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 » Thomas Henry designs
The VCO-555
Post new topic   Reply to topic Moderators: Scott Stites
Page 12 of 16 [377 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Goto page: Previous 1, 2, 3, ..., 10, 11, 12, 13, 14, 15, 16 Next
Author Message
elmegil



Joined: Mar 20, 2012
Posts: 2050
Location: Chicago
Audio files: 16

PostPosted: Fri Apr 28, 2017 1:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
elmegil wrote:
The transistor subs should work, but be aware that the pinouts are opposite (I believe) on the BC* transistors compared to the 2N39* transistors. Double check the data sheets!

As for the 555, if it's not CMOS it won't work right. Not sure the best way to ensure that.


If you are referring to the nasty habit of the bipolar 555 timer to crowbar the power supply, you can try the PAiA Fatman method (which was sold with bipolar 555 chips). In the Fatman, the crowbar effect caused the VCOs to soft synch when they got close together in pitch. The original design powered the 555 timers through 100 ohm resistors with a 100uF cap across the ICs Vcc and Vee terminals. That works "ok", but PAiA's Scott Lee improved it by replacing the 100 ohm resistor with a standard LED (not high brightness). Note that the 555 doesn't draw enough current to light the LED, the LED is used because of it's diode characteristics. The CMOS 555 (7555) doesn't have this issue.



No, there's some other issue that actually affects the tunability of the VCO. At least that's my vague recollection. There is probably discussion of it back in this thread somewhere, but it is important to note that TH specifies the CMOS version of the 555, not the common NE555 (I think the ones I got that are CMOS were TS555), and that several folks have reported variations of it doesn't work when not using CMOS.
Back to top
View user's profile Send private message
alanwilder81



Joined: Sep 03, 2016
Posts: 325
Location: italy

PostPosted: Tue Aug 22, 2017 5:35 am    Post subject: Reply with quote  Mark this post and the followings unread

hello everyone,

My 555 VCO produces nice waveforms, but their output voltage varies with frequency.
The sawtooth and square measure about 4 V
the triangle about 2 V

The effect is most pronounced with triangle signal, as, increasing its frequency it gets to almost 4 V and therefore gets much louder.
I wonder whether or not this is normal.
i believe voltage output should be the consistent regardless frquency.
Any ideas? thanks
Back to top
View user's profile Send private message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Tue Aug 29, 2017 12:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi all,

I've been lurking as this forum as a reader for a while and just started breadboarding this vco as my first project. Thanks for all the great resources!

So after a few initial mistakes (I fried a 555 and the 13700 got pretty hot too but seemed to survive) I can at least see some oscillation on my oscilloscope. I don't actually have any amp or anything where I'm at, so I'm stuck with a cheap 18$ oscilloscope or my earplugs (fried one of those too with 24Vpp Smile

So, I have oscillation around 1.25KHz from 555:s output, but I think I have problems with my exp converter. Turning any pots doesn't make the slightest difference. I have removed some stuff to simplify while breadboarding and maybe I have errored here.

I have pin 2 on IC3 being seemingly grounded. Trying to understand the schematic that would be the summed up linear CV I would guess, so having this being close to ground whichever way I turn the Coarse knob makes me pretty suspicious.

Even if I turn the Coarse knob all the way to 12V I have a voltage drop over R29 from those 12V down to ground. I don't seem to understand how this can be though…

I've tried rebuilding just the cv converter separately to see if I can isolate but it would be so super nice if there where any reference voltages or something that I could check against. I get the same grounded pin 2 on IC3 there (the lowest breadboard)

PS.

Never mind the top two, that's a Bass++ and a simplified MFOS amp still in progress Smile


breadboard vco555.png
 Description:
first attempt breadboarding…
 Filesize:  9.89 MB
 Viewed:  129 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

breadboard vco555.png


Back to top
View user's profile Send private message
alanwilder81



Joined: Sep 03, 2016
Posts: 325
Location: italy

PostPosted: Tue Aug 29, 2017 4:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

dunno
Back to top
View user's profile Send private message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Wed Aug 30, 2017 1:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Slept on it, but I'm still super stuck.

