Add pre-out on Sony stereo receiver

[Gobulebarbu]

Hi! I just bought a power amp for my sound system and I would like to add a preamp out to my stereo amplifier (Sony str-vx450). I have the schematics and I believe I know where to add my RCA connectors. However I'm not that knowledgeable in electronics and I don't want to mess things up...

There is a left and right tone amp out going to the power amp, that's where I believe I should intercept the signal - just before driver impedance det IC701

There are two jumpers in that region on which the voltage modulates with the volume rheostat from 0.006v to 1.5v is that the best place to solder my wires? Would it be cleaner to simply connect to an existing connector? In that case I can't see which one...

Also, where should I take the ground for my output? Directly on the chassis?


Thanks for helping! It is greatly appreciated!

 

[Gobulebarbu]

Better schematics pictures here:
http://cl.ly/image/1I3r3T2H3O31
http://cl.ly/image/3Y0L2p17191z

 

[KrisBlueNZ]

Hi there and welcome to Electronics Point

Personally I would take the signal at the top of the volume control. The amplifier you're feeding it into will have its own volume and tone controls, and if you provide a flat signal at maximum amplitude, you can use the two sets of controls independently. Also forcing volume control to be done at the second amplifier maximises immunity to interference, since the signal being passed between the units is always at a high amplitude.

I would connect directly to the terminals of the volume control. Be aware that connecting two independent units like this could cause an earth loop (see https://en.wikipedia.org/wiki/Ground_loop_(electricity)).

 

[Gobulebarbu]

Hi! Thanks for the answer! I plan on using he amplifier as a pre-amp for my power amp therefore I would need the volume knob!

My poweramp is a bryston 3bst (http://bryston.com/PDF/Manuals/3B-8BST_MANUAL.pdf)
It has a ground signal lift switch... Is it there to prevent the ground loop hum?

 

[KrisBlueNZ]

Yes, that's what the ground lift switch is for.

You should have the new power amp physically close to the signal source to minimise the length of the signal leads. Use screened cables, of course.