Attenuator for Direct out Mod

[RSRecords]

Adding direct outs to an Electrodyne e802 mixer. Mic pre (M100a) output is 50 ohms and the line driver (LA1800) is 15k input. The line driver has a gain of 20dB min. so I'd like to pad the output of the mic pre by 10 to 15 dB and insert possibly fader before the line driver. The mic pres will also fee the LCR buses of the mixer via 10k resistors and a 10k potentiometer.
Questions:

1. what impedances relevant for the calculation of the attenuator. L pad or T?
2. Possible to use the 10k pot that feeds the bus switches for the direct out level too.
   
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Edit: mic pre is capable of +18db Max into 600ohm load.

 

[ruffrecords]

It's unbalanced so an L pad will be fine. A 22K series resistor and a 5K1 to ground will get you about 14dB attenuation with minimal extra load on the mic pre and a source impedance comfortably below the line driver's 15K input impedance.

Cheers

Ian

 

[RSRecords]

Thanks Ian. So the line driver's input impedance is the determining factor here?

Taking it from the 10k pot out should work eh?

 

[ruffrecords]

Thanks Ian. So the line driver's input impedance is the determining factor here?

That and not loading the driving source too much.

Taking it from the 10k pot out should work eh?

It will alter the law of the 10K pot a little but there are already a pair of 10Ks hanging off it when in the centre position so an extra 22K should not make much difference. Option B using a separate pot pre the 10K pot would also work and not affect the law of the 10K pot. Just depends on the drive capability of the mic pre output which I guess is unknown.

Cheers

Ian

 

[RSRecords]

So adding a line input to this little side car. Hoping to work with the single +24v rail. Here's what I have so far. "XTO1" feeds a relay that swaps the mixer input and direct output from either line input to mic input.
This is essentially straight off the jensen data sheet. Not sure where to connect transformer case though.