A Super-Simple 6DJ8 Headphone Amp

[ludoo]

Nemo, could you post a pic (or two, top/bottom) of the board? The one on ebay is almost illegible and mine will take a few days to get here.

 

[Nemo de Monet]

Here you go:

I hadn't noticed before, but the top and bottom copper traces are perfectly symmetrical! How bizarre...

 

[ludoo]

Quote:

Originally Posted by Nemo de Monet /img/forum/go_quote.gif Here you go

Thanks!

 

[ludoo]

One quick question: did you find suitable heatsinks? I could not find any of sufficient dimensions with a single center pin.

Another question: the resistors in front of the LM317 (R104/R105) don't look like 1/4W ones in the pics of the built amplifier

but look more like 2W resistors. On the schematics, though, the only resistor with a power spec is R101, rated at 1W. 2W for R104/R105 makes sense (well maybe half of that as they are in parallel), or not? I am just a noob full of questions...

 

[DKJones96]

I found these, 4 pcs and they look almost exactly like what comes on the board. They have taller versions of the same thing but the enclosure I'm going to use would need holes cut in it to clear them and I'd prefer to not do that for anything but the tube itself.
4 pcs HEATSINK SILVER HS-3523 TO-220 WONDERCO TAIWAN - eBay (item 140288394246 end time Feb-08-09 22:31:04 PST)

My questions is where do you get 2w resistors? I've got thousands of 1/2w and 1/4w resistors which I guess I could run in parallel but the lower values that this board takes I don't have.

 

[Nemo de Monet]

The Wonderco heatsinks are the only ones I can recall seeing with a centre pin like that, but IMO you can use anything that'll physically fit on the board - there are a number of Aavid heatsinks that should work, for example. I don't really think mechanical rigidity is a major issue for this amp... and I'm trying to keep the DIY version as Australia-proof as possible, so I don't want to just come out and say, you know, "this is the only part that will work here".

The resistors in the completed amp do look pretty high-power (I think they're probably 1W, not 2W - just a different manufacturer, hence different size from the 1W, R101), but I don't know if that's really necessary; old builds of Sijosae's MHHA used, I think, 1/4W resistors in most of the positions, which is what I plan to do. If you want to play it safe, Mouser carries audiophile-approved 2W resistors from Koa that are widely agreed to be identical to Kiwame, and they're not obscenely expensive. There are other 1W and 2W film resistors (carbon or metal film; you almost certainly want to avoid wirewound ones) that will work just as well.

I for one don't see why R101 is 1W, anyway. Isn't it just an attenuator, between the signal in and ground? It's basically parallel to the volume pot, which is, what, 1/4W? Am I misinterpreting that?

 

[DKJones96]

What's the worst that could happen? If you burn up a resistor replace that one with a higher wattage one.

What is the tube pinout? I can't seem to find anything that's useful in my quest to determine what pins the heater runs on. I could see a power resistor if it's in series with the heater but not at the 101/201 position.

 

[luvdunhill]

Quote:

Originally Posted by ludoo /img/forum/go_quote.gif One quick question: did you find suitable heatsinks? I could not find any of sufficient dimensions with a single center pin.

I'd check the Fischer catalog, I seem to remember heat sinks with that center pin .. of course, we cannot get those here in North America, so I've only user a few Fischer parts and usually try and find substitutes.

 

[Nemo de Monet]

Pins 4 and 5 are the heater per here. It's confusing, because that's apparently from the bottom. (The shield, pin 9, is the one next to R202 that isn't connected to anything.) So, the heater are the one that connects to ground, on the right side of the socket, and the pin right next to it whose trace passes under R102. R104/R105 would seem to be the ones that are on the heater circuit.

R101/R201 (1MOhm) are between ground and the grid; R102/R202 (100 Ohm) are between ground and the cathode. What they actually do, I can't really say - toob theory is weak in this one. (As Donald Sutherland said in Kelly's Heroes - "I only ride 'em, I dunno what makes 'em work".)

 

[ludoo]

Quote:

Originally Posted by DKJones96 /img/forum/go_quote.gif I found these, 4 pcs and they look almost exactly like what comes on the board.

