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Is it possible? Good RIAA phono amp using new tubes?

Hi. I'm looking at building a matching MC/MM phono stage for the RedRoo amplifier. I keep on coming back to using an input transformer and a D3A input tube with ccs anode load, per Stuart Yaniger's design in the articles section on this forum.

Trouble is the D3A is getting expensive and goodness knows how long they will be available for.

Has anyone tried paralleling 6DJ8/6922 in this position to reduce noise, followed by a cathode follower to drive the RIAA network, or any other solution? I know John Broskie uses the 6DJ8 CCDA circuit in his RIAA pre-amp, and I like his designs for their simplicity, but not sure about the tube noise.

Any ideas or comments greatly appreciated!
 
I have got good results with soviet made 6S3P-EV high gm triode. Those tube are still easily available and not expensive. Attached my schematic. Noise level is 6 dB lower than typical 12AX7 design.
 

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Frankly, properly culled, phono grade, specimens of the Sovtek 12AX7LPS are just fine. Some MM carts. and SUTs interact adversely with the high CMiller exhibited by the 'X7 triode, but most do not.

The tweaked RCA setup I'm associated with deals with the drive capability and bass extension issues of the original. If you want to completely dispose of the high 'X7 CMiller matter, use a 6GK5 in the 1st gain block and rework the RIAA network so it deals with the plate resistance difference.

FWIW, I suspect you could use an unbypassed cathode bias resistor in combination with a 6GK5 (to enhance linearity), given that the documented RP of the type is pretty darned "short".
 

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Sovtek 12AX7LPS are just fine.....I suspect you could use an unbypassed cathode bias resistor in combination with a 6GK5 (to enhance linearity), given that the documented RP of the type is pretty darned "short".

I see that Tavish also gives the 12AX7 a pretty good rating. I think I remember the 6GK5 from television sets.. I'll try them also.
 
Most of the thermal/Johnson noise in a phono stage fed from an MM cartridge is from the loading resistor. More important noise sources are often hum, from poor interconnection, and 1/f noise, completely, individually valve-specific. High Gm input valves are an idea from the 1980s that made sense at the time (attempts to feed directly from contemporary MC phono cartridges).


Discussion of phono stage noise without reference to the inductive source's demands are wrong-headed.


All good fortune,
Chris
 
Despite its low transconductance, the ECC83 / 12AX7 is also remarkably good according to Merlin Blencowe's AES article, "Noise in triodes with particular reference to phono preamplifiers", Journal of the Audio Engineering Society, vol. 61, no. 11, November 2013, pages 911...916, see also Flicker Noise dominates triode noise in audio (AES) - diyAudio Apparently ECC83's have remarkably low 1/f noise.

Attached is a list of optimal bias currents for minimum noise for a few valves - too little current aggravates white noise and too much current aggravates 1/f noise, so there is an optimum. I've also calculated a kind of weighted average equivalent input noise density, that is, an amount of white noise at the amplifier input that would result in the same weighted noise as the actual noise of the valve (which is partly white and partly 1/f). The EF86 data are based on a very limited set of measurements I took, the others are calculated from Merlin Blencowe's data and datasheet transconductance graphs. The "RIAA and 20 Hz to 20 kHz brick-wall" column is included for completeness, but it is really useless as it hardly has any relation with how much noise you would hear.

For comparison, according to measurements from xx3stksm, record surface noise on a clean record is typically around -60 dB RIAA- and A-weighted with respect to 1 kHz, 5 cm/s. The noise bandwidth of RIAA- and A-weighting is about 3219 Hz. Hence, for a 5 mV at 1 kHz, 5 cm/s moving-magnet cartridge, record surface noise is equivalent to 88.13 nV/sqrt(Hz) average with A- and RIAA-weighting and for an insensitive 0.3 mV moving-coil cartridge without step-up transformer, it would be 5.288 nV/sqrt(Hz).

