MFOS VCO wiring issue

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

Moderators: Kent, Joe., analogdigital, infradead, lisa, parasitk, plord, sduck

Post Reply
User avatar
haricots
Droppin' Loads
Posts: 1501
Joined: Fri Jun 06, 2008 2:32 pm
Location: Chelsea & Cowansville, QC, Canada

MFOS VCO wiring issue

Post by haricots » Wed Aug 06, 2008 11:01 am

So I've slapped together my MFOS VCO kit from Bridechamber but I'm having an issue. The output is really quiet until I touch any metal part (jack, back of pots, stooge plate) with a jack coming out of my powered Blacet rack. I'm assuming that this is some sort of grounding issue.

From the pic below you can see all the jacks are grounded together starting at CV1 and ending at the Sync jack. Should there not be a connection to ground from the Sync jack to the board somewhere? I don't get how this works. I assume the pots are grounded to the board through either lug 1 or 3.

Image

A couple of the pots that Bridechamber added to the circuit (see below pic - noting changes) are grounded to the extra ground holes on the circuit board. Now I have no idea if I have done this correctly but I have noticed when testing the circuit there does not seem to be continuity between all the grounds.

Image

Any help would be appreciated!!
Last edited by haricots on Fri Aug 15, 2008 2:52 pm, edited 2 times in total.

User avatar
futuresoundsystems
<3 CMOS
Posts: 1033
Joined: Thu May 15, 2008 11:42 am
Location: Bristol, England
Contact:

Re: MFOS VCO wiring issue

Post by futuresoundsystems » Wed Aug 06, 2008 11:05 am

haricots wrote:Should there not be a connection to ground from the Sync jack to the board somewhere?
There definitely is supposed to be a connection back to ground on the PCB.
Unique designs and ideas in sound since 2005:
http://www.futuresoundsystems.co.uk

User avatar
johnnymad
turbo wiggler
Posts: 1107
Joined: Wed Jul 09, 2008 9:55 pm
Location: Baton Rouge, Louisiana

Re: MFOS VCO wiring issue

Post by johnnymad » Wed Aug 06, 2008 1:45 pm

futuresoundsystems wrote:There definitely is supposed to be a connection back to ground on the PCB.
i don't think so. i've built three of these and they all work wired that way. i did ground the panel by connecting ground to a screw drilled through the front panel.

User avatar
haricots
Droppin' Loads
Posts: 1501
Joined: Fri Jun 06, 2008 2:32 pm
Location: Chelsea & Cowansville, QC, Canada

Post by haricots » Wed Aug 06, 2008 4:00 pm

Hmmm, so I assume the Sync jack is then grounded to the faceplate then?

User avatar
eyehue
High Desert
Posts: 246
Joined: Tue Jul 08, 2008 2:45 am
Location: flagstaff, arizona

Re: MFOS VCO wiring issue

Post by eyehue » Wed Aug 06, 2008 4:11 pm

futuresoundsystems wrote:
haricots wrote:Should there not be a connection to ground from the Sync jack to the board somewhere?
There definitely is supposed to be a connection back to ground on the PCB.
i agree.

there are several extra ground pads on the pcb, run a wire from one to either end of the jack green ground wires shown in the pic. the pots are fine as is. i've built one of these and this is how i wired it, works great. it's good practice, too, this way you could build one in a wood case or on a lexan panel also. when using all metal plates and racks, it is also a good practice to have them grounded already in the method johnnymad described.

User avatar
haricots
Droppin' Loads
Posts: 1501
Joined: Fri Jun 06, 2008 2:32 pm
Location: Chelsea & Cowansville, QC, Canada

Post by haricots » Wed Aug 06, 2008 4:29 pm

Thanks for the help people!

