Born Again Vinylista Phono Stage

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Nick
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#16 Re: Born Again Vinylista Phono Stage

Post by Nick »

Be back in 6 months.
Its taken me 30 times that so far.
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#17 Re: Born Again Vinylista Phono Stage

Post by Cressy Snr »

Yes, I can imagine it has. There looks to be a lot more to phono stage design than meets the eye and I don't want to be in the same situation as I was with amps.
I have neither the money, time or inclination to be building large numbers of experiments like I have done with amps over the past ten years or so. Makes good forum copy, but it's not necessarily good for the wallet and I've done enough, God knows, to last the average diyer a lifetime :)
This needs to be got right first time so will by necessity be a very long term project and I will be using a bought one during the process.
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Mike H
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#18 Re: Born Again Vinylista Phono Stage

Post by Mike H »

Yes and for similar reasons I've been thinking of going back to basics with the improved Lenco VV7 pre-amp below - dare I mention transistors .. Image

http://www.douglas-self.com/ampins/disc ... Q-RIAA.htm

I have sim'ed it in LTspice and seems to do the job OK - may still be pants to listen to mind you - but I like that the EQ network's component values are not stupidly awkward to source. My personal pref being for polystyrene foil caps.

Still not actually built it yet. Idea was something that could be incorporated into the actual TT plinth.

EDIT: had to tweak something in the sim to get output DC exactly half of supply, but that was all I think.
 
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#19 Re: Born Again Vinylista Phono Stage

Post by thomas »

Cressy Snr wrote:
This needs to be got right first time …....

:D I admire your ambition !
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#20 Re: Born Again Vinylista Phono Stage

Post by Mike H »

An oft repeated mantra ... :D
 
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Nick
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#21 Re: Born Again Vinylista Phono Stage

Post by Nick »

This needs to be got right first time …....
the only way you can do that is to define "right" as in one or more ways less that as good as it could be.

Your choice.

A good start (IMHO) would be to begin with the assumption it will not be the final version and ignore things like boxes and neatness.
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#22 Re: Born Again Vinylista Phono Stage

Post by IslandPink »

The chances of building a phono stage that's the final one are negligible :D
A good start would be to decide the approx gain required and whether or not you can afford good step-up transformers.
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#23 Re: Born Again Vinylista Phono Stage

Post by Cressy Snr »

Guess it's breadboard time then :)
My definition of right would be for the stage to follow the inverse RIAA as closely as possible to give a flat response.
It needs to have a massive overload margin to handle clicks and scratches and to avoid distortion on sibilants.
We also need vanishingly low levels of noise, which makes DC heaters and regulation mandatory.
Not a bad list to start with. I' m only going for MM cartridges; not interested in MCs - far too expensive.
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#24 Re: Born Again Vinylista Phono Stage

Post by IslandPink »

Ah good of course, no step-ups required.
Right, for ref. my phono with D3a>RIAA>D3a gives enough gain from a 0.35mV MC ( + 10x step-up ) to equal a CD player output. I think it slightly exceeds Nick's DAC from memory. So from 3.5mV MM cart that would be the same. That's two mu=77 valves either side of the RIAA, they have R anode loads so probably in practice making just under 60x apiece. So you can go for 2 or 3 stages and various valves, but you'll need the total product of the mu's of the valves to be around 5000 or 6000x .
I would definitely recommend a regulated supply. Mine is basic but works very well in my opinion :D , this just uses a VR shunt from a CCS to define 300V. You don't need much shunt current as the circuit doesn't swing that much - I have about 20mA. This shunt is not quiet enough for the first stage, so that uses an additional 1.8R/22uF decoupling.
If you go for some of Nick's ideas on shunts, you may be able to avoid this.
Parts choice hugely affect tone and transparency.
Caps : avoid PIOs in the coupling or decoupling PS locations. I couldn't get them transparent enough at these low signal levels. Use poly's, my choice would be Mundorf Zn but Thomas differs !
Resistors - carbon composition in the signal path for me.
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#25 Re: Born Again Vinylista Phono Stage

Post by Nick »

Andrew and I have a HV shunt reg PCB's design that may help with the supply side.
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#26 Re: Born Again Vinylista Phono Stage

Post by Cressy Snr »

That would be great Nick.
It'd definitely get me off to a good start!
Thanks :)
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#27 Re: Born Again Vinylista Phono Stage

Post by thomas »

