fractionMan
Custom Title
Yeah, I've blown one amp up completely and banged another one into "I'll only work on one channel" land 
The building your own portable soundsystem thread
- Thread starter fractionMan
- Start date
stuff_it
Too skool for cool
fractionMan
Custom Title
Don't 
I didn't buy it!
I didn't buy it!
fractionMan
Custom Title
Also fits neatly on a pannier rack!
junglevip
Marijuana leads to heron
What could possibly go wrong?
Besides, it been a while since I practiced the art of cannibalization and I am sure to have plenty of spares by the endFM: I like the cab man!
junglevip
Marijuana leads to heron
My brother in law made me a pre-amp for my ukulele (great little things) to amplify a piezo pickup that I got for £1.50. It was a bit noisy and needs to be reconfigured because of the high impedance (fuck knows what this means, I am trained as a programer). If/when we get some stable prototypes together ill post that stuff up too (the design and whotnot)
fractionMan
Custom Title
lepai lp-838
cheap (7 or 8 quid) 2.1 chinese amp
Ok, so this thing has varying specs depending on where you look. Lepai themselves have it at 2x15w + 20w sub.
The quick review is that it's louder than the 2020 with more bass. It comes at a price though. It's nowhere near as nice sounding as the tripath based amp. The loudness comes not really from the extra watts, but as far as I can tell, more gain. It's super loud from my HTC desire. In fact it distorts badly at full whack. It's got a separate volume knob for the sub channel, and after fiddling for a while it seems like ti's happiest on about 2/3 power. Any more than that and the bass becomes a mess. The normal channels fair better at 3/4 volume with the phone at about 8/10 power. With these settings it's still louder than the 2020 by a fair margin, has masses more bass but does sound a bit ropey and way less controlled.
It's roughly the same size but looks less blocky.
It also eats more batteries. Not sure how much more as I've not got an ampmeter. It took a sla 7ah battery down from 12.7 to 12.5 in two hours, which my back of an envelope calcs lead me to believe is about twice as much as a 2020. I could be way off here though. It certainly pushes more air due to the sub channel.
Basically if you want to make a decent amount of noise off 12v with mp3 player sources at a well low price and are more concerned with volume than quality (house music is fine for example) it's def worth a look.
cheap (7 or 8 quid) 2.1 chinese amp
Ok, so this thing has varying specs depending on where you look. Lepai themselves have it at 2x15w + 20w sub.
The quick review is that it's louder than the 2020 with more bass. It comes at a price though. It's nowhere near as nice sounding as the tripath based amp. The loudness comes not really from the extra watts, but as far as I can tell, more gain. It's super loud from my HTC desire. In fact it distorts badly at full whack. It's got a separate volume knob for the sub channel, and after fiddling for a while it seems like ti's happiest on about 2/3 power. Any more than that and the bass becomes a mess. The normal channels fair better at 3/4 volume with the phone at about 8/10 power. With these settings it's still louder than the 2020 by a fair margin, has masses more bass but does sound a bit ropey and way less controlled.
It's roughly the same size but looks less blocky.
It also eats more batteries. Not sure how much more as I've not got an ampmeter. It took a sla 7ah battery down from 12.7 to 12.5 in two hours, which my back of an envelope calcs lead me to believe is about twice as much as a 2020. I could be way off here though. It certainly pushes more air due to the sub channel.
Basically if you want to make a decent amount of noise off 12v with mp3 player sources at a well low price and are more concerned with volume than quality (house music is fine for example) it's def worth a look.
fractionMan
Custom Title
I was thinking about building a couple of boxes and looking at the golden ratio (for ascetics) when I stumbled upon this: http://www.soton.ac.uk/~apm3/diyaudio/Irrational.html
Turns out it doesn't only look better, it sounds better!
Turns out it doesn't only look better, it sounds better!
junglevip
Marijuana leads to heron
Not a perfect start! Got the cables made up plugged it all in then turns out I have bought the wrong size power plug it works but it is wobbly. The mono adapter is also less than perfect its got a half in half out thing going on to get it to work.
When it was running in mono the speaker seemed to be as loud as the stereo pair, I am not sure if there is some cancellation going on there
I did get sound out of it and it is ok noticeably louder than the just the acoustic bass on its own, fairly good sounding too. The low E barely registers, that isn't really a surprise though. I should point out that the speakers are not in enclosures and just resting on the sofa.
My masterplan of taking the world by storm with portable bass amps has been put on hold and I am no longer going to bid on this; the total spend is about £40. All the stuff is can be reused in other systems if need be. Next thing to try, stereo input. We roll again
When it was running in mono the speaker seemed to be as loud as the stereo pair, I am not sure if there is some cancellation going on there
I did get sound out of it and it is ok noticeably louder than the just the acoustic bass on its own, fairly good sounding too. The low E barely registers, that isn't really a surprise though. I should point out that the speakers are not in enclosures and just resting on the sofa.
My masterplan of taking the world by storm with portable bass amps has been put on hold and I am no longer going to bid on this; the total spend is about £40. All the stuff is can be reused in other systems if need be. Next thing to try, stereo input. We roll again
fractionMan
Custom Title
The bass will really take off in an enclosure it makes a massive difference. For testing you can use an old biscuit/sweet tin with a 5.5" hole cut in the bottom (that was you can just rest the "top" on the floor and not need to fit the lid back on it). It's not perfect but it does give you a better idea. Mine's celebrations!
You've probably got a 2.1mm power plug. The lepai uses 2.5. Stupid plugs really as I've got a different tripath amp that uses 2.1. There are adapters and I think you can get them in maplins. Have you tried an mp3 player through it?
