Phono stage design considerations part 1: choosing 1st stage tube

[Salas]

Hi!



I generally use MC step up transformers.

I did try a D3a phono stage with a MC direct in once and it was well usable.
But I prefer to have the MC step up. No point in trying to avoid the transformer at the inout when the entire phono stage is transformer coupled

Best regards

Thomas

I just wonder how far 65 milliSiemens of thermionic transconductance could carry you in the presence of heaters, grid damping etc. If you had any squeaky clean success with direct LMC in. Same as with SUT success.

 

[Joshua_G]

Hi Thomas,
Thank you.

To drive a 600 Ohm LCR RIAA puts very different requirements on the 1st tube compared to a RC RIAA with medium or high impedance.

What are the requirements for the 1^st stage tube which are specific to 600 Ohm LCR RIAA?

Also, which 600 Ohm LCR RIAA did you use?

18ma plate current. It is very high on the list of my favourite tubes for this application, only topped by EC8020 or WE437. I prefer it over E810F, E55L.
I used it with Lundahl LL1692A

So, EC8020 or WE437 would be a better choice.
Did I get you correctly?
Also, which one is of higher preference, the EC8020 or WE437?

I prefer the tubes mentioned above over the 6AM4. I just listed it since it would full fill the requirements for availability and low cost

The requirements for availability and low cost are at the bottom of my priorities. That is, when two tubes may equally meet the higher priorities, I'll choose the one which is of more availability and lower cost. I wouldn't choose a tube based primarily on availability and low cost, when that tube falls short in the other requirements.

 

[Joshua_G]

Hi Salas,
Thank you.

Noise in high gain MC like 60dB-63dB (X1000-1400) is THE consideration priority. Not just a parameter. If you can't fetch the signal across strongly over the noise floor then its so contaminated that you lose much original information. That alone renders the tonality of what portion remains intact a purely cosmetic exercise.

Indeed, low noise and microphonics are of the highest priorities when it comes to a phono stage.
Yet, after the desired low noise was met, there are also other considerations. There are other parameters, besides noise, which impact the sound quality.
Therefore I'm trying to look at noise figure, along other parameters.

I know of your folded simplistic and the enthusiastic users' impressions it received.
I'd love to compare it to a tube-based one.
For such comparison to take place, I need to have the best possible tube-based phono stage I may come up with.

 

[Joshua_G]

Hi Salas,

I just wonder how far 65 milliSiemens of thermionic transconductance could carry you in the presence of heaters, grid damping etc. If you had any squeaky clean success with direct LMC in. Same as with SUT success.

Would you care to elaborate?
I didn't follow you here, while it seems to me very important.

 

[Salas]

Hi Salas,
Thank you.



Indeed, low noise and microphonics are of the highest priorities when it comes to a phono stage.
Yet, after the desired low noise was met, there are also other considerations. There are other parameters, besides noise, which impact the sound quality.
Therefore I'm trying to look at noise figure, along other parameters.

I know of your folded simplistic and the enthusiastic users' impressions it received.
I'd love to compare it to a tube-based one.
For such comparison to take place, I need to have the best possible tube-based phono stage I may come up with.

It will be unfair to the tubes. To go at 0.5nVrtHZ with tubes it will create SUT costs and general discipline of design, execution, housekeeping, PSUs galore, & parts, that will set you back 20 times the FS build cost and time.

 

[Vinylsavor]

Hi!

What are the requirements for the 1^st stage tube which are specific to 600 Ohm LCR RIAA?

It needs to be able to drive 600 Ohms which is a tough load. I do it by transformer coupling with a step down transformer. Then the tube needs to have moderately low rp to be usable with a transformer. Also a high amplification factor is desirable since part of the gain is lost through the step down transformer.

I'd say a mu of 50 or more and a high transconductance.

There are other means to drive a 600 Ohm RIAA. It has been done with cathode followers and cap coupled. I prefer the transformer coupling

Also, which 600 Ohm LCR RIAA did you use?

Various, for example Tango EQ600P or Tango EQ2L. Also discrete coils from intact audio.

So, EC8020 or WE437 would be a better choice.

Ultimately I prefer the EC8020 but it is very difficult to find and very expensive. The D3a is a good alternative which is obtainable

Best regards

Thomas

 

[Salas]

Hi Salas,



Would you care to elaborate?
I didn't follow you here, while it seems to me very important.

I was asking Thomas if he could utilize the about 55-65mS gm of those exotic tube types cleanly without problems of noise ingress from subsystems in the envelope or needed resistive patches that contribute Johnson. With straight MC in in mind. A figure on paper is one thing, someone's info from experience with the real beast is another thing, as you know. That is why I asked him.

 

[Joshua_G]

Hi Salas,
Thank you.

It will be unfair to the tubes.

May be so, yet I intend to make that comparison.

To go at 0.5nVrtHZ with tubes it will create SUT costs and general discipline of design, execution, housekeeping, PSUs galore, & parts, that will set you back 20 times the FS build cost and time.

Regarding cost comparison, you are absolutely correct.
In this project I'm looking for the best sound quality I can possibly attain, not for the best 'value for money'.

Again, acceptable low noise is mandatory for a phono stage. That goes without saying.
Yet, the lowest noise figure in itself doesn't guaranty best sound quality. Possibly, under certain circumstance, some compromise on noise figure may yield better sound quality – which is what I'd like to try and compare.

 

[Joshua_G]

Hi Thomas,
Thank you.

