17th October 2016

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**1****Passive Sum two signals - Resistor Value Help**

Hello folks,

I am putting together a pedal board for my two acoustic guitars which each have a pair of pickups in them.

Basically I want to sum each pair to mono and have been doing some reading on the values keeping in mind impedances of the chain.

The two signals to sum would be coming from two separate preamp/EQs with output impedances of 1Kohm and 100 ohms respectively.

After summing they would be going into a Hall of Fame Reverb which has an input impedance of 1 meg Ohm, if bypassed I guess the summing network would "see" the DI box placed after the Reverb which also has input impedance of 1Mohm.

Going by the 10:1 rule that would dictate that I need 10Kohm resistors to sum the two channels prior to the TC Reverb pedal given that one of the EQs has an output impedance of 1K.

I understand that 10Kohm resistors would give a 10Kinput impedance at the summing network and roughly a 6db drop in signal.

Is 10K the best value to use or is there a gremlin in these details that I am missing?

Perhaps it would be best to sum after the reverb given that the reverb pedal has a lower output impedance (100 ohms) and accepts a stereo signal. Bypassed of course though I would be in the same scenario.

Any help or advice greatly appreciated!!

Many thanks in advance.

I am putting together a pedal board for my two acoustic guitars which each have a pair of pickups in them.

Basically I want to sum each pair to mono and have been doing some reading on the values keeping in mind impedances of the chain.

The two signals to sum would be coming from two separate preamp/EQs with output impedances of 1Kohm and 100 ohms respectively.

After summing they would be going into a Hall of Fame Reverb which has an input impedance of 1 meg Ohm, if bypassed I guess the summing network would "see" the DI box placed after the Reverb which also has input impedance of 1Mohm.

Going by the 10:1 rule that would dictate that I need 10Kohm resistors to sum the two channels prior to the TC Reverb pedal given that one of the EQs has an output impedance of 1K.

I understand that 10Kohm resistors would give a 10Kinput impedance at the summing network and roughly a 6db drop in signal.

Is 10K the best value to use or is there a gremlin in these details that I am missing?

Perhaps it would be best to sum after the reverb given that the reverb pedal has a lower output impedance (100 ohms) and accepts a stereo signal. Bypassed of course though I would be in the same scenario.

Any help or advice greatly appreciated!!

Many thanks in advance.