Ludwig Phase II - resistor on fire - need debug help

[robotmonster]

Thanks for the help so far guys, I could not have made it this far without you! I've been busy with the circuit and made solid progress in the meantime. It is still not ready to be boxed, but I have some good news to report and more issues to chase you about.

Diode fix brought me luck because right at the spot where cathode should be connected, junction was bridged to ground on my board (doh!), so figuring that out was a big step forward. Repeater and Modulation started working! I marked it on the layout image below if it can be of help to someone (No.1)

Had really weird voltage measurements on Q7 and Q8 before the diode fix, voltages were modulating in quite different numbers (saw between 20-30v and 0-20v on my scope), and after the 15V zener was installed everything got in place per notes in the build doc (0-13.5v or so). And there was no bleed through the switch. So that one is also out of the way.

I was immediately curious about filter functions and modulation, but found that only VOWEL switch was working / producing some modulated whine. I started randomizing with trim pots and intensity values, and I managed to hear first YOY out of it!

At this point I started all sorts of checks due to not having PARALLEL and COUNTER switches working. Here is what I have verified FYI for the Nth time:

1) Confirmed all the resistors values visually using color codes
2) Confirmed all the transistor values visually
3) Confirmed all the capacitors values visually
4) Soldered 10K pot for testing in place of rocker pedal stereo jack

PARALLEL and COUNTER switches were still not working, so I decided to check traces once more. This time I placed transparent silk screen on top of the actual traces to check visually for more bridges (where things were tight), was super detailed in it and I did find another one (No.2). So after all that, I am super confident now that there are no bridges left, and that I got all the parts right and now all 3 filter switches are working as expected. With some random trim-pot and intensity settings, I could sweep using rocker pot and dial in modulation on all filter modes. Each had a slightly different quality (in between loud squeals), so that was also starting to look good.



Analyzed the Tuning thread for a couple of days, and was trying to tune the circuit, and I did to a point, but could not get very far with taming the whine. I will post more details about it in the next post. At the time of writing my previous post, voltages on lot of transistors were quite off, so I decided to do another sweep of measurements after doing my first attempt at tuning (and with all the errors out of the way). I did find few values still off, and at this point I need some advice to be able to continue.

I am posting my measurements below next to the values from build doc, but here are some general questions before I get down to tuning business and troubles I had around it:

1) Is it an issue because I used 5% tolerance resistors on almost all places, so voltages are a bit wrong (relevant to tuning issues also)?
2) When effect is engaged with everything else switched off, signal has some filter ring to it, is this normal or should it be identical to clean signal, considering that all the switches are off and modulation/rocker pedal not sweeping the filter?
3) What is the difference between Voice Fuzz and Fuzz toggle? Voice Fuzz I can not work out, but I found that other position (Fuzz) makes it possible to engage Repeater effect via 3-way switch. I can hear slight drop in volume when switching from Voice Fuzz to Fuzz, but I guess we can attribute this to Repeater circuit? I can hear the repeater chopping the fuzz away so that part is looking good. I suppose clean signal does not go through repeater circuit ever in this effect?

Here is the table of voltages for your reference (if it can be of any help) after I did initial sweep of tuning (more on it after this post):



Comments table:
1) With DMM probe connected 1.7v starts climbing to 2.1v and beyond.
2) Per above but oddly, with probe against Collector of this transistor, voltage declines slowly down below 1v. So I can not take exact measurement. If I put DMM in between these collectors it reads around 1.2 and a bit unstable (Still not at 0.2v as specified)
3) For Q3, Q4, Q7, Q8 I found that Base toggles opposite to Collector. If C=13.5V then B=0V, else if C=0V then B=0.7V. Also found that these voltages remain at their (alternating) values depending on the moment when animation is switched off.
4) With animation on it goes from 0-4V so quite different there.
5) Not at 13.5 like others, maybe because I used 15v zener?

[robotmonster]

For tuning I followed this thread:
http://www.diystompboxes.com/smfforum/index.php?topic=94478.msg815106#msg815106

I hope it is ok to post my progress and questions here instead, due to relevance to above.

Firstly, I got my head around CP's and TP's and cross referenced them from old schematics. Here is what I have done:

If you're using a grounding input jack (like the original), don't forget to insert a cable, or dummy plug, to unground the circuit.

