Remember These?

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Cressy Snr
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Re: Remember These?

Post by Cressy Snr » Tue Jan 08, 2019 2:15 pm

Interesting this morning listening to vinyl, through the OTL. The sound is uncoloured. Whether this is a good thing depends on how you like your analogue to sound, because vinyl warmth is utterly absent. This lack of coloration certainly allows you to hear right into the recording. The JBE turntable sounds like CD when playing through the OTL, but there's none of the sterility that can accompany some varieties of digital sound.

The top end from the Audio Technica cart is smooth detailed and extended. Sibilance is completely absent from this combination, and I mean completely, which can only be a good thing with the dreaded vinyl, from my point of view. Bass from the JBE is dry and controlled and I can definitely hear that direct drive sound that the Flat Earth was so critical of and TBH it's easy to see their argument, up to a point. But then the DD turntable/OTL combination treats everything played through it with an even-handedness, that just lets the music come through clearly. It's just that this particular listener has never heard vinyl come out of a system, the way it comes through this one and it takes a bit of getting used to. It's all very posh and civilised; something vinyl as I knew it could never be accused of.

I think these single tube OTLs are revelatory in what they can accomplish with recorded music. Lack of power could be a deal breaker for most people however.
Our suffering arises from our desire for control and stability in a world that is utterly uncontrollable and highly unstable.

RhythMick
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Re: Remember These?

Post by RhythMick » Tue Jan 08, 2019 9:01 pm

To Owston! To Owston! Huzzah...

Sounds like a really nice job. Can't wait to hear them. If you're not taking it to Owston I'd like to pop in.

Cressy Snr
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Re: Remember These?

Post by Cressy Snr » Tue Jan 08, 2019 10:23 pm

RhythMick wrote:
Tue Jan 08, 2019 9:01 pm
To Owston! To Owston! Huzzah...

Sounds like a really nice job. Can't wait to hear them. If you're not taking it to Owston I'd like to pop in.
Well it's going to Nick's place on Saturday, (12th) so you are welcome to pop over to my place on the Sunday (13th) if you want a listen. After that I'm tearing it down to put it in a box :)
Our suffering arises from our desire for control and stability in a world that is utterly uncontrollable and highly unstable.

RhythMick
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Re: Remember These?

Post by RhythMick » Tue Jan 08, 2019 11:30 pm

Cressy Snr wrote:
Tue Jan 08, 2019 10:23 pm
RhythMick wrote:
Tue Jan 08, 2019 9:01 pm
To Owston! To Owston! Huzzah...

Sounds like a really nice job. Can't wait to hear them. If you're not taking it to Owston I'd like to pop in.
Well it's going to Nick's place on Saturday, (12th) so you are welcome to pop over to my place on the Sunday (13th) if you want a listen. After that I'm tearing it down to put it in a box :)
Surely you'll be able to bring it to Owston ? Unfortunately my priority this weekend will be finishing my own build.

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Thermionic Idler
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Re: Remember These?

Post by Thermionic Idler » Wed Jan 09, 2019 12:31 am

I'd really love to hear these actually Steve, and I'm back in Chesterfield this weekend - as we won't have a presence in the North for very much longer, am I OK to pop over on Sunday?

With these, and Ray's 13E1 build as well, and my Beasts (surely I'll get them finished this year) we'll have quite a collection of OTL's.
Deck: Garrard 301
Audio Origami PU7
Van Den Hul Black Beauty
Phono: Whest PS30RDT
Pre-amp - Scratch built AMB α24/LCDuino
Amp - Transcendent "Son of Beast" 15W OTL
Speakers - FF225WK Metronomes

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Ray P
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Re: Remember These?

Post by Ray P » Wed Jan 09, 2019 5:55 am

Thermionic Idler wrote:
Wed Jan 09, 2019 12:31 am
With these, and Ray's 13E1 build as well, and my Beasts (surely I'll get them finished this year) we'll have quite a collection of OTL's.
I still have my 300B SE-OTLs too...

