the result and assessing input sensitivity and tonal issues.

Etc...

[steve s]

Thanks Alex, appreciated, but that highlights to me that your real interest is amplifier design possibly not out and out sound quality,
or maybe just a lack of funds?
Voicing an amplifier is a term i dont quite understand, it should just amplify?

Steve

[Alex Kitic]

Thanks Alex, appreciated, but that highlights to me that your real interest is amplifier design possibly not out and out sound quality,
or maybe just a lack of funds?

My interest in amplifier design dates back to my childhood. Instead of becoming an engineer I became an economist - its the damnation of all the children with multiple talents, the parents can do whatever they please with them (try to force a child who has no talent or interest whatsoever in history, geography and social sciences - to study social sciences, or economics... or vice versa, try to force a child who has no talent for math to study physics or mathematics). Thus I had to do a lot of learning on my own - something that is not difficult when you are talented and interested. Parents or no parents, we have the right to make some choices in our lives.

My interest is EXCLUSIVELY SOUND QUALITY. I like to say that the problem is not whether I might have the funds to squander in some amp, but the fact that it is not superior to what I can design and build myself.

NOTA BENE: DESIGN. I design my own stuff, and it is not "repetitio" of the designs of others - it's as genuine and original as it gets to be when we talk about an obsolete technology roughly 100 years old. In designing, I use some very powerful tools, like my brain, my knowledge, and spice modeling. Some of those tools were not available throughout most part of the XX century.

Besides sound quality, I am also interested in the other aspects of designing amplifiers, like efficiency, durability, "idiot proof" aspects, etc. which is why you don't need to think too much when building an RH amp: just follow the schematics and if you do not make any mistakes in the wiring, everything will work from the very first instant, as if by magic...

It is very interesting that you should ask such a question? What makes you think that I am not primarily interested in sound quality, or that there is some "lack of funds" issue? Maybe because I live in Serbia where wages are inferior to what you are used to, or because I am currently unemployed and cannot afford to buy myself a new shirt or pair of shoes - or the fact that I am not interested in paying 3-5k EUR or USD, or more, for something I can do better on my own - not only build, but design as well?

BTW, have you built any of my designs, from the "lowly" RH84 towards the more advanced and expensive ones, like the RH300B or one of the RH2A3 versions? Of course you have not: otherwise you would know what is the most important characteristics of my designs... Maybe you should Google a little my name or some keywords like RH84, and see what others think of it - are they happy with the sound?

Voicing an amplifier is a term i dont quite understand, it should just amplify?

Steve

"Voicing" is basically fine-tuning the characteristics of an amp in order to achieve what you intended to... Interestingly enough, it is a term that I have read somewhere on the net, so it is not something I have invented. If you cannot hear the difference in sound between two ECC81 tubes, or two 2A3 tubes, or two rectifiers... than "voicing" is something you will never be able to do or understand.

Amplifiers amplify the signal, as their name says, that is what they are supposed to do. Your statement that amplifiers "should just amplify" implies that you understand very little about sound quality.

It is thus again very strange that you should question my motivation and goals... but you can have it, as long as I have the patience to reply.

[steve s]

Thanks for the reply alex, i was just trying to understand the angle you come from, to me both loud speakers and amplification can both have a significunt effect on sound quality, and they go together... and they need to be both at a similar level in my view to get the best sound. As i have built new amplifiers over the years i have frequenty found that better speakers can highlight the not quite so good , but its loudspeakers that are the real challange for me, i have built so many over the years, and its very difficult to get every aspect of the sound really realistic, but i do get close,
I watched Leonard Cohen at leeds arena last year, in my view the sound i achieve at home exeeded the live (amplified) sound i heard there, and i was in a good seat.. but that is not always the case, so much depends on the recording.
Like many contributors to this forum i have been building amplifiers and speakers for quite a few years, close to 20, i have learnt what i want from them, I dont think i have achieved what i want, but I'm getting close these last few years.
I dont publish anything, why would i want to? I'm open about what i build, many of the people around here have heard my creations but i would say not everyone gets what i'm trying to achieve. But that does not matter to me.
I use the type of valves i want to, and keep trying to push my boundaries with the speakers i build. And that makes this a good hobby for me.
I have so many of manufactures loudspeakers and valve amplifiers you cannot imagine...but i choose to build my own for good reason.. Sound quality? So i know just a little?

[steve s]

Amplifiers amplify the signal, as their name says, that is what they are supposed to do. Your statement that amplifiers "should just amplify" implies that you understand very little about sound quality.
.

All amplifiers take something away from the signal, as in the signal is not wholly reproduced.

[rowuk]

I think that the idea of a straight wire with gain got a lot of unnecessary traction by the press. What we really need is much, much different.

If we compare a fine 12" or 15" woofer to a dome or ribbon tweeter, we have very conflicting requirements. If feeding a full range speaker system, the amplifier has to be able to output current to grab the woofer voice coil by the balls, but also needs the finesse to "tickle" the tweeters. When we mix technologies in speaker systems, we place incredible requirements on the amplifier to optimally drive them at the same time. If we recognize that there is no such thing as a "linear" speaker driver, then we start to see that in the better playback systems we will require synergy.

We can get "results" with a mini system and a single driver mini speaker, but when we get to the point of truly leveraging technology for better sonics, then the dreaming stops.

I remember the UK press of the 60s and 70s (yes, I am that old). At that time the most important piece of kit was the source - for most a tweakable record deck. The claim was - it doesn't get any better further down the playback chain. During the same time in the USA, there was much more emphasis on the loudspeakers with the argument being that we can spread comprimise out and still end up with superior playback.

Today we have none of this. Every stage of the press and even "common knowledge" is seriously flawed when it comes to technology vs sonics - still most of us get decent playback. If we want "better" playback, we have to stop dreaming and find out what the real issues are. As far as amplifiers go, I think that there are a couple of universal truths that we need to isolate opinion and fact. I think a couple of facts that probably will get no heat would be the following (no mention of the sonic signature!):

1) Difficult speakers to drive need amplifiers that exert greater control
2) Plugging quality speakers into different amplifiers results in a different sound, not just because of the sonics of the amp, rather the complementary behaviour of the amp vs the speaker
3) single ended triodes without feedback have little ability to negotiate difficult speakers
4) single ended triodes WITH feedback are a rare breed due to the typically extremely low output not being compatible with standard speaker technology. Common knowledge also makes feedback a devil.
5) Pentodes give us the opportunity to get more power, they require feedback more or less by nature which helps them get along with difficult speakers better.
6) Push Pull designs offer a lot of power and when with feedback the possibility to drive difficult speaker loads. Lack of symmetry due to tubes being different and aging differently is surely an issue.
7) very few of us have had an opportunity to compare "premier" examples of each technology in a short period of time with the respective qualified speaker systems.

I think that we need to think about those things before even getting to sonic qualities.