Debugging Boss Slow Gear Help

Malius · January 06, 2012, 07:46:34 AM

Hi guys, I've tried building a Boss Slow Gear, but I'm getting no sound from it.

I followed the debugging guidelines so here are all the details you need.

Please help me as this is a uni project that I really need to get working!

1.What does it do, not do, and sound like?
It has no sound at all at the output. The LED works to show the effect is on, but no audible sound.
2.Name of the circuit = Boss Slow Gear
3.Source of the circuit (URL of schematic or project) = topopiccione.atspace.com/PJ03bossSG1.html I followed it very closely. I don't think there was anything I consciously changed.
4.Any modifications to the circuit? Y I added an LED to the circuit to show it was on. The positive comes off the switch and the ground is connected to the ground on the main circuit board
5.Any parts substitutions? The only things I have changed to my knowledge are using a rotary pot instead of the trim and a 22k pot rather than 20k for P2 "attack".
6.Positive ground to negative ground conversion? If I'm honest I'm not sure
7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? => 9.57v
Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it My output is not connected to ground. Could this be a problem? I have no sleeve connector on it (see picture). With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead = 9.18v
Voltage at the circuit board end of the black battery lead = 0v

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

Multimeter is set to 20v FYI

Component Name (description) V

T1 BC550 (yes I checked the pinouts) E = 1.12 B = 1.71 C = 1.16
T2 2SK30A D = 1.66 G = 2.17 S = 1.66
T3 BC549 E = 0.45 B = 0.97 C = 1.16
T4 BC549 E = 3.13 B = 3.65 C = 4.14
T5 BC549 E = 3.46 B = 4.14 C = 3.46
T6 BC549 E = 3.45 B = 3.42 C = 3.45

IC1 496-741 1 = 0.01 5 = 6
CA3140E2 2 = 4.58 6 = 7.18
3 = 4.48 7 = 4.61
4 = 0 8 = 0.01

D1 5.6V Zener Anode = 0 Cathode = 1.65

http://img.photobucket.com/albums/v287/Malius/IMG_0021.jpg
http://img.photobucket.com/albums/v287/Malius/IMG_0020.jpg
http://img.photobucket.com/albums/v287/Malius/IMG_0019.jpg
http://img.photobucket.com/albums/v287/Malius/IMG_0018.jpg
http://img.photobucket.com/albums/v287/Malius/IMG_0022.jpg
http://img.photobucket.com/albums/v287/Malius/IMG_0023.jpg
http://img.photobucket.com/albums/v287/Malius/IMG_0024.jpg
http://img.photobucket.com/albums/v287/Malius/IMG_0028.jpg
http://img.photobucket.com/albums/v287/Malius/IMG_0027.jpg
http://img.photobucket.com/albums/v287/Malius/IMG_0026.jpg
http://img.photobucket.com/albums/v287/Malius/IMG_0025.jpg

And this is how it is boxed
http://img.photobucket.com/albums/v287/Malius/IMG_0017.jpg

Thank for your time and help!

Malius · January 06, 2012, 07:58:22 AM

Oh it might also be worth mentioning I get a clean signal when the bypass is engaged.

seedlings · January 06, 2012, 09:20:34 AM

I'm interested in this circuit. Why no ground on the output?

CHAD

Malius · January 06, 2012, 11:04:13 AM

The circuit at the back if you're referring to that is just an LED and a resistor.

As for the ground I don't really have an idea. My mate who doing an electronics degree thought I was being clever because it's grounded to the box. I can't claim any conscious decision.

seedlings · January 06, 2012, 01:39:52 PM

Chassis ground *can* cause lots of noise problems and should be avoided. Connect it to your circuit ground.

CA3140
Pin 7 should have 9 volts DC
Pins 6 and 2 should have 0 volts DC
Pin 1, 5 and 8 should not be connected to anything

Double check components connected to those pins.

CHAD

*edit: the schematic you link to doesn't pull up. Does your schematic look like this: http://www.buildyourownclone.com/lazysprocketV1.pdf

Malius · January 06, 2012, 02:05:47 PM

Quote from: seedlings on January 06, 2012, 01:39:52 PM
Chassis ground *can* cause lots of noise problems and should be avoided. Connect it to your circuit ground.

CA3140
Pin 7 should have 9 volts DC
Pins 6 and 2 should have 0 volts DC
Pin 1, 5 and 8 should not be connected to anything

Double check components connected to those pins.

CHAD

*edit: the schematic you link to doesn't pull up. Does your schematic look like this: http://www.buildyourownclone.com/lazysprocketV1.pdf

Okay, so I should connect the output ring/sleeve to ground. I thought so.

Pins 1, 5 & 8 do have nothing connected but I tested them anyway as per the debugging instructions. I will double check 2, 6 & 7 in the morning.

