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srpp or m-follower?

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Hi

I'm planning to build a preamp.I'm between an SRPP and m-follower circuit.
I know the advantages for the follower circuit from Morgan Jones' book that uses the E88CC for the upper stage and the ECC82 for the lower stage.
I find it very nice to build it but what about the SRPP circuits?
I know that they're good,too.
And Morgan doesn't have any information about these circuits.
I have some other books with schems on SRPPs circuits(with ECC82,6N1P,ECC83...) but with not so much information.

Which is the best circuit?And why?
 
The Mu follower lower tube indeed runs under optimal conditions, enabling much higher gain, almost mu in fact, for the stage.

The SRPP loads the lower tube right down, typically returning a gain around 40% of the lower mu (unbypassed) and 60% (bypassed). This certainly indicates a heavy plate loading.

In my opinion, and I'm only one guy, comparisons between the two topologies, all other things being equal (same tube), the SRPP has better sonics, more musical.

I suspect this is because the distortion spectrum, though much larger for the SRPP, is more favorable somehow. This to me would indicate perhaps more H2 and H3 in the lower gain SRPP.

Cheers,

Hugh
 
diyAudio Senior Member
Joined 2002
Hi,

I'm planning to build a preamp.I'm between an SRPP and m-follower circuit.

If it's for a linestage only I'd definetely go for the SRPP and leave the lower cathode unbypassed.

I suspect this is because the distortion spectrum, though much larger for the SRPP, is more favorable somehow. This to me would indicate perhaps more H2 and H3 in the lower gain SRPP.

I agree...

In between the classic SRPP and the µ-follower there's also the "optimised" SRPP.

Cheers,;)
 
Mu

GAK said:
Hi

I'm planning to build a preamp.I'm between an SRPP and m-follower circuit.
I know the advantages for the follower circuit from Morgan Jones' book that uses the E88CC for the upper stage and the ECC82 for the lower stage.
I find it very nice to build it but what about the SRPP circuits?
I know that they're good,too.
And Morgan doesn't have any information about these circuits.
I have some other books with schems on SRPPs circuits(with ECC82,6N1P,ECC83...) but with not so much information.

Which is the best circuit?And why?


Mu. For all the tech reason's Dhaen outlined below, as well as the fact it sounds a whole lot better. Every SRPP I've ever heard, has sucked. Then again you might like it's flavour.

Personally, I don't bother with tubes for the upper half anymore. There are a number of SS solutions that measure and sound better providing you're not sand-o-phobic.

Gary Pimm has some excellent CCS (constant current sources) that work in mu stages beautifully well. This one would be my suggestion, and only takes a B+ about 50V above the tubes anode voltage to work in a linestage.

Also look at his schematics page for more variations incl some hybrid tube/fet designs and the detail on the theory and how to set them up.

Another variation using depletion mode devices can be found at Bas' mosfet page
This has the advantage of not needing the batteries, but the batteries lasted for months in mine and I could detect no change in voltage; according to Gary the battery life shouldn't be much shorter than their shelf life. I've built both and am using the DN2540 cascode version in my "linestage" at the moment. It's very, very good sounding, so much so that I can't be bothered playing with anything else. The tube I'm using is the 12B4A, which is excellent sounding, has about the right amount of gain, and is cheap ($US3) and available. It does like a DC heater supply in a linestage though. I'd suggest giving it a try at Va-k ~ 120V, Ia = 30mA and a B+ around 200V.

Everything You Ever Wanted To Know About SRPP But Were Afraid To Ask
 
I have built and road tested SRPPs, mu followers with tube and mosfet uppers, and I strongly disagree with the last poster.

It is generally a fact that in this game we rarely compare apples and apples; controlled experiments with identical operating points, tubes, and output loading are rare. Consequently preferences one way or the other are often based on false premises.

As long as the distortion is not high order - viz 5th and higher - a THD up to about 1% is close to irrelevant to the sonics. But you will notice big differences in sound between different tube operating points and topologies.

