luvdunhill

I've heard this from two very avid Dunhill tin smokers, but cannot seem to confirm or deny this on the Interwebs.

edit: Is it true that Dunhill no longer makes pipe tobacco? If so, it's a sad day and age.

VSGs are probably my favorite cigar, definitely up there with the Opus X and upper-end Fuentes.

If you're doing that, I'd recommend spacing the transistors out as far as possible. Heck, make a single "dual channel" board and evenly space the transistors across the whole thing. This is the only way you'll be able to spread the heat effectively without using the mounting bracket as a heat spreader. I think you'll get very good results if you go this route... something like this: I think you have plenty of room on the original board for whatever you're doing with the controller board (and my gain relay suggestion ), and I assumed by Icarium's comment that this wouldn't be backported to the first revision. My comment was more or less, "why not?"

At what point does the rising temperature of the board start to counteract the benefit from the tighter tolerances that the SMD devices have? I'm glad I raised all my devices off the board itself, but I'm wondering what happens in this case with SMD. It would be nice if there was feature parity between the two board layouts, IMHO.

yeah, I totally agree. At this point, I'm drawing the current I'd expect to be seeing with eight output devices. We need to decide on a reasonable adjustment range though, or at least a lower limit. DigiPete: Yeah, I have a build thread in mind and have been taking notes.

heh, my dad is a EE professor and they have a commercial resistor bridge I could match the resistors on. ok, I ran a few more numbers, you can check my math given the numbers above. The output of the buffers are running at 15.5mA quiescent, which I'd assume means these transistors are dissipating 500mW and are rated to 800mW. The input is running at ~5mA. The two CCSes for the buffers are running at 5mA and 8mA, and are dissipating 150mW-250mW. No wonder these are toasty.

I think aardvark baguette might have ...

Why no RIP threads for Ed McMahon and Farrah Fawcett?

Doesn't Berning, Bada, Decware and Antique Sound Labs have amps that would qualify? Here's an interesting one: http://cgi.ebay.com.sg/Chazz-2-Headphone-Amplifier-Assembled_W0QQcmdZViewItemQQitemZ260380466884

I was thinking about a Wheatstone bridge, or driving 100 mi to my dad's lab

Hey Steve, I just remembered I have a sub I could work you a deal on. I'll never use it, and it's way to heavy to ship. It's a 15" (I think) Citation THX sub (Harmon Kardon's upper end line, I believe). Really nice. It's been moved around a bit, but it doesn't show too much. I suppose we never had a formal agreement for the ribbon speakers, I'd be willing to trade it straight-up for that labor in a heart beat

yes Welcome to the world of MOSFETs. This is the main reason I've been hoarding the old Toshiba devices, as they are by far the most complimentary devices I've found, maybe they'll make their way into a headphone amp. If you want a good read, look at Charles Hansens comments with regard to lateral versus vertical FETs. Anyways, even without empirical data we can predict this. Check the second graph on the datasheets here: http://ezphysics.nchu.edu.tw/prophys/ael/File/Datasheet/sk214e2.pdf http://ezphysics.nchu.edu.tw/prophys/ael/File/Datasheet/sj77e2.pdf You can take the parameters from the circuit, but for discussions sake, let's arbitrarily choose Id = 200mA and Vds = -4V. For the 2SJ this corresponds to Vgs -3.0V for the 2SK this corresponds to Vgs 2.0V. That's a 1.0V difference right there. If you want to run the actual numbers from the DynaFET, don't forget to figure in graph number four, which shows transfer characteristic as a function of Tc, you'll need to figure this in to get the measured numbers to add up, which they do. But remember, the important thing is that all of the devices draw the same amount of current through the 2 ohm ballast resistors, and this is why the devices need to be matched. The 21mA difference in this case was from the absolute worse match in the pool. The other side had a 7mA difference, which was a better matched pair. The other pairs and quads should be even better. Also, I didn't match the 2 ohm resistors (I think they are 5% tolerance), and I'd recommend doing that as well. That thread and picking Kevin's brain. The kicker was keeping things stable, with respect to temperature, and the servo design. That and the literal 1% yeild of appropriate devices in the matching process. There are 8 JFETs (four if you have access to V grade devices), and 4 four MOSFETS and the rest of the devices are resistors. It's all about matching. I need to draw up some boards, but the distribution would have to be rather clandestine...

I would think the output impedance of the sigma11 would be lower than the STEPS, but what do I know. I've found this to be one of the major differences in the audibility of power supplies.

yeah, I guess the 500mA on the datasheet is a guideline. Needless to say, I lunged for the power switch pretty quick... more or less was a pulse test I have had them running at max current for a bit though, just for the heck of it and they survived.

A few numbers for j4cbo and digger945: FETs drawing 329mA, 322mA, 336mA, 315mA. Total draw on negative rail is 710mA. Toroid (160VA I think?) is cold to the touch. Gate voltages 3.39V, 3.22V, 4.55V, 4.57V 2Ω/2W resistors dissipating 0.286W (definitely want to try down to 1Ω, devices are well-matched and we have plenty of dissipation available even at 0.5W.. could stack the resistors and go even lower..) 4.7Ω/1W resistors dissipating 0.001W 10Ω/1W resistors dissipating 0.0002W 221Ω (R27-R30) 1.11V, 1.11V, 1.74V, 1.73V across them I agree with digger945 that we need to work out a solution for lower bias, but I'm pleased as punch so far. I'm assuming we will want to run the same dissipation numbers with around half this current draw, as well as maybe a quarter? I run these same FETs at 70mA in the Blowtorch... but it's a preamp after all. They sound better in this application at 100mA, but I've never had the heat sinking to go higher than that, so stuck with 70mA.

I don't quite understand. The gate voltage is directly proportional to the current draw of the output stage. So, you are saying that the thing gets hot? Well, yes it does. How low do you want to go? I'd be willing to try to lower things, but it seems that raising the pot is the ticket, to say 50K? Let me know what you'd like to try and I can give it a go. At this point I'd like to look closely at the buffers and try to get them to run a bit cooler. I need to somehow work on the back side of the board so I can measure some voltages here and there. I'll also get some music flowing for Naaman

Conrad MF35-151.5: Conrad Heatsinks - Products

pics. Note current, servo (or lack thereof), and offset. It was actually at 0.00mV for like a minute, so I wasn't trying too hard to get the money shot

2mV without the servo. More like +-1mV. even at the lowest bias, the buffers run pretty toasty. So fracking hard to get a probe in edgewise on these boards. Anyone know how much current you can put through a sigma22, assuming unlimited heat sinking for the four MOSFETs? Kinda wish I was using four simga22s

hm, pin 6 is 18.3V to ground .....

still playing with it. Starts out with 0.1 offset gets down to less than 0.1mV (the resolution of my hand held DMM). This is the trimmers set at 500 and not touched at all. I'd say they are sorta not needed. Much better than my Dynahi version. I'd say these heat sinks are rather perfect, and the long hours of matching are rather worth it. The minimum bias with the 20K pot is 750mA. Lamers may need to up this value. Accidentally had the bias at 3A for a bit... oops. Running at 1A now. The transistors in the buffer are hot, I cannot touch them for more than a second.

it works

Muse Model 9 Signaure. Wait... crap. I'm half tempted to buy one of the upper end models that will also play SACD... but haven't found a good deal on one and have to free up lots of cash to afford one...

Bigger than 19" x 13.77" x 6"? If so, then I must make mine bigger!!!!1!