And yes the schematic is very similar. Hopefully this link works http://topopiccione.atspace.com/PJ03BossSG1.html it also has the PCB layout on there which I followed.

Thanks for your help,

Mike

Malius · January 07, 2012, 07:02:39 AM

Right, I've just attached the output to the ground.

I also rechecked some values.

Red battery at circuit = 9.29v
Black battery at circuit = 0v

Op pins

2 = 4.58v
6 = 7.18v
7 = 4.61v

Pin 2 is connected to R16 & R17 on my link. (R17/R20 on yours)
Pin 6 is connected to R18 & C11 on mine. (R19 & C11 yours)
Pin 7 is connected to the other end of R17, as well as R19 & C12, mine (R20, R21 & C12) Yours.

[EDIT] I've just done an audio test. I now get some signal through the effect circuitry.

I put the amp on the gain channel so I could notice changes better. When engaging the circuit there is a huge signal loss, it is only barely audible. Playing with the trim changes it from fully to the left a clean sound to the right being more distorted. Changing the sensitivity seems to change the level of the signal and the attack doesn't seem to do much.

Malius · January 10, 2012, 06:43:47 AM

Sorry to bump, but can anyone help me further? I really need to get this working? My evaluation of it is due on the 23rd.

Any help will be greatly appreciated!

seedlings · January 10, 2012, 10:04:43 AM

If you're using a ca3140, this datasheet http://www.intersil.com/data/fn/fn957.pdf says pin 7 goes to +V, or 9V battery. So on your schematic it will connect to R18 and C11. You should measure 9V on pin 7.
Pin 2 goes to the junction of R16 and R17
Pin 3 goes to the junction of R15 and C9
Pin 6 goes to the junction of R19, C12 and R17

CHAD

Paul Marossy · January 10, 2012, 10:27:31 AM

I built this thing some time ago and I couldn't get it to work at all. It's one of the few projects I've done that I just couldn't get to work.

PRR · January 11, 2012, 01:40:33 AM

> T1 BC550 (yes I checked the pinouts) E = 1.12 B = 1.71 C = 1.16
> T3 BC549 E = 0.45 B = 0.97 C = 1.16

The schematic clearly shows T1 T3 Collectors go to +9V.

> D1 5.6V Zener Anode = 0 Cathode = 1.65

That point should be 5V-6V, not under 2V.

Power aint getting where it gotta be. Check your work. (Again.)

When T1 T3 voltages are decent (C=9V, E=4V-7V), remove FET and see if signal will pass unity-gain no-effect. Break the R12 C8 joint and move the loose end of C8 over to IC1 pin 6, this should be LOUD DISTORTED but recognizable.

However... if it didn't work for Marossy, that's a BIG hint that something is wrong. At a glance I don't see a glitch, so someone's gotta go over the analysis, and I don't think that would be you this week.

How about a '741 diode-clipper? Proven-correct, useful, quick.

Malius · January 11, 2012, 06:32:35 AM

Quote from: seedlings on January 10, 2012, 10:04:43 AM
If you're using a ca3140, this datasheet http://www.intersil.com/data/fn/fn957.pdf says pin 7 goes to +V, or 9V battery. So on your schematic it will connect to R18 and C11. You should measure 9V on pin 7.
Pin 2 goes to the junction of R16 and R17
Pin 3 goes to the junction of R15 and C9
Pin 6 goes to the junction of R19, C12 and R17

CHAD

Okay, so I think that with that op Amp, pins 6 and 7 are the wrong way round from the layout I used. It didn't occur to me that different 741 amps could have different pin-outs. I guess I should have checked.

[EDIT] I've been stupid and been reading the 5-8 pin side of the op amp up the wrong way. So it is indeed the correct way round. My fault. I checked the supply to pin 7. It is receiving just over +9V until it gets to R18, then after R18 it drops to +7V. So could that be a short or something there?

However if I swap those two pins round pin 7 will only be getting 7.13V, so something isn't quite right with the supply to that. Any ideas?

Quote from: PRR on January 11, 2012, 01:40:33 AM
> T1 BC550 (yes I checked the pinouts) E = 1.12 B = 1.71 C = 1.16
> T3 BC549 E = 0.45 B = 0.97 C = 1.16

The schematic clearly shows T1 T3 Collectors go to +9V.

I've just noticed that I never actually bothered to put the connector in between those and the +9v part of the circuit, doh!

Quote from: PRR on January 11, 2012, 01:40:33 AM
> D1 5.6V Zener Anode = 0 Cathode = 1.65

That point should be 5V-6V, not under 2V.

Power aint getting where it gotta be. Check your work. (Again.)

This could do with the +9V not being connected again as it's the same part of the circuit.

