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
Is there a better way to do what I am attempting?
Thanks for any input,
J
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
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.😀
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
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
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
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
But he might want to play along to MP3 tracks as I do.
The MP3 player output will be larger than the guitar.
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.
Way too hard...
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.
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.
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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)
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The "stereo active mixer"... looks like a good starting point. Notice that it uses "dual gang" pots. Use a stereo input jack instead of the two as shown. The balance control is nice but not necessary. If you don't use the balance pot (take out the pot and the second resistor) then change the feedback resistor to 10K. If you increase the value of the feedback resistor then you get gain (nothing wrong with it other than be careful to not clip the signal with too much). You don't need anything after the first opamp; the rest re-inverts the signal and provides a "master" volume control. Not needed with the LM386.
It sounds like you might be new at this so I'll point out a couple of things that may (or may not) be obvious. If not maybe someone reading this is (new) and can use the info...
The circuit as shown assumes a split supply. This means you'll need two 9V batteries (or a split DC supply). Connect two battery leads (black and red)together. This is "ground" (or common). This connects to everywhere it says ground. The red is "+" and the black is "-" (not shown in the circuit; look at the data sheet for the opamp you are using for these pins). If you try and use one 9V it will not work. To use one battery requires more components to bias the circuit (beyond this discussion). When people are starting out I recommend sticking with two 9V.
The LM386 will still only use one 9V battery. Connect as normal. You're going to use two LM386 parts (left and right).
Decouple the supply. Again, it's assumed that the supply pins on every active part will have decoupling caps on the pins. Use something like 0.1uF ceramic and 10-100uF electrolytic (or tantalum) in parallel. Watch polarity of the caps. On the "negative" rail the postive side of the polarized caps connects to "ground". Ignoring this will result in a wonky circuit.
Use a "star ground" on anything audio. Simply put connect all grounds back to the same point (very simply put; this is a huge topic. If you start building anything past this circuit do some reading on the net; lot's of good info on this forum and and around the net).
Use shielded cable on the inputs. At the very least twist all supply, signal wires and output wires together (respectively). You don't need (or should use) shielded wire on the outputs.
You say you have LM386 parts already. This is an ok part but a real pig when it comes to current consumption. You're going to eat batteries like crazy. There are better parts available with much lower stand-by current out there. Use an on/off switch.
It sounds like you might be new at this so I'll point out a couple of things that may (or may not) be obvious. If not maybe someone reading this is (new) and can use the info...
The circuit as shown assumes a split supply. This means you'll need two 9V batteries (or a split DC supply). Connect two battery leads (black and red)together. This is "ground" (or common). This connects to everywhere it says ground. The red is "+" and the black is "-" (not shown in the circuit; look at the data sheet for the opamp you are using for these pins). If you try and use one 9V it will not work. To use one battery requires more components to bias the circuit (beyond this discussion). When people are starting out I recommend sticking with two 9V.
The LM386 will still only use one 9V battery. Connect as normal. You're going to use two LM386 parts (left and right).
Decouple the supply. Again, it's assumed that the supply pins on every active part will have decoupling caps on the pins. Use something like 0.1uF ceramic and 10-100uF electrolytic (or tantalum) in parallel. Watch polarity of the caps. On the "negative" rail the postive side of the polarized caps connects to "ground". Ignoring this will result in a wonky circuit.
Use a "star ground" on anything audio. Simply put connect all grounds back to the same point (very simply put; this is a huge topic. If you start building anything past this circuit do some reading on the net; lot's of good info on this forum and and around the net).
Use shielded cable on the inputs. At the very least twist all supply, signal wires and output wires together (respectively). You don't need (or should use) shielded wire on the outputs.
You say you have LM386 parts already. This is an ok part but a real pig when it comes to current consumption. You're going to eat batteries like crazy. There are better parts available with much lower stand-by current out there. Use an on/off switch.
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Sounds good. I will post a schematic when I get a little ways along for critique.
It's been awhile since I messed with op amps and I am completely new to mixing signals. I have built several headphone amps for guitars out of a 386. I like the 386 because I can run it off a single 9v and use a smaller enclosure. I kinda like that, but it is not entirely necessary. I am planning on using mostly SMD components to keep the size of the circuit board as small as possible. Someone on another forum mentioned that I might have problems with heat if I use the SMD amps.
I will do the best I can on the circuit, but I may need some help when I get a little further along on this. I want to build it as reliable as possible.
I built a stereo LM3876 amp not to long ago so I am very familiar with star grounds and the like.
I don't have to use LM386's. It's not like op amps are that expensive. I think I may have a couple of TL082's floating around also. Like I said before, I just really like the idea of a single 9v battery. I am not scared of the extra components to bias the system, so I may study up on this a bit and see what is involved. Did you get a chance to look at the power portion of the TL071 that I posted above? Is that anywhere near right?
Anyways, thanks for your reply's and input. I really appreciate it!
Jeremy
Complete redesign
I completely redesigned my headphone amp. I have yet to add the power supply section for the buffer/mixer, but I wanted to make sure I was close before I wasted any more time.
The buffer/mixer portion I found HERE. I eliminated the balance feature and some of the inputs from circuit 4.
The amp portion I took directly from the TDA2822 DATASHEET.
Please let me know if I need to add or remove any necessary/unnecessary components. I am thinking maybe I need a 1M resistor to ground on the guitar input to set the impedance, but I am not sure.
HERE is the preliminary schematic.
