gk71 Matrix amp

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Paul Barker
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#31 Re: gk71 Matrix amp

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I should add, especially as Stephie raised “the knee of the curves” I already drew the loadline 6k by holding a piece of paper over ipad screen, and the operating point for one misses the uggly wobble towards the knee, if we used considerably more shallow a loadline we’d hit danger, but 6k looks immune to the gk71’s uggly knee . raising b+ shifts the load line up and away should that become an issue and my dissipation is under utilized, so no downside. I will therefore set up the power supply for stepped b+ voltages in 100v increments within reason, as it involves selecting where in a vr string the 572b shunt reg joins the grid and some resistors or diodes to loose the excess voltage before the shunt valve. (since we have no capacitors). It will be a pitta to set up but it can be set up andremain reliable for specific B+ voltages. The source transformer is 2800vct there are a pair and they’re boatanchores, but I probs only use a single, you cant monoblock a Matrix amp, its one power supply, so I have plenty of voltage to waste through series diodes or resistance of more chokes but probably a combination.

Our very generous Ed gave me a 2k5 250mA dc supply (switch mode) with a knob for volts adjust so I could breadboard with that and 250 mA just scrapes in,for the amp, ok for experimenting. If it sounds great and Ed wants to build it he can have his power supply!
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Nick
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#32 Re: gk71 Matrix amp

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you cant monoblock a Matrix amp, its one power supply
Well, more to the point, its a shared output transformer.
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#33 Re: gk71 Matrix amp

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Yep, been too busy to read up the Matrix theory but learning to implement it is half way guiding me there.

I’ll be honest I had a small panic about geting the input transformer phases correct for matrix, but what the heck, no sound and that’s the first port of call.

I love that it’s Stephies favourite amp. I was persuaded by the mention the kt88 matrix bettered Stephies 845 amp. Any time Ive conversed with Stephie which would be over 20 years ago its always come back straight and to the point and subtle no modern day fancy hifi phrasiology. Stephie probably has some chromazomes found in Yorkshire where a spade is a spade not gargon spoken by hifi comic reviewers.
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#34 Re: gk71 Matrix amp

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Stephie is now advising on spice over in SIM part of Intact Audio Forum. Way over my head. Some here use spice you might want to have a look.
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#35 Re: gk71 Matrix amp

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Paul Barker wrote: Tue Jun 23, 2020 4:58 am Stephie is now advising on spice over in SIM part of Intact Audio Forum. Way over my head. Some here use spice you might want to have a look.
Been using her drop down valve model selection for years. Makes things very easy.
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Paul Barker
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#36 Re: gk71 Matrix amp

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‘fraid I’m a real baby in spice terms not even learned any of it.

Maybe we could section parts of the meeting days for people with specialist knowledge to show and tell.

I could construct one of my Stephie style shunt reg capacitorless power Supplies for instance.
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#37 Re: gk71 Matrix amp

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Paul Barker wrote: Tue Jun 23, 2020 9:22 am ‘fraid I’m a real baby in spice terms not even learned any of it.

Maybe we could section parts of the meeting days for people with specialist knowledge to show and tell.

I could construct one of my Stephie style shunt reg capacitorless power Supplies for instance.
That would help. I was a fumbler and knew next to nothing until I came across the Sim section and learnt by following Stephie's tutorials on Intact.

Download some of the working sims there and then mess about. I'm still a relative simpleton using it but it is brilliant and helps with understanding stuff.
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#38 Re: gk71 Matrix amp

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Paul Barker wrote: Tue Jun 23, 2020 9:22 am
Maybe we could section parts of the meeting days
fight club?
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#39 Re: gk71 Matrix amp

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First rule..
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#40 Re: gk71 Matrix amp

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Maybe we could section parts of the meeting days for people with specialist knowledge to show and tell.
There are instructions both on this forum, Intact Audio and on the net about how to use LTSpice in general and specifically for valves. Its not that complex, but then neither is it simple, You have to start with a simple circuit and learn how to use it. It assumes you have some understanding of computers and electronics.
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#41 Re: gk71 Matrix amp

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Thanks Nick
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#42 Re: gk71 Matrix amp

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Some items required found:
Lundahl 1620PP from John Caswell.
An old breadboard with choice of two inter stage options, I’ll go with AE Amorphous. The power for the 800v line. The final two stages of No capacitors power supply (also “after Stephie” I think it’s called an Lr supply but with active shunt Regulation.)

Image
ImageImageImage

You might spot the power transformers are 2920 VCT 250mA each. Firstly, current requirements 200mA for output stage without stress and the shunt regulator current, which tips me over the one transformer but anyway with two there is the type of excess HR referred to in his Flesh and Blood Sound Practices article.

As there is only integrated with Matrix the pair will be Rectified individually with u19’s summed after two parallel lines of 250mA chokes Prior to the final 500mA boat anchor potted in oil double c core from when things were made properly. Finally the shunt regulation! You can see a pair of 572b I think they’re Svetlana. and two vr strings which you pick you’re grid bias for each 572b.

Obviously there are two elephants in the room. 1/ the power transformers are wound for 60hz 2/ as standard they will provide 1,314 less rectifier and transformer resistance drop, chokes’ resistance drop Calculated from circuit quiescent current and 872b shunt current (which for perfection would be as close as possible to quiescent current).

1/ my mains it 240v all the live long day week month year century. So I’ll connect to 260v. Right there 2920 drops to 93% at full power.
2/ the rest of voltage drop required I’ll know when I’ve calculated the rectifiers and dc resistances with the 572b with vr tubes headroom required to function well and whatever comes as an output voltage after I’ve factored in signal current, that’s when I can amend plan to arrive at 800v. But you start simple and build it up adjust on test.

I could just add high wattage resistors prior to 572b’s or I could use zenners to drop bigger sums but I’m not keen on that.series pass valves would suit my ethos better. But also I could lose the excess in ac with another transformer.

Plenty of fat to chew!
Last edited by Paul Barker on Thu Jun 25, 2020 1:33 am, edited 3 times in total.
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#43 Re: gk71 Matrix amp

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Interesting stuff. This is shaping up to be another power supply on a sack-trolley amp.
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#44 Re: gk71 Matrix amp

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It won’t be pretty.
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#45 Re: gk71 Matrix amp

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Paul Barker wrote: Wed Jun 24, 2020 8:40 pm It won’t be pretty.
I could always build it in the van and use long speaker cables and an extension lead lol.
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