Really Cheap Compressor

jrc4558 · Post by **jrc4558** » 13 Apr 2010, 16:55

Another pcb for this one. If you guys want, I can post the ExpressPCB file for it.

mictester · Post by **mictester** » 13 Apr 2010, 18:01

The original .zip file I posted had a Vero and a PCB, both of which were quickly done in DIY Layout Creator, on a Tube train, in London, on the way to work! Here's the PCB (which I've made several times):

: Really Cheap Compressor PCB.gif (18.47 KiB) Viewed 2528 times

It's pretty small, has the option of board-mounted pots, and allows a light shield to be fitted over the LEDs and LDR.

Enjoy!

soggybag · Post by **soggybag** » 13 Apr 2010, 18:52

Those are nice layouts. How do you mate the LEDs and the LDR? Do face them both at the LDR one over the top of the other. Should the LEDs be as close to the LDR are possible?

jrc4558 · Post by **jrc4558** » 13 Apr 2010, 19:15

Just put a pair of LEDs and an LDR into same piece of heatshrink tubing. make sure the contraption is lightproof. That should do it.

mictester · Post by **mictester** » 13 Apr 2010, 19:24

soggybag wrote:Those are nice layouts. How do you mate the LEDs and the LDR? Do face them both at the LDR one over the top of the other. Should the LEDs be as close to the LDR are possible?

The LEDs are stacked above each other, and point straight at the face of the LDR. On a few builds, I used pairs of rectangular LEDs that I had from another project, and I glued them together as a dual, bi-directional LED!

dune2k · Post by **dune2k** » 13 Apr 2010, 19:30

mictester wrote:
soggybag wrote:Those are nice layouts. How do you mate the LEDs and the LDR? Do face them both at the LDR one over the top of the other. Should the LEDs be as close to the LDR are possible?
The LEDs are stacked above each other, and point straight at the face of the LDR. On a few builds, I used pairs of rectangular LEDs that I had from another project, and I glued them together as a dual, bi-directional LED!

Hm...nice idea!

mictester · Post by **mictester** » 13 Apr 2010, 19:49

dune2k wrote:
mictester wrote:
soggybag wrote:Those are nice layouts. How do you mate the LEDs and the LDR? Do face them both at the LDR one over the top of the other. Should the LEDs be as close to the LDR are possible?
The LEDs are stacked above each other, and point straight at the face of the LDR. On a few builds, I used pairs of rectangular LEDs that I had from another project, and I glued them together as a dual, bi-directional LED!
Hm...nice idea!

Thanks.

I don't usually bother with the heatshrink - I just use a light-tight diecast box!

YuGi · Post by **YuGi** » 18 Apr 2010, 12:24

Hi,
the right LED type is green standard or transparent body?

mictester · Post by **mictester** » 18 Apr 2010, 18:56

YuGi wrote:Hi,
the right LED type is green standard or transparent body?

It doesn't matter much. Either green or yellow LEDs work OK - I've used clear ones and coloured ones, with equally good results.

livingnote · Post by **livingnote** » 28 Apr 2010, 08:15

Okay, here's mine:

Really nice with the vactrol, and works just like that out of the box. Some small changes still to the
control board surface etc. (got both pots going in the wrong direction but otherwise fine) and it sounds
really "Sultans of Swing"...

The red LED is antiparallel to the vactrol, I decided I wanted to know what is actually going on in there
and was surprised that it isn't as bright as I thought it would be...but there you go.

Also it has this little power regulator inside that consists of a Graetz bridge, a coupla caps and a transistor
with a Zener to ground plus 1K "stabilize the base" leak resistor, so now you can't screw up polarity, power
it with anything up to about (possibly) 30V, even feed it AC and set the internal voltage to your taste with
the Zener diode.

