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this makes me smile a lot

Close to finish casing my balanced CFP amp. Waiting for a 4-pin XLR socket. This one runs on 26VDC rails and 220mA bias current. I am posting an unfinished amp because I want to report that I tried OPA551 for the servo OP and it appears to work fine at less than half the cost of OPA445 but only good to 30VDC. something to consider for those that may be in the process of sourcing parts for their builds. The bias current proves tricky to dial in. It drifts downwards as the amp warms up and seem to continue to go lower even after a hour of operation. The range of drifting is significant too. I am observing 70mA and possibly higher.

So I've been looking at a bunch of tube/solid state hybrid dynamic amp schematics, and every one of them is some form of bad, or really bad. (one person/ex company in particular) Low voltage plate, capacitve coupling of a high impedance source into a low impedance, poor balance etc. There had to be a better way. true balanced input. dc coupling. low impedance output. no feedback. proper use of a tube (pure transconducance) etc so I came up with this, work in progress. 4 x 3 inches ubaltobaltubeschem.PDF

Thanks! The bias current drifts at 22VDC rails sitting in open air as well. I do think that it drifts more with higher supply rails and with all the guts in the chassis (re: higher running temperature). By the way, although this chassis makes for a compact and neat build, I would suggest using a larger chassis unless you like your amp to run rather warm. The heatsinks for the amp boards are adequate (45 C after 5 hours) but I think the pass transistors of the GRLV are putting out lots of heat - case temperature is about 55 C bolted to the bottom plate. It probably has to do with my stupidity - I am using a 28vac trafo so the pass transistors have to drop 12VDC and provide over 1A current. I should probably have opted for a trafo with 24 vac secondaries. (EDIT: I should mention that the Antek AS1228 secondaries (28 vac) sag to about 26.5 vac with this heavy load and with that input the GRLV could not sustain regulation for 28VDC rails as I originally planned. I am not certain how high a regulated output a 24 vac trafo can provide.) This amp rekindles my love for the LCD 2. Thanks Kevin for yet another great amp that seems curiously overlooked by many. And thanks to congo5 for leading me to it and all the help and advices through my build.

Scones to start the week off right - chocolate coconut chocolate chip. Sorry, Brent, USPS says I can't ship them.

A few more things, and I guess I missed taking a photo of the things from Friday..

I love corn bread, I'm going to have to try out that recipe.

My experience ties with Wink's, both with 280 and 380. I was lucky to grab a used pair of 280's, where the seller's dad had put on a basic Canare cable via a 3-pin XLR jack (pretty pro job, looked like the connector always belonged on the cup). More comfortable, less grating highs, and some great isolation for someone who doesn't do so well with IEM's. And then the 380 came in and sucked the royal one. Thankfully I hung on to the 280's until about 2 years ago.

Yeah, I just use whatever I have around for 1.7V red LEDs... FLV110, others through the years.

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I did, I found no video but a Spotify link which was good enough

I find all these reports of the HD250 very interesting. Firstly, as far as I can remember all the ones I have had were the older version. Seondly, the HD600/HD650 with new pads were definitely tighter on my scone than the HD280. Thirdly, I have bought and given away all my HD280's to friends who wanted a 'phone with good isolation but didn't want noise cancelling. The first HD280 was bought for US$70 brand new and sounded like cardboard until they were used for over 20 hours. Then other 4 were a mix of new and used units and pretty well sounded the same as a good run-in set from the get-go. They were IME pretty good sounding phones for mixing desks. In fact, going from memory, they sounded better than the AKG K240SS I heard at a meet on Saturday. I also once bought a HD380 which was extremely coloured, and a real disappointment, It would probably suited a person who wanted to upgrade from the original Beats to something a bit better without the woeful doof doof bass. Hope this helps....

Looks a lot like the front end of an electrostatic headphone amp (T8000-ish), but with relatively low voltage transistors (except for the KSA1156). You could always substitute a MOSFET current source for the input tube tail CCS.

