Hi everyone,
I have built a DEFX Larry (Mutron Flanger clone) inside a Morley power wah volume pedal. I am powering it with 18V DC as indicated in the build document (https://drive.google.com/file/d/1LDdOgaEvKD7LMD93oQv7EVDiAeX3N072/view). The pedal turns on fine as does the rate LED. The pedal stomp switch also turns on the pedal LED. There is some flanging sound but it seems not completely right, but I have not completed the calibration so that makes sense. I have taken some photos of the fully populated PCB and enclosure in case it will help.
PCB component side
(https://i.postimg.cc/LnnJh82X/PCB-COMPONENTS-SIDE.jpg) (https://postimg.cc/LnnJh82X)
PCB control side
(https://i.postimg.cc/LnwnPF8V/PCB-CONTROL-SIDE.jpg) (https://postimg.cc/LnwnPF8V)
I have started calibrating the pedal and I have been able to calibrate the clock successfully. I did have to change C18 to 68pF for it to work. The next step is biasing the MN3007 BBD IC using a 400 Hz sinewave of 1.25V to 2.5V.
(https://i.postimg.cc/0z3k3Ywd/CALIBRATION-INSTRUCTIONS-FROM-BUILD-DOCUMENT.png) (https://postimg.cc/0z3k3Ywd)
The schematic is provided in the build document and it has a section showing TRIM5 trimmer which does the biasing of the MN3007.
(https://i.postimg.cc/JsSZRBXM/SCHEMATIC-TRIM5-MN3007.png) (https://postimg.cc/JsSZRBXM)
Now for the actual problem that I am having, irrespective of whether I add the 1.5V 400 Hz sine wave to the TP3 test point or not, the output of the MN3007 at TP2, shows the following:
TRIM5 fully turned left
(https://i.postimg.cc/t1XyZBW5/TP2-TRIM5-FULL-LEFT.jpg) (https://postimg.cc/t1XyZBW5)
TRIM5 in the middle
(https://i.postimg.cc/4KBGzp1T/TP2-TRIM5-MIDDLE.jpg) (https://postimg.cc/4KBGzp1T)
TRIM5 full right
(https://i.postimg.cc/N590BCk2/TP2-TRIM5-FULL-RIGHT.jpg) (https://postimg.cc/N590BCk2)
From reading the calibration section of the documentation, it seems to suggest that feeding the sine wave in at TP3, would also have the sine wave appear at the output of the MN3007 IC. It might be asymmetrical or distorted but TRIM5 would allow to adjust the sine wave so that it is symmetrical and not distorted. As shown in the above photos though, you can see that there is no sine wave whatsoever.
I would be grateful if the experts could give me a hand with this one.
Cheers,
Mart
As a first guess, I'd say check that the R63 and R64 100K resistors to +Ve actually have good connections. If one wasn't soldered correctly, you might see what you're looking at.
As a second guess, you need to make sure that Trim5 is set correctly, so that what's going *into* the BBD is where it needs to be. If you don't have a signal generator,/oscilloscope just play some audio from your phone through the effect, and then tweak the trim until you get the best sound from the other end. You can get pretty close like this, and once you have one end pretty good, you can tweak the other to get that right too.
HTH, good luck!
please be measuring the values of R61 and R62. and what voltage appears at their junction?
Quote from: duck_arse on July 09, 2023, 11:16:12 AM
please be measuring the values of R61 and R62. and what voltage appears at their junction?
I just measured the two resistors and here are the results:
R61: 0V
R62: 15V
R61-R62 junction: 1.11V
Quote from: ElectricDruid on July 08, 2023, 06:54:28 PM
As a first guess, I'd say check that the R63 and R64 100K resistors to +Ve actually have good connections. If one wasn't soldered correctly, you might see what you're looking at.
As a second guess, you need to make sure that Trim5 is set correctly, so that what's going *into* the BBD is where it needs to be. If you don't have a signal generator,/oscilloscope just play some audio from your phone through the effect, and then tweak the trim until you get the best sound from the other end. You can get pretty close like this, and once you have one end pretty good, you can tweak the other to get that right too.
