!!The Pseudo 0.5 258J Build/Mod Thread!!

From circuitbending to homebrew stompboxes & synths, keep the DIY spirit alive!

Moderators: Kent, luketeaford, Joe.

Post Reply
User avatar
beautyofdecay_
no maps for this area
Posts: 348
Joined: Sun Feb 27, 2011 2:26 pm
Location: Netherlands

Post by beautyofdecay_ » Wed May 11, 2011 3:57 am

boothnavy wrote:well, somewhat...

which side of those 100k resistors would you add the 4.7M from the fine wiper to? to the TL072 side or the other side of the 100Ks?
Here is an updated wiring diagram. Hope that clears everything up ;)
boothnavy wrote:I am still unclear about the difference between inputs CV 1/2 and the 1v/oct pad that is on the PCB. Is the 1v/oct input just log from 0-10v? and the CV inputs are bi-polar (- causes + voltage to go down and + causes + voltage to go up) as discussed earlier?
Yes.
Attachments
Updated wiring diagram for 258J with Pugix freq fine mod
Updated wiring diagram for 258J with Pugix freq fine mod
258J-wiringdiagram-updated.jpg (256.8 KiB) Viewed 2689 times

User avatar
Peake
I'm in ur DIY. Filling cases with Buchla
Posts: 7971
Joined: Fri Nov 07, 2008 10:00 pm
Location: Loss Angeles

Post by Peake » Wed May 11, 2011 1:22 pm

pugix wrote:
J3RK wrote:
Peake wrote:Remember remember the FM pot should be audio taper, preferably 50K (don't know if 100K will give you "more" or "less").

Also of important note, unless Verbos/J3RK has changed anything- Buchla use a 15V modulation range. The Waveform control input expects 15V signals to provide the full output of the saw/square waveform.
I didn't change anything, so unless Mark did, it's probably the same. With 10V I've got it trimmed to do pretty well, though I imagine it could go a touch further in either direction to be perfect. I've got a clean sine to nice sounding saws and squares though with the usual (non Buchla) voltages.
Peake,

Thanks for the audio taper suggestion for the linear FM pot. But it may not be needed, because the 10K in series with the 15uf cap will load a 100K linear taper pot, causing it to have a 'warped' taper anyway. An audio taper would exaggerate this effect. 50K even more so. I guess I'm saying that I don't think that 50K vs 100K, audio vs linear taper, will make a lot of difference. Try different pots and see what works for you. It's DIY. :goo: I'm going to experiment with the values of the resistor and cap, as well.

About the waveform CV input, I also noticed the 680K there, giving it the same sensitivity as the pot, i.e. 15V. I was thinking of using a 330K or smaller to increase the sensitivity. You could add a panel pot for the level of the waveform CV. Not sure if I'm adding that. I also noted the 150K (opt) resistor that simply terminates the end of that CV input to ground, needed if you have a banana jack on that input, so it doesn't float. A switched jack, normalled to ground would be a good idea, or an attenuator pot, in which case you wouldn't need the optional 150K.
I've owned originals and the action of the FM pot was just right. But you're correct, try out and stick with whatever ends up pleasing you.
This is not the place I'd imagined it to be.

User avatar
Peake
I'm in ur DIY. Filling cases with Buchla
Posts: 7971
Joined: Fri Nov 07, 2008 10:00 pm
Location: Loss Angeles

Post by Peake » Wed May 11, 2011 1:29 pm

beautyofdecay, P3 and P2 are, on the front panel, entirely separate control inputs with attenuation. Your wiring diagram does not reflect this.
This is not the place I'd imagined it to be.

User avatar
J3RK
Super Deluxe Wiggler
Posts: 6801
Joined: Tue Dec 22, 2009 12:46 pm
Location: Seattle

Post by J3RK » Wed May 11, 2011 3:07 pm

I really love this thread! There's tons of interesting information in here now. I'm using a pretty simplistic setup in my easelishitemthing, but would love to build an ultra-deluxe, all-mod version of this too now.
:nana:

Exp FM mod, output amp, waveshape/wavebutcher pots, maybe a discrete OTA, possibly a MAT for exponential conversion (not sure how much this would do, but it's the one method I haven't tried,) etc. etc.

