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Author Topic: Battery-powered "Busking" amp.  (Read 33316 times)

darwindeathcat

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Battery-powered "Busking" amp.
« on: October 19, 2009, 01:59:26 PM »
Hi all, This is something I've been thinking about for a good while now, and I thought I'd poll the knowledgeable crowd here to see if anyone has any words of wisdom for me before I start in on it.
 
So here's the idea:

I want to build me a small battery powered busking amp for playing amplified blues harp on the street. I have a little pignose that I use now, but I'd like an amp with bit more bottom-end and that can actually clean up a little if I want (the piggy is all dirt, all the time). I've built a couple of lm386 chip amps, and I'm not really enamored with them either.
So, what I've got now to work with is a Hitachi HA 13001 single supply chip amp that I've built from a kit. It was way too noisy when powered from a wall supply (even with a well-filtered PS), but  I think it have WAY less hum on battery power, which should be doable since it requires only +8 to +18 V at ~1amp. The pignose is powered with 6 rechargeable AA's (9volts) and lasts quite a while. The current draw is nowhere near as high as 1 amp though (I think it's ~300mA), so I don't know if this battery configuration will work well for the Hitachi chip, or not. I can get a 4-5 AH 12 volt sealed lead acid battery for about $15 at Fry's Electronics. I'm assuming that if the amplifier circuit is pulling 1 Amp (on average) that means that a 4-5 AH lead acid battery will give me 4-5 hours of continuous play time. Is that a safe assumption? Following this logic, if I'm using 2100 mAH double A's in series, I would only get ~2 hours if the circuit is drawing 1 amp? Does that make sense?
   Oh, I'll be using a modified ROG peppermill for a preamp, which let's me dial in clean or go to some pretty nice overdrive if I want.

Pros and cons of battery type:

 To go the AA route, I would not have to buy anything (I have battery holders already and an external charger too), but I'm not sure how quickly the batteries would drain. For the 12volt I'd be spending ~25 bucks for the battery and charger, but it *should* give longer play time. If I go with the AA's I'm cool for the preamp supply too (9volts), but I'd have to use a regulator if I went with the 12volt. I know that the 12 volt will get me louder output (data sheet says it'll put somewhere in the realm of 15 watts into 4 ohms at 12volts/1.5-2 amps, so i'll prob get 10watts), but I'm cool with lower output (it'll prob be more like 5-6 watts running on 9v using a bunch of in series 2100 mAH AA batts) if it's easier/cheaper for me to build. It will still be PLENTY loud enough. I'll run this amp through 2 vintage 8" speakers as well (in parallel for 4 ohm load), so that should help get more of the low end out (the piggy I use now only has one 6" speaker).

Future:

What about other battery-powered amp designs (beyond lm386)? Anyone experiment with 12volt single supply chips meant for car audio? These could be very cool if paired with 12 volt "space charged" tube preamps... Thoughts?
« Last Edit: October 19, 2009, 03:42:58 PM by darwindeathcat »
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iTzALLgoOD

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Re: Battery-powered "Busking" amp.
« Reply #1 on: October 19, 2009, 03:01:34 PM »
You can check out the TDA2003. Its a 10 watt chip. My little brother has a little generic practice amp that uses it.  I had to replace the input jack and checked it out while I was in there.  It runs on 12 volts and has provisions for "C" batteries IIRC.

Brymus

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Re: Battery-powered "Busking" amp.
« Reply #2 on: October 19, 2009, 07:38:56 PM »
http://www.ssguitar.com/index.php?topic=1212.0
Uses car amp chip,runs on 12-18V and yeah AA batteries about 2 hrs full volume.
The TDA20** series have more info available as far as projects go.
So I have done what your asking and it works great,IDK about the battery from Frys
but that sounds about right,and I could use two of em 8)

darwindeathcat

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Re: Battery-powered "Busking" amp.
« Reply #3 on: October 20, 2009, 03:46:04 PM »
Thanks for the confirmation Brymus. That is exactly what I was hoping/expecting. I think that, since I have all the parts and won't have to front any more money, I'm going to start out with the AA route. I have enough rechargeable AA's for two rounds of 6 batts, which would give me about 4 hours of street time (plenty for now). If the amp is working out well and I like the sound, then I may invest the ~25 bucks for the 12volt LA battery upgrade to take the hassle out of the multiple recharges that the AA battery scheme will need. I'll post some pics when I get it together. I'm thinking of using a little hard-sided vintage suitcase for the chassis. It'll have a nice handle and stuff, and IMO will be perfect for this kind of portable amp...

