Author Topic: LM386 Preamp sounds horrible, do i have the wrong capacitors?  (Read 5672 times)

valvefreak

Hi,
I've designed and breadborded a simple 12AX7 Overdrive pedal with an lm386 as a Preamp to kick the signal into the tube.
here's a scematic of the preamp section:
http://imageshack.com/a/img901/9926/yjW03e.jpg

C1 = 10F, 25V, Electrolytic
C2 = 10nF Ceramic
C3 = 10nF Ceramic
R1 = 100K Pot
 :icon_exclaim: Pin 2 is not grounded, because its internally grounded through a 50K resistor.
 :icon_exclaim: The output goes into a 500K pot which biases the tube and brings the signal in.

The problem is, that the lower frequencies are very distorted, so the lower notes sound horrible when they're palm muted.
I have tried to change the capacitors and got a better sound when i changed C3 from 10nF to 100pF (Ceramic), i could only hear the highs. that was better, but it was not as powerful and it had no bass at all. Have i configured the LM386 wrong? do i need Film caps? ???
The Valve works and sounds perfect, i bypassed the lm386 and i got a wonderful sound which of course had nearly no distortion/overdrive.

So here's the big question: How do i get the LM386 to sound good?
« Last Edit: April 22, 2015, 11:44:50 AM by valvefreak »
Don't let the magic smoke come out!

valvefreak

Re: LM386 Preamp sounds horrible, do i have the wrong capacitors?
« Reply #1 on: April 22, 2015, 01:48:42 PM »
Well, i solved the problem... :icon_confused: the guitar has died somehow, thats why it sounded so bassy :D
excuse me for wasting your time  :icon_biggrin:
it sounds great with active pickups! Rock n Roll! :icon_twisted:
Don't let the magic smoke come out!

FiveseveN

Re: LM386 Preamp sounds horrible, do i have the wrong capacitors?
« Reply #2 on: April 22, 2015, 03:32:59 PM »
Well, keep in mind that the 386 has a 50 k input impedance. Why did you decide to use this particular chip and not an op amp, FET or BJT gain stage? It doesn't sound like you're driving a heavy load or are interested in its brand of distortion.
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)

valvefreak

Re: LM386 Preamp sounds horrible, do i have the wrong capacitors?
« Reply #3 on: April 23, 2015, 11:12:23 AM »
To be honest, i dont know much about impedance and stuff like that  :icon_confused:
It was just the chip i knew, i got one and tried it out... it seems to work fine. especially the gain control is a great feature, but i don't know if other ICs have one too. (are there any?)
what IC would you recommend if i were to build a distortion pedal (for example)?
Don't let the magic smoke come out!