Thanks, I got those too as they're cheaper for me than getting some from the US.

Quote:

Originally Posted by DKJones96 /img/forum/go_quote.gif My questions is where do you get 2w resistors?

I get them from a local store, but they only carry a few values. The 2W I got once look exactly like those on the board used for the LM317.

Quote:

Originally Posted by Nemo de Monet /img/forum/go_quote.gif The resistors in the completed amp do look pretty high-power (I think they're probably 1W, not 2W - just a different manufacturer, hence different size from the 1W, R101), but I don't know if that's really necessary; old builds of Sijosae's MHHA used, I think, 1/4W resistors in most of the positions, which is what I plan to do.

I will probably do the same, except for those that set the LM317 voltage.

Quote:

Originally Posted by DKJones96 /img/forum/go_quote.gif What is the tube pinout? I can't seem to find anything that's useful in my quest to determine what pins the heater runs on. I could see a power resistor if it's in series with the heater but not at the 101/201 position.

ECC88 @ The National Valve Museum Edit: Nemo beat me to it.

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif I'd check the Fischer catalog, I seem to remember heat sinks with that center pin .. of course, we cannot get those here in North America, so I've only user a few Fischer parts and usually try and find substitutes.

Interesting, I will have a look as buying things from Germany is definitely cheaper for me than from the US.

 

[ludoo]

Quote:

Originally Posted by Nemo de Monet /img/forum/go_quote.gif R101/R201 (1MOhm) are between ground and the grid; R102/R202 (100 Ohm) are between ground and the cathode. What they actually do, I can't really say - toob theory is weak in this one. (As Donald Sutherland said in Kelly's Heroes - "I only ride 'em, I dunno what makes 'em work".)

A noob guess is the 1mohm is for the grid leak, the 100ohm biases the cathode. Been reading quite a bit lately, but digesting and understanding knowledge takes much longer.

 

[DKJones96]

Quote:

Originally Posted by ludoo /img/forum/go_quote.gif Thanks, I got those too as they're cheaper for me than getting some from the US.

I'm in the US and it was still cheaper than buying in the US!

 

[dBel84]

Quote:

Originally Posted by Nemo de Monet /img/forum/go_quote.gif There are some 2SK117 available on eBay at the moment, and at good prices, but it doesn't really help much, since B & D seem to be the only decent place to get the 2SK310s. There are also some 2SK310 on eBay, but they're listed by the most useless electronic vendor ever, at a ridiculous price. MCM have 2SK310s - at, again, a ridiculous price - and apparently stock 2SK117s, though they're on backorder at the moment. Nobody else that I've checked seems to have the 2SK310s, or the 2SK311, its higher-powered sibling. There are *electrical* substitutes for the 2SK310, but I have no idea how they *sound*, and none of them seem to be used much (at all?) in audio designs, or are themselves obsolete or unobtanium. I suspect that there are a number of other FETs that can be substituted in this position, but have no idea what they are. Anyone?

The input jfets I would stick to. The mosfet can be substituted for something like the IRF510. People will argue that the sound will be very different but you are running the mosfet SE either way and you are going to get that grungy mosfet sound that is ever so sweet , don't build this amp if you are looking for the lowest THD ratings.

ludoo has convinced me to build one with his enthusiasm

I am guessing it will perform well and it is a simple amp to build P2P.

..dB

 

[ludoo]

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif ludoo has convinced me to build one with his enthusiasm I am guessing it will perform well and it is a simple amp to build P2P.

 

[Nemo de Monet]

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif The input jfets I would stick to. The mosfet can be substituted for something like the IRF510. People will argue that the sound will be very different but you are running the mosfet SE either way and you are going to get that grungy mosfet sound that is ever so sweet , don't build this amp if you are looking for the lowest THD ratings.

The IRF510 was one of the devices I was looking at as a substitute; it's cheap and available pretty much everywhere.

I'm not looking for the lowest possible THD ratings.

I fully expect this amp to have a bit (more than a bit?) of "character", owing to its design and components. Besides, it's cheap, it's easy, and I've got most of the parts laying around, including a bunch of Russian Mystery Tubes that I think will work in this amp...