HTH, good luck!
I measured both R63 and R64 and they are at 15V so they seem to be fine. I looked at this build document from armdnrdy (Larry) who did the original clone I believe, and the sine wave signal should just be coming through normally? I am not sure I understand how the sine wave would go into the MN3007 and would come out not transformed... Maybe someone can educate me?
(https://i.postimg.cc/gwMD4byt/TRIM5-adjustment.png) (https://postimg.cc/gwMD4byt)
Aside from that I am still not much clear on what is going on. Why does the wave form at TP2 look so strange with TRIM5 set full left, right, or in the middle?
QuoteNow for the actual problem that I am having, irrespective of whether I add the 1.5V 400 Hz sine wave to the TP3 test point or not, the output of the MN3007 at TP2, shows the following:
TRIM5 fully turned left
What's wrong is you are looking at the waveform with a very fast us/dev setting on the oscilloscope so you are seeing samples with glitches and not the 400Hz sine wave cycles.
A 400Hz signal has a period of 2.5ms. Suppose you want to see 4 or 5 periods on the display, that's 10ms to 12.5ms. Your oscilloscope has 14 horizontal divisions which means you need 10ms/14 = 0.7ms/div to 12.5ms/14 = 0.9ms/div. So you need to set the oscilloscope to 500us/div or 1ms/div, a lot slower that what you have at the moment.
When your monitor the output of the BBD and adjust TRIM5 you should see the waveforms similar to the blue analog scope waveforms you just posted.
Hint: connect channel 1 to the input waveform and trigger off that, then connect channel 2 to the BBD output/test point. The input signal is clean so the oscilloscope will trigger better.
@spacekid71
When you power your Mutron Flanger pedal.... are you seeing the Rate LED light up at all? Like, even when the pedal is not activated?? I had to make adjustments to a resistor value in my build to get the Rate LED to be dim enough to not be noticably "on." Otherwise, it was dimly lit constantly as long as power was plugged in.
Hi Govmnt_Lacky,
Just had a look at the RATE LED and it seems to be behaving correctly. Will let you know if I notice anything suspicious in the same vein as you are describing.
Cheers,
Mart
Quote from: Rob Strand on July 10, 2023, 12:59:05 AM
What's wrong is you are looking at the waveform with a very fast us/dev setting on the oscilloscope so you are seeing samples with glitches and not the 400Hz sine wave cycles.
A 400Hz signal has a period of 2.5ms. Suppose you want to see 4 or 5 periods on the display, that's 10ms to 12.5ms. Your oscilloscope has 14 horizontal divisions which means you need 10ms/14 = 0.7ms/div to 12.5ms/14 = 0.9ms/div. So you need to set the oscilloscope to 500us/div or 1ms/div, a lot slower that what you have at the moment.
When your monitor the output of the BBD and adjust TRIM5 you should see the waveforms similar to the blue analog scope waveforms you just posted.
Hint: connect channel 1 to the input waveform and trigger off that, then connect channel 2 to the BBD output/test point. The input signal is clean so the oscilloscope will trigger better.
Thanks for taking the time to explain this to me, I appreciate it. I understand what you are saying so I am applying the 400 Hz sine wave at the input jack and I have set the oscilloscope to 1ms/div and connected it up to TP3 (yellow) and TP2 (purple). The three photos are showing TRIM5 set fully left, middle, and fully right. I must still be doing something wrong because the signal at the BBD output does not seem normal. I am either not measuring correctly still, or there is something wrong with the circuit around the BBD chip.
(https://i.postimg.cc/SX2TW2DV/image-6487327-1.jpg) (https://postimg.cc/SX2TW2DV)
(https://i.postimg.cc/6y6NCcR0/image-6487327-3.jpg) (https://postimg.cc/6y6NCcR0)
(https://i.postimg.cc/v4kFFdKq/image-6487327.jpg) (https://postimg.cc/v4kFFdKq)
(https://i.postimg.cc/56rkjSmj/image-6487327-2.jpg) (https://postimg.cc/56rkjSmj)
QuoteThanks for taking the time to explain this to me, I appreciate it. I understand what you are saying so I am applying the 400 Hz sine wave at the input jack and I have set the oscilloscope to 1ms/div and connected it up to TP3 (yellow) and TP2 (purple). The three photos are showing TRIM5 set fully left, middle, and fully right. I must still be doing something wrong because the signal at the BBD output does not seem normal. I am either not measuring correctly still, or there is something wrong with the circuit around the BBD chip.