Done

Set trimmer R65 to full counter clockwise (in the orignals). I'm not sure of the orientation in the clone, but in any case, if you're turning it and start getting bad oscillation, crank it all the way the other way. Measure resistance between the trimmer and C28 (opposite T.P. 9), and then dial in the trimmer to get 22K on the DMM. This balances against the 22K resistor on the other filter, before it hits C.P. 6 fall board. Set all other trimmers to their center position.

Done

With animation off, pedal toe down, no fuzz, FFM INTENSITY set to MAX, and a dummy plug in the input (to unground it, if using grounding input), the voltage at C.P. 18 console, with COUNTER mode ON, should be set at around 7.3 - 7.4v using trimmer R20. This will change slightly during tuning, but it's a close starting point.

Done

Set the rate voltage at pin 28 console to 20v, using R4. I find that this give the best balance between low and high speed.

Done

I find that 3.800v at T.P. 3 seems to be the sweet spot for the main filters voltage. Adjust R29 to achieve this. It's critical to be as accurate as possible here, since very slight changes, yields quite audible changes. This is why I prefer multi-turn trimmers. 3.800v seems to give the most formant action in all three modes. It may vary by 0.005v switching between vowel, and parallel, so split the difference.

Done

Next, set the opposing voltages in COUNTER mode. This will be the true test of your patience, and ultimately render judgement as to whether or not you deserve one of these units. I found that it's best to start here, so ask your secretary to clear your schedule for the day, put on a pot of coffee, and let's get down to business. Once this mode is balanced out, the other two modes pretty well fall into place. It's important to achieve balanced opposing voltages between toe down, and heel down. This is done by testing between pins 8 and 9 fallboard. Record the voltages, in toe and heel down positions on one pin, and then again on the other. What you're shooting for is something like this;
C.P. 8 fall board - toe 2.7v, heel 6.3v.
C.P. 9 fall board - toe 6.3v, heel 2.7v.

This is where the fun starts.

Firstly I had hard time identifying CP8 and CP9:

CP9 looks like it is a wiper of a RF55 trimmer so that is what I have used.
CP8 I was not sure about if it is a wiper of RF77, but I have used the connection point between RF51 and RF77 trimmer instead, because using a wiper of RF77 was giving me weird voltages (below 1v in heal pos. and similar) and I could not balance it out many ways I tried. Also I was reading posts from Ry in the tuning thread where he even used a different spot for CP9 (not wiper) so I was starting to get confused fast. Can someone please confirm exact spots in the circuit for these two points?

I noticed that CP8 min value was fixed at 1.3V (unless I moved RF77 from centered position) regardless of R20 and R31, so I decided to balance with that. I could hardly get values above 2V without hammering the RF77 trimmer all the way, and if so I had hard time balancing with other one (RF55). So at the end I managed to balance with values of 1.3v min and 6.3v max on both points (depending on what end the rocker pot was set). However squeal is horribly loud in heel position, and I get only useful range within small travel of rocker pot, plus I have to reduce intensity to hear anything pleasing. Got a bit stuck here after trying for some hours.

T.P. 2 voltages should be between 4 - 4.5v toe down, and 13 - 13.5v heel down at this point.

I checked this next, but I got confused where exactly is TP2 is. Old schematic shows it at wiper of the Rocker pot, but how could heel read 13.5 since wiper would be grounded then? 3rd lug = GND? Can someone please confirm the location of this point.

After all this, I started running out of ideas fast, and decided to do another round of transistor measurements (posted in previous post). I am considering (due to my lack of EE knowledge) to try replacing all the semiconductors (transitors/diodes) on both boards due to errors in voltage measurements, since I have confirmed everything else and I also had some shorts which could have potentially damaged something? Maybe try with a new set of multi-turn trim pots? Also not sure if 5% resistors were good idea due to these balancing issues?

Phew. I hope all this is readable enough with English not being my first language. Not expecting people to solve the world for me, but if you have any bright tips from my ranting above, they would come as greatly appreciated! Again, many thanks to you all helpful people.

[Keppy]

At the risk of adding yet another confusing tuning post when there's already a lengthy thread, here is the tuning procedure I developed for my own reference, with no ambiguous test points.

• With the power off, set Rf65 to 22k.
  
• With the power on & Animation off, set the right leg of Rf29 to 3.8v (wiper faces you)
• With the Animation toggle set to Fast Start, set the right leg of R4 to 20v.
• Counter mode, heel down, measure voltage on Rf77 wiper. Use R32 to set the voltage to ~6.7v. Switch to toe down, should be ~2.7v. If off by more than .3v, adjust rocker pot and try again.
• Measure voltages on Rf55 wiper. Adjust R20 so they match the voltages on R77 but in reverse.
• Animation on, Rate min, Counter mode, search for and destroy squeals using Rf62, Rf55, Rf41 & Rf77. Do this with toe down and heel down.
  
