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Author Topic: Small Clone chorus debugging!  (Read 1281 times)
MohiZ
Posts: 217

Jouni R-P, Finland


Small Clone chorus debugging!
« on: February 06, 2009, 04:08:05 PM »

Hi there!

I've just finished my Small Clone from tonepad.com, but the problem is it doesn't change the input signal at all (in other words, it doesn't "chorus"). Using my tactical Audio Probe I've found that in the chorusing section the last place I can hear the guitar signal is in pin 3 of the MN3007.  Now, I'm just a beginner, but from the schematics it looks like the signal should also be heard while probing pins 7, 8, 1, and pins 14, 4, 5, and 6 on the CD4047?

I measured some voltages to help, maybe someone has an idea about the whereabouts of the problem  Huh

About the transistor values, I really don't know which pins are which, so I've listed them left to right on Q1 and Q2 and up to down with Q3, looking at the tonepad.com schematic.

D1:
A 8.10
C 7.66

D2:
A 0.08
C 7.4

Q1:
7.71
7.14
0.0

Q2:
5.60
6.16
9.18

Q3:
8.53
9.15
9.18

CD4047
1: 8.4
2: 0
3: 7.3
4: 8.5
5: 8.5
6: 8.5
7: 0
8: 0
9: 0
10: 4.5
11: 4.5
12: 0
13: 8.4
14: 8.5

MN3007:
1: 8.53
2: 4.25
3: 8.03
4: 0
5: 0
6: 4.24
7: 6.33
8: 6.33

LM358:
1: 1 - 2.6 (fluctuates about that much with a cycle of a few seconds)
2: 4.14
3: 4.11
4: 0
5: 1 - 3.5 (fluctuates)
6: 2.25
7: 0 - 8 (fluctuates)
8: 9.18

4558:
1: 4.65
2: 4.66
3: 4.54
4: 0
5: 4.6
6: 4.6
7: 4.55
8: 9.18

ps. it might also be something stupid, as I said I'm a beginner  icon_redface
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oskar
Posts: 866


Oskar Wallgren


Re: Small Clone chorus debugging!
« Reply #1 on: February 06, 2009, 05:58:31 PM »

I've just finished my Small Clone from tonepad.com, but the problem is it doesn't change the input signal at all (in other words, it doesn't "chorus"). Using my tactical Audio Probe I've found that in the chorusing section the last place I can hear the guitar signal is in pin 3 of the MN3007.  Now, I'm just a beginner, but from the schematics it looks like the signal should also be heard while probing pins 7, 8, 1, and pins 14, 4, 5, and 6 on the CD4047?
signal in pin 3 and out pin 7, 8. That is where you'll here a signal.
pin 2 and 6 should see squarewaves at opposite phases ( one is high while the other is low and vice versa )
pin 1 on the mn3007 and pin 4,5,6 and 14 on the 4047 are connected to V+ via Q3. Shouldn't be a signal there.

Quote
About the transistor values, I really don't know which pins are which, so I've listed them left to right on Q1 and Q2 and up to down with Q3, looking at the tonepad.com schematic.
Home assignment: Find out the pinout of the transistors. You really need to know this. Check up the datasheets.

Quote
CD4047
1: 8.4
2: 0
3: 7.3
4: 8.5
5: 8.5
6: 8.5
7: 0
8: 0
9: 0
10: 4.5     <-------------------    clock!
11: 4.5     <-------------------    clock!
12: 0
13: 8.4
14: 8.5

MN3007:
1: 8.53
2: 4.25      <--------------- clock!
3: 8.03
4: 0
5: 0
6: 4.24      <----------------clock!
7: 6.33
8: 6.33

LM358:
1: 1 - 2.6 (fluctuates about that much with a cycle of a few seconds)
2: 4.14
3: 4.11
4: 0
5: 1 - 3.5 (fluctuates)
6: 2.25
7: 0 - 8 (fluctuates)
8: 9.18

The reason you see ~4.5 volt pin 10 and 11 is they see a 50% duty-cycle squarewave.
The same is true for pin 2 and 6 of the MN3007.
The delaychip seem to be getting the clock it needs ( and the LFO, LM358 seem to sweep the clocks frequency too )

Quote
4558:
1: 4.65
2: 4.66
3: 4.54
4: 0
5: 4.6
6: 4.6
7: 4.55
8: 9.18
Good voltages...

Focus on the MN3007.
The signal is lost after the delaychip/ MN3007. The chip is getting all voltages it needs and also clock.
Is it socketed?
Check for cold solders.
Measure continuity from the pins on the IC to the respective solderpads.
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MohiZ
Posts: 217

Jouni R-P, Finland


Re: Small Clone chorus debugging!
« Reply #2 on: February 06, 2009, 06:18:44 PM »

Continuity was fine, and I happened to have another MN3007 for another project and tried swapping that, but still no luck  Undecided Seems the IC is fine. I gotta call it a day and get back to it tomorrow, it's past 2 am in Finland  Wink
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oskar
Posts: 866


Oskar Wallgren


Re: Small Clone chorus debugging!
« Reply #3 on: February 07, 2009, 09:42:34 AM »

The clock could be running too fast for the delaychip. If the 150p cap is wrong value the 4047 might operate happily up to many MHz and the delaychip will go down way before that.
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MohiZ
Posts: 217

Jouni R-P, Finland


Re: Small Clone chorus debugging!
« Reply #4 on: February 07, 2009, 11:57:40 AM »

I have a ceramic cap with the number 151 on it. That's correct for 150 pF, isn't it? Also, when I probe some of the pins on the delay chip, I hear a faint high-pitched sound going up and down, which I suspect is the clock? I did notice that I had put as many as THREE caps in wrong places on the board, but I swapped them resulting in no improvement  icon_confused Could there be any other reason why the delay chip would not function in a correct way?
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oskar
Posts: 866


Oskar Wallgren


Re: Small Clone chorus debugging!
« Reply #5 on: February 07, 2009, 12:24:16 PM »

I have a ceramic cap with the number 151 on it. That's correct for 150 pF, isn't it?
Yup...

