Author Topic: Throttlebox + Baxandall unwanted distortion  (Read 689 times)

juan_felt

Throttlebox + Baxandall unwanted distortion
« on: January 22, 2018, 04:45:19 PM »
Hi People!

I have built a throttlebox, eliminated the tone and mids section, and added an active baxandall after the gain section.
This is the schematic of the build:

It works properly (as in all the controls do what they are supposed to do), but the distortion doesen't sound very well. It is tight and hi-gainish, but when you let the notes ring, as they decay there is an unwanted clipping sort of added to the proper clipping sound. It sounds as if it was not properly biased.

I tried bypassing the baxandall and the noise dissappears. I tried the same circuit on another pedal and it works well (no noise).

What do you think could be going on? Do you see any obvious mistakes on the schematic.

Sorry for my english!

Thanks in advance:)

J


ElectricDruid

Re: Throttlebox + Baxandall unwanted distortion
« Reply #1 on: January 22, 2018, 06:10:38 PM »
Where did R8/3K3 come from? Was it on the end of the Throttlebox schematic? It looks a bit superfluous  (sorry, fancy word for "unnecessary" = not needed). Given that the Baxandall has a fairly low input impedance, I'd prefer not to have more resistance in series with it.

The only other thing that jumps out at me is that the Switch SW1 doesn't need to be DPDT. SPDT would do, with Both ends of the two caps connected together at the end without the switch. The unused cap can just sit there with one end unconnected, that's no problem.

The trouble is I doubt either of those things are anything to do with your problem. Sorry not to be more use.


samhay

Re: Throttlebox + Baxandall unwanted distortion
« Reply #2 on: January 23, 2018, 03:54:03 AM »
You are using an active tone control.
This means IC1B can both cut and boost the signal...

What happens to the unwanted clipping if you set the tone controls to be flat and/or cut?
I'm a refugee of the great dropbox purge of '17.
Project details (schematics, layouts, etc) are slowly being added here: http://samdump.wordpress.com

marcelomd

Re: Throttlebox + Baxandall unwanted distortion
« Reply #3 on: January 23, 2018, 07:34:35 AM »
Hi,

Maybe the signal is too hot coming out of the gain stages and is clipping the tone stage (either its input or while boosting).

juan_felt

Re: Throttlebox + Baxandall unwanted distortion
« Reply #4 on: January 23, 2018, 12:34:14 PM »
You are using an active tone control.
This means IC1B can both cut and boost the signal...

What happens to the unwanted clipping if you set the tone controls to be flat and/or cut?

Hi! The noise is still there...

juan_felt

Re: Throttlebox + Baxandall unwanted distortion
« Reply #5 on: January 23, 2018, 12:34:53 PM »
Hi,

Maybe the signal is too hot coming out of the gain stages and is clipping the tone stage (either its input or while boosting).

Hi,

I will try to lower it and see what happens... Thanks!

juan_felt

Re: Throttlebox + Baxandall unwanted distortion
« Reply #6 on: February 14, 2018, 10:56:42 AM »
Hi,

Maybe the signal is too hot coming out of the gain stages and is clipping the tone stage (either its input or while boosting).

Hi Marcelomd, I tried using a bigger resistor before the baxandall (instead of the 3k3) and it works! I have to find the proper value, because it really lowers the overall volume and treble content.
Is there another way to lower the signal other than using the resistor?

Thanks!!

marcelomd

Re: Throttlebox + Baxandall unwanted distortion
« Reply #7 on: February 14, 2018, 12:43:31 PM »
Quote
Hi Marcelomd, I tried using a bigger resistor before the baxandall (instead of the 3k3) and it works! I have to find the proper value, because it really lowers the overall volume and treble content.
Is there another way to lower the signal other than using the resistor?

Hmmm, maybe the limiter resistor and the tone network are interacting. You can try a large value trimpot/potentiometer/divisor, like a volume control, between the stages so It will not load the gain stage.

Someone correct me here =)

PRR

Re: Throttlebox + Baxandall unwanted distortion
« Reply #8 on: February 14, 2018, 04:10:22 PM »
> I tried using a bigger resistor before the baxandall (instead of the 3k3) and it works! I have to find the proper value, because it really lowers the overall volume and treble content.

R8 really should not be there. It messes-up the tone control.

But you DO need to drop level after the high-level clipper and the tone control.

You want a voltage *divider*.


juan_felt

Re: Throttlebox + Baxandall unwanted distortion
« Reply #9 on: February 15, 2018, 08:51:11 AM »
> I tried using a bigger resistor before the baxandall (instead of the 3k3) and it works! I have to find the proper value, because it really lowers the overall volume and treble content.

R8 really should not be there. It messes-up the tone control.

But you DO need to drop level after the high-level clipper and the tone control.

You want a voltage *divider*.


Hi PRR,

Thanks for your reply with the picture. I just tried that and I don't notice any change in the level. I used a 10k resistor, but I can't tell any difference.

The only way I found I could get rid of the clipping noise is by raising R8 to 10k.

Why does this resistor mess with the tone control?

Again, thank you so much for helping me understand better whats going on, and for solving the issue.

Cheers!
J

PRR

Re: Throttlebox + Baxandall unwanted distortion
« Reply #10 on: February 16, 2018, 05:54:54 PM »
10K against the stock 3K does little.

1K against the stock 3K should do a lot.