6B4G - The Resurrection Shuffle

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Ray P
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#391 Re: 6B4G - The Resurrection Shuffle

Post by Ray P »

Hi Steve, the latest John Broskie blog popped into my mailbox this morning and I thought of you...

http://tubecad.com/2018/01/blog0409.htm

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#392 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

Yes, it's interesting that he came up years ago, with the stuff I'm only just finding out; probably because he's an engineer/ scientist :lol:

I'm one of those unstable, arty types, who over the years, has failed to ask the right questions of those capable of answering them, so has struggled a bit as a consequence, to get beyond the "good" and move towards the "great" amp.

Here's Herb Reichert again, in Sound Practices issue 14, talking about The Feral Eye 2A3 pp amp he worked on with the New York Triode Mafia.

I have a confession to make. By any rational standard, I am not qualified to design an audio amplifier. I have built every feasible circuit. I have read dozens of books and even studied in the classroom of my mentor Arthur Loesch. Still, after almost twenty years of trying, I feel radically unprepared for the chore.

I am a slow learner and I have the worst memory in the world, which may be an asset but it sure is embarrassment. I sound like a darn fool when discussing mathematical problems. I continue to ask the same dumb questions and rely on the advice and consul of guys like Steve Berger, J.C. Morrison, Komuro, Andy Grove, Kondo and Nobu Shishido. Without their help this amplifier would not exist.

On close examination, the only real talents I can muster are a basic ability to paint pictures and a potential to (sometimes) be quiet and listen. My (imagined?) capacity to glimpse a painting, read poem or visualize the forces of nature is the source of my belief that I can indeed design audio amplifiers.


I identify with all of the above. :lol:
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#393 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

It now has a name.
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Badge is about as sophisticated as a Dymo label, but it adds a certain degree of unpretentious, staff toilet door signage charm. :lol:
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Paul Barker
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#394 Re: 6B4G - The Resurrection Shuffle

Post by Paul Barker »

Well you really are making really great sounds in your house with your own design of speaker and your own design of amplifier, so you don't need to apologise.

That badge is pretty damn godawfull though.
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#395 Re: 6B4G - The Resurrection Shuffle

Post by jack »

Paul Barker wrote: Sat Jan 20, 2018 2:31 pm That badge is pretty damn godawfull though.
Yeh. The kerning on that "T" is completely out :)
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#396 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

Paul Barker wrote: Sat Jan 20, 2018 2:31 pm
That badge is pretty damn godawfull though.
Yes it is isn't it. :lol:
Not really apologising Paul (except for that badge) just trying to give an insight into the way my design mind works.
It would be a sight easier, if I could get a handle on using the right mathematical process for the right purpose. I have no problem with the pure maths itself, except I'm slow, it is choosing the right operation for the answer I'm after. Hard to explain to those who are good at applied maths.

But as I've managed to get PSUD installed and running on my Mac, the PSU side of things, which is arguably the most important, is going to make me a ruddy sight more productive in terms of getting it right or near to right, early on.
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#397 Re: 6B4G - The Resurrection Shuffle

Post by jack »

There is absolutely nothing wrong in not having a good grasp of the maths - that's what simulators like LTspice and PSUD are for.

Knowing the maths helps with theory, and simulators are just practical implementations of the theory. However they depend entirely on the accuracy of the device models they use in order to produce results that match practical implementations.

At the end of the day, maths & simulators etc. help the design process, but it's only your ears that really matter.

If you are interested in the "why" things change the sound the way they do, then knowing the maths & physics is essential.
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#398 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

Got rid of that toilet door sign and instead, put on one of my old Northern Soul lapel badges from the 70s, depicting the header for the old 1960s "Stateside" record label, that issued soul recordings under license from the American labels.

I used to have this badge on the lapel of my old Crombie coat. Apt that it has finished up on the Pink SET; an amp that plays Northern and classic soul like a true veteran. :wink:

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Much better.
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#399 Re: 6B4G - The Resurrection Shuffle

Post by jack »

Cressy Snr wrote: Sun Jan 21, 2018 12:57 pm Much better.
Spot on...
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#400 Re: 6B4G - The Resurrection Shuffle

Post by IslandPink »

He he - top notch !
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#401 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

Right....PSU number 12 !
Sitting listening this morning and another of my blasted valve rectifiers went west! :x
Clearly, valve rectifiers are not compatible with my power supply ideas.
I stopped the simulated PSU eating valve rectifiers almost immediately; it now just eats them after a week or so, but you can't simulate a week's worth of usage in PSUD :lol:

So...one of the made up SiC, Schottky equipped bridges from the defunct Barbarik monos was plumbed in; no soft start, no nothing, just throw the switch and wham!
And you know what? Using the 375V transformer secondary I get a smooth rise to 375V followed immediately by a smooth, fall to 307V at the 2A3s, all within the space of a couple of seconds, as the filaments come up to temp.
I can live with that. What's more, I get textbook 2A3 op points, 4W power output, killer bass, a sound that does not suffer any ill effects, due to the lack of a pretty glowing rectifier, AND it'll be reliable going forward.
After 4 hours, the mains TX is cool, the choke is barely warm and 15W of 5V heater power has been saved.
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Dunno why this one has been such hard going. :scratch:
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#402 Re: 6B4G - The Resurrection Shuffle

Post by simon »

Curious. And a bit frustrating.
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#403 Re: 6B4G - The Resurrection Shuffle

Post by simon »

Hmm. I read somewhere t'other day that SS bridges should have the rectifiers snubbed and a 0.01uF 3kV rated cap across the secondary (at this sort of HT) to deal with switching spikes. Didn't get any further researching this but maybe someone can comment?
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#404 Re: 6B4G - The Resurrection Shuffle

Post by jack »

simon wrote: Mon Jan 22, 2018 11:39 pm Hmm. I read somewhere t'other day that SS bridges should have the rectifiers snubbed and a 0.01uF 3kV rated cap across the secondary (at this sort of HT) to deal with switching spikes. Didn't get any further researching this but maybe someone can comment?
We've discussed this at length. It comes from a Morgan Jones article in Linear Audio a year or so ago about snubbing the ringing from xfrmr secondaries - Nick (the other one) produced a neat board to help get to the right values easily.

Snubbing the actual diodes now seems to be discouraged as it lets RF and noise into the DC side of the system.

See http://www.audio-talk.co.uk/phpBB3/view ... 76#p141173
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#405 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

I think that all the old fears about using SS bridge rectifiers have, since 2011 when HV silicon carbide schottky rectifier diodes became available, are much reduced.

I found this:
The most important difference between the p-n and Schottky diode is reverse recovery time, when the diode switches from non-conducting to conducting state and vice versa. Where in a p-n diode the reverse recovery time can be in the order of hundreds of nanoseconds and less than 100 ns for fast diodes, Schottky diodes do not have a recovery time, as there is nothing to recover from (i.e. no charge carrier depletion region at the junction). The switching time is ~100 ps for the small signal diodes, and up to tens of nanoseconds for special high-capacity power diodes


Of course, that's not going to help with transformer ringing, but I would have thought that the transformer secondary would ring, regardless of the type of rectifier used.

I have snubbed the transformer secondary, but it's no use putting the components on the diagram, as the values I use are not going to be the values you use unless you have exactly the same transformer as me.

On the evidence of the observed startup sequence in my own amp, I wouldn't be afraid to use a SS bridge with no slow-start arrangements when the output valves are only audio valves and are direct-heated. DH power valves will start drawing very quickly.
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