Quote
Also, when I probe some of the pins on the delay chip, I hear a faint high-pitched sound going up and down, which I suspect is the clock?
Yup... If the clock is slow enough to be audioprobed it should definitely drive the delay chip.

Quote
I did notice that I had put as many as THREE caps in wrong places on the board, but I swapped them resulting in no improvement  icon_confused Could there be any other reason why the delay chip would not function in a correct way?
How is your soldering? Maybe you should rework the socket joints.
It isn't very likely that both delaychips are toasted but I know a guy who bought five of the same chip and they were all wrong/dead...
You've got ~8V on pin3 and that looks a bit high to me. Is that voltage affected in any way by the 100k trimpot?
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MohiZ
Posts: 217

Jouni R-P, Finland


Re: Small Clone chorus debugging!
« Reply #6 on: February 07, 2009, 01:20:06 PM »

Yeah! Got it to work!  Grin I resoldered all the socket joints and adjusted the trimpot so that the voltage in pin 3 of the delay chip is now 4.24 volts. I did tweak the trimmer yesterday but it must have been the wrong caps that prevented it from working then, and after I fixed that, I didn't pay attention to the trimpot anymore. How much should the voltage ideally be?
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oskar
Posts: 866


Oskar Wallgren


Re: Small Clone chorus debugging!
« Reply #7 on: February 07, 2009, 02:41:59 PM »

Onnentoivotus!    Grin

The Tonepad stuff is good but basically two details strike me as rather odd. 1. Whenever you're in a discussion with someone about the circuits you wish for some sort of enummeration of the components and 2. No information on trimpot settings. I guess you can just go by ear but since half of the point of the diy stuff (the good half if you ask me) is the tweek it until you drop dead aspect, so you sure want that information.
I think for the chorus effect to be optimal the original signal and the delayed should be the same level. Just trim for most distinct effect by ear.
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johnravacio
Posts: 25


Re: Small Clone chorus debugging!
« Reply #8 on: March 15, 2012, 10:02:35 AM »

Hey guys, this thread has been very helpful to me. I got the same problem on this on my Small Clone and started measuring the volts on MN3007. I found out that Pin 3 measured 8.0++ volts so I looked around and spotted the root cause. It was the 33K resistor(connected to PIN3) soldered to the adjacent resistor 12K. Boom! problem solved.

Now I'm just curious how did you guys know what are the expected volt measurements for each PIN? I looked at the datasheets but found no clue.

I'm a Software Developer by profession and only knows very basic about electronics. Any insights? Thanks!
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PRR
Posts: 6043


Paul R. - Maine USA


Re: Small Clone chorus debugging!
« Reply #9 on: March 15, 2012, 02:40:15 PM »

> I'm a Software Developer by profession and only knows very basic about electronics. Any insights?

Audio electronics IS programming. But not any language taught in Computer Science (well, not since 1955).

If you know BASIC you know this:

FOR i = 0 to 9

If this runs a million times, what is the average value of i ? Probably 4.5 (though some dialects of BASIC treat FOR differently).

If you pause it and find that i is 23, or -7, is that OK?

It takes dozens or hundeds of hours of study to understand computer programming enough to answer "any" simple question.

It takes about the same time to understand analog electronics programming enough to answer "any" simple question such as "what's a reasonable voltage here?"

Peeking at common Answers:

Signal voltage must stay between supply pin voltages. ("0 >= i <= 9".) Signal voltage varies both ways. Therefore the steady DC voltage on a signal pin is "usually" half-way between the supply rails. With common 0V and +9V rails, around +4.5V. This allows signal to swing both ways without exceeding (even approaching) supply rails.

Most opamps will swing down to 1V and up to 8V. 4.5V is good.

The MN3007 is an oddball. (It also has only very-Japanese datasheets, cryptic to euro-language readers.) It uses mostly a single polarity of transistor. IIRC, it swings down lower than it swings up. This varies depending on supply: at 15V supply you bias it 8V, a hair above half, but at 9V we bias a hair below half. Jouni seems to have mis-set this along the way.

As Oskar says, a clock pin switching from zero to +9V very fast will tend to read about 4.5V average. That's at 50:50 duty cycle. If it was 10:90 or 90:10 it would read lower or higher.
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johnravacio
Posts: 25


Re: Small Clone chorus debugging!
« Reply #10 on: March 16, 2012, 09:22:47 AM »

Thanks for the helpful insights Paul.

RE: Audio electronics IS programming. But not any language taught in Computer Science (well, not since 1955).

Yes I totally agree. I'm just starting out but it looks like audio electronics is also addicting maybe because of its details and variability that is related to music Smiley


Re: Peeking at common answers:

Hmmm so it looks like the principle for signal voltages is to keep it center of its variability. Regarding "IIRC, it swings down lower than it swings up", is this some kind of Electrical Characteristics right?

Anyway as you've said it would take sometime to understand analog electronics so I bought a book "Teach Yourself Electricity and Electronics" by Stan Gibilsco. Any other books you can recommend?
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