Ludwig Phase II LFO issues [Solved]

[BetterOffShred]

Hey guys, so I got the newest Deadend phase 2 board set and populated it and got it all set up and ran into a couple problems. I read through every troubleshooting thread here I could find with similar problems but none of them really had any definitive fixes- so I apologize if this has been covered somewhere else. 

First what works: Bypass engages the filter and all three filter toggles work, changing the nature of the filter. The treadle works and sweeps the filter. The fuzz works and the fuzz voice toggle works, both fuzz behave as expected.  Stereo stomp works and sends signal to the other output

What doesn't work: The LFO and all its associated features. No drum beat, no sweep, no speed knob. 

I read through the tuning guide and though it might just need to be tuned so I did all that, though step 2 is to test the LFO which  iof course didn't work.   

I pulled the top board and started checking around at Q29 and the PUT. I observed the 3.3k resistor R125 and changing the timing cap to a 2.2u.   After checking and scratching my head I remembered that the Moosapotumus Skippy is a 2646 circuit that has a mod for the 6027 PUT.

This appears to be somewhat similar to the way the PUT is set up in the Ludwig,  and I have a Skippy I built so I tested my PUT which works and saw the LFO rise and fall on the anode.  So I started testing my Ludwig and saw no LFO movement - but now looking at how it is set up the build guide has the following for pin out
A to R124  (this is G in the Skippy from power)
G to C46 and R200 (A in Skippy)
K[C] to R125 and R126 (same in Skippy)
So I swapped G and A on my 6027 and A now seems to rise and fall in voltage as it did on the Skippy.  This fix was recently recommended in a 2018 build though I think that was the older boards.  I guess where I'm at now is hoping someone can verify that my PUT leg swap is indeed correct .. And then perhaps point out any likely spots where I should focus my trouble shooting efforts. 

I have double checked all the components in this area and I don't understand what's happening with Q25-Q8 well enough to know what to expect there, I did check that my zener was putting out right about 15V.
Thanks for looking, sorry if there's a thread exactly like this I missed

[BetterOffShred]

Additional note: I downloaded RG's document and read through t hst and it seems my Q25-Q28 are not flip flopping.. they are referred to as Q3 and Q4 in that build. I'll do some more searching in this area..

[Govmnt_Lacky]

Build docs for the Ludwig P2 indicate that using a PUT for the LFO should have:

A - R124/C44
G - C46+/R200
C - R125/R126

If you are not getting a proper LFO output then you might consider double checking R200, R126, R124, R123 and C44 for proper values. Also double check wiring for the Animation stomp (check for shorts too)

[BetterOffShred]

Yes That is what the build guide says and my PUT doesn't do anything set up like that. I tried it set up like the Skippy which is swapping the A and G and it seems to function at that point.  I also put in a trimmer for the 220r to ground after reading Keppy had to drop that resistance to 0r to get his PUT to fire up, though mine seems to work with that value anywhere from 0r-500r (500r trimmer)
I don't know enough about the PUT operation to say if it's merely coincidence that I'm getting voltage swing by swapping A and G, or if it should be indeed wired like the Skippy.

I have checked all the values in the area and double checked.. And triple checked, reflowed, scraped, brushed.. the animate stomp definitely disengages the voltage to the PUT so I'm pretty certain that works

[Govmnt_Lacky]

Yes That is what the build guide says and my PUT doesn't do anything set up like that. I tried it set up like the Skippy which is swapping the A and G and it seems to function at that point.

Are you saying that with the leg swap your LFO is working? Or are you saying that it is just showing the same readings as the Skippy?

If it is still not working then I would reach out to Dino and seek further guidance on the issue. Other than verifying you have not lost a trace from the PUT I cannot think of anything else to help 

[BetterOffShred]

Well I got it going, and can confirm my 6027 is set up with A and G swapped from the build doc.


A on the right G on the left, K top - this mimics the pin placement in the Skippy LFO

Sadly like the other builds I followed while trouble shooting this I have no smoking gun as to why it didn't fire up. All I did was prod around Q26 and Q27 while reading voltages at the collectors and tweaking the trimmer at R200 (seen in the pic) until 26/27 started to flip flop. Checked collectors at the echo transistors 28 and 25 and they were indeed flip flopping as well. 

I would love for someone who built this board set with a 6027 to confirm or deny my experience here as I'm certainly not a seasoned EE. 
Thanks for looking

[BetterOffShred]

Yes That is what the build guide says and my PUT doesn't do anything set up like that. I tried it set up like the Skippy which is swapping the A and G and it seems to function at that point.

Are you saying that with the leg swap your LFO is working? Or are you saying that it is just showing the same readings as the Skippy?

If it is still not working then I would reach out to Dino and seek further guidance on the issue. Other than verifying you have not lost a trace from the PUT I cannot think of anything else to help 

Thanks for looking and discussing!

Yeah the PUT had voltage swing at the anode which is what triggers the flip flop through C44 according to the RG doc .. but i wasn't getting flip flop at Q26/27 or the echo transistors..

