Aion Quadratron (Lovetone Doppelganger) LFO Issue

[benny_profane]

My quadratron build has a slight issue with the LFOs when dual mode is activated. In single LFO mode, the entire range of knob is useful. In dual LFO mode, the upper third or so locks up the LED at full brightness with no oscillation. Note that at least one other builder has had this issue.

The build has the suggested LEDs (Tayda diffused green). The span pots have been increased to B2K from the original B1K. I've tried tacking a 2k resistor in parallel with the pots to simulate the stock value, although I don't think that this is related to this problem. The problem is exhibited when the pot is completely turned up and there is no resistance between the output of the op amp and the series resistor / LED array.

I've tried swapping the IC6 with another TL022 with no change in behavior.

I pulled one of the LEDs for testing. I'm getting consistent Fv measurements with two different meters for that LED and samples from two different batches of green diffuse LEDs from Tayda.

I'm stuck (much like the LEDs).

BUILD DOCUMENT

 

[r.callison]

Don't have much to offer, but the build doc says this is a potential problem:

HF/LF Span pot values

The original Doppelganger uses 1kB potentiometers for the HF and LF Span controls, which set the intensity of the high and low frequency stages. By increasing the pot value to 2kB, the intensity range is expanded, with more intense settings available at the upper end of the range. The original Doppelganger’s tones are all present in the lower end of the sweep.

Note: Some builders have noticed that the LEDs will “freeze” or stop modulating on the upper end of the range with this mod. This did not happen in our prototype unit, so it’s likely related to variances in the type of LED being used, but since more than one person has experienced this, we are including the precaution. You may need to revert back to 1kB or try different LEDs if this happens with the 2kB pot.

Have you checked against DeadEndFX's build doc? I'm in the process of building their version, but don't have it done to offer comparison yet.

 

[benny_profane]

Thanks for the reply. That note originated with the thread over at MBP and my discussion with Aion. I don't think that the pot value is the issue since the problem arises when the pot resistance is zero.

The DeadEndFX build doc comes from the same source material as the Aion project (i.e., LaceSensor's original trace). LaceSensor is the first person to implement the B2K mod, too (AFAIK).

 

[Nostradoomus]

I’d try a 1K pot just to see. Pots usually have a 20% tolerance so there’s a lot of margin for error there!

 

[benny_profane]

I measured the SPAN controls and they are each within spec (both ~2050 ohms). I tack soldered a 2k resistor across each to simulate 1KB with no change. The problem is exhibited with the control at max anyway. In this position, the SPAN control is shorted. So I really don't think that the value of the pot would impact the behavior here at all.

 

[danfrank]

Personally, I think it's the LED brightness. The Tayda LEDs are rated for 2k-3k mcd, which is way too bright. The DEFX Lola uses an LED that's 5mcd, so I would try to get an LED that's under 100mcd output.
Where Aion went bad on this project is that there wasn't provisions for setting LED brightness or offset to compensate for LED variances. I'm not familiar with the original Lovetone pedal but am wondering if there were trimmers on it to adjust the LED.

 

[benny_profane]

Personally, I think it's the LED brightness. The Tayda LEDs are rated for 2k-3k mcd, which is way too bright. The DEFX Lola uses an LED that's 5mcd, so I would try to get an LED that's under 100mcd output.
Where Aion went bad on this project is that there wasn't provisions for setting LED brightness or offset to compensate for LED variances. I'm not familiar with the original Lovetone pedal but am wondering if there were trimmers on it to adjust the LED.

That's a very good point. What are you doing with your build (sorry for hijacking your build report!)? I had thought about maybe adjusting the series resistors (i.e., the 330R ones), but didn't really know where to start. The DEFX Vital Spark document didn't make a special note about the LED mcd value.

 

[danfrank]

Let me research the DEFX version...
Meanwhile, try LM358 or TL062 in the 3 places where the TL022 ICs are.
You could try placing a 5k or 10k multi-turn trimmer in series with each 330 ohm resistor but that will probably throw off the depth settings when the pedal is on other modes.

 

[benny_profane]

I'll need to place a new components order to get replacement ICs. I think that there is definitely an issue with the LEDs characteristics, though. I took voltage measurements of the LFO with the locked up behavior: There is a voltage swing at the output of the LFO, but it is steady at 2.29V at the output of the buffer before the LED array. I'd rather not alter the value of the series resistor because that could cause other issues and would prefer to use the correct part for the LED. Have you been able to try LEDs with a lower mcd value in your build?

