Better than LM386 on batteries?

Actually, the LM386 is somewhat popular for guitar boxes because of its .. non-hifi tone. See

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for example. The site also has other interesting stuff for guitar use.

My headphone box uses two Philips TDA7050 chips and individual volume controls for two pairs of headphones, pretty much like the datasheet says, and fares quite well with two AA NiMH batteries or alkalines. Haven't used it for guitar. I actually have a terrible sounding Korg Pandora for that :)

Reply to
XTL
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tone.

I've actually got an assortment of LM386 type amplifiers that I use frequently. One is similar to a Ruby that I play into a pair of 6x9 speakers. The only thing with the LM386 is that it eats batteries and distorts VERY easily. Great sound for guitar, but I'm trying to get something with very low distortion for mp3 playback and bass guitar amplification.

Otherwise, yeah. I love the 386 for guitar. It makes a great stompbox too. Check out Aron Nelson's SmashDrive.

-phaeton

Reply to
phaeton

(FidoCAD,

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:

Thanks again for FidoCad. Here's what I did (FidoCad source at bottom of post):

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It works! Unfortunately, it's very faint lest I hit it with a pretty good signal (such as with a preamp in front of this). Then it is faint but distorted. I tried increasing the feedback resistance of the upper opamp but that just adds more distortion. I'm running it from an 18V supply (2 9V batteries stacked). "at rest" my headphones measure at 19-21 Ohms in resistance. Is that kind of high? Could that be sapping the power? I don't have another pair to try instead, unfortunately.

Thanks for any suggestions or help

-phaeton

[FIDOCAD ] LI 65 185 65 170 LI 65 170 90 170 MC 95 190 0 0 080 LI 90 190 95 190 LI 65 195 65 205 LI 65 205 90 205 LI 90 205 90 190 SA 90 190 LI 110 190 105 190 MC 95 150 0 0 080 LI 90 170 90 150 SA 90 150 LI 90 150 95 150 LI 110 155 110 190 LI 105 150 110 150 LI 110 155 110 150 MC 125 195 0 0 045 LI 125 190 125 195 SA 125 190 SA 125 180 LI 125 175 125 180 TY 130 180 5 3 0 0 0 * Headphone SA 110 170 TY 70 160 5 3 0 0 0 * NE5532 MC 65 185 0 0 580 TY 75 185 5 3 0 0 0 * b TY 90 140 4 2 0 0 0 * 100 Ohm TY 90 180 4 2 0 0 0 * 100 Ohm LI 90 130 90 150 LI 76 148 77 148 MC 65 105 0 0 580 SA 90 110 SA 65 105 SA 65 115 LI 90 110 90 150 LI 65 115 65 125 LI 65 125 75 125 MC 75 125 0 0 080 TY 65 130 4 3 0 0 0 * 1M Ohm SA 90 125 LI 85 125 90 125 LI 65 115 55 115 MC 45 115 0 0 080 LI 45 115 35 115 LI 65 105 60 105 LI 60 105 60 215 MC 60 215 0 0 000 TY 70 215 4 3 0 0 0 * V / 2 TY 35 105 4 3 0 0 0 * 10K Ohm RV 10 95 160 225 LI 125 170 125 175 MC 25 115 0 0 170 MC 110 170 0 0 170 TY 115 160 5 3 0 0 0 * 0.22uf LI 120 170 125 170 LI 25 115 15 115 SA 15 115 TY 25 125 5 3 0 0 0 * 0.22uf
Reply to
phaeton

(FidoCAD,

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:

The output capacitor is way to small. For a roll off corner frequency around 20 Hz, it should be about 100 uF. Positive end toward the opamps. A 47 uF might be large enough (rolls off below 40 Hz) and will prevent some inaudible low frequency power being wasted in the opamps.

The 0.22 uF cap you have will roll off everything below

10,000 Hz, so all you get out is the highest treble. Very thin sounding.

Note that the 0.22 uF at the input may roll off the signal below 72 Hz. I would probable increase that to 0.47 to 1 uF.

--
Regards,

John Popelish
Reply to
John Popelish

Hi phaeton,

change the capacitor as suggested by John Popelish

Gianluca

Reply to
LAB

- change the capacitorS

Reply to
LAB

(FidoCAD,

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:

Well, the input impedance is only 10 k ohms so it'll heavily load a guitar pickup. And the 0.22uF coupling cap is a bit on the small side too.

You should use a NON inverting arrangement for best noise and higher input impedance.

Also, you can't drive headphones through a 0.22uF cap ! It'll effectively be a high pass filter and is no doubt where you're losing most of the volume. You need more like 220uF there - or DC couple the signal if it's split rail (the junction of the 2 batteries is 'ground').

You need to learn some more basics I'm afraid.

Graham

Reply to
Eeyore

Thanks John. I did just that (change the caps) and it made a huge difference. It's not quite the "ear splitting" volume level that I was expecting, but it's definitely usable now. Is there a specific name for the equation that you're using to calculate the rolloff freqs? I've always used the freq=(1/(2*PI*R1*C1)) for R/C pairs but when there's no resistor involved I'm not sure where to go. I initially chose .22uF because most guitar stompbox circuits have .1uF input and output caps, and since this is for a bass guitar (one more octave down) I figured that .22uF should be appropriate.

I also noticed that the difference in sound quality and volume is very minor between running it from 9V or 18V. In that case, I may just go 9V.

Agreed. Learning by doing and reading, when I have time. Asking lots of questions, but trying hard to not be a pest. If I ever am, feel free to kindly send me away with "go read up on X" or "go read this link". For some things though, I just don't know where to start, and I just need someone to point me in the general direction of the pinata.

Fwiw, I'm going to also go with your previous suggestion of using JFET type opamps as the 'preamp section' for the high impedance. I'll use that area for tone shaping and signal splitting. These NE5532s will drive the headphones.

Right now I am also using the pair of 9V batteries to make +9V and -9V with their junction point as ground (like you mentioned).

Thanks everyone!

-phaeton

Reply to
phaeton

(snip)

That is the right formula, but the resistance for the output is the parallel combination of the two opamp output resistors in series (plus) the headphone resistance or

50+20. Set frequency to 20 Hz and solve for C1.
--
Regards,

John Popelish
Reply to
John Popelish

The resistor was 10k.

On 9V you will lose maximum signal level handling (it'll clip earlier) but that may not be an issue for you.

Here's a good source of info on op-amps. Theory, practice the works.

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Graham

Reply to
Eeyore

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