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 
go to the radio page Live at electro-music.com radio 1 Please visit the chat
  host / artist show at your time
today> Program postponed until Sunday at the same time this week only Chez Mosc
 Forum index » DIY Hardware and Software
Performance‘s troubleshooting thread
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 1 [20 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Sun Mar 28, 2021 7:59 am    Post subject: Performance‘s troubleshooting thread
Subject description: MS-20 VCF V. 2....
Reply with quote  Mark this post and the followings unread

EDIT: instead of making another thread whenever I have trouble getting my stuff working I just edit the sub-title including what’s troublesome at the moment so there’s no more spam than necessary!

Here’s how it started (MS-20 VCF is SOLVED but will get a complete rebuild asap....): [...]build a MS-20 filter clone for my eurorack synth and as so many I chose René Schmitz schematic from his fabulous SDIY page. It is built on stripboard and uses one LM13700 instead of CA3080. Both ICs (LM13700 and TL074) get their power correctly and cutoff and both channels of CV-control seem to behave properly as well. After some minor troubleshooting it started working so I thought it would be okay but the resonance pot is not doing anything at all (or just very, very little - almost unnoticable). Here‘s the thing: it doesn‘t scream at all! I‘ve checked the schematic and my soldering over and over again - it just doesn‘t work although it should. The only thing that‘s different from René‘s version ist the fact that I used 100kb-pots instead of 47kb but since cutoff control and CV attenuation work very properly this should not be the reason for its misbehavior. The resonance pot is 100ka as it should. One thing I noticed, though, is that the green LEDs won‘t light up (only when I accidentally touched the board and shorted something while in stalling it into the rack). Any ideas or solutions? I already thought about changing the resistor value for the one going from the opamp terminal where the LEDs are connected to ground, changing the value of the resonance pot or changing the LEDs for red ones or 1n4148s as in the original design but that‘s it. What could I measure, what could I change to make it work? Cheers and thanks to all.

Here‘s a link to a video I made to demonstrate the problem. Upper pot obviously is cutoff, middle pot is resonance, lower pots are CV-attenuators. Other modules involved are Doepfer A-110-1 and a dual LFO based on Niklas Rönnberg‘s design.

https://youtu.be/AvKQ7cnTzMY

Last edited by PERFORMANCE on Sat May 15, 2021 8:53 am; edited 4 times in total
Back to top
View user's profile Send private message
dk



Joined: Feb 12, 2019
Posts: 108
Location: Europe

PostPosted: Sun Mar 28, 2021 9:39 am    Post subject: Reply with quote  Mark this post and the followings unread

I built Takeda's version, which looks part for part the same (at least after a quick glance). Screaming is definitely not a problem Smile

In your video it sounds like the resonance isn't working at all... which layout did you use? There is at least one floating around with errors on it, specifically where the resonance feedback resistor and diodes/LED's aren't going between the correct rows...

_________________
Horrors Of Dial-Up!
Back to top
View user's profile Send private message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Sun Mar 28, 2021 11:27 am    Post subject: Reply with quote  Mark this post and the followings unread

dk wrote:
I built Takeda's version, which looks part for part the same (at least after a quick glance). Screaming is definitely not a problem Smile

In your video it sounds like the resonance isn't working at all... which layout did you use? There is at least one floating around with errors on it, specifically where the resonance feedback resistor and diodes/LED's aren't going between the correct rows...


Hey, thanks for your reply!

I drew up my own layout from the original Schmitz-schematic (i generally like this more than jsut copying the stripboard layouts floating around so I can follow what I'm actually doing). I'll attach it below!

And yes, you're right: there seems not really much going on when tweaking the resonance knob. I already swapped the orenientation of both LEDS but it didn't seem to have an effect at all (makes sense, since they're supposed to be wired in parallel thus making not a difference in which comes first...).


