Re: Brunetti Mercury
Posted by Frank_NH on Feb 18, 2016; 7:10pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/Brunetti-Mercury-tp25277p28205.html
Hey Paul,
Good to hear! I actually did rebuild this last night with the posted layout (and all metal film resistors) but haven't had time to check it out.
Some notes:
* The op amp can be any single op amp - I actually used an LF351 (because that's what I had on hand). But this pedal might benefit from a rail-to-rail op amp since the op amp can potentially clip here (though there's high head room with an 18V supply). But given that the 741 is used in circuits like the distortion+ without feedback diodes at 9V, it's a good choice for this circuit. I'm going to try it out myself.
* For Q1 and Q2, you can use J201, 2N5457, 2N5458 or other N-channel JFETs you have on hand. However, for better bias control, you can change the trimmer values for your JFET as follows:
Q1: J201=50K, J202, 2N5457=20K, 2N5458=10K
Q2: J201=50K, J202, 2N5457=10K, 2N5458=5K
Note that the gains will change with the JFETs. For example, my spreadsheet calculations show that for Q1 with a source bypass cap, the J201 gets a gain of 32, the 2N5457 = 23, and the 2N5458 = 18. This is an area which is ripe for experimentation based on your tastes. I like lower gains when they're cascaded like this, but that's me.
BTW Q3 is just a voltage follower (JFET buffer) so a 2N5457 works well there (no sense wasting a good J201 for a buffer!).
* Definitely use the LT1054 charge pump here. I basically modded the original schematic to employ this chip as it is capable of higher currents and seems more robust overall.
---
I'll post a slightly modded layout later which only has some tweaks to part positions for easier fabrication. Still, somehow I manage to place big 47uF, 100uF electrolytic caps next to crowded parts of the layout!
Finally, one of the reasons I like this circuit (and chose to make my own layout for it) is that it roughly simulates an IC boost/distortion circuit overdriving an amp (as simulated by the JFET stages). With the high headroom from 18V, it's not as compressed as your standard tube screamer, and it uses NO diodes for clipping. Quite cool!
URL: http://guitar-fx-layouts.238.s1.nabble.com/Brunetti-Mercury-tp25277p28205.html
Hey Paul,
Good to hear! I actually did rebuild this last night with the posted layout (and all metal film resistors) but haven't had time to check it out.
Some notes:
* The op amp can be any single op amp - I actually used an LF351 (because that's what I had on hand). But this pedal might benefit from a rail-to-rail op amp since the op amp can potentially clip here (though there's high head room with an 18V supply). But given that the 741 is used in circuits like the distortion+ without feedback diodes at 9V, it's a good choice for this circuit. I'm going to try it out myself.
* For Q1 and Q2, you can use J201, 2N5457, 2N5458 or other N-channel JFETs you have on hand. However, for better bias control, you can change the trimmer values for your JFET as follows:
Q1: J201=50K, J202, 2N5457=20K, 2N5458=10K
Q2: J201=50K, J202, 2N5457=10K, 2N5458=5K
Note that the gains will change with the JFETs. For example, my spreadsheet calculations show that for Q1 with a source bypass cap, the J201 gets a gain of 32, the 2N5457 = 23, and the 2N5458 = 18. This is an area which is ripe for experimentation based on your tastes. I like lower gains when they're cascaded like this, but that's me.
BTW Q3 is just a voltage follower (JFET buffer) so a 2N5457 works well there (no sense wasting a good J201 for a buffer!).
* Definitely use the LT1054 charge pump here. I basically modded the original schematic to employ this chip as it is capable of higher currents and seems more robust overall.
---
I'll post a slightly modded layout later which only has some tweaks to part positions for easier fabrication. Still, somehow I manage to place big 47uF, 100uF electrolytic caps next to crowded parts of the layout!
Finally, one of the reasons I like this circuit (and chose to make my own layout for it) is that it roughly simulates an IC boost/distortion circuit overdriving an amp (as simulated by the JFET stages). With the high headroom from 18V, it's not as compressed as your standard tube screamer, and it uses NO diodes for clipping. Quite cool!
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