Hi all, I know this is fairly simple one for the experts so hopefully someone would be willing to help me locate where to tap into for some pre-outs. I've had this 1991 Technics SA-GX303 since new and I for whatever reason, it just has a really great sound to it and would like to continue using it but need a sub feed.
Anyway, I have the service manual but I'm not educated enough to know where I should tap into for a pre-out to feed a sub. Any help would be greatly appreciated. Thanks!
SM is here:
Technics-SAGX-303-Service-Manual.pdf - Google Drive
Anyway, I have the service manual but I'm not educated enough to know where I should tap into for a pre-out to feed a sub. Any help would be greatly appreciated. Thanks!
SM is here:
Technics-SAGX-303-Service-Manual.pdf - Google Drive
Looks like just after coupling capacitors C519/C520, to have volume controlled signals.
You may want to use 10uF coupling capacitors from these points out.
You may want to use 10uF coupling capacitors from these points out.
Yep, looking for true pre-outs.
@Rayma - Cool thanks! So the coupling caps would be to block out any DC thump? Question...so the 10uF caps would be wired in series or parallel with the rca jack? I'm assuming the voltage requirement would be low. Still learning so many thanks!
@Rayma - Cool thanks! So the coupling caps would be to block out any DC thump? Question...so the 10uF caps would be wired in series or parallel with the rca jack? I'm assuming the voltage requirement would be low. Still learning so many thanks!
Series connection to RCA hot, use a 35V or 50V non-polar electrolytic.
Use insulating sleeve over the bare leads if they will be exposed.
If necessary, strip some insulation off a thin wire to get some.
UES1V100MEM Nichicon | Capacitors | DigiKey
Use insulating sleeve over the bare leads if they will be exposed.
If necessary, strip some insulation off a thin wire to get some.
UES1V100MEM Nichicon | Capacitors | DigiKey
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Ok guys, this has been very helpful. I tried using the headphone jack as my sub out and although it works, it appears the headphone jack output is quite a bit stronger then a true pre-out? Is that usually the case? I have another unit, a NAD, that does have true pre-out that I had been using since my Technics didn't have a pre or sub out. I had the gain on the sub at about the 1:00 o'clock setting. When I switched over to the Technics and headphone jack, I had to turn the sub gain way down to just above zero. I'm assuming this is because the headphone jack is expecting a much higher impedance? Do you think it's safe to run the sub with that much input gain?
Thanks again guys.
Thanks again guys.
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The headphone output can be attenuated.
Try something cheap and cheerful like this kenable 3.5mm Headphone Volume Control for Stereo 3.5mm: Amazon.co.uk: Electronics to see if it works.
Try something cheap and cheerful like this kenable 3.5mm Headphone Volume Control for Stereo 3.5mm: Amazon.co.uk: Electronics to see if it works.
Well after some more testing, i don't think the headphone jack is the best route. When turning up the volume the sub starts to show some superfluous cone movement. It's easy to see when i switch the sub input from the headphone jack over to my NAD with preouts.
I think I'll try tapping off C519/520 as suggested. There's an pair of "video" in/out jacks on the back I have never used so I'm thinking I'll just reroute those with a 10uF cap and see if that works better.
I think I'll try tapping off C519/520 as suggested. There's an pair of "video" in/out jacks on the back I have never used so I'm thinking I'll just reroute those with a 10uF cap and see if that works better.
@rayma - this got me thinking. I have an older Mitsubishi with pre-outs. I don't use it because it has a on/off thump out the pre-outs. Would adding a 10uF cap on those outputs remove that thump?
The headphone jack is driven by the power amplifier, so there is lots more gain than you need.
You could use a series 10k and a shunt 330R to get back down to a reasonable gain level.
You could use a series 10k and a shunt 330R to get back down to a reasonable gain level.
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Cool. Thanks again rayma. I think I'm gonna try your original suggestion for the pre-outs. And If I can get rid of that thump from the Mits, that'd be icing on the cake!
Gotcha. Will give that another go then as I'm obviously a novice.
So 33ohm resistor in series with the existing R619 (left) and R629 (rt) resistors correct?
Thanks!
So 33ohm resistor in series with the existing R619 (left) and R629 (rt) resistors correct?
Thanks!
OK cool. That helps. When you say "inside" the headphone plug are are you referring to the external plug? That would be an even better route as I could leave the actual internal HP jack stock and just have the reduction in gain when plugging in the sub.
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