Single ended headphone amplifier

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audiodesign

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dsavitsk

dsavitsk

diyAudio Member
Joined 2005
diyaudio.ecp.cc
athos56 said:
So would it be possible to put a resistor between the secondary of the opt so that 32ohm headphones could be used? Or maybe a different transformer??
Click to expand...

The Sowter 8988 and 9351 are both designed just for this. In the US, Electra-Print will make you a custom 5 or 10K:32 OPT for not too much.

As for the original design, I think 9mA/180V is a little low for the D3a. rp is closer to 4K than the 2K it is capable of and it does not look like a super linear spot. Maybe OK for high Z phones, but run it with more current at a lower voltage (~20mA/150V) for low Z.

You can spend all day searching for just the right cathode bypass cap and never find it. It, and the final PS cap, are both right in the signal path and represent the real limiting factor here. For the cathode bypass, I think you are better off with some sort of fixed bias -- LED, battery, etc. It is a huge improvement over a resistor and a cap.

For the PS cap, there are a number of solutions -- I found a gas tube shunt regulator worked well. But, you may never get rid of all the caps, so the existing regulator should be fine, too.

I don't mean to sound too critical -- overall it is a good way to run headphones.
 
athos56

athos56

Member
Joined 2006
dsavitsk said:


The Sowter 8988 and 9351 are both designed just for this. In the US, Electra-Print will make you a custom 5 or 10K:32 OPT for not too much.

As for the original design, I think 9mA/180V is a little low for the D3a. rp is closer to 4K than the 2K it is capable of and it does not look like a super linear spot. Maybe OK for high Z phones, but run it with more current at a lower voltage (~20mA/150V) for low Z.

You can spend all day searching for just the right cathode bypass cap and never find it. It, and the final PS cap, are both right in the signal path and represent the real limiting factor here. For the cathode bypass, I think you are better off with some sort of fixed bias -- LED, battery, etc. It is a huge improvement over a resistor and a cap.

For the PS cap, there are a number of solutions -- I found a gas tube shunt regulator worked well. But, you may never get rid of all the caps, so the existing regulator should be fine, too.

I don't mean to sound too critical -- overall it is a good way to run headphones.
Click to expand...

Thanks for the info, I asked because this SE design looked simpler than the transformerless Aikidio design I was looking at.
 
dsavitsk

dsavitsk

diyAudio Member
Joined 2005
diyaudio.ecp.cc
If you are looking for Grado specific transformer coupled amps, try these from my website:

This one is almost the exact same amp as audiodesign's
http://www.ecp.cc/semha.html

And this is the improvement:
http://www.ecp.cc/SSS.html

These are parafeed designs:
http://www.ecp.cc/less-pressivo-plus-plus.html
http://www.ecp.cc/less-pressivo-plus.html


and this one I posted to Headwize two days ago:
http://headwize.com/ubb/showpage.php?fnum=3&tid=7627

Also, member Kevinkr has a WE417 - 71a design floating around that is worth looking into.
 
C

Cauhtemoc

Member
Joined 2007
audiodesign said:
This could be the schematic.

An Rout about 14ohm is not the top to drive 32ohm but there is no better design using a single tube on single ended design.

The D3A is the unique tube with a very low anodic resistance and enough voltage gain.
Click to expand...

4 Vrms into Grados is unbelievably loud, even 1 Vrms would be enough. If you want a better transformer you would probably have to go for something like an LL1620. Not exactly cheap, but pretty much as good as it gets.
 
athos56

athos56

Member
Joined 2006
Well....

I saw some NOS d3a's so I picked them up. I figured I could use the same supply as in my Tube buffer which put out ~250v. Put a pair of 0B3's bypassed with a .o1uf cap after the last RC for 180v and a nice glow :) (i think the load resistor would have to be 1k?) Should fit nicely into the same size case as my buffer as well. Two questions.

If 4 Vrms is too much is there a simple way to bring it down a bit?

Could I use my buffer for the volume control or should I put a pot in it and run it straight from the source?
 
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