luvdunhill

dude that is sooo last night...

We had 0day for Chrome the second it was publically released. Literally that second. The same will happen for ChromeOS, I bet.

more like 1/4 of a discrete I/V

I think that's where the magic pebbles go.

some green things with "tooleaudio" printed on them

whatever les_garten is smoking telling off jp#s like that...

I dunno how to explain it. Maybe someone else can better. But, this calculation is fail: 18W / 60V = 300mA / 8 FETs = 37.5mA per FET this calculation is win: 18W / 60V = 300mA / 4 FET pairs = 75mA per FET Then power per device is 75mA * 30V. And with 75mA * 30V * 8 devices = 18W we're back to where we started.

no, four pairs at 75mA through each pair. Remember, current is calculated (edit: maybe "defined" is a better word, I dunno) from rail to rail. So, if one n-ch flows 75mA then the other complimentary p-ch device flows 75mA.

no. The original design was 150mA per FET with 4 devices. See the posts above. Once you doubled to eight, it requires double the heat sink. Instead, Kevin halved the bias so he didn't have to go out and by a larger heat sink, or go from 2 boards per heat sink to one, or run the die temperature way up.

See Kevin's post above. Nothing has changed. Four FETs @ 150mA or 8 FETs @ 75mA. Same heat. I ran them harder just as a proof of concept, but this has always been the recommended current.

Would it help if I sent you a 160VA 2x30 toroid? Probably could drop it in the cheapest flat rate USPS box.

Ok, I see. I thought you recommending 75mA for the 4 FET version. In which case, nothing changes it's just as hot as we thought. So balanced would be 72W. My recommendation of heat sink still stands.

COBOL absolutely should fulfill a foreign language requirement

well, okay, but I for one interpreted your comment in post #19 as designing towards 150mA: HeadWize: DIY Workshop > My newest in the dyna series "If you run the default of 150 ma per fet, the 2 ohm resistors are fine." In hindsight, I see how that comment could have been misconstrued in a number of different ways. All that said, I think more than 75mA is better. I know there are quotes from Borbely who uses these FETs in one of his design that many of his customers preferred them at > 100mA, and I tend to agree. Here's a quote from his old website: "More is Better (sometimes)! Although the fact is well known that MOSFETS require a lot of current to sound super, I believed that the suggested 40mA or so in the output stage was optimal. Until one of our customers suggested to try more. Mind you the tiny heatsink we are supplying with the Kit can

Well, 2.5dB +/- 2dB

3 minutes? heh. Try the other feedback setting as well, once you get accustomed to this version. Need to recruit more advocates for adding a switch here

She'd probably just take it to Ray to fix anyways Oh, pabbi1, so far things have been pretty boring, except for this little "incident":

Has anyone ever looked at, or used these On Semi parts? Look interesting to me. (Mouser part numbers below): 863-MPSW56RLRAG 863-MPSA56RLRAG 863-MPSW06RLRAG 863-MPSA06RLRAG The "W" devices are rated to 1W @ 25C in free air.

I think that the MF30-100 is a solid recommendation for the DynaFET at this point. This is based on the results of my heat sink and some crude math. This heat sink is 300mm wide, 100mm tall with 30 48mm fins. The base is 8mm thick. It is rated as 0.32 C/W @ 80C, or around 0.35 @ 60C. That results in 171W at @60C. Given two boards of 4 devices and 30V rails, that right at Kevin's recommendation of 150mA, at a conservative die temperature. I wouldn't even recommend using 8 devices with these. This is my standard recommendation, if anyone is looking for one. If you're using another heat sink that you don't trust the C/W rating for one reason or another, you can use a crude method of comparing the two based on dimensions alone.

This is the prefect chance to do a little perf board project.

They are the .1%, 25 PPM/C versions: http://www.prpinc.com/pdf/Audio_PR9372_Series.pdf

I wish I could buy those PRP resistors

By "unmodded" do you mean pre-production?

I did testing specifically for your case. Just crank the pot all the way to it's maximum resistance (assuming that the series resistor I'm suggesting is added to the PCB) and pray that things don't get too hot From my testing, this will put you at nearly exactly the same current as the Dynahi output stage uses, and you should be fine. You'll have a bit more current in the PSU (you said you could dissipate a bit more heat here, so again, you should be fine), but the output stage should flow roughly the same. We can go from there.

Well, I would recommend helping out the servo somewhat, otherwise it's a bit slow as it has to overcome the fact that the MOSFETs aren't so complimentary, so it would depend on your definition of warm up. From what I've seen, it looks like 5 minutes is about the minimum for things to really settle down and the bias to drop down from the turn-on peak to steady state. During this first 5 minutes, 200mA extra current isn't all that uncommon (worse case), before the negative tempco of the MOSFETs starts to work its magic. This will also depend on how large your heat sinks are, I'd presume. During the next 5 minutes after that, it will hit the point where it becomes rock solid, only varying around 10mA during this period. Anyways, I have written down 478R / 518R for one test and 478R / 523R for another. Worse case, just install one pot... I think with 470 / 510 it will work just fine.