Help with Tayda Tone Bender kit

[neiltheseal]

I just put together a tone bender PCB from Tayda. After soldering everything I find that the pedal doesn't work. When I hit the switch the LED lights up but there is no sound. When I turn it off i can hear the clean tone of the guitar.

I'm new to building pedals and new to the forum. I have sucessfully built two kits (one a Tayda fuzz factory and the other an Ali Express Klone) but I am stumped on this.

I followed the instructions provided on their website https://www.taydakits.com/instructions/tone-bender.I made an NPN silicon version and followed the suggested instructions (to the best of my ability) such as reversing the polarity of the electrolytic capacitors and putting the 9v+ where it says 9v-.

I'm using BC108 transistors but tried 2n3904 as well. I just don't know where I might have gone wrong.

I have done some research and it seems the problem might be biasing the first transistor, but I have no idea how do do this. Any help would be appreciated.

[mauman]

Welcome!

Could we see a picture of the other side of the board?

There are different versions of the Tone Bender, and this one is a Mark II.  The first transistor (Q1) doesn't require biasing.  Q2 and Q3 do need biasing, you can use the two trim pots for that.  Here's a process for that.  You'll first be using the Q2 trim pot while measuring Q3 for a rough bias of both, then individually biasing Q2 and Q3 using their own trim pots. 

1. Set BIAS2 trim pot and BIAS3 trim pot about in the middle of their range.  Apply 9V power to the PCB.
2.  Using a voltmeter set for DC volts, touch the black lead to ground (GND lug on the PCB is good) and the red lead to the Bias3 test point just under the BIAS3 trim pot.
3. You're going to use the BIAS2 trim pot to roughly bias both Q2 and Q3 at the same time.  Measure Q3's collector at the Bias3 test point and adjust the BIAS2 trim pot until the Bias3 test point reads close to 8.5V DC on your meter. 
4. Now fine-tune the bias on Q2 using the same BIAS2 trimmer.  Move the red lead of your meter to the Bias2 test point.  Slowly adjust the BIAS2 trim pot until the Q2 Bias2 test point reads about 0.15 VDC (150 mV) on your meter.
5. Now fine-tune the bias on Q3, this time using the BIAS3 trimmer.  Check the Bias3 test point again.  If it's not somewhere close to 8.5V DC, adjust the BIAS3 trim pot until it is.
6. Recheck the Bias2 test point, and if needed, adjust BIAS2 trim pot to bring it back to 0.15V (150 mV).  This adjustment is more important than getting Q3 right at 8.5V.
7. Recheck Bias3 test point again for around 8.5V, adjust with BIAS3 trimmer if needed.

If this doesn't work, please post the voltage readings of the collector, base and emitter of  Q1, Q2 and Q3 so we can see what's happening.  Something like this:
Q1: C 8.5, B 0.05, E 0
Q2: C 0.15, B 0.07, E0
Q3: C 8.5, B 0.15, E 0.1

[NorthCoast]

I have done some research and it seems the problem might be biasing the first transistor, but I have no idea how do do this. Any help would be appreciated.

Hi and welcome,

Try putting a 470k resistor between the base and collector of Q1, and then biasing as mauman described.

[neiltheseal]

Thanks for your responses. Here is the other side of the pcb.

I'll try the biasing when I finish work and update.

RE the 470k resistor between the base and collector of Q1, do you essentially mean solder a resister between these 2 points on the PCB (probably the back as there is no room on the front)?

[NorthCoast]

RE the 470k resistor between the base and collector of Q1, do you essentially mean solder a resister between these 2 points on the PCB (probably the back as there is no room on the front)?

Yeah, basically however you can get a 470k connected to the base and collector.

When I first typed it in, I wasn't thinking about how to actually physically do this... sorry about that.


Edited to add:

You could also try removing Q1 and running a few wires from the socket to an offboard 2n3904 and a resistor. Either solder the wires directly to the parts, or use a piece of perfboard if you have it. This would be temporary just to see if this solves the problem, and then we can go from there.

[BrianS]

Just an observation but are your ELECTROLYTIC caps oriented correctly?  Most of my caps are negative on the striped side of the cap.  If they’re like that then C2,5 and 6 are backwards.

Reflow all your solder points.  It looks like you may have an arch on the bottom left. 

[mauman]

Just an observation but are your ELECTROLYTIC caps oriented correctly?  Most of my caps are negative on the striped side of the cap.  If they’re like that then C2,5 and 6 are backwards.

Good eyes!  He's using a +9V supply rather than -9V, so those EL caps have correctly been reversed to accommodate that.

[BrianS]

Just an observation but are your ELECTROLYTIC caps oriented correctly?  Most of my caps are negative on the striped side of the cap.  If they’re like that then C2,5 and 6 are backwards.

Good eyes!  He's using a +9V supply rather than -9V, so those EL caps have correctly been reversed to accommodate that.

Certainly would have helped if I kept reading his post.  Just started looking at the pictures and pulled the board up on Tayda.  Sorry about that. 

[neiltheseal]

Not a problem. I checked the caps and they are correct. I think you were right about the bridge though. I fixed that, added the 470k and tweaked the trimpots and now it works! Sounds great also.

You guys are the best.

Although a new problem. When plugged into the dc input there is a loud humming feedback sound. This is not an issue when i use a 9v battery?

Does anybody know why I might be getting the feedback from the DC input?

[neiltheseal]

Here is a video with the sound issue. Does anybody know why there is this high pitched noise but only when the dc is plugged in? No issue with just the 9v battery.

Sorry if this is an obvious question!

[jimilee]

That’s an interesting AC power supply, is it for pedals, or generic?


Sent from my iPhone using Tapatalk

[mauman]

Some pedals are more sensitive to noise on the DC supply than others, and some DC supplies have more noise.
 If you combine a sensitive pedal with a noisy supply, that's what it sounds like.  A different supply might work better, or just stick with 9V batteries.

[jimilee]

What he said. I ask, because I've never seen a dc pedal power supply with a ferrite bead.

[jwin615]

What he said. I ask, because I've never seen a dc pedal power supply with a ferrite bead.

Harman put them on a good deal of the digital pedals of the bush and Obama admins.

[neiltheseal]

That’s an interesting AC power supply, is it for pedals, or generic?


Sent from my iPhone using Tapatalk

It's one of these. I just used the dc plug to connect the power board not one from the board to pedal for ease of use. The sound is present when i connect from the power board to the pedal too.

https://www.swamp.net.au/swamp-iso-10-isolated-power-supply-station-for-guitar-effects-pedals