MUFF WIGGLER Forum Index
 FAQ & Terms of UseFAQ & Terms Of Use   Wiggler RadioMW Radio   Muff Wiggler TwitterTwitter   Support the site @ PatreonPatreon 
 SearchSearch   RegisterSign up   Log inLog in 
WIGGLING 'LITE' IN GUEST MODE

Passive Panning Pot Problem
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Passive Panning Pot Problem
ac
Hi everyone!

I'm DIYing a little mixer, and I ran into a problem that I haven't come across before. I wonder I could ask for some help?

It's a very simple panning mixer where each input passes through a pot to set its overall level, and then another pot is used to passively pan the channel to the left or right. All of the panned signals are mixed together with resistors and sent off to two op-amps. Here's a schematic of one input stage:



The circuit works perfectly on a case that has a MakeNoise power board, and also in a separate Monorocket case with a larger power supply, but I tried my mixer in my Doepfer Mini Case and I noticed something odd.

With the MakeNoise and Monorocket power, the apparent level as I rotate through the panning pot feels like this graph:



But in the Doepfer case it spikes back up just before the end:



What am I doing wrong? Any ideas? And again the only difference is the case that it's plugged in to. I know that I shouldn't expect the *best* results by panning passively through a pot like this, but I don't know why it behaves differently between my cases.

I'd appreciate any advice I can get! Thanks!
Andy
guest
what do L and R go to? just mono jacks?

are you sure its the case (you should be able to use the module with no case since it requires no power)? usually the sort of behaviour you describe is due to a bad spot at the end of the pot where the wiper comes off the track.
JohnLRice
Was the signal source always the same in each instance and always in the same case as the mixer?

Also measure the power supply rails in each case to see if they are all reasonably and similarly symmetrical.
ac
guest wrote:
what do L and R go to? just mono jacks?


Hey thanks for the reply.

Actually only the mixing and panning are passive, those L and R get bussed together with the other inputs and then make their way to an op amp like so:



So it is powered, just not the mixing and panning portion.
ac
JohnLRice wrote:
Was the signal source always the same in each instance and always in the same case as the mixer?

Also measure the power supply rails in each case to see if they are all reasonably and similarly symmetrical.


Yep, the signal is the same and hadn't moved from the Monorocket case. I'll actually try again by moving the module making the signal into the Doepfer case and see what happens.

The Doepfer case measures +- 11.7v and the case with MakeNoise power measures +-12.1v
MUFF WIGGLER Forum Index -> Music Tech DIY  
Page 1 of 1
Powered by phpBB © phpBB Group