I poked around with my probe and tweaked the 500r trimmer (set at 0R) and that seemed to bring the flip flop to life

So now my only question is as above if the A and G pins are swapped to make this PUT trigger more like the Skippy

Edit: I think the PUT needs a certain swing strength to trigger the flip flop which corresponds to C44 having been some different values possibly according to the RG doc..

I was not saying I changed any values to match the Skippy, just the pin placement - which did make the PUT trigger

[R.G.]

UJTs and PUTs are IMHO, not the best solution to how they were used. They're just all they had at the time this and similar designs were made.
UJTs were highly variable, to the point that manufacturers would make a wafer, and sort them heavily into different part number, much like how JFETs and some bipolars were made. They still varied. PUTs were an attempt to make the circuits more predictable by using resistors to program a trip voltage instead of relying on the resistance of the semiconductor bar inside the UJT. It helped, but still there are issues. I placed the PUT option on the boards to try to help builders make them, because the 6027 was/is more available than the original UJT part as well as more controllable. As I remember that layout, I thought about putting an IC circuit on the board as an alternate just to get around the UJT/PUT circuit entirely, but decided that "original" was what more people would want rather than "improved". 
I'm glad you were able to get it to work by flipping pins. It may be that you got a 6027 from a maker that just shuffled the pinout. It happens.

[Keppy]

I also put in a trimmer for the 220r to ground after reading Keppy had to drop that resistance to 0r to get his PUT to fire up

When the PUT went into the doc, it was still a theoretical substitution. As far as I know, no one had successfully built it with a PUT until I did, and that was a few years after the original clone project. The circuit did not work as presented in the doc, but after looking up some PUT circuits online I grounded the emitter and that worked like a charm with no other mods or pinout issues. I'm not sure if the doc ever got updated.

I feel your pain with the LFO problems. Besides the PUT shenanigans, the very first clone I built had the UJT bases swapped due to an error on the factory schematic. I had to look up UJT oscillator circuits to figure out that the schem (and thus the prototype layout) was wrong. I've killed lots of hours on this oscillator.

[BetterOffShred]

I have 2 different makes of 6027 and both are the same pin out. I'm asking if the anode is supposed to be connected to C46 and R200 like how the Skippy wires the PUT. In your Ludwig guide on Geo it specifies that the anode replaces the emitter pin which seems to confirm the Skippy wiring.  I'm just trying to clarify at this point without saying "the build guide is mislabeled"  my pins labeled in sharpie:



Anyway thanks so much for looking. I appreciate all the hard work that went into this device and reading through all the years of research and builds was pretty impressive. 

[BetterOffShred]

Now to tune the pedal and filters again after all the work!

Just to confirm.. my 6027 build is now fully functional. I'm not 100% certain the trimmer in place of the 220r at R126 set to essentially zero was the magic bullet, but it seems to have gotten my flip flop going.  Thanks again everyone who made this possible

[digi2t]

This sets in motion a doubt that perhaps there is an error in the silkscreen of the new design boards, that flew past our radar? I will check tonight.

Otherwise (if the silkscreen is correct), perhaps we should insert a note regarding this possibility for future builders.

[BetterOffShred]

Yes I didn't want to raise any false alarms.  Let me know if you need anything  from my build

[R.G.]

I'm pretty sure I still have the original design docs from that in the back of the backup server somewhere if that will help with this. Just yell.

[BetterOffShred]

Thanks RG, I got these two items from your build doc which kind of furthered my "Skippy style" beliefs





So I guess we will just see what Dino finds later

I appreciate the conversation.

[digi2t]

I've examined both boards (R.G. original, and new DEFX versions), and the silkscreening is OK.

I did come across a similar issue in the troubleshooting threads. There was more than one thread, the original debugging thread, and the later troubleshooting thread, so sometimes finding the exact morsel of info to solve your issue might be tough.

Anyway, it starts here; https://www.diystompboxes.com/smfforum/index.php?topic=120574.0

And ends about halfway down the page with the resolution being jumpering of the 220R resistor.

Flipping the G and C legs may have solved the issue for someone at some point, that why I'm suggesting it in the thread, though I didn't have time to scour through all the pages to find the provenance of the suggestion. It may have been a simple as someone not having put the right legs into the right holes. From what I've read though, it seems that while the 2N6027 might be a bit more finicky to get going, people have been able to use it as a replacement for the 2N2646.

In any case, I've made a note to add flipping the G and C legs around (or should I say ensure that they are in the correct pads?), and replacing the 220R resistor with a jumper, to the DEFX build doc.

[BetterOffShred]

Yes I found that thread and referenced it above, though to be clear I swapped anode and gate.  Cathode did not move

RG's doc above I snipped indicates placing anode in the emitter spot for the PUT swap which according to his diagram is the pad connected to r200 and C46 in the DEFX build.

This is consistent with how the Skippy LFO is set up swapping from a UJT to a PUT

The thread you referenced lead me to put the trimmer in for R126 after reading Keppy used a jumper  - which I ended up setting at nearly no resistance - the Skippy uses a 33r

The DEFX schematic shows emitter on the UJT connected to C46/R200 - the RG one does too
Looking at the visiblet trace you can see R200/C46 attached to the pad B1/G  - the schematics and RG's notes indicate this should be E/A.   Sorry if I'm missing something



Thanks for looking