Would love to hear Steve's breadboard through his speakers but the trek up from Somerset isn't doable this weekend. Looking forward to the outcome of Nick's probing though.

Cressy Snr
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Re: Remember These?

Post by Cressy Snr » Wed Jan 09, 2019 9:13 am

RhythMick wrote:
Tue Jan 08, 2019 11:30 pm
Cressy Snr wrote:
Tue Jan 08, 2019 10:23 pm
RhythMick wrote:
Tue Jan 08, 2019 9:01 pm
To Owston! To Owston! Huzzah...

Sounds like a really nice job. Can't wait to hear them. If you're not taking it to Owston I'd like to pop in.
Well it's going to Nick's place on Saturday, (12th) so you are welcome to pop over to my place on the Sunday (13th) if you want a listen. After that I'm tearing it down to put it in a box :)
Surely you'll be able to bring it to Owston ? Unfortunately my priority this weekend will be finishing my own build.
Aye, it'll be in a box by then I would have thought. :D
Our suffering arises from our desire for control and stability in a world that is utterly uncontrollable and highly unstable.

Cressy Snr
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Re: Remember These?

Post by Cressy Snr » Wed Jan 09, 2019 9:15 am

Thermionic Idler wrote:
Wed Jan 09, 2019 12:31 am
I'd really love to hear these actually Steve, and I'm back in Chesterfield this weekend - as we won't have a presence in the North for very much longer, am I OK to pop over on Sunday?
Yep no problem, look fwd to it. :)
Our suffering arises from our desire for control and stability in a world that is utterly uncontrollable and highly unstable.

Cressy Snr
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Re: Remember These?

Post by Cressy Snr » Thu Jan 10, 2019 12:53 pm

OK,
So starting this afternoon, I'm beginning a bit of a revamp of the design. Reading some of Bruce's stuff, I'm sure I can substantially reduce the weight, the complexity and the overall noise performance of the design and improve stability.
I have a random VLF signal in the system somewhere, something is beating with something somewhere at a very low level, and when the two VLF signals add, they produce a low frequency pulse that dies away as they part. so that needs getting rid of. A bit of scopery yesterday, identified the problem, but as yet I havent located the cause. It's only millivolts at the output but it's a fault condition nevertheless and needs getting rid of.

If this was not a cathode follower output stage, the random signal would have been amplified and would have shown up as cone flap, similar to the problem that affected the original WAD Phono 2, way back. The Phono/Pre 2 would flap your speaker cones at random, intervals with no record playing.
Our suffering arises from our desire for control and stability in a world that is utterly uncontrollable and highly unstable.

izzy wizzy
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Re: Remember These?

Post by izzy wizzy » Thu Jan 10, 2019 1:24 pm

First place I'd look is you have no RC decoupling between stage 1 and 2. Might not have to be much. Not sure of the power supply feeding that part; is it shared between channels? Is it regulated?

Cheers,
Stephen

Cressy Snr
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Re: Remember These?

Post by Cressy Snr » Thu Jan 10, 2019 7:01 pm

izzy wizzy wrote:
Thu Jan 10, 2019 1:24 pm
First place I'd look is you have no RC decoupling between stage 1 and 2. Might not have to be much. Not sure of the power supply feeding that part; is it shared between channels? Is it regulated?

Cheers,
Stephen
Yes, that's where I've concentrated the effort with the redesign.
So, what we have now is a complete redesign of the power supply. There is now just the one power supply feeding both stages. The supply is now CLCLCRC as below:

CLC-(output stage takeoff, both channels)-LC-(driver stage takeoff, both channels)-RC-(input stage takeoff, both channels)
The last cap in the supply that feeds the input stage half of each 5687 is positioned as close as possible to the valve itself without being unduly affected by the radiant heat from the power valves.
The input stage heaters are now DC, using one of my DIYHS DC modules intended for DHTs. This has considerably lowered the the amp's noise floor.
Due to the system being fed from the one power supply, the available HT to the input and driver stages has been almost halved, from roughly 310V to just over 160V, so the cathode resistor values, have had to be adjusted to compensate.

