greetings folks
I'm looking for input on how to design a mixer for 80 magnetic coil pickups.
I'm doing a project with a tonewheel generator from a hammond organ where I'd like to control the output from each tone wheel with a digital potentiometer.
I have a novice understanding of electrical signals, impedance etc so the first problem I'm trying to solve is how to sum multiple pickups without significant loss of signal.
My first observation was that I can connect a single pickup to a guitar amp and get a pretty good signal, then connecting a second pickup significantly drops the output of both pickups (due to the increased overall resistance as I understand it)
Can anyone advise on a passive or active mixer design for this use case (suitable for either a guitar amp or a mixer input)?
Thanks!
I'm looking for input on how to design a mixer for 80 magnetic coil pickups.
I'm doing a project with a tonewheel generator from a hammond organ where I'd like to control the output from each tone wheel with a digital potentiometer.
I have a novice understanding of electrical signals, impedance etc so the first problem I'm trying to solve is how to sum multiple pickups without significant loss of signal.
My first observation was that I can connect a single pickup to a guitar amp and get a pretty good signal, then connecting a second pickup significantly drops the output of both pickups (due to the increased overall resistance as I understand it)
Can anyone advise on a passive or active mixer design for this use case (suitable for either a guitar amp or a mixer input)?
Thanks!
What happens if You connect several pickups to several mixer's High-Z (Instrument) input channels ?
You could replicate 80 channels, but summed noise would also increase.
You could replicate 80 channels, but summed noise would also increase.
The level drops due to the _decreased_ overall resistance - each coil is a load for the other.
I think you need to buffer each signal and drive through resistors into a summing bus at virtual ground.
I think you need to buffer each signal and drive through resistors into a summing bus at virtual ground.
Low impedance pups can be connected series.
High impedance pups can be connected parallel.
Up around 80 a series-parallel array may be best.
Yes, the output of a single pup is reduced by all the others.
The only sane way to adjust levels individually is to to slide the coil closer/further from the string/wheel. At 80 pups, pot-per-pup is just insane loss for passive pickups. 80 preamps+pots is insane complication.
High impedance pups can be connected parallel.
Up around 80 a series-parallel array may be best.
Yes, the output of a single pup is reduced by all the others.
The only sane way to adjust levels individually is to to slide the coil closer/further from the string/wheel. At 80 pups, pot-per-pup is just insane loss for passive pickups. 80 preamps+pots is insane complication.
Why is the original method of mechanical adjustment not good for you? You can find the schematics of B3 online, that you could get inspiration from.
The goal I'm aiming at is creating a digital mixer to control each pickup of the TWG with a microcontroller like an arduino or bela board. It might not be exactly 80, but it's around there.
I want to be able to play the thing with MIDI or control voltage or whatever, so the idea is to do so with digital potentiometers (since all pickups are constantly sounding at the same time)
yeah I could use digital relays to mechanically make contacts but then I would not have individual volume control of each signal (plus relays make a loud click)
cheaper than digital pots to use LDR coupler which do not make a loud click. Those need one digital output to turn on, natural for a controller. Advanced Photonics NSL32-SR2
The original hammond transformer did a nice job of mixing while making a relatively contant volume, 1 note or 20. Something to do with the saturation of the core. Resistor adder mixer, your volume grows to 20 notes, instead of saturating it clips, which sounds awful.
The original hammond transformer did a nice job of mixing while making a relatively contant volume, 1 note or 20. Something to do with the saturation of the core. Resistor adder mixer, your volume grows to 20 notes, instead of saturating it clips, which sounds awful.
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thanks indianajo, I was also considering using LDR couplers but was kinda hoping for amplitude control. I think you're right though that a simpler digital on/off is more sensible.
could I simply repurpose the matching transformer from the hammond for my circuit?
could I simply repurpose the matching transformer from the hammond for my circuit?
The original Hammond design IS a resistive adder. The wiring harness from the interface where the signal leads from each TWG pickup coil enter the manuals to the key contacts consists of resistive enamelled wire, and the matching transformers are of low input impedance. I don't think that their cores saturate, as this would be sounding awfully. Instead I assume it's just the right value of all those wire resistors that gives a balanced sound.
Years ago I've found somewhere in the WWW a report of someone who had replaced all those resisitive wires in a C-2 that had gone rotten by foam goof by 122 x 9 = 1098 individual resistors (he gave a full chart of the values) and reconstructed the harness using solderable enamelled magnet wire. What a mess 😱!
Best regards!
Years ago I've found somewhere in the WWW a report of someone who had replaced all those resisitive wires in a C-2 that had gone rotten by foam goof by 122 x 9 = 1098 individual resistors (he gave a full chart of the values) and reconstructed the harness using solderable enamelled magnet wire. What a mess 😱!
Best regards!
I think the hammond mixing transformers are part of the sound. I don't think them being after LDRs instead of key contacts should hurt anything. But don't cut off the TG to key chassis wires, per KayP's point.
If the wires are gone the resistor chart can be accessed on organforum.com
If the wires are gone the resistor chart can be accessed on organforum.com