Adding pre-outs to Luxman L-85V?

[drabina]

Does anybody have any information on how to add pre-outs to Luxman L-85V? I think long time ago I came across a post or info on the internet where somebody added RCA outs in the back but I can't find it now. Would like to add pre-outs to my Luxman to try it with the Onkyo Integra amp I have.

 

[cademan]

Usually you can tap into the center lugs of the volume control but you should have some electronics experience to know where to tap into the preamp section right before the main power amp section.

A schematic would also be helpful in determining where you could tap in to do this but I am sorry as I don't have the schematic for this particular unit. Have you tried the hi-fi engine website for a schematic?

 

[Blue Shadow]

drabina shared his schematic with the HiFiEngine. Shouldn't be too hard to find the wiring taking the signal to the power amp section.

One issue, not necessarily with this unit, but the L-580 and other in that series have the signal processor after the volume and before the tone controls/power amps and that signal if very low, 200mV, not enough to drive most amps to full output. Probably different in the L-85 but worth a check before doing all the work. At full volume you would like to see a couple volts, I'd guess.

 

[Blue Shadow]

No response and posts on other sites. Since I haven't done it, have you seen EWs install on a Kenwood KA amp? It is here on ak and it shows what he did. With the schematic you have posted I would take some measurements and see if you have the drive and if so, think about how to interrupt that signal and go to the back panel to a set of RCA jacks for preamp output and then how to get back to where you cut the signal from power amp input jacks. Then use a jumper to connect the pre to power when you want to use the unit as an integrated amp.

 

[JURB]

If you get it from the volume on that, it looks like you lose some of the preamp functions. Much better to pick it off at R501 and R601. If you want a loop, like a main in as well that is where to break the circuit. Then you'll need the customary resistor to ground to keep the input coupling caps properly charged, like one megs or whatever.

You might want to consider a switch because if the next amp needs more signal you could be clipping the hell out of the Luxman amp and not know it. Normally clipping SHOULD NOT hurt a solid state amp that has no transformers, but should is the operative word here. You could have a silky smooth set of outputs in there that just happen to be on the edge in voltage. Now you are not loading the power supply if the speakers are off. Also, it was built in 1975 so it was not made for our hot 125 nominal AC now. Too much voltage - poof.

All considered I think it well worth a toggle switch and a couple of resistors. You can use 100K, 75K, it is really super non-critical, just keep it over 50K at least.

 

[drabina]

Thank you all for replying. I will have to dig into the schematic to see if I can even pull that off. My electronics knowledge is very basic. I have to admit, that I am having second thoughts since the Luxman is in very nice condition and fully rebuilt. Not sure if I want to drill holes (even in the back) for new RCA outputs and a switch.

 

[JURB]

I would not drill holes in the back. Drill in the bottom. In fact the simplest way is to drill one hole in the bottom big enough for four shielded cables and get a set of RCA extenders. The female ends go to the main in and the males go to the pre out for good reason of course. Then you need a pair of gender changers, like Lesbian plugs - female to female to connect a regular set of cables to go out to the amp.

Then, when not in use you just plug them together and maybe use a wire tie so they don't get tangled up.

If you drill a really neat hole in the bottom, if you ever have to undo the modification it is just a matter of taking it out and reconnecting it inside as per original. One hole in the bottom is not likely to be noticed at all, though if you ever sell it for vintage audiophile prices you should disclose that the hole is not stock.(maybe even offer to leave the modification in)

At least that's the way I would do it. All the stuff should be available at the usual places, probably Parts Express for this stuff. A pair of RCA extensions, male to female and then a pair of female to female barrel connectors. (like you would use to connect two pairs of RCA cables with)