Low Powered Tube based headphone amp
Jun 20, 2012 at 8:39 AM Thread Starter Post #1 of 14
enforcer

enforcer

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I'm looking to build a desktop headphone tube amplifier and need some recommendations. Ive been researching plans for a few of the kits, the most popular seems to be the "Starving Student" amp. In reading through some of the information I've found, I've noticed that people are driving some headphones with fairly high impedance's. I'm very entry level into the Hi-Fi world and am currently using some Denon AH-D500 headphones. Some like em, some hate em. In any event there great for me right now. The input impedance is 25 ohms with doesn't seem like much compared to some of the setups I've been reading about. Here is my wish list......
 
  1. Tube amp design - Utilizes fairly easy tubes to source
  2. Capable of safely driving 25 ohm Denon AH-5000 without overloading them
  3. Sub $200
  4. Very well documented plans
  5. Straight forward design for Nubie/Amateur electronics hobbyist (I can run a soldering iron well)
  6. Simple and fairly compact 
  7. Will last years and years with minimal tweaking
 
That's the wish list, now how close can i get? Honestly I really love the "Starving Student" for its simple design and small footprint. This one really got my creative juices flowing. My issues are I to make sure I'm not going to kill my headphones, and I've heard the 19j6 tubes are getting harder to source these days. I want to make sure i can enjoy this for years to come!
 
Jun 20, 2012 at 10:01 AM Post #2 of 14
With tubes and this budget there is not much to think up, so I would reccomend Starving Student. I once made something like SS (I used different tubes, different MOSFETs, bigger output caps and added caps on input for safety) just for fun and if I remeber correctly the output impedance was around 1ohm which is OK for 25ohm headphones.
 
Jun 20, 2012 at 11:04 AM Post #3 of 14
the SS is just tube input, the solid state output will be fine with your denons. the only thing that will overload your headphones is if you turn the volume up too high, so just lower the voltage gain on the input stage; i'm sure that option will be covered in the threads. the power into 25ohms is going to be less than the power into high impedance phones anyway.
 
You might need to up the bias on the fets to give more current for the denons and you could always add a touch more feedback to get the outputZ down if thats an issue, which I doubt it will be provided enough current.
 
you will probably want to up the bias if you want to maintain class A output into the lower impedance anyway.
 
Jun 20, 2012 at 7:18 PM Post #4 of 14
My SS amp in that photo has been used daily at work for about four years and is still working great.
Luckily, I bought a few dozen 19j6 at the time, but none have gone bad so far.
 
Good Luck,
Brian (oldking)
 
Jun 21, 2012 at 9:13 AM Post #5 of 14
Quote:
amarokcz said:
With tubes and this budget there is not much to think up, so I would reccomend Starving Student. I once made something like SS (I used different tubes, different MOSFETs, bigger output caps and added caps on input for safety) just for fun and if I remeber correctly the output impedance was around 1ohm which is OK for 25ohm headphones.
Click to expand...

 
Heh I was thinking the same thing. The SSMH seems to meet all my needs. I believe im going to go ahead and use the SSMH 12AU7 variation in order to build with some more common tubes, or at least ones with more more avalability :) 
 
Do you have a diagrahm of the circuit you built? I would be curious how yours varied. 
 
 
Quote:
oldking said:
My SS amp in that photo has been used daily at work for about four years and is still working great.
Luckily, I bought a few dozen 19j6 at the time, but none have gone bad so far.
 
Good Luck,
Brian (oldking)
Click to expand...

 
Thats great to hear! To be honest it was your amp that really set me over the "oh I gotta build one of these things" edge. I hope I have the same stability with the 12AU7 circuit as you have with the 19j6. 
 
Since you have been using yours for a while. What are some of the "features" of it? When I say features I mean the little bugs and things you just learn are part of the game. Ive heard some discussion about having headphones plugged in when powering on vs plugging in after powering up to avoid the thump... Things like that. 
 
Jun 21, 2012 at 11:38 AM Post #6 of 14
Mine was just Starving student adapted to the fact, that I didn't want to use parts other than I already had home.
 
Schematic is here. Mosfets are IRF630, AC voltage source was 18V transformer (~24V DC at filter cap, but works even with 40V), the zig-zag shaped resistor is heater and tube is double triode with 6.3V heater (I think I used old ECC85).
 
Jun 21, 2012 at 12:33 PM Post #8 of 14
Quote:
amarokcz said:
Mine was just Starving student adapted to the fact, that I didn't want to use parts other than I already had home.
 
Schematic is here. Mosfets are IRF630, AC voltage source was 18V transformer (~24V DC at filter cap, but works even with 40V), the zig-zag shaped resistor is heater and tube is double triode with 6.3V heater (I think I used old ECC85).
Click to expand...

Heh. Hats off to that! Since I need to order parts, I guess I probably wont need to adapt anything. Tks for posting your drawing though!
 
Jun 23, 2012 at 4:46 AM Post #9 of 14
My phones have been ath-m40fs and ath-m50
 
There is no real pop for me when power on/off. I leave the phones plugged in always.
 
The all-black one is the first one I built, and I used typical insulated straight-thru RCA jacks.
I switch inputs from time to time, and those jacks have had a tendency to loosen.
When an input looses ground, there will be VERY loud buzz (oscillation?). Don't 'hot' swap inputs.
 
I switched to using these Neutrik NF2D RCA which are just awesome, and look better in my design.
http://www.flickr.com/photos/oldking/3139398004/in/set-72157608008797293
 
I'll get some photos that show more assembly details.
--
Brian
 
Jun 25, 2012 at 8:24 AM Post #11 of 14
Upon request, I've posted more photos for reference:
    http://www.flickr.com/photos/oldking/sets/72157608008797293/
 
All metal work was with a bench-top drill press and a 'stepped' drill bit (works great).
--
brian
 
Jun 25, 2012 at 9:42 AM Post #12 of 14
Quote:
civilmonkey said:
I made this amp and it sounds pretty good.  Tube sound, lots of thump, and be made quite cheaply.
 
One thing is that you need to carefully consider the power supply here, noisy supplies were had a lot of hiss, quieter ones were way better.
 
http://diyaudioprojects.com/Solid/12AU7-IRF510-LM317-Headamp/
Click to expand...

This was actually another design I was considering. I really like the size of this one. Other than the power supply how has it been working and for how long have you had yours?
 
Jun 26, 2012 at 7:57 AM Post #13 of 14
Quote:
enforcer said:
This was actually another design I was considering. I really like the size of this one. Other than the power supply how has it been working and for how long have you had yours?
Click to expand...

Sorry, can't comment.  I made it for my brother and sent it away.  I just recall it was afun sounding amp, made you want to bob your head.  Sound was greatly affected by the tube.  The part count is so low, it's not too much of a build as a trial.
 
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