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The "Lovely Cube" Headphone Amp (Lehmann Black Cube Linear Clone)
Feb 22, 2011 at 2:08 PM Post #514 of 1,624
 
Quote:
blablabla said:
Agree. Even signal resistor can change sound signature...
 
 
But stock OPA 2134 is crap... :)
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That's why I swapped it for 2107 (until I get a Burson in the far future)! 
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Feb 22, 2011 at 2:32 PM Post #515 of 1,624


Quote:
jiggad369 said:
 
 
That's why I swapped it for 2107 (until I get a Burson in the far future)! 
tongue.gif
Click to expand...


Burson is excellent.
 
Here is my PCB... http://www3.picturepush.com/photo/a/5133076/img/5133076.jpg
 
I started with red resistors. Now it is time to put there a few pink one, and then some big green made in last decade. I like the old school carbon resistors in output. Also I was not satisfied with voltage drop over diodes, and with their quality (one felt apart), so I found a better solution. It was pity that this diodes could not fit in the holes so I had to improvise. And that is my strong point. See it - improvise - conquer.
 
I left few resistors from the stock package, just to remind me how stock resistors look like.
 
Feb 22, 2011 at 5:10 PM Post #519 of 1,624


Quote:
gwikse said:
Nice :)
 
I have to be a little creative myself. First and foremost around the opa socket. But I think the easy solution to this is to mount the capacitors angled underneath the pcb.
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Tried before. Was not successful. It is hard to place some capacitors underneath PCB. Especially some MKP caps. I have big problems with ERO caps. They are like small boxes.
 
Feb 22, 2011 at 5:33 PM Post #520 of 1,624


Quote:
blablabla said:
Tried before. Was not successful. It is hard to place some capacitors underneath PCB. Especially some MKP caps. I have big problems with ERO caps. They are like small boxes.
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I`ll design the case around the finished (in 3d first) board. So as long as it is possible to get to the solder joints (wich are on both top and bottom of the pcb) it should not be a problem unless I am missing something?
 
Feb 22, 2011 at 5:42 PM Post #521 of 1,624


Quote:
jiggad369 said:
 
Sorry I'm new to transistors so still trying to learn. Are those all compatible replacements in the LC?
 
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Almost everything that has similar technical data. Or bigger. Most important things are VCBO, VCEO, VEBO, IC because they will prevent you from burning things right after "turn on".
Next are VCB, VCE etc... "saturation" if you want to do fine tuning on your amp (I do not have enough patience to do that and just use transistor with similar specification.) And for sound important are hFE gain and linearity, frequency and noise figure. After that important are drawings that tell you where goes gain within heat and collector current. (Probably, I forgot something...)
 
As far as I know, BC109C and BC179C work flawlessly. But have to be careful because they have lower VCBO, VBEO, VCEO.
 
2SA1015 and 2SC1815 also work (they have bigger specs so you will not fry anything), but it is pain in the ass to solder them properly because different pin out. And also pain in the ass to find good (should I say "genuine") parts. Well, at least within specification...
 
2N5087 and 2N5088 I did not try and I would avoid them because low VEBO (3V). I mean I did not make any measurements to be shure that VEBO will not go above 3V... Besides you have to watch over Ic current because they are small signal transistors with Ic maximum 20 mA. So you will have to put in a circuit resistors with bigger value to limit current.
 
And... If you fail with BC transistors, your headphones will get almost 1.5V DC signal. Which is, if you do not have Sextetts or something with 600ohm resistance, quite high and will roast your headphone coils like chicken. You have to be sure, and do a lot of testing, before listening. Same thing goes with opamp. If opamp fails, then only what you can do, is to call nearest seller and ask him if he has another headphones in stock. I did that half year ago. But I am not eager to do that again... :/
 
Matrix M Stage had relay that was able to limit incoming signal. But that relay was on input, not on output... Again barbecue... LOL. Probably someone was not sure if people would plug amplifier (RCA) into wall socket instead sound card or mp3 player...
 
 
 
 
Feb 22, 2011 at 5:45 PM Post #522 of 1,624


Quote:
gwikse said:
I`ll design the case around the finished (in 3d first) board. So as long as it is possible to get to the solder joints (wich are on both top and bottom of the pcb) it should not be a problem unless I am missing something?
Click to expand...


Forgot to say, I use stock case...
 
But you gave me good idea. I have some metal boxes in the cellar... Maybe I could use them an put there bigger transformer (100VA) instead stock one (30VA)... Interesting.
 
Feb 22, 2011 at 11:43 PM Post #523 of 1,624
Ok the more I read about transistors, the more I'm getting confused.
I decided to go with MJE243/MJE253 then read that it will not go well with high impedence phones like the Sextett (600). 
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What is the best option for the replacing the BD139/140?
 
 
Feb 23, 2011 at 5:05 AM Post #524 of 1,624

 
Quote:
jiggad369 said:
Ok the more I read about transistors, the more I'm getting confused.
I decided to go with MJE243/MJE253 then read that it will not go well with high impedence phones like the Sextett (600). 
confused_face_2.gif

 
What is the best option for the replacing the BD139/140?
 
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You can try old Soviet germanium transistors GT402-GT404 (ГТ402-ГТ404 in Russian) instead BD140-BD139. I don't know how they change the sound, but they change for sure. I guess that sound will be smoother, more like tubes. But max temperature has to be 50...55°С.

 
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