Looking for a 1Meg Digital pot

[msi]

I am building a Midibox to control a guitar effect.  The effect requires a 1 Meg pot, but I can't find any SPI compatible pots that would work.  All I have found thus far have been 10k, 50k, or 100k.  I already have the effect built and just need to get the midibox portion working.  

William

[Captain_Hastings]

Yo man! We're probably doing the same thing...  :D

I've been looking for those as well and 10k, 50k and 100k are the only ones i could get hold of... (analog devices & microchip). Another one that's not available is 1K (not in PDIP anyway) but i hope i'm able to build one by linking the 2 tapers of a 10k together and make the total pot value 1k in software (same for 150K, 20K, 22K, 25K)

But it would be difficult to make a 1Meg by linking 10x 100K together...  :-/

Haven't found another solution either...

[Guest Benni]

You're not alone.  ;D

First - sorry for my bad english.

The problem of the 1M log. digital Pot is, if you divide the 1M in 127 steps, is the smallest resistor is only 70Ohm.

My idea was, to put a 10k and a 100k digital pot in serie, and a 100k, two 200k and a 402k resistor switched by bilateral switches (4066) behind. The 4066 could be controlled by a "dout" and combined with the two dig. Pots.

Something like this: http://www.dasgrundprinzip.de/temp/1mdigpot.pdf

[Duggle]

Have you looked at modifying the target circuit (effect) to function with a different resistance? This is almost always possible.

Also, from experience much care has to be taken to avoid noise coupling from the digital to analog parts of the circuit especially if there is signal gain involved.

This is more of a problem when the digipot is being continuously updated than if the setting is only changed with each "patch".

cheers