Instrument headphone amp

[Steve Conner]

$12.99! You could have broken open an old set of computer speakers and got pretty much the same thing. I have a stereo amp board in my desk drawer here with two of those NJM-whatever chips on it.

Of course if you didn't have the speakers kicking around, it might have cost $12.99 to buy them.

[JungleVip]

Oh well never mind! I have just bought audio amplifier projects by r a penfold, the circuits look challenging but I am told they are pretty straightforward

[Ptron]

I breadboarded the Ruby with the tone control inserted. I used a 2k trimpot for the gain and a 100k for the volume because it's what I had. I kept the two 47uf filter caps and the way the headphones are connected through the two 10ohm resistors. It works quite well so I'll roll with it. It actually doesn't sound half bad overdriven if you roll off the highs.

One thing though, it still breaks up before gets deafeningly loud. (Maybe I'm already deaf) I could probably get away with reducing the 10ohms to 5 or 1, right? They just protect against output shorts while plugging in and out, correct?

[J M Fahey]

(Maybe I'm already deaf)

Yes you are, or will be in a short time, and I'm not kidding. (Guess why I'm so certain about that)
Good luck anyway.

[Zipslack]

Early breakup and earphone resistors

The 386 chip is prone to early breakup - it can be hard to get good clean sound at a high volume. Try lowering your input signal/volume and then increasing the gain until it starts to break, then back the gain off a little.

The 10 Ohm and 47nF network from pin 5 help alleviate oscillation. The 10 Ohm resistance from the headphone ring is to help attenuate the signal going to the headphones. Reducing or removing it will allow more volume in the headphones. Unless your headphones are the source of distortion, this won't help your breakup problems, but it could give you more volume out which would give you the same benefit (more volume out without having to drive the chip as hard).

[Ptron]

The 10 Ohm resistance from the headphone ring is to help attenuate the signal going to the headphones.

Oh, really? I had assumed their primary function to be preventing the output from shorting to ground while plugging in the headphones. Well, I'll reduce or remove them then. I can get a fairly clean output, just not at the level I would expect. I'll also give your gain/master suggestion a shot. I had set the gain by maxing the volume and then adjusting the gain for a touch of breakup.

The primarary function of this device will be for me to tune my pedal steel in noisy enviroments so don't worry J M . I won't use it very often, and when I do I will rarely, if ever, need to to max out the volume. I just want it to be available.