Added Pre-Amp Out (NSFAP?)

Drakon

New Member
So I was able to pickup a Quadraphonic Technics SA-7300x, I was super excited to hook up some amps and start rocking out... But to my surprise no Pre-Amp out :(

So I busted out my multi-meter and went to town trying to find anything with line level audio I could use. I noticed a board on the top that appears to control the VU meters with another set of wires heading down into the depths below.

MwygxPm.jpg



Sure enough, after probing the lines they appear to be the Headphone connectors on the front.

So I thought I could use those lines for some RCA connections that I could then use as a Pre-Amp out. I found some high quaility made in USA female RCA jacks and this is what I came up with.

Warning, maybe Not Safe For Audiophiles or collectors but I hope you can forgive some modifications.

F0HIRPq.jpg


GMBFVB2.jpg


Tested each line and they all are working great!

Any suggestions? Could I have done it better? I know I could have lined them up better I just couldn't find my rulers and levels :(
 
Whats the beef? Seems like an improvement. Looks clean, too.

I don't think there is any beef but some people don't like you modifiying things for reasons of there own :p

And thank you, it took only a couple hours but I took my time on the soldering joints and tried to make sure all the cables lined up after they were ran since I didn't have 4 colors of wire to make it easy to trace.
 
Is there a sound/impedance difference between connecting from the on board headphone out as opposed to the headphone jack in the front? Thanks
 
Is there a sound/impedance difference between connecting from the on board headphone out as opposed to the headphone jack in the front? Thanks

No since I came in after the resistor on the board the impedance is near identical, I actually tested each RCA jack with my Sennheiser 650s and everything is the same.

Now with that, my Amp came yesterday and tested and the signal is crazy good... almost to good so I am thinking about adding some impedance to bring the audio down some to the Amp so I can get the VU's bumping on both units :D
 
No since I came in after the resistor on the board the impedance is near identical, I actually tested each RCA jack with my Sennheiser 650s and everything is the same.

Now with that, my Amp came yesterday and tested and the signal is crazy good... almost to good so I am thinking about adding some impedance to bring the audio down some to the Amp so I can get the VU's bumping on both units :D
That's cool,i've been searching for a definitive answer on this very same issue on "non-preout" stereo receivers. I appreciate you sharing on how to go about making it possible Thanks
 
I am not sure why I never thought of this before, but any integrated amp/receiver that has a headphone output could have preamp outputs added quite easily simply by tapping into the headphone jack leads.
 
I am not sure why I never thought of this before, but any integrated amp/receiver that has a headphone output could have preamp outputs added quite easily simply by tapping into the headphone jack leads.

Yeah, I got the idea from someone recommending to someone else on here to use Headphones to RCA leads. So I opened my unit up and started comparing voltage levels and eventually testing out an earbud I soldered some leads to to confirm I got audio out of those lines.

From there it was pretty stright forward :D
 
you're almost always OK to tap the headphone outputs, it's usually designed to supply a lower
voltage/power (example: 120R across the standard speaker outputs to lower voltage) then
your input to the power amp (or any other device) is higher impedance than the typical 8-32R
of headphones and won't load or change the headphone circuits.

I do this regularly with a portable CDP to supply music to test units and an inverse RIAA
to test phono sections.
 
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