I'm in over my head! Lovetone Meatball vero troubleshooting

[Sesh]

Hi DIY'ers

After having done 30ish effects succesfully on vero since I started during the pandemic, I thought I'd take on something more complex. Why not the Lovetone pedals, I thought, they're so damn expensive and rare 2nd hand. And vero layouts exist, so I don't even have to buy a PCB!

Boy, have I been in for a challenge.

I'm using Sabrotones layout: https://www.sabrotone.com/?attachment_id=3088
with Johnk's modifications: http://guitar-fx-layouts.42897.x6.nabble.com/file/n6849/MeatballwMoog-and-RSwitches.png

I'm having some issues with my build. I've triple-checked my layout, reflowed solder three times being extra careful to clean the tip, scored the lines separating the rows countless times with a knife to clean up burs that might short. Changed ICs.

Btw, I'm using the McMeat schematic to lean against: https://farm5.static.flickr.com/4070/4254937718_8846745832_o.jpg

The problem persists: It sends through a very low level signal that is distorted. The sweep LED is turned on at all times in certain throws of the Sweep knob, turned completely off at others. No light in my home-rolled octo-couplers (yellow LEDs) when triggered with a guitar signal. I used 3P4Ts all-around for the switching.

Voltages:
TL074:
1  4,54v      14      4,53v
2  4,58v      13      4,54v
3  4,40v      12      1,59v
4  9,08v      11        0v     
5  4,49v      10      4,49v     
6  4,55v       9       4,26v           
7  4,54v       8       1,56v 

LM1458
1  2,07       8 9,08v
2  1,93       7 1,95v   
3  0            6 1,95v   
4  0            5 1,56v     

Now, in the past I've mostly done fuzzes, including some of the more complex ones, and I've been able to locate the problem area simply by audio tracing. But this being an filtered+enveloped signal mixed into the opamp (as I understand it), I can't trace the signal like I can with the gain stages of a fuzz.

I'd love to get better at troubleshooting... so what do I do with a type of circuit like this? Do I grab the multimeter and measure specific points...? Compare the voltage with the voltages "it is supposed to have" according to the schematic? (and if so, how do I know what voltage it is supposed to have? Something something ohm's law?)

All I can see with my knowledge now is that both chips are getting the 9v where they should, and both are grounded, hence the pins with 0v, where they should. And that ICs are getting the VRef (half of the 9v) where they should.

[Kevin Mitchell]

You know for sure that the LEDs aren't backwards?
Do you have any other 1458 ICs around to try?

Your guitar volume is up? 
(sorry had to ask)

[Sesh]

Yes, the LED cathode is facing downwards as per the layouts. I've exchanged ICs, both TL074 and LM1458, with new chips.
Haha, and yes, guitar volume has been up! I always click the 3dpt on my test pedal with gator-clips to turn off the circuit and see if there's signal through.

[idy]

Meatball on strip board... crazy, man! Or you may go crazy debugging!
The circuit isn't really that complicated, though the stripboard looks nightmarish. There are great PCBs for this...just saying.

Two of your 074 voltages are off. I measured mine, and though its possible your meter is loading the input of the buffer, pin 12, mine reads mid voltage. Same with pin 8...that is the output of the filter section that give LP and should be the same as 9 and 10.

When you turn the sweep switch (not knob, right?) do the opto LEDs light up? They should be the same as the indicator. The sweep selects the "default" for the LEDs; silent input can be off or on. 


If you can spare the time read (skim man, its tedious) through the (long and repetitive) thread called "building the meat sphere."

