Born Again Vinylista Phono Stage

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IslandPink
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#136 Re: Born Again Vinylista Phono Stage

Post by IslandPink »

I will try to read that tomorrow.
On a quick skim through I notice Salas then tried to pooh-pooh Allen Wright's suggestion of shunt-regulating the HV. I don't know what that means ( maybe he never tried it ) but it doesn't add anything to his credibility with me.

For god's sake I just threw another page. Every time I post these days it throws a page :confused3: Please look at Stephen's previous post which is more important than mine !
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#137 Re: Born Again Vinylista Phono Stage

Post by RhythMick »

For me the choice of options isn't something to be anxious about, it's why I do DIY and why I like learning so much. I plan to try...

- D3a pentode single RIAA (per Izzy)
- D3a triode DC into 2nd gain stage - both with single RIAA and split

... all with LTP into LL1660PP output.

I don't really care which I try first. I just need work to stop consuming ALL my time !
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#138 Re: Born Again Vinylista Phono Stage

Post by Nick »

Gave up after the first page, but the original post looks good. Though using a LED bias as a indicator of current doesn't work that well when its a IR led :-)

And WRT the shunt reg question
What (sic) is they insist on recommending HV shunt regs I just can't understand though.
To paraphrase Paul DIrac (one of my heros), given its a statement instead of the question they thought they were asking it can be ignored.
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#139 Re: Born Again Vinylista Phono Stage

Post by izzy wizzy »

Only meant the link for the first post by SY. The rest ... well fairly typical DIYAudio thread. I got up to page 18. The only thing I gleaned was using a pentode to reduce miller for MM use was a good idea as noise levels would still be good with a d3a but was too advanced to consider?!? Oh well ...
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#140 Re: Born Again Vinylista Phono Stage

Post by Cressy Snr »

OK I came up with something constructive today.
It took me three hours to work it all out (pathetic really but I can't go any faster and I'm still not confident despite checking several times)

I decided to compare a pair of valves I have (E88C) with the D3a in triode mode. Both of these in use as the first stage of a RIAA preamp with a magnetic cartridge as the input.
Screenshot 2021-08-23 at 17.15.24.jpeg
Screenshot 2021-08-23 at 17.15.24.jpeg (60.5 KiB) Viewed 3268 times
So what's it all mean?
On the face of it the D3a has too much Miller capacitance in triode mode, just as Stephen warned about, so to me it needs to be used in pentode mode if a moving magnet cartridge is going to be the source.
The E88C looks as if it can be used as the first stage without too much trouble, with a D3a as the the second stage, because 12mA will easily drive its Miller capacitance. Not sure about the higher gain on the output though as the gain structure then seems seems arse about face to me in that respect.

Better to put the D3a as a pentode on the front with the E88C on the output?

Any thoughts?
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#141 Re: Born Again Vinylista Phono Stage

Post by Nick »

1, I would not use a d3a at that op point, maybe 20ma at 140v with 250v b+, or more likely I would use 18-20ma with a CCS load at 140v.

2. You also need to add in the load of the RIAA in parallel with the anode load when working this out.

c. I would try adding 100-200pf in parallel with your existing phono stage to see if you are fighting a real enemy with the input capacitance or not.

4. If the capacitance is a problem, why are you fighting the pentode?
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#142 Re: Born Again Vinylista Phono Stage

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Nick wrote: Mon Aug 23, 2021 6:29 pm 1, I would not use a d3a at that op point,
Oy ! That's more or less what my 1st stage is.
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#143 Re: Born Again Vinylista Phono Stage

Post by Cressy Snr »

Nick wrote: Mon Aug 23, 2021 6:29 pm 1, I would not use a d3a at that op point, maybe 20ma at 140v with 250v b+, or more likely I would use 18-20ma with a CCS load at 140v.

2. You also need to add in the load of the RIAA in parallel with the anode load when working this out.

c. I would try adding 100-200pf in parallel with your existing phono stage to see if you are fighting a real enemy with the input capacitance or not.

