PQ-4 discussion and other parametric EQs

[MrBinns]

PQ-4 has some tapped (4 terminal) pots? Centre tap I guess,

I suspect the tapped pots are real.  You see these used time to time on professional Equalizers.   The centre tap stops the bands interacting with each other.  It tends to be a good thing.  Put it this way:  if you use non centre-tapped pots on a parametric circuit which was designed  for centre-tapped pots the result is no better or worse than any other circuit that doesn't use centre-tapped pots.  For a graphic EQ it would be a different matter.

the last thing posted

[MrBinns]

Idk if the are center tapped.

here is a mt-2. the 3rd pot from the left should be the same as a pq-4.

https://guitar-gear.ru/forum/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=8503

https://i.imgur.com/U4s6IPG.jpg

schematic: http://www.hobby-hour.com/electronics/s/schematics/boss-mt2-metal-zone-schematic.gif

[ubersam]

Those are dual concentric pots. Basically two pots stacked on top of each other, one shaft going through the other. Like this: http://www.stewmac.com/How-To/Online_Resources/Pickups_and_Electronics/Dual_Concentric_Control_Pots.html

[MrBinns]

and one of the stacks is dual ganged! 

[ubersam]

Yup. The dual ganged part is for the mid frequency (2x50K) and the single part is for the mid boost/cut (1x100K). I've seen that topology before, in the PAiA 9303 schematic (page 19, http://www.synthmanuals.com/manuals/paia/9303_four-band_eq/assembly_and_using_manual/9303_four-band_eq_200dpi.pdf). In the PAiA unit though, they are using separate pots, a single and a dual-ganged, instead of a concentric one.

[Kipper4]

Heres the referance schematic

http://www.synthdiy.com/files/2007/boss_pq-4.png

[Rob Strand]

The centre-tap pots are used on the boost/cut pots.

[anotherjim]

...and the centre taps are ac coupled to ground. An electronic centre-off detent?

[MrBinns]

So here are the boost/cut graphs for the mid section with the center tap grounded. the freq is all the way up.





Here is the same thing without the center tap



it looks like it makes the q value consistent.

[Kipper4]

Hows that going MrBinns?
Are you getting the results you want/need?

Edit: I'm currently trying this out as a post distortion eq


http://s1220.photobucket.com/component/Download-File?file=%2Falbums%2Fdd450%2Fbuschfsu%2Feq2.gif

[deadastronaut]

cool..

cheers rich for the pq4 schemo...

(my equalizer is working fine btw)   

but this looks cool too...