You've probably got a 2.1mm power plug. The lepai uses 2.5. Stupid plugs really as I've got a different tripath amp that uses 2.1. There are adapters and I think you can get them in maplins. Have you tried an mp3 player through it?
junglevip
Marijuana leads to heron
I just been on the blower to my in law and explained the halving of volume, he suggested that its in impedance mismatch and to get the scope on it tomorrow. I think its because the amp is expecting a stereo in and its getting a mono through a short circuit. So now its another big day out in Maplin to get a stereo jack to jack and we go again.
I didn't have a biscuit tin so I improvised, I put them in a cupboard, I get quite upset when things dont work as planned and then want to cry my engineering in-law assures me that this is normal. Phew!
I didn't have a biscuit tin so I improvised, I put them in a cupboard, I get quite upset when things dont work as planned and then want to cry
my engineering in-law assures me that this is normal. Phew!
junglevip
Marijuana leads to heron
Ten quid blown of fuel running around for bits. Got a stereo cable did not work, took it back. Borrowed a di box did not make much difference, I think that the output was at guitar/bass line impedance.
I think a guitar to headphones type amp is needed in in between. My knowledge has run out and I need to get some more; hopefully the scope and its operator will be over tomorrow so I can start on the next stage.
I think a guitar to headphones type amp is needed in in between. My knowledge has run out and I need to get some more; hopefully the scope and its operator will be over tomorrow so I can start on the next stage.
junglevip
Marijuana leads to heron
Its definitely an impedance mismatch! The trick now is to buy in another amp (£10) that has headphone type impedance to act as a buffer, pushing the total cost to £50. I have looked at building one but, I am going to build a few circuits on a breadboard first. The total cost so far if you include things like petrol is more like £70.
fractionMan
Custom Title
I think you're right about the headphone amp. Let me know how it goes!
fractionMan
Custom Title
p.s. They always go wrong first time
the only thing headphone outputs are meant to feed is headphones.... impedance is only an issue with amps going to speakers speakers, from bass/preamp to power amp there is pretty much 0 impedance I believe, you just need to get the right output level, which a headphone amp isn't a good way of doing. i would have thought the DI box would be best to feed a power amp, what went wrong when you tried this?
fractionMan
Custom Title
The thing about the lepai tripaths is they work fine with headphone level output. What's a DI box?
all amps can take headphone outputs, that's why people can run their ipods through anything... it just might not have the best results.
a DI box changes an unbalanced input like a guitar or bass to a balanced output (which would take some of the danger out of the bass guitar signal), and may boost it to line level... in which case it would act like a preamp too.
a DI box changes an unbalanced input like a guitar or bass to a balanced output (which would take some of the danger out of the bass guitar signal), and may boost it to line level... in which case it would act like a preamp too.
fractionMan
Custom Title
Ah, ok. Cheers
On a vaguely related note, I can confirm that an iphone drives the lepai much louder than a HTC desire.
On a vaguely related note, I can confirm that an iphone drives the lepai much louder than a HTC desire.
ViolentPanda
Hardly getting over it.
Bread-boarding makes sense. I know someone who built a fuzzface replica on breadboard, couldn't be arsed to point-to-point solder all the components, and is still using it 12 years later, with no mishaps. Lazy fucker!
junglevip
Marijuana leads to heron
Tidy! I just borrowed a zoom bass effects pedal so thats the next test. In the meantime the little headphone amp is on its way. If any one has an idea for a case that'd be a great help
fractionMan
Custom Title
I'd be interested to hear how those speakers perform.
junglevip
Marijuana leads to heron
Yeah, no problem with that, Ill do a review of the system then look at tweaking it and what not. Gonna get the speaker plans for my other in-law to make the box's and use a project from that book I was on about; that is for an 8'' speaker, so ill scale that down for a 6.5'' box.
The question then is whether to go for a closed box or an open backed? I have read that you get more of the bass frequencies from an open back but you cant deliver as much power because of speaker damping(apparently). You need tougher speakers for open backed. Even though the speakers are 45w I think they maybe hi fi speakers not instrument speakers so the damping might help to prevent the speakers from packing in.
Views anyone?
The question then is whether to go for a closed box or an open backed? I have read that you get more of the bass frequencies from an open back but you cant deliver as much power because of speaker damping(apparently). You need tougher speakers for open backed. Even though the speakers are 45w I think they maybe hi fi speakers not instrument speakers so the damping might help to prevent the speakers from packing in.
Views anyone?
fractionMan
Custom Title
My experience is that you get much better (deeper, louder) bass from a sealed box than an open backed one. One of my boxes has a simple hinged back and it's easy to tell the difference.
junglevip
Marijuana leads to heron
I am going to go with closed back, just to protect the speaker a bit. Gotta do some maths today, convert the extension speaker plan to and then multiply all the values by 6.5/8. Probably will go with lining with 1'' fiberglass lining as well.
Any ideas for a high/low pass filter to knock out some of the unwanted frequencies?
Any ideas for a high/low pass filter to knock out some of the unwanted frequencies?
fractionMan
Custom Title
I think at the simplest level you need some sort of coil thing. I posted some link a couple of pages back.
junglevip
Marijuana leads to heron
Spot on! I have submitted the plans for the enclosure to my other for construction
As I say Ill post up pics designs and costs and what not, even if its not so great
ViolentPanda
Hardly getting over it.
Spot on! I have submitted the plans for the enclosure to my other for construction
Just a suggestion, going by FM's use of cases: Why not have a fixed rear baffle mounted on hinges and a catch, so that you can have it closed when playing bass, open when playing an mp3 player through it.
I don't know whether you've ever seen a Pignose practice amp, but they used a similar idea (hinged front panel) on some of their models that made quite a difference to the sound of whatever was played through it. I'm not sure that you're going to get great reproduction of the lowest freqs, whatever you end up doing, but at least it could give you a bit more versatility.
