spritzer

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.

Tru dat!!

Happy Birthday!!!!

Seems he still has thousands of 5687's to peddle. He hasn't totally vanished as he continues to offer new amps to people that placed orders a long time ago. Of those cases I've never seen an amp that actually had the features the people wanted, just some random stuff off the shelf. Could be something in for repair which he fixed and is trying to sell off.

For a desktop rig then the 2050 system is hard to beat. The SR-202 may be the baby of the range but it sounds almost as good as the SR-404LE which the 303/404 do not. The amp may not be a power house but it has more then enough grunt for the Lambdas and it is a design refined which has been refined for over 20 years. Now if you want an Omega, then I'd do what Milos suggested. I never said it was easy but you should be able to do it in 10 minutes. I will hear them soon enough...

Still in hiding was the last I've heard. It's hard to make a comeback when you have tens (if not hundreds) of thousands in gear in for "repair" that would cost a fortune to fix.

Fucking fuckity fuck indeed!

NOS SR-Omega cable... How much was the repair?

I use a Black&Decker heat gun and I can't complain but to be honest I use a small butane torch 90% of the time.

Worked on my DIY KGSS chassis. Mmmm shiny....

I hope it is the same transformer but only time will tell. If it does indeed have 6 wires from the primary then simply measure the DC resistance of the wires to see which wire is which (0-100V-117v).

I have a feeling that that CA stuff isn't half as good as any standard contact cleaner but then again I'm not an optimist. Shorting the switch would be a good idea and it will show you what the problem really is.

Since I don't have an E.90 here I asked Kevin to test his and see what's what. For the record I've never had any problems with the ESP950's I've owned over the years, on Stax amps, adapters, Gilmore amps and that crazy DC-DC supply Marc came up with.

Could be but could you do one thing for me, measure the amp output. If the amp sits at -300V then a +300V bias would result in +600. I seriously doubt that this is the case but it was something which KG did with his DC coupled tube amp.

The voltage sags in a split second and then stays at that value so try turning off the auto ranging on the VC99 and see what is the first number you see, that would be closest to the true value. Also the VC99 isn't as accurate as a Fluke 179 so I'd try decreasing the bias down to 200V or so. The mineral wool is basically glass and that doesn't conduct with these voltages.