6B4G - The Resurrection Shuffle

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Cressy Snr
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Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr » Sat Nov 11, 2017 11:45 pm

Just a word on the design of the amplifier,

The JJ, 2A3-40 is a cracking valve that seems to combine the best qualities of both the 2A3 and the 300B. Paul B had originally advised a three stage circuit with a power valve to drive the output stage, and that is what I have ended up with. With the 2A3-40, we have a valve, whose internals look like a 300B anode structure with 2.5V filaments. Although it is not a 300B (the characteristics are 2A3) I designed it as if it was a 300B I was driving, so the 6005W which is a mil spec 6AQ5, runs at 30mA idle bias.
What we have therefore, is a two stage, 6AU6 into 6AQ5, 2W, single-ended power amplifier, driving a 2A3 output stage. It works beautifully and is as simple as it gets. Combined with a well filtered choke input power supply, it cruises along without stress, producing a clean, detailed, dynamic and believable representation of a recording.
And I've been on the pale ale...and I feel like a pinball.

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pre65
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Re: 6B4G - The Resurrection Shuffle

Post by pre65 » Sun Nov 12, 2017 9:06 am

So, I wonder how it wold sound with 300b fitted ?

I still have two 300b somewhere. :roll:
People are like stained-glass windows. They sparkle and shine when the sun is out, but when the darkness sets in, their true beauty is revealed only if there is a light from within
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Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr » Sun Nov 12, 2017 9:42 am

pre65 wrote:
Sun Nov 12, 2017 9:06 am
So, I wonder how it would sound with 300b fitted ?

I still have two 300b somewhere. :roll:
It would need different filament heating arrangements and also different output transformers.
And I've been on the pale ale...and I feel like a pinball.

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Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr » Sun Nov 12, 2017 10:38 am

Sunday morning aural massage:
Image
And I've been on the pale ale...and I feel like a pinball.

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Re: 6B4G - The Resurrection Shuffle

Post by Ray P » Sun Nov 12, 2017 11:52 am

Very nice Steve...

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Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr » Sat Nov 18, 2017 6:36 pm

Cheers Ray :)

OK we are two weeks on from first firing up and about 8 days on from getting the groovy pink SET working correctly with regard to achieving a consistent, fuss-free startup.
The good bit is, that I cannot find fault with the sound quality. Nothing has reared its head.
It's taken 11 years and quite a few false dawns, but we have arrived at our destination with sanity more or less intact.

The amount of money I've spent on "R&D" is eye watering for a man of my limited means, and I suppose, the burning question has to be, was it worth it in the end? Yes I think it was. I probably would not have achieved the right end result without the 12 year "apprenticeship"
Would I do it all again? Absolutely not - certainly not in the same way, that's for sure, but hindsight is a wonderful thing.

The really good bit of this lot is that I have found a method of building SETs that sound good. It's not the only method, it might not even be the best method, but the three stage topology, consisting of voltage gain stage, power driver and DHT output stage with choke input supply, star/bus mixed grounding and the actual PSU HT dropoffs positioned right next to their corresponding valves, produces a finished amp that is seriously good at playing music.

The fact that the two stages preceeding the output valves, are nothing more than bog standard, cheapo RC coupled jobs (horrors!) does not seem to have had any detrimental effect on the ability of the amp to play music.
Caps in the signal path do not appear (well not on the evidence of what I'm hearing anyway) to be the bad thing they are sometimes made out to be, and I wouldn't hesitate to use them in an amp; not anymore.

So, amp is sorted, omni-speakers are sorted (finally...Lord help me) As I said to Scott at Steve's last week. If I had had the slightest inkling of the creeping horrors that awaited at the end of that particular shadowy fork in the road, nothing, but nothing, would have brought me within a hundred miles of omnis, semi omnis or any fooking other form of omnidirectional anybloodything.

But...somebody has to be daft enough and I've got another one under development, so there'll probably be more :pain10:
before long. :mrgreen:
And I've been on the pale ale...and I feel like a pinball.

