6B4G - The Resurrection Shuffle

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Cressy Snr
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#286 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

Ray P wrote: Sun Nov 19, 2017 9:57 am
Cressy Snr wrote: Sun Nov 19, 2017 9:21 am Shows what you can do with a restricted colour palette.
You only had a tin of pink paint then?
No, I bought that. It was a mad moment in B&Q
Got some funny looks from a couple of builders. :lol: :lol:
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#287 Re: 6B4G - The Resurrection Shuffle

Post by IslandPink »

Cressy Snr wrote: Sun Nov 19, 2017 12:04 am The amp is plenty wide enough in bandwidth and the bass goes down through the floor.
The thing was very carefully designed, with particular attention being paid to avoiding multiple rolloffs and phase shifts, that's why the first stage is biased with a white LED plus other factors were carefully considered, such as adequate spacing from each other of the -3dB poles of the driver and output stage.
Troublemaker here again :D
For sure, what it sounds like, at the end of the day, is the most important thing.
However, you having set out your principles above, I have a couple of observations ...
Looking at your circuit on p.18 ( is that the final one ? )
Stages 1 and 2 and their coupling cap, I have no gripes with, any bass filters are very low.
Then you go from stage 2 to 3 with a 0.1u/100k - this is a 15.9Hz high-pass (-3dB) . ( On my 300B amp I use 0.47u/150k, which is 2.3Hz )
Then on the output stage you have a cathode R of 750R and a small 22uF cap ; this is approx. -3dB down at 20Hz when you allow for the cathode resistance. ( On my 300B amp I use 940R and 150uF which is about 2.5Hz )
So, when you add these to a similar roll-off from the output transformer, you've definitely got significant dB losses and phase rotations up to 40 or 50Hz.
Anyway, I hope you had a good natter and some enjoyable listening with Paul !
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#288 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

But it plays music. That's what counts.
I set out my stall after the frankly nasty period earlier this year over my speakers.
I don't give a monkeys about hi-fi anymore. IMO It's a load of utter bollocks!
Taken me forty-odd years to realise that it is music that counts.

Phase can go fook itself as far as I'm concerned. I don't care as long as it doesn't reach 180 degrees.
I'm not clever enough to be an engineer, mathematician or whatever we decide to call it, I don't understand it, so I've taken a poetic/creative approach to my music making apparatus, including speakers. Much more satisfying for my personality type.

I've become very much aware that the stuff I write grates on people increasingly, I've had enough PMs from an ex member of this forum to know that, but that is not my problem and I'll keep right on being vague, and sloppy in my thinking. I've given up trying to be taken seriously because frankly it's not gonna happen. There are too many clever people on here for my limited brain power to ever be anything more than a source of amusement.
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pre65
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#289 Re: 6B4G - The Resurrection Shuffle

Post by pre65 »

Cressy Snr wrote: Sun Nov 19, 2017 1:28 pm There are too many clever people on here for my limited brain power to ever be anything more than a source of amusement.
Having a bad day Steve ?

There are indeed some clever people on here, and I'm glad, because the information they impart has been of great help to those (like me) who really struggle with the theory and maths involved.

Compared to me Steve, you are a genius. :lol:

And why place so much store in the single forum member who PMs you ? There are plenty more (me included) who have followed your many projects with great interest.
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Paul Barker
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#290 Re: 6B4G - The Resurrection Shuffle

Post by Paul Barker »

Sounds very good.
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#291 Re: 6B4G - The Resurrection Shuffle

Post by ed »

Paul Barker wrote: Sun Nov 19, 2017 3:32 pm Sounds very good.
at least we agree on one thing then...snigger
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#292 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

pre65 wrote: Sun Nov 19, 2017 2:14 pm
Having a bad day Steve ?

There are indeed some clever people on here, and I'm glad, because the information they impart has been of great help to those (like me) who really struggle with the theory and maths involved.


And why place so much store in the single forum member who PMs you ? There are plenty more (me included) who have followed your many projects with great interest.
Why would you think I'm having a bad day? not at all.

Of course I'm extremely grateful for the help, I've had in the past from some very clever people. Without their help I would never have got far.
I understand fully how exasperating it can be for people with engineering related degrees who have to put up with my aparrently sloppy half-baked reasoning and even sloppier grasp of the finer nuances of filters, vectors, superposition, reactance, AC theory and time constants. Believe me gents I feel your pain. I empathise fully with your position and your need to correct what you see as unforgivable howlers.

But as a creative, thinker and a total non-team player, who does not know the meaning of accountability, the value of evidence, paper trails or logic I feel equally exasperated by impenetrable maths being put at me as evidence that I am wrong and have designed a turkey, despite clear testimony from independent listeners that entirely contradicts this position.

