Maxon OD820 clone
Posted: Tue Jul 30, 2013 3:49 pm
Just finished the pedal and wanted to share the pics and some info.
Used my layout, because I use audio caps, and they are much bigger than the regular Polyester type.
Metal Film resistors - 1/8 and 1/4 (because I didn't have some values).
Op-amps! Later about this...
This pedal is Tube Screamer on steroids. More Gain, more Headroom, more clarity!
First of all, the power supply is +-9 volts. Ic ICL7660/max1044 converts 9 volts to positive and negative. Almost like 18 volt
When the gain is on "0" - pedal works like clean boost. When at max - there is plenty of gain.
Jfet buffer in the input and 2 dual opamps for the rest of the circuit. No more transistors. The tone control is the same as on other tube screamers.
So, my favorite part! Op-amps! First tried the 4558 just to see if every thing works. It is, but when the gain at max the overdrive sounds like with some "dust" on it. Very not Clear I can say... TL072's sound the same. I tried lm4562 the Hi-Fi op-amp for 5$, in bouth positions but it adds some shrill sounds when the tone control at max. Opa2604 was much better in bout positions. The last one I tried was the OPA627. On mouser this one goes for 28$ and it's only Mono Op amp. I bought 2 of these on 2 sided PCB ( one on the top, one on the bottom) from ebay that cost me 7.5$ (from china, used, but genuine)! The sound of this op amp is outstanding! Very Clear, no "dust", shrill tones or some other noise. The Headroom is so big, it is even hard to explain with the words.
Yes they are expensive, but they worth it. They love the voltage, so on regular 9v distortion all of the opamps sound almost the same.
So now there is 2 OPA627 and one OPA2604.
Recomed this overdrive for every one who likes Tube Screamers!
Now the PICS!
Used my layout, because I use audio caps, and they are much bigger than the regular Polyester type.
Metal Film resistors - 1/8 and 1/4 (because I didn't have some values).
Op-amps! Later about this...
This pedal is Tube Screamer on steroids. More Gain, more Headroom, more clarity!
First of all, the power supply is +-9 volts. Ic ICL7660/max1044 converts 9 volts to positive and negative. Almost like 18 volt
When the gain is on "0" - pedal works like clean boost. When at max - there is plenty of gain.
Jfet buffer in the input and 2 dual opamps for the rest of the circuit. No more transistors. The tone control is the same as on other tube screamers.
So, my favorite part! Op-amps! First tried the 4558 just to see if every thing works. It is, but when the gain at max the overdrive sounds like with some "dust" on it. Very not Clear I can say... TL072's sound the same. I tried lm4562 the Hi-Fi op-amp for 5$, in bouth positions but it adds some shrill sounds when the tone control at max. Opa2604 was much better in bout positions. The last one I tried was the OPA627. On mouser this one goes for 28$ and it's only Mono Op amp. I bought 2 of these on 2 sided PCB ( one on the top, one on the bottom) from ebay that cost me 7.5$ (from china, used, but genuine)! The sound of this op amp is outstanding! Very Clear, no "dust", shrill tones or some other noise. The Headroom is so big, it is even hard to explain with the words.
Yes they are expensive, but they worth it. They love the voltage, so on regular 9v distortion all of the opamps sound almost the same.
So now there is 2 OPA627 and one OPA2604.
Recomed this overdrive for every one who likes Tube Screamers!
Now the PICS!