IslandPink wrote:Ah good of course, no step-ups required.
Right, for ref. my phono with D3a>RIAA>D3a gives enough gain from a 0.35mV MC ( + 10x step-up ) to equal a CD player output. I think it slightly exceeds Nick's DAC from memory. So from 3.5mV MM cart that would be the same. That's two mu=77 valves either side of the RIAA, they have R anode loads so probably in practice making just under 60x apiece. So you can go for 2 or 3 stages and various valves, but you'll need the total product of the mu's of the valves to be around 5000 or 6000x .
I would definitely recommend a regulated supply. Mine is basic but works very well in my opinion :D , this just uses a VR shunt from a CCS to define 300V. You don't need much shunt current as the circuit doesn't swing that much - I have about 20mA. This shunt is not quiet enough for the first stage, so that uses an additional 1.8R/22uF decoupling.
If you go for some of Nick's ideas on shunts, you may be able to avoid this.
Parts choice hugely affect tone and transparency.
Caps : avoid PIOs in the coupling or decoupling PS locations. I couldn't get them transparent enough at these low signal levels. Use poly's, my choice would be Mundorf Zn but Thomas differs !
Resistors - carbon composition in the signal path for me.
Actually I'm rather pleased with my D3a/D3a or e180f or russian 6j52n effort that I brought to Owston, plenty of gain for mm, only snag I guess is the input capacitance (just under 200pf ), though I'm toying with pentode mode for the next one. Folks here have basically described how I've ended up doing mine, eg rectified raw dc in one box, regulator with the phonostage, Mark's 'Morgan Jones reg' (but with VR's not Zeners) did indeed seem to sound more 'organic' or maybe it just looked nicer, but that's what I've kept. Russian polystyrenes and micas in mine, led biasing and Mark's Mundorfs have indeed grown on me and they are still in mine, 'un snubbed' now.
All good fun, I'm looking forward to seeing what you come up with!
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#28 Re: Born Again Vinylista Phono Stage

Post by IslandPink »

thomas wrote: ....Mark's 'Morgan Jones reg' (but with VR's not Zeners) ...
This was actually an idea from Gary Pimm that appeared in Lynn's Aurora circuits.
Last edited by IslandPink on Sat Aug 27, 2016 10:44 pm, edited 1 time in total.
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Thermionic Idler
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#29 Re: Born Again Vinylista Phono Stage

Post by Thermionic Idler »

Apparently the Transcendent Sound phono is reportedly very good, though I cannot vouch for it myself as I have not heard it.

http://www.transcendentsound.com/Transc ... reamp.html
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#30 Re: Born Again Vinylista Phono Stage

Post by izzy wizzy »

Some things to think about.
EQ
This is one of the key areas. How are you going to do the EQ.
LCR and LR - hardest and most expensive. Maybe not for a first timer. It would seem this is where most people stop after a long phono journey. Probably the best. I haven't got there yet.
Active CR feedback - fallen out of favour. IME, active EQ doesn't fulfill the overload/low dynamic noise requirement. Thay seem to exacerbate surface noise in comparison to passive EQ solutions.
Passice CR - The most popular among DIYers for good reason. It's relatively easy to get to sound good. Can be all-in-one (my favourite) or split which some say can be easier to do but IMO, I don't get that reason. There may be others but I ruled this route out in my journey as most implementations seem to complex for my idea of a phono stage. There is also shunt that can be used with a pentode where the pentode load becomes similar to the series R in the EQ.
EQ Z is important IME and it would seem many others who have made comparisons would agree. I used to think that this couldn't be so so my current phono had a high Z EQ and then a lower Z EQ; series R about 270k vs 27k. I mean, a filter is a filter right? If the driver can drive it and the following stage doesn't load it down, all things are equal aren't they? It would seem not IME and many others would seem to think the same when they have done the comparison all other things being roughly equal i.e. the driver can do both easily. The lower EQ sound less like the EQ curve if that makes sense. It seems to have a more even sound presentation top to bottom and less like a bass boosted thing and a treble cut thing. The lower Z EQ also seems to be more dynamic. Maybe somebody knows technically why but I have no idea.
The catch? The higher value caps for low Z EQs are more expensive and harder to get in low tolerance i.e. better than 1%. I like silver mica which are relatively easily available.

