gofast wrote:
meantime, i was able to get a 12v battery. no noise whatsoever with the battery. now the problem is that at moderately high volume level (that's little higher than where i would comfortably listen), there's a low-mid to bass distortion. what could be causing this? my cap values are: C1=2.7uf, C2=100uf, and C3=200uf. with 100k audio pot to control volume (i know this project calls for 10k, but 100k was all i had).
Not my strong point, but someone will respond; I built mine exactly as spec'ed in the schematic. Sounded TERRIBLY with earbuds (extreme highs), but very, very GOOD with a couple of 'regular' phones - a mid-level Sony and a Sennheiser PX-200 - I don't have any high-dollar phones.
I found the closer the supply voltage was to 12.6 or so, the better. Also (in case it hasn't come up) : the voltage for the 'bias' - is NOT taken at the valve plate (as it is usually interpreted), but at PIN 3 of the LM317 (or the Source pin of the IRF510 - it's same point, electrically). This confused me initially, as I was taking it at the Valve plate, as I think a few others have done.
gofast wrote:
should i try increasing or decreasing the input cap? increase the C3? or could the 100k pot possibly causing the distortion?
Your C1 is equivalent to the schematic (2.7uf not much diff from 2.2uf - it's within normal tolerances).
You could stand to go up on C3 - I think the larger the C3, the more 'lows' will get out unmolested.
C2 is spot on.
gofast wrote:
sorry to pour all these questions, but how long do these batteries last? and once drained, do you charge it with any 12vdc charger? i just read an article about charging these batteries and it says that you must charge as you use it up-otherwise it won't hold power as much- is this true? if so, do you keep the charger connected? and how long does a full charge take?
Is it a gel battery? Gelled Lead-Acid batteries (the big, brick kind are usually found in Uninterruptable Power Supplies) can be recharged at any time.
NiMH may be charged at any time.
LiIon - can be recharged at any time (be sure to use the proper charger, as I understand it, these can pop).
Really, only the OLD NiCAD's need to be drawn down before recharge.
A good sized Gel battery would probably last longest, but this draws 400 ma, almost half an amp.
If you have a 4.5 Amp-Hour battery would be rated to last about 8 hours with this... However, when it's voltage reaches maybe 10.5 volts, it's done and should be charged... Your audio might suffer before then as the battery voltage drops... So I'm guessing maybe a couple or 3 hours.
As to whether charger should be connected - sure. You can certainly run it with a charger connected - the battery just acts as a HUUUUGEE capacitor. You might hear some charging noise, or you might not - depends on the type and quality of the charger.
(heh, sorry for the long post... I'm wordy, I guess...)
Mike Y
Dallas, Texas