No $$ = Poor sound?

[jkrienert]

Hello.
  Finally got in some LM386N-4's and since payday is still a bit away, I am trying to bench test to learn some things.
 
  Realizing I have very few of the specific components for any of the LM386 circuits I could find, I decided to move forward anyway to see what I could get to work out.
  After 4 hours today marathoning through my scrounged parts, I ended up with the included drawing (which was the best I could decipher to be close to some of the measurements from other 386 amps).
 
  It sounds awful. The speaker pushes out to its limit as if its running on ac.
  I am prepared to hear how much of a 'noob' I am, and probably some needed lecturing. It is received with respect and an open stance, because obviously... I have a lot to learn .
  So my best judgment is to wait until I get money for the proper parts. Until then, anyone want to school me on why what I have sounds so terrible (and possible temp. solutions)?
(also to be noted... I am wiring this point to point if that might be part of the problem ... no boards... no $$)
Thanks in future tense!
jmk

[Brymus]

First what ohm rating is the spkr ?
It should be between 4-16 ohms
In my experience the higher the ohms the better the spkr sounds with the 386 (even 32 ohms sounds good)
Also try leaving pins 1 and 8 open this will set the gain to 20 instead of much higher.
You may be getting too much clipping from the 386
You can also try using pin 3 for the input instead of pin 2.
Finally read the data sheet ,the schematic shown in the data sheets does work very well.
Hope that helps some.

[jkrienert]

The speaker I am using is 16ohm, so it should be alright.

Also noted, the terrible sounds happen even when placing a capacitor between 1 and 8, when leaving disconnected, or when having a strait-bridge.

If pin3 is chosen for the input, would pin2 then be considered the ground(common) ?
More or less just a flip flop of the input wires?

The assessment of too much clipping is dead on with the sound. That mixed with the dreaded high freq. squelch.

Could my battery brick be a problem> it is two AA's and 4 AAA's combined in series (total roughly 7.8V+)?

Thanks for the quick response! More to come I hope...

jmk

[jkrienert]

this is one ginormous bump in the road.

you know, about a month ago (fried  due to accidental over-voltage) I had a TD2822, and the circuit seemed a bit more complex.
Yet I had it running no problem as a mini amp direct to my guitar, and it had really good fidelity.

Advice led me to curiosity of the 386, and everyone seems to be getting great sound from it (various web audio clips).
I stand determined! Ive already invested much time and money!!!


jmk

[phector2004]

I'm running high efficiency 32Ω earphones with a 386N1, I find adding a resistor on the output cleans it up a lot. Have you tried sticking a 5k-10k in there? I'm actually using a 4.7k and it sounds great!

Brymus, what would switching to noninverting input do?  

[jkrienert]

hello phector, this is the continuing of my (persuaded) path away from the 4951 to the lm386.

where exactly would the resistor placement be that you mention?



Thanks.
jmk

[Brymus]

I'm running high efficiency 32Ω earphones with a 386N1, I find adding a resistor on the output cleans it up a lot. Have you tried sticking a 5k-10k in there? I'm actually using a 4.7k and it sounds great!

Brymus, what would switching to noninverting input do?  

I found that too adding a resistor at the output helped in some instances.
As far as switching the input IDK what it does but when I was fooling with the 386 IC's I found some instances where the input only worked right on one pin vs the other.
Again IDK why but it did work.It may have been the way I was using mine as part of a larger circuit.
And something to do with phase IDK.
Its been a year since I messed with one.

And yes if you switch pins (2 and 3) for input the other becomes signal ground.

You can see what I did adding a resistor on the output here.
If you ignore the first part of the circuit and focus on the part with the 386.

[Electron Tornado]

Here's a link to the datasheet:

http://pdf1.alldatasheet.com/datasheet-pdf/view/8887/NSC/LM386.html

[jkrienert]

thanks man.

ya, that data sheet is probably my top traveled to site in the last week.
going back to tinker...

be back around shortly.

jmk

(again, I must send respect to ya... alot of people just talk sh*t and gossip on the internet, but when its connection is used for education and learning, I am always thankful. This forum is a prime example.)

[phector2004]

Yup, either the first (top left) or the 3rd (bottom) one should work. I'm currently using the 3rd one, but its for Deadastronaut's distortion pedal, so I'm not sure what a resistor would do on a cleaner output.

Let us know how it goes!

[jkrienert]

Will repost tomorrow evening after the many days works...

Thousand thanks!!!

[PRR]

What IS that "7.8V"?

Meter your 7.8V while playing. If it sags horribly, it will sound awful.

Find a 10 ohm resistor  and one of your 100nFd caps, put this from pin 5 to pin 4 just like the datasheet shows (they call ot 0.05 but 100n will work). Without this, and maybe with hay-wire or too-tight wiring, the '386 gets busy making radio waves and doesn't pay enough attention to the audio.

[petemoore]

  Clicking 7.8vdc across a speaker gives an idea of what the power supply is capable of, not very loud, the chip uses some of this voltage too, so there's not a lot of headroom involved.
  12vdc makes it a little louder, use a regulator or mind that Wallwarts exceed the rated voltage [without a big load] and the LM386 has 15v power supply limit.
  The connecting of stuff that creates boosts across pins 1 and 8 helps make the chip run out of headroom faster.
  Another thing is how much power bass tends to hog...'tightening up' the bass [ie using HP filters] may allow greater percieved volume with less distortion.
  The speaker...since there's only a small amount of power, what the transducer does with it [effeciently create sound waves or become mostly a less effecient heater] matters.