4. If the capacitance is a problem, why are you fighting the pentode?
Hi Nick,
Leaving aside the D3a op point question at the moment, I'm just a bit confused re the pentode issue. I'm not fighting it. I'm simply trying to get my head around the fact that in all my books (Jones, Blencowe being the main ones) the authors advise against pentodes at millivolt signal levels, because of noise. I'm perfectly willing to use a pentode front end, I just don't want excessive hiss that's all.
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#144 Re: Born Again Vinylista Phono Stage

Post by Nick »

The noise as a pentode is more than as triode. So is the gain.
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#145 Re: Born Again Vinylista Phono Stage

Post by izzy wizzy »

The thing with a pentode in the front end of a phono is the theory most folk use. Typical pentodes this may apply to but the d3a is no ordinary pentode. It is in the super car league of valves. It has huge gm as does the E810F. I've only seen Jones and others talk the theory of why it's not a good idea.

The other thing in the front end of a phono is the EQ works in your favour cutting the noise, what there is for you.

The thing I fought for years was the gm issue and focused on mu. IOW gain. Gain is good but only if it can drive the EQ. Leaving LCR aside for the moment, there are gain stages with low input C but they can't drive the EQ or 2nd stage enough so you lose dynamics so need buffering.

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. Unobtanium EC8020 probably being the best triode, hence why folk use these super pentodes connected as triodes. Once I overcame my prejudice and heard a high gm triode and then in the same circuit a high Z EQ vs a low Z EQ driven by the same valve, d3a, I've tried to convince folk this is the way to go. I think NIck and Mark here abouts amongst others have done same.

Connected as a pentode, the gain is way above triode plus EQ negates the noise issue. At the loud levels I use, I can only hear noise if I stick my head in the speaker. You need most of your gain first not 2nd to get the small signals up so they can get mangled in the EQ. Have high gain in the 2nd stage can lead to noise issues. Low gain first stage tend to not sound very dynamic IMO.

These are my prejudices of course and where I put my compromises coz all amplification, esp phonos are full of them. I've lived with noise to chase other attributes but wouldn't again.

Edit: there are pentode phono stages out there but very few on DIY forums.
Last edited by izzy wizzy on Mon Aug 23, 2021 10:00 pm, edited 1 time in total.
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#146 Re: Born Again Vinylista Phono Stage

Post by Nick »

Just worth pointing out that the self noise of a moving magnet cartridge and its 47k load is higher than a D3a as a pentode. If noise if a worry, then you should be using moving coil anyway.
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#147 Re: Born Again Vinylista Phono Stage

Post by Cressy Snr »

Nick wrote: Mon Aug 23, 2021 9:54 pm … If noise if a worry, then you should be using moving coil anyway.
Not gonna happen with an SME 3009 S2 Improved arm. :|
However, I’m convinced about a pentode front end now.
Last edited by Cressy Snr on Mon Aug 23, 2021 10:19 pm, edited 1 time in total.
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#148 Re: Born Again Vinylista Phono Stage

Post by RhythMick »

izzy wizzy wrote: Mon Aug 23, 2021 12:27 am Only meant the link for the first post by SY. The rest ... well fairly typical DIYAudio thread. I got up to page 18. The only thing I gleaned was using a pentode to reduce miller for MM use was a good idea as noise levels would still be good with a d3a but was too advanced to consider?!? Oh well ...
I've read that article a few years ago and it meant less to me. Re-read it just now and got much more of it. It's well written and I agree very useful.
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#149 Re: Born Again Vinylista Phono Stage

Post by Nick »

Cressy Snr wrote: Mon Aug 23, 2021 10:17 pm
Nick wrote: Mon Aug 23, 2021 9:54 pm … If noise if a worry, then you should be using moving coil anyway.
Not gonna happen with an SME 3009 S2 Improved arm. :|
So you don't need to consider the noise of the d3a in pentode or triode.
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#150 Re: Born Again Vinylista Phono Stage

Post by Cressy Snr »

That’ll do me then Nick. Pentode it is once I get the D3As

I can actually get a design started now. :)
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