Purple Plexi - How to pull back some gain ?

[HOTTUBES]

Sounds great so far , but it's got plenty of gain on tap ... just wondering how to tame the beast ??











Thanks for any help !!  ( Sucks being a Noob )

[garcho]

just wondering how to tame the beast

What do you want to do that the potentiometer controls (gain and volume) don't achieve?

[HOTTUBES]

Even with the gain pot at Zero .... it's still got too much .

[Thecomedian]

Feedback biasing. I dont have the knowledge to tell you where or how to do it, though.

if you feel like getting a little crazy, https://www.youtube.com/watch?v=piHi9o5Q4vc

it's basically A -B = C, so you could reduce the gain with a differential amplifier add-on. It may also help you understand how to feedback bias an op-amps pins to get gain where you want (which would be the simpler route). I just find the concepts in the video are relatively illuminating for re-imagining how opamps work.

[gjcamann]

R4 is in parallel with the gain pot, that changes your 1K gain pot to ~300 Ohm pot. If you remove R4 you'll change your gain pot back to 1k giving you more low range in your gain control but will make it a little more touchy at high gains.

Please let me know how this works out, I'm interested in making one of these smashdrive/PP.

[garcho]

There might be "beast" in the DNA of the 386 you'll never get rid of.

[rousejeremy]

If you cut the trace between pins 1 and 8 it would clean right up. Maybe you could splice a pot in between those two pins for some sort of pre-gain?

[gjcamann]

I have to agree with jeremy. That's also a real good idea.

[THOMMO]

I thought the exact same thing of this circuit but seeing as it cleans up awesomely with the guitars volume, I wasn't going to bother altering it.
I am however, going to build another and try the 'pot between pins 1 & 8' idea of Jeremy's. Sounds cool!

[rousejeremy]

How about a dual concentric pot between the cut tracks of pin 1 and 8 and the rest? Maybe you could get a larger sweep of gain range.

[Steee]

Hi

Did this work?

I've got the same problem with a DIY purple plexi, but a pub circuit from Pedal Parts.

[HOTTUBES]

I never tryed it to be honest ... but i might try it on this build !!

I'm doing another one , and trying to remember how to tighten up the low end now , i find this circuit to be
very loose & tubby on the bottom end imo .  

[HOTTUBES]

If you cut the trace between pins 1 and 8 it would clean right up. Maybe you could splice a pot in between those two pins for some sort of pre-gain?

Do you mean cut the vero board trace under the 386 op amp between 1 - 8 pin ??

[rousejeremy]

Yup. Or you could try out some of the "typical applications" here. http://www.ti.com/lit/ds/symlink/lm386.pdf
A 10uF cap between pins 1 and 8 lowers the gain, and a 10uF cap in series with a 1.2K resistor lowers it even more.

[gjcamann]

Well I finally got around to messing with the circuit and thought I'd report some findings.

I found that a pot between pins 1 & 8 (as described above) really helps tame the gain and make it much more usable. And if you disconnect the cap & pot to ground it becomes more of a high gain overdrive in a pretty nice way.

One of my issues with this circuit has been squeeling and/or some non-appealing artifacts in the signal - I think alot of people have had this problem. I found that adding a little resistance (100 Ohm) between pins 1&8 helps resolve this.

Instead of a resistor between 1 & 8, I've tried a cap with/without a resistor but didn't care for it, a pure resistor sounded much butter.

I'm thinking my final incarnation will include the pin 1&8 pot, then have a switch to enable the cap and pot to ground for higher gain.

Standby to see if the next Lovepedal includes this pot.