Adding a pre out to Technics Amp

[AlleyneH]

Good Day
Could anyone assist me with adding a pre out to a Technics SU-VX500 Intergrated Amplifier, I have attached the schematics for this amp. I cant find any info on the Amplifier chip so have no clue which pins are the inputs.


Any help would be most appreciated

 

[jvhb]

Hi, where are the schematics?..

 

[Jakobsson]

R401,R402 maybe

 

[AlleyneH]

Sorry I thoought I had uploaded them, 2nd atempt

 

[AlleyneH]

R401,R402 maybe

Hi Jakobsson
Do you not mean Q401 and Q402?

 

[Ketje]

You can take the signal from here.Earlyer and it's in the middle of the tone-control, later within the final amp feedback loop, both no good.
Inconvineance, the pre-out follows the tone and balance nobs and the volume doesn't go all the way to zero.
A pre-out before the tone/volume needs an extra buffer stage.Input from the top of the first (yes there are two mechanicaly connected) volume potmeter.
Mona

 

[AlleyneH]

Thanks Ketje for your prompt reply, Am I Correct in understanding I would need to insert the 4K7 resistors and if so would 1/4watt surfice? Secondly and I know not my original question but could I break the signal path at this point if I say wanted to have a pre out and main in, Thinking it would make connecting my Digital sound processor less complicated.

 

[Ketje]

Thanks Ketje for your prompt reply, Am I Correct in understanding I would need to insert the 4K7 resistors and if so would 1/4watt surfice?

Those resistors only frevent exesive load (or short) on the signal path, the smallest you can find are big enough.

Secondly and I know not my original question but could I break the signal path at this point if I say wanted to have a pre out and main in, Thinking it would make connecting my Digital sound processor less complicated.

Yes with a source at ground level.But the volume control will stil function on the output section by a somewhat odd manner.More like a linear potmeter.
Mona

 

[AlleyneH]

Thanks for your assistance, I'll give it a try.

 

[amptech]

One way of adding a pre-amplifier line out is straight forwards..

Using two 1k resistors and place each one on the volume pot middle pins followed by adding a fresh screened cable to a choice of sockets at the other end will give you lineout feed.

So you have use of the tone stack plus balance if you wish...

 

[Max Headroom]

....Thinking it would make connecting my Digital sound processor less complicated.

Outboard processor typically should run at standard line levels, and not variable level pre-out.
Use a tape loop.

Dan.

 

[AlleyneH]

One way of adding a pre-amplifier line out is straight forwards..

Using two 1k resistors and place each one on the volume pot middle pins followed by adding a fresh screened cable to a choice of sockets at the other end will give you lineout feed.

So you have use of the tone stack plus balance if you wish...

Thanks Amptech


This worked exactly as I had hoped for