13E1 grids were randomly wandering about by a few millivolts either side of pos and neg so grid resistor value was reduced. It's a whole lot better now. Keeping the grid still, is not easy with these things.

Image

The amp is now relatively light, simple, quiet and sounds as beautiful as ever. Apart from the difference in the valves; the HT voltages being used and the bias points of the input/driver are actually quite close to the Mini Beast I built.
As I am wont to do, I was adding more and more "stuff" and complexity and rapidly disappearing up my backside, so clean slate it had to be.
I'm glad I took the decision that enough was enough and brought the hammer down on the other iteration.
Our suffering arises from our desire for control and stability in a world that is utterly uncontrollable and highly unstable.

izzy wizzy
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Re: Remember These?

Post by izzy wizzy » Thu Jan 10, 2019 7:19 pm

Do you now not think the amp benefits from a seperate PS for the front end? Sometimes these things change as you go through the process.

Cheers,
Stephen

Cressy Snr
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Re: Remember These?

Post by Cressy Snr » Thu Jan 10, 2019 7:35 pm

izzy wizzy wrote:
Thu Jan 10, 2019 7:19 pm
Do you now not think the amp benefits from a seperate PS for the front end? Sometimes these things change as you go through the process.

Cheers,
Stephen
No I don't think it does benefit; at least not the way I did it. I think multiple power supplies do unfortunately, need a lot more skill to implement properly than the level I'm at, particularly in terms of the grounding arrangements. I'm crap at grounding so the one PSU was the right move under the circumstances.

You make changes and hear what you think are improvements, but half the time all you are doing is putting more stuff in the way of the music. But I still think it's useful to chronicle the thought process, providing you are honest with yourself later on down the line.
Our suffering arises from our desire for control and stability in a world that is utterly uncontrollable and highly unstable.

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Re: Remember These?

Post by izzy wizzy » Thu Jan 10, 2019 7:49 pm

Cressy Snr wrote:
Thu Jan 10, 2019 7:35 pm
No I don't think it does benefit; at least not the way I did it. I think multiple power supplies do unfortunately, need a lot more skill to implement properly than the level I'm at, particularly in terms of the grounding arrangements. I'm crap at grounding so the one PSU was the right move under the circumstances.

You make changes and hear what you think are improvements, but half the time all you are doing is putting more stuff in the way of the music. But I still think it's useful to chronicle the thought process, providing you are honest with yourself later on down the line.
This approach works for me too. I like mono supplies. There's a wholeness to the sound/presentation that I like and find more musical. Especially in single ended circuits, the notion of "ground" can be vague with seperate supplies and I think that leads to a vagueness in the presntation that single ground/power supply systems don't have. My 2p worth anyway :)

Cheers,
Stephen

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Re: Remember These?

Post by Cressy Snr » Thu Jan 10, 2019 10:52 pm

izzy wizzy wrote:
Thu Jan 10, 2019 7:49 pm

This approach works for me too. I like mono supplies. There's a wholeness to the sound/presentation that I like and find more musical. Especially in single ended circuits, the notion of "ground" can be vague with seperate supplies and I think that leads to a vagueness in the presntation that single ground/power supply systems don't have. My 2p worth anyway :)

Cheers,
Stephen
As you say, there's a definite "wholeosity" (copyright Dr Gizmo) to the music with the single power supply. This amp never had a mono supply due to the fact that I thought I needed a 300V HT supply for the input stage, which in the first iteration was obtained from a voltage doubler off the second 115V winding on the big toroid.

Once I had eventually got my head around global feedback and the drive requirements (jackass) :oops: I realised that there was no real need for such a high HT voltage on the input and driver stages and that 160V (rectified) off the transformer was quite sufficient. It was only a small leap of logic from there to dump all that three power supply complexity into the bin from a great height and redesign the power distribution from the ground up, DC'ing the input/driver stage heaters whilst I was at it, also seemed like a good move.
Our suffering arises from our desire for control and stability in a world that is utterly uncontrollable and highly unstable.

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