Author Topic: Bass Guitar Headphone Amp w/Aux Input  (Read 331 times)

skypn

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Bass Guitar Headphone Amp w/Aux Input
« on: February 01, 2019, 04:54:48 AM »
This will be my second build.
I know what I want to build, but...What I want is to be able to practice my Bass with my pedals and an aux (i.e. mp3 player, laptop, etc.) using headphones as not to disturb the Mrs. And to try to best re-create the sound I would have if I played though my regular amp, I want to also be able to use the stand alone tube pre-amp I built (note: the pre-amp alone will not drive headphones):

http://www.madbeanpedals.com/forum/index.php?topic=28666.0

I also would like to be able to use a standard pedal 9v wall wart to power the headphone amp.
I found a schematic that is all SS with an aux on The Project Asylum:

https://www.theprojectasylum.com

I'm not sure if I'm allowed to post it here. It's under Electronic Projects/ Musical Instrument Related /
Now, I can read schematics just enough to make myself dangerous. What I want to do is be able to plug my Bass/pre-amp/pedals into an input that wont need any pre-amping, mix it with the aux, then amp it enough for headphones. I think all I need to do is remove the instrument pre-amp portion of the circuit, although I'm not sure what all that includes, and wire a 1/4" mono jack for the instrument input somewhere going into the output stage. My guess is + to the plus side of C4, and the - to ground, and eliminate everything left of, and including C5, which I'm guessing is to remove DC before amping.
I also believe I can completely remove the 12v potion altogether and connect the 9v to ground, and pin 6 of both IC1 and IC2 via a switch and D3.
I don't think I have to worry if it will pass lower frequencies, as the  Bass pre-amp should have that covered. As to any other concerns, or a better way of doing this, I wouldn't have a clue.
I know I am showing my ignorance (defined as just having never been told yet) here, but I am a firm believer that the only stupid question is one you ask of someone who you already know doesn't know the answer, and I am sure the vast majority of posters here do.
TIA

lrgaraujo

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Re: Bass Guitar Headphone Amp w/Aux Input
« Reply #1 on: February 04, 2019, 05:33:13 PM »
No such thing as a stupid question, we were all beginners at some point (and compared to many here, I'm no more than a noob myself).

Now to your questions:
C5 is a power supply filter cap (I would keep it)
Connecting the input jack as you've suggested will work, but LM386 amps seem to work better with a buffer before it (look for the runoffgroove ruby)

I also believe I can completely remove the 12v potion altogether and connect the 9v to ground, and pin 6 of both IC1 and IC2 via a switch and D3.
I'm not sure what you mean by that, but what I think could be the simplest is to remove C16, C17, D4 and IC3 and connect your power supply in place of the battery (and use the existing switch as an on-off)

PS: I love your preamp build

skypn

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Re: Bass Guitar Headphone Amp w/Aux Input
« Reply #2 on: February 11, 2019, 01:12:00 PM »
First, sorry for the delay in answering. Second, thank you for the kind words about my build.

C5 is a power supply filter cap (I would keep it)
Now that you mention it, C5 does look like a filter, thx

Connecting the input jack as you've suggested will work, but LM386 amps seem to work better with a buffer before it (look for the runoffgroove ruby)
Are you saying that the circuit "as is" doesn't include a buffer, or that my proposed mods eliminate it?
I also guess you'd like me to look up "runoffgroove ruby"

I also believe I can completely remove the 12v potion altogether and connect the 9v to ground, and pin 6 of both IC1 and IC2 via a switch and D3.
I'm not sure what you mean by that, but what I think could be the simplest is to remove C16, C17, D4 and IC3 and connect your power supply in place of the battery (and use the existing switch as an on-off)
We were talking about the same thing, we just called it different. 

Thank you again for taking the time to share your thoughts


lrgaraujo

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Re: Bass Guitar Headphone Amp w/Aux Input
« Reply #3 on: February 12, 2019, 08:33:55 AM »

Are you saying that the circuit "as is" doesn't include a buffer, or that my proposed mods eliminate it?
I also guess you'd like me to look up "runoffgroove ruby"

The circuit "as is" does not include a buffer, you're indeed removing a preamp section. Only LM386 amp I've ever built is the Ruby, and the guys over at runoffgroove seem to believe the buffer improves the sound, though the circuit should work without it.

I'd breadboard a buffer (or build it) and try the amp with and without it.

If ultimately you decide not to use the buffer, you're left with a very useful little thing (it's no more than a handfull of components)