electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Articles  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links  |  Store
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
1v per oct keyboard is....microtonal and droopy? FIXED?
Post new topic   Reply to topic Moderators: dnny, Uncle Krunkus, v-un-v
Page 1 of 1 [9 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
Europanaut



Joined: Apr 04, 2014
Posts: 30
Location: Nanaimo, BC, Canada

PostPosted: Thu Feb 26, 2015 1:32 am    Post subject: 1v per oct keyboard is....microtonal and droopy? FIXED? Reply with quote  Mark this post and the followings unread

Certainly not a desirable situation. Well not for me at least.

So it's the Single Buss 1V/Octave Keyboard project. Gate works. Trig works. The keyboard's 100ohm resistor array checks out on the meter. I've tried calibrating the circuit, but it doesn't seem to effect much at this point.

The problem is this. It takes 2.5 octaves to make a minor third. This is somewhat limiting. lol.

Any suggestions on where in the circuit that I should point my diagnostic attention? I've built around 25 MFOS modules, and they all work great, usually first try. But this one is being cranky.

Thanks!

Last edited by Europanaut on Mon Mar 02, 2015 3:58 pm; edited 2 times in total
Back to top
View user's profile Send private message
Europanaut



Joined: Apr 04, 2014
Posts: 30
Location: Nanaimo, BC, Canada

PostPosted: Sat Feb 28, 2015 9:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Gonna dig into this issue tonight. I'll trace the circuit backwards from the keyboard.

No last-minute ideas from the forum?
Back to top
View user's profile Send private message
Europanaut



Joined: Apr 04, 2014
Posts: 30
Location: Nanaimo, BC, Canada

PostPosted: Sun Mar 01, 2015 1:03 am    Post subject: Reply with quote  Mark this post and the followings unread

So, I have no idea why, but the microtonal issue just sort of "went away". And didn't come back all night. So who knows what that was about.

We then replaced R4 with a 27k, and the calibration locked right in. Sounds great.

Except.....the dreaded droop. And the glide doesn't work. Not sure if the two problems are related. EDIT: Glide works. Don't ask.

So, MASSIVE long droops. That's the repair priority. I'm hosting a modular synth meet next weekend, and I'm REALLY hoping to have this fixed by then.

I've found a bunch of references to droops on this forum, but there doesn't seem to be a definitive opinion on the source of the issue. I've read that the 444 and the big poly cap are important to the sample and hold circuit that is supposed to correct the droop, but I don't have replacement caps of that type. I do have a couple of spare 444's, but I'd like to mine the collective experience here on the forum before I start swapping stuff out. A bit of prep can save hours.

Oh, the other thing that we noticed is, the pitch stays solid, no droop, when the synth is first powered up. It's rock solid for about 30 seconds, then starts getting progressively droopier.

I just swapped out the 444. No change.

Running +- 15v.

So any ideas?
Back to top
View user's profile Send private message
PHOBoS



Joined: Jan 14, 2010
Posts: 2007
Location: Moon Base
Audio files: 392

PostPosted: Mon Mar 02, 2015 7:41 am    Post subject: Reply with quote  Mark this post and the followings unread

I don't have any experience with this particular circuit and I doubt I can help
but what kind of capacitor are you currently using for the S&H section ?

_________________
"My perf, it's full of holes!"
http://phobos.000space.com/ http://www.acidtrash.com/ Stickney Synthyards
Back to top
View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger
Europanaut



Joined: Apr 04, 2014
Posts: 30
Location: Nanaimo, BC, Canada

PostPosted: Mon Mar 02, 2015 9:35 am    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
I don't have any experience with this particular circuit and I doubt I can help
but what kind of capacitor are you currently using for the S&H section ?



Hey PHOBoS, thanks for the reply!

I'm using a Polystyrene .01uF Cap for C19. I agree with your suspicions about the health of this cap. Unfortunately, I only had one Polystyrene .01uF cap to try, but will swap out for a .01uf polyester today, just to see what happens.
Back to top
View user's profile Send private message
PHOBoS



Joined: Jan 14, 2010
Posts: 2007
Location: Moon Base
Audio files: 392

PostPosted: Mon Mar 02, 2015 10:28 am    Post subject: Reply with quote  Mark this post and the followings unread

hmm Polystyrene isn't bad for this purpose, unless there is something actually wrong with the cap. At least it's not a ceramic capacitor.
The S&H section is pretty straight forward so if it's not the cap it might have something to do with with the FET Q3 (or maybe Q2).

_________________
"My perf, it's full of holes!"
http://phobos.000space.com/ http://www.acidtrash.com/ Stickney Synthyards
Back to top
View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger
Europanaut



Joined: Apr 04, 2014
Posts: 30
Location: Nanaimo, BC, Canada

PostPosted: Mon Mar 02, 2015 3:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

So here's a weird one. I tried a bunch of different .01uf caps as swaps for C19. No change.

Then, for no reason in particular other than it was on the bench, I tried a .22 film cap. Worked perfectly. No droop. Well, after about 30 seconds or so there's a VERY slow drop off, which from what I understand, is expected.

So I'm happy, and have a perfectly functional single-bus keyboard controller.


But....wtf?
Back to top
View user's profile Send private message
PHOBoS



Joined: Jan 14, 2010
Posts: 2007
Location: Moon Base
Audio files: 392

PostPosted: Mon Mar 02, 2015 4:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

That tells me that somehow the cap gets discharged too fast and there are only 2 things attached to it:
The FET Q3 and the opamp U3c. You mentioned that you already replaced the opamp without any change.
You could check the PCB around the FET for any solder bridges (I doubt that would cause just a bit of a droop though)
and measure if the resistor values (R17/R14) are correct. Or try replacing Q3.

It's nice that you at least got it working now but something is still wrong, unless the caps you tested with were all faulty.

_________________
"My perf, it's full of holes!"
http://phobos.000space.com/ http://www.acidtrash.com/ Stickney Synthyards
Back to top
View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger
Europanaut



Joined: Apr 04, 2014
Posts: 30
Location: Nanaimo, BC, Canada

PostPosted: Mon Mar 02, 2015 4:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
That tells me that somehow the cap gets discharged too fast and there are only 2 things attached to it:
The FET Q3 and the opamp U3c. You mentioned that you already replaced the opamp without any change.
You could check the PCB around the FET for any solder bridges (I doubt that would cause just a bit of a droop though)
and measure if the resistor values (R17/R14) are correct. Or try replacing Q3.

It's nice that you at least got it working now but something is still wrong, unless the caps you tested with were all faulty.


Agreed. I hate it when things are "working" but not really working. But this fix will get me through the synth meet, then I can try replacing Q3.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: dnny, Uncle Krunkus, v-un-v
Page 1 of 1 [9 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Jump to:  

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
e-m mkii

Please support our site. If you click through and buy from
our affiliate partners, we earn a small commission.


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use