luvdunhill

that's good. thanks! no need to grab temperatures. If you don't think the heat sinks for the output stage can take anymore, your instinct is probably right.

what about the PSU heat sinks? If they run hot, is there room to beef them up?

Hey DigiPete and Pars: How much extra heat do you think you can dissipate in your Dyna-? Today's efforts are pretty much geared toward you guys and I'd like some sort of estimate on the lower end bias we need to support. If your heat sinks are pretty much maxed out (cannot hold hand on heat sinks for less than 3 seconds) that's one thing. If they barely get warm, that's another thing.

best damn 1kHz sine wave I've ever heard. Fixing to bump it up to 10kHz, be right back..... bliss...

I can take some measurements for you tomorrow if you'd like, let me know. Now that I've played with the bias, I'm going to recommend to put a series resistor inline with the bias pot. I can calculate the proper value, as there is in fact an upper limit on this value, assuming 4 devices minimum. I replaced the pot with a 50K and still cannot get as low as I'd like (well, as low as *you guys* would like ), so more experimentation is needed. Need to find some 10k resistors, then some desoldering.... then try again, repeat ad nasium.

Using the Squeezebox as source, as I don't have another source with volume control. I'll wire up an attenuator tomorrow. I'm happy with the volume at 50% on the SB. Offset is 0.00mV +- 0.05mV.. unbelievable.

yeah, we've both been staring at amb's beta24 for too long oh, and listening to music now Fostex T50 are driven quite nicely

Unfortunately, that assumes the devices are heatsinked. My rectifiers are running pretty warm at drawing 1A... It would be a huge PITA to have to use an off-board bridge.

I haven't been able to get it in Texas. I've looked at all the tobaccinists in the major cities. I used to be able to even get it in smaller towns quite easily, but not anymore, so I presume the rumor is true. The same is apparently true in Southern California. Not a single tin.

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.