1W mini-amp built-in to bass. Thoughts?

UncleFluffy · #1 03-24-2010, 09:34 PM

I've been noodling around this evening and have breadboarded up a simple 1W amp that's small enough to be fitted inside the control cavity of a bass.

3.5mm headphone jack out, power via the 9V preamp battery (so active only for now), small and no power consumption when not in use.

Not rocket science, but possibly useful for those times when you just want to grab your bass and practice.

The plan is to put the plans out there for anyone else who wants to build one for themselves, so I'd like to ask a couple of quick questions:

- is this useful to you?

- what features would make it even better for you?

Much thanks...

Bmorefoozler · #2 03-24-2010, 09:39 PM

Would it be possible to do it as a headphone amp instead?

bommer · #3 03-24-2010, 09:39 PM

that sounds like an unreal idea.
id buy that if you could sell it and install it into any bass. i hate having to lug my rig around.

the thing I'm curious about is, would you HAVE to use headphones, or would it output the sound so you could hear it in a quiet area

UncleFluffy · #4 03-24-2010, 09:45 PM

It's 1W into a headphone jack - you can plug in phones or a 3.5mm to 1/4" speaker cable if you want so you can connect to a cab if you want.

More intended as something you can plug your ipod headphones into without needing a headphone amp, but possibly usable into a cab as a bedroom practice setup.

(Not currently intending to sell these, just make one and put the plans out there for people to DIY).

bommer · #5 03-24-2010, 09:48 PM

ah alright. looking forward for this DIY! *subscribes*

tercesyrev · #6 03-24-2010, 09:48 PM

I've seen something similar in use. I think Vox makes them. It's a small box, about half the size of a cigarette box. It plugs into the guitar jack. Has a few tone presets and volume. Headphones plug into the box. My brother uses one on his traveler guitar.-

Johnny Mack · #7 03-24-2010, 09:49 PM

can you plug into a larger amp from this and use the 1w amp as sort of a boost in a passive bass?

edit: also im sure you could mod this to a 1/4" out if one so chose to

UncleFluffy · #8 03-24-2010, 09:53 PM

Quote:

Originally Posted by Johnny Mack

can you plug into a larger amp from this and use the 1w amp as sort of a boost in a passive bass?

edit: also im sure you could mod this to a 1/4" out if one so chose to

Right now it's setup to feed off the 9V battery already there in an active bass, but it wouldn't be hard to add a battery clip to run it on a passive instrument.

You could use it as a booster, but I suspect you'd be much better off tone-wise using a real preamp.

Definitely possible to mod to a 1/4" out if you want. Current PCB layout has a 3.5mm on board but that's not essential, just stops you getting the sockets mixed up.

UncleFluffy · #9 03-24-2010, 09:54 PM

Quote:

Originally Posted by tercesyrev

I've seen something similar in use. I think Vox makes them. It's a small box, about half the size of a cigarette box. It plugs into the guitar jack. Has a few tone presets and volume. Headphones plug into the box. My brother uses one on his traveler guitar.-

Yeah, Vox make them - I think they're called "Amplugs". This would be similar but built inside the control cavity of the bass. No power consumption when not in use so you can just fit it and not worry. One less thing to remember to pack.

bobcruz · #10 03-24-2010, 11:10 PM

A headphone output directly from the bass would be awesome. What kind of current draw are you looking at? If it eats batteries it could lose its appeal quickly....

UncleFluffy · #11 03-24-2010, 11:16 PM

Right now, less than 10uA when no headphones plugged in and about 6mA when plugged in but not playing. When playing, it depends on how loud and what you're plugged into.

JimmyM · #12 03-24-2010, 11:52 PM

ac/dc includes a little 1w amp with a tiny cab inside their new box set "backtracks."

http://www.youtube.com/watch?v=pW7srJ8qJU0

if it works for angus, it should work for us

personally, i've got no interest in a 1w amp. but it's fun to build and you learned something, and it might lead to bigger stuff i might be interested in one day, so keep it up!

dDaddybass · #13 03-25-2010, 04:41 AM

You could mount the 3.5 jack in the control cavity plate. I would love to have the plans for this. How hard would it be the add a aux input into this little rig?

Jim C · #14 03-25-2010, 05:31 AM

I'm interested in any headphone amp that does not hiss, has decent tone, and will work with standard impedance headphones; ironicaly, many of the dedicated headphone amps won't do this to my expectations

UncleFluffy · #15 03-25-2010, 09:03 AM

Quote:

Originally Posted by dDaddybass

You could mount the 3.5 jack in the control cavity plate. I would love to have the plans for this. How hard would it be the add a aux input into this little rig?

Control cavity plate is the current plan, at least for the prototype I'm putting in my beater bass. Aux wouldn't be too hard, but probably something I'd add in v2 as v1 is aimed at being as simple as possible.

Quote:

Originally Posted by Jim C

I'm interested in any headphone amp that does not hiss, has decent tone, and will work with standard impedance headphones; ironicaly, many of the dedicated headphone amps won't do this to my expectations

This is optimised for "small and does not suck too badly" rather than ultra-high sound quality. Tone is subjective but it only uses about $3 worth of parts so it's possible to run one up over a rainy afternoon and see if you like it.

Should drive anything you throw at it from 4 ohms to 4k.

lomo · #16 03-25-2010, 11:20 AM

This is a useful thing-but offers very little advantage over the 50 dollar pocket-rockit headphone amp that plugs directly into your output jack without a cable, and then allows you to plug phones into it. That model also has vol and very lmited tone control and some bull*&%$ fx. I guess this takes it a step further and puts it inside the bass.

UncleFluffy · #17 03-25-2010, 11:40 AM

Quote:

Originally Posted by lomo

This is a useful thing-but offers very little advantage over the 50 dollar pocket-rockit headphone amp that plugs directly into your output jack without a cable, and then allows you to plug phones into it. That model also has vol and very lmited tone control and some bull*&%$ fx. I guess this takes it a step further and puts it inside the bass.

Yes, and I expect that this isn't going to sound as good as a $50 amp either. The only real advantage is that it's one less thing to lose / forget to pack.

BassmanPaul · #18 03-25-2010, 11:41 AM

Sorry Uncle but I see it as a pointless exercise. There's enough inside an active bass already without adding more so you could use a set of headphones. As posted there are a myriad products on the market to allow this.

Paul

KramerBassFan · #19 03-25-2010, 12:40 PM

Lets see a schematic and parts list.

Sure, why not.

UncleFluffy · #20 03-25-2010, 12:49 PM

Quote:

Originally Posted by KramerBassFan

Lets see a schematic and parts list.

Sure, why not.

Here ya goes:

Edit: Updated schematic later in the thread.

It's pretty much a standard LM386 amp direct from the Nat Semi application note, with a transistor set up to cut power whenever the phones are disconnected. (I looked around for a 3.5mm jack with a NO switch but it doesn't look like they make them, hence the transistor switch).

PCB layout is 1.25" x 0.75" but that should shrink a little more with some juggling around.

Edit: note that this schematic isn't final. I'm not completely happy with the input biasing and may move stuff about a bit.