[Ericus Rex]

Hi folks!

I'm building a hard-wired Jonokuchi integrated amp (http://www.pmillett.com/jonokuchi.htm) and would like to add a sub out to the circuit. I want a full-range, summed L+R, variable (effected by volume control), pre-out (not amplified).  Is this as simple as tapping off the volume pot outs and splicing L&R at the RCA jack?  Or would I run into feedback or L/R bleed-through issues?  How do I add this?

Thanks!

[poseidonsvoice]

As you suspect. It isn’t straightforward.

See here:

https://www.rane.com/note109.html

And here:

https://www.diyaudio.com/forums/analog-line-level/281509-passive-summing-subwoofer-signal-using-resistors.html

In your particular case, you most definitely have to make sure that the input impedance of your subwoofer plate amp is nice and high since you now have introduced a variable output impedance by insisting on using your volume control. This is a low current, low level signal. So you will probably  have impedance issues particularly at longer interconnect lengths.

An opamp would be a more elegant application here, particularly an instrument amplifier design like the AMB alpha 24.

I’ll be curious to know how you solve your conundrum with a passive analog discrete solution. Even using a transformer would be a challenge. I personally vote for an active circuit! 

Best,
Anand.

[Ericus Rex]

Excellent!  Thank you for the links and info, Anand!  I can handle three resistors so I'll try that route first.

Many thanks again.