Cheers,

DDC
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armstrom

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Re: Battery-powered "Busking" amp.
« Reply #4 on: October 21, 2009, 08:39:22 AM »
For maximum efficiency (battery life) you should look into a "class D" amp. The tripath kits from www.41hz.com are quite good. If you've never soldered SMT components before you should go for one of the through-hole kits. The AMP6-Basic is pretty good and gives 2x25W from a single 12V supply.
-Matt

Slimbo

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Re: Battery-powered "Busking" amp.
« Reply #5 on: October 21, 2009, 06:48:55 PM »
I'm looking at doing the same thing with the 41Hz amp ( http://www.41hz.com/shop/item.asp?catid=42&itemid=43 ) and this little gem:

http://www.spinsemi.com/products.html

http://www.oct-distribution.com/

for a bit on onboard reverb. If anyone has advice I'd appreciate it.

darwindeathcat

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Re: Battery-powered "Busking" amp.
« Reply #6 on: October 22, 2009, 04:29:44 PM »
Slimbo, i haven't heard of that chip, but it seems like it would make a great multi-fx pedal! Have you posted it over on the DIY stompbox forum? If not, I might do that for you...

Also, thanks Slimbo and Armstrom for the suggestion to check out the 41hz modules. I've always been curious about those kits, and I'm glad to hear that they are good and long on battery life. They are definite future options for me if the chipamp I have now doesn't work out well for battery operation...
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darwindeathcat

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Re: Battery-powered "Busking" amp.
« Reply #7 on: October 22, 2009, 04:31:56 PM »
Aha! There is already a kit available for that reverb chip. It's from tonepad: http://tonepad.com/project.asp?id=68

Also it seems that second link is to a prebuilt module. That seems by far the easiest route. Looking at the PDF datasheet for the module, it seems like you just connect up power, input, and output, and you are good to go. I'm not sure if there are pots and switches on board, but you'll probably want to wire your own panel mount ones in anyway... Looks like you can use an 8 position single pole rotary switch to select the effect type, and then you need three pots to adjust the effect parameters. Through on a DPDT (or 3PDT) true bypass stomp switch,and your in business! Seems pretty easy, and at $27.50, it's a damn cheap way of getting a sweet multi-fx modulation pedal...
« Last Edit: October 22, 2009, 04:44:19 PM by darwindeathcat »
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darwindeathcat

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Re: Battery-powered "Busking" amp.
« Reply #8 on: October 22, 2009, 04:50:44 PM »
Scratch all that. I was looking at the wrong datasheets. It seems that module has some terminal posts at one end of the board. The first PDF on the page shows how to connect them up. Three pots, and three spst switches, and an LED gives you full functionality. Takes 5-9 vdc (perfect for battery op). Just connect input and output, and a bypass switch if you want, and go. It may have a buffered throughput, but I can't determine that for sure from the datasheet.
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Slimbo

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Re: Battery-powered "Busking" amp.
« Reply #9 on: October 22, 2009, 08:16:23 PM »
Im pretty keen to have a go at it, but want to get some advice before I start, my DIY projects seem to end up tripling the original estimated budget.

The pre made effects board seem to have the eeprom with pre loaded effects, not the factory ones which is a bonus, one of the factory ones is labeled as "test". The advantage of having two channels on the amp means it may be possible to have some kind of mixer and mix a clean signal with an effects one (I think the correct term for this may be wet and dry signals? Or am I thinking of sandpaper?).

I wonder if there would still be a need for a pre amp, or a simple 3 band eq, or a little distortion, or seperate impedance inputs for mike for the harp, and guitar. Also for efficiant speakers, the Fitzmaurice jack 10 might be worth looking at.
http://www.billfitzmaurice.com/Jack.html

Feel free to post at other forums, the more info the better.
« Last Edit: October 22, 2009, 08:19:15 PM by Slimbo »

darwindeathcat

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Re: Battery-powered "Busking" amp.
« Reply #10 on: October 24, 2009, 09:27:30 PM »
I think you are probably going to need a preamp. Looking at the specs of the chip, it doesn't seem that is has any gain, but also doesn't seem like it sucks volume. If it has any internal amplification, it's to mach the level of output signal with that of the input. That way, the chip works fine as a pedal or an onboard effects processor. If i were to use this as an on board effect, I'd probably stick it between the preamp and the poweramp. This would give optimum placement in the signal chain for these kind of modulation effects.

The guitar-oriented patch set does not need a miking circuit afterwards becasue both channels are "wet". It seems that you get two effects at a time in this set. eg. the right channel will be reverb, and the left will be echo, tremelo, flanger, etc. Turning down the left channel will let you get just reverb, and vice versa. In this way you get a TON more effects, but you never get any dry throughput. You'd have to install a  true bypass switching arrangement if you wanted to get that (not to hard, but it means you have to get at least a DPDT switch. Toggle for an onboard effect, or a more expensive stomp switch for a pedal) In the factory patch set, one channel is "dry" throughput, and the other is the wet signal. You only get one effect at a time with that patch, but you can always have some dry signal.