You would trace signal into the buffer, in pin 12, out 14. It should sound the same. You should also find that same sound on the CCW pin of the blend pot.
The sound should then also go into the filter and into the envelope trigger, the LM 1458


You might try using an LM358 opamp instead. You can read the thread and find out why. You need to get those LEDs triggering or the signal tracing won't help. The LM 1458 converts your signal into DC. You would hear signal entering pin 2 and already sounding trashed there, it is being "half wave rectified" into choppy DC. This gets smoothed out by a capacitor C7, and the other half of the 1458 buffers the voltage so it will drive the LEDs. They picked a clever/simple/sneaky way to make the sweep change; the sweep switch changes what is feeding the LEDs. Either +9 to the plus pins and minus to the opamp, or ground to the minus pin and plus to the opamp output. An opamp, the engineers say "can either source or sink current."

As to further tracing, in the filter section you should be able to hear the signal on 2 and 1, 6 and 7, 9 and 8. Probably on 3, depending on the "resonance" pot.

If you don't want to wait for an LM358 to arrive, the thread above also mentions "biasing" pin 3 pf the 1458. A 100k pot from 9v to that pin should allow you to just "crack" the LEDs and get them to light. The 1458 does not operate below around 2v...
Before I figured this out (biasing and/or 358) I had to boost the guitar on mine to get it to work. That is no longer a problem in my house...

[Sesh]

Meatball on strip board... crazy, man! Or you may go crazy debugging!
The circuit isn't really that complicated, though the stripboard looks nightmarish. There are great PCBs for this...just saying.

Two of your 074 voltages are off. I measured mine, and though its possible your meter is loading the input of the buffer, pin 12, mine reads mid voltage. Same with pin 8...that is the output of the filter section that give LP and should be the same as 9 and 10.

When you turn the sweep switch (not knob, right?) do the opto LEDs light up? They should be the same as the indicator. The sweep selects the "default" for the LEDs; silent input can be off or on. 


If you can spare the time read (skim man, its tedious) through the (long and repetitive) thread called "building the meat sphere."

You would trace signal into the buffer, in pin 12, out 14. It should sound the same. You should also find that same sound on the CCW pin of the blend pot.
The sound should then also go into the filter and into the envelope trigger, the LM 1458


You might try using an LM358 opamp instead. You can read the thread and find out why. You need to get those LEDs triggering or the signal tracing won't help. The LM 1458 converts your signal into DC. You would hear signal entering pin 2 and already sounding trashed there, it is being "half wave rectified" into choppy DC. This gets smoothed out by a capacitor C7, and the other half of the 1458 buffers the voltage so it will drive the LEDs. They picked a clever/simple/sneaky way to make the sweep change; the sweep switch changes what is feeding the LEDs. Either +9 to the plus pins and minus to the opamp, or ground to the minus pin and plus to the opamp output. An opamp, the engineers say "can either source or sink current."

As to further tracing, in the filter section you should be able to hear the signal on 2 and 1, 6 and 7, 9 and 8. Probably on 3, depending on the "resonance" pot.

If you don't want to wait for an LM358 to arrive, the thread above also mentions "biasing" pin 3 pf the 1458. A 100k pot from 9v to that pin should allow you to just "crack" the LEDs and get them to light. The 1458 does not operate below around 2v...
Before I figured this out (biasing and/or 358) I had to boost the guitar on mine to get it to work. That is no longer a problem in my house...

Is the bias thing what Johnk is doing with the small trimmer addon-circuit here? 'Cause I've incorporated that. http://guitar-fx-layouts.42897.x6.nabble.com/file/n6849/MeatballwMoog-and-RSwitches.png

I audio-probed the circuit, and there's sound till the Sensitivity pot CW/lug 3, the low-level, distorted sound starts at middle lug.

[Govmnt_Lacky]

Just a couple "need to know" facts about the Meatball to assist:

1) The Sweep LED will be either ON or OFF based on the setting of the Up/Down rotary. In the Up position, the light will come on when the envelope is actuated. In the Down position,. the LED will be on all the time and go dim when the envelope is actuated.

2) When testing, be sure to set your your Attack pot fully CCW and your Decay pot fully CW. This will ensure that the envelope will actuate at maximum.

[anotherjim]

Is the TL074 pin 8 actually connecting to the circuit? As said, it should hold pin 8 at Vref but only if the preceding circuit can "see" the correcting negative feedback from that output pin.

