Amp Circuit Question

[avengers63]

I pulled this uber-basic 1/2 watt amp schematic from runoffgroove. I got it wired up and working. It doesn't sound bad at all. What I want is to pull the component out that pushes it into overdrive. All I want pure amplification so I can use it as a test amp. Any clue as to what I'd need to do?

[Ripthorn]

The 386 is what gives all the gain. You can reduce the value of the gain pot, but that is all you can do from that standpoint. Running on a higher supply voltage will increase the amount of clean headroom you have, but only to a point. Make sure to check the spec sheet so that you don't give it too much juice and fry it. I would try 12V and see if you like it. If not, you might be able to try 18V (if that is in spec, don't know off the top of my head).

[avengers63]

It runs off a 9v supply.

So, to make sure I'm understanding you correctly.... Making it a pure clean amp ain't happening, and the best I can do is just keep the gain pulled as far down as possible.

[Samba Pa Ti]

check this >

http://www.national.com/ds/LM/LM386.pdf

ive built a few of these amps and they all have gain/colour in the sound, its not really a clean sound at all.

looking at the little gem it looks like its running with standard amount of gain the 386 has to offer (can only go up) putting a 10uf polarised capacitor on pins 1 and 8 makes the gain go up.

(as it says in the modifications leave pins 1 and 8 open for less gain, its already running at the minimum specs).

the 386 supports 18volts max (depending on the version), i find it sounds best at 12volts though and i wouldnt go over 12.

my favourite schematic for the 386 amps is the noisy cricket, it sounds similar to the ruby and the little gem but its got a few more features > http://www.beavisaudio.com/projects/NoisyCricket/#DIY .

[Paul Marossy]

I would do the "Gain Of 20" scenario on this data sheet: http://www.national.com/ds/LM/LM386.pdf

and use the N4 version of the chip with can handle up to a 22V supply voltage, and operate it on at least 18V.

I have never heard an LM386 circuit running on 9V that I have liked, they seem to always sound yucky no matter what when operating at that voltage.

Edited June 12, 2010 by Paul Marossy

[elmo7sharp9]

I pulled this uber-basic 1/2 watt amp schematic from runoffgroove. I got it wired up and working. It doesn't sound bad at all. What I want is to pull the component out that pushes it into overdrive. All I want pure amplification so I can use it as a test amp. Any clue as to what I'd need to do?

Use another solution.

The LM386 is fairly bad, distortion-wise and, even as a headphone amp,

doesn't produce sufficient level for use in a band situation.

I tried several designs for a 6-way headphone distribution amp,

and the LM386 was definitely the worst-sounding.

If you're after a low-power amp, have a look here...

Headwize,

where there are many better alternatives.

[avengers63]

All I want is pure amplification so I can use it as a test amp.

Use another solution.

The LM386... doesn't produce sufficient level for use in a band situation.

I just want something to have in the shop for when I wire up a guitar so I can test it right there.

[Paul Marossy]

I just want something to have in the shop for when I wire up a guitar so I can test it right there.

What you were asking about in the OP will get the job done.

What I want is to pull the component out that pushes it into overdrive. All I want pure amplification so I can use it as a test amp. Any clue as to what I'd need to do?

It would sound a lot better on 18V than it would on 9V, which would require the N4 version of the chip. It's overdriving so much on 9V because it runs out of headroom and really clips the signal. And also, if you lose the 5K pot between pins 1 & 8 and use a 10K volume pot on pin 2 instead, it should clean up a lot more.

Edited June 12, 2010 by Paul Marossy

[Tim37]

hey John what size speaker are you running it through both size and wattage. You will be suprised at how much volume you can pickup by going to a biger more efficiant speaker.

speakers tend to loose efficiency as there wattage rating goes up (the speaker has to be built heavier to handle the wattage) any way you also get volume out of speaker size. just think about it a 4x12 cab is louder than a 1x12 cab running the same amp. i have had real nice luck running a danelector mini amp through a weber 10 that is rated at 15 watts (they dont make that model any more but they have some 25 watt speakers)

any way just some food for thought.

also if your getting in to amp building check out http://www.mintyamps.com/store/ i haven't got one yet but they look interesting and simple enough.

also check craigslist for one of those cheap 10 or 15 watt practice amps some of them sound ok when hooked to a good cab.

[ansil]

i have been quite the lm386 guru [at least thats what my car's tag says lol] there are some really good answers here as seen above. something to try is the bass boost function on the clean setting to help you move some air. but again by the time you get the n-4 which is the only real version for amplification of this chip there is [ie the n-3 is good for parallel outputs and for chip distortion the ones below that are just bull sh1t] by the time you do that you could get a lm380 which has more clean headroom and a larger input impedance more wattage and even the smaller lm380n-e in the eight pin package puts out more power [at least it sounds like it anyway] and is cleaner. keep in mind that you need some sort of impedance amp or buffer stage in there to keep it from loading down. if you want some really sick stuff run a 386 as a preamp into a 380 as a power amp and watch your speakers bleed with gain. its a little noisy but gives a killer sustain and crunch. like a decent sweet child o mine sound. have fun and keep on kicking. but you know they make these great tda chips that have preamp power amp and such all in a box. they even have these ic's with active six band eq preamp you just put in the pots and a couple caps in there and add power. its killer stuff. of course here at my shop i just use the surround sound. i have guitar port and a few other home made inductor and transformer coupled stuff so i can play into it and i can play prerecorded guitars out through a reamper into some amps via remote control in case of shock hazard. well i see i am rambling so it must be late.

ciao

ed

almost forgot

http://www.google.com/url?sa=t&source=...djB5gHBrt5TYRvA

[psw]

Well....the "little gem" is not a great circuit at all...the "rheostat" control is not at all a good idea. The pot between pins one and 8 should bring things down a bit gain wise. There is no pramp in this design at all and this is going to cause all kinds of problems with loading and impedance matching for a guitar running into it...

