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A Super-Simple 6DJ8 Headphone Amp - Page 5

post #61 of 490
Well, the 6DJ8/7DJ8 too are tubes with a half-stupidly high voltage, as their data lists a plate voltage of 90V. And I think there are othes triodes that sound good at lower voltages than those they were built for.
post #62 of 490
I agree. I am running the 7DJ8(PCC88) with just 5.9V on the heater and only 11.9V on the plate. Sounds great.
Of course the tubes are directly connected to a Solid State output, almost exactly the same as your schematic on the first post.
post #63 of 490
I got the PCB today!

I don't think the traces on the top are actual copper traces, I think they are just a colored line, I don't see a single via and the closer I look the more I'm convinced there is only copper on the bottom layer.

I've still got a lot of parts waiting to be received but I can at least get a jump on a few things. I can't remember if I actually ordered the fets or not... lol
post #64 of 490
Thread Starter 
I dunno; seems pointless to print an extra layer (of what, if not copper?) on the board, but I'm sure stranger things have happened.

Here's one incarnation of the same design, only double-sided:



It works out to be just under 2.75 x 3.75 inches; right about half the size of the eBay original. The pot and input/output jacks are left off-board, to provide more flexibility ("Australia-proofing"); the TO-220 devices are along the edge of the board, so you're less restricted with regard to heatsink choices; most resistors spots are sized for Dale RN60s or similar, except a few larger ones where space was left for the big KOA/Kiwame parts; the input caps will more easily accommodate larger box caps (10mm lead spacing); I added a second LED so you can light the tube from below, and have a more conventional power-indicator light, at the same time; otherwise, basically everything is as on the "Xiang Rong" board...
post #65 of 490
That's brilliant! With the TO-220 devices on the edge you can just sink them directly to the aluminum enclosure!

That'd make an easy build... There isn't enough room on this board(XR01) for the input caps I wanted to use but I should be able to use my second best choice.
post #66 of 490
What kind of voltages are we to expect at C102/202? Do we really need a 35v cap there? I have caps on hand here that I want to use and one set is a 470uF 50v pair and the other is a 2200uF 16v pair.

Here are a couple of variations I've installed so far:
-R101 is a 1/2 watt resistor, not 1w(can't find one)
-C105/104 are 470uF 25v instead of 220uF 16v

I'm not sure if I can get the 13 ohm and 2k ohm resistors exactly that set the 317s adj pin. I'm hoping for some out of spec 15 and 2.2k ohm resistors to come through for me. I'm also having to sub high 33 ohm resistors for R109
post #67 of 490
According to the schematic on post 1, C102(the output coupling cap) has 15V on it. It really depends on the voltage of your power supply and what kinda mosfet you use, but I'm guessing that's pretty close for a B+ of 24V.
I wouldn't be too fussy with the 317 bias resistors, I have used anything from 5 to 30ohms in a setup almost exactly like this one. These resistors will however set the current for the mosfet above them on the schematic.
You could also use another 317 in place of the mosfet, provided you get the pins on the 317 crossed if need be, in the correct holes. For the 317 Adjust would be used for the Gate, Input would go to the positive side(Drain on the mosfet) and Output would be towards ground(Source on the mosfet).
post #68 of 490
I just wanted to note, when I said I have used 5 to 30 ohms to set the bias for the LM317(using it as a constant current source for a mosfet or another 317), that was from the Vout(on the 317) to ground, using one resistor(in this case, it looks like you use 2 resistors parallel, which may be to allow you to use smaller rated parts).
post #69 of 490
Thread Starter 
In other words, something like this, right? Interesting... very interesting.
post #70 of 490
Yes, exactly. And my now favorite amp is this...

...as you can see, they are somewhat similar.
I think you guys are gonna like this amp your building.
post #71 of 490
I've got most of the parts I need to complete this thing. It should be done and running by Saturday night or Sunday. I'll get some pics posted of the finished product.

Those heat sinks we linked to look like they will be perfect for even the smaller of the two cases that were linked to. They took a while to come in but it looks like they would even work without having to cut holes in the case.

All I'm waiting for are the fets from Cicon and the time to get the case work done.
post #72 of 490
Thread Starter 
Nice! I'm always relieved when these sorts of things actually turn out as planned.

I have most of the parts, but I'm still waiting for the new capacitors to arrive. I'm sure there's something else I'm missing, as well... isn't there always?
post #73 of 490
I only got the caps and resistors, and am still waiting for the PCB, heatsinks and fets. Well, I also got the tubes and sockets but I had those already.
post #74 of 490
I lack C103, the lead spacing is making finding a cap for that a bit difficult if I want it to sit flush and since it's actually coming together I don't want to order something else and have to wait for yet another part to come in and radioshack's supply of radial leaded electrolytics leaves a lot to be desired.

Oh yeah! My regulated power supply also needs finished. I've got the line filtering, rectification, and DC smoothing taken care of I just need the 317(that came in yesterday) hooked up to turn my 35vdc to 24vdc.
post #75 of 490
Thread Starter 
Stopped at the local surplus store this afternoon, and picked up some old Wima capacitors for $0.25 apiece, as well as some Switchcraft stereo sockets, also for a quarter.

Made the mistake of glancing through the mountain of NOS tubes, and should have heeded my advice, earlier, about such things - I remembered something in this thread earlier about a 7V tube - the 7DJ8 - but for some reason thought it was the 7AU7 instead; the store had a bunch of the latter, and I picked up a pair for $2.50 each. Alas, they're seven-volt 12AU7 subs. Oh, well... I've got a spare SOHA I board, and dropping the heater voltage to 7V shouldn't be too hard.

Moral of the story: do as I say, not as I do.
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