Diy Klon Centaur - Problems - Need help

[Christian Steyn]

Hi all, I started with my first diy pedal project, a Klon Centaur. I used the schematic from "https://www.electrosmash.com/klon-centaur-analysis", all of my component values are right (I think) but there is very quiet/no output. When I engage the pedal, there is a bit of buzz (barely any) and some oscilating noise, but no/quiet output. I can control the volume of the noise with the output pot, so that pot works

But when I turn the pedal off (buffered bypass mode), the buzz and oscilating gets very loud and the guitar signal also gets slightly louder (but still quieter than guitar direct into amp).

Voltages:

Power supply = about 9.3V DC

IC1 (TL072)
1 = 4.25V
2 = 4.25V
3 = 3.25V
4 = 0V
5 = 4.25V
6 = 4.26V
7 = 4.29V
8 = 9.32V

IC2 (TL072)
1 = 4.29V
2 = 4.25V
3 = 4.25V
4 = -7.95V
5 = 0V
6 = -1.14V
7 = -6.54V
8 = 15.75V


IC3 (ICL7660)
1 = 9.31V
2 = 4.13V
3 = 0V
4 = -3.95V
5 = -7.94V
6 = 3.93V
7 = 6.66V
8 = 8.48V

Any help would be greatly appreciated, thanks.

[Christian Steyn]

IC2 seems to me to be the problem, but I dont understand what I did wrong.

[highwater]

First-off, welcome to the forum!

You are definitely correct that IC2 is the (or, at-least, the first) problem. Pin 5 seems to be connected to ground, rather than the 4.5v bias supply... and the other bad voltages on IC2 are in line with what I would expect if that is the mistake.

Most-likely reasons are a short or a wiring error... how did you build the circuit? Did you use a PCB? Perfboard? Stripboard? Breadboard? No matter how you built it, pictures will help.

edit: What sort of buzz are you hearing? That might be a separate issue... the voltage-convertor chips have a tendency to cause buzz/whine-type-noises if they have gone bad and/or are the wrong type (the various extra letters at the end of the part-number really do make a difference in this case).

[Christian Steyn]

Thanks for responding so quickly. I have now fixed the gound problem on IC2 and have attached pictures of the breadboards, but the problem persists.







The buzzing is very loud and is present both when the pedal is on and when it is on bypass. I don't know how to describe the buzzing except that it is deep and muffled and sounds sort of like 60 cyle hum, but the buzzing oscilates like a siren. I can control the volume of the buzzing with the output pot when the pedal is on (when the volume is at 0, the buzzing is also quiet) and the buzzing becomes more trebly when the gain pot is turned up and more bassy when it is turned down. The signal is also very distorted and very muddy and sounds very bad when the pedal is on and the signal is very quiet when the pedal is off (i.e. buffered bypass).

Any help, once more, would be greatly appreciated.

[Christian Steyn]

Oh yeah, and ic voltages are now:

IC1:
1 = 4.20V
2 = 4.19V
3 = 3.52V
4 = 0V
5 = 4.17V
6 = 4.22V
7 = 4.23V
8 = 9.20V

IC2:
1 = 4.49V
2 = 4.18V
3 = 4.18V
4 = -7.79V
5 = 4.19V
6 = 4.19V
7 = 3.61V
8 = 15.47V

IC3:
1 = 9.18V
2 = 4.05V
3 = 0V
4 = -3.84V
5 = -7.71V
6 = 3.87V
7 = 6.58V
8 = 8.41V

[patrick398]

As high quality as those pictures are i still don't think anybody is going to want to diagnose the problem just from looking at them, we may be in quarantine but must draw the line somewhere haha.

From your description of the noise i'm going to suggest you either have DC somewhere where there should not be DC or your grounding isn't right somewhere. The loud buzz that persists even in bypass makes me think it's the latter...but i'm kinda just guessing here.

Are you using true bypass or the actual klon style bypass?

[Christian Steyn]

I'm using the actual klon bypass (buffered bypass), I'll try to get some better pics as soon as I have daylight again. Thanks for helping me out, I'll go through the grounding again to try and see if anything is wrong. How do I know if I have dc somewhere there is not supposed to be dc? and how do I fix it? does that mean that a capacitor is bad? I'm using electrolytic caps for the 1uf, 4.7uf and 47uf caps, I have them connected so that current flows into the positive terminal and out of the negative (i.e. positive terminal first in signal path). Is that the wrong way? I also have 1uf tantalum caps if I need them. Thanks again.

