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The Stax Thread III
Dec 24, 2023 at 5:51 PM Post #24,706 of 25,522
simmconn said:
Unlike the dynamic headphones, the estat is a capacitive load. It doesn’t require much current at all at low frequencies. The amp’s current output capacity determines its max output amplitude at the highest frequency the phones need to reproduce. So the output current does not directly affect the bass performance. However, the non-linearities kick in way before the amp runs out of juice. The deficiencies at the high end indirectly affects the perceived bass quality and quantity.
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So I should see a treble roll off on the Novem if there's not enough juice? Could be interesting to do an FR sweep with my transformer and one with the Novem and see if that shows up
 
Dec 24, 2023 at 6:42 PM Post #24,707 of 25,522
simmconn said:
Unlike the dynamic headphones, the estat is a capacitive load. It doesn’t require much current at all at low frequencies. The amp’s current output capacity determines its max output amplitude at the highest frequency the phones need to reproduce. So the output current does not directly affect the bass performance. However, the non-linearities kick in way before the amp runs out of juice. The deficiencies at the high end indirectly affects the perceived bass quality and quantity.
Click to expand...
I've read from other amp builders that estats aren't purely capacitive and that at the low bass frequencies, the non-capacitive aspects of driver movement result in a drop in effective impedance. I've read spritzer describe the estat impedance curve as a giant bell curve, at the low end the drop is due to "driver loading".

Estat headphones cannot be true ideal capacitors because they have to move the diaphragm, which consumes power. At higher frequencies, you don't need to move the diaphragm very much, so the impedance is dominated by the capacitance. But at low frequencies, any driver needs to move more to produce a given SPL, so intuitively the power requirements of moving a diaphragm further are increased, and more power at a given voltage means more current.

I have acoustically measured using a headphone measurement rig a 3 dB drop in bass below 90 Hz on the SRM-D10 vs a CCS-modded SRM-006t when both amps were volume matched to 80 dB SPL at 300 Hz on a Shangri-La Jr. Something about the D10 could not keep up the bass even when the amps performed similarly at higher frequencies.
 
Dec 24, 2023 at 10:51 PM Post #24,708 of 25,522
SolarCetacean said:
I've read from other amp builders that estats aren't purely capacitive and that at the low bass frequencies, the non-capacitive aspects of driver movement result in a drop in effective impedance. I've read spritzer describe the estat impedance curve as a giant bell curve, at the low end the drop is due to "driver loading".

Estat headphones cannot be true ideal capacitors because they have to move the diaphragm, which consumes power. At higher frequencies, you don't need to move the diaphragm very much, so the impedance is dominated by the capacitance. But at low frequencies, any driver needs to move more to produce a given SPL, so intuitively the power requirements of moving a diaphragm further are increased, and more power at a given voltage means more current.

I have acoustically measured using a headphone measurement rig a 3 dB drop in bass below 90 Hz on the SRM-D10 vs a CCS-modded SRM-006t when both amps were volume matched to 80 dB SPL at 300 Hz on a Shangri-La Jr. Something about the D10 could not keep up the bass even when the amps performed similarly at higher frequencies.
Click to expand...
I've done 'small signal' impedance measurement on the Stax phones using an LCR meter and they are very close to a pure capacitive loading. You brought up a good point that large signal measurement may be different. So I did a rough measurement with a DIY T2 and a pair of SR-404. The frequency is spot-checked from 20Hz to 20KHz. The output voltage is recorded as Vout. The 5.1K output protection resistor in the circuit is used as the sense resistor to measure the output current. The SR-404 is on a miniDSP EARS so it is properly loaded acoustically. You can see that there is no 'bell curve'. The calculated impedance decreases monotonically when frequency goes up, and it is quite close to the impedance modeled after a simple 110pf capacitor (last column).
If I see an acoustic frquency response issue, I would double-check the output amplitude of the amp and see if it is dropped already.
Freq (Hz)
Vout (V)
Vrsense (V)
Iout(A)
Impedance (Ohm)
Imp-C110pf (Ohm)
20​
98.75​
8.50E-03​
1.67E-06​
5.93E+07​
7.23E+07​
50​
98.9​
1.99E-02​
3.90E-06​
2.53E+07​
2.89E+07​
100​
98.9​
3.16E-02​
6.20E-06​
1.60E+07​
1.45E+07​
1.00E+03​
98.9​
3.43E-01​
6.73E-05​
1.47E+06​
1.45E+06​
1.00E+04​
98​
3.3​
6.47E-04​
1.51E+05​
1.45E+05​
2.00E+04​
95.8​
6.445​
1.26E-03​
7.58E+04​
7.23E+04​
 