MS20 1.2.png
 Description:
There might be minor mistakes in the layout but I eventually solved them while buidling/ troubleshooting. Except the resonance part everything should be correct in the actual realisation.
 Filesize:  218.63 KB
 Viewed:  22 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

MS20 1.2.png


Back to top
View user's profile Send private message
dk



Joined: Feb 12, 2019
Posts: 108
Location: Europe

PostPosted: Mon Mar 29, 2021 1:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok, scanning over it this morning on my phone I didn't pick up any glaring errors, but...

The first thing I noticed is a lack of power filtering. I don't know how critical it is for this circuit, but generally having a pair of caps (10u-47u) strapped across your power rails where they connect to the board is good practice. You should probably have decoupling caps (100n?) where power meets your chips for both rails.

Also, on my clone, I have slightly different values around the resonance amp. I actually have less gain there than you should, so I don't think that's the problem. When I hit mine with loads of signal, though, it won't squeal no matter what I do. Have you tried leaving the input disconnected and turning the resonance all the way up? I have a pot with a voltage follower in front of mine to make the input adjustable (see attachment)... with the original values used (100k from input to OTA and 220r to ground), it squealed like crazy but the signal level was too low. I think now I have a 4k7 resistor there (where you have 10k), and for the last 1/3rd of the the pot travel the input signal overpowers the resonance quite a bit. It is audible that I'm adjusting the resonance pot, but it's nothing close to self oscillation.


MS20 filter input.png
 Description:
 Filesize:  32.27 KB
 Viewed:  13 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

MS20 filter input.png



_________________
Horrors Of Dial-Up!
Back to top
View user's profile Send private message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Mon Mar 29, 2021 2:13 am    Post subject: Reply with quote  Mark this post and the followings unread

dk wrote:
The first thing I noticed is a lack of power filtering. I don't know how critical it is for this circuit, but generally having a pair of caps (10u-47u) strapped across your power rails where they connect to the board is good practice. You should probably have decoupling caps (100n?) where power meets your chips for both rails.


Hey! Yes, I should really do that, I did on most of the other builds but didn‘t on this one for no reason - easy fix, though!

Regarding self oscillation: that‘s a thing I wondered about as well. It doesn‘t self oscillate but I‘ll switch a couple of resistors tonight and see what it does to the circuit.

Also thanks for recommending the input buffer - I‘ll simulate that with an attenuater!
Back to top
View user's profile Send private message
dk



Joined: Feb 12, 2019
Posts: 108
Location: Europe

PostPosted: Mon Mar 29, 2021 3:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Just for reference, then, the resistors I have around the resonance amp are a 4k7 from inverted input to ground and a 5k trim pot in parallel with the LED's. I have green LED's in mine. The original Korg units have 10k strapped in parallel to the LED's and 2k2 + a 2k trimmer from the inverted input to ground. That means your version should have more gain than both the original and my own, unless you've accidentally switched those two resistors?

I would still try getting it to self-oscillate with nothing hooked up to the input first, though. The original Korg didn't have the kind of output levels you typically see in Eurorack, so I'm guessing you just need to pad the input down a bit to keep the OTA from being overloaded.

_________________
Horrors Of Dial-Up!
Back to top
View user's profile Send private message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Mon Mar 29, 2021 9:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey!

Thanks again for all the replies. My agenda for tonight looks like this:

- attenuating the input and see if it resonates properly
- change the resistor values around at the resonating op-amp
- change the opamp (I also have LM324s lying around, maybe that helps)
- measure/ change the reso-pot (although it was brand new when installing this might also much unlikely be a cause of error)

also: cleaning the power with caps!

I'll keep the audience updated....
Back to top
View user's profile Send private message
dk



Joined: Feb 12, 2019
Posts: 108
Location: Europe

PostPosted: Mon Mar 29, 2021 12:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sounds good!

Feel free to try with no signal first, though. If it doesn't resonate that way, then the problem will definitely require 'fixing' something in the circuit you've got going on.

As for the op-amp, I think I'm using a TL082. I think in this situation, it's virtually identical to a TL072 (slightly different noise floor, otherwise the same). My buffer only had LM324 written there as it was on the same board as a level shifter run off a single supply, but I'm not sure that chip belongs directly in the filter circuit.... at the very least it's probably not advantageous compared with using the onboard buffers on the LM13700.

