Born Again Vinylista Phono Stage

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Cressy Snr
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#1 Born Again Vinylista Phono Stage

Post by Cressy Snr »

So at the moment I am just casting about for ideas for a phono stage build, as the one I am using at the moment is not mine.
I have the Merln Blencowe book "Designing High Fidelity Tube Preamps" which has an interesting design using a PC97, seven-pin TV triode as the first stage followed by ECC82 second stage and output cathode follower.

Phono stages are not my area of expertise at all. I did a copy of the old RCA "orthophonic" phonograph preamplifier years ago and that sounded alright to me and I did have a WAD Phono II that was OK, but my expensive vinyl source was a pile of poo compared to what I have now.

The way I see it, I have a few options: either use the circuit diagram I still have for the Phono II and build a clone of that, build the Blencowe one, or ask for suggestions from you guys. Or (horrors) try to design my own (yeah right).
I know its a quiet time of year but any help at this stage would be appreciated.
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IDM
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#2 Re: Born Again Vinylista Phono Stage

Post by IDM »

Hi,

I have been using a phonostage designed by Andrew that uses a C3G and ECC88 for the last couple of years and it is excellent. Recently I rebuilt it with the following changes:

1. Changing the ECC88 for a triode strapped E180F.
2. Split the HT with separate salas SSHV2 shunt regulators for the C3G and E180F
3. Replaced all the resistors with carbon films (removing the metal films).
4. Used Russian silver mica caps for the RIAA (the 470nf is a polypropylene)
5. Grid leak bias of the ECC88 (E180F) was changed to cathode bias with a 10R resistor (value from memory)
6. changed the anode load resistor of the ECC88 (E180F) to an 150H anode choke
7. Andrews IDHT regulators used for both the C3G and Ecc88 (E180F)
8. I use Cinemag SUT because I have MC cartridge.

In my opinion it now sounds stunning. The only issue I has was that because I have the PSU in a separate case, I was getting HF instability from the HT umbilical. I now have ferrite cores on the cable and it is fine.

The phonostage is being used with a Linn Troika with an output of 100uV, so very low and it works fine. There really is no hum at all. It is by far the quietest stages I have ever built.

What I keep meaning to try regulating the G2 voltage of the C3G pentode, indeed I have built a statistical regulator to do this but haven't tried it yet as I cannot bring myself to pull the stage apart as I am enjoying listening to it so much.

Cheers
Ian
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izzy wizzy
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#3 Re: Born Again Vinylista Phono Stage

Post by izzy wizzy »

IMO, you want something that has a high gm first valve that can drive a 20k or thereabouts RIAA EQ. 2nd valve to determine the overall gain but lowish rp so can drive output direct. First could be a pentode. LTSPICE is your friend in all this. Something like Mark's would do the trick.

cheers,

Stephen
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#4 Re: Born Again Vinylista Phono Stage

Post by cressy »

Could also do one based on my nuvistor one, Mike, Andrew and nick helped me with that one. It was originally for the 7f8w, i then redesigned the driver stages for the 6ds4/2ds4
The correction between the 2 stages needed minimal alteration so you could do a different driver stage and output stage to match what you have
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Nick
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#5 Re: Born Again Vinylista Phono Stage

Post by Nick »

IMO, you want something that has a high gm first valve
Also IMO.
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IslandPink
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#6 Re: Born Again Vinylista Phono Stage

Post by IslandPink »

Time to wheel out my phono circuit again :D
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Cressy Snr
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#7 Re: Born Again Vinylista Phono Stage

Post by Cressy Snr »

Thanks chaps, some food for thought.
How long this will take I have no idea. It may yet turn into a marathon, like Mark's speaker thread, but now I have some options.:)
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shane
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#8 Re: Born Again Vinylista Phono Stage

Post by shane »

Looking forward to this one, especially if you go the C3G route.
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izzy wizzy
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#9 Re: Born Again Vinylista Phono Stage

Post by izzy wizzy »

And while you're ruminating, look at ideas for ensuring your build will work.

I favour building on a sheet of PCB with PTFE turrets/test terminals, a central tiny PCB star ground glued to the main PCB., all point to point. Keep each stage small and localised; no long wires.

Yes you can get the PSU in the same case but it's risky. I prefer mains iron and initial chokes outside in another box. You'll probably use regs of some kind (I don't) so put them in the audio box.

cheers,

Stephen
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Mike H
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#10 Re: Born Again Vinylista Phono Stage

Post by Mike H »

Nick wrote:
IMO, you want something that has a high gm first valve
Also IMO.
Brice's version for Wireless World mag used a cascoded pair of triodes, ECC82 if memory serves, instead of a pentode for the 1st stage. Just a thought... EQ was a passive network...
 
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izzy wizzy
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#11 Re: Born Again Vinylista Phono Stage

Post by izzy wizzy »

Mike H wrote:
Nick wrote:
IMO, you want something that has a high gm first valve
Also IMO.
Brice's version for Wireless World mag used a cascoded pair of triodes, ECC82 if memory serves, instead of a pentode for the 1st stage. Just a thought... EQ was a passive network...
Main issue with many cascodes is the output Z is high compared with a hot pentode so they normally can't drive a 20k EQ network.

cheers,

Stephen
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#12 Re: Born Again Vinylista Phono Stage

Post by IDM »

To avoid digging around for the schematic of Andrew's original C3G phono stage. This is the one I modified as detailed above.
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Mike H
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#13 Re: Born Again Vinylista Phono Stage

Post by Mike H »

izzy wizzy wrote:
Mike H wrote:
Nick wrote:
Also IMO.
Brice's version for Wireless World mag used a cascoded pair of triodes, ECC82 if memory serves, instead of a pentode for the 1st stage. Just a thought... EQ was a passive network...
Main issue with many cascodes is the output Z is high compared with a hot pentode so they normally can't drive a 20k EQ network.

cheers,

Stephen
Yes, which is why, again if memory serves, it was DC coupled to a cathode follower.
 
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izzy wizzy
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#14 Re: Born Again Vinylista Phono Stage

Post by izzy wizzy »

IDM wrote:To avoid digging around for the schematic of Andrew's original C3G phono stage. This is the one I modified as detailed above.
Nice. Have always liked the idea of shunt EQ tho never got round to trying it due to the large cap required.

cheers,

Stephen
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#15 Re: Born Again Vinylista Phono Stage

Post by Cressy Snr »

Its all Greek to me at the moment.
Need to do some serious studying, both on calculating out eq systems of the split and all in one go variety and keeping noise levels down. I like to know what I'm doing and why
Be back in 6 months.
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