Dec 25, 2023 at 3:16 AM Post #24,709 of 25,522
Merry X’mas all!

Been rotating today. Moving on to the Sigma Pro. :)

IMG_1559.jpeg
 
Dec 25, 2023 at 9:35 AM Post #24,710 of 25,522
Merry Christmas, everyone!!!
I've been on my best behavior this year, so I treated myself to this big present. :grin:

S5QDV3N.jpg
 
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Dec 25, 2023 at 2:35 PM Post #24,712 of 25,522
Does anyone know a good replacement pad for the Stax 007 mk2 that is a little thicker then the stock pad? I had my LCD-2 refurbed earlier this year and the leather pads had the fazor digging into my ear. I replaced with the non-leather pad and holy crap the seal and bass improved dramatically. The stock 007 pads similarly feel like they aren't thick enough.
 
Dec 26, 2023 at 12:34 AM Post #24,713 of 25,522
Svperstar said:
Does anyone know a good replacement pad for the Stax 007 mk2 that is a little thicker then the stock pad? I had my LCD-2 refurbed earlier this year and the leather pads had the fazor digging into my ear. I replaced with the non-leather pad and holy crap the seal and bass improved dramatically. The stock 007 pads similarly feel like they aren't thick enough.
Click to expand...
Pads are pretty personal, so if you're not into this I totally get it.

I've had very good experiences with these pads on a few different DIY builds of mine. I think given their price, if they come in a size that fits 007, I say why not give them a try. Very good acoustic properties ime. The leather portions trap in bass retaining impact. The mesh portion is non-reflective and creates a smooth midrange and treble imho. They also are thicker than 007 pads by a smidge, I believe, you judge:

Ali-Ether pads resized.jpg
P1210001.JPG


I have bought some Stax adapters and if I can get the SRD-7 mkII operational again I'll be listening to some Lambda's. I am trying to get a listen to them with a similar pad to what you see here via the adapters so might be able to give better insight then.
 
Dec 26, 2023 at 1:33 AM Post #24,714 of 25,522
Cool, I need to bust out a tape measure and figure out how many mm the 007 pads are. I really wish the US used Metric like the rest of the world.
 
Dec 27, 2023 at 6:29 AM Post #24,719 of 25,522
Chefguru said:
Wow merry Christmas buddy! Who built this one?
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Thank you! This was built by a very kind and talented guy named Wang. I also had him build my CFA3 amplifier (I posted its photos here: https://www.head-fi.org/threads/kg-cfa3-headphone-amp.938064/post-17805683). He's located in China and apparently doesn't have an account on Head-Fi.
hiso67 said:

Kytuphicanh?​

Tranhieu?​

Lil'knight?​

Felista?​

Click to expand...
I'm not familiar with these guys, but after skimming through the thread, it seems like these builders have somewhat of a bad reputation?
Talking back and forth with Wang over the last half year doesn't make me feel that way; the guy was very nice and seems to know exactly what he's doing. I can't say for sure because I don't have any other T2 or CFA3 to compare, but so far, I'm very satisfied with both amps. All my headphones sound really great with them.
 
Dec 27, 2023 at 6:58 AM Post #24,720 of 25,522
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