You are building something which you hope will sound good, but if it measures well it is merely an intellectual bonus. Math and measure in this game has done a lot of harm over the years, although it's sold a lot of very impressive instruments for measuring distortion...... We are organic lifeforms, not machines, and our ears do not perceive the same things as measuring instruments. We are more subtle, and go for things like 'ambience', 'pace, rhythym and timing', and 'tonal balance'. These are well nigh impossible to measure, but they are highly relevant for anyone into good sound.

If you design commercially you soon come to realize that when assessing gear people put great stock in how in sounds. This is common sense, and shows that when the chips are down, and money is involved, their selection criteria are reasonably rational. If they build their own, however, they often go back to measurements, particularly THD and frequency response, and while these are good places to start, they are only a portion of the art. Any good design still has to be 'voiced'.

You'd like to build a two tube series amplifier (TTSA), but the best configuration, in my view, and after listening to a heap of them, is the conventional plate loaded triode. Pick a nice grunty triode like a 6BX7, or even a pentode like an EL84 wired as triode, and go for it. You'll get good gain, reasonable output impedance, and wonderful sound, and it will be simpler. The difficult part then becomes the power supply, but then power supply is always difficult.....

Cheers,

Hugh
 
diyAudio Senior Member
Joined 2002
Hi,

You'd like to build a two tube series amplifier (TTSA), but the best configuration, in my view, and after listening to a heap of them, is the conventional plate loaded triode. Pick a nice grunty triode like a 6BX7, or even a pentode like an EL84 wired as triode, and go for it. You'll get good gain, reasonable output impedance, and wonderful sound, and it will be simpler. The difficult part then becomes the power supply, but then power supply is always difficult.....

Knowing Brett's design philosophy I think he would agree with your philosophy; he just takes a different road to achieve his goal.
I feel alot of the sonic fingerprints of the SS CCSs are camouflaged by the use of massive amounts of iron; IT xformers etc.
I suppose Brett won't agree and i understand his POV.

Brett, I hope you don't mind this?

While I'm in total agreement with you Hugh, I avoid sand devices as much as I can except for where I feel it either doesn't matter for the sound of things or where I feel that using valves is too much of a hassle...

As far as I'm concerned that usually means heater supplies and other low voltage apps.

When it comes to PS designs, no SS HT regs please: they either die on you or/and make the whole circuit sound like sand.

So for me, it's valved regs ( I don't mind silicon rectifier diodes in this context provided they're snubbered or Schottkys) shunt or series depending.

Sidebar: Any news on the Balanced Pre front? I gave up posting there but have some ideas...

One thing I've always hates was cathode bypass caps...with the advent of BG caps I may revise that prejudice. :)

If there's one thing we seem to have in common it's that we all seem to like decent current running through outr bottles.

Cheers,;)
 
Hi Frank,

Thank you for your post; you write interestingly of SS CCS.

I recall reading an article in Glass Audio (I think!) some years back where someone compared distortion spectra with loading on a 6SN7 triode.

As you increased the loading (viz, reduced the ohms of the plate load resistor), the distortion spectrum begins to increase, mostly generating H2 and H3. With infinite plate resistance (sometimes called a CCS) the Av of the stage almost equalled the mu. The output impedance was then the rp of the tube, and the distortion was extremely low. Interestingly, of course, the Zout was actually lower with a resistive loading.

But CCS loading didn't sound quite as luscious as a resistive plate load chosen around 2.5rp.

This makes no comment on a transformer or choke loaded triode, I should add.

A little understood problem of the CCS loading is noise. When you hold a reference voltage on the base of a CCS transistor, any noise at all is amplified, typically by 60dB and more, to the collector. This means that even microvolts at the base show up as millivolts of grunge at the collector. Consequently, the voltage reference had better be very quiet; I use a LED, but even LEDs create noise. There are tricks to rid this noise further, a good one is splitting the current feed resistor from the LED to ground and running a bypassed lytic from rail to the midpoint of this resistor. However, noise still remains. Only the very best caps at this decoupling point will scotch most of it; a Black Gate here works well, but I've yet to fully explore the possibilities, I know the ZL series from Rubycon are good too.

