Pars

I know the thread is 15 pages, but this info is in here multiple times. Sent from my iPhone using Tapatalk

Yes, you only change one of the two resistors. ((R8+R7)/R7) x Vref ((750 + 1500)/1500) x 10 = 15 Sent from my iPhone using Tapatalk

Happy Birthday Craig!! Sent from my iPhone using Tapatalk

Linear Systems makes one now. Trendsetter has them, and they also have the LSK389. Sent from my iPhone using Tapatalk

Hmmm... interesting.

I am planning on using 1 and 2 above on both boards (ferrites and gate zobels). Bias is currently at ~150mA. I will decrease bias to 75mA and maybe 100mA and take a look at things including RMAA results before deciding where to leave it. The outputs seem to be fine at 150mA temp wise. The buffer transistors previously mentioned run hot but that appears to be unrelated to the bias level. The sim is only showing around 8mA or so running thru any of these, so not quite sure why they are getting toasty. Because of the layout tightness, it is hard to get in to take measurements. Sent from my iPhone using Tapatalk

Yes, that was good (and intense). You kind of need to factor in the unbelievable portions (released?), but good nonetheless. Tom Hardy is something else! Sent from my iPhone using Tapatalk

Put a toggle switch in the load box (33/330) and ran RMAA on the #2 board (Cordell gate zobels only). Still looks good. I had a scope on the outputs and saw a touch of oscillation when I first fired it up. None after. So the 3 "cures" for the oscillation that I have found: Ferrite beads Cordell gate zobels Amb output zobels Board #1 has the ferrite beads. #2 has the Cordell zobels. I think I will put the beads on #2 also and the zobels on #1 and be done. Dynafet2_33_3.pdf Dynafet2_330_4.pdf

I had heard some rumblings back when these were still in production that some users were experiencing failures of the HV BGs at less than their rated voltages? Sent from my iPhone using Tapatalk

Many (many) years ago... I'd have to dig out one of my books to even remember how.

Yeah, I'll rig something up. Any suggestions? The 33 and 330 ohm that I have good?

Put in the zobels (100pf-90.9R) in which seemed to cure this problem. I haven't done much testing yet, but didn't find any oscillation. Hard to find any ground points close by on the bottom (gnd plane is on top). Closest is about 2". Put the cap right on the gate pin. Resistor and teflon tubing later (x4) and done. That is the only change (other than Vbe multiplier resistor values) that I've done to this board from std. config.

Dontcha love marketing? I was laughing reading some of the article titles and thinking how self-serving these were "Television Replaced With Black Gates is Superior to Any Ordinary TVs"... I didn't realize you could watch blackgates?

Of course the 2nd board was too good to be true. Put the 2nd pair of outputs in, oscillating to beat hell now without volume up, nothing plugged in. 70+MHz (0.7 div @ 0.2us/div). Board was acting strange even before I powered it (wasn't even plugged into AC). When I put the scope probe on the R output, it showed some fuzz on the trace. Board was plugged into all I/O. Strange. When powered, the oscillation was independent of volume setting, and with no phones plugged in. Varied at times by just approaching the bench, moving hands, etc. Fun. I'm going to try Cordell's zobels on this one first. Probably use some 100pf Wima FKPs I have with 90.9R or 120 or 150 ohms to gnd. Or I have some 33pf Mica caps. Also had noticed that I hadn't gotten the devices all the way onto the angle brackets (drilled like my dynahi ones), and recalled getting pissed at not being able to accurately hit a good center punch (Starrett) dimple with my drill press, so bought some cheap center bits from Harbor Freight. Redrilled the angle bracket for the good channel. Much better. I'll redo the other one presently. Also discovered my load box is broken; Lorlin rotary switch wasn't working correctly.

Happy Birthday Naaman!

RIP Bill Paxton... http://www.cnn.com/2017/02/26/entertainment/bill-paxton-dead/index.html?adkey=b Wow... 61 way too young.

Speaking of older electrostats, anyone recall the Marantz ones from the '70s, ES1 or something like that? My brother and I used to have a set; he may still have them. Were these any good? I can't say I recall being impressed with them.

Not running any load right now, just straight into an maudio fw box. I do have a load box from tangent's plans (https://tangentsoft.net/audio/hp-dummy.html ) that I could toss on there. It has 33, 330 and I can't recall what else on it. EDIT: it has input and output jacks on it. Its been so long since I built it and used it that I forgot what all is on it

Ran RMAA on the 1st board (R ch). Everything looked fine. Re-ran it with the output zobel on, looked about the same, so my conclusion is it is working. I think for safety I will put on zobels ala Cordell. Need to find a near enough ground on the bottom. Set up the 2nd board with one pair of output devices. It biased right up, offset adjusted and looks good. I could not get this one to oscillate. No zobels or anything other than the stock configuration that I've settled on. I'll document what that is later. I'll add the 2nd pair of output devices and see what happens then. RightMark Audio Analyzer test : Dynahi-L DynaFET-R.pdf

Looks nice Michael! Only a 25VA transformer? I guess it is 700mA per secondary,

Started working on the other board last night, re-configuring it to match the first. I plan on bringing this up without the ferrite beads, but add the gate zobels to it, which I haven't tried yet. These seem more like a snubber than a zobel (cap -> resistor -> gnd). Cordell uses 39pf -> 100R; I don't have any 39pf but do have 33pf, so will probably increase the resistor a bit (120 or 150). The one Cordell uses seems to sim out at -3dB of > 10MHz. I may increase the cap to 100pf, but I'll try it with the 33pf first. I'll report back on how this behaves without the ferrites. I also plan on running RMAA on the first board, with a Dynahi board in the other channel. If things look amiss, or even if not, I will re-run this with the Amb zobel on the output and see what that looks like. If that looks better/different, I may put the Cordell zobels on this board and see what that looks like.

I would. Lately, orders from Arrow have been using fairly large antistat bags for everything. You can also buy them with ziploc-type closures. Places like OfficeMax or staples carry them I believe. Sent from my iPhone using Tapatalk

The best way that I have found is to use heavy stock and number in rows. I use 3M double sided tape to stick the devices on, then put it in an antistat bag. Add the measurement key, or just have that in a spreadsheet. Sent from my iPhone using Tapatalk

Brave man plugging good phones in [emoji4] The ones I am using are real crap Sony something or other. $5 and you overpaid... I would bet that the output zobel would take care of that for sure, the gate zobel (Cordell) probably, and the ferrites probably. Some people do quite involved zobels with inductors etc. from gate to drain. Sent from my iPhone using Tapatalk

Ahh, so that's what the software is for... now onto the maths! Very cool!