User avatar
beautyofdecay_
no maps for this area
Posts: 348
Joined: Sun Feb 27, 2011 2:26 pm
Location: Netherlands

Post by beautyofdecay_ » Thu May 12, 2011 2:14 pm

Peake wrote:beautyofdecay, P3 and P2 are, on the front panel, entirely separate control inputs with attenuation. Your wiring diagram does not reflect this.
You could be right about that. I haven't wired the P3/CV2 part of the wiring diagram yet, so couldn't check if it actualy works... :confused:

User avatar
beautyofdecay_
no maps for this area
Posts: 348
Joined: Sun Feb 27, 2011 2:26 pm
Location: Netherlands

Post by beautyofdecay_ » Thu May 12, 2011 2:34 pm

I've been playing around in Front Panel Designer with a panel design for a mutant complex waveform generator based on the 258J's.
I'm not sure about the knobs yet and placement of some of the controls must still be optimized but here it is anyway :wink:

Oh, and there is a switch now for mod type selection but that must be a push button of course as it should be possible to select any combination of modulation types...
Attachments
DSC_3654.jpg
DSC_3654.jpg (128.66 KiB) Viewed 2540 times

thermionicjunky
Thyratron Genius
Posts: 2252
Joined: Thu May 03, 2007 6:33 pm
Location: Upstate NY

Post by thermionicjunky » Thu May 12, 2011 2:55 pm

beautyofdecay_ wrote:
Peake wrote:beautyofdecay, P3 and P2 are, on the front panel, entirely separate control inputs with attenuation. Your wiring diagram does not reflect this.
You could be right about that. I haven't wired the P3/CV2 part of the wiring diagram yet, so couldn't check if it actualy works... :confused:
It looks like the outer lugs of the pots are being mixed into the inverting and non-inverting control inputs. That's exactly what we want.

User avatar
Peake
I'm in ur DIY. Filling cases with Buchla
Posts: 7971
Joined: Fri Nov 07, 2008 10:00 pm
Location: Loss Angeles

Post by Peake » Thu May 12, 2011 3:11 pm

thermionicjunky wrote:
beautyofdecay_ wrote:
Peake wrote:beautyofdecay, P3 and P2 are, on the front panel, entirely separate control inputs with attenuation. Your wiring diagram does not reflect this.
You could be right about that. I haven't wired the P3/CV2 part of the wiring diagram yet, so couldn't check if it actualy works... :confused:
It looks like the outer lugs of the pots are being mixed into the inverting and non-inverting control inputs. That's exactly what we want.
P2 and P3 are separate -inputs- with individual attenuation fed to the inverting and non-inverting control inputs. The drawing would appear to be a single input to a pair of attenuverting pots in series.

Oh, is the "CV1" input attenuverted by the P2 pot? I'm still not sure if the wiring will work as shown, have you built it and it works?
This is not the place I'd imagined it to be.

User avatar
beautyofdecay_
no maps for this area
Posts: 348
Joined: Sun Feb 27, 2011 2:26 pm
Location: Netherlands

Post by beautyofdecay_ » Thu May 12, 2011 3:20 pm

Peake wrote:Oh, is the "CV1" input attenuverted by the P2 pot? I'm still not sure if the wiring will work as shown, have you built it and it works?
Yes. CV1/P2 works as described. I built that and tested it.
I'll try to wire CV2/P3 tonight and let you know my findings.

User avatar
Neutron7
Oldschool bleeper
Posts: 1991
Joined: Sun May 23, 2010 12:24 pm

Post by Neutron7 » Thu May 12, 2011 3:20 pm

the 6.81k resistor is a bit silly isn't it? a 1% 6.8k resistor is well within the tolerance of 6.81k 1%

If you buy just 1 or 2 the chances are that it will be farther from 6.81k than a hand picked 6.8k.

the 4.99 and 2.49 are a not likely to be found like that though because there is not a close enough common value.

User avatar
Peake
I'm in ur DIY. Filling cases with Buchla
Posts: 7971
Joined: Fri Nov 07, 2008 10:00 pm
Location: Loss Angeles

Post by Peake » Thu May 12, 2011 3:30 pm

Thanks BOD.

Neutron7, enjoying your avatar (a cat in a Mouser box) :hihi:

Plenty of these resistor values on ebay. Be glad there aren't any 49.9K, which is another famous Buchla value (I bought a bag of hundreds of these to stop my mind from wondering...where it will go.
This is not the place I'd imagined it to be.

