SOLVED Byzantium not flanging

[punchy712]

I'm having an issue with my Byzantium where I'm not getting flanging effect. When enabled, all I hear is the input signal and none of the knobs or trim pots change anything.

I used an audio probe and noticed that there was audio going into the V3207D chip (pin 3) but no audio going out (pins 7/8). I was also expecting the V3102D chip to make some sort of noise (pulsating) by I don't hear anything when probing any of the pins. I checked the voltages of both chips and they seem reasonable, but if that would help let me know and I can post them.

I'd appreciate any help as I'm not sure what to check exactly and why there would be absolutely no sound coming out of the V3207D. It's also my first time using these chips, so I'm not sure what to look for.

Excuse the messy wiring between the boards.

 

[Cybercow]

Have you manipulated the trimpots for proper adjustment? While I've personally not built a Byzantium, I've built several flangers and on some, the trimpot settings can be fussy. Use tiny increments to adjust properly till you hear the effect. I'd start with them each centered, then go from there starting with the 25K trimpot VR6 (Pot1 in the schematic).

See this post for more details.

 

[punchy712]

Have you manipulated the trimpots for proper adjustment? While I've personally not built a Byzantium, I've built several flangers and on some, the trimpot settings can be fussy. Use tiny increments to adjust properly till you hear the effect. I'd start with them each centered, then go from there starting with the 25K trimpot VR6 (Pot1 in the schematic).

See this post for more details.

Thank you for looking into it. I went back to it this morning and I forgot that I substituted a 2N5807 instead of the BC560, and didn't realize that I had it backwards. Flipped it around and now it's flanging.

The only part that doesn't seem to be working is the rate knob as it doesn't affect anything. I'll look into adjusting the trimpots first.

 

[punchy712]

No luck on getting the rate working, but one question I want to ask to make sure this isn't the cause. I don't have a TL022 on hand so I used a TL072. My understanding is that this may cause ticking, but it should still work. What I'm seeing when taking the voltage of pin 1 (the output of the rate circuit) is that it changes by just a few mVs (stays around 5V). Could the IC choice cause an issue like this?

 

[punchy712]

Just in case someone has any experience with the expected voltages of this circuit, below are the voltages I took of the ICs and transistors on the BBD board. All voltage readings taken with all knobs turned all the way CCW ("off") and the trim pots in the middle.

Q2

1. 4.28 V
2. 530 mV
3. 0V

Q4

1. 521 mV
2. 521 mV
3. 0V

Q6

1. 172 mV
2. 5.62 V
3. 5.69 V

Q7

1. 5.69 V
2. 1.59 V
3. 1.02 V

IC 1

1. 1.34 V
2. 5.05 V
3. 2.84 V
4. 0 V
5. 3 V
6. 2.8 V
7. 5.08 V
8. 5.69 V

IC 3 (V3207D)

1. 0 V
2. 2.8 V
3. 3.1 V
4. 5.3 V
5. 5.69 V
6. 2.79 V
7. 4.1 V
8. 4.1 V

IC 4 (V3102D)

1. 5.67 V
2. 2.75 V
3. 0 V
4. 2.77 V
5. 5.52 V
6. 155 mV
7. 4.56 V
8. 5.29 V

 

[punchy712]

One more thing I wanted to mention is that I didn't have a 47p to use for the C11 capacitor so I used a 56p as I thought it would be close enough. I'm reading more about the 3102 chip and this capacitor value looks to be important to setting up the available clock frequencies. However, it still seems like I should be okay to use this value, but I could be very mistaken of course.

 

[Cybercow]

No luck on getting the rate working, but one question I want to ask to make sure this isn't the cause. I don't have a TL022 on hand so I used a TL072. My understanding is that this may cause ticking, but it should still work. What I'm seeing when taking the voltage of pin 1 (the output of the rate circuit) is that it changes by just a few mVs (stays around 5V). Could the IC choice cause an issue like this?

Yes, using a TL072 in place of a TL022 will make a difference. The TL022 has a low impedance (BJT In) and low slew-rate (~0.5V/μs) compared to the TL072 with its high input impedance (FET) and high slew-rate (13V/μs).

One more thing I wanted to mention is that I didn't have a 47p to use for the C11 capacitor so I used a 56p as I thought it would be close enough. I'm reading more about the 3102 chip and this capacitor value looks to be important to setting up the available clock frequencies. However, it still seems like I should be okay to use this value, but I could be very mistaken of course.

The 56p in place of the 47p cap at the clock will have bearing on the speed of the 3102 clock chip, but should not affect the flanging too badly. I'd still vie for the 47p in favor of the 56p.

Flangers and other similar types of modulation circuits are more restrictive than most dirt pedals in that subbing parts with different values will not always work. Best to stick with the BOM for best performance.

 

[Giorfida]

Flangers and other similar types of modulation circuits are more restrictive than most dirt pedals in that subbing parts with different values will not always work. Best to stick with the BOM for best performance.

Likely just one of the many reasons modulation pedals were always significantly more expensive than dirt pedals (at least back in the 70s and 80s- before the whole “boutique” thing skewed prices of everything)

 

[punchy712]

Related to the TL072, that looks to most likely be the problem in my case. I breadboarded the "rate" part of the circuit with a TL072, powering it at 9V (and using 4.5V in the inputs) and it works as expected; as soon as I dropped the voltage to around 8.5V, the output was a constant voltage and no "rate" was happening, same as in my pedal circuit.

I have a TL022 coming in today so I'll update this post if that fixes the problem. Apologies for the false alarm in advance if that's the case; I must have mistakenly read somewhere that subbing this transistor would be ok, but it might have been for a circuit where it was powered by more than the 5V here.

I'll ask be getting a 47p and replace it, before boxing it up.

Thank you for your help.

 

[punchy712]

Thanks again for your help. Swapping in the TL022 fixed it all, so to anyone contemplating swapping this out you probably don't want to.