[patrick398]

DC is used to bias op amps and transistors so your guitar signal can be amplified but is also able to swing both negative and positive, caps are used to block the DC whilst allowing AC (your guitar signal) to pass. It's just a hunch, could very well be something else. You could use a multimeter to see if there's DC on your output jack.

Might be time to break out the audio probe, start at the guitar input and follow the signal to see where the noise is introduced

[Christian Steyn]

@patrick398 your initial suggestion was right, the main part of the problem was grounding. I rebuilt it on my breadboard and would you know it... no noise (a little 50 cycle hum from my guitar when on full gain, but this is normal for my cheap guitar). No more oscillation and the sound is now good when the pedal is on. Just a couple of more questions:

Firstly: The volume is still a liitle low on the buffered bypass for some reason and the bypassed signal is a bit thin and trebly. The bypassed volume is less than when my guitar is plugged in directly and I don't know what to make of that, is it supposed to be that way?

Secondly: The gain sounds a little bit scratchy, just a little but enough to be noticed. This scratchyness increases with gain, it is almost gone when the pedal is clean, but returns gradually as the gain increases. Is this because of static or something because the pedal is on a breadboard and not in an enclosure?

Thirdly: The sound is somewhat muffled and the treble pot doesn't seem to do very much. I don't understand this either but the actual Klons are a bit brighter, my diy klon has a TON of low end and the low end increases with gain (i.e. more gain = more muffled). Maybe this is my amp, a Vox Valvetronix VT20+, a beginner amp (has one preamp tube and a solid state power section) which sometimes struggles and buzzes when the sound is too bassy. Any ideas?

Thanks so much for your help patrick398 and highwater, I really appreciate you guys helping get my pedal to where it is now, which sounds pretty damn good to me.

[Christian Steyn]

IC voltages are now:

IC1:
1 = 4.64V
2 = 4.64V
3 = 3.69V
4 = 0V
5 = 4.62V
6 = 4.63V
7 = 4.65V
8 = 9.29V

IC2:
1 = 4.80V
2 = 4.62V
3 = 4.62V
4 = -8.89V
5 = 4.62V
6 = 4.63V
7 = 4.29V
8 = 16.69V

IC3:
1 = 9.29V
2 = 4.60V
3 = 0V
4 = -4.43V
5 = -8.89V
6 = 4.68V
7 = 7.41V
8 = 9.29V

[patrick398]

At a glance your voltages look good but from your description it sounds like something is not right.

Firstly: The volume is still a liitle low on the buffered bypass for some reason and the bypassed signal is a bit thin and trebly. The bypassed volume is less than when my guitar is plugged in directly and I don't know what to make of that, is it supposed to be that way?

The wording is a bit confusing. The volume is less than unity when bypassed? And also sounds thin?
Could be a problem with the bypass switch wiring, if the circuit is actually still connected whilst bypassed it could load down your pickups and cause it to sound thin and weak...again just a hunch.

For your second and third points, not really much i can suggest other than going through the circuit again and make sure everything is connected where it should be. Then double check all component values are correct. Sometimes it's easy to grab a 4K7 when what you wanted was a 47K.

Sorry i can't offer more practical help

[Christian Steyn]

Hi again, I've been offline for a couple of days now. Been drilling all the holes in the enclosure and trying to etch the pcb.

I think the circuit is right now, hopefully. I still feel like the overdrive is a little bit scratchy (or crackly) and I struggle to get a clean sound, there is a LOT of overdrive. I think I've figured out why though. As I previously said, my amp is a Vox VT20+ which is a solid state modeling amp (with one "reactor" tube which does basically nothing), I've read up a bit about how cheap modeling amps take pedals and have found multiple people who claim that theirs do not take pedals well, especially OD. The consensus seems to be that the digital amp does not "know" how to react to the signal from a pedal (as it is expecting a guitar signal) and just compresses it a lot. This would probably account for the TON of overdrive and inability to get a proper clean tone. I'll have to test it on one of my friends' amps when my country's lockdown is over and we can finally leave the house Any thoughts on this "modeler" theory?

