which amp circuit for 2x 50watt 6ohm speakers..12v

[deadastronaut]

i got hold of some technics stereo speakers, i used to own them ages ago and the amp, and it was loud....loud enough to get complaints

on the back of the speaker box it read :

2 way speaker system:
impedance: high 8ohm       low 6ohm 
input high 10w music         low 50w music

the tweeter is a 2inch ,  and the driver is the '6' ohm  4.5- 5'''..


anyway the amp has gone, but rather than waste these i'd like to recycle and build a clean SS  practice amp for them using both 6ohm 5'' speakers. but using a 12v adaptor, the kind that go 3 /4.5 / 6/ 7.5/ 9/ 12....so i can just plug the 12v in it.
without messing around with high voltage stuff..

http://www.ebay.co.uk/itm/LLOYTRON-Universal-Main-AC-DC-Adaptor-3v-4-5v-6v-7-5v-9v-12v-3-PIN-UK-PLUG-BRAND-/110882169846?pt=UK_ConsumerElectronics_PowerAdaptors_SM&hash=item19d117a3f6

any ideas on what circuit i could use , and what comfortable wattage without it distorting i could expect out of 12v? 300ma-600ma adaptor

ive never built an amp, only pedals so it'll be a great little introduction into amps project for me....and my cat.

i have 2 lots of these...btw i like a clean amp and use my pedals for dirt/tone....


any suggestions?...cheers guys.

[Seljer]

The 12V is the limiting factor for your power here.
If you're running the amplifier in a bridged configuration, that means you can swing the voltage across the speaker from +12V to -12V. Clean, you're looking at about (12volts*0.707)^2/6ohms = 12watts or less output power. This would be using something like a TDA1554Q or other car audio IC (car speakers tend to 4ohms or 2ohms so you can get more power while still only running at 12volts).

That and 12volts * 500milliamperes = you can only pull 6watts only from your adapter anyway! You're going to need a bigger power supply.
My advice if you don't want to touch mains wiring is to use a laptop power supply, they're cheap and usually give around 24V at higher currents.


And as far as using dirt, be aware that a typical guitar speaker has a natural high end roll off above 5khz or so. If you use a hifi tweeter that goes up above 10khz your guitar is probably going to sound really harsh when dirty (nice cleans though).

[petey twofinger]

right on to what he said . i found if i use modeling stuff , some of it sounds best with that tweeter in there .

+one on the lap top power supply idea , they put out more ma which is needed for what you are doing . look at resale stores for these .

check this out , 24 volts , 850 ma , the chips are cheap and readily availible , he found his chips in scrap stuff :

http://www.paulinthelab.com/2012/05/tda2030-based-amplifier-veroboard.html

you could also look on ebay , they have all sorts of cheap lil modules that might be perfect .

have fun , good luck , and i would love to see the results .

[Kesh]

TDA2030/TDA2040/TDA2050 are easy and cheap chip amps that work at 12V. Maybe 12 extra components for a single supply amp. But you will need more amps. And a few more volts will help a lot too.

[cab42]

I have built this one http://www.diystompboxes.com/smfforum/index.php?topic=57018.0 by martymart using a tda2050 and a 18 v laptop psu. I used a fetzer valve as preamp.

Very loud and not much noise. Its pretty much by the data sheet. I made a vero layout from the images in the thread.

Unfortunately I did not secure the heatsink to the board and the pins on the ic broke because of the movements, but i recieved a couple of new ones a few days ago and its on the top of my list.

I was planning to use the other tda2050 I bought for another amp, using two laptop power supplies to get +/- 18v.

[Seljer]

As the actual chips are cheap compared to all the periphery, if you want to be really hi-fi about it you could make an active crossover and run a seperate power amp chips for the woofer/tweeter instead of a typical passive corssover.

I was planning to use the other tda2050 I bought for another amp, using two laptop power supplies to get +/- 18v.

Careful with that. Verify that they're floating and not grounded on the AC side.

[cab42]

Careful with that. Verify that they're floating and not grounded on the AC side.

Good advice, thanks

[tca]

I have also a pair of speakers to use... and I was thinking in using a TDA8944J (7W/12V) but the TDA8560Q (6V to 18V) would work to. I like these BTL amplifiers, small part count amplifiers!

Cheers.

[deadastronaut]

thanks for your advice guys, lots of choices chip wise then.



edit :  just looked on ebay at 24v laptop psu's...pretty cheap. will this one be ok?
http://www.ebay.co.uk/itm/Laptop-Notebook-AC-DC-Power-Supply-Adapter-Charger-8-Connectors-12-24V-Adjust-/380469671810?pt=UK_Computing_LaptopAccessories_PowerSupplies&hash=item5895c27782

using a tda2050?...or?

[maartendh]

Probably you are going to spend time and money on some speakers that are not good enough for guitar:  a 6 watt amp might be strong enough to blow the cones out of the speaker frames. If this is not the case, a strong signal from the guitar (e.g. a series of strokes) may cause the cone and therefore the coil to move outside the field of the magnet, making cone movement less controlled by your signal. This will give an odd, and kind of compressed sound.

Old radio speakers (from the 50 or 60-ies will work well, but not the more modern type speakers like these on your pictures, with a rubber ring at the outside of the cone. They are far too sensitive for guitar, except if you use a very small amp (think 0,1 to o,3 watts). At least, this is my experience...

Maarten

[tca]

And don't forget the PUNCH.

[deadastronaut]

^ yep got that...

so i'm restricted to just 1w...

think i'll mess around with the lm308n i have one of those   my roland cube is just 2w and thats ok, so the 308 may be up to the job...

[tca]

so i'm restricted to just 1w...

What about the TDA7056B (12V, 5W under 8Ohm, mono BTL audio amplifier with DC volume control)?

I've tested the TDA7052A which also has a DC volume control, also 1W, and works great. The volume control is not on the signal path! You could inject some varying voltage source in the DC volume control pin and add a tremolo to it (http://www.diystompboxes.com/smfforum/index.php?topic=99407.msg880683). 1W is enough for me, but the TDA7056B with 5W looks like a nice upper bound.

Cheers.

[deadastronaut]

@tiago:  cheers man, i just looked at the datasheet for that

http://pdf1.alldatasheet.com/datasheet-pdf/view/19425/PHILIPS/TDA7056B.html

[tca]

Just to let you know, that I just build a 2x22W TDA1552Q (12V) it works lovely: www.nxp.com/documents/data_sheet/TDA1552Q_CNV.pdf
Just followed the app  circuit and added a dual 10k pot at the input for volume control and it works great with my PC and mp3 player.

Happy builds, cheers.