Is there anything that seems suspicious with any of my measure points here?


measurements debugging.jpg
 Description:
measurements debugging
 Filesize:  997.04 KB
 Viewed:  117 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

measurements debugging.jpg


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



Joined: Sep 29, 2006
Posts: 8
Location: the Netherlands

PostPosted: Wed Aug 30, 2017 4:10 am    Post subject: Reply with quote  Mark this post and the followings unread

pin 2 on IC 3a may be considered as a "virtual earth summing point" of the inverting amp built with it (http://www.electronics-tutorials.ws/opamp/opamp_2.html)
so that being (around) 0V should be OK.

That being said, I am surprised by the -3.3 V at the pin 6, since IC 3b is also an inverting amp
Back to top
View user's profile Send private message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Wed Aug 30, 2017 4:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks!

Yes, I realised this later on that pin 2 on IC 3A would be pushed towards ground by the feedback resistor, was a bit tired there after troubleshooting several hours and I'm just learning about all this Smile

By twisting the Coarse pot I can get from -0.3V to +0.25V on IC3A output pin 1.

IC3B pin 6 is actually around -3.8V now (I've twisted pots and exchanged the 3906:s so maybe because of that)

>That being said, I am surprised by the -3.3 V at the pin 6, since IC 3b is also an inverting amp

Could you elaborate on that? I'm still trying to understand how this circuit should work Smile

There's around 10V on the output from that opamp, but there's a cap going from the output to the inverting input so no DC coming through there.
Back to top
View user's profile Send private message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Wed Aug 30, 2017 6:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Ngh!

After doing more and more troubleshooting and exchanging components to see if anything was borked, I now have something entirely different and no oscillation from the 555 at all:


mearurements 2.jpg
 Description:
New measurements…
 Filesize:  678.87 KB
 Viewed:  114 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

mearurements 2.jpg


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



Joined: Sep 29, 2006
Posts: 8
Location: the Netherlands

PostPosted: Wed Aug 30, 2017 6:24 am    Post subject: Reply with quote  Mark this post and the followings unread

hedefalk wrote:

Could you elaborate on that? I'm still trying to understand how this circuit should work Smile

There's around 10V on the output from that opamp, but there's a cap going from the output to the inverting input so no DC coming through there.


The DC current flows through R23 and Q2, by the way since this is a PNP transistor with the base at 0 V, the emitter should measure something like + 0.7 V, so the -10.5 V also surprises me
Back to top
View user's profile Send private message
gdavis



Joined: Feb 27, 2013
Posts: 359
Location: San Diego
Audio files: 1

PostPosted: Wed Aug 30, 2017 8:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

hedefalk wrote:
Ngh!

After doing more and more troubleshooting and exchanging components to see if anything was borked, I now have something entirely different and no oscillation from the 555 at all:


Check IC3 and it's connections. Pins 8, 9 and 10 should all be the same voltage.

_________________
My synth build blog: http://gndsynth.blogspot.com/
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3923
Location: Germany
Audio files: 23

PostPosted: Thu Aug 31, 2017 12:39 am    Post subject: Reply with quote  Mark this post and the followings unread

hedefalk wrote:
Could you elaborate on that? I'm still trying to understand how this circuit should work Smile

as i see it this is a clever approach of the classic integrator(IC2A)/comparator(IC3C) VCO with C4 being the timing cap, only that the switching is done by the 555 (ISO a JFET).

BTW how did you measure the voltages? It would not make much sense to measure the voltage with a DMM at pins IC3C/p8&9 and IC1/p2&6 since this is where the actual core oscillation happens. Or do you have a scope for the measurements?

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
alanwilder81



Joined: Sep 03, 2016
Posts: 325
Location: italy

PostPosted: Thu Aug 31, 2017 1:26 am    Post subject: Reply with quote  Mark this post and the followings unread

hey mattias Smile
i am trying to make sense of my 555 VCO ouput levels.
Why can't AC saw,tri, square and sin be measured with a DMM ?

I do have an old scope, but the grid doesn't show numbers nor reference points to get a quantitative measurement.


