Need help with calibration of DEFX Larry - Mutron Flanger clone

[spacekid71]

I 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.

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?



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

I will have a look to see if there are any cold solder joints or shorts after the C35.

[Rob Strand]

I 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.

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.

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.

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?

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.

[PRR]

> 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.

[Govmnt_Lacky]

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


Bottom, flipped left/right for x-ray view to match PCB top view.


Here's the connections I see on the PCB:

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)

[spacekid71]

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.

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:



This is that 56 kHz on the scope:



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

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:



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

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.

[Rob Strand]

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...

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?

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!

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.

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.

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

...

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.

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.

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!

[spacekid71]

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?

[Rob Strand]

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.



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?