[sergery]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif I'd like to see some measurements of this amp, but that seems to be so far down on people's list for some strange reason, that I'll have to probably do it myself

What would you like to see? I am not a pro at measuring amps, but I have a function generator, test tracks, a decent scope, the amp of course. How is the measurement performed? I don't suppose there is enough current to loop-back through a resistor to drop some V's. Then again maybe there is? I suppose, as you suggest the capacitance's will have to be accounted for.

 

[pabbi1]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif Alex has some absolutely beautiful measurements (both simulated and with some very fancy Tek scope) for some of his other designs on his website. Pete Millet and Ti have measurements for nearly every design on their respective websites. I'd like to see something like that. Why? It has absolutely nothing to do with how it sounds, or the worth of the design. For me, measuring a project is like casing it up for some people. It's just part of the process. I'm obviously in the minority on this one, but that's cool I'd go up and Dallas and measure Al's, but I'm not exactly sure if my probes are up for the task. When I measured my other 'stat amps, I had a different scope that I cared a lot less for (i.e. invested a lot less money in) My current probes are 1:1 (150 Vrms CAT 1, 6Mhz, 110pF, 1M) or 10:1 (300 Vrms CAT 2, 200Mhz, 17pF, 10M) and I'm not sure they would do a very good job at measuring this or any stat amp. Any advise Alex?

If Mohammed can't make it to the mountain, well...

I'm off all next week, and have both generations of hybrids we can measure... oh, and Vulcan can tag along, after a bit more work. I can even build out another JUST to measure, if needed.

 

[spritzer]

Quote:

Originally Posted by sachu /img/forum/go_quote.gif In my limited experience, the BH wasn't as good an amp for the Koss ESP950 as the eXStatA is. I am only referring to the ESP950 as that's the one I have the most listneing time on in electrostats. The BH just lacked the bottom end. With the BH they were just nice sounding phones. Once i had my eXStatA going they truly transformed the ESP950 into a different beast. My full impressions are in the first few pages of this thread. I still have two eXStatAs to test here. One sand and one hybrid, build no 4 and no 5 respectively. WIll get around to testing them before Chirstmas.

A linear amp is never going to make the ESP950 a bass monster since they are lean in the bass. That's why they are so well regarded as they do not have the woolly bass of the Lambdas and are much cleaner over all.

 

[sachu]

Quote:

Originally Posted by spritzer /img/forum/go_quote.gif A linear amp is never going to make the ESP950 a bass monster since they are lean in the bass. That's why they are so well regarded as they do not have the woolly bass of the Lambdas and are much cleaner over all.

hah...the lambda Pro at least which I owned had no bass to speak of..highly tilted towards treble piercingly so. I had to compeltely undamp them to get any kind of bass out of them and then it was just muddy, loose and all over the place.
The Koss is by no means a bass monster and i didn't indicate it as such. however its abilities were at full or as close as they get in the stock enclosure when driven by the eXStatA rather than the BH.

And the main difference is not even the bass, overall the Koss just sounded much better and in its element on the exStatA than on the BH.

 

[studeb]

The current state of the art:

I hope to have a Pabbi style case made up during the holidays.

 

[runeight]

Well, as it turns out, splitting the panel will only add cost. At this point I will just get both amps and assume that they all will go out.

 

[Beefy]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif In addition to the 12V supply you guys are already using, you could take a 9V battery and strap a 10K trimmer across that and use it to vary Vgs. Then, adjust the trimmer until you get say 10mA Id then write down the Vgs measurement at that point. Then group by Vgs.

I'm at this stage now and flying blind, so I'll just post my best guess and ask for corrections......

First is for Idss, using two 9V batteries and a 10k trimmer to produce a 12V supply. Idss is measured as 1/10th the voltage across the 10ohm resistor.

Second is for Vgs using a 9V battery and a 10k trimmer, which is adjusted to produce 20mV across the 20ohm resistor (1mA). Voltage is measured on a second meter.

 

[runeight]

That looks about right to me.

Here's the latest beta 2 list. Need more sand builders.

 

[Beefy]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif That looks about right to me.

...... really? I felt sure I had the location of the voltmeter wrong for the Vgs, but couldn't work out how else it could possibly be done.

 

[runeight]

You're right, it's wrong.

You need and additional variable voltage source to provide voltage for the GS in parallel with your meter. Set the V- for 12V and then adjust the Vgs until you get 1mA in the load resistor. Then measure the Vgs and match them.

 

[Beefy]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif You need and additional variable voltage source to provide voltage for the GS in parallel with your meter. Set the V- for 12V and then adjust the Vgs until you get 1mA in the load resistor. Then measure the Vgs and match them.

.......?

I think I'm well out of my depth......

 

[runeight]

Unfortunately, the additional supply needs to bias the gate positive with respect to the source. You're gonna need another battery.

 

[Beefy]

Ugh, can someone please put me out of my misery and post the right way to do it?

 

[macm75]

Alex,
Don't forget to add macm75 to the beta 2 list
Again, if there is a tube board open, I'll take it. If not, I would LOVE to build the sand version. Regards, Joe

Quote:

Originally Posted by runeight /img/forum/go_quote.gif Here's the latest beta 2 list. Need more sand builders.

 

[Beefy]

Alright, back from Xmas shopping, how about this then?

Gate is now positive to source by a variable - and measurable - amount.