Perhaps what would be interesting would be to branch off the output of the LED driver to something high-
impedance like ?maybe? a Mosfet so that you can get a kindofa "looking glass" LED on the front panel to
see what's going on inside the vactrol. You can get kinda deceived by the "transparent" action of the box,
and that would give you more of a feel for the actual circuit behavior.

mictester · Post by **mictester** » 28 Apr 2010, 13:40

Perhaps what would be interesting would be to branch off the output of the LED driver to something high-
impedance like ?maybe? a Mosfet so that you can get a kindofa "looking glass" LED on the front panel to
see what's going on inside the vactrol. You can get kinda deceived by the "transparent" action of the box,
and that would give you more of a feel for the actual circuit behavior.

Funny you should suggest that - it's exactly what I did to one at the weekend! I'll post the amendment to the schematic for the "optional indicator" here later - it's just a scribble on a piece of paper at the moment. I'll draw it up properly so that it's easy to read.

soggybag · Post by **soggybag** » 28 Apr 2010, 17:01

Very nice build. What type of vacrtrol is that? Does it contain two LEDs with one photocell? Hard to tell how many leads are coming out.

livingnote · Post by **livingnote** » 28 Apr 2010, 20:58

Thanks

It's a VTL5C3, not sure if there's better ones out there but I just had it lying around.

Got one LED in, the second one sticking up is to find out what now is actually going on in there
when you're not looking, but of course not much as it turns out, so here we go lightshow for the
front panel

soggybag · Post by **soggybag** » 28 Apr 2010, 21:53

I asked because both LEDs should be lighting the LDR. One would probably work. I assume it would be "smoother" with both LEDs. Since they each light on one half of the wave.

livingnote · Post by **livingnote** » 28 Apr 2010, 22:08

Absolutely - that was a point that was bugging me too about the whole construction with the vactrol.

One thought would be to basically paralleletize two vactrols and for that bump up the other feedback
resistor by a factor of 2-you could make the vactrols piggyback on each other. If that would create the
same effect as using one LDR and one vactrol I'm not certain of, but considering all the different spec
LDRs out there it's ears again

soggybag · Post by **soggybag** » 29 Apr 2010, 00:23

I think you could "roll" your own LED/LDR combo thing. Though it seems a little tricky to get both LEDs to light the LDR. I bet in practice this is not that critical. The tricky part is really getting them securely anchored so that dropping the thing doesn't knock them out of place.

mictester · Post by **mictester** » 29 Apr 2010, 01:01

soggybag wrote:I asked because both LEDs should be lighting the LDR. One would probably work. I assume it would be "smoother" with both LEDs. Since they each light on one half of the wave.

It doesn't matter too much - I found that two LEDs gave a bit more range of resistance change on the LDR, so that's why I used them. I built one for my nephew at the weekend, and that has a single LED, and works really well. The LDR was an ORP12, and I used a 7mm LED to cover the whole face of it.

mictester · Post by **mictester** » 29 Apr 2010, 01:04

soggybag wrote:I think you could "roll" your own LED/LDR combo thing. Though it seems a little tricky to get both LEDs to light the LDR. I bet in practice this is not that critical. The tricky part is really getting them securely anchored so that dropping the thing doesn't knock them out of place.

On my earliest builds, I used rectangular LEDs glued together, and then glued down to the PCB. The LDR was mounted to face the LEDs, and was also glued to the PCB to prevent it moving. I've also made others with the LED and LDR shrunk together inside a heatshrink tube.

livingnote · Post by **livingnote** » 04 May 2010, 23:22

Well it sure does work with the vactrol - I remember the "slow" response times of the vactrols were
one of the things that kinda screwed up using one for computer controlling stuff. That plus
serial spread and aging effects...

JOHNO · Post by **JOHNO** » 25 May 2010, 11:57

At the risk of looking stupid, what's going on here? If I compare the schem on the fist page of this thread to the PCB layout also on the first page, thing's dont look right to me. In the schem the 10k resistor is coming for pin 6 of the IC. But on the pcb its coming from pin 7. And the pot is wired differently. Does it all work the same? Could some one please enlighten me? Here is the part of the schem I'm reffering to as i see it on the pcb. Doesn't this make the pot work backwards?
Johno.

RCC schem.png

Really Cheap Compressor [documentation]