MIDIfied Tube Screamer

[m0xpd]

My Tube Screamer clone is now accepting MIDI Control Change Messages to set the Drive, Tone and Level parameters.

Read about it here: http://m0xpd.blogspot.co.uk/2013/01/midified-tube-screamer.html, where I share the PIC interrupt service routine that I wrote to parse the MIDI stream.

[gritz]

Thanks for sharing - am just beginning to nosey round all the posts relating to your project (but I have to go to the bank in a mo...)

How are you finding the digital pots - any zipper noise?

-jonathan-

[m0xpd]

Hi Jonathan

I haven't noticed a great issue with Zipper noise in particular or with "click and pop" more generally. However...

0) the "brute force" solution I first tried with the 4066 analog switch to set the drive did pop ...
    (as described here http://m0xpd.blogspot.co.uk/2012/12/tube-screamer-goes-digital.html)
1) there was some quiet but audible "zip" when the overall pedal gain was close to its maximum gain configurations when I was using the "Increment/Decrement" pots (such as AD5220) - this isn't there with the MCP4131s or the AD5242 I use now.
2) in my experience, one of the greatest hazards for generating switching spuriae over digital pots is the presence of dc. In the Tube Screamer, the dc is well handled (not least because of the care taken in biasing the FETs used for bypass switching)

HOWEVER...

3) To be honest, I've not done a lot of exhaustive testing! I've played through it several times at "domestic" levels and didn't hear anything that sounded like a show-stopper. But this hasn't been the closing stages of product development - just fun and games!

m0xpd

[gritz]

Thanks for that - I'm weighing up the possibilities of integrating digi pots into some of my (very) analogue stuff for MIDIfication purposes, so your blog is going to be very useful. Agreed about the pitfall of DC across any pot that's getting waggled in realtime too.

More googling and datsheets to wade through!

jonathan