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Re: 6B4G - The Resurrection Shuffle

Post by Thermionic Idler » Sat Nov 18, 2017 8:51 pm

I remember, I think was it last year, when I was in the process of attempting to design my own amplifier, reading Lynn Olson's site where he extolled the benefits of driving a DHT output stage with a proper power valve - 2a3 driving 300B for example. I tried to design something that was both no-compromise and not too expensive / unwieldy to build - I just ended up disappearing up my own backside with it all and finally decided my first scratch-builds should be proven high-performance circuits developed by people who know more than I do!

So I think a lot of your success here is down to the fact that you're giving the 2a3 a good kick up the arse - in a lot of other circuits, the driver stage runs out of juice before the output valve does.

Nothing wrong with cap-coupling - the Transcendent amps give superb performance and the circuits have two lots of cap coupling in.

I'd really love to try something along similar lines with 6SN7 -> triode connected EL84 -> JJ 2A3 but that's for another day, way down the line!
Deck: Garrard 301
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Re: 6B4G - The Resurrection Shuffle

Post by IslandPink » Sat Nov 18, 2017 10:12 pm

Well I'm going to be contrary here and say I wouldn't favour a three-gain-stage amp myself for a 2A3 as it's a lot easier to drive than a 300B. the problem with three-stage amps are there are a lot more components ( caps, chokes ) that cause bass rolloffs. I think all you need is a driver that has about 8 to 10ma current and a good voltage swing and you're laughing. For that reason a pentode like a C3g seems enough. If you've got enough system gain you can avoid the cathode by-pass cap on that, so there is another bass rolloff gone. I suppose these 2A3's are slightly more beefy, but I did build a 3-stage 300B amp with 45 ( choke-loaded ) driving it, and there was a touch more midrange tone than the C3m driver, but the bass and timing wasn't as good. The 4P1L pentode I now use is better than the C3m. I had a very good result with 4P1L driving GK-71 and that's where I would like to go eventually if I could build a 600v or 700v shunt supply.

I prefer ( one ) cap coupling to transformer-coupling in SE, because the TX for SE always has limited inductance - hence bass problems.
I'll scuttle back into my cave now.
White flags of winter chimneys waving truce against the moon ( Mitchell )

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Re: 6B4G - The Resurrection Shuffle

Post by IslandPink » Sat Nov 18, 2017 10:58 pm

Of course comments above assume you're trying to make a wide-band amplifier .... which may not be the case - and approaches to subtly favour the mids and vocals are of course valid :)
White flags of winter chimneys waving truce against the moon ( Mitchell )

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Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr » 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.

I'm not interested anymore in notions of "enough" drive. I want powerful, unimpeachable driving ability with endless headroom.
The effortless way this amp plays music, doing what is asked of it without drama tells me I've done it right.

"Ah but that amount of welly is surely just asking for trouble with grid current and consequent blocking isnt it?".... I say yeah whatever.
I have no idea how I would set out to deliberately build an amp that would favour the mids and vocals. You're way overestimating my abilities there Mark. :lol:
And I've been on the pale ale...and I feel like a pinball.

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Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr » Sun Nov 19, 2017 9:21 am

The thing with the 2A3-40 is that if you want the extra power they claim for the valve, then you need to design it as if you were driving a 300B. Still not quite as hard to drive but if you want the extra power you have to design to get it.

Design it as a "normal" 2A3 amplifier and the JJ is just another good 2A3. Crank up the HT and kick its backside and it becomes a seriously good modern production DHT - IMO a steal at the price they are asking for it.

The dissipation levels I am running at, put the output stage within the dissipation range of the expensive EML solid plate 2A3. That would be interesting, but it's way beyond my means.

A direct coupled, two halves of a 5687 in cascade format would be another good, way of getting at the capabilities of the JJ and it is something I considered, given that I had 300B levels of HT, to facilitate the scheme, but I decided against it in the end, because I had no 5687s. The amp ended up being built with what I had lying around and on a limited budget.

For me, it gives great ratio of sound to the pound.
Shows what you can do with a restricted colour palette.
And I've been on the pale ale...and I feel like a pinball.

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Re: 6B4G - The Resurrection Shuffle

Post by Ray P » 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?