I can only observe a consistent waves ampliture across the whole frquency spectrum, yet, if the voltages are measured with th DMM ,they considerably vary from 2 V to 4 V roughly Very Happy
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3923
Location: Germany
Audio files: 23

PostPosted: Thu Aug 31, 2017 2:17 am    Post subject: Reply with quote  Mark this post and the followings unread

alanwilder81 wrote:
hey mattias Smile
i am trying to make sense of my 555 VCO ouput levels.
Why can't AC saw,tri, square and sin be measured with a DMM ?

it could, but what would the reading tell you? you would see the RMS reading, however, you could not tell if there is an oscillation or not.

my idea is: maybe one cannot hear the VCO module on it´s actual outputs because there is something wrong between the core and the outputs. i would start from the inside to the outside and make sure that the core is working.

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Thu Aug 31, 2017 2:25 am    Post subject: Reply with quote  Mark this post and the followings unread

gdavis wrote:

Check IC3 and it's connections. Pins 8, 9 and 10 should all be the same voltage.


They are not. non-inverting input (pin 10 is negative close to ground, -0.2V and and 8, 9 (output and inverting input) are saturated pos on around +10.3V it seems. Why should they be the same? There's no feedback resistor?

This circuit is really hard to understand for me, I guess it was probably not the best thing to start with as a newb Smile
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3923
Location: Germany
Audio files: 23

PostPosted: Thu Aug 31, 2017 2:30 am    Post subject: Reply with quote  Mark this post and the followings unread

you read my post above?
_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Thu Aug 31, 2017 2:33 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
hedefalk wrote:
Could you elaborate on that? I'm still trying to understand how this circuit should work Smile

as i see it this is a clever approach of the classic integrator(IC2A)/comparator(IC3C) VCO with C4 being the timing cap, only that the switching is done by the 555 (ISO a JFET).

BTW how did you measure the voltages? It would not make much sense to measure the voltage with a DMM at pins IC3C/p8&9 and IC1/p2&6 since this is where the actual core oscillation happens. Or do you have a scope for the measurements?


I'm using this cheap ebay 18$ digital scope. I actually bricked my multimeter so I'm only using that scope to measure everything.

I HAD oscillation at one point on these pins but at 47kHz (could this be what a saturated +12V CV would give?) but at this point I have no oscillation, but around +10V constant.
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3923
Location: Germany
Audio files: 23

PostPosted: Thu Aug 31, 2017 3:12 am    Post subject: Reply with quote  Mark this post and the followings unread

are you powering this circuit from 12V or from 15V?

measuring the voltage on the control pin of the OTA is not that simple. this input is a current input. it normally sits on the negative supply and should go up just a little bit when you feed this circuit a CV.

anyways, maybe you should start from scratch with just the OTA, IC3C and the 555.
leave off the expo for a start, just connect a 100k pot (between +V and -V)with wiper via 56k to the OTAs control input.

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Thu Aug 31, 2017 3:19 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
are you powering this circuit from 12V or from 15V?

measuring the voltage on the control pin of the OTA is not that simple. this input is a current input. it normally sits on the negative supply and should go up just a little bit when you feed this circuit a CV.

anyways, maybe you should start from scratch with just the OTA, IC3C and the 555.
leave off the expo for a start, just connect a 100k pot (between +V and -V)with wiper via 56k to the OTAs control input.


I'm using 12V (eurorack)

Thanks, I'll try that! Sorry if stupid question, but that's the amp bias input you mean on the OTA? Pin 1?
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3923
Location: Germany
Audio files: 23

PostPosted: Thu Aug 31, 2017 3:27 am    Post subject: Reply with quote  Mark this post and the followings unread

yes, pin1.

and if you measured -12V on the OTAs pin1 then this is the negative supply. i think it is a safe bet that you either got no control voltage/current to this pin (see my post above), or that your OTA is fried.
pin1 (pin 16 resp) sitting on the negative supply no matter what you do is a safe sign for a dead LM13700.

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
alanwilder81



Joined: Sep 03, 2016
Posts: 325
Location: italy

PostPosted: Thu Aug 31, 2017 3:58 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks Mattias,
I can hear my VCO oscillating and sounds awesome.
The waves look perfect on the scope.

i am trying to find a way to measure their amplitude.
and trying to understand why, when sweeping the coarse tune knob, my regular DMM reads a voltage fluctuation, while the oscilloscope shows a perfectly consistent amplitude Very Happy

so , i believe DMM is not right to measure AC ?
cheers
Back to top
View user's profile Send private message
hedefalk



