LM386 Bass Response Improvement

[Guitar Toad]

I built this headphone amp LM386 Headphone Amp. I did build this with the switch between pins 1 and 8.  As I listen with my headphones the bass response is not as good as I would like it.

I found the following on the LM386 data sheet:

For example,
we can compensate poor speaker bass response by frequency
shaping the feedback path. This is done with a series
RC from pin 1 to 5 (paralleling the internal 15 kW resistor).
For 6 dB effective bass boost: R . 15 kW, the lowest value
for good stable operation is R = 10 kW if pin 8 is open. If pins
1 and 8 are bypassed then R as low as 2 kW can be used.

How do I do this?

[Guitar Toad]

I found the answer to my question in the opening of this thread...But, it produced another question...On page 5 of this  LM386 Data Sheet, is shows the Amplifier with Bass Boost. It shows a lead from pin 7 which is the bypass to ground. It has a capacitor symbol except that next to it  says BYPASS instead of a cap value. What does that mean?

[Peter Snowberg]

The dashed line just means it's optional... recommended, but still optional.

Bypass caps are for filtering noise on power supplies. Adding a 10uF cap there will improve performance.

[RDV]

The best way to improve the performance of an LM386 is to throw it away and use an LM3886.



RDV

[Guitar Toad]

The best way to improve the performance of an LM386 is to throw it away and use an LM3886.



RDV

Thanks, RDV.
Wow, 68 watts. That looks like a bit much for a head phone amp. Do you have a schematic?

[Peter Snowberg]

http://www.elixant.com/~stompbox/smfforum/index.php?topic=37049.0 

Also go to Google and type in "chipamp".

[RDV]

The best way to improve the performance of an LM386 is to throw it away and use an LM3886.



RDV

Thanks, RDV.
Wow, 68 watts. That looks like a bit much for a head phone amp. Do you have a schematic?

I'm really not impressed with the performance of the LM386 as anything but a distorted guitar amp, and then I only really like it through a 412 cab.

There are many ways to build better headphone amps out there, but most of them are more complicated as they use discreet components rather than an IC. There are some decent sounding headphone amps that can be made using opamps. Type "Headwize" into google and search that site for some ideas.

RDV

[Joecool85]

I like the little lm386 circuits.  But, mostly just because they are so damn easy.

[vanhansen]

Sheesh, Ricky.  I know you like the 3886 but for headphones?   Good gosh, that'll blow your ears clean off. 

I'd like to get a fuller sound out of mine as well but need to finish it first.  It's just sitting there with no enclosure.  For a simple no-frills beginner thing, that's fine.  Some of those Headwize circuits are pretty cool though.

[Joecool85]

Come one, a lm3886 would make a great headphone amp!  Sure, you'd have to plug in to an AC outlet, but it would crank!  I would recommend building your own headphones though, probably with a couple nice 10" drivers.  Might get a little heavy, but your neck will build up the strength to hold it up after a while.   

[Guitar Toad]

I built this LM386 headphone amp as my first build. I wanted to use it as a test circuit now to learn how current drains and various RC insertions will affect the tone and gain of this amp. My next project will be to do Aron's beginner NPN Booster from Gus Smalley. I already know that capacitors function as frequency filters. Now, I want to learn what other adjustments to a circuit can be accomplished by adding resistors and capacitors in series and in parallel in various places.

Is there a thread or page somewhere that basically analyzes a circuit and discusses the function of each component by it's placement in the circuit? I'm sure that it's all Ohm's Law stuff. But, I think some examples of applying Ohm's Law would help me a great deal.

Thanks for your help.

BTW, You guys have me wanting to build an LM3886 chip amp now....Thanks alot.

[Joecool85]

Your welcome.

It's because of this site that I'm building mine lol.

[Guitar Toad]

I would still like some assistance if available. I want to do the bass boost mod and the gain boost mod to my LM386 headphone amp. The gain boost involves pins 1 and 8 and the bass boost uses pins 1 and 5. How do I do both mod's simultaneously? This  is what I built LM386 Headphone Amp And the two mods that I want to combine are on page 5 of this data sheet.

Thank you.

The LM3886 stuff is interesting will have to wait a little while.

[Joecool85]

Wait...what page 5?

Gain mod, just hook pin 1 to lug 2 of a 1-5k linear pot, and pin 8 to lug 3 of the same pot.

The other mod I'm not sure about.

[vanhansen]

Wait...what page 5?

Gain mod, just hook pin 1 to lug 2 of a 1-5k linear pot, and pin 8 to lug 3 of the same pot.

The other mod I'm not sure about.

Page 5 of the LM386 datasheet.

The Gain mod is nice but that is better with a 1-5k pot or a SPDT switch like I've used between pins 1 and 8.  I'm not sure of a way to incorporate them both in to the same circuit.  To get the bass mod incorporated as well, I think another switch would be need but can't see how it would go in with the Gain mod in place too because both use pin 1.

[Peter Snowberg]

The Bass boost is already doing the same thing as the gain boost with the difference being that it's applied only to the bass frequencies. You can only squeeze so much gain out of a 386.

You may be able to add the two together with some success, but I've never tried it.

Try adding a 5K pot in series with a 10uF cap between pins 1 and 8, and then add the 10K/0.033uF cap between pins 1 and 5.