If you can't get self-oscillation without any input signal present, then go to town on the resonance amp section. It's gotta be something there. A micro solder bridge. Pot acting up. Resistors reversed. Whatever, but I'll bet it's there somewhere.

Best of luck!

_________________
Horrors Of Dial-Up!
Back to top
View user's profile Send private message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Thu Apr 01, 2021 4:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Okay...I got it to scream now. I build a little patchbay with female pin headers to change both resistors on the resonance-amp and the LEDs. Didn't work with any of the resistors I treid BUT worked when I entirely ditched the resistor in parallel with the LEDs....now gotta work around the fact that it's starting to scream at 1/3 of the Reso Pot!
Back to top
View user's profile Send private message
dk



Joined: Feb 12, 2019
Posts: 108
Location: Europe

PostPosted: Fri Apr 02, 2021 1:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Good to hear!

Perhaps try a trim pot in place of the resistor parallel to the LED's so you can adjust the onset of squealing?

_________________
Horrors Of Dial-Up!
Back to top
View user's profile Send private message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Sun Apr 04, 2021 7:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

dk wrote:
Good to hear!

Perhaps try a trim pot in place of the resistor parallel to the LED's so you can adjust the onset of squealing?


I will try that. I like the overall sound right now so there actually is no need to change it right now. What really bothers me is the fact that I don't really understand what is going on with the resistor in parallel and why the resonance only seems to work at all when it's omitted (I've tried many values just down to 80ohms and it still only started working when the resistor was bridged/ omitted). Anyway - thanks again very much for your help, I'll post a video of its operation soon!

Next module btw will be a dual "Fastest Envelope In The West", also by René.
Back to top
View user's profile Send private message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Wed Apr 14, 2021 2:37 am    Post subject: Reply with quote  Mark this post and the followings unread

okay, update: after working really great the filter suddenly died. i didn't have the chance to properly troubleshoot it but i suspect there's a mechanical failure in the pcb due to the massive changes i made to get it work properly. i'll build another one from the ground up because i love the sound, i will keep you updated on this and finally post a demo. meanwhile there are other modules scheduled, a dual EG, baby 8 sequencer, dual VCA, more mixers and buffers and i'm currently designing a stripboard benjolin (but that's a big thing...)
Back to top
View user's profile Send private message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Sat Apr 24, 2021 10:28 pm    Post subject: Fastest Envelope in the West
Subject description: René Schmitz‘ classic
Reply with quote  Mark this post and the followings unread

So, the MS-20 VCF did eventually work almost properly but died when I accidentally plugged something around somehow.....anyway, due to all the troubleshooting and rebuilding the stripboard had become a mess anyway so I will build another board from scratch and make it a clean build this time.

MEANWHILE: another Schmitzbit is bothering me - a dual „Fastest Envelope In The West“. Once again I designed and carefully counter checked the stripboard layout with the schematic, then soldered everyhting together (the first EG so far, not the second, almost identical board), made a crappy panel, attached all the parts plus additional LEDs and got it running sort of...

Attack and Release do work properly (although I need to change the direction of the pots still) but decay and sustain don‘t respond to any change in knob position. It feels like full sustain all the time. Gate time is having an impact on the length of the sustained part but decay is not noticeable and the level of sustain also doesn‘t change with the turn of a knob. Any ideas? Haven‘t measured any voltages yet but will within the next few days.

