Just wondering how the circuit shown in the pdf would work for a headphone amp.
http://www.mif.pg.gda.pl/homepages/frank/sheets/137/1/12AL8.pdf
Cheers
Lar
http://www.mif.pg.gda.pl/homepages/frank/sheets/137/1/12AL8.pdf
Cheers
Lar
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
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!
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!
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...
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...
Last edited:
Yeah - watch out for the seriously funny typo's throughout the article... A little interpretive skill is required, but not much.
It depends on the headphones! Most are quoted with a 'XX dB at 1 mW' rating. From there you can work out how much power you need. For each extra 3 dB of sound pressure the power required will double.
Most modern headphones will be subjectively loud with 5 to 10 mW.
The circuit that you referenced seems to have no major advantages, unless you are desperate for a low voltage circuit.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.