The bridechamber version of this VCO has a couple extra pots which I've already grounded to the extra ground pads on the pcb. Can I simply insert the jack ground in there too (twist two wires together)? Or do pots generally not need to be grounded if there isn't an audio signal going through it. Sorry for the lack of understanding but I'm trying to wrap my head around these concepts .... :confused:

User avatar
eyehue
High Desert
Posts: 246
Joined: Tue Jul 08, 2008 2:45 am
Location: flagstaff, arizona

Post by eyehue » Wed Aug 06, 2008 4:36 pm

depending on the function, not all pots require ground. however, the body of the pots may be grounded simply by being in contact with the grounded face plate. i wouldn't bother adding extra wires to them, especially if your metal case and plates are grounded. i've seen some people actually ground the body of the pots (when using wood cases) by soldering a wire to the flat back of the pots, i don't think it's necessary here. i did not build the Bridechamber version, though, and he is a nice guy and i'm sure would answer an email from you about this situation.

oh, to answer your question, you should be able to connect your jack ground to the pot ground.

hope i am not just confusing the situation more.

User avatar
johnnymad
turbo wiggler
Posts: 1107
Joined: Wed Jul 09, 2008 9:55 pm
Location: Baton Rouge, Louisiana

Post by johnnymad » Wed Aug 06, 2008 6:40 pm

did you check all of your wiring? you might have a cold joint somewhere that's starving some of your jacks. my oscillator worked even without the panel grounded. grounding the panel just kept it from buzzing whenever it was touched.

User avatar
neandrewthal
full clout y'all
Posts: 3682
Joined: Fri Jul 25, 2008 10:30 pm
Location: Spending warm summer days indoors writing frightening verse to a buck-toothed girl in Luxembourg

Re: MFOS VCO wiring issue

Post by neandrewthal » Thu Aug 07, 2008 2:33 am

haricots wrote: The output is really quite until I touch a any metal part (jack, back of pots, stooge plate) with a jack coming out of my powered Blacet rack.

This would lead me to believe that you need to ground the jacks to the PCB (or anything which is grounded to the PCB) because they are not grounded as is but when you plug in a cable from your blacet rack you are grounding them through your blacet power supply since all the jacks in your blacet modules are grounded.
haricots wrote: I assume the pots are grounded to the board through either lug 1 or 3.
The only pots that should be connected to ground are the 3 "extra" ones on the bridechamber panels. They are attenuators so lug 1 of each should be grounded so your CV input signal is completely sucked to ground when the pot is fully counter-clockwise.

User avatar
haricots
Droppin' Loads
Posts: 1501
Joined: Fri Jun 06, 2008 2:32 pm
Location: Chelsea & Cowansville, QC, Canada

Post by haricots » Fri Aug 08, 2008 2:18 pm

well, it looks like i grounded the wrong lugs. i thought this was standard but i guess not. i moved all the grounds to the proper lugs on the sockets but now i cannot get it to produce a sound at all. very frustrating!!! :help:

i have confirmed that power is flowing but the signal is lost. i wonder if i fried a component. :(

here's an embarrassingly noobish question - you know how on most circuit boards there are extra holes used for probing? i for some reason assumed these all could be used as grounds. i had grounded the jacks to one of these said holes - could I have fried something this way? :doh:

jeebus i need to take a course or something. i'll never get my x0xb0x built at this rate.

User avatar
neandrewthal
full clout y'all
Posts: 3682
Joined: Fri Jul 25, 2008 10:30 pm
Location: Spending warm summer days indoors writing frightening verse to a buck-toothed girl in Luxembourg

Post by neandrewthal » Sat Aug 09, 2008 1:21 am

haricots wrote:
i have confirmed that power is flowing but the signal is lost. i wonder if i fried a component. :(
I would suggest swapping all the chips (if you have spares) and if that doesn't work, build Ray's signal tracer shown here
then listen at pin 1 and 7 of U4(TL084) You should get a ramp and saw wave respectively. If not and your chip is good then your problem is in the oscillator core section. If yes, then your problem is in the waveshapers. Either way, it narrows down your search.
haricots wrote: here's an embarrassingly noobish question - you know how on most circuit boards there are extra holes used for probing? i for some reason assumed these all could be used as grounds. i had grounded the jacks to one of these said holes - could I have fried something this way? :doh:
I think you mean the holes that go through the board to connect the traces on the top and bottom together. I don't think you'd fry anything this way, but I've had a lot of chips that don't work for no apparent reason. I use sockets, so I never overheated them with the soldering iron. Maybe static? Anyway, that's why I like to swap out the chips before I go too crazy troubleshooting, usually works for me.

