Valve Itch phono

[merlin el mago]

Oooooops Salas conected heater ground to elevated tubes

False alarm, ground heater connect right to lower valves

 

[merlin el mago]

Salas both SUT connections are OK?

 

[stajo]

I wonder If it would be possible to duplicate/mirror the circuit to make it balanced

 

[Salas]

Salas both SUT connections are OK?

Just put 20K on Valve Itch's input when using the 977 as SUT and nothing on the SUT itself. The other explanations and ways perplex you, so skip them.

 

[merlin el mago]

Thanks Salas I will use this schematic as per your advice,

 

[Salas]

I wonder If it would be possible to duplicate/mirror the circuit to make it balanced

Of course but you will never have the level of matching required for good CMRR with so loose tolerances that tubes will produce in open loop circuits like that.
To the contrary when using a balanced impedance primary SUT like the Jensen you automatically enjoy very good CMRR.

 

[stajo]

Yea. Stupid idea. Better use an OPT

 

[Salas]

If you will combine an SUT on input and a center tapped 1:1 OPT on output then you get a fully balanced stage regarding its connectivity to outside.

 

[merlin el mago]

Salas changed 47K for 18K but I didn't hear music on Left channel? Right channel still sounds down...

 

[Salas]

Try the diode trick.

 

[merlin el mago]

The same like your advice to use the Itch only for MM?

 

[Salas]

Yes. Just do it and if it will all work normally I will explain why.

 

[merlin el mago]

OK I will put, one question I have to left unconnected pin 9 or connected to gnd?

 

[Salas]

To gnd.

 

[merlin el mago]

OK I left connected to gnd & try with diodes connecteds

 

[merlin el mago]

No sound Left channel, Right channel only noise when volume goes to max.

 

[Salas]

Was the build working before with the same SUTs and input valve?
Change valve? Check connections?

 

[merlin el mago]

Right channel sounded before with the same SUT & input valve.

 

[Salas]

But you had no left channel before also?

 

[merlin el mago]

Yes no sound Left channel, with or without diode.