Born Again Vinylista Phono Stage

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RhythMick
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#151 Re: Born Again Vinylista Phono Stage

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izzy wizzy wrote: Mon Aug 23, 2021 9:40 pm
High gm triodes all come with the penalty of high miller around 200pF then with cable capacitance >100pF you are well up there and over what most MM will take.
Why is capacitance less of a concern for MC carts ? Asking for a friend...
RhythMick
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#152 Re: Born Again Vinylista Phono Stage

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Cressy Snr wrote: Mon Aug 23, 2021 10:20 pm That’ll do me then Nick. Pentode it is once I get the D3As

I can actually get a design started now. :)
Steve - by coincidence I'm building a phono stage right now along similar lines. I'm also starting with D3a pentode. I've no doubt we'll diverge but lets keep sharing notes. And remember I'm not far away (t'other side of Barnsley) if you need input, resistors/caps of various values, a hand, shoulder to cry on, beer ... I also have several boxes of valves ...
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IslandPink
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#153 Re: Born Again Vinylista Phono Stage

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Steve - despite you being convinced, i will just add that when at Colin's a couple of years ago, we ran Denon 103R ( 0.35mV ) direct into Nick's Reference phono as a comparison to using step-ups. The phono uses pentode with CCS and parallel resistor as the first gain stage. (Can't remember if you use D3a or E810F or 6J52P Nick? .... )
Anyway, it was just about quiet enough to use. I think Nick would comment that in a quiet room, you would hear some hiss between tracks, I think you would have to get up from the sitting position, though.
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izzy wizzy
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#154 Re: Born Again Vinylista Phono Stage

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RhythMick wrote: Mon Aug 23, 2021 10:27 pm
izzy wizzy wrote: Mon Aug 23, 2021 9:40 pm
High gm triodes all come with the penalty of high miller around 200pF then with cable capacitance >100pF you are well up there and over what most MM will take.
Why is capacitance less of a concern for MC carts ? Asking for a friend...
Most MCs are very low impedance, low volts, high current (relatively) and have a rising top end so capacitance is not usually a problem. MM is the opposite.

Some higher Z MC carts maybe not so much but that's another story and not so sure of my calcs on that front.

From a personal POV, anything to downgrade capacitance in coupling/driving circuits is a good thing.
RhythMick
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#155 Re: Born Again Vinylista Phono Stage

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izzy wizzy wrote: Mon Aug 23, 2021 10:49 pm
Most MCs are very low impedance, low volts, high current (relatively) and have a rising top end so capacitance is not usually a problem. MM is the opposite.

Some higher Z MC carts maybe not so much but that's another story and not so sure of my calcs on that front.

From a personal POV, anything to downgrade capacitance in coupling/driving circuits is a good thing.
Thanks
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Nick
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#156 Re: Born Again Vinylista Phono Stage

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IslandPink wrote: Mon Aug 23, 2021 10:35 pm Steve - despite you being convinced, i will just add that when at Colin's a couple of years ago, we ran Denon 103R ( 0.35mV ) direct into Nick's Reference phono as a comparison to using step-ups. The phono uses pentode with CCS and parallel resistor as the first gain stage. (Can't remember if you use D3a or E810F or 6J52P Nick? .... )
Anyway, it was just about quiet enough to use. I think Nick would comment that in a quiet room, you would hear some hiss between tracks, I think you would have to get up from the sitting position, though.

D3a
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Cressy Snr
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#157 Re: Born Again Vinylista Phono Stage

Post by Cressy Snr »

Right! Back with pentodes. I enjoyed playing with them, so this should be fun.
Pentode front end and all in one go eq:
Screenshot 2021-08-24 at 12.48.23.png
Screenshot 2021-08-24 at 12.48.23.png (34.68 KiB) Viewed 3397 times
No component values yet except the obvious ones.
Need to decide on the output stage valve before the eq can be calculated.
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Nick
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#158 Re: Born Again Vinylista Phono Stage

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You also need a g2 stopper. Given your previous worries about noise I would reconsider connecting that VR tube directly to the input grid.
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#159 Re: Born Again Vinylista Phono Stage

Post by Cressy Snr »

Nick wrote: Tue Aug 24, 2021 12:57 pm You also need a g2 stopper. Given your previous worries about noise I would reconsider connecting that VR tube directly to the input grid.
OOPS!
That needs just a conventional dropper and bypass cap.
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#160 Re: Born Again Vinylista Phono Stage

Post by IslandPink »

Or what Nick did with a mosfet. However you could try that later and tells us how it sounds different.
Nick, in your phono , is the G2 voltage stabilised w.r.t. the cathode or to ground ?
I remember in power amps the best result came with the VR tube connected between cathode and G2.
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Nick
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#161 Re: Born Again Vinylista Phono Stage

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WRT ground, I was unsure if coupling to the cathode was injecting noise or not WRT g1 (which has higher gain).
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#162 Re: Born Again Vinylista Phono Stage

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That needs just a conventional dropper and bypass cap.
If you do that, consider the impedance looking into g2 when it comes to sizing the bipass cap.
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#163 Re: Born Again Vinylista Phono Stage

Post by Cressy Snr »

So onto the all in one go eq. Let’s see what happens.
Screenshot 2021-08-24 at 20.01.40.png
Screenshot 2021-08-24 at 20.01.40.png (43.51 KiB) Viewed 3314 times
Blinking heck.
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RhythMick
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#164 Re: Born Again Vinylista Phono Stage

Post by RhythMick »

Going out on a limb, possible someone will correct me. I believe R1 is the series total of the output resistance of the previous stage and the actual resistor. So if the calculators show R1 as 24K and the output resistance is 3K then you need a 21K series resistor.

Zout of previous stage calculated as anode load parallel with the valve plate resistance I think?

Be interesting to see how close I am...
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izzy wizzy
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#165 Re: Born Again Vinylista Phono Stage

Post by izzy wizzy »

RhythMick wrote: Tue Aug 24, 2021 8:43 pm Going out on a limb, possible someone will correct me. I believe R1 is the series total of the output resistance of the previous stage and the actual resistor. So if the calculators show R1 as 24K and the output resistance is 3K then you need a 21K series resistor.

Zout of previous stage calculated as anode load parallel with the valve plate resistance I think?

Be interesting to see how close I am...
That will be very close. But there's other rolloffs in there. The varying load of the eq on the first stage, the load of the 2nd stage grid varying with the coupling cap, decoupling cap Z changes reflected into the anode are some others. I also compensate for the output stage coupling.

Depends on how accurate you want to be. It's surprising the effect of very small changes on aspects of timing and stuff you wouldn't think the EQ has. I go for as accurate as possible which sounds silly so try to get the theory within a 0.1dB window at least.
Last edited by izzy wizzy on Tue Aug 24, 2021 9:12 pm, edited 1 time in total.
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