To be honest I cannot follow the documentation.
The schematic has test points labelled PAD7 etc, which are very hard to find and read, but the instructions talk about test points TP2 etc.. The PAD number and TP number don't match up. So when you are probing TP2 I cannot work out what point TPx is on the schematic. That makes it impossible for me to know where you are actually probing. If the instructions have typos you might actually be probing the wrong point. I can guess where the test points *should be* on the schematic but that doesn't help if the documentation doesn't match the PCB.
To side step those issues you could try probing pin 3 and/or pin 1 of IC10. You should get a sine-wave coming out.
Quote from: Rob Strand on July 10, 2023, 11:41:54 PM
To be honest I cannot follow the documentation.
The schematic has test points labelled PAD7 etc, which are very hard to find and read, but the instructions talk about test points TP2 etc.. The PAD number and TP number don't match up. So when you are probing TP2 I cannot work out what point TPx is on the schematic. That makes it impossible for me to know where you are actually probing. If the instructions have typos you might actually be probing the wrong point. I can guess where the test points *should be* on the schematic but that doesn't help if the documentation doesn't match the PCB.
To side step those issues you could try probing pin 3 and/or pin 1 of IC10. You should get a sine-wave coming out.
Yeah it is difficult that TP points and pad numbers don't line up. I have looked at this with the PCB and the schematic and used continuity on my multimeter to figure it out.
TP3 = PAD3
TP2 = PAD7
So TP3 is the tip of the input jack and TP2 is at the intersection of TRIM6 and Q3.
QuoteYeah it is difficult that TP points and pad numbers don't line up. I have looked at this with the PCB and the schematic and used continuity on my multimeter to figure it out.
TP3 = PAD3
TP2 = PAD7
So TP3 is the tip of the input jack and TP2 is at the intersection of TRIM6 and Q3.
OK got it, so it is like that.
The TP2 signal obviously isn't correct. There will be some glitches at that point but the waveform should sort of follow a sine wave.
At this point I'd do some basic checks:
1) Check the supply voltages: BBD power IC9 pin 1 and BBD bias IC9 pin 4.
Also check ground is getting to the BBD IC9 pin 5 using continuity - measure at the IC pin not the PCB.
2) With 400hz sine wave signal applied to the pedal input, check the sine wave is present on
IC9 pin 3 (BBD analog input).
3) Make sure the both clocks are getting to the BBD chip.
With the oscilloscope on a fast sweep and no analog input, and using both channels:
Make sure you are seeing clocks on both pins IC9 pins 2 and 6 and that
the signals are complementary. You can also check the same signals at IC6.
Take note of the clock voltages, they should swing zero to +VE.
Ignore the voltages on the pic:
(https://i.postimg.cc/3k4388Yt/example-bbd-complementary-clocks.png) (https://postimg.cc/3k4388Yt)
If you get that far then there's no real reason not to get a glitchy sine wave at TP2 (TRIM6). If you don't the BBD chip might have a problem. What to do from there is a little tricky without replacing the BBD chip, a costly experiment.
Another angle is to run the pedal at a lower voltage like 12V or 15V to see if it comes to life. Perhaps the modern BBD chip doesn't like 18V. 18V is the absolute maximum voltage for that chip and it's usually unwise to operate at absolute maximum!
You could also try soldering another 1k in parallel with R61 (1k2) to see if it does anything. You could even try a very low value like 100 ohm. I don't think it's going to help but if the BBD chip has an issue it might kick it in the right direction.
Quote from: Rob Strand on July 11, 2023, 09:14:10 PM
Another angle is to run the pedal at a lower voltage like 12V or 15V to see if it comes to life. Perhaps the modern BBD chip doesn't like 18V. 18V is the absolute maximum voltage for that chip and it's usually unwise to operate at absolute maximum!
