Home Built Small Stone (CA3080) not phasing....

[bryantabuteau]

Hi,

I put together a small stone clone based on the schems and pcb layouts from the tonepad site (using 5 CA3080 OTA).  This was a few years ago.  It didn't work first off, and it got cast aside for a while.  I've finally got around to learning a bit more about electronics and built a few simpler things, and now i'm back trying to get this to work.  

1.  The switching all works fine.  Thats been tested.
2. When switched on, the signal goes thorugh the circuit but is unaffected.
3.  I traced it through with an audio probe and the signal is going through both halves of the circuit, it looks like it sort of mixes the affected side and the non-affected side.

I've got voltages for the ICs :
IC1-IC4
approx :
1:0
2:3.4
3:3.4
4:0
5:0.75
6:4-4.5  - changes
7:7.7-8.6 - changes
8:0

IC5
approx :
1:0
2:2.7-7 changes
3:2.4-7 changes
4:0
5:0.6
6:6.7
7:7.2-8 changes
8:0


those are all approx, and I imagine they change with the rate knob,
but can anyone tell me if any of those are completely off, so I can track down what the error may be?

[puretube]

well, the LFO seems to work!
with a link to the circuit, you`d probably soon get some help from London...
:wink:

(iirc, it`s that circuit with the 2 transistors after each OTA? - pinout? -
the smallstone will always put some signal out, even with the shifters not working...).

[petemoore]

What took me a while to figure out is, two of the arrows in the transistors circles on the schematic point the other way, indicating where the two PNP transistors go and to make sure all the emitters go where the arrows indicate. I believe I used 2n3904's. And two 2n5087's for the PNP's.

[bryantabuteau]

Thanks, I'll double check all my transistor orientations, I'm using 2N5087 and 2N5088 transistors for the circuit, and it is the one with the two transistors following the output of the CA3080s.  I can't link to the schematic I used, since its from the tonepad site, and they are stored as pdfs retrieved by scripts to prevent deep linking.  Maybe I could find a similar schem elsewhere though....

The pinout of the CA3080 is :

NC | 1   8| NC
-IN | 2   7| V+
+IN | 3   6| OUT
 V- | 4   5| Bias Current

the circuit has the LFO connected to pin 5 (bias current), and this seems to be working.  V+ is consistently high, tho it does seem to change, which doesn't make sense to me according to the circuit.  V- is consistently 0 which is, I assume correct given a 0v ground reference.  -IN and +IN both seem to be very close in value, not knowing exactly what this chip does, I'm not sure whether that should be correct, because the -IN is connected in a feedback loop to OUT, I imagine it should be slightly different.  Maybe it is, and my voltage measurements are too clunky for the differences that should exists.


heres the link to the layouts and schematics I'm using :
http://www.tonepad.com/project.asp?id=11

datasheet for CA3080
http://www.chipcatalog.com/Intersil/Datasheet/CA3080.htm

[puretube]

test:
http://www.tonepad.com/getFile.asp?id=7
:?:

[bryantabuteau]

Okay, I've made some progress....

I had 2 transistors in the wrong position.  I blame the original schem that didn't have part numbers marked  I swapped them out (NPN to PNP and vice versa) and now I have some phasing going on   With the colour switch one way i've got a repetitive high pitch whine, and with it the other way, I get a subtle phasing effect.  Not much 'depth' to it.  SOunds like the effected signal is not getting boosted enough compared to the unaffected signal its getting mixed with.  My next check is gonna be the two transistors following each CA3080 and resistor values all over the board.    Am I headed in the right direction?

[puretube]

that was xactly what I meant with "pinout": the right tr. at the right place in the right orientation pinned out correctly.
(I`s not looking for IC`s data... )

wish ya success!!!

[bryantabuteau]

Rockin.  I corrected some silly non grounding of my output jack and now I have a very nice phaser.  Sounds great.  Flicking the color switch results in some VERY lound siren type effects, and thats what i'll concentrate on fixing next, but that standard phase works great.

[puretube]

check the Rs to the right of Q10 in the schem;
is the 4k7 really going to ground?
is the 27k really 27k or rather 2k7?

[StephenGiles]

Ah, is the 27k really 27k or 2k7 - been there and got the teeshirt Ton!! This illustrates my rule number 1 - build in good light, preferably daylight! There have been many occasions when bad light has resulted in wrong components being used, most notably on the output to ground where I had 4R7 instead of 47k - I probably needed stronger glasses as well!
Stephen

[bryantabuteau]

Cool...

I checked all the resistors over and over, but I hadn't made any mistakes.  I decided to implement an anti volume drop mod(or an anti ticking one, i can't recall) I read somewhere while I was at it, and changed R11 (the 3k3 resistor off the emmitter of Q10) to 10K.  This fixed the problem.  The phaser sounds sweet now.  Very different to the Reissue Phase 90 I have when the colour switch is engaged, so It should be lotsa fun finding some new uses in some new songs.

THank you to everyone who gave me suggestions and helped troubleshoot.  It was greatly appreciated.

Next up....A nice simple tremelo.  Or maybe an Octave Up Thingy.