I completely redesigned my headphone amp. I have yet to add the power supply section for the buffer/mixer, but I wanted to make sure I was close before I wasted any more time.
The buffer/mixer portion I found HERE. I eliminated the balance feature and some of the inputs from circuit 4.
The amp portion I took directly from the TDA2822 DATASHEET.
Please let me know if I need to add or remove any necessary/unnecessary components. I am thinking maybe I need a 1M resistor to ground on the guitar input to set the impedance, but I am not sure.
HERE is the preliminary schematic.
It looks good. Instead of connecting the non-inverting input of the opamp to ground, create a virtual ground. Make a voltage divider between V+ and ground. A couple of 100K resistors will do. Bypass the bottom resistor with a 0.1uF cap. The center junction is now your virtual ground; tie the "+" input to this point. Now you can run the opamp from just a 9V battery (or whatever). Of course, don't forget to decouple the the V+ with a ceramic and electrolytic/tantalum caps as well. Same goes with the output amp.
The guitar input can use a 1M ohm to ground; this just keeps the input tied to ground so that there is no noise on the input when nothing is plugged in. You can do this on all the inputs.
I don't know what the 100 ohm resistors are for (R6 and R8)?
The output caps are way too small. These need to be 100uF minimum; 470uF is better.
It's cool that you're undertaking this. If you aren't opposed to buying parts and can spend a few dollars then I'd suggest looking at some of the parts from TI, National and Maxim. In particular look for parts that have BTL outputs (no big fat output caps are needed). Some of these devices have great specs for current consumption (they're made for use in cell phones) and really great audio response. Same for the TLO82; lot's of better parts available and most designed to run from a single supply and down around +3.3V.
The guitar input can use a 1M ohm to ground; this just keeps the input tied to ground so that there is no noise on the input when nothing is plugged in. You can do this on all the inputs.
I don't know what the 100 ohm resistors are for (R6 and R8)?
The output caps are way too small. These need to be 100uF minimum; 470uF is better.
It's cool that you're undertaking this. If you aren't opposed to buying parts and can spend a few dollars then I'd suggest looking at some of the parts from TI, National and Maxim. In particular look for parts that have BTL outputs (no big fat output caps are needed). Some of these devices have great specs for current consumption (they're made for use in cell phones) and really great audio response. Same for the TLO82; lot's of better parts available and most designed to run from a single supply and down around +3.3V.
Ok, I guess before I go any further, I need to decide which amps I am going to use.
I looked at some of the stuff you directed me to, and I proceeded to get very overwhelmed!🙄 Any chance on leading a blind horse to water?😀 I could use some advice on the proper amps to use. I did find this amp that seemed to me to be a good one for the amp portion, but I am not at all an engineer. I am not at all opposed to spending a few dollars to get something that is cool when I am done. I will probably end up making several of these for friends before it is all over if it sounds good.
I would rather use single supply amps for both stages if possible, but not completely necessary if I can still run the whole thing from a couple of AAA batteries or a 9 volt.
Thanks for all of your advice!
J
I looked at some of the stuff you directed me to, and I proceeded to get very overwhelmed!🙄 Any chance on leading a blind horse to water?😀 I could use some advice on the proper amps to use. I did find this amp that seemed to me to be a good one for the amp portion, but I am not at all an engineer. I am not at all opposed to spending a few dollars to get something that is cool when I am done. I will probably end up making several of these for friends before it is all over if it sounds good.
I would rather use single supply amps for both stages if possible, but not completely necessary if I can still run the whole thing from a couple of AAA batteries or a 9 volt.
Thanks for all of your advice!
J
I decided to try to build a variation of this amp with the parts I had on hand so I designed and bread-boarded this circuit.
Everything works pretty good except that I am not happy with the volume through the guitar input. I would like to do two things and am not sure how to go about it.
First, I would like to make the TL082 use a single voltage. I can't find any info that I can understand on how to do that.
Second, I would like to add a bit of gain to the buffer. I tried adding a 100K resistor in series from pin 1 to pin 2 and a 10K from pin 2 to ground. If I have figured right, that should give me a gain of 11. I saw virtually no change.
Any thoughts on either of those would be greatly appreciated.
Thanks
J
Everything works pretty good except that I am not happy with the volume through the guitar input. I would like to do two things and am not sure how to go about it.
First, I would like to make the TL082 use a single voltage. I can't find any info that I can understand on how to do that.
Second, I would like to add a bit of gain to the buffer. I tried adding a 100K resistor in series from pin 1 to pin 2 and a 10K from pin 2 to ground. If I have figured right, that should give me a gain of 11. I saw virtually no change.
Any thoughts on either of those would be greatly appreciated.
Thanks
J
Yes your buffer needs some gain.
Simply putting a resistor from 1 to 2 wont do that.
Put a 100k from 1 to 2 then from pin 2 put a 10k through a 10uf 63v capacitor to ground for a gain of 10. You might have to adjust one of these resistors to get the correct gain.
I think you may have missed where I said I put a 10K to ground. I didn't however use the 10uF cap. Will that make the noticeable difference?
Try it with the capacitor.
The capacaitor gives ac gain without upsetting the dc conditions.
You might need even more gain but be careful you dont get to the point where you start losing bandwidth.
Wow thanks man! That cap made all the difference in the world! It's amazing what one component can do for a circuit!
Any thoughts on how to make the op amp a single supply?
Any thoughts on how to make the op amp a single supply?
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