JimL

I agree that touch is a BIG part of it. I haven't tried many electric pianos but the ones I have tried didn't seem to match the touch of a real piano. And I favor a stiffer action, like a concert grand rather than the soft ones that a lot of upright pianos have, because a too-soft action makes it difficult to get a good pianissimo. Actually when I was shopping around for a piano the best action I found was on a 7 foot Fazioli - that piano made me sound better than I know I am - just couldn't afford one. Ended up with a Falcone - the original made near Boston, not the Sejung made ones.

Has Shure or someone else published the pin-out for the KSE1500 plug? Without that you can't make an adapter. Not to mention that you need a 6 wire cable to fit the 6 pin lemo jack, although since the voltages are relatively low there is no need to use special HV insulation.

Apparently another problem that has cropped up is that someone who substituted a linear power supply for the stock switching supply caused the on-off switch on the amp to go AWOL, so whenever the LPS is turned on the amp turns on regardless of the amp power switch being off. The "solution" is to ban linear power supplies. And Monoprice has no repair facilities so they refer it to a local repair shop - I wonder if they cover the cost of repairs - that's a rhetorical question,

Why would that happen - is there a HV transient that blows the MOSFET?

Of course it's a bloke. No woman would be so stupid. ?

Wow. It cost me less than $500 to build mine.

Or, if you're cheap like me, build the SRX Plus. Based on an original Stax circuit, with constant current loads and sources to set the operating conditions.

1) Install 5 megohm safety resistor in the bias supply following the last bias cap if there isn't one or it is a different value. 2) Toss the output chokes and install good constant current loads with appropriate heatsinks. 3) Install 5 kilohm safety resistors in the output if there aren't any. If you are in the mood, put in a somewhat higher voltage transformer that will allow you to install a regulated power supply. That should fix the major issues, don't know if there are others.

I use Shure SE535 iem's on airplane flights because it provides decent environmental isolation and the noise level is high enough even with them that I figure I wouldn't get any significant benefit from anything better.

For me the issue is not so much sound bleeding out as environmental sound bleeding in with open headphones. It's pretty noisy out there in a lot of places.

Also note the low input impedance of 1 kilohm for the amp.

Electrostatic headphones and speakers have the least distortion when they have a constant charge on the diaphragm. This was established at least as far back as PJ Walker who designed the original Quad electrostatic speaker. The "rationale" for having a "large" capacitor in the bias supply, e.g. 1 uf or more, is to smooth out any residual AC so the diaphragm charge and voltage remain constant. However, once the diaphragm is charged, the amount of current needed to maintain the charge is minuscule, so that in fact even a "small" capacitor (Stax uses 0.1 uf) is more than sufficient. This is illustrated by the fact that if you use an old Stax converter box, which contains a step-up transformer and bias supply but no active electronics, charge up the headphones and then disconnect the bias supply from AC, the headphones will continue to play for some time. The large value safety resistor used by Stax (about 5 megohms) between the last bias capacitor and the diaphragm ensure that any current traveling to the diaphragm is very low so the diaphragm cannot get zapped. Companies like iFi and Woo that don't follow these design parameters either don't understand or ignore these facts. iFi Audio's use of a high voltage battery to "power" the bias supply is, IMHO, an expensive solution in search of a non-existent problem.

As I've said before, I am surprised that they didn't make the T8000 an updated T1 by substituting constant current loads for the resistors - it's an easy and obvious switch that brings it up to current standards. They already have a constant current load circuit in their solid state designs, and it's not as if the T1 is a purely tube design that can't be "polluted" with solid state elements.

As an illustration, when I was young and innocent I once decided to discharge a power supply capacitor by putting a screwdriver across its terminals. The resulting spark produced a 2mm divot in the blade. A plastic diaphragm is a bit more delicate than a tool steel screwdriver blade. To quote somebody or other: "Good judgment comes from experience. Experience comes from bad judgment."

Actually, I did a long time ago and commented on that, but totally forgot, my bad. By the German copy of the SRM323 are you referring to the Highend Amp Sirius by chance? You could also consider the SRM-T1 series, which many people think is a nice match for any Lambda series phone - although they are old enough to need replacement of electrolytic caps, which you can do yourself if you know how to desolder and solder, or any electronics technician should be able to do it for you if you don't. The SRM006T is basically the updated T1 series, although I have seen a couple comments that the T1 sounds a bit better. See comments further up the page about the difference between the SRM 323 and 353.

Wait, so the top-of-the-line T8000 uses a cheap tail resistor on the input instead of a current source? Are they at least running it from B- to make it as big as possible? Are they also using resistors instead of current sources elsewhere in the circuit? I think I'll stick with my old T1 with CCS output loads.

Ah, did not realize that, thought the 323 and 353 had similar circuits. Oh, well, live and learn. Is this a biasing issue?

Although if @zoide has single-ended sources I'm not sure there is any advantage to the 353 over the 323, other than that new amplifier smell. ?

If someone is building a GG for you they should also set the balance/offset, so you should be good to go.

Birgir is correct, it costs nothing extra to do it right.

Sorry, didn't mean to be insulting. Carry on.

Note that KG's boards are designed to use the ceramic insulators - you can see the thickness of the insulator outlined on the board where there are on-board heat sinks. Considering the minimal cost and the fact that they have been used on many successful builds without issues, I don't see the point in playing around with mica or silicon insulators, other than contrariiess.

For a cascode stage (SRX, T2) I prefer to use one tube as the lower and one tube as the upper. The reason is that the input tube cathode sits at ground (roughly), whereas the upper tube cathode sits a a positive voltage. Most input tube types specify a maximum filament-to-cathode voltage of 100 volts max. So the potential issue if you use a dual triode tube per side is that either the lower or upper cathode filament-to-cathode voltage will exceed that maximum, leading to shortened tube life. OTOH, if you use one tube for the lower and another tube for the upper and float both filaments, you don't have that issue.

A few comments: 1) absolutely agree with KG and spritzer about ONLY using the ceramic insulators. This was explicitly stated in the parts list in my article. 2) the safety resistors are 5.1k, NOT 51k 3) for the T1, a 4.7 megohm resistor also needs to be added to the bias lines going to the output sockets - Mouser has a 1/2 watt 4.7 meg/1600 volt resistor that does the job. Don't know if the 006 already has this. 4) I recommend setting the CCS at low voltages before installing the circuit board - if you don't have a low voltage PS a 9 volt battery will do the job.

No problem. Dropping R19 to around 19k should do the trick. Also, if R12 is increased to 11.8k, the gain structure will remain unchanged.