But the point is that this CCS grunge, extending right up into the supersonic range, is significant and damages the music, chiefly by robbing resolution and greying over the 'black between the notes'.

Thus, I'm not in favor of CCS use with tubes, but I do admit that power supply design for plate loaded triodes is not trivial, and very difficult, in fact.

Cheers,

Hugh
 
fdegrove said:
Knowing Brett's design philosophy I think he would agree with your philosophy; he just takes a different road to achieve his goal.
I feel alot of the sonic fingerprints of the SS CCSs are camouflaged by the use of massive amounts of iron; IT xformers etc.
I suppose Brett won't agree and i understand his POV.

If you're referring to my system, I have only two peices of iron in the signal path, an S&B TVC and the poweramp OPT, and two coupling caps in 4 stages from cart to speaker.

And, no, I don't agree with your analysis Frank.

As for the noise issue raised, I don't hear it on a system that's very sensitive to noise (106dB/1W speakers), so to me it's moot.

Harmonic spectra; Whilst what Hugh says about the spectra is true, the IMD will be lower with a CCS-mu stage, and having speakers with very low IMD, I hear that clearly and it annoys me considerably more than THD.

I've tried enough circuits and variations of them over time that I trust my ears on what I prefer, and to my ears SRPP sucks. I'm also pretty good at telling quickly what has potential and play with op-points etc to see if I can improve it to my ears. Hell, two different tubes from the same box often sound different unless you have a curve tracer and are able to match them closely. Measurement was always secondary, but interesting nonetheless.

A mu-stage will generally have a lower Zout than any sensible R loaded CC stage, same tube and op-point. An EL84 is a great little tube triode loaded, but it suffers from a heap of input capacitance which needs to be driven (>200pF) and are generally a bit microphonic in linestage apps IME. Lynn Olson commented it's like a 6SN7 with grunt (paraphrasing), and I'd agree.

As Hugh's 5th paragraph in the post immediately after my previous one is a barely concealed cheap swipe at me, if we were face to face, I'd be more blunt in my response, but basically, get stuffed. I've spent a long time in the electronics field designing and building commercial products and I understand the tradeoffs inherent in business. Because you design commercially has little to do with the ultimate performance of your product and far more to do with marketing, sustainability (esp to availability of NOS tubes), size, shipping weight, legal liability, heat, power consumption, hype, follow-the-leader etc. As for people buying what sounds best, bollocks, they buy what they beleive sounds good, or what they're told sounds good, as most haven't heard anything better. For example, your business was built on amplifier modules that few people ever get to hear in their system before they buy them, so once a lot of time money and effort is expended in doing so, most people are going to convince themselves it sounds great even if it sounds like a sack of shite (NB: I've never heard an AKSA amp, so I'm not commenting on the sonics of these amps). This also happens with people who buy manufactured products, especially when they spend a lot of money on them.

All that said, I do wonder at the topology of the AKSA tube amp stages. Low loaded CC or SRPP perhaps?

This comment in the post before was almost funny; 'black between the notes', because this is one of the main criteria I use (and have for years) and is not one of my systems lesser points.

Last point. Hugh, so far you've tried to skewer me with all sorts of presumption about the topologies of the circuits I use, what I have/haven't tried, how I test etc, and you've been nailed every time, so just give it up. It's boring the eff out of me. We obviously disagree and because you're "an audio manufacturer" I'm not the least bit impressed and I'm definitely not one of the mass of groupies that pervade the hobby. Then again, I don't have to run around and justify my design decisions, as I have few of the limitations you do, and I'd rather my gear performed like a McLaren F1 (road) than an R16.
 
diyAudio Senior Member
Joined 2002
Hi,

First of all apologies are in order for the typos in my latest post, I should get a screening secretary...

I recall reading an article in Glass Audio (I think!) some years back where someone compared distortion spectra with loading on a 6SN7 triode.

Have that one too.

The essence is not the THD but what it is made of.

IMHO IMD is the worst enemy, NOT THD which is just another meaningless number for the measuremant brigade to hang their coats on.

But CCS loading didn't sound quite as luscious as a resistive plate load chosen around 2.5rp.

