spritzer

This wouldn't be a fair comparison since the HE90 output runs at a lower bias (500V) and has a higher value ballast resistor compared to the Stax output.

Happy Birthday Nate!!

The new ones certainly do. I only use a cheap Tag though, my brother got the watch bug... Edit: Should say that I'm not talking about the noise in the gears but rather the wristband rattling

Since I've never heard the squealing noise it's hard to know what's going on but the phones having a physical shock causing the squeal could point to dust issues. The dust covers on the ESP950 are suspect so it ic certainly a possibility in combination of the lack of an output capacitor on the KG bias supplies.

I usually call them Rattle-X (way funnier in Icelandic though)

Team Tag does indeed approve!

Great work there Colin. I've had to do this a few too many times and I get angrier at Stax each time. I've seen this on pretty much any amp built after 2000 so there are a lot of 100V amps which are a pain to convert but not all.

The non SE version certainly did but those output tubes look like 6H30's so probably less heat involved Very much Krell KCT...

Good luck Nate.

Stax probably have a few T2's still in use and given how similar it is to the basic BH design, they sure know how the phones sound when properly driven. I do think that a redesigned 007t with ECC99's and a simple CCS would put the Stax amps back in the running, especially if the Yen finally drops a bit in value.

I'd say 36.345%, with a margin of error of 0.003%... For me the music just snaps into focus with more power. The imaging is more precise, bass is more linear, treble extends further etc.

The only semi sensible readings I've been able to get when measuring any of the SRD supplies is with my VTVM and they are still a bit off. The Mk2 SB unit has an 82V transient suppressor and a 7 stage multiplier but I can't find my schematic of the Mk1 SB unit so I don't know if they stuck to the two stage design with an 82V entry and thus only having 160V bias. As for the diaphragm shorting out into either stator, I've never heard that present as crackling. More like squealing as the diaphragm is oscillating due to the forces acting on it not being equally distributed. Crackling has always been due to excessive bias. Also if the diaphragm were shorting out then you would get drops in volume but only gradual as the high resistance of the diaphragm stops and real amount of power from moving across it. You can normally listen to an ESP with no bias for at least a couple of minutes until the charge is fully drained.

Are you using a 5M ballast resistor with them on the exstata? I never had any issues with the bias on 3 different sets and multiple bias supplies but something really strange is going on here. Long live Koss and their overly complicated ESP designs.

It's rather more complicated then that as you have to account for the load presented on the voltage multiplier as well. The 10M load presented by DMM is very low compared to the diaphragm so I'd personally not go this route. I'd rather measure the AC input input in the the bias supply, see what the value of the transient suppressor is (i.e. the two zener's back to back) and then do the math.

If you have a variable bias supply to see how they act at 300V and upwards while playing with ballast resistor values. When the first of the Meier HE90's shipped then users were experiencing noise issues with them running off a Stax 4M7 Pro output jack but they were better when fitted with an inline 5M resistor. Worth a shot...

You might be right there Marc but it could also be so that Koss can eliminate the amp as the source of the issue. With the SP amps then the phones were often blamed for something which was clearly the amp malfunctioning. OTOH the E90 has so much voltage output capability that a 300V bias should be more then enough. I'm looking at the only pics I have of an E90 and the bias clearly comes off a large trace (which goes around the edge of the board) and into a voltage divider (can't read the values though as there are wires in the way) and with the bias wire connected between the ballast resistor and a cap. What bothers me is that Stax never used this setup even when they used voltage dividers off the B+. They always use a separate ballast resistor... Anybody with an ESP950 want to do some experiments?

The Sr-Omega beats the HE60 hands down at everything except maybe comfort. The HE60 is just so damn light...

Most modern transformers are designed to handle both 50/60Hz so that shouldn't be an issue. Fair enough...

Tru dat. If the gear is meant for the Japanese market only (i.e. most of the older high end stuff) is unfortunately 100V only.

Plitron's certainly aren't cheap...

SumR only makes the transformers so you need some chassis to put it in. Something simple like aluminum plates attached to a wooden frame would do the trick.

I don't think it is a good idea to run 100V gear off 120v. In terms of tube gear with unregulated PSU's, you are seeing a lot more voltage on the secondary which is then further stepped up by being rectified. Lets say a 400VAC output from the transformer which would give us 564VDC. Now run the amp off 120V and you have 480VAC which is 677VDc and that could be too much for the capacitors. This is an extreme case but many tube amps run at these voltages (or even higher) and use very simple PSU's. I have no idea without looking inside but they do look a lot like one of my cheap ones (230V to 100v/117V) and it is good, not great. I have a huge vintage transformer which is better but then it is really heavy. It's also got multiple taps so I can fine tune the output voltage. I would try to find some surplus stuff in your area but something like these in the link should be more then good enough. Then there are always custom Plitron's and SumR units...

You right click on it and go to route trace or something like that. At least that's how it was on the older version, haven't used the new one much.

Yes and no. I auto route one trace at a time and then fix it if I have to. Most of them I do tweak if just for the cleaner look.

The only issue I have with step up/down transformer is that their build quality is often quite bad since they are built to a price. Few have cores large enough to do the job properly since they try to keep the weight down. OTOH a well built step down should even bring benefits over connection directly to the wall by offering galvanic isolation and removing all DC from the power line. You can have somebody like SumR make you a proper main transformer which should cost a lot less then the price difference is between imported and domestic models.