Rob,
This pedal runs with a 12 or 15V regulator. As long as input voltage (AC or DC) does not exceed the regulator's requirement then the BBD should see nothing more than the regulator's output voltage.
Quote from: Govmnt_Lacky on July 12, 2023, 07:15:39 AM
Quote from: Rob Strand on July 11, 2023, 09:14:10 PM
Another angle is to run the pedal at a lower voltage like 12V or 15V to see if it comes to life. Perhaps the modern BBD chip doesn't like 18V. 18V is the absolute maximum voltage for that chip and it's usually unwise to operate at absolute maximum!
Rob,
This pedal runs with a 12 or 15V regulator. As long as input voltage (AC or DC) does not exceed the regulator's requirement then the BBD should see nothing more than the regulator's output voltage.
Thanks, found it. I must have been zoomed in and scrolled past that section. Before I could only find the Vref voltage divider stuff.
Looks like 15V on the parts list.
Quote from: Rob Strand on July 11, 2023, 09:14:10 PM
OK got it, so it is like that.
The TP2 signal obviously isn't correct. There will be some glitches at that point but the waveform should sort of follow a sine wave.
At this point I'd do some basic checks:
1) Check the supply voltages: BBD power IC9 pin 1 and BBD bias IC9 pin 4.
Also check ground is getting to the BBD IC9 pin 5 using continuity - measure at the IC pin not the PCB.
2) With 400hz sine wave signal applied to the pedal input, check the sine wave is present on
IC9 pin 3 (BBD analog input).
3) Make sure the both clocks are getting to the BBD chip.
With the oscilloscope on a fast sweep and no analog input, and using both channels:
Make sure you are seeing clocks on both pins IC9 pins 2 and 6 and that
the signals are complementary. You can also check the same signals at IC6.
Take note of the clock voltages, they should swing zero to +VE.
Ignore the voltages on the pic:
(https://i.postimg.cc/3k4388Yt/example-bbd-complementary-clocks.png) (https://postimg.cc/3k4388Yt)
If you get that far then there's no real reason not to get a glitchy sine wave at TP2 (TRIM6). If you don't the BBD chip might have a problem. What to do from there is a little tricky without replacing the BBD chip, a costly experiment.
Another angle is to run the pedal at a lower voltage like 12V or 15V to see if it comes to life. Perhaps the modern BBD chip doesn't like 18V. 18V is the absolute maximum voltage for that chip and it's usually unwise to operate at absolute maximum!
You could also try soldering another 1k in parallel with R61 (1k2) to see if it does anything. You could even try a very low value like 100 ohm. I don't think it's going to help but if the BBD chip has an issue it might kick it in the right direction.
Thank you for your detailed explanation on how to investigate. I have some preliminary results from the investigation:
IC9 (MN3007) - pin1: 14.98V
IC9 (MN3007) - pin4: 1.11V
IC9 (MN3007) - pin5: GND verified using continuity
IC8 (NE571) - pin7: 400 Hz sine wave available
It looks like I lose the 400 Hz sine wave after it passes through R57. I have taken part of the schematic and indicated where the signal is okay still and where it is lost. Maybe the 1N34a and 1N914 diodes have something to do with it?
(https://i.postimg.cc/Wqwx1zKM/sine-wave-investigation.png) (https://postimg.cc/Wqwx1zKM)
QuoteIt looks like I lose the 400 Hz sine wave after it passes through R57. I have taken part of the schematic and indicated where the signal is okay still and where it is lost. Maybe the 1N34a and 1N914 diodes have something to do with it
That's good progress. Highly likely to be the 1N34A's. You might have some leaky or damaged devices. If you just want to keep going on the BBD verification what you can do is replace one or both of the 1N34A's with 1N914's. Deal with the 1N34A issue later later.
Just in case there's a soldering or PCB issue, make sure you are getting continuity from diode side of R57 (2k2) to C35 (47n).
There's a good chance things will start working once you sort out the loss of signal issue.
