My next little project

jerluwoo · 7th December 2008, 08:38 PM

Just wanted to share the plans for my next little amp project. It's a small 8 watt class A amp. Waiting for the parts from mouser to get started. The sims for this circuit are excellent. It should turn out to be a very nice sounding little amp.

jerluwoo · 7th December 2008, 08:39 PM

The fourier sim from Multisim 10. 8 watts output.

stinius · 7th December 2008, 08:56 PM

It seems like a good little amp, I haven't done any calculations, but it is a well known topology.

Maby you have just forgotten to draw a C from the collector of Q5 to the base of Q4.

Stinius

jerluwoo · 8th December 2008, 12:36 AM

I didn't forget it, I just prefer not to use a cdom there if possible. Have successfully done so on other amps which made a large difference in the clarity of the treble. More air up there if ya know what I mean.

lineup · 8th December 2008, 01:12 AM

good amplifier, jerluwoo

the 2SC1815 and 2SA1015 small signal transistors are very good ones
they are still possible to find and buy

the supply of this verision is low (+-15VDC), so I imagine a Class A output?
input has got ~3mA in each
and a good current mirror (Geln Kleinschmidt will be happy

)
second stage works ~5 mA

the output arrangement is a typical Jerluwoo design
Quasi complementary N-Channel
simple but working!

the input rolloff freq is <= 150.000 Hertz

R28, 100ohm, connects the input to 0V

jerluwoo · 8th December 2008, 05:39 AM

Thanks Lineup. I thought you might reconize this output stage. Of course it runs class A at 1.25 amps idle current, a little extra than needed to keep the output transistors in their linear hfe curves. I've yet to find another that is as simple and stable that sounds better. The current mirror of course was modeled after the discussion between Glen and others about the the same subject. With simulated distortion of .001% , I would expect somewhere around .05% or better real world with good beta matching of the input stage.

lineup · 8th December 2008, 06:08 PM

I stay in touch to read your reports.
Who knows. When you post your images, quite a few may want to build
a nice Class that takes 'only' 30-50 Watt idle power per channel.
And outputs like 10 Watt RMS pure class A with good quality.

Regards

8th December 2008, 01:12 AM	#5
lineup diyAudio Member Join Date: Dec 2005 Location: the north	good amplifier, jerluwoo the 2SC1815 and 2SA1015 small signal transistors are very good ones they are still possible to find and buy the supply of this verision is low (+-15VDC), so I imagine a Class A output? input has got ~3mA in each and a good current mirror (Geln Kleinschmidt will be happy ) second stage works ~5 mA the output arrangement is a typical Jerluwoo design Quasi complementary N-Channel simple but working! the input rolloff freq is <= 150.000 Hertz R28, 100ohm, connects the input to 0V __________________ lineup

8th December 2008, 06:08 PM	#7
lineup diyAudio Member Join Date: Dec 2005 Location: the north	I stay in touch to read your reports. Who knows. When you post your images, quite a few may want to build a nice Class that takes 'only' 30-50 Watt idle power per channel. And outputs like 10 Watt RMS pure class A with good quality. Regards __________________ lineup

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7th December 2008, 08:56 PM	#3
stinius diyAudio Member Join Date: Oct 2008	It seems like a good little amp, I haven't done any calculations, but it is a well known topology. Maby you have just forgotten to draw a C from the collector of Q5 to the base of Q4. Stinius

8th December 2008, 12:36 AM	#4
jerluwoo diyAudio Member Join Date: Feb 2006 Location: Ashland,Ky U.S	I didn't forget it, I just prefer not to use a cdom there if possible. Have successfully done so on other amps which made a large difference in the clarity of the treble. More air up there if ya know what I mean.

8th December 2008, 05:39 AM	#6
jerluwoo diyAudio Member Join Date: Feb 2006 Location: Ashland,Ky U.S	Thanks Lineup. I thought you might reconize this output stage. Of course it runs class A at 1.25 amps idle current, a little extra than needed to keep the output transistors in their linear hfe curves. I've yet to find another that is as simple and stable that sounds better. The current mirror of course was modeled after the discussion between Glen and others about the the same subject. With simulated distortion of .001% , I would expect somewhere around .05% or better real world with good beta matching of the input stage.

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