I really don't have a clue what the bloody hell Mark is talking about, but I absolutely support his right to say what he thinks as indeed he is entitled to and must, lest anyone copy my circuit without knowing the full facts about the compromises inherent in it.

Indeed Morgan Jones takes apart the Williamson amplifier, the Mullard 5-20 and the QUAD 22, and suggests improvements to bring them up to date, but that doesn't stop these amps, in their raw state, of which I have heard all three, sounding fantastic.

Let's think a little bit here. I wanna tell you a story. I was talking to Nick when I went to his place a few weeks ago to get help with component values for transformer snubber networks. It was nothing to do with the job in hand but Nick said something that stuck in my mind. Now I'm like a hoover when someone says something like Nick said. It gets stored for future reference.

So get on with it man! What did Nick say?
OK he was talking about 300B SETs sounding fantastic on digital and less than fantastic on vinyl. Something along the lines of wide bandwidth engineering causing warp signals to saturate output transformers. A solid state amp couldn't care less as long as it has enough power, but a low power SET does not want to have to be dealing with high amplitude warp signals it has limited power as it is and needs to be using what it has, to maximum effect not be wasting precious resources puffing and blowing bass cones in and out. See the language I'm using? I convert engineering terms into stuff I can understand.

Now I know feck all about poles and care even less, but MJ for one says that if you make a three stage amp, they become important.
He tells you how to calculate them so you need to consider them or you get an oscillator not an amp. JamesD said long ago about using staged filter frequencies that are ten times the preceeding one so you don't get unusual behaviours within the signal path. These things from experts stick in my head. So that's what I did. Simples......except it isn't is it - it never is.

"Ah but you didn't take into account phase shifts from your filters, so your bass will be crap" except it is anything but crap and motors along with PRaT in spades, textures galore and welly unheard by me from any other device I have built. The bass cones flap not a millimetre.

I'm perfectly well aware that things are not as simple as I think, BUT I've long since learned from this pastime and from the work I have done with kids/adults that you solve one problem and by doing so you create another. You choose your compromises based on what you think is the order of importance. I chose frequency and not phase. My vnyl sound just as good as my digital, via the 2A3 amp. So my choice is the correct choice; a choice I made based in the first instance on what Nick said and in the second, on what James said so long ago. It was an informed choice based on expert opinion not ignorance. I don't of course write down every thought in my head that goes into a design, that would be tedious in the extreme.

My personality type comprises less than 4% of the population, so it means that if I'm in a room with a hundred people then 96 of them are going to tell me I'm wrong, whatever I do.

That upsets me greatly because when you work extra hard and think things out carefully, which is another one of the traits of my personality type, that has led to much paralysis by analysis, you get mightily pissed off when somebody tells you you are incorrect because you have missed something, when you have actually not missed it at all but have analysed the problem to death and rejected their point as unimportant.

The paradoxical nature of my type is that we think, think and think again about anything and everything, yet at the same time appear outwardly to be undisciplined and sloppy. It is something that nothing can be done about I'm afraid and members are just going to have to live with it. That's the way I am. I'm being myself.
Last edited by Cressy Snr on Sun Nov 19, 2017 6:42 pm, edited 1 time in total.
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#293 Re: 6B4G - The Resurrection Shuffle

Post by IslandPink »

Sorry I upset you. I was just thinking there were some places where the circuit could improve, which is where the analysis above came from.
Cressy Snr wrote: Sun Nov 19, 2017 6:25 pm Now I know feck all about poles and care even less, but MJ for one says that if you make a three stage amp, they become important.
He tells you how to calculate them so you need to consider them or you get an oscillator not an amp. JamesD said long ago about using staged filter frequencies that are ten times the preceeding one so you don't get unusual behaviours within the signal path. These things from experts stick in my head So that's what I did. Simples......except it isn't.

"Ah but you didn't take into account phase shifts from your filters, so your bass will be crap" except it is anything but crap and motors along with PRaT in spades, textures galore and welly unheard by me from any other device I have built. The bass cones flap not a millimetre.
I must have a chat with Nick about the MJ/James D stuff you mention above. I was aware of the need to watch out for close time constants causing oscillation in power supplies, but hadn't tried to do anything like this in a power amp. I can understand how you got the circuit values above, if this was the concern.
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#294 Re: 6B4G - The Resurrection Shuffle

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ed wrote: Sun Nov 19, 2017 4:12 pm
Paul Barker wrote: Sun Nov 19, 2017 3:32 pm Sounds very good.
at least we agree on one thing then...snigger
a like emoticon.
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#295 Re: 6B4G - The Resurrection Shuffle

Post by Paul Barker »

If anyone read Steves long post. I am same personality profile as him so were both 4%ers that cant get along with the 96% of a group situation.