Optimising µ usually equals amplifying the CCSs sonic footprint to the max.
Unpleasant sounding usually, except for some JFETs which can sound rather sweet but make the whole circuit sound JFET anyway...

A little understood problem of the CCS loading is noise. When you hold a reference voltage on the base of a CCS transistor, any noise at all is amplified, typically by 60dB and more, to the collector. This means that even microvolts at the base show up as millivolts of grunge at the collector. Consequently, the voltage reference had better be very quiet; I use a LED, but even LEDs create noise.

I shouldn't comment, you're dead on the money.

If ever you find copies of the defunct Hi-Fi Answers in OZ please read them, I got most of my little twists from their editor, Jimmy Hughes and the friends we have in common.

Look at CCS noise this way; it's unrelated to the signal and usually exhibits itself as narrowband noise.
Valve Johnson noise OTOH is much more smeared across the audioband and hence much less obtrusive.

Thus, I'm not in favor of CCS use with tubes, but I do admit that power supply design for plate loaded triodes is not trivial, and very difficult, in fact.

Agreed, although more expensive than difficult IMHO.


Cheers,;)
 
Hi Brett,

At the risk of boring others, I will say we are not on the same wavelength here; I had no intention of having a 'cheap swipe' at you. I believe you are so angry you misread my intentions. In fact, I was trying to avoid mentioning you, or involving you, knowing you are pretty touchy.

I accept your 'get stuffed!'. No problem at all. Best if we don't address each other in this forum. There are people whose personalities are so pungent, even through the written word, that it's better they don't speak. We appear to be two such.

Your presumptions about my business are way off. I won't correct any of it; I don't see the point. But you made this comment:

so far you've tried to skewer me with all sorts of presumption about the topologies of the circuits I use, what I have/haven't tried, how I test etc, and you've been nailed every time, so just give it up. It's boring the eff out of me.

I have NOT tried to skewer you, Brett. I mean that quite genuinely. Oddly enough, you made such an accusation of me at one point, which I ignored. I recognize your expertise, you are clearly very experienced and clever. But where getting along with people is concerned, you could be more tolerant. It would be fatuous of you or I to ever attempt to impress each other, so call it off.

If you want to have the last word, email me privately, but please, not here.

Sincerely,

Hugh
 
Drifting a bit from the thread........

Diplomacy is a most essential character that one must develop. It helps the water flow continuously. Without it everything breaks down and nothing good comes of it.

So for anyone who gets offended easily , they should also consider that they may be just 'imagining' that others are trying to offend them purposely. That leads to nasty words and unpleasantness for everyone on the forum. Keep all nasty replies to personal emails - I think the others don't want it. I surely do not want to come on to the forum and see all kinds of unpleasant text. Everytime I log on I am in a happy state of mind. Why should someone ruin it. Unfortunately I cannot avoid it since I cannot know the contents without reading it first.

No one is super clever on their own. We are all manipulating data fed into our brain and coming up with newer or repeated ideas. From that point of view everyone is also as stupid as the other. You can look at it anyway. So no point fighting over silly things. It is VERY EASY to say in plain pleasant language that you do not like what someone said - implied or otherwise. Only kids fight because they are not developed enough. I think we are all mature humans!
Thanks to all those who keep trying to keep the forum clean , happy and friendly. It's a great forum, lets make it SHINE with happiness!
 
Hugh,

I was going to email you, but there are a couple of things I'd like to say on record.

Firstly, as I re-read my earlier post, there may be the possibility in some peoples mind that I have impugned you, your company or your business practices. Whilst I have never had any financial dealings with you or used your products, I have no doubt whatsoever that you are a person of integrity and that your products are good and any dealings with you would be handled in a professional and honourable way at all times. If you or anyone else feels I meant something else I sincerely apologise.

My comments on the business aspects were intended to be generic about the marketing of audio gear in general and the mentality of many 'philes to the reasons behind it's purchase, which are seldom rational. From other experiences in my life I know I'm right. Perhaps this is a worthy topic for a thread of it's own.