Disclaimer: I am no electronics genius (as you probably know from the way I fucked up your memory man) but I do know my way around this circuit, as I've spent a good deal of time troubleshooting it myself)

User avatar
Kwote
Voltage Controlled Crackpot
Posts: 3107
Joined: Fri Oct 26, 2007 3:24 pm
Location: SF Bay Area

Post by Kwote » Sat Aug 09, 2008 1:55 am

neandrewthal wrote:Disclaimer: I am no electronics genius (as you probably know from the way I fucked up your memory man)
LOL
Self expression is as essential as breathing
kwotemusic.com
my other sites

User avatar
haricots
Droppin' Loads
Posts: 1501
Joined: Fri Jun 06, 2008 2:32 pm
Location: Chelsea & Cowansville, QC, Canada

Post by haricots » Sat Aug 09, 2008 9:12 am

Thanks neandrewthal. I have a signal tracer (from BYOC) so I'll give it a try. I was hoping there was a way to hear the output of a chip this way. Now let's hope I built the tracer correctly as it was my second project ever and I was a lot shittier at this back then (hard to believe, hehe). Of course I opted not to use sockets which will bite me in the ass now. Oh well.

Did you get your Memory Man back yet? I have two things with him still that have been sitting there for 1.5 yrs now. :eek:

User avatar
futuresoundsystems
<3 CMOS
Posts: 1033
Joined: Thu May 15, 2008 11:42 am
Location: Bristol, England
Contact:

Re: MFOS VCO wiring issue

Post by futuresoundsystems » Sat Aug 09, 2008 2:21 pm

johnnymad wrote:
futuresoundsystems wrote:There definitely is supposed to be a connection back to ground on the PCB.
i don't think so. i've built three of these and they all work wired that way. i did ground the panel by connecting ground to a screw drilled through the front panel.
Strange, obviously you should ground the front panel but I would've thought there'd be ground back to the actual PCB too... I'll be building some MFOS modules soon, it'll be interesting seeing how Ray's done this.
Unique designs and ideas in sound since 2005:
http://www.futuresoundsystems.co.uk

User avatar
haricots
Droppin' Loads
Posts: 1501
Joined: Fri Jun 06, 2008 2:32 pm
Location: Chelsea & Cowansville, QC, Canada

Post by haricots » Fri Aug 15, 2008 2:49 pm

Is it normal for the bracket to be grounded? My continuity tester shows a connection between ground and the bracket itself. Also all the pot cases seem to show a ground signal except for one (PW) - seems odd but what do I know.

I've gotten a little further with troubleshooting this VCO. This is what's outstanding:

1) I cannot get a Sine output. Does anyone know what IC/pins I can test for this signal?

2) Tuning seems a little odd - the last 1/3 of the pot is the only usable area. I'm finding it impossible to get a nice tuned spread using the VC trimmer. I didn't install the optional HF VC trimmer circuit because it scares me.

3) I think I have the PW and PWM pots mixed up.

Yeah, I suck. :hihi: I swear this isn't the first thing I've built but man o man am I having trouble with this one. :bang:

User avatar
johnnymad
turbo wiggler
Posts: 1107
Joined: Wed Jul 09, 2008 9:55 pm
Location: Baton Rouge, Louisiana

Post by johnnymad » Fri Aug 15, 2008 2:52 pm

have you tried tweaking the two or three sine trimpots? one or more may be turned down all the way.

User avatar
haricots
Droppin' Loads
Posts: 1501
Joined: Fri Jun 06, 2008 2:32 pm
Location: Chelsea & Cowansville, QC, Canada

Post by haricots » Fri Aug 15, 2008 2:54 pm

I did in fact. I thought for sure it would the Sine Lvl trimmer. I should test for resistance on that one tonight.

User avatar
johnnymad
turbo wiggler
Posts: 1107
Joined: Wed Jul 09, 2008 9:55 pm
Location: Baton Rouge, Louisiana

Post by johnnymad » Fri Aug 15, 2008 2:57 pm

crap. i thought that would fix it. maybe you should leave it alone for a while and come back. it might be something so simple that you can't see it.

Post Reply

Return to “Music Tech DIY”