 

[djmiyta]

I'll need to place a new components order to get replacement ICs. I think that there is definitely an issue with the LEDs characteristics, though. I took voltage measurements of the LFO with the locked up behavior: There is a voltage swing at the output of the LFO, but it is steady at 2.29V at the output of the buffer before the LED array. I'd rather not alter the value of the series resistor because that could cause other issues and would prefer to use the correct part for the LED. Have you been able to try LEDs with a lower mcd value in your build?

have you finished your build of? Did it work? Did you change anything? I have the boards from AION and DEFX for both doppelganger and meatball so far
I've completed both DEFX builds with only very very little effect from the meatball. I know whatever my prob is it's something I did. Any way you could post IC voltages for me(or us) if you did get yours working? Thank you

 

[jeffwhitfield]

I built the same pedal and used the same green LED's from Tayda. No issues. However, I will say that the effect didn't feel all that strong at first. So I went back in and updated both the LED's and the LDR's based on a suggestion I read somewhere on a different forum. Basically, given that each of the LFO's use a pair of LED's and LDR's, one of the ways you can intensify the effect is to match up the LED's and LDR's by measuring them with a tester.

For LED's, I think it's the forward voltage drop that you're looking for. I bought a handful of LED's, about 20 I think, and just tested a few to see if I could get some that matched pretty closely. I think the reasoning of this is that when a pair of LED's are shifting together having them at a similar forward voltage drop helps insure that they are at the same relative brightness when changing.

For the LDR's, you'll want pairs that are similar in initial resistance. When they're doing nothing, they'll still offer a level of resistance but will vary a little. It's that variance in initial resistance that might cause a pair to not oscillate as strongly as it should. Matching up each pair so that they're similar in initial resistance will help curb that issue...at least in theory.

So, yeah, I did this with mine and it did make a difference, especially in Dual LFO mode. Still had to play with it and, yeah, the Span knobs are a little weird with 2K pots. I might end up changing them to 1K pots just so they're more consistent. On mine, if I turn up a Span pot all the way, it cancels out the oscillation for that LFO...which I suppose for an extended range makes sense. Hell, if you could hookup an expression pedal to the span then that 2K pot might actually make more sense.

 

[carlinb17]

I recently went back at my doppelgänger from Aion, I built it with the 2k knobs for span and I used tayda leds and the ldr he recommended from Amazon. I also decided to totally deviate from the build diagram and instead of using 3mm green leds for showing the rate I used blue 3mm ones and put them in the rate knobs… I should have known better. I have had issues in the past with the leds I use for rate having a negative impact on the sound or build. I had the same lockup and failure to fire for my rate leds mentioned in the documentation. So I swapped out to b1k and that made it sound better but didn’t fix the rate lockup. So I ripped out the rate leds that were built into the pots… the forward voltage for the blue ones were 2.7 and the green ones I replaced it with were 1.9. And it works. Sounds better I’m not going to pretend I know the science behind the voltage bleed off for the leds and how that affects any number of issues with the build but it does.

 

[benny_profane]

have you finished your build of? Did it work? Did you change anything? I have the boards from AION and DEFX for both doppelganger and meatball so far
I've completed both DEFX builds with only very very little effect from the meatball. I know whatever my prob is it's something I did. Any way you could post IC voltages for me(or us) if you did get yours working? Thank you

I have mine finished up, but I haven't taken voltages. I'll try to see if I can soon. What issues are you experiencing?

I don't think that the B2K modification has anything to do with the lockup issue. Since the pot is completely open when the lockup is occurring (i.e., 0Ω), that shouldn't be the issue. I replaced the LEDs with sub 20 mcd devices with no change in behavior. I think that @jeffwhitfield's post above is correct in re the depth of phase being rather limited since it is only two stages. If I were to work on this unit further, I'd be more deliberate with matching the LDRs. As it stands, I think it's important manage expectations about the pedal (i.e., it's a rather subtle phaser), and not try to make it something it is not without substantial modifications.

 

[djmiyta]

I

I have mine finished up, but I haven't taken voltages. I'll try to see if I can soon. What issues are you experiencing?

I don't think that the B2K modification has anything to do with the lockup issue. Since the pot is completely open when the lockup is occurring (i.e., 0Ω), that shouldn't be the issue. I replaced the LEDs with sub 20 mcd devices with no change in behavior. I think that @jeffwhitfield's post above is correct in re the depth of phase being rather limited since it is only two stages. If I were to work on this unit further, I'd be more deliberate with matching the LDRs. As it stands, I think it's important manage expectations about the pedal (i.e., it's a rather subtle phaser), and not try to make it something it is not without substantial modifications.

I seriously came to the same conclusion. I got mine phasing (finally) found I am having odd behavior though intermittently the 2nd LFO led stops working .Stopping that phasing so there’s phase silence phase. I’m sure it’s builder error, but maybe bad toggle or cold joint.I now have a working one maybe I’ll get the DEFX board working.
Thanks for info Are doing the meatball as well?

 

[benny_profane]

Ensure that all of your switch joints are good and verify the parts in the second LFO. There's a lot of switching going on there, so a lot of points of failure. A wrong component value could also lock up the LFO. Did you sub any parts?

An no, I didn't pick up the Meatball, sorry.