• Repeat step 6 with Parallel and Vowel modes.

This should all be redundant to what you've been working with, except that these instructions refer to the trimpot lugs instead of test points from the schematic. Hopefully this clears up the schematic confusion, so you can get on with tuning/debugging.

Any more detailed or otherwise useful observations I could give are on page 1 of the thread you linked, but this procedure is what I do, as simple and brief as I could make it.

[Keppy]

1) Is it an issue because I used 5% tolerance resistors on almost all places, so voltages are a bit wrong (relevant to tuning issues also)?

Probably not. This thing was originally manufactured in the 70s. 5% is probably better than most of the originals.

2) When effect is engaged with everything else switched off, signal has some filter ring to it, is this normal or should it be identical to clean signal, considering that all the switches are off and modulation/rocker pedal not sweeping the filter?

This is normal. If you turn this thing on with the fuzz and formants turned off, it sounds terrible. Honky and nasally, right? It's really not meant to be used without the fuzz or formants.

3) What is the difference between Voice Fuzz and Fuzz toggle? Voice Fuzz I can not work out, but I found that other position (Fuzz) makes it possible to engage Repeater effect via 3-way switch. I can hear slight drop in volume when switching from Voice Fuzz to Fuzz, but I guess we can attribute this to Repeater circuit? I can hear the repeater chopping the fuzz away so that part is looking good. I suppose clean signal does not go through repeater circuit ever in this effect?

- Fuzz is an intense fuzz which is gated at extreme settings (try setting Fuzz Mix at halfway in this mode).
- Voice Fuzz is a more classic-sounding fuzz (try setting Fuzz Mix all the way up in this mode).

See notes below if that isn't what you hear.

Here is the table of voltages for your reference (if it can be of any help) after I did initial sweep of tuning (more on it after this post):

The first voltage reading that looks concerning to me is Q5. That transistor's voltages will change when you adjust R20, though, which is part of the tuning process. It's also affected by the rocker pot, so it will look wrong if you don't have the pot set as specified in the build doc when you take your measurement.

QF5/QF6 also look odd. Their collectors are connected, meaning they MUST be the same, but they're listed half a volt apart. Either you measured wrong, or one of the collectors is lifted.

[robotmonster]

Thanks Keppy, that clears a lot of confusion for me.

Counter mode, heel down, measure voltage on Rf77 wiper. Use R32 to set the voltage to ~6.7v. Switch to toe down, should be ~2.7v. If off by more than .3v, adjust rocker pot and try again.

Did you mean adjust trim pot and try again? (In this case R32?) Or is there a way to adjust rocker pot?

The first voltage reading that looks concerning to me is Q5. That transistor's voltages will change when you adjust R20, though, which is part of the tuning process. It's also affected by the rocker pot, so it will look wrong if you don't have the pot set as specified in the build doc when you take your measurement.

Yep Q5 was also bugging me, being the only transistor on console board looking wrong. I will try to pop a new one in and will see if that helps.

QF5/QF6 also look odd. Their collectors are connected, meaning they MUST be the same, but they're listed half a volt apart. Either you measured wrong, or one of the collectors is lifted.

Yes, QF5/QF6 are being really weird. I have a good quality meter from Fluke and when I put a probe against the collector, voltage is being unstable. It goes slowly up or down depending on which transistor's leg I am touching. If I put the probe right in between the two legs then it kind of fluctuates around 1.2V but not stable as in other spots. I will try to replace these two and check connections to all adjacent components and report back.

QF7 is also looking way off, not sure what can I do with that one.

[Keppy]

Counter mode, heel down, measure voltage on Rf77 wiper. Use R32 to set the voltage to ~6.7v. Switch to toe down, should be ~2.7v. If off by more than .3v, adjust rocker pot and try again.

Did you mean adjust trim pot and try again? (In this case R32?) Or is there a way to adjust rocker pot?

Most enclosures don't allow the rocker pot to use it's full range, so the range available can be fine tuned by rotating the body of the pot a few degrees relative to the enclosure, or by moving the pot shaft one tooth over on the gear. That's what the instructions refer to.

Since you're currently using a pot without an enclosure, that doesn't apply. Since your pot has full rotation, though, you may have more trouble than usual eliminating squeals, since they occur mostly at extreme settings which are usually limited by the enclosure.

