Valve Itch phono

[grataku]

'HV' on the LM317 is not really what I thought it was. It's a 60V parts vs a 40V standard.

 

[Peppe]

By the way, that RC between output and ground is for helping LM317's stability. A cheaper 47uF electrolytic capacitor alone could do that trick instead of the 0.47uF 630V Wima MKP and the 4.7 Ohm resistor to give it artificial ESR. Maybe the original link's guy didn't have a high voltage electrolytic handy. Or he wanted it to sound different (kinda speedier/cooler), who knows.

I guess a footprint that allows either of the two caps could be an option. The 4R7 resistor could be shorter with the electrolytic.

A minor mystery of the schematic is the lack of R3. Probably never been there. 🤔

 

[grataku]

Probably covered already but is there any x-talk when criss-crossing L+R channel on a single the dual triode to lift the filament supply? I guess there is no other choice here.

 

[Salas]

Haven't measured cross-talk 20Hz-20kHz. Could be somewhat worse than if it was a non criss-cross circuit. But it performs with good image separation so it must be sufficient for covering cartridges spec which practically achieve 30dB L-R at best.

 

[grataku]

I found a thread and it seems the separation is well above 50dB, it is useful if the tubes has a shield. I will have to look at the datasheets.

 

[Salas]

The 6N2P input stage valve in this phono does have a screen connected to pin 9. But 50dB separation I have not met on test discs. Usually 20-25dB and up to 28-29dB at 1kHz for carefully assembled carts using line contact stylus when the whole vinyl rig is geometrically very well set. Most of the times not even reading the same figure between channels.

 

[grataku]

I was talking about triode xtalk separation, not the pickup separation.

 

[Salas]

In this case even if only -50dB crosstalk in the phono electronics certainly covers any vinyl rig's separation potential.

 

[Salas]

I found a thread and it seems the separation is well above 50dB, it is useful if the tubes has a shield. I will have to look at the datasheets.

This one? In post #57 there Merlinb also measured the 6N2P for x-talk and it fared best. It was a nice original choice for the Valve Itch.

 

[Milos P.]

Hi, can Valve Itch drive 50k pot (volume pot in front of my power amp)?

Thank you

 

[grataku]

It better! If it can't drive a 50k load you can throw it in the garbaggio! 😉

 

[Milos P.]

Thanks

 

[Salas]

It better! If it can't drive a 50k load you can throw it in the garbaggio! 😉

V1.2 has about 800Ω Ζο (output impedance). So its sufficient.

 

[Salas]

Hi, can Valve Itch drive 50k pot (volume pot in front of my power amp)?

Thank you

Yes it can. Output is taken from the top valve's cathode of the Mu-Follower. So its a low impedance output.

 

[Milos P.]

Great, thank you!

 

[merlin el mago]

Salas I own two FT-3 Russian teflon caps with rating 200V, could I use them as output coupling caps?
-Attached schematic used you marked output voltage 190V.
-The input impedance of mine 801A DHT preamp is 150K so no problem about FR.
TIA
Felipe

 

[Salas]

Felipe, hi

Its close. You have to monitor with the DMM first that the voltage at the spot does not climb over 190V during start up, normal operation, turn down, in your build.

 

[merlin el mago]

Hi Salas,

Thanks for support, yes it's very close voltage (it's the reason I asked you), I will do as you suggest monitoring with the DMM the B+ voltage does not climb over 190V during start up.

Have a nice day
Felipe

 

[merlin el mago]

Salas measured:

-After 1 hour right channel +2,70V left channel -1,15V

Are OK the values?

How many time have I to left the Itch off to measure at start up?

Thanks & cheers
Felipe

 

[stajo]

What are you measuring Merlin? You shall measure between V4 cathode and ground