Adding pre-out to Xindak V30 KT88 amp

[chillysalsa]

I am hoping to add a pre out to this amp, but I can't find a schematic. From what I've read and see inside, it's basically running what looks like one side of a 12AX7, feeding into an 6SN7 as either a driver or phase inverter for a pair of push pull KT88s.

What is normally the best place I could connect the pre out jack, just after the 12AX7?

 

[chrisng]

Don't know is the best place or not, put a voltage divider at output transformer secondary can provide a line level output.

 

[chillysalsa]

But what resistor values to use to make sure the output impedance is pretty low and doesn't change with different connections on it? Or should it have a buffer?

 

[rayma]

Do you want a constant output level, or a level that is adjusted by the volume control?
What will you use the preamp out jacks for? Tubes work at higher impedance levels,
so a buffer is likely to be needed.

 

[chrisng]

what resistor values to use to make sure the output impedance is pretty low and doesn't change with different connections on it?

This idea is came from a speaker level to line level converter.
Put a 10kΩ in series and 1kΩ across the line level output will provide about 10:1 voltage attenuation (-20dB).

 

[artosalo]

Or use 100 ohms/10 ohms resistors to get even lower output impedance.