Quote from: spacekid71 on July 12, 2023, 02:01:26 PM
It looks like I lose the 400 Hz sine wave after it passes through R57. I have taken part of the schematic and indicated where the signal is okay still and where it is lost. Maybe the 1N34a and 1N914 diodes have something to do with it?
You can always use your multimeter in diode mode to verify that you are getting the proper voltage drop across the diodes. 1N914s should be about 0.6V and the 1N34As should be around 0.35V. It could be something as simple as needing a solder re-flow on the contacts.
Good Luck! ;D
Probably shouldn't overlook the possibility of (solder) shorts on the PCB around that area of the circuit and around the BBD pins.
So I had another look at things just now. I measured the 1N34as and the 1N914s and they came in at around 0.27V and 0.62V respectively. I did reflow all four diodes but that hasn't make any difference. The left side of R57 (on the schematic) gives me 400 Hz but the right side give me about ten times as much, around 4.0 kHz.
I decided to remove C35 (47 nF) just to see if the 400 Hz would appear on the right side of R57 and on the left side of C35, and it did...
One other thing I noticed is that the BOM says to use 1N4148 for D9, D10, D11, D12, but the schematic shows 1N914. I replaced the 1N4148s that I had put just in case, but that hasn't changed anything.
I am wondering what could increase the frequency from 400 to 4000 Hz. Any ideas? I can do some measurements if that would help.
Quote from: spacekid71 on July 15, 2023, 05:38:55 PM
So I had another look at things just now. I measured the 1N34as and the 1N914s and they came in at around 0.27V and 0.62V respectively. I did reflow all four diodes but that hasn't make any difference. The left side of R57 (on the schematic) gives me 400 Hz but the right side give me about ten times as much, around 4.0 kHz.
I decided to remove C35 (47 nF) just to see if the 400 Hz would appear on the right side of R57 and on the left side of C35, and it did...
...
I am wondering what could increase the frequency from 400 to 4000 Hz. Any ideas? I can do some measurements if that would help.
The short/problem is probably on the BBD side of C35. Perhaps check for shorts around the BBD pins, or even check for shorts to ground on the BBD input using the DMM contnuity.
The 4kHz is probably an artifact of the short. The signal should be very low. (A pic of the waveform might help but really the problem is around the BBD.)
It doesn't make 100% sense to me as the cap would short low frequencies less as far as the diodes are concerned.
Quote
One other thing I noticed is that the BOM says to use 1N4148 for D9, D10, D11, D12, but the schematic shows 1N914. I replaced the 1N4148s that I had put just in case, but that hasn't changed anything.
So it doesn't look like the diodes are the issue but for the sake of correctness:
The schematic has a bug for sure. Each pair of diodes should be a 1N4148 in series with a 1N34A.
Here's a PCB pic of the real unit around the diodes:
Top
(https://i.postimg.cc/Sjbg20Cm/diodes-pcb-top.png) (https://postimg.cc/Sjbg20Cm)
Bottom, flipped left/right for x-ray view to match PCB top view.
(https://i.postimg.cc/fJTjmMLQ/diodes-pcb-bottom-xray-view.png) (https://postimg.cc/fJTjmMLQ)
Here's the connections I see on the PCB:
(https://i.postimg.cc/56xpgwsG/diodes-sch-fix.png) (https://postimg.cc/56xpgwsG)
I found the schematic of the Mutron Flanger clone by armdnrdy https://drive.google.com/file/d/15IIMwS8AwjmBziqMyLhTAggNXyvtkafo/view?usp=sharing (https://drive.google.com/file/d/15IIMwS8AwjmBziqMyLhTAggNXyvtkafo/view?usp=sharing). This is an adaptation of the original Mutron Flanger using a MN3007 instead of a SAD1024. Armdnrdy is Larry who is also on this forum but he doesn't seem to be active anymore.
The Dead End FX Larry is based on armdnrdy's Mutron Flanger clone so I decided to compare them with regards to the diodes we are talking about and it looks like the schematic is the same and uses two 1N34a's and two 1N914s.