 

[jeffwhitfield]

I have mine finished up, but I haven't taken voltages. I'll try to see if I can soon. What issues are you experiencing?

I don't think that the B2K modification has anything to do with the lockup issue. Since the pot is completely open when the lockup is occurring (i.e., 0Ω), that shouldn't be the issue. I replaced the LEDs with sub 20 mcd devices with no change in behavior. I think that @jeffwhitfield's post above is correct in re the depth of phase being rather limited since it is only two stages. If I were to work on this unit further, I'd be more deliberate with matching the LDRs. As it stands, I think it's important manage expectations about the pedal (i.e., it's a rather subtle phaser), and not try to make it something it is not without substantial modifications.

Mileage will vary indeed. Based on demos of the original I don’t think it was ever meant to be a deep phaser effect. A little more on the subtler side but more harmonically rich. Sounds more elegant to me. I like it with cleaner tones for sure. Highly distorted tones just don’t sound as good to me. For that, a more traditional phaser is needed.

 

[djmiyta]

Just an update got my double ganger run at a 100%.Odd thing one of my LFO leds was in backwards but was working intermittently if I switched a few switches but then I thought maybe that’s how it operated. I pulled it apart 1 more time and caught the culprit and fixed his ass good and now I have a working Lovetone clone!!
It is a quirky kinda pedal for a phaser I have an Arion delay and with all the pots maxed you get but a whisper of delay subtle but there ,so far, that’s how my clone is, tho we haven’t gotten intimate yet I’m hoping my feeling will change after. Is that TMI ?

 

[djmiyta]

Final post on my 2 AION Lovetone clones. The more time spent the more wants to be spent. Most of the effect are at somewhat extremes of the pots and both pedals seem to work way better driven by hotter signal like my OD into HM-2 into Meat type thing anyways a bit of a learning curve for me but way way worth the trouble.For some reason the AION boards were pretty trouble free compared to DEFX board and that’s not a knock to their board at all.
Build 1 or 2 for yourself you will not regret it once you learn them they’re awesome pedals
Green Tayda diffused LED and GL5537 worked in both Spectrum and Quadratron no problems make sure (for me at least ) the jacks are isolated and switched and wired correctly.
Thanks to everybody for their help, wisdom ,and input. And now on to my next buildz z z z a. Man do I love building pedals. Up next G2 Animal, Cranky Chuck, TWEQ tone, BE-OD and a Siracha(?)

 

[soggybag]

I was having the same issue as the original post. With the span controls all the way the LEDs seem to stop. I don’t think the LFO is “locking up” instead I think the minimum voltage coming through is high enough to keep the LED lit. This means you’re not seeing the it dim But, the LFO is still running.

Look at the schematic, the span pot is in series with the 330r resistor and the LED. Replacing R27-R32 with larger value might help.

 

[Audiohub]

I finished the Quadratron phaser recently, and like it a lot. Like others here, I spent some time tweaking it to my liking. I used the photocells available from Amazon, and matched a set of 4 from them, measuring the resistance at a medium and high light level (as well as in the dark, covered with a coffee cup). Once I had those, I made a matched set of LEDs by measuring their effect on a test photocell when set to a fixed higher brightness.
I tried both lower and higher brightness LEDs, and went with the brighter LEDs in the end, which gave a wider sweep (further excursion into the treble frequencies).
The biggest help was replacing the 10K sweep bias resistors R43 and R44 with a 20K trimmer, allowing me to set the LFO bias point by ear, so that it could be placed to cover the entire available sweep range smoothly, without asymmetrically "flattening out" at the top or bottom of the range. This may be the culprit behind the "Freezing" some people have reported in the upper LFO range of their builds; just a guess, as I did not experience this problem in my build. I also changed the 220K resistors paralleling each photocell to a lower value (132K in my build) which set the desired low point of the frequency sweep when the LEDs were off.
I also disabled the part of the DUAL LFO footswitch that shorts out the additional dropping diodes in the LED circuit, which limits a lower sweep range in the DUAL mode (lift the wire going to C2 on the footswitch board).
Some other useful mods were using a 3 position ON/OFF/ON toggle switch in the SLOW position. This gave me 3 possible speed ranges for LFO 1 (which can now go into ring mod territory, an interesting effect).
I replaced C18 with a 1uf cap, C19 with a 47uf cap, and soldered a 220uf cap from unused outer lug on the switch to ground (scraped off a bit of the etch resist nearby to make a ground connection). C20 causes a bit of "slew" in the SQUARE mode; I eliminated it in my build, as I liked the snappier effect this gave. Additionally, I changed R35 and R38 to 1K to increase the upper speed range of each control, and changed C21 to 47uf to slow down LFO 2 to a more serene rate in the lower range. I used TLO62s for the LFOs, and they worked fine with no ticking.
I hope this helps others in their build, and as always, YMMV.