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How exactly can I power my Banzai V2 via one power source? (Eg how to do a rail splitter I guess.)

post #1 of 11
Thread Starter 
So I was hoping to switch from the rather messy battery setups I've been using (my latest being two 4x AAA packs) to a lithium ion through a DC-DC converter (well, I wasn't sure about how well that would work, but I'm told that the amp should be able to filter out any noise from it.) I don't know why, but I had just assumed the batteries were connected in parallel. However, from initial testing it seems it's not quite as simple as even being in series. From quick searching around it seems that I need to do a rail splitter if I want to go to one power source. To be honest though, I'm not exactly sure how to go about doing that.

Is there anything else I should know? Maybe I should do further filtering because of the DC-DC converter? I'll admit, I know which end of the soldering iron to use and maybe a few basics, but things like building filters tend to be beyond me, so I'm not sure what it would take.
post #2 of 11

A lithium cell has 3.7V (mostly), so you'll need two 2x lithium packs. You might get away with two 1x lithiums, if your phones don't need much drive, many don't. Batteries easily deal with large short-term current demands such as drum hits, and hence are unlikely to limit the dynamic range of the amplifier.

 

It's really better not to use a DC-DC converter, because they can be noisy, and batteries are very quiet, by and large. It's also a complication. Better not to present the amp with noise to filter out, than drive a converter from a battery. Rail splitters likewise have their problems.

 

A pair of batteries with a centre tap is, in many ways, the ideal portable solution in terms of sound quality.

 

w

post #3 of 11
Thread Starter 
I'd like to try to make this work. It would require another month to get another of the same type of battery and interface to use for one (Chinese website with free shipping and me with a very very low budget to dedicate to this at this point.) Plus there's the added complexity of trying to fix anything more inside the case as lithium ion batteries worth using are fairly large (well, I'll admit there are smaller ones, but it does me no good if I'm better off with NiMH AAAs.)

Two batteries on their own isn't enough anyway. I'd need two to each power connector to get sufficient voltage I believe. The AD8620 I'm using in it seems to be fairly hungry voltage-wise from my understanding and I'm not sure that two cells would be sufficient on their own, but instead it would probably require four. The headphones don't need much (modified 50 ohm Sennheiser HD555s which are ridiculously efficient besides having such a low impedance,) but the OPAMP does need more than most on its own. Actually, even the JRC chip that normally comes with the Banzai V2 needs a decent amount of voltage (4V according to said search results) and lithium ion would fall under sufficient voltage ranges very quickly indeed (the most I think I've ever seen was 4.35 for my SGS3 and I don't think anything else would ever overcharge a lithium ion battery by so much, so 4.2 is pretty much a normal "full" charge.)

I realize the DC-DC converter is going to be noisy, but is there anything I can do to just filter it before it gets to the amp in the first place perhaps? With it I could easily set it to an ideal voltage and the battery can go down to pretty much an ideally low voltage (it has no protection circuit built in -- the protected ones were too big to fit my case -- but the DC-DC converter I got has a minimum operating voltage that's above the safe minimum charge for the battery so basically I just recharge after it stops working and I'm set.)
Edited by Nazo - 9/12/13 at 7:06pm
post #4 of 11

Do you have any idea what the switching frequency of the DC-DC converter is?

 

The problem is that the converter will already have some filtration built in, adding more is likely to be bulky, heavy or expensive, or all 3.

 

Why don't you try it, listen to it, and see if the SQ is degraded. If not, you've got a solution.

 

w

post #5 of 11
Thread Starter 
Quote:
Originally Posted by wakibaki View Post

Do you have any idea what the switching frequency of the DC-DC converter is?

The problem is that the converter will already have some filtration built in, adding more is likely to be bulky, heavy or expensive, or all 3.
No clue. Here it is if you can tell anything from the page: http://dx.com/p/dc-3-34v-to-dc-4-35v-adjustable-boost-converter-charger-module-149681 As you can see, they don't say very much there. I was going for something cheap (not much of a budget to do this on) and small enough to fit in there well with the other stuff.
Quote:
If not, you've got a solution.
I still don't really know how to do a rail splitter though. With a DC-DC converter I'll have only one power source for its two inputs. So it's not really a solution since it won't work as things stand right now.
post #6 of 11
Quote:
Originally Posted by Nazo View Post
I still don't really know how to do a rail splitter though.