Then, to clarify my previous post, yes, the volume/gain on the buffered bypass is less than unity. The picture below is the circuit diagram of the output stage, where the switch is.



As you can see, the switch is "jumped" by the two 68K resistors (R242 & R243), could this be the "problem in the bypass switch wiring" you suggest in the quote below?

The wording is a bit confusing. The volume is less than unity when bypassed? And also sounds thin?
Could be a problem with the bypass switch wiring, if the circuit is actually still connected whilst bypassed it could load down your pickups and cause it to sound thin and weak...again just a hunch.

Once more, thank you for your help and advice.

[Christian Steyn]

Also, I almost forgot, I replaced the 1uf electrolytic caps with tantalum caps and I think it sounds better. May just be psycological but there's someting good about those caps.

[willienillie]

I would advise against building anything from an Electrosmash schematic.  They are notorious for errors in their schematics.  I have not looked over their Klon schematic though, maybe it's totally correct.  My advice would be to do a simple google search and find the common schematic drawn by Martin Chittum in 2009, known to be correct.  I won't post it here because there is a rule on this forum against it, an agreement with the circuit's creator.  I think the small fragment you posted is probably fine, though.

[Christian Steyn]

Thanks, I wasn't aware that electrosmash wasn't reliable, but I probably should have done my due diligence and will in the future.

[antonis]

I still feel like the overdrive is a little bit scratchy (or crackly) and I struggle to get a clean sound

That's because there is DC flowing through Gain pot (RV-GAIN_a)..
Its wiper is wired to +4.5V point, which point goes to DC ground via R30..
DC voltage gain is higher than unity, due to abscence of DC blocking capacitor inside NFB loop, so there is DC flowing from pin 7 through R12, R11, R10, pot lower lug,wiper and R30 to GND..

A cap between pot lower lug & R10 should make Gain setting more quite and smooth..
(don't try it on pot wiper 'cause you'll "break" pin 5 bias..)

[Christian Steyn]

Thanks antonis. Just to be sure, on the pic below, the highlighted yellow and red circle is where the cap should go, right?



Then, what should the cap value be? 1uf? and what type of cap? I have electrolytic, tantalum or ceramic?

As always, thanks all.

[antonis]

Yes, just about there..
(although in would also be OK on the other leg of R10..)

That cap forms a HPF toghether with R10 & Gain low lug - wiper resistance..
Its value should be extracted from f = 0.159/(R10 x C), where f is your frequency of interest for lowest (Full CW) pot resistance setting..
(you might take into account the lowering of that frequency with pot wiper travel..)

Or just throw there any cap of equal to or greater vaue than 2.2μF and don't bother anymore..

[Christian Steyn]

Ok, I used 3 1uf electrolytic caps in paralell for a total of 3uf. I put them between R10 and R11 (i.e. on the other side of R10) with the positive terminal facing R10. Is that the correct polarity?

The buffered bypass is now much louder, like it sould be.

And there is less distortion now. It used to sound like a fuzz pedal but now it sounds like a klon...(I think)

Just two more concerns:
1. I still get the odd noise here and there. It works brilliantly one moment and terribly the next, I suppose this is probably just due to bad connections on the breadboard?

2. There is not a lot of treble and the treble pot doesn't make any (or much of a) noticable change. Any ideas?

As always, thanks, I appreciate all the help.

[Christian Steyn]

I also just scared the s**t out of myself by accidentally connecting just below 3V DC to the power supply section instead of 9V (the icl7660s apparently causes a high pitched squeal at about 3V DC), which reminds me of another question: I'm running the pedal on an improvised power supply made from two 5V DC power supplies (one of which is a blackberry charger) in series. They are not proper pedal power supplies. The total input voltage is around 10V to 10.3V. I researched the icl7660s and it can take up to 12V, so this should be okay, right? or might this be causing some of my problems?

PS: the reason for doing this is that I've already gone through three 9V batteries on this project. They go so quickly, the pedal burns through them roughly at a rate of 0.01V decrease every 10 seconds or so. Meaning that if I run the pedal with new battery (that meaures about 9V at the start), the battery measures about 7V thirty minutes later. Could this indicate a problem as well, or is it normal for Klons to be this thirsty?