We can't tell much from pin 9 voltage, because that's also getting Vref from the preceding stages.

The similarity between pin 8 and pin 12 voltage is just coincidence I think since pin 14 is as expected and as said, pin 12 reads low due to meter probe loading.

[idy]

Biasing the 1458 is not what the layout is doing. The "Moog mod" changes the feedback of the filter, I think it prevents you from starting an earthquake with a bass and large amp (the resonance goes down a bit for lower frequencies, (?))

The other little board could be your problem. It adds 100k(!) trimmers to the LEDs that drive the LDRs. They already have 100 ohms+300ohms+ the intensity pot, so they aren't in any danger... the original does not have these trimmers, and if you really were trying to fine tune the brightness, (which is what the intensity pot is there for) you might put a pair of 1k to 5k trimmers on that board. But 100k is going to keep those LEDs dark! At least turn them all the way down, 0ohms.

I'm not sure that Moog mod is correct. That could be messing up pin 8. I would consider removing it and putting a 10k resistor from pin 8 to pin 2 of the 074. That is "stock." That 10k on the layout (pin 2 of 074)...can't figure what it is doing going to the 'A3' of the mode switch...don't like that....not like the schematic....I've got a bad feeling about this....

What you are seeing on the sensitivity pot is good. It is the "trimmer" on the input to the 1458 rectifier. On pin 3 your signal, on the wiper the input (with feedback) of the circuit turning sound into DC.

[idy]

Also I can't find the source for that layout. maybe they explain what they are up to...

[idy]

Found the source in the chat room... Better re-read that chat! There are things missing from the layout! Just because someone says it is "working" doesn't mean...much.
One more missing thing: a 220K parallel to VTL1 resistor side. Just like VTL2 has a 120k next to it. Probably not your problem...but again, there are verified layouts out there, and two great pcbs (musicpcb.com and deadendfx.com) and the guys in this chat bring up the fact that this layout is missing the effects loop, one of the best parts of this monster.

[Sesh]

Found the source in the chat room... Better re-read that chat! There are things missing from the layout! Just because someone says it is "working" doesn't mean...much.
One more missing thing: a 220K parallel to VTL1 resistor side. Just like VTL2 has a 120k next to it. Probably not your problem...but again, there are verified layouts out there, and two great pcbs (musicpcb.com and deadendfx.com) and the guys in this chat bring up the fact that this layout is missing the effects loop, one of the best parts of this monster.

I know, I know. I got both String Ringer and Flanger with no name clone PCBs from Dead End that I'm building, too. But I started with Meatball way back at the start of last year when I got into stripboard and it's been in the drawer ever since due to the level of difficulty.

But you were absolutely right. That layout was error-riddled. I should note that I followed Sabrotones almost all the way and only sought out Johnks because I was in doubt how to wire the pots with 3P4Ts because I couldn't find the rotaries with the odd number of poles and throws on the Sabrotone layout. Didn't even add the Moog-mod.

I got rid of the add-on board with the way too large trimmers, exchanged the 3p4t of Johnk's layout with a 3PDT (those I had lying around!) of Sabrotones layout and wired that. I also resoldered around the problematic pins 8 and 12 of the TL074.

I got the LEDs to light up in correspondance with my output. Success. Alas, no filter sound. And the voltages (pin 8 and 12) of the TL074 are still the same. Try exchanging the components around those pins or what do you say?

[idy]

Good work. You also apparently caught the missing resistor making ref or else there would be no 4.5v on the opamps....

...time to signal trace. Maybe a looper pedal with a handy riff to the input and follow the sound into the filter section.

Maybe pull that 10k out and connect it from pin 2 to 8. You can add the Moog thing later. Mine is a 100k R and 470n C in parallel, switched into being in series with that 10k.

[Sesh]

Good work. You also apparently caught the missing resistor making ref or else there would be no 4.5v on the opamps....