I feel a little cursed, btw, because the first ADSR I wanted to build - Nicolas‘ ADSR With looping function and such - also worked kind of but never really did what it was supposed to do (it‘s the only module so far that has been entirely neglected - 8 other modules over the last few weeks have been more or less succesfully built!). So if you know your way around magic in SDIY please destroy that curse! If you‘re a muggle please help with your expertise in electronics!
Back to top
View user's profile Send private message
gabbagabi



Joined: Nov 29, 2008
Posts: 633
Location: Berlin by n8
Audio files: 23

PostPosted: Sun Apr 25, 2021 1:29 am    Post subject: Reply with quote  Mark this post and the followings unread

I had a chat with my Healer,
After throwing some resistors and two obsolete Transistors (pnp!) Into some ferric Chlorid,
He read out that Long and intensive Sessions on
The breadboard before and while soldering
Can Break the curse

Wtf where is this smoke coming from ?
Back to top
View user's profile Send private message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Wed May 12, 2021 10:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

gabbagabi wrote:
I had a chat with my Healer,
After throwing some resistors and two obsolete Transistors (pnp!) Into some ferric Chlorid,
He read out that Long and intensive Sessions on
The breadboard before and while soldering
Can Break the curse

Wtf where is this smoke coming from ?


Haha, didn't react on this yet - sorry! Thanks for talking to your healer. As so often destiny had already been fulfilled before I noticed - the first of both envelopes (I first built one and tested it, then built the other one and sandwiched both stripboards behind an 8 hp eurorack panel containing all the ADSR knobs and Gate inputs and EG outputs) did actually work correctly in the first place - I just didn't properly give it the "right" gates and got confused because the pots were soldered in the wrong way around. Now both work like a charm and can react really snappy as they are supposed to!

Next up ist the rebuild of the Renè Schmitz MS-20 VCF, followed by a dual MFOS VCA from scratch, some more buffered multiples, another mixer and a Baby 8 sequencer. Hopefully until June I will be also able to at least design a stripboard benjolin based on Epoch Modular's schematic and a Scott Bernardi VC Delay (the later would be so great to have). On the non modular side there still is an already designed Boss DS-1 clone and a PT2399-based Chorus Pedal scheduled for the upcoming weeks...gotta make the best of the hopefully last weeks of lockdown and before finally getting vaccinated.
Back to top
View user's profile Send private message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Sat May 15, 2021 9:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Okay, okay.....it really must be cursed. The second iteration of my MS-20 VCF based on Renè Schmitz's design behaved the same as the first did, so I went through all the troubles but this time didn't even get it to scream at all.......needs another design, I guess. Maybe I should also just stick to somebody elses stipbad layout - but most of them are too spacious. Or does anybody of you have a stripboard layout of that filter suitable for eurorack levels (power and audio) on a 100x50mm board (or even smaller)?

Meanwhile I'm going to concentrate on other modules to not fall into frustration over this.
Back to top
View user's profile Send private message
gabbagabi



Joined: Nov 29, 2008
Posts: 633
Location: Berlin by n8
Audio files: 23

PostPosted: Sat May 15, 2021 11:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Sad to hear,
but may you should really consider the ever repeated Phrase "breadboard first" ?
Back to top
View user's profile Send private message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Sat May 15, 2021 8:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

gabbagabi wrote:
Sad to hear,
but may you should really consider the ever repeated Phrase "breadboard first" ?


hrrrrrnnggggggggggggggggggg..........wanted to build a "bench supply" for that purpose anyway but i hate those flimsy breadboards....but it's a good idea, I even invested in some better quality breadboards recently.
Back to top
View user's profile Send private message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Sat Jun 05, 2021 8:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

okay, bench supply is ready and already helped a lot troubleshooting another module. Now I'm gonna give the MS20 a thrid try. I will breadboard it first this time but also already made a different design.

See below!


0003 MS20 3.0.png
 Description:
 Filesize:  82.26 KB
 Viewed:  5 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

0003 MS20 3.0.png


Back to top
View user's profile Send private message
PERFORMANCE



Joined: Jun 11, 2020
Posts: 26
Location: Germany

PostPosted: Sat Jun 05, 2021 8:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

PERFORMANCE wrote:
okay, bench supply is ready and already helped a lot troubleshooting another module. Now I'm gonna give the MS20 a thrid try. I will breadboard it first this time but also already made a different design.

See below!


well, already figured out some errors (input, lm13700 power...).
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 1 [20 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
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


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