Smallest Class A Preamp/Headphone Amp Design?

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m0b1liz3

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Joined 2008
Yep I already know about that one but I don't think it is Class A and probably not well suited for preamp duty but looks like a cool cheap project.

I was thinking about the Morgan Jones modified HP amp but don't know if they are simple enough for me to make as a beginner. I have no idea what they sound like either. If someone has a BOM and build diary that would be cool.
 
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GlidingDutchman

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Joined 2007

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Bandersnatch

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Joined 2003
hey-Hey!!!,
I have built a linestage amp that can serve as a headphone amp. It runs a LTP of 6C45 and a 20k:600/150 output tx. The OPT will deliver a Watt, and the load line shows the tubes capable of roughly 60% more than that. B+ is ~170V. The PS isn't all that small, and neither is its heater supply. Build with a switcher supply and it can be *VERY* small...:)
cheers,
Douglas
 
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Bandersnatch

Member
Joined 2003
Wikkid said:

LOL.. starving student sounds JUST about right!

My interest is in cheapest not smallest..
As I don't listen thru cans very often, but when I do, I'd prefer
good sound...
Click to expand...

Lots of cost savings can be had with careful/skilled shopping.

Also, the 'Class A' category is a bit of a red-herring. All SE has to be Class A, and it is trivially simple to do PP in Class A too.
cheers,
Douglas
 
M

m0b1liz3

Member
Joined 2008
Bandersnatch said:
hey-Hey!!!,
I have built a linestage amp that can serve as a headphone amp. It runs a LTP of 6C45 and a 20k:600/150 output tx. The OPT will deliver a Watt, and the load line shows the tubes capable of roughly 60% more than that. B+ is ~170V. The PS isn't all that small, and neither is its heater supply. Build with a switcher supply and it can be *VERY* small...:)
cheers,
Douglas
Click to expand...


Sounds good, can it be built be a complete moron? lol I like the sounds of that one so far. At 1Watt it could be used for biamping tweeters later on right? Ultimately I think that will be how I will want my set up since I enjoy speakers more than headphones but have to do the headphone thing alot in my current situation.
 
B

Bandersnatch

Member
Joined 2003
m0b1liz3 said:



Sounds good, can it be built be a complete moron? lol I like the sounds of that one so far. At 1Watt it could be used for biamping tweeters later on right? Ultimately I think that will be how I will want my set up since I enjoy speakers more than headphones but have to do the headphone thing alot in my current situation.
Click to expand...

I don't know about 'complete moron'...I suspect that one of those folks would just buy one off the rack...:)

It is fairly simple; single stage LC filter for B+, LC stage for DC heaters. The LTP has a CCS in the cathodes. The negative rail is done with a 25V/450 mA/$6 Radio Shack power TX and some 50V 'lytics. The CCS is depletion-mode Supertex MOSFET based.

The design does need a good OPT. I chose old Chicago BO-2's. They are usually quite inexpensive at auction. Fortunately I now have three; two in service and one ready to be unwound and documented for making more. Go right ahead an' bid them up now...:)
cheers,
Douglas
 
kstagger

kstagger

Member
Joined 2003
6streetbridge.blogspot.com/
This headphone circuit (6N1p) - small footprint there
http://headwize.com/projects/showfile.php?file=bender_prj.htm

or (6922)
http://headwize.com/projects/showfile.php?file=cmoy5_prj.htm

will work. Both use a White Cathode Follower and will work with ~300 ohm headphones. 6922 version also has the option of loop feedback to drop down the output impedance even more. I've built a similar circuit (using an EF86 triode connected as the gain section) and found it to be a good performer. The headphone section was admittedly an afterthought, but one of my condo living friends uses it exclusively for his daily listening.

An externally hosted image should be here but it was not working when we last tested it.
 
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m0b1liz3

Member
Joined 2008
Actually, GlidingDutchman, I take back what I said about it needing to be tube. That project looks simple enough that I might even tackle it! I need to work my way up in complexity of projects first and if it sounds as good as you say then it may be a good one to do. Do you have a parts list? Can that HP amp double as a preamp easily?
 
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