My test from this afternoon showed that when I removed the C35 (47 nF) capacitor, the 400 Hz signal passes the diode section fine. When I put the C35 capacitor back, the signal goes to around 4000 Hz after C35, so it doesn't look like the diodes are the problem, but I may be wrong. I have added an image to the post. Could the signal go to 4000 Hz because of any wrong or faulty parts in the sections in red? Or maybe the MN3007 itself causes the issue?
(https://i.postimg.cc/ZW63sg8n/diode-section-other-sections.png) (https://postimg.cc/ZW63sg8n)
Finally, the initial topic where Larry and Dino worked together with some other people to clone the Mutron Flanger:
https://www.diystompboxes.com/smfforum/index.php?topic=103542.0 (https://www.diystompboxes.com/smfforum/index.php?topic=103542.0)
I will have a look to see if there are any cold solder joints or shorts after the C35.
QuoteI found the schematic of the Mutron Flanger clone by armdnrdy https://drive.google.com/file/d/15IIMwS8AwjmBziqMyLhTAggNXyvtkafo/view?usp=sharing. This is an adaptation of the original Mutron Flanger using a MN3007 instead of a SAD1024. Armdnrdy is Larry who is also on this forum but he doesn't seem to be active anymore.
That schematic has the same error on the diodes.
QuoteThe Dead End FX Larry is based on armdnrdy's Mutron Flanger clone so I decided to compare them with regards to the diodes we are talking about and it looks like the schematic is the same and uses two 1N34a's and two 1N914s.
It's not the fact there's two of each type of diode. The issue is how those diodes (2x1N914 and 2x1N34A) are connected. The fix I posted makes 100% sense to me. The PCB pics I posted are from an original unit not a clone.
QuoteMy test from this afternoon showed that when I removed the C35 (47 nF) capacitor, the 400 Hz signal passes the diode section fine. When I put the C35 capacitor back, the signal goes to around 4000 Hz after C35, so it doesn't look like the diodes are the problem, but I may be wrong. I have added an image to the post. Could the signal go to 4000 Hz because of any wrong or faulty parts in the sections in red? Or maybe the MN3007 itself causes the issue?
Can you check if the C35 cap is shorted? That would cause some weird behaviour.
With C35 out of circuit and you measure the C35 pin on the BBD side (ie. the BBD input), what AC signal do you see? any 4kHz? What DC voltage do you see at the same point?
With C35 in circuit what DC voltage you see on the diodes? and what DC voltage do you see at the BBD input.
If the DC voltage voltage on the BBD input pin changes between when C35 is out of circuit and C35 is in circuit, then C35 must be leaking DC current which will then flow through the diodes.
> the BOM says to use 1N4148 for D9, D10, D11, D12, but the schematic shows 1N914.
The all-purpose Silicon diode used to be 1N914. I still say 9-1-4 to myself.
Some decades ago the process improved and the 1N4148 became the all-purpose Silicon diode with equal or better specs than 914.
Quote from: Rob Strand on July 15, 2023, 08:26:25 PM
The schematic has a bug for sure. Each pair of diodes should be a 1N4148 in series with a 1N34A.
Here's a PCB pic of the real unit around the diodes:
Top
(https://i.postimg.cc/Sjbg20Cm/diodes-pcb-top.png) (https://postimg.cc/Sjbg20Cm)
Bottom, flipped left/right for x-ray view to match PCB top view.
(https://i.postimg.cc/fJTjmMLQ/diodes-pcb-bottom-xray-view.png) (https://postimg.cc/fJTjmMLQ)
Here's the connections I see on the PCB:
(https://i.postimg.cc/56xpgwsG/diodes-sch-fix.png) (https://postimg.cc/56xpgwsG)
Schematic of the original unit confirms this. Each pair should have a 1N4148 and 1N34A. Might want to confirm the connections on the PCB.
EDIT: Looks like the pairs are incorrect in both the DEFX and original Larry documents (when compared to pics of the original PCB and factory schematic)
Quote from: Rob Strand on July 16, 2023, 01:02:41 AM
Can you check if the C35 cap is shorted? That would cause some weird behaviour.
