mwl168

If the arcing is between B+ and O- why only one of the terminal block pins is charred?

There is no short supply of people with more money than sense. Some of these people cannot even tell when the left and right speakers are wired out of phase from each other. The only way they know to "judge" good gears from bad is by looking at price tags and reading BS reviews. Plenty of companies out there with little pride in their products know this well and are more than happy to exploit this phenomenon.

Maybe Kicad knows something we don't?

I have also been listening to my Grounded Grid with a matched quad of the beam tetrode EH 6CA7 and like its sound a lot. JJ and EH seem to be the only manufactures of current production beam tetrode 6CA7. Most other current production tubes labeled 6CA7 are really EL34 pentode.

Try this one on eBay, I've bought them and they work very well. http://www.ebay.com/itm/100pc-CMC-8P-Tube-Socket-Gold-Plated-Pin-Hex-Snap-2x10mm-Hole/130342225019?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

I don't use a preamp. My DAC has a digital volume control and it feeds the headphone amps directly.

At long last, I cased my KGSSHV - my first foray into Kevin's Wonderful World of DIY ES Headphone Amps. Although its glory has been over-shadowed by the HV Carbon and the Grounded Grid alike, the KGSSHV is really a damned fine sounding amp in its own right to my ears especially when set up to run at higher output current. There are many versions of KGSSHV out there starting from the on-board heatsink version that runs around 5mA output current to the later off-board versions. This one runs at a toasty 15mA and raised VAS current and is powered by the same GRHV/GRLV universal PSU I use also for my Carbon, Blue Hawaii and Grounded Grid.

Welcome to Head Case Boinger! Coming from my own experience of building a KGSSHV as my first KG ES amp and later built the HV Carbon and others, I would say the HV Carbon is the easier build with current production parts that are much easier and less costly to source and probably a better sounding amp overall. I have the Carbon V5 and V6 amp boards and the biggest difference is that the V6 has ground plane while the V5 does not. Many here have built both versions successfully. I built the latest KGSSHV off-board heatsink version but don't recall its version but can find out if you like me to. I cannot help you with the amp boards but PM me if you are interested in the GRHV and GRLV PCB. I have a few spare sets on hand. Good luck with your DIY ES amp journey! It's lots of fun!

Thanks Kevin. One suggestion, would it be better to turn the 100VDC/Ground terminal block 90 degrees so the wires won't be crossing each other?

Speaking of such, anyone has update on the new Stax USA distributor?

And maybe move the speakers a few feet away from the back wall too if possible.

Kevin mentioned in his post some time ago that the opto servo only works in one direction and it needs the cold-start offset to be +15VDC or higher to function IIRC.

I think having only one jumper shorted is the correct way. IIRC, to engage the opto servo, you need to have both the OP27 and 4N25 installed and short the jumper next to 4N25. To engage the OP27 servo, you short the other jumper and don't need to install the 4N25 and leave the jumper next to 4N25 open.

To date I have been using my Grounded Grid without either of the servo enabled. Similar to my Blue Hawaii, it takes the GG about 80 minutes to reach stable state offset without the servo even though it runs much cooler compare to the Blue Hawaii. Last night I engaged the opto servo and made some observations this morning. I am using OP27 and 4N25. I have TL081 on hand but cannot use them in place of the OP27 because I run 18VDC rails on my front end. I first adjusted the cold-start offset to +12VDC (reference to ground) in order for the servo to work. I measured the offset between the left channel + output to ground, the right channel exhibits very similar operation. The balance has been previously adjusted to as close to 0 VDC as I could after the amp is fully warmed up. With the opto servo engaged and from a stone cold start (time pint T, room temp regulated to 24 C), the offset is about - 3.3VDC, it steadily went down to - 0.3VDC at T + 3 min.. At T + 5 min. point the offset is about + 0.3VDC. It went down to + 0.005 VDC at T + 29 min.. At the T + 60 min. point the offset is about - 0.16VDC and the heatsink temp is at a steady 36 C. At this point I lost patience and decided I prefer to listen to some music instead of staring at the voltage meter. I've read in the thread somewhere that the TL081 is faster acting than the OP27. At a fraction of the cost of OP27, I think the TL081 is worth a try if your front end supply rail is less than 18VDC (TL081's max. voltage supply rating). Hope someone can chime in and share their experience.

The whole thing somehow looks much better to me with the tubes in. Pictured are the fat bottle EH 6CA7.

Must be eating lots of Salmon sashimi

Ah, it makes perfect sense now. Hi, 老外!

The decorative rings arrived. I fitted them to the chassis mostly to cover the poor drilling job of the holes. These rings have 54mm outer diameter and 36mm inner diameter and are about 10mm tall. One thing of caution - they make installing and removing the tubes much more difficult because they get in the way of grabbing the tube base.

If you are referring to the 50 ohm resistors on the EL34 plate CCS, 1VDC measured across the resistor gives you 20mA ( I = V/R, 1/50 = .02) of plate current which I think is conventional. I've know builders that run their Blue Hawaii from 18mA up to 25mA. The Blue Hawaii runs HOT, so need to take into account the heatsink size.

...wearing your pajama.

Thanks! I posted about this "universal" PSU in the Carbon thread I think. It's a GRHV tuned for 400VDC rails and a GRLV tuned for 18VDC rails. It also has 2 sets of 6.3vac/4A secondaries from the Antek AS3T325 transformer (300VA, 325v/450mA x 2 and 6.3v/4A x 2). I put a switch and thermistors on the 325v secondaries to function as a manual B+ delay. I originally had one resistor in series with each of the two 6.3vac secondaries to lower the filament supply to the EL34 but have removed them a few weeks ago when I realized I was already losing a few 10th of volts between the tranny and the amp board. I bought a 7-pin female chassis socket I intend to replace the male one I am using now but have not gotten around to do it. I don't have small children in the house to worry about but I have been known to do stupid things that only 5 years old would do (according to my wife).

A few more pics of the Grounded Grid with the top cover on, including a side-by-side with the Blue Hawaii built using the same chassis. Got a set of tube socket rings coming. Will decide if to use them when I have them in hand. Drilled a few more holes on both the top and bottom plate of the Blue Hawaii to help ventilation inside the chassis and hope it'll run cooler. Will likely do the same for the GG.

Not familiar with the circuit and the board you are using. But if it's like other KG ES amps, you need to disable the offset servo when you adjust the offset trim pot then enable the servo afterwards.

Thanks! the chassis is BZ3608A I purchased from TaoBao. Also available on eBay. It should fit the Megatron fine except you don't need heatsinks for the Megatron.

Another Grounded Grid lives. Have been listening to it for about a week. Powered by the same GRHV/GRLV PSU I use to power my KGSSHV, Carbon and Blue Hawaii. 400VDC rails and 20mA plate current. Using EH 6CA7 - the true beam tetrode not pentode. Runs much cooler than the Blue Hawaii. A tough job remains to drill the holes on the top plate. This is one fine sounding amp!