Valve Itch phono

[Salas]

In my case I stuck to the ECC88 since it shouldn't overload an existing MM stage. If you design from scratch then that would make life a little easier.

Ciao,

I looked into it a bit and I think it could be running just at 10mS in total as it is, with such a Jfet CCS about 6mA is to be expected. So something like 1.5mA per triode. Half the transconductance of a 5mA 2SK170GR for the whole composite pre pre in other words. 5mA per triode can boost to 20mS for 3dB better SNR. DN2540 can provide and its actually a good CCS down to a 20-25mA minimum level. Two in self biased cascode is even better high Z vs. Freq.

The Itch itself could push its input transconductance a bit also if there is raw DC spare for 320V B+ and R3 became 330 Ohm in combination. Little thing, but it could be better driving its EQ network in the highs. To maybe avoid double up experiments and more Miller for Stajo.

 

[stajo]

320 V, of course. There is always juice

 

[stajo]

Found this ol physical topology scetch of a combined Itch+6V6 pre. Its bouncing around in my head again. Question is how many SSHV's I will need for the ultimate experience.

 

[Salas]

Single, you can't do double mono since the twin envelope valves functions are intertwined between channels.

 

[stajo]

Where except in filaments?

 

[Salas]

One bottle is the bootstrap CCS part to the other bottle which is the gain part in the mu followers. Since you got to heater lift the upper part it can't be a single bottle per channel with its innards playing different roles.

 

[stajo]

Yes but the triodes are still separate in each bottle. Thats why I scetched as I did, with one triodehalf per side (only one channel is drawn).

 

[dirkwright]

Back to my sweet little cheapy www.lundahl.se/pdf/1550.pdf‎ then. I should be able to use it both in 6 and 12 dB step up to get modern standard output voltages dont you think? Seems like they even appreciate some grid capacistance.

http://www.lundahl.se/pdf/1550.pdf

better?

 

[Salas]

Yes but the triodes are still separate in each bottle. Thats why I scetched as I did, with one triodehalf per side (only one channel is drawn).

The heater lift refers to one B+ and its common to both channels CCSs. The envelope elements are close together too, don't know if double rails could really mean good separation gain. Rather mixed enough already.

 

[stajo]

The space between the cathodes and filaments (which are interconnected) are often just a thin oxide layer. Thats where the closest interaction is. But all the electrodes are still electrically separated.

 

[Salas]

http://www.lundahl.se/pdf/1550.pdf

better?

It also talks optimum square response Zobel like Sowter and Jensen do.

 

[Salas]

The space between the cathodes and filaments (which are interconnected) are often just a thin oxide layer. Thats where the closest interaction is. But all the electrodes are still electrically separated.

Alright, if you plan to spare the space and expense for separate rails...

 

[stajo]

I dont know yet, just reasoning. Initial tests will go from one source. I dont know if the upper small triodes likes to be connected to 6V6 anode loads either.

 

[dirkwright]

It also talks optimum square response Zobel like Sowter and Jensen do.

I'm sorry, I wasn't suggesting anything by my post. In a previous post, the link did not work. I was merely providing a working link.

I have not followed the latest topics of discussion in this thread so I don't know what's going on. Sorry for the confusion.

 

[Salas]

I see you provided a working link only. But we had a discussion on secondary optimums so the others will get the drift.

 

[dirkwright]

I see you provided a working link only. But we had a discussion on secondary optimums so the others will get the drift.

OK, so, is someone trying to use an input transformer with your "valve itch" phono pre? Some of the Lundahl transformers don't require an RC network on the secondary for good response.

 

[Salas]

Was trying until he bought a high output MC cartridge in the course of the discussion.

 

[stajo]

Was trying until he bought a high output MC cartridge in the course of the discussion.

It was too many loose parameters. Now I have one fixed

 

[dirkwright]

Was trying until he bought a high output MC cartridge in the course of the discussion.

Ah, ok, thanks.

I had considered using a step-up input transformer for MM cartridges, but the high source impedance for them makes a transformer basically useless as far as I understand, as well as the fact that there really isn't a suitable one out there. I did find a Jensen that would work, but the ratio was only 1:1.414 and thus did not really improve S/N at all. If it were desired to use an input transformer to convert balanced to unbalanced, then any of the 1:1 high impedance input transformers will work.

 

[stajo]

The little I know of MM carts say they need to be tuned in with a small amount of pF. A tranny would be devestating in that logic. Thanks for working the link Dirkwright!