This means that once you're sure it's working, you should plug in the expression pedal to tune it up. The tuning is affected by the rocker enclosure.

QF7 is also looking way off, not sure what can I do with that one.

QF7 collector is affected by the rocker pot, RF77, and even the formant toggles. If yours weren't set as expected, then your reading there will be off, and will probably continue to be off until it's tuned up.

[robotmonster]

Good news everyone! I think my Phase II works just fine and is ready to be boxed! I managed to dial in sounds of awesomeness across the board without any squeals. All functions seem to be working well and pedal sounds GREAT! I watched some videos now, that you guys posted on youtube, and it acts/sounds pretty much identical (minor tuning variations aside).

With the power on & Animation off, set the right leg of Rf29 to 3.8v (wiper faces you)

I have used the wiper of this trimmer to set 3.8V, because on the schematic it shows lambda at that spot.

QF7 collector is affected by the rocker pot, RF77, and even the formant toggles. If yours weren't set as expected, then your reading there will be off, and will probably continue to be off until it's tuned up.

That is so awesome to hear because it was the last one I was not sure about.

The first voltage reading that looks concerning to me is Q5. That transistor's voltages will change when you adjust R20, though, which is part of the tuning process. It's also affected by the rocker pot, so it will look wrong if you don't have the pot set as specified in the build doc when you take your measurement.

This is true indeed. My rocker was set heel I believe so reading was close to zero. When I moved to max I could dial in 8.1V via R20 so that one also checks out.

QF5/QF6 also look odd. Their collectors are connected, meaning they MUST be the same, but they're listed half a volt apart. Either you measured wrong, or one of the collectors is lifted.

Yes, these are connected and should read the same, but something funny is happening when I put a probe on them. Could this be parasitic capacitance or something in those lines? I had different reading because I did not measure them at the same time. And when I attach probe on them voltage starts slowly climbing or falling depending to which transistor probe is closest to. Latest reading I got was 0.8V on both (probe was only briefly touching the wire, that connects two collectors with a switch). So I guess I can sign those off as well considering that unit is sounding nicely otherwise?

Most enclosures don't allow the rocker pot to use it's full range, so the range available can be fine tuned by rotating the body of the pot a few degrees relative to the enclosure, or by moving the pot shaft one tooth over on the gear. That's what the instructions refer to.

Balancing around R31 and R20 was still confusing to me after all your previous posts, but now I understand why - limited travel of the rocker pedal, so we use only a central subset of the pot travel, and these are used to compensate for it. I got them sort of in 2.7V / 6.3V ballpark only when pot was not set to extreme ends. Maybe it was 2.7/6.3 vs 2.7/6.9 or something, but by ear, I could hear that it was not really that critical at all to get nice sounds in COUNTER mode. In this mode filters live in the opposite ends and meet at a point when moving the rocker pot close to the center, so I understood it mainly a matter of centering this spot on the pedal and setting ranges for two opposite filters at each extreme end of the rocker pedal.

After I got that roughly sorted, I started tweaking Rf62, Rf55, Rf41 & Rf77 with animation on and was actually easy to get rid of ALL whining. While doing so I was just sweeping rocker pot the full range slowly back and forth, to find out which squeal is attributed to which trimmer. It is like a dedicated squeal-EQ with 4 bands (excluding RF29 and RF65). RF77 being mainly responsible for low end thump, and higher squeal frequencies moving towards RF62. I kind of got them tuned JUST to stop the squeal but as close to squeal as possible.

Because of the full range of 10k pot, I tuned R31 and R20 by ear at the end, and after all squeals were eliminated, by sweeping 10K rocker pot fully end to end, I could hear some thumping or faint harmonics at the extreme ends, so I tweaked these by ear just to get rid of that and balance filter frequencies ring at each end with fuzz fully maxed. So I actually did manage to get the full 10k range without any squeals and pedal was modulating nicely and sounding beautiful!

So happy having this build finally complete. Learned a lot in the process by doing it and your help guys was very motivating and much appreciated.

Now just to give it a day with a drill press to put it inside the enclosure and it is getting an honorable place on my pedalboard

I am already thinking about mounting a 10K pot on the back, and have it switched with a Rocker pedal jack. Will do some research to see what else you have been posting about the input section improvements & other mods as well.

One more time, many many thanks to you all for helping my pedal dream come true! <3

[Keppy]

Congratulations on getting it working! It's a tough build.