That is, the only cases where valve noise is really critical are MC amplifiers without step-up transformer and during the silence between records, when there is no record surface noise.
 

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Trouble is the D3A is getting expensive and goodness knows how long they will be available for.
The 6J52P is basically a Russian D3a, and is not hard to obtain.

Has anyone tried paralleling 6DJ8/6922 in this position to reduce noise,
Of course. It's one of the best choices for a low noise input, and generally does not suffer so badly from microphonics as the D3a types.

It's worth pointing out that a CCS can make noise worse by adding it's own silicon shot noise; the circuit details matter. And many people run the tubes too hot in the mistaken belief that more gm is always good, when it actually makes flicker noise worse, which is most noticeable in a phono stage. Personally I woudn't waste my time with a CCS; it's hard to beat a simple resistor-loaded 6DJ8 running at a couple of milliamps.
 
Can you point me to some more info on this phono pre?

Attached some test results and the schematic of the power supply.
The LEDs at the cathodes are "big/yellow" (see photo) creating 2.0...2.1 V bias voltage.
 

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With this circuit, Junior phono I got the following resuslts:
12BZ7
G= 49,6 dB,s/n = -73,2 dB weighted A

12AX7
G = 48 dB , s/n = 74 dB

5965
G=41 db s/n = 78 dB

7062
G= 42,6 s/n= 80 dB

ECC81
G= 41,3 s/n = 73 dB

In attach the diagram, I use always this condfiguration where the RIAA network is at low Z

And it is possible to change the tubes ( with a matrix for filaments) and the gain ( with jumper.
In my opinion very good results.

Walter

Walter
 

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Hi. I'm looking at building a matching MC/MM phono stage for the RedRoo amplifier. I keep on coming back to using an input transformer and a D3A input tube with ccs anode load, per Stuart Yaniger's design in the articles section on this forum.

Trouble is the D3A is getting expensive and goodness knows how long they will be available for.

Has anyone tried paralleling 6DJ8/6922 in this position to reduce noise, followed by a cathode follower to drive the RIAA network, or any other solution? I know John Broskie uses the 6DJ8 CCDA circuit in his RIAA pre-amp, and I like his designs for their simplicity, but not sure about the tube noise.

Any ideas or comments greatly appreciated!
the input transformer will make the SNR with an mc cart irrelevant in relation to the tube...you only need to settle on a tube good enough for mm and 12ax7 is good enough for any mm cart.D3A has its own performance which i consider very hard to beat if everything is right , but looking at that junior schematic it looks well thought although i'm not sure e88cc can drive such low impedance riaa with good linearity at low frequency .It's even lower than the one found in LME49710 datasheet and in my experience very low impedance RC passive riaa is a bit detrimental to the sound, I mean it sound a little too clean ... Believe it or not , the riaa network found in LME49710 had the best sound of all i tried with d3a , i only mis lcr passive riaa experience .As for anode loading i have to admit i only tried some sort of mu-followers and gyrators made with ultra low noise bipolar transistors and high voltage depletion mos-fets, but simple resistor loading might be enough as it allows the tube a little bit more distortion and i'm not sure everyone wants an ultra clean preamp based on tubes....I think i'm guilty in the first degree of building two of the most complicated hybrid phono preamps ever made, but i rarely advise someone to follow my ways cause more expensive or more elaborate doesn't necesarily mean better for every pair of ears.
 

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With this circuit, Junior phono I got the following resuslts:
12BZ7
G= 49,6 dB,s/n = -73,2 dB weighted A

12AX7
G = 48 dB , s/n = 74 dB

5965
G=41 db s/n = 78 dB

7062
G= 42,6 s/n= 80 dB

ECC81
G= 41,3 s/n = 73 dB

In attach the diagram, I use always this condfiguration where the RIAA network is at low Z

And it is possible to change the tubes ( with a matrix for filaments) and the gain ( with jumper.
In my opinion very good results.

Walter

Walter
What is the value of R_TAR1 and R_TAR102 and how to decide ?