[Gurner]

Your pot wiring at the input looks suspect - I'm assuming you've simply ommited one connection becuase it should have three connections, else that makes it wired like a rheostat (vs the potential divider you need).

Also, the few LM386s I've had a scope on, has shown that they are prone to fugly 'nasties' on their output signal *unless* you have the zobel network in place (your original schematic hasn't)....



(the the 0.05uf cap an 10 Ohm resistor in series to ground from pin 5's ouput.).

An LM386 can be configured to yield  extreme gain (x200), which is going to sound awful in a lot of situations. I'd leave the gain at it's minimum (x40), by making sure pins 1 & 8 aren't interconnected (unlike the piccie above, which shows a cap in between pins 1 & 8 ! )

If you're using a small speaker, you could attenuate some of  the bass by reducing the output cap size.

Finally, you do realise that the input impedance of an LM386 is too low to connect directly to a guitar - you need a buffer/preamp in front of the LM386 to stop it sucking tone (which is likely to be the main issue)

Personally, I think the LM386 is pash (Scottish for bad)....I'm perplexed at the continuing DIY community's loyaly to it. A veritable  plethora of similar low power BTL ICs now exist, which negate the need for a large decoupling cap on the output ...so no high pass filter 'presented' to the output signal etc. (also any supply ripple produced with a BTL IC is at twice the frequency of your signal, not to mention twice the punching power for it's size ve a single end non BTL IC like the LM386))

[deadastronaut]

@gurner...argghhhh you said 'zobel'....ha ha ha...i know someone else who constantly mentions that  !!!!...

[Electron Tornado]

Also, the few LM386s I've had a scope on, has shown that they are prone to fugly 'nasties' on their output signal *unless* you have the zobel network in place (your original schematic hasn't)....

(the the 0.05uf cap an 10 Ohm resistor in series to ground from pin 5's ouput.).

Can you elaborate on the "fugly nasties" on the output signal and what the zobel network does to alleviate them? I used the 386 in a distortion pedal.

Thanks.

[Gurner]

Also, the few LM386s I've had a scope on, has shown that they are prone to fugly 'nasties' on their output signal *unless* you have the zobel network in place (your original schematic hasn't)....

(the the 0.05uf cap an 10 Ohm resistor in series to ground from pin 5's ouput.).

Can you elaborate on the "fugly nasties" on the output signal and what the zobel network does to alleviate them? I used the 386 in a distortion pedal.

Thanks.

Sure, when I push a sig gen sourced sine wave into a circuit - & when shooting for a clean distortion free circuit, I expect to see a nice clean sine wave coming out of it What I saw on the output when using an LM386 is a sine wave output but with hf noise (oscillations) following the outline sine wave shape**  - in practise whether these would be heard, with a typical small speaker often used, I doubt it (& certainly not likely ever to be heard in a distortion type config), but nevertheless they're there put in the resistor & cap ....the sine wave cleans up....not 100%, but a lot better..

But like I say, there are chips a plenty that don't require such a cap/resistor to clean the signal up...so why the allegance to the LM386 I don't know? A TDA7052 is a BTL IC I'd use in preference, but the signal needs taming into it, since you get twice the output power into the same load (vs an LM386). The TDA7052 is clean as a whistle

** & before anyone chimes in with "aah, but was HF you saw because of this, that & the other" - nah, it was the LM386. 

[jefe]

But like I say, there are chips a plenty that don't require such a cap/resistor to clean the signal up...so why the allegance to the LM386 I don't know? A TDA7052 is a BTL IC I'd use in preference, but the signal needs taming into it, since you get twice the output power into the same load (vs an LM386). The TDA7052 is clean as a whistle

The LM386 has an adjustable gain. I don't know if any other chips have that option, and I think that's one of the reasons that the LM386 is so popular. Also, when you look at how the LM386 is used in distortion circuits, well... I think some of that "nastiness" you're referring to might be a good thing. I mean, who wants a "clean" distortion effect? 

[deadastronaut]

@gurner

yeah looks like a cool amp...nice one!.

i like the 386 for an easy hi gain distortion..very simple. but very nice n chunky on guitar..with a j201 in front...

i wouldnt really use a 386 for clean......(though i have tried)...with poor results..ha ha..

[Gurner]

But like I say, there are chips a plenty that don't require such a cap/resistor to clean the signal up...so why the allegance to the LM386 I don't know? A TDA7052 is a BTL IC I'd use in preference, but the signal needs taming into it, since you get twice the output power into the same load (vs an LM386). The TDA7052 is clean as a whistle

The LM386 has an adjustable gain. I don't know if any other chips have that option, and I think that's one of the reasons that the LM386 is so popular. Also, when you look at how the LM386 is used in distortion circuits, well... I think some of that "nastiness" you're referring to might be a good thing. I mean, who wants a "clean" distortion effect?  

If you want adjustable gain variant, easy - use the TDA7052A (it has a pin to put a DC volume control pot on). ...it's a  true 'on the fly' gain adjustable. (furthermore the pot isn't in the signal path so no crackles & pops with age - also put gnd onto pin 4, the TDA7052A's output is muted - no such ability with the LM386)

Point taken about the distortion, but that said, I'd rather have an amp that's capable of both clean & dirty.The TDa7052A will do both (just crank it's dedicated volume control right up!)  Not totally sure what the Op wants from the LM386...distortion or clean, my comments about the LM386 relate to it's visible level of filthyness (vs other ICs in the same ballpark)