the X-Panner was first and foremost meant as an extension board for the PS3100 resonators. it is a simplified design, not using top notch VCAs, leaving off trimmers. i mentioned it several times in the thread.
however, if you think you wanted to make more out of it and improve it's performance, i will develop a workaround and describe it in the documentation. this will take a while, i think.
i personally are absolutely satisfied with it's performance. i built it with 1% resistors and transistors from the same batch.
for all who want to start to experiment just now, i quote yves ussons comments on the circuit (he was so very kind to take a closer look, referring to VCA 1 in the schematic):
yusynth wrote:
In such a circuit the CV bleed-through is mainly due to the mis-balance of the differential transistor stage. The idea behind a cascode circuit is that the collector currents created by the current sink is perfectly balanced and therefore cancel each other in the differential circuit built around the AOP. If there is a slight inbalance in the values of Q1 and Q2, R1,R2,R4,R5,R11,R3. Usually it is a good practice to have a small trimmer (say 1K) inserted between R1 and R2 and the +15V rail : the trimmer connected by its extreme terminals to R1 and R2 and its wiper pin connected to +15V. This way one can adjust the trimmer to minimize the unbalance and reduce the CV bleed-through.
Another point could be improved by using DC blocking caps (say 10µF) in the signal inputs of your VC-panner.
_________________
cheers,
matthias
____________
Big Boss at fonitronik
Tech Buddy at Random*Source
however, if you think you wanted to make more out of it and improve it's performance, i will develop a workaround and describe it in the documentation. this will take a while, i think.
Joined: Mar 07, 2009 Posts: 53 Location: Sydney, Australia
Posted: Fri May 22, 2009 4:29 am Post subject:
Fonik, that sounds a great idea. Personally I'm keen to build mine for the fun of having an old-school discrete-core VCA circuit with a character of its own...perfection is boring!
Usually it is a good practice to have a small trimmer (say 1K) inserted between R1 and R2 and the +15V rail : the trimmer connected by its extreme terminals to R1 and R2 and its wiper pin connected to +15V. This way one can adjust the trimmer to minimize the unbalance and reduce the CV bleed-through.
.
that's it!!!
first I tried this with a 1k trim and cv-amount became a bit less, but not enough. than I changed to a 50k trim, and voila: cv gone!!
so far I only changed the left channel (R1,2 & R23,24), but it's working and I think I'll make this mod permanent.
I know this might be a dumb question, but how did you add this trimmer since there's no space on the board for it? Something like a trimmer seems more awkward to mount off-board. Did you use a small proto-board or something?
Thanks!
Rvlt wrote:
hey,
thanks for your input everyone!!!
fonik wrote:
yusynth wrote:
Usually it is a good practice to have a small trimmer (say 1K) inserted between R1 and R2 and the +15V rail : the trimmer connected by its extreme terminals to R1 and R2 and its wiper pin connected to +15V. This way one can adjust the trimmer to minimize the unbalance and reduce the CV bleed-through.
.
that's it!!!
first I tried this with a 1k trim and cv-amount became a bit less, but not enough. than I changed to a 50k trim, and voila: cv gone!!
so far I only changed the left channel (R1,2 & R23,24), but it's working and I think I'll make this mod permanent.
take a look at the PCB. VCA 1 for example. R1, R2 are the resistors of concern. i will try to lift off the legs of the resistors connected to +V, solder them to a trimmer, which wiper will be soldered to one of the left pads, where R1 or R2 has been soldered to. i will see how that works an post a picture. _________________
cheers,
matthias
____________
Big Boss at fonitronik
Tech Buddy at Random*Source
I know this might be a dumb question, but how did you add this trimmer since there's no space on the board for it? Something like a trimmer seems more awkward to mount off-board. Did you use a small proto-board or something?
Thanks!
I used standard piher trimmers and bent & cut the outer legs. you have to file the remaining middle leg of the trimmer since it's a bit too large for the hole.
I put the mod on both of my xpan boards and now have a pimped resonator and a standalone x-panner, all working fine.
don't know if everyone needs to add trimmers for offset adjustment, but in my case it made sense. I guess I had bad luck with transistors (different batches ..)