...time to signal trace. Maybe a looper pedal with a handy riff to the input and follow the sound into the filter section.

Maybe pull that 10k out and connect it from pin 2 to 8. You can add the Moog thing later. Mine is a 100k R and 470n C in parallel, switched into being in series with that 10k.

Okay, update.

I traced the filter section all the way to the Intensity pot. You were right about the choppy sound! It sounds very distorted in pin 1 and gradually gets smoothed and reduced in level.

I removed and inserted the components around Pin 8 again making sure that they're connected. R18 (The 10k) is definitely connected from pin 2 to 8, I can trace the voltage dropping from 3,25 pin (2) to 1,41 (pin 8 ) through the resistor.

Anotherjim said the low level indicated that the pin isn't connected to the circuit. If the LEDs light up, shouldn't this part of the circuit be connected?

[idy]

The LEDs are lit by the 1458. If they light, that part is working. The 074 is the buffer on the input and the filter. The LEDs would still light if you pulled the 074 out, they are independent.

If Jim says pin 8 is suspicious, he probably is right. What's funny is that the two other pins of that opamp look OK... that should not be. 10 goes to vref, looks ok. 9 is attached to the previous stage through the LDR/120K resistor. And I'm officially in over my head.  I can tell you the three stages together make a "state variable filter", but trying to trouble shoot it, I don't know.  Maybe turn the power off and check to resistance to ground from pin 8.

I checked mine...the numbers go up as some caps charge and then it reads over range, basically no path to ground.

[Sesh]

The LEDs are lit by the 1458. If they light, that part is working. The 074 is the buffer on the input and the filter. The LEDs would still light if you pulled the 074 out, they are independent.

If Jim says pin 8 is suspicious, he probably is right. What's funny is that the two other pins of that opamp look OK... that should not be. 10 goes to vref, looks ok. 9 is attached to the previous stage through the LDR/120K resistor. And I'm officially in over my head.  I can tell you the three stages together make a "state variable filter", but trying to trouble shoot it, I don't know.  Maybe turn the power off and check to resistance to ground from pin 8.

I checked mine...the numbers go up as some caps charge and then it reads over range, basically no path to ground.

Sorry, I was too fast with the assessment.

There's still issues, but... We got sound!! Totally quackety-quack. Pin 8 measure 4,5v! All the pots seem to work as they're supposed to. Bandwidth only works on one setting, gonna check the connecting caps on the one setting that doesn't work.

And the main issue: A lower level signal overall and a low level distortion underneath the signal. Despite the octo-coupler LEDs lighting up, the sweep indicator doesn't, even when toggled for "on" on the Sweep switch.

Might it be the troubled LM1458... ? I'm also going to try Green LEDs as opposed to the yellow ones I have in now.

[anotherjim]

Didn't properly explain what I was thinking about the wrong pin8 volts.
When you only see a capacitor for the feedback to the -input, it still works as though it has a resistor, but only when the input voltage to the -input changes as that's the only time current flows in the feedback. It should hold the output at Vref as that was the last change in input to happen.

[Sesh]

And it works! As intended.

Thank you so much, y'all.

[Paul_5]

I'm tinkering with the sabrotone layout and am able to get the leds flashing in response, but the 'filter' is just one pitch - meaning that there isn't any sweep up or down. Could someone point me in the direction of the part of the circuit that does the sweep?

[idy]

The "1458" is the envelope trigger.
Signal goes through "bandwidth" switch and caps, into pin 2. What comes out pin 1 is DC, which is buffered by the second half of "1458."

What kind of "1458" did you use?

Many long conversations about this opamp not always triggering, and now the word is LM358 is better. There is a long repetitive thread called "building the meat sphere." It is worth skimming for the hot parts.

The other option is to "bias" pin 3. 100k trimmer from 9v to pin 3. You should be able to light the LEDs or have them just barely off. Which is where you want them to rest. The trimmer allows you to "force" the trigger. You can read about this. Earlier on same thread?