TECHNICS ST GT650 TUNER Mod

[RCruz]

Yes, that should do the trick (at least I can't think of any reason why it wouldn't). Maybe it is a good idea to disconnect the electrolytic capacitor at the base of Q701 (C707?) to make the relay switch faster and reduce contact wear. You won't need a diode for clamping the voltage at switch-off, as this is already taken care of by the zener (in forward conduction mode) and Q701.

Thank you again Marcel

I will post here my results

 

[RCruz]

Lifting Q701 emitter and feeding there the shunt output was a disaster... Loads of distortion and the tuner started to pick up sveveral stations at the same time (superimposed).

After looking carefully to the schematic I see the TX (10Vac) is connected to C705 C706 as to form a voltage doubler... Maybe lifting Q701 emitter causes some instability.

So I powered the AN6554 output quad opamp directly from the shunt and got a nice improvement in spatiality and detail presentation.... pics will be here soon

 

[RCruz]

Pics

Next I will verify if the onboard +14v is enough to power a relay to switch the external psu on/off.

I also replaced the output caps (3.3u 50v by 47u cerafines) and the onboard psu caps to 2200u Pana FC.

After some hours burning in I am pleased with the result... wider sounstage, better detail, "bigger" presentation.

This is all just for fun because this player is very limited.... it can not be compared with a high end machine off course.

Maybe I will replace the output quad opamp by a LME49740.... That might be a good improvement.

 

[RCruz]

As time goes by, sound gets better and better.... after all it was worth the try.

 

[rrrremus]

I own a GT550 ( GT650 but without LW ) and i am having reception issues. I saw a few months ago a thread on another site ( that got removed in the mean time ) of a front end upgrade on such a unit. Does anyone here have enough FM tuner experience to recommend an easy replaceable frontend for this tuner ?
Another problem i am having is with L301 adjustable filter that needs readjustment about every 6 months.

 

[RCruz]

Some more pics of the tuner.

I used the inboard 14v psu line to power a relay that switches the BiB PSU using the tuner´s standby button.

Works perfectly.

Powering the output quad opamp with a dedicated shunt psu proved worthwhile.

 

[RCruz]

PS:

How can I post bigger and more detailed pictures... what format should I use ?