Nakamichi sr-4a pre-outs. Is it possible to add pre-outs

[Richard_James]

So Nakamichi Sr-4a has signal processing jumpers to power amp. Those jumpers are for adding an equilizer or some signal processing unit.
Those pre-out jumpers don't modulate volume. The "pre jumpers" send full volume voltage to power amplifier part of this receiver.

I often need pre-outs whose voltage output can be modulated with volume knob. To run a sub woofer or send pre-amp signal to a power amp.

The manual is around 28mb in size so I could not attach it. It's available on hifiengine but it's an extra hustle to make an account there


Nakamichi SR-4 - Manual - Remote Control Stasis Receiver - HiFi Engine

I am fairly capable. Basically I would like some help finding the spot where pre amp signal is sent to power amp.

Thank you

 

[PRR]

Sequence is selector, tape switch, jumpers, Volume controls, line-amp, tone-amp, power amp.

You probably want to tap the power amp feed.

Tone Control PCB, connector CN-44, pins 2 and 5 signal, other pins ground.

Depending how it's built, it may be easier to find these points on the Tone Switch.

Gain of power amp is 23, so about 1V max signal here.

 

[Richard_James]

Thanks for this reply. I will try to locate those connectors inside the amp tomorrow. And to confirm my findings could I connect headphones to those connectors . 1v should be enough to power ear phones right

 

[Richard_James]

So connector 2 and 5 is either left or right channel
And all others (1,3,4,6) are ground?
So when I plug in ear phones 2 and 5 will be either left or right . And i could connect ground of headphones to any of 1,3,4 or 6 connectors?

 

[Richard_James]

So found cn44 on the board. 1,3,4,6 look like grounds. All connected together. Will test later today

 

[PRR]

..could I connect headphones to those connectors . ...

You originally asked "To run a sub woofer or send pre-amp signal to a power amp." Not direct to headphones.

You "can". It won't be very loud. There's 1k of resistance in series. While 300 Ohm phones may do OK, 32 Ohm phones will be quite quiet.

Run this to a "headphone" amp and then to headphones.

 

[Richard_James]

Yes exactly. I need pre amplifier outputs
Headphones ideas was just a way to monitor if those jumpers are the correct jumpers. Don't want to send full 1v into. A power amp.
Is there another good way to monitor line level output? Oscilloscope? Or maybe something cheaper

 

[Richard_James]

So I tapped in connector 44. Used headphones to confirm volume and tone controls work.

One quick question.
Do grounds of rca jacks connect to chasis eventually?(in general and in this receiver in particular)

I would like to only run signal wires from pin 2 and 5 to the rear pannel. Tight space and I don't want to clutter it with many extra soldered wires



I have 2 types of rca jacks. Please See images to visualize

 

[Richard_James]

Found replyi in this thread


grounding RCA inputs