Headphone Guitar amp with mp3 input

[jman 31]

I was wondering if you guys could take a look at this circuit for me. I adapted it from HERE and added the third input for a guitar. The main thing I am concerned about is if the guitar channel will mesh properly into the mp3 signal in this configuration.

Is there a better way to do what I am attempting?

Thanks for any input,
J

[Minion]

I would personally put a High impedance Buffer before the LM386 on the guitar input as a Guitar likes so see a High impedance Load , the way it is will cause some signal loss .... It would also be good to have a way of disconnecting the Guitar part of the circuit when useing the MP3 Input and disconnection the MP3 part when useing the guitar part , or at least use Shorting input jacks so that the unused parts of the circuit dont contribute Noise .....


Otherwize it should work but the LM386 is a very noisy part especially for headphones , even a TL072 would be quieter ......


Cheers

[jman 31]

Originally Posted by Minion

I would personally put a High impedance Buffer before the LM386 on the guitar input as a Guitar likes so see a High impedance Load , the way it is will cause some signal loss .... It would also be good to have a way of disconnecting the Guitar part of the circuit when useing the MP3 Input and disconnection the MP3 part when useing the guitar part , or at least use Shorting input jacks so that the unused parts of the circuit dont contribute Noise .....


Otherwize it should work but the LM386 is a very noisy part especially for headphones , even a TL072 would be quieter ......


Cheers

Thanks for the advice Minion. What would you use for a high impedance buffer?

I am using the LM386's because I have a bunch of them laying around and thought I would use them for something.

[Minion]

For a High impedance buffer you can use a Lowly TL071 , but any fet input opamp will work , set it for say 470k to 1m input impedance and also remember that for a standard opamp you will need to make a Voltage divider and referance the Input to half Supply .....

You could also make the buffer with Gain and a gain pot , or even drop the buffer if you say you use a Effects pedal before the amp as the pedal will act as a Buffer ....


Cheers

[jman 31]

Ok, I've added a buffer to the best of my ability using the TL071 as suggested by Minion. I also split the supply using a voltage divider as close as I could to this example. Voltage Divider Img.

Here is my revised schematic with the buffer added. I am not at all sure it's right so don't laugh too hard!

Am I anywhere close?
Thanks
J

[nigelwright7557]

Originally Posted by Minion

I would personally put a High impedance Buffer before the LM386 on the guitar input as a Guitar likes so see a High impedance Load , the way it is will cause some signal loss .... It would also be good to have a way of disconnecting the Guitar part of the circuit when useing the MP3 Input and disconnection the MP3 part when useing the guitar part , or at least use Shorting input jacks so that the unused parts of the circuit dont contribute Noise .....


Otherwize it should work but the LM386 is a very noisy part especially for headphones , even a TL072 would be quieter ......


Cheers

But he might want to play along to MP3 tracks as I do.

The MP3 player output will be larger than the guitar.

[jman 31]

Originally Posted by nigelwright7557

But he might want to play along to MP3 tracks as I do.

The MP3 player output will be larger than the guitar input.

That is correct. I am using the 100K trimmers to try to equal the volume a bit. The rest of the adjustment will be with the mp3 player and guitar volume controls. That was my theory anyways.

[nigelwright7557]

Originally Posted by jman 31

That is correct. I am using the 100K trimmers to try to equal the volume a bit. The rest of the adjustment will be with the mp3 player and guitar volume controls. That was my theory anyways.

Its best to keep the guitar volume fully up.
The same goes for the Mp3 player.
Adjust the gain in the preamp for each.

[mtripoli]

Dudes,

This is way more complicated than it needs to be. You only need one "mixer" on the input to the LM386. Check this out:http://www.scarydesign.com/pbp/MIXER.PDF
You only need one op-amp for a mono input. Duplicate the circuit for stereo. None of the component values are critical. The circuit as drawn uses split supplies (+/- on the opamp) but can be changed to run single-ended by biasing the (+) input to Vcc/2. Use a ganged pot on the input to run stereo. There are thousands of reference designs like this on the net...

EDIT: I looked at your last post with the schematic. When running off a battery you do not need the 10 ohm resistors in the supply leg of the LM386. The 15K resistor on the output back to pin 1 has a DC component on it. If you are using this for "bass boost" or something it needs a cap. Don't neglect pin 7 with a bypass cap; this will lower the noise in the circuit.

[jman 31]

Originally Posted by mtripoli

Dudes,

This is way more complicated than it needs to be. You only need one "mixer" on the input to the LM386. Check this out:http://www.scarydesign.com/pbp/MIXER.PDF
You only need one op-amp for a mono input. Duplicate the circuit for stereo. None of the component values are critical. The circuit as drawn uses split supplies (+/- on the opamp) but can be changed to run single-ended by biasing the (+) input to Vcc/2. Use a ganged pot on the input to run stereo. There are thousands of reference designs like this on the net...

EDIT: I looked at your last post with the schematic. When running off a battery you do not need the 10 ohm resistors in the supply leg of the LM386. The 15K resistor on the output back to pin 1 has a DC component on it. If you are using this for "bass boost" or something it needs a cap. Don't neglect pin 7 with a bypass cap; this will lower the noise in the circuit.

Ok, thanks for the info. I am going to look over that schematic you posted and see if I can figure it all out. How would you get the guitar signal into both of the channels when I do it with stereo?

How about THIS (circuit 4)