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Portable music power source

post #1 of 9
Thread Starter 
Hi guys,

my current portable setup runs like

Nomad JB --> TA ---> Beyerdynamic DT 770 (250)

i wanna get a bit more omphh into the system as the TA on 2 AA's loses a bit of the low end etc. i've tried running at 5V and it does sound quite a bit better.

I was thinking of using a 12V SLA to powr the whole lot but not sure how to get the 2 sets of rails i would need.
unless the the TA can take a higher voltage i would be looking at +/- 5V and +/- 12V.

could some one help me with the design of the voltage regulator setup ??

easily avaliable reg's are
7805/LM340T5 - +5V
7905/LM320T5 - -5V
7812/LM340T12 - +12V
7912/LM320T12 - -12V

their all fixed voltage and 1 Amp.

how would i wire this up ? would it create much heat ? ( it needs to go inside a carry bag )

any other ideas

btw i looked at multiple D cells but would rather an SLA.
post #2 of 9

I strongly recommend against your upgrade plan. TA does not have simple power supply like Chu Moy amp. TA has DC-DC convertor. This is another name for high frequency switching step up regulator. This is how HeadRoom is successfully use high performance opamps with very low battery voltages and last very long.

However, this switching process pose pretty stringent requirements. One of them is input voltage from batteries. You cannot simply change the voltage like we, HeadFi-DIYers, do with Chu Moy amp. Upping the battery voltage will stress components uses in the amp. (Tolerence of the component may not be able to handle higher voltage needs due to your "upgrade")

Also, note that due to DC-DC convertor, performance is not dependent on the quality of power you supply to the battery slots assuming any "reasonable person" will supply clean enough power to begin with. The quality of TA is dominantly dependent on the quality of DC-DC convertor. So using LM340 supply would not maky any appreciable difference given that high voltage does not blow DC-DC convertor.

You can do two things possibly. One you can improve DC-DC convertor. This is impossible unless you are highly trained and know what you are doing. Two, you can bypass DC-DC convertor. This is actually ultimate upgrade. Batteries offer cleaner power than any DC power supply unit theoretically. You will have to know what you are doing but this is hell a lot more easier than the former alternative.

Dring DT770 from TA is rather ... not optimal solution. TA cannot offer high voltage swing like other HeadRoom amps or amps like SHA-1 (or my new amp!!) This high voltage swing you need for DT770 since it has very high impedance (600 ohms). TA will inevitably fail to offer good voltage swing and one of obvious symptoms would be recession and inaccuracy of bassline.

You should consider units with higher voltage swing capabilities. If portability matters, good choices are high voltage swing version Chu Moy amp and HeadRoom Supreme. I do not know any other commercial portable headphone amp which satisfy such requirement. You see, DT770 (or AKG K240M) was not designed for portable use. You can see this by the fact that DT770 can be driven by any stationally headphone system/preamp etc.

For you, I sorta recommend against going into TA and redesigning the power supply and other things. ... But if you want to you can upgrade TA using the methods I told you earlier. But I can promise you it ain't gonna be a "piece of cake."

post #3 of 9
Thread Starter 
i was actually looking at pretending that my sla was an extenal power source ( eg wall wart ) which i have used to power the TA upto 5V. This does make a differnce to the sound ( for the better ).
Secondly my DT770's are the 250ohm version so they are a bit friendlier to the output of the TA.

I am i the process of building a ChuMoy and i figured it could also use the same powr supply i am looking to build now to power that.
post #4 of 9
It's probably best to just replace the TA with a DIY amp. I don't know if a plain CMoy will beat the TA, even if you don't like crossfeed, but perhaps one of the higher end amps would do the job. Two simple ones to build are a Hansen (if you like crossfeed) or a CHA47 (no crossfeed, still on the Hansen board). These may sound better than a TA, and are a whole lot easier to modify to suit your tastes.
post #5 of 9
Thread Starter 
As i said i am build
Chumoy atm but that is gonna take me a while
I want an portable powersource anyways to extend the battery life of my NJB as its pretty short ( 4hrs )

any help ?
post #6 of 9
Thread Starter 
can anyone help me ???
post #7 of 9
I think no one's answering because no one is comfortable telling you how to modify a commercial product's power system. We can give you all kinds of advice with DIY amps because there are many of us here that have built them, and we know how they're designed and what they can handle. The NJB -- you'd have to tear it apart and nearly reverse-engineer it to be sure you know what futzing with the power supply will do to it in advance.

However --

[insert standard disclaimer here]

-- increasing the number of batteries is probably safe, as long as you just parallel them for longer battery life. But putting them in series is risky, especially with a complicated device like the NJB.
post #8 of 9
Thread Starter 
where the heck did u get that idea ???

i want to get an SLA battery ( sealed lead acid ) and connect a couple of power regs to it. thereby allowing me to connect it like an external power supply to some of my equipment.

It doesn't matter what the equipment is.

I take it from the sheer lack of responces that understand what i am tryoing to do that noone has played with vreg's before.

i guess i will go try and find a book on it.
post #9 of 9
I'm sure a lot of people who frequent here have played with voltage regulators. Most modern voltage regulators are easy to use and hard to break. Just look at the LM117/317 datasheet. Lots of good information in it.
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