Musikding Rat Clone Compensation Capacitor

[Alex85]

Hello,

I built a Rat Clone (kit from Musikding.de) that came with the OP07 operational amplifier and a 33 pF compensation capacitor. As far as I know, the OP07 has an integrated compensation capacitor as standard, so the external compensation capacitor is not necessary. However, when I built the pedal, I didn't know this and therefore I used the external 33 pF compensation capacitor with the OP07 operational amplifier.


So now I have some questions:


1. The newer Rat 2 pedals use the OP07 operational amplifier. Does this mean that the compensation capacitor is no longer used on the Rat 2 circuit boards? Could someone check their Rat 2 pedal to see if the compensation capacitor is still installed there?


2. When the external compensation capacitor is used together with the OP07 (which has an internal operational amplifier), does this additional capacitor have a negative effect on the sound of the pedal?


Since I have never played a Rat, I don't know how it should sound.


Thank you very much for your answers!

 

[Cybercow]

Hello,

I built a Rat Clone (kit from Musikding.de) that came with the OP07 operational amplifier and a 33 pF compensation capacitor. As far as I know, the OP07 has an integrated compensation capacitor as standard, so the external compensation capacitor is not necessary. However, when I built the pedal, I didn't know this and therefore I used the external 33 pF compensation capacitor with the OP07 operational amplifier.


So now I have some questions:


1. The newer Rat 2 pedals use the OP07 operational amplifier. Does this mean that the compensation capacitor is no longer used on the Rat 2 circuit boards? Could someone check their Rat 2 pedal to see if the compensation capacitor is still installed there?

Yes. Use the 33pF (C4) cap.

2. When the external compensation capacitor is used together with the OP07 (which has an internal operational amplifier), does this additional capacitor have a negative effect on the sound of the pedal?

No. Using the 33pF cap does NOT have a negative impact on the sound. It's part of the circuit design and used in most every Rat build.

Since I have never played a Rat, I don't know how it should sound.


Thank you very much for your answers!

 

[andrewsrea]

I just reviewed the datasheet and internal block diagram of the OP07 IC. It does not indicate being internally compensated.

I recommend socketing the cap and trying out values to see which you prefer, as well as no cap. I can tell you the no cap will be harsh.

 

[lowpitch]

Disagree. Pins 1 and 8 on an OP07 serve a different purpose compared to the LM308 and I don't see how a capacitor here should have any effect on tone or otherwise. These pins tap into the input bias network of the OP07 and are used to correct for offset voltages. They would need to be connected to a DC reference voltage to have an effect on anything from what I can tell and putting a capacitor across them does nothing.