User avatar
J3RK
Super Deluxe Wiggler
Posts: 6801
Joined: Tue Dec 22, 2009 12:46 pm
Location: Seattle

Post by J3RK » Thu May 12, 2011 5:26 pm

Neutron7 wrote:the 6.81k resistor is a bit silly isn't it? a 1% 6.8k resistor is well within the tolerance of 6.81k 1%

If you buy just 1 or 2 the chances are that it will be farther from 6.81k than a hand picked 6.8k.

the 4.99 and 2.49 are a not likely to be found like that though because there is not a close enough common value.
I've bought several batches of 6.81K from Mouser, and every one that I measured was exactly 6.81K I thought the same thing initially. I think this value must have been carefully picked, or why bother differentiating from the 6.8Ks everywhere else? (not that I personally think it's hugely critical, but using a value like that just makes me think it was chosen carefully.)

My 2.49K and 4.99Ks are also very close or spot on, so even though they're 1%, I think these odd values are generally a little more accurate. At least that's been my experience through this project.

Like I said though, how much it matters, I don't know.

User avatar
J3RK
Super Deluxe Wiggler
Posts: 6801
Joined: Tue Dec 22, 2009 12:46 pm
Location: Seattle

Post by J3RK » Thu May 12, 2011 5:28 pm

beautyofdecay_ wrote:
Peake wrote:Oh, is the "CV1" input attenuverted by the P2 pot? I'm still not sure if the wiring will work as shown, have you built it and it works?
Yes. CV1/P2 works as described. I built that and tested it.
I'll try to wire CV2/P3 tonight and let you know my findings.
I can also confirm this behavior on mine. P2 is a bipolar control for Control In/CV1. (I don't have fine control pots though, as I'll be switching mine to 10-turn instead.)

BoD: I like your panel layout.

User avatar
emdot_ambient
Super Deluxe Wiggler
Posts: 3368
Joined: Thu Oct 15, 2009 11:40 am
Location: Frederick, Maryland USA

Post by emdot_ambient » Thu May 12, 2011 6:29 pm

Peake wrote:...Be glad there aren't any 49.9K, which is another famous Buchla value...
I just got a Mouser order in....and found that I had accidentally ordered 49.9K rather than 4.99K :roll:

User avatar
J3RK
Super Deluxe Wiggler
Posts: 6801
Joined: Tue Dec 22, 2009 12:46 pm
Location: Seattle

Post by J3RK » Thu May 12, 2011 7:11 pm

emdot_ambient wrote:
Peake wrote:...Be glad there aren't any 49.9K, which is another famous Buchla value...
I just got a Mouser order in....and found that I had accidentally ordered 49.9K rather than 4.99K :roll:
Well, if you have some 281s to build, you'll be all set. I think there are a few on those if I'm not mistaken. :party: This happened to me with my trim pots. I'm pretty sure it was them and not me too, because I selected 100R, 100K, 1M, and 20K using the mouse from the value dropdown. I don't see how I could have accidentally ordered 200K instead of 20K with that method. (maybe if I searched that could have happened, but I always use the filters.) The 200Ks are working fine anyway. :mrgreen:

active
Common Wiggler
Posts: 216
Joined: Wed Jan 13, 2010 11:20 am
Location: Brooklyn, NY

Post by active » Thu May 12, 2011 7:34 pm

emdot_ambient wrote:
Peake wrote:...Be glad there aren't any 49.9K, which is another famous Buchla value...
I just got a Mouser order in....and found that I had accidentally ordered 49.9K rather than 4.99K :roll:
i ordered a 2.49 instead of a 2.49k. wobble! :hmm:

User avatar
emdot_ambient
Super Deluxe Wiggler
Posts: 3368
Joined: Thu Oct 15, 2009 11:40 am
Location: Frederick, Maryland USA

Post by emdot_ambient » Thu May 12, 2011 8:45 pm

J3RK wrote:
emdot_ambient wrote:
Peake wrote:...Be glad there aren't any 49.9K, which is another famous Buchla value...
I just got a Mouser order in....and found that I had accidentally ordered 49.9K rather than 4.99K :roll:
Well, if you have some 281s to build, you'll be all set.
I do have 2 of the new double 281s...but thing is, they're already almost completely built...and I already had enough 49.9Ks for them.

