saint gillis
Well-known member
You're right PRR, I'm gonna measure the mismatch in DBs for 10 steps or so and share it!
Baxandall Volume Control
- Thread starter ej_whyte
- Start date
Help Support GroupDIY Audio Forum:
Mismatch due to the pot can generally be corrected by adding a law-steering resistor between wiper and one of the ends.saint gillis said:
> We can find a similar gain control in the SSL4000
http://www.gyraf.dk/schematics/SSL_82E01_Channel_Amplifier.GIF
Not so similar. In Self's 1983 article this is Fig.2(a), modified to not go to zero gain. Self points out that gain depends on the ratio of a good resistor to a sloppy pot track (the "2.21K" is very nearly right, but the "28K" is surely 25K or 30K). And yeah, in this configuration ON611 is a gain-trim, setting overall gain, not travel-tracking. R60 is DC bias and little to do with gain.
Also a Line In Trim is not really expected to "track". You set each channel so it pots-up OK with the main Fader at a mark, then use the Fader to make both channels fade-up/down together.
http://www.gyraf.dk/schematics/SSL_82E01_Channel_Amplifier.GIF
Not so similar. In Self's 1983 article this is Fig.2(a), modified to not go to zero gain. Self points out that gain depends on the ratio of a good resistor to a sloppy pot track (the "2.21K" is very nearly right, but the "28K" is surely 25K or 30K). And yeah, in this configuration ON611 is a gain-trim, setting overall gain, not travel-tracking. R60 is DC bias and little to do with gain.
Also a Line In Trim is not really expected to "track". You set each channel so it pots-up OK with the main Fader at a mark, then use the Fader to make both channels fade-up/down together.
saint gillis
Well-known member
abbey road d enfer said:
I measured the pot's resistance at 8 different rotation steps, created an excel file to find the best combination of resistors across the wiper and both ends or even between both end, it helped reducing the mismatch but it's still not satisfying enough (on the device where I used this active gain control there is also an output pad to be able to add a bit of saturation and at high gain setting the mismatch between left and right becomes annoying). I must say I used cheap alpha pots..
So my question is "will an expensive 10K lin stereo ALPS pot will solve this? or should I use a stepped switch, and in this case it is a bit stupid to choose the active volume control design but at least it will be precise.."
