Tycobrahe octavia problem (SOLVED)

[brejna]

Hi, I recently build tycobrahe octavia on the tonepad layout and I am having problem with humbucher pickups. When I strum harder on heavier strings it sounds like fast fade in. What could cause this?
Thanks
Brane

[strat68]

If I understand you, it's only humbuckers?  I have this same issue with a Red Llama and Fuzz factory clones.  It's only when the guitar volume is turned up past 5-6 or the pedal controls cranked.  Sounds like some type of overload somewhere along the line which I have no clue how to fix. 

I built the Madbean version without issues like this for both a Strat and Les Paul.  See of there's a difference in these version.

[brejna]

If I understand you, it's only humbuckers?  I have this same issue with a Red Llama and Fuzz factory clones.  It's only when the guitar volume is turned up past 5-6 or the pedal controls cranked.  Sounds like some type of overload somewhere along the line which I have no clue how to fix. 

I built the Madbean version without issues like this for both a Strat and Les Paul.  See of there's a difference in these version.

Yes you are right, I have exact problem. From schematic from MB and tonepad, there are no differences. I've already build it without these issues. Maybe it is because of transistor hfe..

[brejna]

Could diodes be problem? I've used 1n34a - germanium diodes (Semtech)

[jimilee]

Did you measure your diodes first?

[brejna]

Did you measure your diodes first?

I didn't.. but I measure them few moments ago. It says 0.3v? Is that in the datasheets or?

[jimilee]

Did you measure it in the circuit?

[brejna]

Yes I did, but I have toggle to switch one diode and it shows same value..

[jball85]

I have a problem similar to this when using my Les Paul's neck humbucker (Seymour 59), with too much bass and gain. It happens when I run a booster with an OCD on y strat's neck pickup too. Especially with a fuzz type effect, It's almost as if there is a compressor in the line massively compressing the start of the note I hit. Don't know if that's the same issue, but I assume its from using too much gain.

[strat68]

I have a problem similar to this when using my Les Paul's neck humbucker (Seymour 59), with too much bass and gain. It happens when I run a booster with an OCD on y strat's neck pickup too. Especially with a fuzz type effect, It's almost as if there is a compressor in the line massively compressing the start of the note I hit. Don't know if that's the same issue, but I assume its from using too much gain.

That sounds exactly what I was describing in my first post above. 

[brejna]

Any ideas how to deal with it?

[midwayfair]

Q1 is biased with its base reference voltage being tied to +9V and ground instead of a 1/2 voltage Vb or just as often the collector and "ground" (for Q1, "ground" is actually the +9V rail).

This biasing method isn't the most stable, but it does create little bit of a saggy sound sometimes. I've used it in a few circuits, like the Clipper Ship.

Either PRR or RG explained it to me that there's a danger that when the input signal gets large enough, the transistor gets stuck in an "on" position and completely clips the signal at the Fv of across the base and emitter. It would momentarily misbias and that means that it needs a little bit of time to recover. This would cause exactly the behavior you're describing.

You can try desoldering the side of R2 that's attached to ground and resolder it to the junction of R5 and Q1. It'll look ugly, but it might work. No guarantees here. You might have to change R5 as well if it does work. Measure the voltage on the collector of Q1 first to make sure you can find the right voltage by altering R5 again if/when you need to change it.

This doesn't mean you won't necessarily still cause some bad behavior with higher output pickups. You'll also change the sound of the circuit. You could maybe try replacing the pulldown with a 500K pot or something like that if you want an input gain control.

[brejna]

Q1 is biased with its base reference voltage being tied to +9V and ground instead of a 1/2 voltage Vb or just as often the collector and "ground" (for Q1, "ground" is actually the +9V rail).

This biasing method isn't the most stable, but it does create little bit of a saggy sound sometimes. I've used it in a few circuits, like the Clipper Ship.

Either PRR or RG explained it to me that there's a danger that when the input signal gets large enough, the transistor gets stuck in an "on" position and completely clips the signal at the Fv of across the base and emitter. It would momentarily misbias and that means that it needs a little bit of time to recover. This would cause exactly the behavior you're describing.

You can try desoldering the side of R2 that's attached to ground and resolder it to the junction of R5 and Q1. It'll look ugly, but it might work. No guarantees here. You might have to change R5 as well if it does work. Measure the voltage on the collector of Q1 first to make sure you can find the right voltage by altering R5 again if/when you need to change it.

This doesn't mean you won't necessarily still cause some bad behavior with higher output pickups. You'll also change the sound of the circuit. You could maybe try replacing the pulldown with a 500K pot or something like that if you want an input gain control.

Thanks for infos, I'll report if there is improvement..

[brejna]

You can try desoldering the side of R2 that's attached to ground and resolder it to the junction of R5 and Q1.

Thanks Jon, this one did the trick. It has little bit more highs, but I never use it alone so it is ok.
Cheers

[midwayfair]

woohoo, lucky guess on my part, I guess!