On board arrangement would be mcuh cheaper to pull off than the stompbox version because using toggle switches to trigger all the different fx combos and for the bypass will be MUCH cheaper than all the stomp switches you'd have to buy for a stompbox. And you won't have to bother with a separate enclosure and all the extra jacks and stuff. This board just screams to me to be put in an amp as an onboard unit. It would make a cool amp bitchin'!  You could also even retrofit it to an existing amp too. How cool would that be?
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Slimbo

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Re: Battery-powered "Busking" amp.
« Reply #11 on: October 26, 2009, 07:16:45 PM »
I don't know if the chip is stereo out, do you mean it applies effects to separate channels then mixes them internally for a mono output?

Re the mike input, I meant there will be different impedance between a guitar and a mike, or is it fairly simple to built a High Z / Low Z switch on the amps input? Maybe it would it be better to have a low Z XLR socket for mikes and separate High Z for the guitar input.

I don't know if I read it wrong but I thought if you have the echo and the reverb level at zero on the pots, you will have a clean signal. But I think you still need to be able to switch between options.

On this link there is schematics for a guitar pedal, http://www.oct-distribution.com/datasheets/SKRM-C8-G01.pdf , they have used a multi op amp chip, there is bypass and what must be volume as well. Also an IC connected to the 8 position switch, I think that IC connects to the EEPROM and not the 3 switches on the main effects chip as the main chip cannot be programmed. So we need another PCB.

I can follow most of the schematic, but what is the opamp with pins 12, 13 and 14 for? Is it just connected up in this way because it is unused?

I have no experience with harp through amps, how essential will eq'ing be? Is it common to cut the highs out for example? And does anyone use distortion?

Edit: http://www.runoffgroove.com/tonemender.html
This site rocks. Hows this for some EQ?

« Last Edit: October 26, 2009, 09:20:35 PM by Slimbo »

darwindeathcat

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Re: Battery-powered "Busking" amp.
« Reply #12 on: October 31, 2009, 02:27:22 PM »
The way I understood it is that the chip IS stereo, but the guitar fx patch set uses both channels for effects (left for reverb, right for other effects), thereby basically creating a "mono" fx box. Here's a quote:

"This is a mono‐in/mono‐out program set perfect for stomp boxes and guitar amp applications.
The output of this set is designed to be used directly and NOT mixed back in with the dry signal."

But if you use the factory patchset, it only uses the left channel for various reverb/delay, leaving the right as throughput dry signal, which you would then have to mix back to the left channel for a mono output.

Yes, it's easy to create a high and lo z input. Look at the fetzer valve article at runoffgroove to see how to do this. You'll need 1/4" jacks that have normally closed switches attached.

In that schemo, it looks like they use the opamp to buffer the input and output. I'm not good at interpreting opamp schematics because I don't ever really use them, so I can't tell if they are getting any gain from it. If the module is supposed to be used as an fx pedal, I would assume they've designed it to have no gain (unity).

Eqing is the heart of designing effects that sound good for harp. You need to cut freq's below 100hz and above 1600hz. Give a bump around 200-400 hz. Usually, you'll need to use higher-than-normal coupling caps (likek 0.1-0.047 uf instead of the standard 0.022 uf) to let more bass through. But  you have to change the freq dist at each stage in an overdrive to achieve the best sound. For example, you may need to make the signal overly bright into one gain stage, or else it'll sound muddy. Then, in the next stage, you might have to really cut the treble or else it'll sound tinny... anyway, IMO, proper EQuing through the whole circuit is the main reason an overdrive will sound good for harp...
« Last Edit: November 17, 2009, 10:01:05 PM by darwindeathcat »
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Slimbo

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Re: Battery-powered "Busking" amp.
« Reply #13 on: November 15, 2009, 06:46:22 PM »
This looks like a cheap way to get into one of those chip amps:

http://shop.ebay.co.uk/?_from=R40&_trksid=m38&_nkw=Lepai+TA2020+

There are people modding them if you search. I'll have to try to find a circuit diagram.

Brymus

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Re: Battery-powered "Busking" amp.
« Reply #14 on: November 15, 2009, 07:01:37 PM »
I think you meant Hz and Khz not Mhz as that would be way beyond the range of any instrument I know of.
The usual HiFi range is 20hz - 20 khz
Just clarifing for others who may not know the difference,