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Loud Community designed 9v battery powered amplifier.

Started by No6h, June 18, 2015, 02:46:19 AM

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No6h

Hi I would like to design a portable but loud 9v amp. I would like to make it 1x10. I have never designed a complicated circuit in my life so this would be a great achievement. Thanks in advance.i also want a effects loop.

J M Fahey

Well, 9V powered amps have HUGE problems to put out more than 1W or so, *maybe* 2W are achievable, and then you have the problem of it eating batteries by the dozen.

Any reason for you needing a 9V one?

If you need portable power, feeding it from a 12V7AH gel cell battery may give you up to 30W RMS; if no portable needs, and mains power (110/220V) is available, the Sky is the limit.

That's the main problem; effects loops and other stuff is minor in comparison.

Joe

As Mr. Fahey indicated, a 9v battery wouldn't really cut it. However, old boom-boxes could run for awhile on eight D-cells. And there are rechargeable batteries with pretty high capacities now. So it's not a bad idea, especially for people wanting to build some sort of amp without getting into the dangers of line-powered equipment.

No6h

I wouldn't mind working with DC power supplies, if that would work

Joe

Sure, that would work. Search for 12v audio amplifier schematics and you'll find a lot of different things.


blackcorvo

If you want high capacity and portability, I'd go with some 3.7v "tactical flashlight" batteries.  3 of those in series give you 11.1v, and if you get the 5600mAH models, I'm guessing they'll last you over 10hrs of play time with any chip power amp up to like 5w.

No6h

I was going to start with a basic 12v 12ax7 preamp and a SS power amp. (TL072 of LM386N4). Sort of similar to a Tube Cricket, but with a higher output and a improved tone stack.

J M Fahey

If you use an LM386 you are definitely inside the Cricket power class, i.e. <1W

No6h

http://www.canakit.com/20w-bridged-audio-amplifier-kit-CK193-UK193.html?gclid=CM_jme-qycUCFZSCaQod-QwANg I noticed this on another forum, any good? I dont mind having 2 volume controls, my 30w Marshall does. Is it compatible with the 12ax7 Preamp and also it it safe to connect two wires per terminal to the DC jack? or would i need a +12v and Ground bus (a strip of copper wire)?

phatt

False economy to build low wattage bridged amps,, :loco
You can get an LM1875 chip to do the similar power and likely cost less money.

As example; http://chipamp.com/product/non-inverting-lm1875-stereo-kit/
That is stereo so two 20 watt amps for under $50 with recto and filter caps.

I just googled lm1875 Kits and found complete lm1875 boards for under $10.

In this game you eventually learn to read the fine print and forget the fancy words like; 500 watts pmpo,, Dual recto,, military grade,, gold plated,, hi gain,, extended range. :duh

And of course the one you just mentioned, bridged mode.

Bridged mode might look clever but introduces other issues which will likely go unnoticed by the novice. Issues such as you can no longer run 4 ohm speakers in bridged mode and both terminals are Hot, no ground or common.
Bridged mode is for high wattage PA rigs where the user usually knows what and how to impliment the idea to advantage.

For a small 10~20 Watt guitar amp,,, silly. 8|

~70% of the cost of any amplifier is the Chassis, Transformer and rectification, then speakers and cab. The actual pcb and parts are often the cheapest components.

There are other chip amps besides the one I mention that will do similar or better.

If you want the cheapest deal with least amount of fuss then the lm383 (Car audio chip) might be a good project as it's specifically designed for a single 12 volt supply so you can run it from a wall wart/plug pak. saves on the cost of a psu setup.
Some computer power packs in the 12 ~20 Volt range often have plenty of current ability which maybe a cheap and easy way to go.
With the right power supply the chip will output around 5~7 watts good for a small amp build.

As for the triode preamp,, nah,  Again hardly worth the fuss with such a small amplifier, start with simple stuff. 8|
Phil.

No6h

Im currently building a small 386 amp, and just want to move up in quality of output and volume, really.

J M Fahey

That 12V tube amp will be happy to deliver > 0.1W`(not a typo, 1/10th of a watt)  .... if that much.

Seriously, if you have 12V available, the very best amps are those designed for car radios and such, the designer had a car battery in his mind when he started drawing the first lines on a blank paper.

LateDev

Anode current is around 75mA for a 12AL8 from my tattered reference book. :)

J M Fahey

Does it claim any output power?
Are single ended 1k to 4/8 ohms transformers available?
Price if so?

I bet a $2 LM383/TDA2003 suddenly becomes interesting  ;)

LateDev

#14
Output power is determined by the characteristic curves, which I don't have access to. However it also depends a lot on the transformer used.

As far as the transformers are concerned, if you got to Hammond or Sowter, or indeed any company that produces quality transformers for audio, they will be able to supply whatever you want.

I did wonder about the validity of the current figure shown, so did a search which may help. The book is tattered and sello-taped together.

http://www.diyaudio.com/forums/tubes-valves/255577-12al8-head-amp-utc-output-transformer.html

The circuit shown claims 40mW into the 800 ohm Load.

Data Sheet http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCUQFjAA&url=http%3A%2F%2Ffrank.pocnet.net%2Fsheets%2F127%2F1%2F12AL8.pdf&ei=Nl2RVcK3HMHC7gaRjLrwBg&usg=AFQjCNHaXi67E9EqKxXg4n2-cG8semS7Ow&bvm=bv.96783405,d.ZGU