New Slow Loris Circuit Changes

[aflynt]

Hello,

I just built the Slow Loris using the older V2 PCB I ordered last year, and I noticed that there is now a new version with a few circuit tweaks. In addition to the Reutz pot, removal of the asymmetric diode option, and lowering C3 to 30pF (all of which I think I understand the effect of) there are a few other minor tweaks here and there. I was curious about what sonic effect these other changes would have. These are the differences I saw but would like to understand better:

- The opamp bias voltage connection has been moved from the junction of R2 (1k) and C2 to the junction of R2 and C1.
- A 22n cap (C12) has been added right before Q1.
- In the power supply, the second filter cap (C11) has been increased to 47uF and an additional 100n cap to ground (C12) has been added.

Thanks,
-Aaron

[plesur]

I can't help with the electronics theory but it is interesting to compare the schematics from the build documents to this schematic by RG and Jack Orman.

[madbean]

There are tons of small variations on the circuit. That's actually the only schematic I've seen that included an input buffer.

Before doing the newest version, I went back and looked at a lot of different schems and permutations of the Rat and just picked what seemed to have the highest consensus and best sounding version to me. The biasing  resistor position is pretty near inconsequential as far as I can tell (you see it both before and after the 1k depending on whose schematic you are reading!), and the filtering is just, well filtering. You will also see the 4u7 and 1k at the output of the opamp drawn both ways. I think the 22n cap was an omission based on what I thought to be the case in the M'OD (it's been a few years--I honestly don't remember exactly---could just be an error on my part) but I added it back to keep it consistent with the Rat. It probably does some minor tone shaping and influence the input impedance of output buffer, but fortunately the de-coupling is already taken care of with the 4u7 cap earlier. Not having it should not have a big impact, but you could add it in on the older PCB. I'd be happy to draw up a simple mod to do this, if you like.

[aflynt]

Thanks for the info! I'm pretty happy with how it sounds to far. I've already put a 1K RA pot in place of R4 and hard wired it for symmetric silicon diodes in the clipping section. It's replacing my old Rat II that I modified in a similar fashion (Reutz pot) a few years back. So far the new one sounds the same or better than the old one. The only difference I hear is that this new one seems a bit darker, but that may be due to the reversal of the filter pot leads interacting with the taper of the 100kA. That or the higher value for C3. Anyway, the differences are pretty subtle. It seems that the character of the Rat itself is so strong that the effects of minor circuit tweaks and component tolerances are minimized.

I kind of am curious how to get that 22n on the old board. I've socketed Q1. Maybe just wire the cap in series with the leg and put the cap lead in the socket along with the other 2 tranny leads?

-Aaron