Sansamp TRI A.C. guts pic and question

[MetalGuy]

The more I look at this picture the more these things look to me like regular pots. Shouldn't there be encoders or something instead? If these are regular pots how does the uC read and store the values for the three presets and stuff? Maybe the "digital" guys could help?

[tommy.genes]

IIRC, Tech21 doesn't use rotaray encoders. They use analog pots, put a fixed voltage across them and feed that into an A/D converter to get a digital readout of their value. I actually think rotory encoders would be better and here's why.

I have a PSA-1 and have had the following problem. When any one of the pots (and there are eight of them on a PSA-1) is in a position significantly different from the value stored in memory, if vibrations from the speaker cabinet cause one of them to move ever so slightly, the uP reads this as a change and jumps to the "new" value, which can cause your tone to go to crap mid-song. If the pots were rotary encoders, the vibration-induced movement would only result in small changes to the tone.

Even aside from the mid-song "what the $&@#?" moments, I just think the thing would be much more intuitive if turning the knob clockwise, for example, would increment the parameter from the stored value rather than possibly dropping way down and having to be brought back to the original value before increasing beyond that.

-- T. G. --

[MetalGuy]

What you described really sucks but I'm wondering how an already stored preset/patch can change values if Edit /or whatever/ function is not active? It shouldn't be independent of any vibrations.

If the pots were rotary encoders, the vibration-induced movement would only result in small changes to the tone.

I think it  depends on the type of the digital pot used - if you have a 256 position digital pot and a 16 or 24 position rotary encoder it should increment value in several steps at a time otherwise you'll need to turn the encoder 16/11 times until you reach the max pot value.

[12afael]

I wonder how they implement the digital pots.
the potted part is a little small for the complete audio part and pots .

[Peter Snowberg]

They should be using detented pots. 

Notice that its a PIC microcontroller running the show in there. 

[MetalGuy]

Who knows what's on the other side this PCB. Analog's AD5263 is 4 pots in a TSSOP24 package for example - it's smaller than a dime.

http://www.analog.com/en/prod/0%2C2877%2CAD5263%2C00.html

[tommy.genes]

What you described really sucks but I'm wondering how an already stored preset/patch can change values if Edit /or whatever/ function is not active? It shouldn't be independent of any vibrations.

I should point out that my PSA is over ten years old at this point, so they may well have corrected my problem, especially with the recent release of the PSA-1.1. Also, there is a mode where you can "turn off" the front panel knobs, but I didn't want to use that since I still wanted volume control. The PSA-1.1 has a separate master volume - maybe it is not be affected by the lock out.

I've moved back to an integrated amp (Eden WT-800) for playing out because it's much easier to use, but I've kept the PSA-1 around for recording and occasional guitar dabbling.

-- T. G. --