ISO "Simplest" possible amplifier - Page 2

moray james · 22nd February 2009, 12:55 AM

http://www.diyaudio.com/forums/show...&threadid=42259

http://www.dddac.de/op06.htm

amz-fx · 22nd February 2009, 11:17 PM

Dano,

I built a small amp similar to this one and it worked just fine on 9v to 12v, but not terribly loud.

I would suggest that R1 be changed 100k or even 1M. Also the C1 input capacitor needs to be turned around so the plus side is to the mosfet.

When used with 9v, mine did not get hot enough that a heat sink was even necessary, though I did not drive it hard for long periods.

regards, Jack

http://www.muzique.com/

Fuling · 22nd February 2009, 11:23 PM

I´ve built a couple of amps quite similar to the one in post 3 and with the right speakers this topology has some nice features.
(fullrange drivers sometimes sounds better mated with high Zout amps).

Driving the Mosfets input capacitance requires and active preamp though.

djk · 23rd February 2009, 02:29 PM

"Any ideas on what I've done wrong?"

You don't have a schematic that's useable.

130mA?

If R2 was an active current source, then 130mA of bias would be 0.092 mA into an 8 ohm speaker. (I^2)R=0.067W

67milliwatts.

Throw away this schematic.

Read this:

http://www.passdiy.com/pdf/zenamp.pdf

Circuit board here:

http://www.audioxpress.com/bksprods/...ts/pcbp-11.htm

dano12 · 23rd February 2009, 03:21 PM

Thanks guys for all the advice.

Turned out that I hadn't properly grounded the source of the FET (doh!). After doing that it fires up fine.

I'm running it at 18 volts, the FET barely gets warm but the 50 ohm resistor get's very hot. I'll take the recommendation and remount it on a heat sink.

Jack, thanks for the ideas. I actually used your excellent MOSFET boost as a preamp.

I'll reverse the cap and do some more tinkering tonight.

woody · 23rd February 2009, 03:38 PM

If you are running it at 18v you could replace that 50 ohm
resistor with a 12v turn signal light bulb.

What are you using as a input source? If your input source
is a something like a cd or sound card you might get better
results with these componints using them in a source follower.

dano12 · 23rd February 2009, 11:28 PM

As far as I'm concerned, mission accomplished with this one. I fashioned a hillbilly heatsink for the power resistor, stuck a single transistor pre-amp in front of it, stuck it in a computer CDROM cage and called it a day.

It makes a nice little guitar amp, drives an 8 ohm cab very well.

I think now I'll move on to some of the better suggestions posted here.

Thanks again for the pointers!

djk · 24th February 2009, 12:18 AM

If you replace the resistor with an LM317 regulator it will double the efficiency of the amplifier, and double the output power, and the regulator will probably cost less than the resistor.

mosfets · 24th February 2009, 12:19 AM

Quote:

Originally posted by dano12
... I fashioned a hillbilly heatsink for the power resistor, stuck a single transistor pre-amp in front of it, stuck it in a computer CDROM cage and called it a day

That is the coolest piece of crXp I've ever seen on DIY! I want one just like it STAT.

PMA · 24th February 2009, 01:35 PM

http://sound.westhost.com/project83.htm

22nd February 2009, 12:55 AM	#11
moray james diyAudio Member Join Date: Aug 2003 Location: Calgary on the Bow	check these... http://www.diyaudio.com/forums/show...&threadid=42259 http://www.dddac.de/op06.htm __________________ moray james

23rd February 2009, 02:29 PM	#14
djk diyAudio Member Join Date: Feb 2001 Location: USA	"Any ideas on what I've done wrong?" You don't have a schematic that's useable. 130mA? If R2 was an active current source, then 130mA of bias would be 0.092 mA into an 8 ohm speaker. (I^2)R=0.067W 67milliwatts. Throw away this schematic. Read this: http://www.passdiy.com/pdf/zenamp.pdf Circuit board here: http://www.audioxpress.com/bksprods/...ts/pcbp-11.htm __________________ Candidates for the Darwin Award should not read this author.

24th February 2009, 12:18 AM	#18
djk diyAudio Member Join Date: Feb 2001 Location: USA	If you replace the resistor with an LM317 regulator it will double the efficiency of the amplifier, and double the output power, and the regulator will probably cost less than the resistor. __________________ Candidates for the Darwin Award should not read this author.

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22nd February 2009, 11:17 PM	#12
amz-fx diyAudio Member Join Date: Sep 2004 Location: s. Louisiana	Dano, I built a small amp similar to this one and it worked just fine on 9v to 12v, but not terribly loud. I would suggest that R1 be changed 100k or even 1M. Also the C1 input capacitor needs to be turned around so the plus side is to the mosfet. When used with 9v, mine did not get hot enough that a heat sink was even necessary, though I did not drive it hard for long periods. regards, Jack http://www.muzique.com/

22nd February 2009, 11:23 PM	#13
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	I´ve built a couple of amps quite similar to the one in post 3 and with the right speakers this topology has some nice features. (fullrange drivers sometimes sounds better mated with high Zout amps). Driving the Mosfets input capacitance requires and active preamp though.

23rd February 2009, 03:21 PM	#15
dano12 diyAudio Member Join Date: Mar 2006 Location: NoVa	Thanks guys for all the advice. Turned out that I hadn't properly grounded the source of the FET (doh!). After doing that it fires up fine. I'm running it at 18 volts, the FET barely gets warm but the 50 ohm resistor get's very hot. I'll take the recommendation and remount it on a heat sink. Jack, thanks for the ideas. I actually used your excellent MOSFET boost as a preamp. I'll reverse the cap and do some more tinkering tonight.

23rd February 2009, 03:38 PM	#16
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	If you are running it at 18v you could replace that 50 ohm resistor with a 12v turn signal light bulb. What are you using as a input source? If your input source is a something like a cd or sound card you might get better results with these componints using them in a source follower.

23rd February 2009, 11:28 PM	#17
dano12 diyAudio Member Join Date: Mar 2006 Location: NoVa	As far as I'm concerned, mission accomplished with this one. I fashioned a hillbilly heatsink for the power resistor, stuck a single transistor pre-amp in front of it, stuck it in a computer CDROM cage and called it a day. It makes a nice little guitar amp, drives an 8 ohm cab very well. I think now I'll move on to some of the better suggestions posted here. Thanks again for the pointers!

24th February 2009, 01:35 PM	#20
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	http://sound.westhost.com/project83.htm

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