 

Here is an article to get you started.

post #7 of 11
Thread Starter 
Thanks. Between the budget issues and the fact that I'm just not a great electrician, I think I'm going to try just using the simple 2x resistors and 2x capacitors as with other CMoys according to that article. That did indeed look all too familiar and I should be able to pull that off easily enough. Just one question I guess. How should I connect this setup to the inputs of the Banzai V2? I'm guessing that polarity would matter, so I'd rather hook it up right the first time. I've fried an ordinary CMoy including even the chip once before from accidentally reversing polarities, so apparently it doesn't take very long... EDIT: Nevermind. I asked that before I'd had my morning coffee...
Edited by Nazo - 9/15/13 at 9:28pm
post #8 of 11
Thread Starter 
Ok, so this is my second DC-DC converter and as far as I can tell I've fried it too. That's two in a row. Upon searching around to see if somehow or other I've been using them wrong (I have no clue how that could ever be possible, but it was the only explanation I could think of) I found a video on Youtube covering one of these with almost the exact same setup. Same PCB layout and same basic components, just differences in which regulator, size of transistor, and etc were being used. I couldn't help but to notice that the inputs and outputs were on the opposite sides... I believe that these might have been wired backwards somehow. It used so much power so fast that it must have been a direct short and the metal connectors turned red even. (I guess I'm just lucky that they didn't explode.) At this point I'm curious because that's two in a row that basically have done the same thing from two different sources. Is there something I've been doing wrong in how I wired them or somewhere else along the way, or is possible that two different manufacturers have managed to label them wrong? Either way, I guess that particular DC-DC converter is fried and doesn't work anymore even if I switch it around.

Rather than buying a new one, I think I'm going to try something a little different. I just found out that there is an official lithium ion battery size (10440) that's essentially the same as a AAA battery intended for certain specialized applications. Apparently these are not actually that terribly uncommon as I can see them in a lot of places and besides tons of options shipping from China on DealExtreme and etc, I actually found some here in the US on eBay in new, unopened condition. I'll have to get the ones with the protective caps so they won't go below that 2.5V limit I guess, but otherwise they might just work. (At the very worst, their capacity is roughly on par with NiMH 9V batteries, but these should be a lot smaller and easier to deal with.) I was misunderstanding how the Banzai V2 worked (I had mistakenly thought it was using two battery connections in series to get a higher voltage based on the person selling it advertising it as having higher volume or something silly like that and the fact that I've heard of people using 18V or even more for really high impedance headphones) and thought it was like the other CMoys. Now that I better understand that, I realize I don't need quite such a high voltage as I needed before on each individual connector at least. (To my understanding I need 5V for this chip, so if I'm doing a two pack on each connector that means the batteries should shut off before I reach that voltage anyway.) I'm a little concerned about the low capacity, but it's still at least equal to a NiMH 9V but a heck of a lot easier to deal with for me and a decent amount smaller even in a pack (I might even be able to move it to a smaller case.) I guess I'm going to at least give them a try anyway. I guess absolute worst case scenario I can rig up a USB charger using them or something if they don't work out in this. This way I can avoid the mess of a converter and a rail splitter while still going rechargeable and at least fitting in the same case (if not smaller, though I think a mint tin is still too small probably.)

I'm still really curious what happened to that DC-DC converter though... Even if I didn't use it on this it could have potentially been useful.
post #9 of 11
Thread Starter 
Ok, so I've apparently managed to fry my current amp through a bit of carelessness (ironically when trying to connect a backup battery while charging those lithium-ion batteries -- the lithium ion batteries actually worked great, but just didn't last as long as I'd really like.) So now I'm pretty much going to have to go to an amp that only takes one power supply anyway (due to lack of many options since the Banzai V2 isn't even available anymore and funds, I'm getting a used JDS Labs CMoyBB v2.03.) I actually have a few 18650 batteries which have probably at least 2400mAh (they're kind of old and originally were supposed to be a bare minimum of 2550mAh) which I'm thinking would work a lot better than these probably ~300mAh even with the loss of efficiency in using a DC-DC converter. That uber-cheap converter from DX is definitely broken, but I got another from eBay a bit ago that seems to work beautifully for other things, so I'm thinking I may as well put it to use for this idea after all. It's based around the LM2577, which has a switching frequency of 50KHz if that means anything useful (should I add any sort of inductor or something for filtering maybe?) I also have a super-cheap micro-sized charger which I could also put in there with it, thus making it possible to charge without even opening the case.

I'm also wondering -- if I power something else (specifically a Fiio D3) from the same battery in parallel, will that be a problem (as far as noise/etc is concerned)? It seems the D3 can run from a lithium-ion battery directly (no conversion needed) so I'm wondering if it would cause noise or something if I connected it in parallel to the battery before the DC-DC converter. The D3 seems to use very little power, so I think the battery can handle it.
post #10 of 11
Quote:
Originally Posted by Nazo View Post

I'm also wondering -- if I power something else (specifically a Fiio D3) from the same battery in parallel, will that be a problem (as far as noise/etc is concerned)? It seems the D3 can run from a lithium-ion battery directly (no conversion needed) so I'm wondering if it would cause noise or something if I connected it in parallel to the battery before the DC-DC converter. The D3 seems to use very little power, so I think the battery can handle it.

 

I cant be bothered to read this, but I will give the most helpful advice so far. 

 

When you start to use railsplitters, voltage converters, and doing funky things with half of your battery supply ground is not necessarily ground and there is great potential to fry your gear. 

 

Draw a schematic. 

 

I hope you enjoyed my pun. 

post #11 of 11
Thread Starter 
Ok:

I'm actually asking in reference to wakibaki's earlier question as to the switching frequency of the converter.
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