DIY Audio Projects Forum

I'm just making a wild guess or two, but if the (max) voltage and correct polarity were observed, these could have just been bad electrolytic capacitors. Were they very old?

470uf with a 35v rating is certainly within your tolerance (20V power input)

However: the fact that they (the electrolytics themselves...) were WARM makes me think they were reversed...
I've done this exact thing - soldered a 50V electrolytic into an old Heathkit morse keyer... After about 20 minutes - POP. It just happens, no matter how hard you're paying attention...heh.

You certainly can do it this way (but making *darn sure* the electrolytics are + to + and - to -...), but the NP-100V12 only draws about 400 milli-amps, so I'd really recommend an LM317M. It can regulate in excess of 500 ma, your output voltage is more controllable (and is less reliant on the input voltage), there is thermal overload protection (it'll shutdown if it gets too hot), short-circuit limiting, and the hum / ripple / noise drop on power input will be upwards of 65db.

(PDF Datasheet: http://focus.ti.com/lit/ds/symlink/lm317m.pdf)
(LM317 Calculator: http://diyaudioprojects.com/Technical/V ... Regulator/)

You'll still need some sort of heat-sink on the LM317...

Mike Yancey
Dallas, Texas

they were brand new from radio shack. 4700uf 35v 85 degree.

i made sure all the polarity is exactly as in the above diagram i made. unless what i drew up there is wrong, i put them in exactly order.

is this the PS circuit link shown on the first post of this thread? the "Millet Max regulator circuit"?

Yes.
Be advised that the one I copied from the Millet Max uses too much resistance on the ADJ pin.
They're using about 27 VDC; I believe the correct ADJ resistance is 1260 ohm (approx) for 13 VDC, so a 2K Trimpot is ideal.

Mike Y

thanks for the help!

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).

should i try increasing or decreasing the input cap? increase the C3? or could the 100k pot possibly causing the distortion?

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?

thanks again for any input.

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.

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.

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

Try an electrolytic capacitor, ex. 2200 ~ 4700 uF paralleled to the battery.

thank you - both mike and kramme for your replies and help!

i'm using a several different headphones such as AKG and Sennheiser.
it's good to be able to use the low impedance K-701 with this amp.

good thing is that it seems like i've eliminated most problems other than the distortion at higher volume level. i will try what you guys have suggested and report back.

thank you once again!

interesting gofast, i look forward to see your report.

i've tried a 220uf electrolytic parallel to the battery, and seems like the improvement, if there's any, is very subtle. i didn't have extra 4700uf or other larger values to try...so i'll try this again later, but will it make much difference?

could it be the 100k pot that's causing this?

anyways, here's picture of my build. sorry about blurry cellphone picture.

The build of yours, looks great ...congrats.
I like the knob. Is it only allowed, to listen christian related music ?

100 k pot is okay ( not a problem ).

220 uF is rather small. Try to imagine you're thirsty, then you wouldn't choose a small cup, but instead a larger cup. I guess it's the best way i can illustrate it, to make you understand. ( Cola bottle = battery, cups = caps ).