I have tested both sides with my multimeter on continuity and the C35 capacitor is not shorting out.
Quote from: Rob Strand on July 16, 2023, 01:02:41 AM
With C35 out of circuit and you measure the C35 pin on the BBD side (ie. the BBD input), what AC signal do you see? any 4kHz? What DC voltage do you see at the same point?
With the C35 cap out of circuit, I see the following AC at the input, output, and clock pins:
(https://i.postimg.cc/ZW7xPHf4/AC-C35-out-of-circuit.png) (https://postimg.cc/ZW7xPHf4)
This is that 56 kHz on the scope:
(https://i.postimg.cc/87XLfb4W/56kHz.jpg) (https://postimg.cc/87XLfb4W)
It looks like the clock signal on pins 2 and 6 is coming into the BBD and coming out at pins 7 and 8 with no signal at pin 3 coming in.
I see the following DC voltages on the pins of the BBD with the C35 cap out of circuit:
1: 14.99V
2: 7.5V
3: 6.65V
4: 1.11V
5: 0V
6: 7.5V
7: 5.99V
8: 5.99V
Quote from: Rob Strand on July 16, 2023, 01:02:41 AM
With C35 in circuit what DC voltage you see on the diodes? and what DC voltage do you see at the BBD input.
With the C35 cap in circuit, I get the following DC readings:
(https://i.postimg.cc/V5c1cPwr/C35-in-circuit-DC-voltages.png) (https://postimg.cc/V5c1cPwr)
And on the BBD:
C35 in circuit
1: 14.97V
2: 7.48V
3: 6.63V
4: 1.11V
5: 0V
6: 7.48V
7: 5.87V
8: 5.87V
Quote from: Rob Strand on July 16, 2023, 01:02:41 AM
If the DC voltage voltage on the BBD input pin changes between when C35 is out of circuit and C35 is in circuit, then C35 must be leaking DC current which will then flow through the diodes.
It doesn't seem to leak current I think, the difference is about 0.02V on pin 3 of the BBD between C35 being in and out of circuit. What does seem very strange though is that the DC voltages around the diodes look very suspicious when the C35 cap is in circuit.
I guess it does seem to point at the diodes, but other people have built the DEFX Larry and they had no problem with it.
Finally, I was wondering how the 400 Hz sinewave that is suggested for calibration purposes could come out of the 7 and 8 pins on the BBD as a sine wave with the clock signals coming into pin 2 and 6. Wouldn't it be normal that the sinewave gets modified by the clock signal. This is a flanger so I am wondering what the output from the BBD should look like.
QuoteI decided to remove C35 (47 nF) just to see if the 400 Hz would appear on the right side of R57 and on the left side of C35, and it did...
QuoteMy test from this afternoon showed that when I removed the C35 (47 nF) capacitor, the 400 Hz signal passes the diode section fine. When I put the C35 capacitor back, the signal goes to around 4000 Hz after C35, so it doesn't look like the diodes are the problem, but I may be wrong. I have added an image to the post. Could the signal go to 4000 Hz because of any wrong or faulty parts in the sections in red? Or maybe the MN3007 itself causes the issue?
From these previous results, when C35 is out of circuit the AC signal makes it to the diodes. However with C35 in circuit the AC signal at the diodes is lost, probably lost due to a short in the following circuit. From that it is clear at least that C35 can't be open circuit.
Also it's unlikely to be caused by the diodes!
QuoteIt doesn't seem to leak current I think, the difference is about 0.02V on pin 3 of the BBD between C35 being in and out of circuit. What does seem very strange though is that the DC voltages around the diodes look very suspicious when the C35 cap is in circuit.
The change in DC voltage is very small. So there's no a lot going for the C35 leaky theory. It could be on a very fine margin where there is a small leak.
The other point is the AC signal is lost with C35 in circuit so it has to be a loading or shorting issue.
QuoteI see the following DC voltages on the pins of the BBD with the C35 cap out of circuit:
1: 14.99V
2: 7.5V
3: 6.65V
4: 1.11V
5: 0V
6: 7.5V
7: 5.99V
8: 5.99V
...
