Colorsound Vocalizer vero

[digi2t]

OK... I've been thinking, how the hell are we sure that the tranny is shown in the right orientation in the schematic. I mean, the guy could have just taken it for granted that the emitter was on the 3K resistor side. Maybe the it's in the wrong way? I'm sending a PM to R.G.. The reason why I'm questioning this is because I was reading this article; www.geofex.com/pcb_layouts/layouts/d&rpub.pdf , when I noticed that the tranny feeding pin 5 of the 3080 isn't orientated the same way as the Vocalizer schem. 

Just had another thought... You're using conductive plastic pot, right? Check your pot as well. Maybe too much heat from the soldering iron?

Just a shot in the dark  

[pinkjimiphoton]

naah, the pot works the same as always.

but...the transistor?

i've tried every pnp i have. and it makes almost no difference which way the transistor is plugged in!!!!!!

silicon doesn't sound as good, ge sounds better and works better...probably cuz of the leakage. i tried a couple different ge pnp's, they all sounded the same...either way it seems to work the same...go figure!!

did you get them custom pots in yet bro?

[digi2t]

There shouldn't be a change in the audio, since the transistor is not in the audio path.

Also, seeing as how the diodes are silicon, would the tranny have to be silicon, germanium, or just any PNP tranny?

My best guess is that it needs to be silicon PNP. With silicon diodes setting the idle current (that's what they do) one of the diodes compensates for the base emitter drop of the transistor, and the other two force two silicon drops to appear across that 3K, resulting in a resting current of (0.6V +0.6V)/3K = 400uA from the transistor. The two pots raise the base, starving the diode chain, and lowering the current below that amount into the OTA.

I know you've been having a rough time with this one. One thing that comes to mind is that the 3080 is *very* fragile if you feed too much current into pin 5. If it goes over 1ma, they just quietly die. A probe short or a wrong hookup can kill them dead.

Could it be the 3080 is toast?

Are you getting any swing at the collector with the pedal movement? I think Boris mentioned something about checking pin 6 as well. Guess we'll wait and see.

[pinkjimiphoton]

checking now...

pin one

heel / toe 0v

2

heel   4.15  toe 3.93

3  same as 2

4  0

5  heel  .51   toe  .63

6  heel 4.15  toe 3.92

7  9.58

8   0


i'd say the 3080 chip is working.

4136n, same way, heel then toe

1  4.22   3.99

2  4.10    3.87

3   4/40     4.18

4   4.05   3.83

5  4.17    3.94

6   4:19   3.95

7   0

8   4.07  3.84

9  4.05    3.82

10   3.50   bounces around and settles 3.26

11  9.58

12   3.50   3.27

13   4.05   3.82

14   4.07  3.84


that seems to be working too.

mp16b

e  3.31   2.20

b  3.93  2.16

c  .61  2.30

so  .....what do you think bro?

[tiges_ tendres]

Transistor voltages look off to me.  Collector seems too low.

[pinkjimiphoton]

hmmm...this thing was working great til last nite, too.

tried a couple other transistors, they all read about the same.

[digi2t]

What are you getting for voltage either side of the 1K2 resistor (before purple wire)?

[pinkjimiphoton]

let me go check.

btw...check your facebook wall and your pm's there.   

[digi2t]

Thanks bro! That's for the Whine-O-Wah from what I can tell. If you follow the name of the file (SD-WW part).

Thanks for the Vocalizer stuff from Boris. I already had a PCB layout, but I can compare the two to make sure.

[pinkjimiphoton]

4.09 on the top rail, 4.01 on the second of r 17

[digi2t]

4.09 on the top rail, 4.01 on the second of r 17

Hmm, schem says we should see 4.7v on the top rail. 1N750A is a 4.7v Zener, so 4.7v should be present here, unless your battery is below 4.7v. I'm working on it. Gonna try to breadboard this next week.

[Ronan]

I was thinking the same...the battery voltage is 9.58V at pin 11 of the 4136. Looks like 0.5V has gone missing from the 4.7V supply. You got a 1N750 zener in there Jimi?

Another thing that may not be right is the voltage change on the collector of the tranny  (0.61V to 2.30V) does not appear at pin 5 of the 3080, there is only a change of 0.51V to 0.63V at pin 5. Unfortunately I am not familiar with the 3080, but it doesn't look right, from the datasheet, the typical bias current at pin 5 is 2 microamps, and the typical bias voltage at pin 5 is 0.7V, but we have 700 microamps (0.7mA) flowing through that R5 2K2 resistor with 0.63V at pin 5.

