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A Super-Simple 6DJ8 Headphone Amp - Page 9

post #121 of 471
2/26/09 at 12:33am
Thread Starter 
Well, for kicks, I dug out the 19VDC, 3.2A laptop power supply I've been running one of my Pimetas on, and not only does it power my 6DJ8 amp just fine... but with no hum, either. (To be fair, I'm in a different location than when I was testing earlier, but still...)

I don't hear any noticeable distortion, but I've only been listening to it for a few minutes, and I don't have my output devices biased nearly as high as I think some folks do. I can very much tell, though, that this amp really sings with a line-level signal, but doesn't seem to do nearly as well with the signal out of a headphone jack.

This is my second hybrid amp, after a fairly nice 'SOHA Mk. I' I built a while back, and so far I'm mighty impressed with the sound. I don't know quite how to describe it, except to say that it's extremely musical: everything that's good about the SOHA Mk. I, and then some, without any of the SOHA's annoyances. I <3 it.
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post #122 of 471
2/26/09 at 1:17am
Okay, I took a couple of measurements. The amp seems to be acting like you guys are describing, the 310s are warm and the 317s are hot. I can see a slight glow within the tube and it's warm to the touch after being on for a few minutes. However, I'm reading 3.56v out of both 317s and only 2.31 at pin 4. Still nothing but a hum.

Could the low heater voltage be making the tube not pass audio? Even after being on a while? No idea wtf I did wrong lol I followed the resistor values to the T!!!!
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post #123 of 471
2/26/09 at 1:28am
Thread Starter 
It's entirely possible that it won't operate anything like correctly at 2.3V heater voltage. Why you're getting that low of a voltage, on the other hand... I dunno.

What are you feeding it an audio signal from, and have you tried turning it all the way up? When I feed mine from an MP3 player, I need to turn it all the way up to get to a decent listening volume, and don't even begin to hear a thing until about 12 o'clock on the dial, so to speak.

Mine's more-or-less per the schematic; the only resistors I changed were R110/R210, like I said; I've got 1200uf Elnas for C102/C202, and some 2.2uf film caps for C101/C201, only because they fit. Oh, and because I misread the schematic when I was rummaging through my parts boxes, I've got a (cough!) 12000uf Nichicon cap for C103; even by Head-Fi standards, I think that's a wee bit excessive.

I don't know how useful it'll be, but you might want to post a photo of your board; maybe someone will spot something...
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post #124 of 471
2/26/09 at 1:31am
I think my LED is wrong. That would explain the low voltages.

**EDIT**

Repalced LED with diode... still no go. still 2.x volts.
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post #125 of 471
2/26/09 at 2:03am
Forgive the use of flash, I don't normally use it for stuff like this but I don't have my tripod with me.



The tube is actually a 6N1 but the only difference I've found between the 6DJ8 and the 6N1 are the heater currents... Unless this is a current feedback setup I don't see that causing it. I should probably also mention that when the amp is first started it only gets about 1.6 volts to pin 4. As the heater warms up voltage rises to 2.2.
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post #126 of 471
2/26/09 at 8:57am
If you trace what leads to pin 4, what do you measure for voltage coming out of BG201 and BG101 (pin #1 in both cases if I'm not mistaken)? Theoretically, they should both be putting out the same voltage. My thought process is that either BG101 or BG201 is not putting anything out, or something in between may be reducing the voltage (R106?).

Also, mine runs with or without a LED (makes no difference).
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post #127 of 471
2/26/09 at 8:59am
Quote:
Originally Posted by Nemo de Monet View Post
Well, for kicks, I dug out the 19VDC, 3.2A laptop power supply I've been running one of my Pimetas on, and not only does it power my 6DJ8 amp just fine... but with no hum, either.
I'm using HD600s and can hear the low notes clipping when using a 19v supply, especially at higher volumes. The amp does not hum, just sounds bad (like there is sand in the speakers). Could the 19v supply work with lower impedance headphones? I will try tonight...
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post #128 of 471
2/26/09 at 2:14pm
If someone could do me a quick favor. I could use in-circuit measurements of R104-5/R204-5 (ADJ on the 317 to OUT) I'm currently reading exactly 7.5 ohms on both sides(R1/R2). I'm thinking it has to be some sort of resistor value that's messing it up, maybe. I'm getting 20v to the 317s but I'm not getting 6.3v out. Since they're both getting hot I can only assume that one of them isn't actually dead.

Tonight I'll pull the tube and see what kind of voltage I get with no load on the heater circuit though. If it's ~6v with no tube in there I'll have to assume I got a bad batch of 317s because my power supply is doing the same thing. When the amp is off it gives me the calculated 24.5v for output but when I turn the amp on voltage drops to around 6 volts.
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post #129 of 471
2/26/09 at 2:45pm
The pads for LM317s FETs are pretty close, is it possible you have a solder bridge on one of them?
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post #130 of 471
2/26/09 at 4:48pm
That was the first thing I checked for, I might be missing one tho, I'll take a picture tonight and post it of the bottom.
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post #131 of 471
2/26/09 at 5:00pm
I haven't been keeping track of everything that's been going on lately, but I wanted to mention that if someone substituted parts for the K310 or K117, then those alternate parts may have a different pinout that could cause a problem.
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post #132 of 471
2/26/09 at 5:04pm
Thread Starter 
Quote:
Originally Posted by DKJones96 View Post
If someone could do me a quick favor. I could use in-circuit measurements of R104-5/R204-5 (ADJ on the 317 to OUT) I'm currently reading exactly 7.5 ohms on both sides(R1/R2).
I measured mine and got around 7.2 ohms for each side, though it jumped around a bit.

I wonder if your problem isn't, indirectly, the tube you're using; the 6N1P has a much higher heater current than the 6DJ8, and I don't know what kind of power supply you've got, but I wonder if it can't keep handle the resulting current draw.

Quote:
Originally Posted by kansei
I'm using HD600s and can hear the low notes clipping when using a 19v supply, especially at higher volumes. The amp does not hum, just sounds bad (like there is sand in the speakers). Could the 19v supply work with lower impedance headphones? I will try tonight...
I've listened to mine at 19V for several hours now - with 40 and 60 ohm 'phones - and don't hear any signs of clipping, at all, nor any unpleasantness. Now that it's burned in a bit, it just gets better and better...
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post #133 of 471
2/26/09 at 5:39pm
I think I solved it!!! Thanks Nemo!

I was looking over the schematic and noticed that these 317s aren't actually setup to be constant voltage regulators. The increased current draw is pulling them low because they are set for a particular amount of current. At 7.5 ohms each 317 will provide 167mA which is great for the 6DJ8 at 350mA but not for the 6N1P at 600mA. I actually need 4.5 ohms.
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post #134 of 471
2/26/09 at 5:52pm
Thread Starter 
That would explain it, I bet.

If that's the case, just put another 13ohm resistor in parallel with the 15 and the other 13, and you should get right about 4.5 ohms.

Here's hoping that works... it'd be really nice to have this design working solidly with dirt-cheap 6N1Ps. I thought I had some laying around, but they turned out to be some other sort of Soviet tube.
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post #135 of 471
2/27/09 at 12:35am
I got sound! It clips badly and the audio is only slightly louder than the hum but something actually comes out of the headphones now. I'm going to search for more volts and see if that clears it up.

I've got 6.21v at the heater using 15/13/10 ohms, 13/13/10 gave me 6.6v and it clipped there too, dang tube runs as warm as the 317s!
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