Joined: Aug 29, 2017
Posts: 49
Location: Stockholm, Sweden

PostPosted: Thu Aug 31, 2017 3:59 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm more and more expecting these cheap Chinese breadboards I'm using…

And yes the OTAs pin 1 stays at -12V no matter what. I'm into my third LM13700, I'll try one more (only have 5) before I rebuild from scratch. Not good if my current setup is instantly frying those chips Smile

I did what you suggested with the current one though. I have triangle oscillation in OTA pin 5. YEY! And I can control the frequency with the 100k pot. I'll probably just sit here and twist that knob all day - this is the first time I've heard anything, been just watching that scope for a few days Smile

Still, the OTA pin1 is constant -12V. So the voltage drop over the 56k resistor is the whole diff between anything I turn the pot voltage divider to. Anything from -12 to +12 and the other side of the resistor is still -12K. You sure about the OTA being dead then?

By the way, when I probe pin 1 with the scope, the tone rises a couple of octaves - I guess the scopes impedance isn't very high? Or is this just the case since this is a current input?

Thanks a lot for all the help
Back to top
View user's profile Send private message
alanwilder81



Joined: Sep 03, 2016
Posts: 325
Location: italy

PostPosted: Thu Aug 31, 2017 4:15 am    Post subject: Reply with quote  Mark this post and the followings unread

and thanks foe explaining the topology of the VCO.
so the core can be narrowed down to the mere 13700, 555 and IC 3 c ?
how do i go if i want to leave out the hard sync ? leave the 555 pin 4 unconnected ? Smile
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3923
Location: Germany
Audio files: 23

PostPosted: Thu Aug 31, 2017 4:18 am    Post subject: Reply with quote  Mark this post and the followings unread

hedefalk wrote:
I did what you suggested with the current one though. I have triangle oscillation in OTA pin 5. YEY! And I can control the frequency with the 100k pot. I'll probably just sit here and twist that knob all day - this is the first time I've heard anything, been just watching that scope for a few days Smile

now this is a starting point, isn't it?
so you just have to re-build the expo section now. make sure that you have the transistors in the correct pinout and orientation. if you are in doubt refer to the datasheet, or take a look here:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

Quote:
Still, the OTA pin1 is constant -12V. So the voltage drop over the 56k resistor is the whole diff between anything I turn the pot voltage divider to.

the 56k converts the voltage to a current that is suitable for the OTA (Ohm's Law). remember, the OTAs bias input works with current, not with voltage.

Quote:
Anything from -12 to +12 and the other side of the resistor is still -12K. You sure about the OTA being dead then?

IIRC one expects just a tiny change in the mV range. maybe you simply cannot see it on the scope with the current setting.

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
fonik



Joined: Jun 07, 2006
Posts: 3923
Location: Germany
Audio files: 23

PostPosted: Thu Aug 31, 2017 4:21 am    Post subject: Reply with quote  Mark this post and the followings unread

alanwilder81 wrote:
and thanks foe explaining the topology of the VCO.
so the core can be narrowed down to the mere 13700, 555 and IC 3 c ?
how do i go if i want to leave out the hard sync ? leave the 555 pin 4 unconnected ? Smile

do as hedefalk did, use the 4k7 (R15) pull-up resistor.

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
fonik



Joined: Jun 07, 2006
Posts: 3923
Location: Germany
Audio files: 23

PostPosted: Thu Aug 31, 2017 4:24 am    Post subject: Reply with quote  Mark this post and the followings unread

alanwilder81 wrote:
thanks Mattias,
I can hear my VCO oscillating and sounds awesome.
The waves look perfect on the scope.

i am trying to find a way to measure their amplitude.
and trying to understand why, when sweeping the coarse tune knob, my regular DMM reads a voltage fluctuation, while the oscilloscope shows a perfectly consistent amplitude Very Happy

so , i believe DMM is not right to measure AC ?
cheers

a DMM has a ~V function, however, it does not help, when you even don't know if it oscillates at all.

i use my scope to measure the amplitude. for our simple synth DIY tasks a cheap USB scope is enough, i believe.

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic Moderators: Scott Stites
Page 12 of 16 [377 Posts]
View unread posts
View new posts in the last week
Goto page: Previous 1, 2, 3, ..., 10, 11, 12, 13, 14, 15, 16 Next
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software » Thomas Henry designs
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