It needs to be able to drive 600 Ohms which is a tough load. I do it by transformer coupling with a step down transformer. Then the tube needs to have moderately low rp to be usable with a transformer. Also a high amplification factor is desirable since part of the gain is lost through the step down transformer.

I'd say a mu of 50 or more and a high transconductance.

Thank you.

There are other means to drive a 600 Ohm RIAA. It has been done with cathode followers and cap coupled. I prefer the transformer coupling

Instinctively, transformer coupling being better sounds correct to me.

Various, for example Tango EQ600P or Tango EQ2L.

AFAIK, Tango is out of production and those EQ's are unobtainable.

Also discrete coils from intact audio.

Are they shelf products, or do they need to be produced under specific order?

Ultimately I prefer the EC8020 but it is very difficult to find and very expensive. The D3a is a good alternative which is obtainable

Thank you very much.

 

[Salas]

Hi Salas,
Thank you.



May be so, yet I intend to make that comparison.



Regarding cost comparison, you are absolutely correct.
In this project I'm looking for the best sound quality I can possibly attain, not for the best 'value for money'.

Again, acceptable low noise is mandatory for a phono stage. That goes without saying.
Yet, the lowest noise figure in itself doesn't guaranty best sound quality. Possibly, under certain circumstance, some compromise on noise figure may yield better sound quality – which is what I'd like to try and compare.

Its a noble cause to try make a purely tube (hybrid input stage is cheating big time) phono with largely comparable noise floor level and shape to JFETs or BJTs for genuine LMC carts. Blood sweat and tears but in case of success to meet JC classics or Pass Labs input noise and gain levels for instance it will reward a unique sonic signature. Absolutely comparable THD level to SS is not a priority, but you must nail the noise and hum thing.

 

[45]

get away from tubes as far as possible

That's my suggestion too, for a phono stage.

 

[Joshua_G]

I was asking Thomas if he could utilize the about 55-65mS gm of those exotic tube types cleanly without problems of noise ingress from subsystems in the envelope or needed resistive patches that contribute Johnson. With straight MC in in mind. A figure on paper is one thing, someone's info from experience with the real beast is another thing, as you know. That is why I asked him.

Indeed, it looks like straight MC with tubes only may potentially be a less favorable approach.
Yet, Thomas said it was well usable. (From that statement I get it wasn't the optimum architecture).

On a side note, I'm interested in comparing SUT with JFET's based MC pre-pre, possibly complementary, folded cascode, a' la' John Curl.

But first, the MM stage needs to be up and running.

 

[Joshua_G]

Its a noble cause to try make a purely tube (hybrid input stage is cheating big time) phono with largely comparable noise floor level and shape to JFETs or BJTs for genuine LMC carts. Blood sweat and tears but in case of success to meet JC classics or Pass Labs input noise and gain levels for instance it will reward a unique sonic signature. Absolutely comparable THD level to SS is not a priority, but you must nail the noise and hum thing.

Thank you.
Why do you consider hybrid input stage to be cheating?
Blood sweat and tears is my lot in any case…
BTW, my cartridge is genuine LMC (ZYX R1000).

Again, I'm willing to sacrifice noise figure, to a degree – should there be a sound quality pay off. I don't intend to compete and compare noise figure in itself – as long as the noise is sufficiently low.

 

[Joshua_G]

That's my suggestion too, for a phono stage.

Thank you very much for your suggestion.
Yet, I'm going to build tubes based RIIA stage.

 

[Salas]

Thank you.
Why do you consider hybrid input stage to be cheating?

Because the input stage is all that counts in LMC and ribbon microphone preamps. If its performance is based on silicon then its make believe you are building with tubes. Even if you got 10 bottles further on. Its just SS decorated with tube tones.

 

[Vinylsavor]

Hi

Yet, Thomas said it was well usable. (From that statement I get it wasn't the optimum architecture).

Usable yes, but a stretch. I did it just briefly to see how it performs. I generally use MC step ups.

Best regards

Thomas

 

[PMA]

Noise in high gain MC like 60dB-63dB (X1000-1400) is THE consideration priority. Not just a parameter. If you can't fetch the signal across strongly over the noise floor then its so contaminated that you lose much original information. That alone renders the tonality of what portion remains intact a purely cosmetic exercise.

I am supporting this.

 

[Koifarm]

Is this the kind of harmonics you looking for?

This all tube mc/mm phono stage has tubes with very low millercap.(25pf), very low noise (-80db).

 

[Joshua_G]

Because the input stage is all that counts in LMC and ribbon microphone preamps. If its performance is based on silicon then its make believe you are building with tubes. Even if you got 10 bottles further on. Its just SS decorated with tube tones.

Possibly so, possibly not so.
Possibly, even for LMC, the input stage isn't the only thing that determines the sound parameters of the entire phono stage. Possibly the next stages also have some impact on the overall sound parameters and sound quality.
I wouldn't know without trying.

 

[euro21]

When the measurements of D3a and C3g were so good, why do you use 5751 based phono stage?

I haven't enough time.
Hungarian proverb: Twenty-four hours a day... plus the night.
Designing and building components is my late night project.

This phono (highly modified Audio Innovations 200) is very good for me, just as my turntable (Roksan Xerxes, SME IV tonearm, Supex 900S pickup, EAR MC3 SUT).

C3g phono was the challenge (designing and building in two weeks to Hungarian Triode Fest).