Yes, we use 8" speakers because they break up quicker (ie. at lower volume) plus they aren't too bass heavy. I use speakers salvaged from old electronics. So far, the best I've found are 8" speakers from old organs. Great Tone! Some people report that the cheap Jensen MOD series 8" sound good for harp, and others will swear by Webers. I get my vintage speakers for about $5-10 bucks each, versus ~$25 for the cheapest new speakers, but you definitely will have to put the time in and search around to find those old drivers. Read the reviews of various speakers at this blog: http://bluesharpamps.blogspot.com/ He reviews both Jensens and Webers, and is thought to be a reliable source.

And yes, Adam mentions the 8" speakers in that vid.

Here's a link to the announcement and discussion of that sweet octoboard reverb module from diystompboxes. My comments and replies from Frank are at the end:

http://www.diystompboxes.com/smfforum/index.php?topic=79388.0

Thanks for that link! It's a lot of reading, but I will definitely skim through that... Yes, the way to go is to split the input signal, and send it to both channels. Best is to have some small series resistance on each channel input after the split (1kohm on each leg of the split will do). Then send the output of each channel to it's own speaker. If it's truly 2x20watts, then doing it this way, the amp will be putting a full 20 watts through each speaker, making about as loud as a 40 watt amp. The amp will be loud, anyway.

Yes your sm58 will sound AWESOME for harp. It's own of the go-to dynamic mics that pros use (that and the sm57). It won't sound like a bullet mic (they use ceramic or crystal elements), but IMO, you are better off with a dynamic mic for a solid state amp anyway. Especially if you are using that Sansamp first. It will let you get any kind of sound you want. Should be a killer harp rig!

I do not know too much about the battery stuff. That's why I started this thread, actually... I'm pretty sure that class T amps draw MUCH less power than other chip amps of comparble wattage, so you might get quite a few hours out of it. Remember that you are not going to be blasting at full volume all the time, so you should be able to get a bit more time than the math tells you when calculating with peak values. Using RMS power consumption values should get you a closer estimate. Given what I've been able to learn about batteries, that one you picked sounds like it will work fine. I'm not sure what kind of power supply circuitry one should use for battery operation. I suppose at minimum, some small series resistance (100 ohms?) and at least one large cap to ground (about 100uf or so) couldn't hurt. Make sure these are rated for reasonably high power. Prob 1 or 2 watts for the resistor, and at least 20 volts on the cap. Someone else can better answer these questions though...

The best cheap 4" speaker you can find relatively easily for an lm386 amp will come from an old tape player. I'm not talking about a boombox, I'm talking about those flatish rectangular ones that your teacher had when you were in grade-school. You know, the kind that only plays tapes, and has no radio or anything. Get an old one. The older the better. You can almost always find them at the Goodwill or at Salvation, usually for less than $5. GREAT little speakers in those older ones. This is what I used for my own noisy cricket, and it sounds really good. Far better than with the drivers that came out of old computer speakers and intercoms that I also tried. I never tried old tv speakers, so they might also be good, but that seems like a bigger hassle unless you happen to have a crappy old tv sitting around.

Yeah Brymus, I meant Hz. I edited it to say Hz now. Sorry...

Slimbo, that Lepai amp module looks interesting, and CHEAP! It says class T, that means it's using a Tripath chip. Someone would have to take the plunge to see if it sounds good though.... On e-bay usa, they are going for around $24 with shipping. (http://shop.ebay.com/i.html?_kw=Lepai%20TA2020&_fcid=1&_localstpos=85282&_sc=1&_sop=15&_sticky=1&_stpos=85282&gbr=1) Not a bad price at all for 20 watt X 2 channels, already assembled.

Here's the specs:

Features:

   * Tripath power IC.
   * Mini size design is good fit for home audio, car,motor bike and other audio device.
   * It has flash rainbow light in the front panel and very colorful at night.
   * Aluminum alloy case makes it looks more beautiful and good to distribute heat.
   * Compact Size: approx. 115mm (D) X 140mm (W) X 42mm (H)

Specifications:

   * P.M.P.O: 2X180W
   * R.M.S: 2X20W
   * Input power:12v 2A DC
   * Input sensitivity: 200mv
   * Input impedance:47k
   * Frequence response: 20Hz-20kHz
   * Speaker impedance :4-8ohm
   * Minimum THD :<0.05%
   * Signal noise to ratio: >100db
   * RCA input : 1 slot (mp3/cd available)

Follow this link to see a gut shot. It has an op-amp based preamp, and build wuality looks pretty good! http://cgi.ebay.com/Lepai-TA2020-Class-T-Amp-Mini-Stereo-Amplifier-Adapter_W0QQitemZ290369860539QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item439b6473bb

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...

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?

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.

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...

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...

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

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?

Beavis Audio Research sells an improved version of this type of perf board, that's optimized for audio circuit prototyping. I haven't used the Beavis board, but I love these radio shack board. WAY easier than normal perf, and easier than stripboard too (no tracks that you need to cut and direct transfer from the breadboard layout means less chance of making mistakes when laying out the final circuit to be soldered).

Rat shack also has a small "IC" board that's great for making DIY chipamps. Again, Beavis Audio has used one of these for his Noisy Cricket LM386 amp. You can get the info at his site...

Thanks, I'll check those tubes out. I'm a total Tube newb, so i'm not sure I have the engineering knowhow to convert a high voltage tube amp circuit to 12volt one (I think that's a pretty tall order). I'm interested in circuits that run within the range of voltages that most common chipamp have already. I'm interested in building this as a hybrid amp. Let the chipamp make it loud,and let the tube preamp color the sound. I'm aware of the valvcaster and derivatives (Valvelitzer, etc.) and definitely am interested in those. I happen to have those 6au6 and 6ba6 pentode tubes already (from an old radio), so it would be cool to use them, especially because i've read that "cranked pentode distortion" is a good sounding thing.... I've got a few schematics, so I at least have a place to start with these tubes, but i was just fishing here for some sage advice to keep me from heading ff in the wrong direction! I suppose it's time to just breadboard it and see!

I should add that I have on hand several 6au6 and 6ba6 tubes. The two circuits I'm aware of that can use these in fairly low voltage are the Jon Anderson "Lonewolf" (and the derivative "werewolf", designed by Adriano "Renegadarian" of the diystompbox forum), which runs at +36 volts(werewolf at +50 volts), and the Doug Hammond "Pentode driver" that runs at +/- 12volts.

  It's likely that I'll give one of these a go (prob the pentode driver first), but would appreciate any other suggestions.