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Re: 6B4G - The Resurrection Shuffle

Post by Paul Barker » Sun Nov 19, 2017 10:22 am

Cressy Snr wrote:
Sat Nov 18, 2017 6:36 pm

Caps in the signal path do not appear (well not on the evidence of what I'm hearing anyway) to be the bad thing they are sometimes made out to be, and I wouldn't hesitate to use them in an amp; not anymore.
Can of worms behind that statement friend.

“Caps in the signal path” of an se amp. coupling caps, cathode bypass caps, power supply smoothing caps.

we juggle their relative influence from place to place when we try to eliminate the only one thta ever gets the blaim by the ignorant. The poor old coupling cap.

But of truh all the caps truly in the signla path are detrimental to sound. I know because hvaing made amps entirely devoid of caps, they sound better by a country mile.

So we often live with our caps for convenience purposes and buy the est we can afford for the projectand every penny will reap a benefit.

You can condition your brain to negate the detrimental sound of caps in an amp, its a natural fetaure of our humanity to filter the information we hear. But turn on a capacitorless amp imediately after you listened to your amp full of caps and you will be like theperson who says “I didn’t realise the clock was ticking until it was turned off”. Your brain is fooling your friend.

But sure, you will have made a greta sounding map your brain cna work with to give you pleasure.

I’m on the way to Anthsin aminute and hope to pop round later.

See you soon.
I can do it right or I can do it now, but I can't do it right now.

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Re: 6B4G - The Resurrection Shuffle

Post by Paul Barker » Sun Nov 19, 2017 10:22 am

Cressy Snr wrote:
Sat Nov 18, 2017 6:36 pm
Cheers Ray :)

OK we are two weeks on from first firing up and about 8 days on from getting the groovy pink SET working correctly with regard to achieving a consistent, fuss-free startup.
The good bit is, that I cannot find fault with the sound quality. Nothing has reared its head.
It's taken 11 years and quite a few false dawns, but we have arrived at our destination with sanity more or less intact.

The amount of money I've spent on "R&D" is eye watering for a man of my limited means, and I suppose, the burning question has to be, was it worth it in the end? Yes I think it was. I probably would not have achieved the right end result without the 12 year "apprenticeship"
Would I do it all again? Absolutely not - certainly not in the same way, that's for sure, but hindsight is a wonderful thing.

The really good bit of this lot is that I have found a method of building SETs that sound good. It's not the only method, it might not even be the best method, but the three stage topology, consisting of voltage gain stage, power driver and DHT output stage with choke input supply, star/bus mixed grounding and the actual PSU HT dropoffs positioned right next to their corresponding valves, produces a finished amp that is seriously good at playing music.

The fact that the two stages preceeding the output valves, are nothing more than bog standard, cheapo RC coupled jobs (horrors!) does not seem to have had any detrimental effect on the ability of the amp to play music.
Caps in the signal path do not appear (well not on the evidence of what I'm hearing anyway) to be the bad thing they are sometimes made out to be, and I wouldn't hesitate to use them in an amp; not anymore.

So, amp is sorted, omni-speakers are sorted (finally...Lord help me) As I said to Scott at Steve's last week. If I had had the slightest inkling of the creeping horrors that awaited at the end of that particular shadowy fork in the road, nothing, but nothing, would have brought me within a hundred miles of omnis, semi omnis or any fooking other form of omnidirectional anybloodything.

But...somebody has to be daft enough and I've got another one under development, so there'll probably be more :pain10:
before long. :mrgreen:
sorry folks i wrote a long reply to this then found i wasnt logged in and its all lost. life is too short to thpe it all again.

I’ll pop round when Ive completed my business with Anth if thats ok?
I can do it right or I can do it now, but I can't do it right now.

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Cressy Snr
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Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr » Sun Nov 19, 2017 11:16 am

Look fwd to seeing you Paul.
I write too much.

I have 12 years of experience with valve amps. Or to put it another way, I have six months of experience, repeated 24 times.
Last edited by Cressy Snr on Sun Nov 19, 2017 11:24 am, edited 1 time in total.
And I've been on the pale ale...and I feel like a pinball.

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