DSC00151.JPG
Description:
Filesize:
651.23 KB
Viewed:
446 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.
DSC00159.JPG
Description:
Filesize:
629.9 KB
Viewed:
429 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.
I used standard piher trimmers and bent & cut the outer legs. you have to file the remaining middle leg of the trimmer since it's a bit too large for the hole.
I put the mod on both of my xpan boards and now have a pimped resonator and a standalone x-panner, all working fine.
good job. nice work. thanks for sharing the pix. _________________
cheers,
matthias
____________
Big Boss at fonitronik
Tech Buddy at Random*Source
I just finished building the Panner/Fader module and it seems to be working good , I did have to add the trimmers to it though (was easy enough).
I noticed that the pan knob has only a small part of its rotation at the center that is effective, after maybe 10 degrees rotation left or right the signal is panned hard left or right, is this correct? If so, is there as way make the panning more linear throughout he rotation of the knob?
Matthias, do you have any X-Pan-Fader boards left? Please say yes... I desperately need to buy another, I pulled a couple of pads off whilst de-soldering those 47K resistors. _________________
I noticed that the pan knob has only a small part of its rotation at the center that is effective, after maybe 10 degrees rotation left or right the signal is panned hard left or right, is this correct?
i will check that. i cannot recall any issues of an odd behaviour of the pot. anyone? _________________
cheers,
matthias
____________
Big Boss at fonitronik
Tech Buddy at Random*Source
I noticed that the pan knob has only a small part of its rotation at the center that is effective, after maybe 10 degrees rotation left or right the signal is panned hard left or right, is this correct?
i will check that. i cannot recall any issues of an odd behaviour of the pot. anyone?
Nope. Both of my xpanners working fine here, pan knob and everything else..
I did have a small incident after building the module, I wired the pot wrong and shorted it out when I turned it CW. I replaced the pot and it seems to pan correctly (although with only the small working range), could I have damaged one of the ICs or transistors?
Edit: I had the wrong resistor value in for R55, I had 560R not 560K replacing this should fix it.
glad you (nearly) solved it. quite a little bit release for me. _________________
cheers,
matthias
____________
Big Boss at fonitronik
Tech Buddy at Random*Source
Hi Matthias, I noticed people are adding trimmers to the board, my understanding is that it only needs trimmers if you intend to use it in standalone mode (without the resonators).
Does the updated documentation curb the need for trimmers in all cases? _________________
Hi Matthias, I noticed people are adding trimmers to the board, my understanding is that it only needs trimmers if you intend to use it in standalone mode (without the resonators).
Does the updated documentation curb the need for trimmers in all cases?
IMHO the trimmers are not needed if you use the module with the internal tri LFO.
however, i still have to update the documentation to show how one could easily add trimmers to get more out of it. i still believe this is okay, considering the decent pricing of the board and what it originally meant to be. _________________
cheers,
matthias
____________
Big Boss at fonitronik
Tech Buddy at Random*Source
I have another query regarding the 3100 resonator; R35 is 3.3MΩ, if I put 3x10MΩ resistors in parallel, I get 3.33MΩ... Is this acceptable, or must I use exactly 3.3MΩ ? _________________
they look like 1%, but that's negotiable these days, especially since these came from china. I'll test them first, if they're <3.33MΩ then I'll use them, if they're over, I'll have to look elsewhere. I may have some 3MΩ @ 5%, I guess as long as I'm close to the mark, it should be ok. Just as long as it's not critical _________________
today i put trimmers to a blank x-panner board. took me just a view minutes (no unsoldering necessary).
i shot a view pictures and will amend the documentation this week to make it more clear. but since the pictures are already taken i thought i could post them anyways...
BTW go to the flickR set and you will see the description for each picture.
_________________
cheers,
matthias
____________
Big Boss at fonitronik
Tech Buddy at Random*Source
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum You cannot attach files in this forum You can download files in this forum
Forum index » DIY Hardware and Software » fonik's place
FAQ
Calendar
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
Chat Room
, I did have to add the trimmers to it though (was easy enough).
replacing this should fix it.