First Stage
This is the biggy IME. Like low Z EQ, I could not understand why a high gm valve could be any better than a high mu valve or high gain first stage. Gain is gain right? I was very resistant to moving away from 6SL7 fist stage as for me, compared to everything else I'd tried, SRPP, mu follower, cascodes of all types, a single triode gain stage, biased right so little to no microphonics, did something that all those others didn't; made me want to listen and not be annoying. That's a very personal thing.
So I tried the d3a as a triode. Similar gain but way lower rp and way more gm; roughly similar mu. This was a game changer. It had a similar effect to the EQ. Seems to me now, low Z comtributes hugely to a phono stage having effortless ease and stable sound; an effortless presentation. Again, high gm valves are more dynamic. Again although I've read all about the technical reasons why, and I can appreciate these, I don't really see why it contributes to better sound but there it is. Gain, at this point, with these little signals, is not just gain but something else is going on.
Again, if you look around at other people's phono journies, there is some correlation here.
Triode or pentode? I was open on this. Technically there is much literature that will turn you away from pentodes. However having tried pentode (easy to switch with something like the d3a) I've stuck with it. As a MM user, this might be attractive as high gm valves have very high input capacitance which might add up and leave you with little flexibility when cables are involved too. Pentodes get round that and I like the sound of the d3a this way in this position.
A pentode also opens up shunt EQ whereby the EQ is coupled directly to the stage omitting the series R. With these high gm valves, the EQ network will probably need to be lower Z (a good thing it would seem) however cap valves are starting to get large and to get them in close tolerances more difficult. This is a detour I haven't taken but it would seem a good idea. Look at what Ian posted earlier. Dave Slagle on his forum went this route. Pete Millet did a high Z version of this in his pentode phono. Cap values can start to get quite high with very high gm valves.
A pentode is also a good way of driving an LCR if you ever want to go there.
There has to be a catch here somewhere? High gm valves can be hard to get right. You'll hear all about how hard it is to tame oscillation (a hard icy sound usually being the give away). Cracked carbon grid stoppers, tight to the pins, short signal lengths/loops, components tight/near a ground plane and it should be fine.
Biasing is another difficulty as RC cathode bias means a very very big cathode decoupler. LED cathode bias or schottky diode bias seems to win out for many people. This didn't work as well for me as battery bias. It can be in series with the grid or under the grid. Under the grid won't work for you. When comparing the two, I couldn't tell the difference.

Second Stage
So many options but the key IMHO is interfacing with the outside world. In the end, I went differential so I could use transformer coupled out and direct couple to the first stage. I needed to drive a TVC and long interconnects.

Power Supply
Don't skimp here and be open to ideas. I have issues with regulation but those are my issues. Others have no problems here. You will hear everything in the power supply at these signal levels. Heaters need to be DC. The regulators, even on the heaters, are audible. Again, I don't regulate the heaters either. The downside to my methods is a massive very heavy power supply as all the smoothing is done with iron, even the heaters. Choke input for all, MV recitifers blah blah. Probably a silly idea.
More practical and easier, smaller, cheaper is to regulate and there are many options.
Keep open to RC decoupling of stages especially the first. With high LF gain, motorboating and LF stability can be an ever present problem or issue to solve.
I like a seperate PSU to get the noisy (electrically and mechanically) items out of the way. All in one box can be a challenge. There are enough of those in phono stages without adding to them.
I like a mono power supply compared to a stereo supply; a more together sound. I decouple by stage early on rather than by channel; again preferred when compared like for like.
Be aware of your journey and types of valve and stage currents. A 6SL7 might run 1mA, a d3a 20mA, an E55 even more. That's quite a range. I went differential on the output and despite thinking I'd designed in enough PSU current headroom, ran out to do it as I wanted with 100mA chokes (2 d3a and 4 5687) so had to compromise on 5687 current.

The rest is window dressing - cap types, resistor types and so on. We all have our faves.

Probably controversial ... I don't measure the frequency response. I rely entirely on LTSPICE and tight tolerance components. This is a subject in itself. I doubt many DIYers can measure a phono stage accurately enough so given the requirements of this to do it properly (my properly, no one elses) I don't. The top end is not too hard to get right with calcs. The bottom end almost impossible with calcs due to so many interactions IMHO hence LTSPICE. It's not that hard to learn. In the past I've used really complex spreadsheets to calce the values but nothing beats a sim IME. Interactions on the bottom part of the EQ include driver valve rp and ra, power supply z, coupling cap value, second stage load R and C. All combine to create a lot of interacting impedances especially at low level. Look at it right down to 2Hz as bumps with rising EQ can cause some major interactions leading to cone flap/LF overload, cartridge resonances feeding forward and so on if not dealt with. Combine that with an all-in-one EQ and it becomes .... just learn LTSPICE instead, than trying to crack it with all the calcs.

Hope this helps rather than put you off. There is so much mileage at these signal levels for very little expenditure other than time.

cheers,

Stephen
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