VCO2100 Mod - AC/DC FM Coupling Selector

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Muff Wiggler
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VCO2100 Mod - AC/DC FM Coupling Selector

Post by Muff Wiggler » Sun Aug 19, 2007 12:40 am

The original design of the VCO2100 has an FM input that is AC coupled for use with audio signals. For those who would also like to use DC coupling, Blacet has thoughtfully included circuitry on the PCB that makes it very easy to add a switch to select between the two - this circuitry is done, you simply need to add the switch.

To perform this modification, simply connect an SPST switch between the two points on the PCB labelled "OPT". These points are located just below the C2 capacitor, near the pots at the edge of the board. As easy as it gets. AC coupling for audio signals, DC coupling for slower moving control voltage signals.

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Post by Muff Wiggler » Wed Apr 02, 2008 12:52 am

ok, took some pics to make it easier.

Step 1: Take the module out of your rack, and remove the power connector. Next, remove the faceplate and drill a hole to mount your switch. Or be like me and just drill it out without removing the faceplate, or any wires or jacks. Scary.

Mount an SPST switch in the hole, and make a fancy label if you want.

Image

Step 2: Look at the component side of the PCB, and locate the two empty holes labelled "OPT". They are circled in red in the below photo. On your unmodified board, these will be clean holes and will not have the solder that is shown in my pic.

Image

Step 3: From the underside of the PCB (the opposide side to what you used to locate the OPT holes in the previous step), push two wires up through the two empty OPT holes. Solder them to the two lugs of your switch as shown in the photo below. Flip the board over and solder the ends that poke out onto the component side, so you'll now have the two solder blobs as shown in the above photo.

Image

Take out your multimeter and check continuity between both sides of the PCB and your new wires, as well as between the solder point at the component side of the PCB and the corresponding lug on the SPST switch.

You are done - enjoy.

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Post by Kwote » Wed Apr 02, 2008 1:17 am

solid. it doesn't get any clearer than that. thanks!
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Post by Muff Wiggler » Wed Apr 02, 2008 1:23 am

my pleasure 8) this is certainly the very easiest mod to get started with, and a good confidence boost. Very simple mod with very little chance to damage anything in the process.

Only hairy part is drilling that hole - unless you are patient and remove all the jacks (the pots are very easy to remove and re-attach being PCB mounted) to get the faceplate free - then it's a breeze. I'm not that patient, I've modded 4 of them and I've always done the seat-of-the-pants drill-between-the-wires-and-be-careful-for-the-pcb job. Probably not a good idea.

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Post by Kwote » Wed Apr 02, 2008 1:26 am

yeah. no way i'd do that. i don't have any issue taking the faceplate off. if i can put it on i can certainly take it off. 8)
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Post by Muff Wiggler » Wed Apr 02, 2008 1:33 am

reposted from the other thread, but very important info on drilling and panel removal, I want it here as well in case anyone is reading this thread, misses the other one (the LFO thread) and embarks on some panel drilling.....

-------------------

Modules with 'flying wire' jacks, like the VCO and most of the other 2U-wide modules will be harder to take the faceplate off, because of all the jumble of jacks-on-wires you will end up with (and don't lose track of which jack is which!). I've always done the risky thing and drilled those without removing the panel. Patience is good though.

The panels drill very easily - I don't have a vice, I've only ever used a hand to hold the module down while I drilled it, just holding the faceplate down on a piece of wood. Make sure you have a proper drill. I only have a hand-drill, not a press, and as stated no vise or clamps. I think this is OK, but *do* have a proper power drill. I don't recommend trying this using a drillbit in a power screwdriver.

PLEASE NOTE -

A *VERY* important piece of advice for drilling panels - *ALWAYS* start with the smallest possible drillbit you have, and make a pilot hole. Then work your way up to the right size by using larger and larger drillbits. Far easier to control and less messy and more accurate this way. TRUST ME.

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Post by consumed » Wed Apr 02, 2008 8:43 am

having drilled and fucked up a few original (and unreplaceable) stooge panels myself, i would suggest the following:

1. get and use a center punch. this establishes the 'dent' that will become your initial pilot hole. a center punch only requires a hammer.

2. take your time, beginning with a tiny pilot hole.

3. remove your faceplate and screw it down to a piece of wood/plywood face up before drilling. this will secure the faceplate and reduce the possibility of having your finger tore up or torn off when the drillbit snags and spins your faceplate around with it.

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Post by Kwote » Wed Apr 02, 2008 10:40 am

consumed wrote:having drilled and fucked up a few original (and unreplaceable) stooge panels myself, i would suggest the following:

1. get and use a center punch. this establishes the 'dent' that will become your initial pilot hole. a center punch only requires a hammer.

2. take your time, beginning with a tiny pilot hole.

3. remove your faceplate and screw it down to a piece of wood/plywood face up before drilling. this will secure the faceplate and reduce the possibility of having your finger tore up or torn off when the drillbit snags and spins your faceplate around with it.
great advice. i think i'll probably end up getting a vice or clamp too. in the long run i think getting the proper tools pays off.

i'll just clamp the wood down to ensure everything goes smoother.
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Post by Muff Wiggler » Wed Apr 02, 2008 11:03 am

that is seriously good advice - while Blacet panels are far thinner and easier to drill than Stooge panels are - it's still very wise advice....

i'm impatient and lazy and often take many unnecessary risks because of it. don't be like me.

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Post by Kwote » Wed Apr 02, 2008 11:10 am

Muff Wiggler wrote:that is seriously good advice - while Blacet panels are far thinner and easier to drill than Stooge panels are - it's still very wise advice....

i'm impatient and lazy and often take many unnecessary risks because of it. don't be like me.
just don't lose a finger on us bro :lol:

i don't wanna have to start callin you stubby wiggler.
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Post by Cat-A-Tonic » Sun Dec 06, 2009 7:40 am

An SPST switch is essentially an on/off,
and an SPDT is an on-A/on-B, right?

So if you only wire the inner lug and one side lug of an SPDT,
but leave the other side unconnected...
does it operate as an SPST?

In this VCO mod, is the switch merely taking a capacitor out of the circuit for DC coupling (switch off),
and capacitor in circuit for AC coupling (switch on)?

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Post by BugBrand » Sun Dec 06, 2009 7:56 am

Cat-A-Tonic wrote:An SPST switch is essentially an on/off,
and an SPDT is an on-A/on-B, right?

So if you only wire the inner lug and one side lug of an SPDT,
but leave the other side unconnected...
does it operate as an SPST?

In this VCO mod, is the switch merely taking a capacitor out of the circuit for DC coupling (switch off),
and capacitor in circuit for AC coupling (switch on)?
Yup -- personally I never buy SPST switches -> just buy SPDT because they can be used as SPST and the price difference ain't much.

So, yeah, with the switch one-way in this case you'll have the cap in-circuit, while switching it the other way will short-out the cap (ie take it out of circuit)

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Post by Cat-A-Tonic » Sun Dec 06, 2009 8:04 am

Thanks again Tom!

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