mdc
Well-known member
In the spirit of sharing breadboard projects, here's a circuit I pieced together over the past few weeks.
On the breadboard...
Got some PCBs...
Realised I made a few goofs laying it out, tweaked to suit, and here's the adjusted schematic...
The LND150 MOSFETs are popular with solid state amp folks, and they have similar characteristics to a 12AX7. In this circuit they're basically just being used as you would any other FET, but I like how it turned out. It may work just as well with a different JFET or MOSFET with the appropriate tweaks.
The LND150 is still in production as a through-hole part and the specs are pretty consistent. That said, there's enough mojo floating around to merit trimmers which I added on the revised board. Also given the clipping and everything else, I'm honestly not sure how crucial the biasing is. As long as it's over 5V it's probably not going to sound too different. I shot for 6.6V on Q1 and Q2.
This particular BJT differential pair is something I pulled out of a radio magazine from the 60s, it's sort of useful inasmuch as it works with a single-ended supply. It blows up nicely. Gain matching the pair isn't super important since you probably want some asymmetry. The emitter follower makes the tone circuit sound a little better than it did without. It's obviously a muff tone control with some values that sound nice to me. Very subtle mid cut at 12:00.
Anyway! It's simple and sounds somewhere between a rat and a muff with a nice amount of range to the gain. It has a kind of ragged top end that I like a lot.
On the breadboard...
Got some PCBs...
Realised I made a few goofs laying it out, tweaked to suit, and here's the adjusted schematic...
The LND150 MOSFETs are popular with solid state amp folks, and they have similar characteristics to a 12AX7. In this circuit they're basically just being used as you would any other FET, but I like how it turned out. It may work just as well with a different JFET or MOSFET with the appropriate tweaks.
The LND150 is still in production as a through-hole part and the specs are pretty consistent. That said, there's enough mojo floating around to merit trimmers which I added on the revised board. Also given the clipping and everything else, I'm honestly not sure how crucial the biasing is. As long as it's over 5V it's probably not going to sound too different. I shot for 6.6V on Q1 and Q2.
This particular BJT differential pair is something I pulled out of a radio magazine from the 60s, it's sort of useful inasmuch as it works with a single-ended supply. It blows up nicely. Gain matching the pair isn't super important since you probably want some asymmetry. The emitter follower makes the tone circuit sound a little better than it did without. It's obviously a muff tone control with some values that sound nice to me. Very subtle mid cut at 12:00.
Anyway! It's simple and sounds somewhere between a rat and a muff with a nice amount of range to the gain. It has a kind of ragged top end that I like a lot.
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