Oh well. I'm just prepared for, uh, whatever.

User avatar
J3RK
Super Deluxe Wiggler
Posts: 6801
Joined: Tue Dec 22, 2009 12:46 pm
Location: Seattle

Post by J3RK » Fri May 13, 2011 12:51 am

If you have spare 49.9k resistors, you're prepared for anything!

User avatar
boothnavy
Ultra Wiggler
Posts: 999
Joined: Mon Mar 29, 2010 9:18 pm
Location: Westlake Village
Contact:

Post by boothnavy » Fri May 13, 2011 6:48 am

Maybe use them in place of a 50K 10% :razz:
boothnavy - synthesist

www.analogcraftsman.com

User avatar
negativspace
Manhattan Analog
Posts: 6575
Joined: Tue Apr 13, 2010 2:50 am
Location: Manhattan, KS, USA
Contact:

Post by negativspace » Fri May 13, 2011 8:26 am

I like using 49.9ks in situations where a 47k is specified to 'halve' a 100k. Turns out that's often enough that I keep a healthy stock on hand. Guess I'm prepared for anything. :sb:

User avatar
Neutron7
Oldschool bleeper
Posts: 1991
Joined: Sun May 23, 2010 12:24 pm

Post by Neutron7 » Fri May 13, 2011 10:17 am

I am going to use el cheapo SMD tempcos , and mount it to a thin strip of veroboard.

They only have a 1.8k one (not 2k) does anyone have an idea if that's OK, or should i put it in series with a 180 ohm one?

[EDIT] used a temporary 2k resistor till i can get a tempco sorted out.


[EDIT] Never mind, it is oscillating now i had to reseat the ICs. just trying to figure out why the sine looks so non sinelike now. then ill finish the other one and build a panel!

User avatar
Neutron7
Oldschool bleeper
Posts: 1991
Joined: Sun May 23, 2010 12:24 pm

Post by Neutron7 » Fri May 13, 2011 3:29 pm

I can see a really nice sine by probing the sine shaper next to the diodes, but when i try to get the sine on the output by adjusting the 20k pot, it seems like it does not have enough adjustment, the sine gets almost there, with a double hump on top, but then the trimmer runs out of turns.

User avatar
beautyofdecay_
no maps for this area
Posts: 348
Joined: Sun Feb 27, 2011 2:26 pm
Location: Netherlands

Post by beautyofdecay_ » Fri May 13, 2011 4:12 pm

Neutron7 wrote:I can see a really nice sine by probing the sine shaper next to the diodes, but when i try to get the sine on the output by adjusting the 20k pot, it seems like it does not have enough adjustment, the sine gets almost there, with a double hump on top, but then the trimmer runs out of turns.
I have the same "problem" (see page 9 of this thread for some screen shots).
Haven't had time to try to "fix" that and I'm not sure I'm going to fix it... 8_)

User avatar
Neutron7
Oldschool bleeper
Posts: 1991
Joined: Sun May 23, 2010 12:24 pm

Post by Neutron7 » Fri May 13, 2011 5:34 pm

beautyofdecay_ wrote:
Neutron7 wrote:I can see a really nice sine by probing the sine shaper next to the diodes, but when i try to get the sine on the output by adjusting the 20k pot, it seems like it does not have enough adjustment, the sine gets almost there, with a double hump on top, but then the trimmer runs out of turns.
I have the same "problem" (see page 9 of this thread for some screen shots).
Haven't had time to try to "fix" that and I'm not sure I'm going to fix it... 8_)

Now i am thinking i might do the same thing and separately amplify the sine output. it will be cool to use the Sine for cross-mod output while hearing the waveshaped version.

User avatar
J3RK
Super Deluxe Wiggler
Posts: 6801
Joined: Tue Dec 22, 2009 12:46 pm
Location: Seattle

Post by J3RK » Fri May 13, 2011 5:40 pm

Odd, mine fades all the way to sine and then passes it. I'd say maybe it's because of my incorrect trimmer there, but it also behaves on my other one that has the correct trimmer. I can definitely get the multi-peak sine as well, but mine do go to full-sine. As soon as my scope shows up, I'll grab some screenshots.

Post Reply

Return to “Music Tech DIY”