Such a mystery...

[pinkjimiphoton]

hmmmm...

i will look tomorrow at that diode, maybe it's popped?

it sounds like bad diode clipping.

the pedal still works as in passing signal with the 3080 pulled out, tried 4  4136's...all same.

also tried another pair of pnp's...makes no diff which way they are put in. really weird.

beginning to suspect the damn pot....conductive plastic may be too conductive

[ORK]

I was thinking the same...the battery voltage is 9.58V at pin 11 of the 4136. Looks like 0.5V has gone missing from the 4.7V supply. You got a 1N750 zener in there Jimi?

Another thing that may not be right is the voltage change on the collector of the tranny  (0.61V to 2.30V) does not appear at pin 5 of the 3080, there is only a change of 0.51V to 0.63V at pin 5. Unfortunately I am not familiar with the 3080, but it doesn't look right, from the datasheet, the typical bias current at pin 5 is 2 microamps, and the typical bias voltage at pin 5 is 0.7V, but we have 700 microamps (0.7mA) flowing through that R5 2K2 resistor with 0.63V at pin 5.

Such a mystery...

The OTA 3080 is being controlled by a current going into the control pin5. Not by a voltage at that pin. The voltage at the collector of the transistor is being converted into a control-current by the 2k2 resistor between the collector and pin5. You can look at pin5 like being a diode with cathode to ground, where the voltage at the anode only varies a small amount depending on the current passing through it.

[Ronan]

Thanks ORK, I had a deeper look at the datasheet.
0.61-0.51/2200 = 45uA and 2.3-0.63/2200 = 760uA which means the tranny is doing its job perfectly and the 3080 is probably fine.
Just looking for possibilities, anything eliminated is one less thing to worry about.

Edit: but that doesn't explain why the pot that controls the tranny had to be grounded...mystery.

Jimi, any chance of unsoldering the purple wire from the pot, pulling out the tranny, then measuring the voltages on the e b and c sockets for the tranny?

[pinkjimiphoton]

i can do that, probably not today tho. too many other projects, like re-assembling my pedal board for a show tonite.

beginning to wonder if the conductive pot is conducting, or has become damaged by being molested so much.

gonna check that zener, i got a bunch of them for this project. whatever is on the schem/layout is on the board, in precision resistances and the best caps i could get that would fit.

i think the 3080 is fine, so is the transister and the other chip....i bet it's diode failure, letting too much voltage thru or something. it really seems to depend on the intensity of the input as to whether it makes that nasty unmusical distortion...so gonna check the input caps etc too.

damn...so much to do today...and ya KNOW this is gonna get messed with...  lol   

[Ronan]

It's possible there's a mistake in the schematic. Pin 4 of the quad IC is connected to pin 9 via a 47K resistor. Shouldn't this 47K resistor connect pin 9 to the 4.7V rail? Anyone care to comment? Have I lost the plot again?  

I was comparing the schematic to that of the ehx talking pedal,they are remarkably similar...

[digi2t]

It's possible there's a mistake in the schematic. Pin 4 of the quad IC is connected to pin 9 via a 47K resistor. Shouldn't this 47K resistor connect pin 9 to the 4.7V rail?

I have a PCB layout of the Vocalizer as well, and it's not the case. It's here; http://www.aronnelson.com/gallery/main.php/v/digi2t/Information/Colorsound_20Vocalizer_LAY_5D_1_.pdf.html . Just click "Download document".

FWIW, I went over my layout again, and I can't see any errors. I compared to both the schematic, and the PCB, and everything jives. The fact that Jimi's not getting 4.7v after the Zener worries me though. Especially just before R17. That resistor is right on the rail, at the top, and there is not much before it that could be draining voltage. Maybe a solder bridge to one of the 1N4148's? That, or the pot, although I would really be amazed that it's the pot, but maybe.

[pinkjimiphoton]

gonna try and replace that zener...wondering if when i hooked up the original circuit if the sweep at the end of the pot pulled too much current, and roasted that?

[Ronan]

I have a PCB layout of the Vocalizer as well, and it's not the case. It's here;

Yep, fair enough.