And I finally made some cast-iron-skillet cornbread. It at least looks good, actual taste testing to commence shortly with the white bean chicken chili that Maura made.

Nothing so quickly, this more of a long term issue.

I’ve had my 650 for over 10 years and have never had a problem. On the other hand the headband 280 pro broke after a year and I treat everything I own with care. In addition, my head is much smaller than the average headphone wearer. Plus, they were so so uncomfortable whereas the 650 and 600 are one of the most comfortable pairs of headphones ever made in my opinion. Not to mention, the 280 pro sound like crap. So I completely agree with Dusty. I am actually somewhat interested in the DT1770 to use in the office. I would love to have a closed pair of headphones that sound decent, isolate, and are comfortable. The DT 770 are one of the most comfortable pair of headphones I ever owned and isolated like crazy but were way too dark/muddy sounding. So far, I have just heard people complain about the DT1770 being too bright which is probably a good sign.

Since we've had some more talk about garbage like Lampi dacs...there is something else we have to discuss - the ifi iesl. Long story short, I was asked to look into this for a mafia member and well... I wouldn't connect my phones into this. So let's start at the beginning, the transformers have either a 1:16 ratio or 1:32 depending on the impedance switch. The former is certainly on the low side so you need some power to push this. Their claims for the transformer construction is all fine and dandy for output transformers but they never touch on the stuff that actually matters for electrostatic step up operation. The transformer capacitance is paramount and so is to keep the inductance in check. Let's just focus on the shit that doesn't matter instead... Now onto the bias supply and their capacitor "battery" claims are just so full of shit that it isn't even funny. First of though, how is the high voltage for the batteries generated? I can't see any transformer that could do that from the low voltage DC input. There are some chokes but nothing substantial enough. Also, how are they switching the bias? Those cheap arse switches? Sure fucking hope not and no normal relay can handle these voltages. Now for the really bad news, see the first picture, the string of resistors in front of the 5 pin connectors? Those pretty much have to be the ballast resistors run in series to increase the voltage handling. They are also high value resistors but I can't quite make out the value of them. Now follow the trace on left and see the cap that is there? Yup it is 10nf/1kV so it sure looks like the fucktards put a cap after the ballast resistor. Never, ever do that if you like the coating on the diaphragms... As for the whole capacitor based supply claims, if they run them in parallel then they have 3uf roughly of charge which is quite a bit and I for one wouldn't want to have that sitting on the bias supply should anything go wrong. I also wonder if their dielectric claims extended to the rest of the circuit? The PCB's leak at these voltages as do the switches and connectors.

I dig that ^ Fratellis song. Have it on a favorite in some playlist...DEEZER I think. Anyhoo....for whatever reason it flashed me back to some vinyl I have from back in college HS

I had a 280Pro about 12 years ago. Piece of junk. It’s brutally uncomfortable, painful everywhere it touches after 15min of use. It also causes listening fatigue within 30min if you can sit through the pain — probably hot treble, but I blocked it out of my mind. To add insult to injury, the cheap plastic where the cups connect to the headband will snap and break within the first month, as it can’t survive the strain of being put on and taken off the wearer’s head.

Women.

Sadly, Alexa only locks things for you. She refuses to unlock

Apropos the last image - there happens to be a place in the North East of England called Longbenton Meanwhile you can spend $1k and buy Nathan Myhrvold's new five-volume book "Modernist Bread: The Art and Science". I think I'll pass on that purchase.......

Swapped out all the smoke alarms in the house with Nest Protect 2G units. They talk to you, which is a little weird. Hopefully they're not also listening -- no mic in the specs but who knows in these paranoid days? Anyway, now have the outside security cameras and indoor thermostats and smokes all accessible on my phone in one app, which I like. Probably would have preferred to use Apple HomeKit as a platform, but the device ecosystem isn't there at the moment.

Plenty of room. After all, 0s don't take any space.