***NEW*** LM386 practice amp with FET preamp for more gain.

[mac]

I was looking for a small practice amp like the Ruby Amp. I realized that I could make it a litlle more on the dark side of the gain by using the fet as an amplifier not as a buffer. I added some leds and voilà:



Not a Vox AC30 but it kicks the 12" HH of my LC30 decently. Hope you like it.

mac

[John Lyons]

Looks cool, I'll have to look at it closer....

Thanks for posting.

If you get a sound clip I'd like to hear it!

John

[mac]

working on the sound sample... 

mac

[blustrat]

Nice! Do you think it will work fine also as a stompbox? I know the smashdrive also uses a 386.

[mac]

There are a couple of LM386 based pedals at ROG. Maybe replacing everything after pin 5 and using a 0.1uf to 1uF and a volume pot of about 100k. I designed it to be a small practice amp so as not to disturb the whole building with LC30. To be honest, I did not consider the possiblity to use it as  a stomp.

mac

[mac]

A small input cap of about 10nF to 100nF can be placed.

mac

[ezanker]

Thanks for sharing!

So, do you get a pretty nice clean sound as well?  How does it sound with a booster or distortion/overdrive/fuzz in front of it?

Thanks,
EZ

[mac]

Thanks for sharing!

So, do you get a pretty nice clean sound as well?  How does it sound with a booster or distortion/overdrive/fuzz in front of it?

Thanks,
EZ

With the pots at min. Did not try pedals.

Sound sample here:

http://guitarfxs.tripod.com/mp3/jade.mp3

If tripod does not allow remote download copy the link to the address field of another browser window and hit return.

Full gas, crappy mic, uninspired, from the breadboard with some nice radio station on the back... the diodes, and some crt noise.

mac

[QSQCaito]

Nice

When trying to dload:

"This file is hosted by Tripod, a Lycos®Network Site, and is not available for download. Please check out Tripod's Help system for more information about Remote Loading and our Remote Loading policy. "


BTW, where are you from?

cheers

DAC

[mac]

Nice
When trying to dload:
"This file is hosted by Tripod, a Lycos®Network Site, and is not available for download. Please check out Tripod's Help system for more information about Remote Loading and our Remote Loading policy. "
BTW, where are you from?
cheers
DAC

Copy the link in another browser window.

Argentina.

mac

[John Lyons]

That sounds nice!
It has a good growl to it.
Good job on this.

John

[tjcombs]

Do you have a layout available? My layout skills have ended me up with 2 unworking pedals so far.

[brett]

Hi
It would be interesting to try different diodes and different biasing in the compression section.

BTW, the 386 is only good for half a watt from 9V, despite lots of references to it producing 1W.  (the spec sheet quotes it at 0.7W at 10%THD, but it only produces about 0.4W at reasonable distortion levels). 
cheers

[scaesic]

iv been thinking about doing somethign similar, mosfet boost > ruby in one circuit inside an old practice combo. was thinking about running the ruby at 18 and the mosfet at 9vs so the power amp has a bit more headroom. i tried scoping out some alternative chips to give more power at low voltages/curent consumptyion but iv been pretty unsuccesful.

[petemoore]

   Nifty looking pre-amp-comp section !

[mac]

Do you have a layout available? My layout skills have ended me up with 2 unworking pedals so far.

Possible mods to the schematic: a big cap to ground, 47uf to 100uf, a switch to choose different diodes and a 4th 100k-B pot instead of the fixed R6.

Hi
It would be interesting to try different diodes and different biasing in the compression section.
BTW, the 386 is only good for half a watt from 9V, despite lots of references to it producing 1W.  (the spec sheet quotes it at 0.7W at 10%THD, but it only produces about 0.4W at reasonable distortion levels). 
cheers

I tried with 4148 and 1n60 but I prefer the leds. Also You can play with R5 and R7 from 2k2 to 22k and with R6 from 4k7 to 100k to get different textures. R5 and R7 need not be equal.
As is it sounds loud for what is intended. To get 1w or 2w from 18v maybe two bridged 386? I don't remember if National datasheet has a schem of a this.

BTW, chip is UTC LM386. I should buy a National to see if they work the same or not.

mac

[mac]

Me c... en tripod!!!

Sound sample here:

http://geocities.com/guitarfxs/mp3/jade.mp3

[ezanker]

For a bridged 386, see ROG's Little Gem MKII: http://www.runoffgroove.com/littlegem.html
EZ

[mac]

For a bridged 386, see ROG's Little Gem MKII: http://www.runoffgroove.com/littlegem.html
EZ

I knew I have seen a bridged 386 somewhere... lol

mac

[yertle]

The clip sounds nice!

Could you explain what de diode's in the pre-amp section do (i know what the do but i haven't seen diode's used like you use em in your amp) and which 'path' the sound signal follows?