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12AU7 amp I built with parts from my stash...
Mar 24, 2013 at 1:35 AM Thread Starter Post #1 of 16
vixr

vixr

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Well, I was surfing the web and came across this amp... So I checked my stash and found I had all the parts or combinations of parts to build it...sounds pretty good. I etched up 3 boards and built it this evening...It uses a high quality 12VDC wall wart I had laying around...
 

 

 

 
Mar 24, 2013 at 10:09 PM Post #2 of 16
A cool variant on the starving student theme, and more versatile, IMO. You can use a wide range of PSUs if you regulate the heater supply, like maybe some of the laptop bricks I've got lying around. I think I'll build one for a bit of low-stress entertainment.
 
w
 
Mar 24, 2013 at 11:40 PM Post #3 of 16
Quote:
wakibaki said:
A cool variant on the starving student theme, and more versatile, IMO. You can use a wide range of PSUs if you regulate the heater supply, like maybe some of the laptop bricks I've got lying around. I think I'll build one for a bit of low-stress entertainment.
 
w
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It was fun and as nerdy as it is, I had all the parts to build it. I etched the boards in about an hour and had the whole thing built in 3. It takes about a minute for the DC offset to go below 10mV...I rolled in an old 12AU7 Mullard and it sounds fabulous and I have a NOS Japanese tube (the one in the picture) that sounds good too. The new JJ ECC82 I have distorts badly at about 3/4 throttle.
 
Mar 26, 2013 at 11:14 AM Post #4 of 16
Well, I listened to this amp for 6 hours yesterday at work and all morning today and I'm impressed. It sounds good...considering the cost of the parts and the simple build up. I used some of my precious cerafine caps but I think this amp is begging for some Muse KZ...I also used some generic polypropylene films for input. The LM317s get damn hot and need heatsinks, IMHO...  Not a lot of gain here with my HD600s, but still plenty loud. I am surprised at the amount of detail thats here, decent bass and not crashy. Just enough tube warmth to be pleasant but still some decent depth and detail. I give it a thumbs up.
 
Mar 26, 2013 at 11:22 AM Post #5 of 16
Quote:
wakibaki said:
A cool variant on the starving student theme, and more versatile, IMO. You can use a wide range of PSUs if you regulate the heater supply, like maybe some of the laptop bricks I've got lying around. I think I'll build one for a bit of low-stress entertainment.
 
w
Click to expand...

I hooked it up to a small 12V scooter battery rated at 7Ah and it lowered the bias a bit so I just re-adjusted the trimmers and ran it for 4 hours with hardly any voltage drop...the trimmers kept the bias at acceptable levels until I turned it off. Kinda cool...
 
Mar 26, 2013 at 10:37 PM Post #6 of 16
I've drawn up a PCB, but I haven't got a 12AU7, and a tube that likes fairly low voltage is really required. I have got some 6N6Ps, I wonder if they'll work? I'm going for 19V supply...
 

 
I can't seem to get much performance out of it, no matter how I tweak it.... Maybe I'm just expecting too much.
frown.gif


 

 
w 
 
Mar 26, 2013 at 11:44 PM Post #7 of 16
Quote:
wakibaki said:
I can't seem to get much performance out of it, no matter how I tweak it.... Maybe I'm just expecting too much.
frown.gif

 
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wow...the numbers don't lie...I would have bet that it had better specs than this. I did wrap a .47uF bypass film cap around the output electrolytics. Your PCB looks awesome.
 
Mar 27, 2013 at 3:26 PM Post #9 of 16
Yes, it's more a question of not being able to drive it very hard before running into grid current. Even with the 12AU7 I can't get much more than 0.6V between cathode and grid, and as the current comes down and the output impedance goes up I get more concerned about not being able to drive the gate capacitance of the FET. Of course the tube model is probably unreliable at these low values of B+, I've just got used to being able to do some optimization in the simulator.
 
w
 
Mar 27, 2013 at 4:11 PM Post #10 of 16
Quote:
wakibaki said:
Yes, it's more a question of not being able to drive it very hard before running into grid current. Even with the 12AU7 I can't get much more than 0.6V between cathode and grid, and as the current comes down and the output impedance goes up I get more concerned about not being able to drive the gate capacitance of the FET. Of course the tube model is probably unreliable at these low values of B+, I've just got used to being able to do some optimization in the simulator.
 
w
Click to expand...

I am lost when it comes to the EE talk... I'm blessed with the ability to follow complex instuctions and fairly good motor skills. I do know that it sounds pretty good for the time and money spent...
wink.gif

 
Apr 24, 2013 at 3:33 PM Post #13 of 16
Quote:
wakibaki said:
I can't seem to get much performance out of it, no matter how I tweak it.... Maybe I'm just expecting too much.
frown.gif


 
Click to expand...

 
22Kohm plate resistor is a little low for a 12au7, even with HV across it.
Why not switch to a plate CCS?
 
CRD or JFET would be easy. A bit more expensive, but I bet the sound makes the difference worth it. 
 
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