As I walked into the house he had classical on apple music. It was a surprise. The speakers are very good, so good that I would probbaly manage with them instead of OB. They are very like OB in sound stage. You can sit off axis, as I did all the time and picture the 3d soundstage.

The amp was a typical set. Very good with the usual set characteristics thta are marmite here. You are a set lover or not. It suits the speakers.
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#296 Re: 6B4G - The Resurrection Shuffle

Post by izzy wizzy »

I'm glad to have followed this amp build to it's very happy conclusion Steve.

I think you hit upon some very valid points about bass response, poles, rolloffs and so on. You can do a simple calcs and find where the poles are, rolloffs and so on. Sure staggering is a good idea but unless you sim the whole amp, you won't get close with a calculator alone. When I sim a phono stage I look for good extension but after 20Hz, a steep roll off to avoid transformer resonance issues that lead into TT arm resonances, record warps issues, bass feedback and so on. In the past, I've gone for raw extension but it just doesn't sound as good and can lead to other problems. I'll lose a bit here of all places to limit issues elsewhere.

There are bass humps and dips in all of the amp so as Steve says, choices have to be made. And the ultimate test is how it sounds. Bass pump is very real in vinyl and a great sapper of power. Super low LF is an issue. If you have circuits with transformer coupling then bass resonanace can be even more problematic as input and output transformers can react with other coupling caps and psu caps. Parafeed just adds to these combinations. Parafeed issues can occur when you might not even know or have control over with say a preamp output cap feeding into a power amp input transformer. Staggered LC smoothing stages in PSUs is another. TVCs have real issues with this and why some people can't get on with them plus drive issues.

Many fans of parafeed talk about not being able to calculate the coupling cap but rather listen to a range of values until it sounds right. I'm thinking Daves Slagle and Davenport, Keving Carter are just some I've read on this. I hear Slagle talking often about qty of inductance where real world vaues can be much lower than calculated (don't ask me why but I believe him) for decent low end.

I'm not sure phase is such a big issue down low. Look at peeps who use sub woofs. They are placed to minimise room interaction and are not usually aligned with phase in mind. I would imagine trying to even measure this stuff to be fraught with room interaction, where you sit, where the speakers are etc.

Resonance is everywhere in our circuits, our transducers and our rooms. It is the essence of music itself. We need our gizmos to produce that and sure, a bit of technical knowledge can go a long way but ulimately, it needs to sound good and so our ears will be the thing that works it out in the end.

cheers,

Stephen
Last edited by izzy wizzy on Sun Nov 19, 2017 8:32 pm, edited 1 time in total.
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#297 Re: 6B4G - The Resurrection Shuffle

Post by steve s »

I was very impressed with Steve's amp, it's nice to hear some consensus, interesting comments from Nick regarding sets and vinyl
My finding for quite a few years now but never thought to blame the ultra low frequencies
I'll be watching the bass cones in future....
Regarding bass levels, Steve set was the equal of the a20 solid state amp which was played when he brought his amp round which made me feel my px25 amp had lost something in its latest guise....
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#298 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

Thanks for that bit of explanation Stephen.
It has made things clear and provided reassurance that I'm not completely daft. :D
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#299 Re: 6B4G - The Resurrection Shuffle

Post by IslandPink »

Stephen, do you believe that RC filters in different parts of a power amp interact with each other in a resonant way ?
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#300 Re: 6B4G - The Resurrection Shuffle

Post by izzy wizzy »

IslandPink wrote: Sun Nov 19, 2017 9:15 pm Stephen, do you believe that RC filters in different parts of a power amp interact with each other in a resonant way ?
In a vinyl system, you can push the LF low enough to excite resonances in other parts of the system and those can eat power and cause bad sound, overload etc. Cascade issues with RC filters can cause ripples like they do with different filter types. Is a ripple that is seen in some filter types a resonance? Are beat frequencies in power supplies that lead to motorboating a resonant RC filter interacting? This can be an issue in a two stage amp never mind a 3 stage. Are these just different names/terms for resonance?

A regulator can hide these issues and some people don't experience them as their first choice is to regulate because regulation is always better ;)

As usual, most of my experience is with phono stages, some with transformers, TVCs and so on so it's hard to isolate and say RC filters interact but I think yes they can in conjunction with circuit topology and PSU configuration.

cheers,

Stephen
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