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12AU7 amp I built with parts from my stash...

post #1 of 16
Thread Starter 

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...

 

 

 

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

post #3 of 16
Thread Starter 
Quote:
Originally Posted by wakibaki View Post

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

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.

post #4 of 16
Thread Starter 

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.


Edited by vixr - 3/26/13 at 8:18am
post #5 of 16
Thread Starter 
Quote:
Originally Posted by wakibaki View Post

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

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...

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

 

 

post #7 of 16
Thread Starter 
Quote:
Originally Posted by wakibaki View Post

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

 

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.

post #8 of 16
Quote:
Originally Posted by wakibaki View Post

 

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 

That's almost all 2nd harmonic, the other distortion products aren't that bad

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

post #10 of 16
Thread Starter 
Quote:
Originally Posted by wakibaki View Post

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

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

post #11 of 16

Sorry, I've been doing that EE talk for so long I just slip into it without noticing. I'll try and make some progress with building it. I may be gone for some time...

post #12 of 16

This is great.  I have some 12AU7s lying around just waiting for a project like this.  Thanks!!!

post #13 of 16
Quote:
Originally Posted by wakibaki View Post

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

 

 

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. 

post #14 of 16
Thread Starter 
Quote:
Originally Posted by nikongod View Post

 

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. 

Sir, you have my attention...how would you do the change?

 

post #15 of 16
Quote:
Originally Posted by vixr View Post

Sir, you have my attention...how would you do the change?

 

 

Any chance to increase the power supply voltage to 24V? That would be the first thing. 

 

I will draw a schematic of what I am thinking of shortly. 

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