Valve Itch phono

[hego]

Which is the last revisión?

 

[merlin el mago]

This one Rev 1.2

 

[hego]

Thank´s , Felipe.

 

[merlin el mago]

Your welcome, it's a nice phono preamp.

Salas I have a DC offset in left channel of 9VDC, it's possible having an output cap?

Dont you have one already? (C6)

Yes.

 

[vgeorge]

Measure with the preamp connected and check again.

 

[merlin el mago]

George also I see the woofer outward when preamp connected.

 

[stajo]

George also I see the woofer outward when preamp connected.

Then you have dc on poweramp out. If woofer stays out that is.

 

[merlin el mago]

It's strange phono Itch have output cap & preamp too. Can be power amp, I will check tomorrow.

 

[vgeorge]

Check dc at every connection between components, to see were the problem is then.

 

[merlin el mago]

Was the AD820N in the servo DC offset of Borbely power amp.

 

[stajo]

Was the AD820N in the servo DC offset of Borbely power amp.

 

[Salas]

Lucky having surviving woofers

 

[stajo]

Lucky having surviving woofers

Woofer yoga

 

[merlin el mago]

Lucky having surviving woofers

Fortunately the woofer survive.

 

[Bigun]

Maybe silly question, but, why not put 6SN7 above input triode where it's higher gm will provide lower drive resistance ?

 

[analog_sa]

There seems to be a 22k resistor...

 

[stajo]

Maybe silly question, but, why not put 6SN7 above input triode where it's higher gm will provide lower drive resistance ?

Would you run it at <1mA or bypass the input tube with a resistor? Or go wild and parallell 3-4 input tubes

There seems to be a 22k resistor...

Would be recalculated if so

 

[chat72]

I've built this prephono, the details is excellent.
I've used 6n2pev and 6h8c.

However I have RFI , I can hear the radio clearly. How to get rid of it?
I use ground wire running from RCA to power supply. No hum only RFI. Can grid stopper kill this RFI?

Another problem is I use one tube for both upper and lower part of the circuit. Therefore when I lift the heater around 90v . For 6h8c tube, one side will see heater-carthode around +90v another side will see around 100v.
This will shorten the life of 6h8c right?

 

[stajo]

However I have RFI , I can hear the radio clearly.

Is there a grounded metal boxing sealing the circuit?

Are the cartridge wiring twisted?

Do you use MC stepup or high level PUP?

 

[chat72]

Is there a grounded metal boxing sealing the circuit?

Are the cartridge wiring twisted?

Do you use MC stepup or high level PUP?

Signal+supply ground is float, it's woodenbox.

I use mm cartridge and wiring is twisted.