Expresso- Expression Multiplexer: General Questions Thread

[Bricksnbeatles]

Just ordered an Expresso pcb, and since I had some questions about it, I thought it might be a good idea to have a general questions thread for it, especially since its a PPCB original, so there isn't the trove of info out there that there is for, say, a tubescreamer circuit.

I'll start with these questions for @Robert ...

First, as far as the Digi-pots go, am I correct in assuming that the MCP41010 can be subbed out for a MCP41050 or MCP41100 if a 50k or 100k expression output is needed? and that not all three digi-pots necessarily need to be the same value— say, 10k for A and B, and 100k for C?

Secondly, is there a specific expression input value-range that it's designed to work with?

Lastly, am i correct in my understanding of the MCP41010 datasheet that the maximum rating of the voltage divider is equivalent to the 5v supply voltage of the chip? So otherwise, the expresso should only be used with pedals that stick to the 0-5v CV standard, and not anything that uses a 0-9v CV? This should be as simple as connecting a multimeter to the ring and sleeve connections of a pedal's expression jack to see that the reference voltage is sub-5v, right?

 

[Feral Feline]

In case you haven't already done so, here's a link to the USER PDF for Mission Engineering's Expressionator:

https://missionengineering.com/wp-content/uploads/2022/07/Mission-Expressionator-User-Guide_2up.pdf

 

[Robert]

I was planning to start a thread like this so I'm glad you did.

You should be able to substitute any value from the MCP41xxx series, the values can be different for each channel.

Due to the nature of the digital pot ICs the Expresso will work better with some circuits than others so it might be helpful to keep a list of what works best. These are the same digital pot ICs used in the OBNE Expression Ramper so compatibility with pedals should be similar.

 

[mckillacuddy]

I’m curious whether we can get it to play nice with the stonedeaf tone circuit

 

[Bricksnbeatles]

I’m curious whether we can get it to play nice with the stonedeaf tone circuit

Don’t think so. That one needed a special dual gang expression pedal setup

 

[Robert]

I’m curious whether we can get it to play nice with the stonedeaf tone circuit

Not by itself because of the dual-gang pot @Bricksnbeatles mentioned, but I have an adapter circuit that in theory should make it possible.

 

[Bricksnbeatles]

Not by itself because of the dual-gang pot @Bricksnbeatles mentioned, but I have an adapter circuit that in theory should make it possible.

Would that adapter circuit happen to involve a MCP42010 retrofit daughterboard?

 

[alfasprinter]

I just built the pedal tonight. I’ve got it running but I’m finding the sweep on my JHS Emporer and Unicorn is limited. It only gets them to half speed. I’m using an M Audio expression pedal and when I plug that in directly to the JHS pedals it’s operating normally. Any idea what I could change to get it working correctly?

 

[Robert]

What is the resistance of the expression pedal? Does it match the digital potentiometer IC?

Plug a TRS cable into one of the Expresso outputs and measure the resistance between the Tip and Ring with the expression pedal at minimum and again at maximum.

 

[alfasprinter]

If I just measure directly on the m-audio expression pedal it’s:
Tip to ring - 11.48 ohm Min and Max
Tip to sleeve - 0.99 ohm Min and 12.46 Max

The output resistance via the expresso when the connected m-audio expression pedal is connected is:
Tip to ring - 9.30 ohm Min and 2.62 Max
Tip to sleeve - 0.81 ohm Min and 7.57 Max

I don’t know if the sleeve info is helpful. My 3x JHS pedals that have an expression option all work normally with the m-audio pedal plugged in directly.