spritzer

I do have two 450V transformers in stock so that would be workable. Perhaps we should take the T2 psu board and adapt it to the HV for offboard sinks? I'm also going to cut the onboard pcb files down in size when I have time.

They did but I had to pay extra since they were more expensive to source now. Didn't have much of a choice but I'll never buy anything from them again. They were quick to shut up about me having to test the parts on arrival once I told them with a reputable seller such as Mouser or Bdent there was no need for testing.

That's what I keep telling myself when I buy these large lots. WRT upping the HV bias keep in mind just how far the transistors can be pushed. 20mA at 500V is a lot of power and the PSU needs to be oversized as well. My plan is to lower the rails to 400-450V and increase the current that much more.

If these are the same Dalbani then I sent them 600 or so fake 1968's earlier this year. They were an utter pain to deal with and tried to make it all my fault for not testing the parts when I got them.

Those look horrible and sound even worse.

HD800 and a roll of tape?

To change the current in the fourth stage you have to increase the voltage reference, i.e. the led.

Yeah, inrush current is a concern but even the simple tricks used in the Firstwatt amps will make it much easier to deal with. The problem we are talking about is the insufficient current draw from that huge core so the output voltage will rise. The PSU has only a single prereg cap so 500V is the max operating voltage and the transformer could easily reach 340-345VAC which is right on the limit. This also makes it harder for the PSU to regulate to the correct voltage and excess voltage will just lead to more heat.

Nylon will do just fine and if you are going to use the Antek 400VA transformers then look out for excessive rise in output voltage as the amp doesn't draw that much.

The only problem I see is heat with something like this. The BH runs hot, very hot and I've seen enough of them burnt up to know there is no such thing as enough ventilation. That means over spec everything, transformers, heatsinks and ventilation slots. Those PCB's also have some known issues so take care with the standoffs you use and where you use them as some high voltage lines are a bit too close for comfort. The mosfet heatsinks have to be grounded and use the thick pads on them. The amp gets rather hot there so you might want to look into some larger sinks there as well.

Thanks Todd!!

Australian, Canadian, Swedish and British, all brilliant in their own way.

Rake Billable Hours Wire in the Blood Foyle's War Wallander (both versions)

It's a lovely sight when one of these springs to life.

Hell yeah!!!

I've tried to get the Senn engineers to open up about this but they just refused to answer. Very German of them too... After a few hours the 120ohm adapter test has ended in utter failure. The sound was just too soft and bloated with it in place so while the top end bite was diminished a bit it also killed the near ESP bass these cans do so well.

I agree but half the fun of DIY is to try crazy shit. Only reason I'm building a "lovely cube" type amp...

Not cheap and no mention of the actual specs.

I just made a short adapter cable with 120ohm resistors (Vishay metal film) inline for the Dynalo/HD800 combo. The volume difference makes A-B comparisons all but impossible but there is a clear change to the sound. Whether this is better or worse only time will tell...

The plot thickens... We tend to have that effect on people. Here the Senn reps contact me first and then tell the other Sennheiser distributors stories about "this crazy guy". They really liked the story of me bringing a gigantic 20+kg amp (ESX) to power the HE60's for a comparison against the HD800.

I'm sure Tyll is right about the origins of that standard. Knowing the Germans they might still be using it though... Does anybody know the spec of the Beyer A1 amp? I couldn't find the schematic either... I'm with Justin on this. Those resistors (5.1K actually) are there for short circuit protection should the stator become grounded or touch the housing. This is a problem with the metal case headphones and the previous solution was to wire 10M resistors from the stators to the housing.

That is sad.

I'm going to order some boards soon, one for me and one for Kevin.

There is certainly something to the IEC standard in all of this but I've never gotten the Sennheiser engineers to reveal anything in my discussions with them. Still, this is easy enough to test with adapters so some cheap TRS plugs are on my shopping list... Funny story, does anybody know why the new Sennheiser amp has a window on top? To save crazy people like me time ripping it apart... This is what the head of Sennheiser R&D said at the recent distributors meeting but I'm still going to get one and rip it apart...

The HE60's are also better... More neutral and with a more honest soundstage. They just love powerful amps and work perfectly on Stax Pro bias outputs (with an extra ballast resistor inside the plug). They also weigh nothing so very, very comfy.