[runswithaliens]

I can't seem to find just the right amp/pre-amp I need but the TU882 is very close from what I can tell, so I am hoping somebody with DIY experience might be able to tell me if the following is advisable:
 
I would like to get the TU882 kit and then convert the pass-through RCA outs on the back to be full pre-amp outs so that the sound is receiving the benefit of the tubes and effected by the volume control. Also to then add a switch to be able to turn the pre-amp outs on or off independent of the headphone outs (or switch between headphones and pre-amp). This would be to drive my powered JBL monitors.
 
I wonder if it would it be as easy as just changing the location from which the RCA out wires are attached and adding in a switch or is it a semi-major project that would require adding other various electronic parts?
 
I am a rank beginner but have purchased a soldering station and practice kit so far and wouldn't tackle the TU882 until I feel confident.
 
Thanks for any advice in this matter.

 

[xxbaker]

Should be pretty easy.  Just take what's supposed to be connected to the headphone jack and connect it to a DPDT switch, then have one side of the switch go to the headphone jack and another go to the preamp out.  This way you can toggle between them.  To get it so that both can be on at the same time you split the signal that would normally go to the headphone jack and send it to two DPST switches; one connects to preamp out, one connects to headphone jack.  Then one switch controls whether the headphone jack is on or off and the other controls whether the preamp is on or off.  I wouldn't do it this way due to paralleling of the outputs, redundant seeming switches, etc.  The first way makes sense to me though.

 

[runswithaliens]

So then the level of headphone out is the same or nearly the same as pre-amp outs in general and so no attenuation of the signal is necessary for the pre-amp? I guess that was my main concern. It occurs to me though with this amp having the variable impedance settings that  would help getting the correct level?
 
The studio monitors have their own volume controls to help matching up with pre-amps as well now that I think about it. Here is what the JBL manual says about the inputs: "Connect Professional +4dBu and -10 dBV signal sources to either the XLR or ¼" input connectors. Connect consumer -10dBV level equipment to the RCA input connectors."
 
Here is what the amp lists as its output: "[size=x-small]Rated output / 200mW(RL＝6Ω or 32Ω or 600Ω)
Output impedance / LOW 4～20Ω、MID 20～100Ω、HIGH 100～1kΩ"[/size]
 
Are those matching up in any friendly way, electronically speaking?

 

[Mr.Unknown]

Do people have schematic of thisheadamp.

 

[xxbaker]

No attenuation should be necessary.  I run HD650s out of my bijou which also has preamp outs through a DPDT switch.  I had to lower the gain on my poweramp a bit to get matching levels, but HD650 are one of the less efficient headphones I believe and it works quite well now.
 
You'll be using the RCA inputs on the speakers.  For output impedance any of those should work fine.  You want the input impedance of your poweramp(speakers) to be at least 10x the output impedance of your preamp.  This gives you a "bridging impedance" which is ideal for audio connections.  You can probably just leave it on whatever setting you have it set for your headphones as Poweramps usually have much higher input impedances than headphones (thousands of ohms).  So to answer your question directly, yes they'll match up well electronically.