Quote from: PRR on January 11, 2012, 01:40:33 AM
When T1 T3 voltages are decent (C=9V, E=4V-7V), remove FET and see if signal will pass unity-gain no-effect. Break the R12 C8 joint and move the loose end of C8 over to IC1 pin 6, this should be LOUD DISTORTED but recognizable.

How about a '741 diode-clipper? Proven-correct, useful, quick.

I'm sorry, I don't understand.

seedlings · January 11, 2012, 09:21:48 AM

After fixing the wiring errors, what are all the voltages now? With no voltage to T1 and T3 it can never work

CHAD

Malius · January 11, 2012, 01:29:23 PM

Yeah that was me just being forgetful and forgetting something I had left till last.

The voltages are now as follows:

Voltage at the circuit board end of the red battery lead = 9.15v
Voltage at the circuit board end of the black battery lead = 0v

Component Name (description) V

T1 BC550 (yes I checked the pinouts) E = 3.68 B = 4.11 C = 9.14
T2 2SK30A D = 5.13 G = 1.22 S = 5.34
T3 BC549 E = 6.50 B = 6.62 C = 9.09
T4 BC549 E = 1.29 B = 1.90 C = 1.37
T5 BC549 E = 0.64 B = 1.36 C = 0.64
T6 BC549 E = 0.64 B = 0.63 C = 0.64

IC1 496-741 1 = 0.00 5 = 0
CA3140E2 2 = 4.48 6 = 4.57
3 = 4.42 7 = 6.97
4 = 0 8 = 5.96

D1 5.6V Zener Anode = 0 Cathode = 5.34

T4 looks as if it should get +9V at the collector, but aren't R20 & R18 working as voltage dividers?

Gurner · January 11, 2012, 02:23:34 PM

It's the first time I've looked at this schematic (& it looks like a hammer to crack a nut - but hey, it's 30 years old).

As PRR says....remove the FET T2 (which is operating as a shunt - i.e. shunting the attack portion of the signal to ground) ....if you still don't have an output, then your problem is related to the upper part of the signal path (T1 & T3), which at least elimates 60% of the curcuit to debug!

Malius · January 14, 2012, 10:40:10 AM

Hello again guys.

Right, I've just done an aural test now that I added +9V to the T1 & T3 part of the circuit. I am getting a normal signal output, but no effect.

The pots have the following effect:

Sensitivity pot; appears to have no affect on signal
Trimpot (actual pot rather than using a trim); affects how much signal is coming through (full anti-clockwise, very slight signal, full-clockwise same level signal as bypass.
Attack; Doesn't appear to do much, but if it's full-clockwise and the trim is just at the threshold of being a good signal it sounds as if there is a very slight volume swell, though that may be a placebo effect.

Are you sure removing the T2 JFet is a good idea? Everything I read suggests it si a very important part of the circuit and is used to slowly open up and let the signal through, i.e. the volume swell.

Any other ideas?

Malius · January 15, 2012, 07:48:32 AM

Sorry to be a pain, but has anyone got any more ideas? I'm running out of time

Seven64 · January 15, 2012, 01:38:53 PM

is your 3pdt switch wired as the diagram shows?

i had it wired up how i thought was correct and it never worked. i switched everything except the 3pdt switch and it still didn't work. then i switched the 3pdt and within 5 minutes i had it working great!

http://www.generalguitargadgets.com/pdf/ggg_sgo_lo_wiring.pdf

seedlings · January 15, 2012, 08:15:09 PM

Quote from: Malius on January 14, 2012, 10:40:10 AM
Are you sure removing the T2 JFet is a good idea? Everything I read suggests it si a very important part of the circuit and is used to slowly open up and let the signal through, i.e. the volume swell.

It is, for troubleshooting purposes, a good idea, but you say you do have *some* sound with the effect engaged now. So...

What are all the voltages now?

CHAD

PRR · January 16, 2012, 01:34:54 AM

> Are you sure removing the T2 JFet is a good idea?

Either two experienced circuit benders are yanking your chain, or it IS a useful step in debugging. You do have to be careful about free advice, but if you've skimmed some of Gurner's posts you see he's no chain-yanker.

You got low-no signal. It could be mis-wiring anywhere around T1 T3, _or_ it could be something about T2. With T2 out, signal should flow like a simple buffer (what it then is). If not, bebug the buffer. If it buffers fine, now we stare at T2.

However:

> T4 BC549 E = 1.29 B = 1.90 C = 1.37

R20 and R21 have the same value, and flow the same DC current. (The only side-paths are through the huge 390K and caps that block DC.) How-come R21 has 1.29V and R20 has 9.15V-1.37V= 7.78V? Wrong part? Wrong connection?

How come B of T5 and C of T4 have the "same" voltage? Is C13 shorted?

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Debugging Boss Slow Gear Help