Looking for recommendation for Phono Stage

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izzy wizzy
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#31 Re: Looking for recommendation for Phono Stage

Post by izzy wizzy »

Nick wrote: Sat Jan 19, 2019 3:26 pm By all means, I have sold a few of them and I am rather pleased with the design itself so happy to see what people think.
It's got 3 of my favourite small signal valves in it. If I could get a 6072 into mine somewhere I would :)

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Stephen
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#32 Re: Looking for recommendation for Phono Stage

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Why? What do you like about those valves?
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#33 Re: Looking for recommendation for Phono Stage

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I like the D3a 5687 combo and a previous phono I really liked had 6072 mu follower with 6SL7 up front I think. Anything I had with the 6072 sounded nice. The first pairing are a bit more direct which I like these days but because I like lowish Z EQ and Tx coupling that rules out the 6072 unless it's buffered.

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Stephen
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#34 Re: Looking for recommendation for Phono Stage

Post by izzy wizzy »

A question for Nick and Mark. You both use RC cathode bias on the first valve. I'm beginning to think battery bias has a bit of an issue and a steeper LF rolloff with RC biasing might help. In the model, 1000u looks a good value on the cathode. How did you both arrive at the values you used? And Nick, can you say what make you used? Mark's is unobtanium now and maybe I shouldn't risk my squashed one.

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Stephen
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#35 Re: Looking for recommendation for Phono Stage

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Built it and measured it and tweeked. I use a Elna Silmic. A early version of the circuit used half the 6072s as the cathode follower driving g2, but I found it a very sensitive position and unless you used a low noise valve the cathode follower added more noise than the front end. The only one I found that was quiet enough was the EH gold pin 6072a and they have stopped making them (though I did buy a few). So I tried the mosfet and it made the problem go away. That gave be a spare triode so the SRPP ish gain stage. It was originally just a resistor loaded triode. As it is the d3a front end gives a steady gain of 40dB with surprisingly low distortion. You can almost get whatever gain you want by playing with the anode resistor and the amount of feedback via g2.

Its usable with a 0.35mv cartridge without a stepup (Marks heard it like that), but the noise is audible in that case when not playing a LP. Put a stepup on the front and its silent.
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#36 Re: Looking for recommendation for Phono Stage

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Nick wrote: Sat Jan 19, 2019 7:55 pm Built it and measured it and tweeked. I use a Elna Silmic. A early version of the circuit used half the 6072s as the cathode follower driving g2, but I found it a very sensitive position and unless you used a low noise valve the cathode follower added more noise than the front end. The only one I found that was quiet enough was the EH gold pin 6072a and they have stopped making them (though I did buy a few). So I tried the mosfet and it made the problem go away. That gave be a spare triode so the SRPP ish gain stage. It was originally just a resistor loaded triode. As it is the d3a front end gives a steady gain of 40dB with surprisingly low distortion. You can almost get whatever gain you want by playing with the anode resistor and the amount of feedback via g2.

Its usable with a 0.35mv cartridge without a stepup (Marks heard it like that), but the noise is audible in that case when not playing a LP. Put a stepup on the front and its silent.
Nick is that the unit you demonstrated at Owston?
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#37 Re: Looking for recommendation for Phono Stage

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#38 Re: Looking for recommendation for Phono Stage

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izzy wizzy wrote: Sat Jan 19, 2019 6:14 pm A question for Nick and Mark. You both use RC cathode bias on the first valve. I'm beginning to think battery bias has a bit of an issue and a steeper LF rolloff with RC biasing might help. In the model, 1000u looks a good value on the cathode. How did you both arrive at the values you used? And Nick, can you say what make you used? Mark's is unobtanium now and maybe I shouldn't risk my squashed one.
Cheers,
Stephen
I think the 1000u is overkill, I just wanted to get the LF corner from that part 'out of the picture' - so it wouldn't give you some LF roll-off there at that value. Maybe I didn't have a BG 'NX' red one that was smaller. 470u ought to do it.
What would be interesting is if you want to do this, could you try the green Panasonic ones, which I have used so far only in the input to a solid-state amp. They seem good, Nick likes them. They are non-polar , 'ES' is it ? The folklore is you use two to make up the value, turned opposite ways ( like Peter Q always used to advise with the NX Black Gates ) .
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#39 Re: Looking for recommendation for Phono Stage

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I think you mean the Nichicon Bipolar MUSE ones.
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#40 Re: Looking for recommendation for Phono Stage

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Nichinon Smichinon .
I think you are correct !
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#41 Re: Looking for recommendation for Phono Stage

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IslandPink wrote: Sun Jan 20, 2019 5:31 pm Nichinon Smichinon .
I think you are correct !
You are of course right, I couldn't possibly know if what you said was what you meant to say, or if you meant to say something else. All I can say with some confidence is the green bipolar caps I like are the Nichicon ES Bipolar MUSE ones.

:-)
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#42 Re: Looking for recommendation for Phono Stage

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This is excellent news as they are cheap. I'll give them a go soonish.

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#43 Re: Looking for recommendation for Phono Stage

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So, if I'm going to experiment then I ought to adopt a scientific method. All when I get back from skiing of course, having a fab time over here.

So what's the best way to measure the performance of a stage? I'll start with setting up the D3a SE in triode mode and move on from there to try more esoteric options. I'm a bit of a scope newbie, I have a picoscope. I could feed in a square wave, use that to measure gain. How should I measure how well the square wave is being reproduced?

Point me in the right direction and I'll research.
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#44 Re: Looking for recommendation for Phono Stage

Post by izzy wizzy »

I model in LTSPICE, make it, fiddle a bit with values, listen, remodel and round and round. I can't measure accurately enough so don't bother.

I reckon getting the EQ right is only possible in a model (calculators aren't up to the job) and small changes can alter the character quite a bit hence it's importance in understanding whatever sound you're after or getting.

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Stephen
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#45 Re: Looking for recommendation for Phono Stage

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RhythMick wrote: Sun Jan 20, 2019 7:09 pm So, if I'm going to experiment then I ought to adopt a scientific method. All when I get back from skiing of course, having a fab time over here.

So what's the best way to measure the performance of a stage? I'll start with setting up the D3a SE in triode mode and move on from there to try more esoteric options. I'm a bit of a scope newbie, I have a picoscope. I could feed in a square wave, use that to measure gain. How should I measure how well the square wave is being reproduced?

Point me in the right direction and I'll research.
Well listening is always good. A inverse RIAA and square wave is a good place to start seeing how good the eq is, but TBH the main reason I have a shelf of test kit behind the workbench is measuring phono stages. But a square wave and inverse RIAA is the place to start. What its not so good at telling you is how it will sound.
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