Question re Izzy Wizzy phono stage

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RhythMick
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#1 Question re Izzy Wizzy phono stage

Post by RhythMick »

Following in the path of Izzy of this parish I'm working on a phono stage using some of design for inspiration.

The signal path is D3a (pentode) into passive RIAA , then a pair of valves in push pull across an LL1660PP for balanced output.

I'm struggling to see how the phase is split? SE D3a into RIAA I see. I don't see any phase splitter, just a 510k resistor? Someone explain that please?
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Nick
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#2 Re: Question re Izzy Wizzy phono stage

Post by Nick »

Its sort or a cathode coupled phase splitter also relying on the transformer to improve balance. Interestingly, as drawn the grids have no path to ground. I guess it will find a place between the d3a anode voltage and the cathode voltage across the shared cathode resistor.
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RhythMick
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#3 Re: Question re Izzy Wizzy phono stage

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Nick wrote: Fri Jul 02, 2021 9:26 pm Its sort or a cathode coupled phase splitter also relying on the transformer to improve balance. Interestingly, as drawn the grids have no path to ground. I guess it will find a place between the d3a anode voltage and the cathode voltage across the shared cathode resistor.
Would ac ground through the cap ?

Anyway it works for Steve so I'll give it a listen. I don't understand it though. When the RIAA output goes positive both the grids will go positive? I'm sure I've got that wrong but I just can't see it.
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Nick
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#4 Re: Question re Izzy Wizzy phono stage

Post by Nick »

Would ac ground through the cap
Yes, but like you say its the DC conditions I was unsure of. Yes, if the grids go +ve, then the voltage across the cathode resistor will increase to match, I guess the d3a anode at say 130v, that will mean you are getting something like 23ma through each triode, so with the transformer coupling putting the anode at b+ voltage it all hangs together nicely. Cunning direct coupling.
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Nick
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#5 Re: Question re Izzy Wizzy phono stage

Post by Nick »

When the RIAA output goes positive both the grids will go positive
Sorry, I ignored this as I thought you meant DC. No at AC the second grid is tied to 0v, so the AC signal is only on the first grid, the transformer will force it into balance acting like an AC only CCS.
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RhythMick
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#6 Re: Question re Izzy Wizzy phono stage

Post by RhythMick »

Nick wrote: Fri Jul 02, 2021 10:07 pm
When the RIAA output goes positive both the grids will go positive
Sorry, I ignored this as I thought you meant DC. No at AC the second grid is tied to 0v, so the AC signal is only on the first grid, the transformer will force it into balance acting like an AC only CCS.
Oh I see . Long tailed pair with second grid grounded. Thank you Nick.
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izzy wizzy
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#7 Re: Question re Izzy Wizzy phono stage

Post by izzy wizzy »

Before anyone goes buying parts to make this thing (which is always scary) may I point out a few things.

The output stage is an odd one for a phono or stage earlier than a power amp. I only did it as I had the transformer and it was a better solution than the other things I tried plus I'm allergic to capacitors and value galvanic isolation sonically . I now have a single ended tx to try but it's months away from getting here down under.

It works as Nick says. I've tried a pimm ccs in the tail and I really couldn't tell if it was there or not which was a surprise. Technically it is in the sim in that the balance is better. I'm no expert but in the sim I thought the distortion profile looked more single ended. With the ccs, the even harmonics were suppressed. At the low levels in a phono, the worst features of this circuit aren't as apparent as in a power amp.

Another advantage is the biasing comes for free and bias schemes have a significant effect on sound IMHO . Whether that is offset by circuit imbalance is another thing. When all my stuff arives I'll be able to finally put the the se opt in and find out.

Variations of this thing have been built and developed by others. One by Salectric who has been taking his in a direction different to mine for years and has been built by a few on hifihaven forum. He now has an opt; a se nickel one by Dave Slagle.

Mark, Salectric and many others use the d3a triode. It's easy with a resistor swap in the eq to try it as pentode. I very much like it that way but I could also see that it be system/taste dependent.
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#8 Re: Question re Izzy Wizzy phono stage

Post by RhythMick »

Thanks. I'm definitely working up to building something similar. For me the joy of this hobby, quite aside from getting to listen to some pretty damned good music and revel in the fact that I built some of them, is that I can try changes for myself instead of having to read between the lines others write. DIY brings so much.
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#9 Re: Question re Izzy Wizzy phono stage

Post by RhythMick »

Oh and I already have the key components : LL1660PP, D3a, chocie of output valves
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izzy wizzy
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#10 Re: Question re Izzy Wizzy phono stage

Post by izzy wizzy »

If you need help with the sim to choose EQ values, happy to help. Will be interested to see what direction you take.
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#11 Re: Question re Izzy Wizzy phono stage

Post by RhythMick »

izzy wizzy wrote: Sun Jul 04, 2021 12:50 pm If you need help with the sim to choose EQ values, happy to help. Will be interested to see what direction you take.
Many thanks
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#12 Re: Question re Izzy Wizzy phono stage

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izzy wizzy wrote: Sun Jul 04, 2021 12:50 pm If you need help with the sim to choose EQ values, happy to help. Will be interested to see what direction you take.
Actually do you have a file you could send me for your circuit? I have LTSpice and have done a couple of things but wouldn't know how to use the D3a or 5687 models...
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izzy wizzy
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#13 Re: Question re Izzy Wizzy phono stage

Post by izzy wizzy »

Sure. You'll have to tell what exact circuit you want as I have so many variations even from the latest shown on my site.
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#14 Re: Question re Izzy Wizzy phono stage

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izzy wizzy wrote: Tue Jul 20, 2021 11:00 pm Sure. You'll have to tell what exact circuit you want as I have so many variations even from the latest shown on my site.
Well the circuit I am looking at is your current phono from the website. D3a pentode DC coupled via single stage RIAA into 5687 LTP into LL1660.
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izzy wizzy
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#15 Re: Question re Izzy Wizzy phono stage

Post by izzy wizzy »

Here it is. It's a bit of a mess but seems to work fine.

My LTSPICE is setup like the Tutorials on Intact Audio with the files by Stephie Bench so uses drop down tube models. I'm not sure this will work with LTSPICE using the regular models.

Make sure you have the latest version.
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