[sandbasser]

What's the status of the actual Group Buy for these boards??

 

[cobaltmute]

Post #62

 

[sandbasser]

cobaltmute -

Sorry, must have missed that posting. Thanks for all you've done for the forum (and avocation). I hope everything turns out fine.

 

[Nemo de Monet]

There is no actual group buy, per se. There's simply the individual buy, so to speak. Get 'em before they're gone, et cetera.

 

[cobaltmute]

Nemo, take the trailing slash off your link in your signature. It doesn't work otherwise.

 

[Nemo de Monet]

Thanks. It's fixed now.

 

[Nemo de Monet]

If anyone's interested, I've received the first of these buffer boards from Seeed; they took exactly two weeks to arrive from China. They're everything we were hoping for - tiny, well-made, and inexpensive. So, yay.

So, get ordering, already.

 

[ludoo]

I got mines (4 boards) this morning. No pics as they are at home, but the boards are really tiny.

I plan on using them in a (maxed) YAHA. Will try to find the time to start the build this weekend.

 

[Nemo de Monet]

Many, many months ago, Mono said:

Quote:

Originally Posted by mono /img/forum/go_quote.gif I don't claim to know which transistors have the best synergy with any particular combo of amp and cans but something capable of more current than BC327/337 would be nice, to move up to a TO-126 size like BD139/140 for the output pair, and in that case if the amp is for home use to bias it further, replace 1K resistors with 470 Ohm.

A couple weeks ago I was placing a BatchPCB order, and was for some reason reminded of this comment, so I whipped something up in Eagle and had a couple copies fabbed:

I used BD139s, BD140s, and 2N5486s, with 470 Ohm resistors as suggested, and it sounds a little livelier and more detailed than the BC327/BC337/1K resistor version we've all come to know and love.

(It also seems to have much more controlled - i.e. less "flabby" - bass, but I could be wrong as my current setup doesn't easily allow A/B tests...) My test amp that I'm using runs on roughly +/-9V rails, and the transistors don't get appreciably warm or anything; is there likely to be any benefit from going to a higher bias current - 330 Ohm or so, perhaps? Since I used 0805 resistors, swapping them around isn't the simplest thing in the world....

 

[mono]

Higher bias increases clarity to my ears, the higher current transistor gives more controlled bass.


I'm too lazy to do the math, but the optimal bias current to keep it in class A will depend on your volume level and the load (cans). 470 Ohm to 330 isn't a big change though, since 2N5486 is only ~ 14mA IDSS, you could also try jumpering the spot instead of a resistor for the max bias current.

If you don't have hot tweezers to pick the resistor off, nor fast enough hands to heat both sides to a molten state to flick it off, then try using two soldering irons on each end simultaneously (or a hot air gun).

There is another option, not the most aesthetically pleasing but with the 470 Ohm resistor already on the board, just stack a 1K on top of or beside it (in parallel) for ~ 320 Ohm. Or do that with a jumper wire which can more easily be removed for the max bias.

 

[Nemo de Monet]

I have a hot air soldering station; that's not a problem. I just really really hate SMD rework... and I kind of buried the resistors in among the through-hole transistors, making things even more fun.

I'll try building a second set with a 0 Ohm resistor, and see if that does anything more than waste electricity.

I don't think heat is going to be an issue - I managed to get the BD1** devices somewhat warm to the touch by powering a pair of 5W 8 Ohm bookshelf speakers to very, very loud levels; probably in excess of 1W peak. (This from what is basically a CMoy, on +/-9V rails, fed from an MP3 player.) With headphones, even some of the grossly inefficient ones I've got laying around... not so much so, no.

 

[cobaltmute]

I was reading this thread where FallenAngel was biasing BD139s with 100mA. You need heatsinks but you can go alot deeper on the bias.

I heard tell elsewhere of using J309 as a constant current source. Idss can get up ~30mA. Or you can look at J310 which the datasheet shows as a Idss of 24mA to 60mA. I suspect you can drop either of these in on the board.

I've been playing with DACs lately, but been definitely having the urge to working with these boards again.

 

[Nemo de Monet]

Quote:

Originally Posted by cobaltmute /img/forum/go_quote.gif I was reading this thread where FallenAngel was biasing BD139s with 100mA. You need heatsinks but you can go alot deeper on the bias.

Oh, definitely. The question is really whether there's any benefit to doing so. (Okay, okay, this is Head-Fi, so the real question is "why not?"...)

Quote:

I heard tell elsewhere of using J309 as a constant current source. Idss can get up ~30mA. Or you can look at J310 which the datasheet shows as a Idss of 24mA to 60mA. I suspect you can drop either of these in on the board.

Looks like the J309 and J310 are perfectly pin-compatible, so those should be good substitutes for people seeking more power.

Quote:

I've been playing with DACs lately, but been definitely having the urge to working with these boards again.

A seller on eBay used to sell these fairly decent stereo buffers for $10 each with free shipping; I've used 'em on a couple projects, and for $10 shipped, they're hard to beat. I went to pick up another one a couple weeks back, and discovered the price has jumped to $20 a pop, and I though heck, for that price, I can make a set of boards for a higher-powered Monofied Sijosae buffer, tack 'em on to a BatchPCB order, populate 'em with parts I've got laying around, and still come out ahead. Sure, there are other options, but why use one FET when six will do the job better?

 

[mono]

Seems like it's time for you to do a layout with a POT instead of a fixed resistance, then blind test it.

I may be crazy but I think I hear a difference when bias goes up enough to heat the transistors. I mean they sound better before they warm up too much. Now that I wrote that someone is bound to come along and feel they sound better hot rather than worse.

 

[cobaltmute]

Quote:

Originally Posted by mono /img/forum/go_quote.gif I may be crazy but I think I hear a difference when bias goes up enough to heat the transistors. I mean they sound better before they warm up too much.

But is that a function of bias or heat? Bias normally equals heat, but if you could bias deep and keep it cool, would that sound better?

So many variables with the biggest being human preference. That's what all makes it interesting.