Overdriven LM380 vs LM386

[Quarterflip]

So I'm making a kinda fendery little distortion pedal, and I've got a fetzer valve going into a LM386 N1. When pushed it sounds quite nice, aside from the terrible fizz decay which seems to be a common thing with LM386's. I've tried a whole load of things to try and fix it, got caps everywhere, zobel network, all the stuff that should help but it's still pretty bad. It also doesn't have too much headroom before it overdrives.

I've been looking at the LM380 as a potential replacement for it, but I'm wondering if it still has that fizz that the LM386 does?

[nocentelli]

Interesting. I have a LM380 somewhere, ordered in error when I wanted LM308. I have never thought to try it as a distortion device like you might a 386

[PBE6]

Apparently changing the component values in the Zobel network to cut down the bandwidth helps:
http://www.projectguitar.com/forums/topic/43472-lm386-based-sustainer-note/

[Quarterflip]

Apparently changing the component values in the Zobel network to cut down the bandwidth helps:
http://www.projectguitar.com/forums/topic/43472-lm386-based-sustainer-note/

Yeah this helped a bit, still pretty bad fizz though.

[caspercody]

It's been awhile, but look at the Purple Plexi or Krank Distortus Maximus. These were the only 386 pedals I built that did not have the fizz.

I think it might have been putting big caps on the power supply filtering. I think Dead Astronaut has a tread about this fizz issue.

[slashandburn]

Pin seven plays a role in power supply filtering with the lm386 iirc. I think I started putting a 10uf on there, not sure of the reasoning behind that. A lot of schematics seem to ignore it completely. 

Edit: The Lm380 I think needs at least 10v (18v optimal?). It also doesn't have that neat little "two pins wired straight to a pot for a gain control" feature.

[Quarterflip]

It's been awhile, but look at the Purple Plexi or Krank Distortus Maximus. These were the only 386 pedals I built that did not have the fizz.

That lovepedal still has a fair bit of fizz, but that krank seems to have fixed the problem. Interesting how they've put a zobel on pins 1 and 8.

Would putting my tonestack after the LM386 rather than before make a difference?

[slashandburn]

http://www.thegearpage.net/board/index.php?threads/d-a-m-sonic-titan-note-decay.973457/page-2
Likewise the krank has a fat old cap on the bypass pin which the Plexi and others omit.
There's a discussion here about the 386 "decay fizz" might be worth a looks, it's mostly all been covered here. The usual LM386 suggestions:
bypass cap on pin 7.
Filter cap as close to pin 6 as you can get it.
Etc etc

One guy says some people have reported the fizz isn't there on the N4 version of the LM386. I'm dubious, but that would be easier to experiment with than the 380, since it at least has the same pinout.

[EBRAddict]

I think it might have been putting big caps on the power supply filtering. I think Dead Astronaut has a tread about this fizz issue.

Most of my LM386 issues have been cleared up by cleaning up the power. With one breadboard experiment I was running V+ down one rail and all the way down the other and was getting horrible fizz. I re-routed the V+ directly to the power supply and the fizz went away. Likewise running on an older battery will have bad decay fizz.

YMMV

[PRR]

> cleaning up the power.

+1

[erintse]

Learn more LM380 vs LM386 with avaq: https://www.avaq.com/technology/lm380-vs-lm386-what-are-differences-and-how-to-choose

[Box_Stuffer]

I just completed a pretty bad@ss 386 based distortion I call the Blue Rajah. I used the "AM radio amplifier" schematic from the datasheet as the basis and built on from there. You have to go in through the inverting input (pin 2) to be able to add clipping diodes.

I put a pair of germanium hard clippers on the output stage so when you kick it on it is a smooth compressed overdrive. Then there is a gain loop from pin 1 to 8 with 4148 silicon diodes and as you phase them in it gets more crunch and harmonics. The downside is that you get a lot more treble along with the gain, but there is a tone control for that. I would say it has an early ZZ Top kind of sound.

[Box_Stuffer]

One guy says some people have reported the fizz isn't there on the N4 version of the LM386. I'm dubious, but that would be easier to experiment with than the 380, since it at least has the same pinout.

I got some cheap N-1s on ebay and I have been using them for random projects. At Stompboxparts.com they only have N-3s and N-4s , so I ordered some N-4s that I have been using for a distortion circuit. They sound fine and I haven't noticed any fizz that wasn't intentional. I have not really compared the 2 in the same circuit, but I have also heard that the N-4 is cleaner and they are MUCH louder than the N-1.

[Mark Hammer]

Blue Rajah.    I like the allusion to "Mystery Men".

[Box_Stuffer]

Blue Rajah.    I like the allusion to "Mystery Men".

Yeah - that movie is CLASSIC. RIP to The Spleen!!

The name also came about because I got the original idea for the 386 distortion with diodes from a Youtube video I saw of some Indian guys making what they called "Blues Distortion". I made one and it sounded terrible and I was having trouble with keeping it stable. So I started over and made something better, but the name has stuck.