suggestions about my own ovedrive

[fuzzo]

hi every one ,

I did this overdrive, fine but there's a kind of mid boost . Not a problem with the pedal alone, but it is when there's  another pedals after.

the schematic :
http://img147.imageshack.us/my.php?image=hotdrive3gu1.png

Have you got suggestions to do about this schemo ? increase cap in RC filter of the second stage (47nf to 100nf ? more) to attenuate the mid boost ? anything else ?

thx

[dschwartz]

i cant see the schem...

[fuzzo]

damn it !

http://img147.imageshack.us/my.php?image=hotdrive3gu1.png

[fuzzo]

sorry double post

[Gus]

The 4.5VDC ref connection for the opamps is drawn wrong the ref node should be at the center of the 10Ks not ground

Are the gain stages wired like the schematic is drawn?

The output filter section is load depended.  Check at 1 meg loading(tube amp input) and then 470k (TS input etc) load and  100K loading and ..........

  The rat has a buffer after the filter to keep a constant load for the filter so it does not change with what is after the rat. 

The way you have the filter drawn, it is a good practice to wire the not connected lug of the filter pot to the wiper of the pot this helps REDUCE any noise caused by the wiper bouncing on the resistive material because there is always a path.

[fuzzo]

The 4.5VDC ref connection for the opamps is drawn wrong the ref node should be at the center of the 10Ks not ground

Yeah, i did a mistake, of course is at the center of voltage divider

The output filter section is load depended.  Check at 1 meg loading(tube amp input) and then 470k (TS input etc) load and  100K loading and ..........

The output filter section is load depended.  Check at 1 meg loading(tube amp input) and then 470k (TS input etc) load and  100K loading and ..........

  The rat has a buffer after the filter to keep a constant load for the filter so it does not change with what is after the rat.

I didn't know that can change the "tone" of the pedal, you think I must put a buffer before the gain stages ? What effect if I change the "load R" ? I used an 1M R 'cause I see this values on each schematics i saw.

The way you have the filter drawn, it is a good practice to wire the not connected lug of the filter pot to the wiper of the pot this helps REDUCE any noise caused by the wiper bouncing on the resistive material because there is always a path.

yes I know, but I must buy new metal pot (alpha) , I use at this moment the cheapest  I know, black pot with platic axe. But I haven't any noise problems.

I change the 47nf in the RC filter of the second AOP to a 100nf and the bass is more present, mid boost seems to be cut.

[Gus]

A buffer after the tone control and before the volume control.
http://www.diystompboxes.com/pedals/PCRAT1.GIF


The load resistance I am posting about is the input resistance of the effect or amp after your effect circuit.

If I understood your first post the sound changes when you had different circuits after it?

Are the 4.7ks in the feedback network connect to the opamps outputs as drawn or are they connected to the - pins?

[fuzzo]

If I understood your first post the sound changes when you had different circuits after it?

not exactly, it adds its tone like does a tube screamer with its mids boost trough a overdrive chanel of an amp.

Are the 4.7ks in the feedback network connect to the opamps outputs as drawn or are they connected to the - pins?

It's connected like a standart RC filter , similar to an ovedrive schemo.

[hoopshot]

If you put a Big Muff-style tone control in there, you will get a midrange
reduction. I think it would just drop in after the second op-amp.

Is the linear pot used for tone control?

[zyxwyvu]

If I understood your first post the sound changes when you had different circuits after it?

not exactly, it adds its tone like does a tube screamer with its mids boost trough a overdrive chanel of an amp.

With the large resistors on the output, it may not be able to drive other pedals very well. This will affect the tone and volume when placed before other pedals.

Are the 4.7ks in the feedback network connect to the opamps outputs as drawn or are they connected to the - pins?

It's connected like a standart RC filter , similar to an ovedrive schemo.

If it's connected as shown, the opamps will have a gain of 1. The 4.7k resistors should be tied to the negative inputs. I'm not sure if you have done this already - I couldn't tell from your response.

[fuzzo]

If it's connected as shown, the opamps will have a gain of 1. The 4.7k resistors should be tied to the negative inputs. I'm not sure if you have done this already - I couldn't tell from your response.

Yes  i think it's a mistake in the schematic, the gain of AOP isn't 1, It adds gain for sure.

[rnfr]

why don't you just get rid of that 470k resistor and what that does?  (as explained above)

[fuzzo]

You talk about the R before the volume pot ?