And on the BBD:
C35 in circuit
1: 14.97V
2: 7.48V
3: 6.63V
4: 1.11V
5: 0V
6: 7.48V
7: 5.87V
8: 5.87V
The fact the DC voltage at pin 3 is an OK voltage and is unchanged with C35 in or out means pin 3 looks OK. It also proves there isn't a dead short to ground on the BBD input pin, or the BBD side of C35.
So that leave very little to work with! I see two possibilities:
- The BBD chip is dead and it is shorting out the signal. However the fact the DC bias voltage looks OK
seems to mean the short is happening in a very weird manner.
- So all I'm left with is thinking maybe you should check the power pins of the BBD have a zero ohm connection
to the +15V outputs of the regulator. CMOS chips have internal diodes so it's possible you measure voltage
on the BBD power pins which is originating from the CMOS clocks and not from the power supply itself.
I don't have much faith in this theory but it needs to be checked to take it off the list.
Perhap another thing to do is to just replace C35 and put an end to any doubts about C35. That result would be very conclusive over fine arguments trying to derive the fault from observations.
QuoteFinally, I was wondering how the 400 Hz sinewave that is suggested for calibration purposes could come out of the 7 and 8 pins on the BBD as a sine wave with the clock signals coming into pin 2 and 6. Wouldn't it be normal that the sinewave gets modified by the clock signal. This is a flanger so I am wondering what the output from the BBD should look like.
It's perfectly normal. The BBD is sampling device. It takes a sample at the input pin and shuffles it through the device then it appears again at the output. The output is of course delayed, that's the whole point of the BBD. The output signal isn't as clean as the input but it does represent a sampled version of the input with a few glitches added.
The overriding problem is when C35 is in place the AC signal on the diodes is lost. If the 400Hz sinewave signal doesn't make it to the BBD input (pin 3) then the BBD sampling cannot be sampling a sinewave there and hence it can never appear at the output.
We knew that whole set of symptoms some time back however we still haven't found a cause!
So I was so fed up that I pulled the 4011N (IC6) out to see what effect it would have on pin 3 of the BBD device (IC9) and low and behold, I was getting the beautiful 400 Hz sinewave! Really strange that the clock is modifying the input signal like that. Does that mean that the BBD is faulty?
Quote from: spacekid71 on July 23, 2023, 03:35:23 PM
So I was so fed up that I pulled the 4011N (IC6) out to see what effect it would have on pin 3 of the BBD device (IC9) and low and behold, I was getting the beautiful 400 Hz sinewave! Really strange that the clock is modifying the input signal like that. Does that mean that the BBD is faulty?
The clock causes the sampling at the input.
Remember there's two clocks. Have you checked they are out of phase like the pic I posted here?
See item 3:
https://www.diystompboxes.com/smfforum/index.php?topic=130842.msg1270239#msg1270239
You need to connect the oscilloscope to one clock signal, get it to trigger etc like you have done in the past. Then observe the other clock signal with the other oscilloscope channel at the same time.
What you are seeing with the clock is probably a symptom of another issue. The clock itself isn't the cause.
What I think in happening in your experiment is when you remove the CD4011 the BBD clock inputs are floating. The open state is turning both sets sampling switches either on or off. It's not something I've done in the past, so I don't know what to expect. I wouldn't expect the input to get shorted.
(https://www.rolandcorp.com.au/blog/wp-content/uploads/2014/07/MN3007-2.jpg)
Are you getting any signal at the BBD output? It's possible you can turn on all the switches.
With the CD4011 out, you could try connecting a 100k resistor in series with each input and then trying all four clock signal combination by connecting the other end of the 100k's to ground or +V (+15V).
RCP1 RCP2
gnd gnd
+V gnd
gnd +V
+V +V
To be honest I don't know how to interpret the result but at least you can see what combinations are blocking the input. Maybe check the BBD output as well.
You need to be careful carrying out this type of experiment. One slip and the BBD could fry, if it's not already fried.
As for the weird clock input combinations. Maybe someone else can shine some light on the what happens?