Technically I disagree with much of what you've posted, based on my experience, but I seldom comment upon that with which I don't have direct personal experience. F'rinstance, whilst I can do SS design, I'm not as well versed in it as I am hollowstate so I seldom comment on that, except around regs, CCS etc.

You are correct that we are both opinionated individuals who obviously have very different opinions. However, as I've said to you before, I'm very blunt in what I say and how I say it and the medium of the internet fails to convey any emotion aspect. I am not responsible for another's emotion response to anything; they are, as am I for what others say to/about me and my response to that. I was not angry with you at all, nor am I now. And I would appreciate the armchair psychology is kept away, esp because you have no idea about the real content of anything I type here (except perhaps for technicalities). If I misunderstood you before, I'm sorry, but I still don't think I did. There are about 50 different ways I could use the word "mate" next to Hugh in a sentence, all with different meanings, and unless you were here in person you'd have no idea which way I meant it.

I will endeavour to not post comments on your posts in the future, but that doesn't mean I won't.
 
Re: Mu

Brett said:
Every SRPP I've ever heard, has sucked. Then again you might like it's flavour.

I have a friend who dislikes SRPP topology, and I respect his choice, much like I respect your opinion.

For me anyway, I like SRPP used as a driver stage for my 2A3, so you can say I'm one who likes its flavor.

We recently made a simple pre-amp where SRPP is again used with the Rk unbypassed. Several people who auditioned it, liked what they heard.

My belief is that there is no best, in reply to the original question.

I have a cap-coupled 2A3 and 300B, a direct-coupled 2A3 and I like them all. In fact, I'm working on an ultrapath 45 and I hope to like it too.

Cheers.

OT: My friend ordered and built an AKSA amp, he swears by it and is extremely happy with the results.
 
Hi Brett,

Thank you for your post. Appreciated.

Everybody has opinions. I hold some of mine strongly, but I should not make categoric statements, lest people are misled, or prove me wrong!

Make as many comments on my posts as you like, I have no problem with that. I've been wrong before, and if you can get past the emotion to my thought processes and correct me, I will appreciate it.

I have to be honest and say that it really doesn't matter what you, or I, or anyone else thinks of each other. What is important is what we think of ourselves. I'm quite happy with my ethics, though I can't be as sure about my technical opinions.

Besides, the Ongaku uses an SRPP input stage and is often described as a wonderful amplifier. I suspect most of this comes back to operating point, regardless of topology. Even so, I still prefer the plate loaded triode!

My apologies for any disharmony this might have caused others.

Cheers,

Hugh
 
Wonderful it may be. It's also quite hilarious. Two highly respected and experienced audiophiles and engineers who generally agree on 95% of all audio issues make such a fuss about the remaining 5% :) Can you not choose a more fitting opponent (like a hardened objectivist or someone who is convinced that a GC is way better than any PP valve or AKSA amp) for the bar brawl?
 
Hi

we are here just for fun and to change ideas,advices,experience and knowledge.Nothing is better than the other and all these depends on what somebody wants.
I know guys who prefer listening with pure class A 2A3 SE amps with horns and guys that hate horns and prefer P-P.But who is wrong?
Everything depends on the "feeling" of listening.On what kind of music you are listen.And so on.

Brett has right but Aksa has right,too.

I have a problem with SS circuits and I don't like to use them at all.And this because I love tubes.Not for an other reason.
Noone can told me that I'm wrong.
Aksa prefers sonically a line stage with a simple triode.His ears prefers that.
Brett has achieved good hybrid stages and his happy too.
I thing noone is wrong.
Our ears and our feelings will define this.
An other example is that some people listen with CDplayers and other are vinyl junkies.
I'm extremely a vinyl junkie but I had listen very good music to friends from CDs.I like vinyl cause I love it for my reasons.But I can't prove to someone else that acoustically is better.
It's like music.I can't prove to anyone that Jazz is better than classic music.

So let's continue the thread cause I haven't decided what kind of line stage to choose,yet.
Now I'm between SRPP with ECC82 and I like the idea with the simple triode.
Aksa do you have an other idea except the 6BX7?
What about a single triode?
 
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