Resistance coupled cascaded amplifier

diamondsouled · 9th September 2009, 12:11 AM

Just wondering how the circuit shown in the pdf would work for a headphone amp.

http://www.mif.pg.gda.pl/homepages/f...37/1/12AL8.pdf

Cheers

Lar

aardvarkash10 · 9th September 2009, 12:24 AM

40mW @ 10% THD?

diamondsouled · 9th September 2009, 01:13 AM

Quote:

Originally Posted by aardvarkash10

40mW @ 10% THD?

That would be at full output so for 20mW the THD should be far lower.

Not sure how many mW it would take to run some head phones.

Also I'm sure the circuit could be tweaked.

Cheers

Lar

aardvarkash10 · 9th September 2009, 01:34 AM

I would CCS load the pentode with a LM device (you are limited to 30v DC by the tube anyway, so a 317 would probably do it) with your headphones para-coupled off the anode.

You'll need a 28-32V DC supply, but the current loading is not very taxing, so a simple voltage trebler off a 12V AC wallwart would probably get you there.

You will also have to seriously reduce the input voltage from any modern device with a 2V-pp line output voltage - a voltage divider at the input would acheive that.

Accept that you will need to be driving a pair of high impedance (600 ohm) phones - 32 ohm ain't gonna cut it here!

If you already have the tubes, your project cost to a breadboard stage is maybe 10 bux - give it a go!

diamondsouled · 9th September 2009, 01:48 AM

Came across a nice quad of Sylvania 12AL8s.

Nice looking tube anywho with long black box plates.

Cheers

Lar

aardvarkash10 · 9th September 2009, 02:09 AM

mu-follower could be interesting... http://www7.taosnet.com/f10/mustage.html

diamondsouled · 9th September 2009, 02:14 AM

Quote:

Originally Posted by aardvarkash10

mu-follower could be interesting... http://www7.taosnet.com/f10/mustage.html

Seeing that the 12AL8 is a triode/tetrode would this work?

Cheers

Lar

aardvarkash10 · 02:26 AM

in fact the article goes into that in some detail - input to the triode, pentode (tetrode) stacked on top, output from the cathode of the pentode. Also check out valvewizard's mu-follower page at http://www.valvewizard.co.uk/

In essence a mu-follower is a CCS loaded triode, but this way its all glass, not glass and sand. Hey, if you have four tubes, you could build both and do a side by side comparison! Cost you twenty dollars now...

diamondsouled · 9th September 2009, 02:25 AM

Quote:

Originally Posted by aardvarkash10

in fact the article goes into that in some detail - input to the triode, pentode (tetrode) stacked on top, output from the cathode of the pentode. Also check out valvewizard's mu-follower page at http://www.valvewizard.co.uk/

Oooo, cool. Will have to print that one off a give it a good read.

Thanks

Lar

aardvarkash10 · 9th September 2009, 02:33 AM

Quote:

Originally Posted by diamondsouled

Oooo, cool. Will have to print that one off a give it a good read.

Thanks

Lar

Yeah - watch out for the seriously funny typo's throughout the article... A little interpretive skill is required, but not much.

9th September 2009, 12:11 AM	#1
diamondsouled diyAudio Member Join Date: Oct 2007	Resistance coupled cascaded amplifier Just wondering how the circuit shown in the pdf would work for a headphone amp. http://www.mif.pg.gda.pl/homepages/f...37/1/12AL8.pdf Cheers Lar

9th September 2009, 12:24 AM	#2
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	hmmmmn - is it worth it? 40mW @ 10% THD? __________________ Yes, conservatism thrives on low intelligence and poor information. But the liberals in politics... continue to back off, yielding to the supremacy of the stupid. It's turkeys all the way down. - George Monbiot, guardian.co.uk, 6 Feb 2012

9th September 2009, 01:34 AM	#4
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	ok, well if you are inclined to try... I would CCS load the pentode with a LM device (you are limited to 30v DC by the tube anyway, so a 317 would probably do it) with your headphones para-coupled off the anode. You'll need a 28-32V DC supply, but the current loading is not very taxing, so a simple voltage trebler off a 12V AC wallwart would probably get you there. You will also have to seriously reduce the input voltage from any modern device with a 2V-pp line output voltage - a voltage divider at the input would acheive that. Accept that you will need to be driving a pair of high impedance (600 ohm) phones - 32 ohm ain't gonna cut it here! If you already have the tubes, your project cost to a breadboard stage is maybe 10 bux - give it a go! __________________ Yes, conservatism thrives on low intelligence and poor information. But the liberals in politics... continue to back off, yielding to the supremacy of the stupid. It's turkeys all the way down. - George Monbiot, guardian.co.uk, 6 Feb 2012

9th September 2009, 02:09 AM	#6
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	alternatively... mu-follower could be interesting... http://www7.taosnet.com/f10/mustage.html __________________ Yes, conservatism thrives on low intelligence and poor information. But the liberals in politics... continue to back off, yielding to the supremacy of the stupid. It's turkeys all the way down. - George Monbiot, guardian.co.uk, 6 Feb 2012

9th September 2009, 02:21 AM	#8
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	yep in fact the article goes into that in some detail - input to the triode, pentode (tetrode) stacked on top, output from the cathode of the pentode. Also check out valvewizard's mu-follower page at http://www.valvewizard.co.uk/ In essence a mu-follower is a CCS loaded triode, but this way its all glass, not glass and sand. Hey, if you have four tubes, you could build both and do a side by side comparison! Cost you twenty dollars now... __________________ Yes, conservatism thrives on low intelligence and poor information. But the liberals in politics... continue to back off, yielding to the supremacy of the stupid. It's turkeys all the way down. - George Monbiot, guardian.co.uk, 6 Feb 2012 Last edited by aardvarkash10; 9th September 2009 at 02:26 AM.

9th September 2009, 01:48 AM	#5
diamondsouled diyAudio Member Join Date: Oct 2007	Came across a nice quad of Sylvania 12AL8s. Nice looking tube anywho with long black box plates. Cheers Lar

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