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help! modifications on a vintage pre-amp Answered

I found a working pre-amp inside a turntable from the 60's. The turntable was scrapt, so I remove the pre-amp from inside.

Now I want to put it inside a vintage radio wooden box, the problem I got, 5 potentiometers on the pre-amp, but I need to modify this so it will only have 2, becuz the radio box has only 2. I will use an iPad with this pre-amp, so there really no need for extra audio adjustments like treble or bass...

So one for volume, the other for open and close.

How do I modify the circuit of this pre-amp so there will be no sound problem ?
Do I remplace the gradable resistors with a standard value resistor, if this is how to do it, what value should I use ?

I've done some tests, if I skip the potentiometer and I'm getting too much static.
I' would appreciate help on this!

thank everyone !


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user
iceng

Best Answer 4 years ago

ONE. Simply hack saw the 3 pot shafts you don't need they are soft brass
and you can still turn the stubs later on
( especially if you saw a slot for a screwdriver in the stub )

TWO.. Add a shaft extension using rubber hose  or plastic tube or shrink-tube a shaft segment
for the for the pots you need to stick out.

NEVER ... Try to relocate the actual pot !  Even if you are good at solder wiring....
Moving component pots out of the way will open the wiring to electrical hum and
other induced noises the builders carefully avoided through the design.process.

A

I cant tell from this point of view but some pots you can pull the shaft by removing the locking ring. Then if you need to adjust them later just reinsert the shaft.

Top marks Joe,

There are only a few people who know that factoid.

40 years playing with this stuff has its upside.

I would say guess what I got this week but you would never guess I got a submarine sonar and an astrograph.

Joe

Good for you, jobs like that are my idea of having good fun !
Maybe you can release test data,  so  that I  understand how sonar creates such
a graph...

A

The astrograph is a night navigation by the stars device from WWII R.C.A.F. a basic before GPS tool, not much use today but the sonar I plan to convert into a time domain reflectometer.

The old ones work like an oscilloscope with a built in signal generator making them ideal to convert into a reflectometer.

Personally i would keep the amp as is and modify the case. But if you can't stand to mess with the case then i would hope you wouldn't want to mess with the amp.

You have a real simple solution here. Disconnect the unwanted pots from teh case of the amp and move them out of the way. If wires are too short then splice in added wire length. But don't try to modify the amp to remove the other pots.

If you are dead set on removing the pots then find the ideal settings of the unwanted pots. Measure the resistance the pot is set at and replace the pot with the equivalent resistor.