luvdunhill

TO3P, not TO3 Similar to a TO-247 package. Yes, the metal can TO3 would be pretty hard to do. For how to mount and heat sink, it would be similar to TO-220, see the 2 pics posted above. I don't have any immediate plans for using these output devices. The Hitachi LFETs are probably some of the more counterfeited devices out there. The Magnetec/Semelab/"whoever the heck in the UK they are now" versions are pretty cool, but cost an absolute fortune, and for matched versions, you better forget it (they were often sold as matched sets, and if you don't find them this way on the used market, you're kinda hosed). I think these versions (and their other "improved" devices) are probably the holy grail of (L)FETs available for power amp use.

What about putting in a subpanel in your listening room? I've been contemplating whether or not there are merits in this topology for a while. I think there are a number of proponents of this over at Audiogon ... you could ask over there as well.

part of the reason I've started attributing this fact to is the relatively poor channel separation that vinyl rigs have... it's like built in crossfeed

Jacob: Looks fantastic to me! I do need to sit down and verify the schematic though... I have a few questions. What footprint are the large output resistors? I think it would be nice to accommodate two Digikey part P2.0W-2BK-ND per location (used in a lot of Nelson Pass designs) and if someone wants to drop a lot of cash, the Mills MRA-5. Also, could the TO-220 regulators be omitted for the TO-92 versions? Basically these just have to regulate the Iq of the opamp at a 15V drop? I'd increase the pitch of the four PSU bypass films. I think something with LS=5mm and 5.5Wx7.2L (i.e. Wima FKP2 10nF) would work well. Finally, what are the dimensions of the large PSU rail caps? 5mm pitch by 10mm diameter? I just want to have a particular cap in mind for that spot before we commit on the boards, as it seems that we have room to increase the size slightly.... We should look at the standard candidates from Panasonic and Nichicon. Very nice by the way.

dunno yet. crossing fingers though...

man, I had no idea how big this custom R-core would be......puny Ebay model shown for scale.

Ok, just remember power doesn't (always) equal gain. You can have a 500W amp with zero voltage gain.

I think we went over this in the thread somewhere, have a look for the exact output per device. It of course depends on the number of output devices and how it is biased, so you could scale it back (or up) quite a bit. Let me ask it this way, how much would power would you like?

Jacob: pesky me again... so, I was thinking... would it be possible to add another set of pads, similar to the photos below to support the TO-3P Hitachi laterals? They share the same pinout and it seems to me that they could be accommodated pretty easily.. the deal is you would obviously not populate all 8 spots, since you'd want to run them harder, so this would deal with the fact that things would look kinda silly with 8 TO-3P devices next to each other. I see this was talked about a bit at headwize and I don't think the daughter-board idea is worth the effort, but adding 2 more pads for half the devices might be more reasonable. What do you think? This would be outside the scope of the group buy, but perhaps a nice addition for someone to play with down the line (i.e. speaker amp applications).

looks like our calipers are ~0.06mm off from each other. Thanks, this was very helpful! oh one more thing, do you happen to have a 3.5mm diameter drill bit? perhaps you could measure the diameter of that for me as well

don't underestimate first reflections that take place on the ceiling. I think there is a lot of advantage to treating this location... a close second would be the rear wall. One book I would recommend that is somewhat tangential to this subject, but allows you to approach it in a more subjective manner is TESTING LOUDSPEAKERS by Joseph D'Appolito. Pretty much the de facto standard and depending on whether or not you plan on setting up a measurement jig to measure the various changes you make to the room, this can be a fantastic resource.

yeah, your numbers vary a bit from mine. I'm surprised you see any variance from pin3-4 and pin2-3 and pin5-4, I do see a little, but I think that's just variance in the plug construction. The trick is that the line that passes through the two pins under measurements must be perpendicular to the calipers, or you're measurement will be off a bit. How about 7.86mm for this measurement (pin3-4,pin2-3,pin5-4), how does that look? Also, I get 2.39mm for the pin width, so this could just be calibration error between our calipers.

nah, then we wouldn't have the joy of answering upteen PMs about this if it was in concise form somewhere.

I just measured the male WPI connector. It varies by 5%, in that the pins are 5% closer to the center. Interestingly enough, each pin is 0.2" away from it's closest neighbor, center-to-center. Now to decode Spritzer's results.

obviously you didn't get the memo: HeadWize - Project: All-Triode Direct-Drive Amps for Electrostatic and Electret Headphones by Kevin Gilmore

ok, moving this to the Stax thread. Here are the measurements I get for the male Stax plug: pin1-2,pin1-5,pin5-4: 0.212"+-0.005" pin2-4: 0.425"+-0.005" (twice the above distance) pin3-1,pin3-5: 0.411"+-0.005" ... interesting asymmetry, not what I would have guessed. Perhaps that's why the WPI sockets don't fit so well (I've never used one myself). edit: Spritzer, perhaps you could check this on a 6-pin plug as well? Perhaps it is more symmetric?

removing SMD opamps isn't my idea of a fun night ... I'd recommend clipping all the legs off, basically destroying the old opamp, then use flux on the area and finally solder wick to pull the old legs off.

Jacob / Others: Has anyone considered using CMOS FET switches? I notice Analog Devices and Siliconix among others sell these. I know that both BAT and Ayre uses these in some of their equipment.

yes, they will be compatible with the Dynahi boards. Thanks for the offer

Colorado might work better for my version... you guys don't have to turn on the AC in March

I will prototype one channel and take it with my other projects up to Pete Millet to run through some tests. No promise on time frame though, as he's out of the country a lot and I have some other things that take priority. My one requirement is that we nail down the board dimensions and location of the output FETs and agree not to change those specs, if there is a second run.

CTC Blowtorches for everyone!

Chris main point was the "accessories", and his main issue was the sigma22. I don't see any reason that this won't work, and Kevin and Ti have stated the same thing. Nate's point is more general. The parts and topology in this amp are very standard. I'm not sure I understand the risk. It's not like your going to find another JFET to use or something else more suitable for VAS stage. And the diamond buffer is pretty straightforward, wouldn't you agree? I would agree if we were ordering resistors, but it's not as if the semiconductors won't work in this topology. If you have a particular concern about parts and their intended use in the circuit, please let us know!

if/when Jacob reads this thread I'd like to offer another suggestion of adding another set of pads right next to the current pads, but spaced out slightly axially so a second resistor can be piggybacked on top of the (currently) single ballast resistor per output device. I'd like to experiment with lowering the ballast resistor, as I'm expecting we will get good matching...plus this will allow more power handing here in case we want to up the bias substantially.

I'm glad this thread was made, 'cause there isn't one a day over at HF or anything...