freestompboxes.org

Hi all,

I "conceived" an ovedrive with 3 gain mods, a cool ovedrive for all stuff like Cream , hendrix , zz top , stoner rock (nebula, QSTA ), blues ect....

So the schematic


You can also just put a simple tone control like proco rat (it works well too)


As you can see it's just a tubescreamer gain stage with a kind of boost stage after it. The two extrem side of switch connect a resistor in parallel with the one of 1M, It reduces gain. Also, It creates a high pass filter with the little cap ( 120pf), more the gain is high more you lost a litle of treble. (it avoid to have a bunch of harsh treble when the third mode is engaged).

With the gain switch and the baxendall, you can have a lot of tone possibilities, dark, mid boost, scoop mids, neutral tone, bassy, ect...


To people who wants do one i post the striplayout I used :


and a pic of mine:


I'm proud of this one, the sound is very funny .

But, isn't for metal even if the final gain stage has a lot of drive, but it can be great for a boost on overdrive channel !

Don't hesistate to post comments !

-Devastator-

Some design comments:
-I'm curious as to why such a large resistor in series with the output (470k)? Seems like it would contribute a lot of noise.
-Have you tried a smaller biasing resistor on the second stage of the opamp? 1M seems overkill to me, or this due to the specs of the opamp (I'm not familiar with the LM2924)?
-You probably don't need a decoupling cap between the two stages (the 100n) but you do need one at the output of stage two of the opamp (before the tone control).
-The 120p in the loop creates a low pass filter (attenuates highs), not a high pass.
-You've got your RC filters coming off the output of each stage of the opamp. They should come off the inverting end of the opamp....is this a schematic error?

These comments aren't meant to be critical....I'm just curious as to your thought process in the design.

no problems I could do errors.

Have you tried a smaller biasing resistor on the second stage of the opamp? 1M seems overkill to me, or this due to the specs of the opamp (I'm not familiar with the LM2924)?

I did this one in seeing all schemas I found. All has 1M resistors to bias the inputs, so I did the same thing. For the AOP i didn't use a LM2924, I used what I've in my stock, a JRC022 who was in a Boss GE7. I'll try to change it to a burr brown or better AOP (NE5532?)

I'm curious as to why such a large resistor in series with the output (470k)? Seems like it would contribute a lot of noise.

It's to reduce to outup level, which is very big. It's a voltage divider.

You probably don't need a decoupling cap between the two stages (the 100n) but you do need one at the output of stage two of the opamp (before the tone control).

oh , i did another mistake in the schematic , you can see this cap in the layout (C5=100n).

The 120p in the loop creates a low pass filter (attenuates highs), not a high pass.

yes, i know , I mix up both filters. In french these terms don't mean the same thing. For me high=treble and low=bass

-You've got your RC filters coming off the output of each stage of the opamp. They should come off the inverting end of the opamp....is this a schematic error?

yeah, I it's a mistake in my schema.


So, I'll correct the schemas and correct my first post ( ) I didn't see all these errors before posting. But the striplayout is right.

thanks for your answer!

Edit: why I can't edit my first post ?, so the right schema w// baxendall)