In short, this is a poor design, far better is say a ruby or whatever that has a preamp buffer (if you use a stomp box into the amp, this will provide the necessary buffer) and of course, a bigger speaker will get far better results. Not only is a 9volt battery going to be severely limited in headroom, it isn't going to last long in an amp, even a little one...a wall wart even at 9 volts will provide the amps needed regardless of voltage to improve things.

The LM386 amps are ok, but they are limited. 1/2-1 watt max...but if you max out any amp it is going to distort badly, the solution, turn it down...but then it is going to be very quiet...helps to have more speaker to move more 'air'...if you are running headphones, make sure they are 8 ohms, many cheap headphones are 32ohms and stereo so a complete mismatch to what the amp 'wants'...

I'd investigate running a stompbox into it...most boss for instance buffer the signal even when off...maybe looking to see if you could update the design and loose the rheostat control...plenty to choose from on RoG and elsewhere as mentioned.

Great though to see that it worked for you, that's a start for sure. I've always kept a little amp about that I found on the side of the road and just plug in, mains power and a bigger speaker in an enclosure...and free...

[avengers63]

Great input from everyone. It's all much appreciated.

Let's not lost track of the goal - Something really basic that will make a reasonable clean sound for use as a test amp in the shop. I don't need any more than conversation-level volume, no overdrive, no tone knobs. Just pure, basic, clean amplification for the workshop.

For a speaker, I could honestly care less what's used. If I could get away with it, I'd scavenge some stereo speakers and use them. If I had to get a "real" guitar speaker, I might as well get a used practice amp and be done with it.

[psw]

Fair...if it's working ok for you...then I'd first try an 8ohm speaker (or two 4 ohm speakers in series) and mount them in some kind of box with a secure baffle for the speaker mounting that wont move around. You might fins some car speakers for instance that would work out, something say 6" out of an old radio. However, if you use a tiny computer speaker or something, it will be impossible to get a decent sound at any volume with guitar frequencies, especially the bass strings. Often you can find a suitable stereo speaker boxed already and could mount the amp inside it!

Ultimately, a used practice amp is generally the 'way to go' in my experience...there is only so much these things can do, and if actually running off a battery, you will eat up a lot of batteries that is going to cost a fair bit in the long run...performance greatly diminishes as batteries die, including distortion of course.

Otherwise, the lack of a preamp in this design is going to be a problem, the likelihood is that it will load the pickups deadening tone and so not give anything like a decent approximation as to how a guitar or it's pickups really sound. It need not be much, a simple sing transistor type that if found in most other LM386 designs such as the ruby or noisy cricket will suffice, or as I say use a stomp box (or at least test this to hear the difference) as a substitute.

[Tim37]

if you use a tiny computer speaker or something, it will be impossible to get a decent sound at any volume with guitar frequencies, especially the bass strings.

theres a thought find ya a pair of those amplified comp speakers and rip the amp out of them, i have hears of it being done on the cigar box forums just dont expect good tone.

[Paul Marossy]

Otherwise, the lack of a preamp in this design is going to be a problem, the likelihood is that it will load the pickups deadening tone and so not give anything like a decent approximation as to how a guitar or it's pickups really sound. It need not be much, a simple sing transistor type that if found in most other LM386 designs such as the ruby or noisy cricket will suffice, or as I say use a stomp box (or at least test this to hear the difference) as a substitute.

Yeah, something with an input buffer would work better. The Little Gem Mark II would even work better.

[psw]

true, and with two chips more power...so more clean headroom...but a lot of power consumption...not really practical for batteries.

Things like the ruby or others are a better proposition, no buffer and a huge rheostat on the speaker to use as a volume control (which is one of those "what were they thinking of" moments...

as an alternative 'volume control' a 1k pot between pins I and 8 of the chip (the top two connections on either side of the chip) will provide a gain control from 20x to 200x amplification...still lacks a preamp, but a better move that will use less juice and be a better deal...20x will be fairly low but fairly clean...so the volume control will never go to zero or off.

to do this connect the centre tag of a pot and an outer to either pin, swap as necessary so the control turns the right way...less resistance means more gain.

Oh...on the circuit it even has a 5k pot illustrated, which would do the job...on the layout it would appear that the two pins 1 & 8 which are the ones either side on the right hand side are wired together...if so, break that and put a pot in there to adjust gain and loose the rheostat as this is going to waste power in heat and not be very effective at all. Stompbo, easy buffer and should improve things...