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Taking a step back and a nap is always good advice. Thank you.

At the same time, my hearing is not good enough to differentiate in a shop environment between amplifiers without level matching the headphone. Before buying, I would like to be sure (to some extent) that I pick the right amplifier.

Measuring the unloaded voltage in a Stax plug output up to 50 V looks safe to me with a CAT III 600 V DMM. On the other hand, bare wires in some configuration for loaded voltage measurements look less safe - for me and the devices.

So, if anybody in this forum has ever tried to level match a single electrostatic headphone with several amplifiers for auditory comparison purposes then I would highly appreciate your feedback.

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Isn't everybody glad that I'm crazy enough to buy this stuff and have Kevin rip it apart?   

I have compared the 009 and 009S running from the same amp (T8000) today. The room was somewhat quiet, but I had only two source options: my iPhone (connected through Apple's lightning adapter direc

Ok...I had an interesting morning.  It isn't every day that one takes apart HE90 drivers.    Sorry no picks as I was too freaked out while handling something so delicate and well...fucking unobtainium

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I would use a known source with a known signal, then a SPL meter at a measured distance. That should be harmless. Within a 3dB range your listening sessions should be perfectly equivalent.

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6 hours ago, Torpedo said:

I would use a known source with a known signal, then a SPL meter at a measured distance. That should be harmless. Within a 3dB range your listening sessions should be perfectly equivalent.

I agree that such a setup would give matched volumes within a 3 dB range. I guess that such a range can be also achieved by simply listening one amp after the other and matching volumes by short-term memory.

The only problem for me with this approach is that I tend to prefer higher SPL in direct comparison, so I would very likely buy the amplifier which gives the higher volume.

A sine signal with 50 V can be measured with a moderate DMM with an accuracy of 0.03 dB, so this would neutralise my bias for higher volumes. The problem with the Stax setup is that I cannot access the wires when loaded with the 009S. And in the unloaded case the measured voltage at the amplifier output can be far off the voltage over the headphone due to the unknown and likely different output impedances of the amplifiers.

Any ideas how to match the volumes within, say, 0.1 dB? Thank you.

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I doubt anyone selling a stax amp is going to let you

Probe about with a meter in their showroom.

Not many private sellers either. I'm pretty sure you

can pull the d10 from the list. Not enough power.

The d50 and 353x are new enough I haven't heard them.

A used srm717 would drive about anything well. 

And if you didn't like it, it would be easy to resell.

If you want it new,srm727. 

Edited by ktm
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Agree that measuring an amplifier with a device in a store isn’t practical.

Assuming the ultimate goal here is to find an amp that you like the sound the most, I would pick one or two good recordings that I am very familiar with, keeping the front end and headphone consistent and simply listen to the different amps at the volume you like and as consistent as you can sense and go back and forth as needed. Then go with the one you like the most overall.

Make sure the front end and amps are properly warmed up when you do this.

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Thank you ktm and mwl168 for your feedback. I guess that you are right that probing in a shop would not work.

The process suggested by mwl looks practical. It is just that Stax devices can be quite pricey (e.g. 700 S/T vs. D50), so I would like to make my comparison as neutral as possible. If I narrow down the amplifiers to, say, two then maybe I might be allowed to audition them at home.

Measuring the unloaded voltage and adjusting for the output impedance will probably not work with a high accuracy, at least nobody suggested an idea for it. The only way seems to be to measure the loaded voltage. And since I cannot solder, I only have one idea:

  • For some configuration of headphone, amplfiier and input I will set the volume control to normal listening level. I guess this will be less than 50 V output.
  • I reduce the input to the amplifier by a factor of, say, 10. Then the voltage at the driver (electrodes) is only around 5 V.
  • I get the cheapest 5-pin Stax extension cable (probably still close to 100$), make five parallel cuts in the middle of the extension cable of 10 cm to separate all wires while keeping their insulations intact. (In pariticular bias needs to have undamaged insulation.) Of course, the cable is detached from the circuit when doing this.
  • I remove the insulation for one channel, say, from L+ and L- for ca. 1 cm each.
  • I connect the amplifier, extension cable and headphone and I measure the voltage from L+ to L- and set it to exactly 5.000 V for each amplifier via its volume control. When this is done for all amplifiers, I remove the extension cable and plug the headphone directly into the amplifier.
  • In the end, I turn up the volume of the input to the amplifiers and keep it constant thereafter.

Any feedback would be welcome, in particular if you share a good reason to keep me from tinkering with an extension cable.

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11 hours ago, ktm said:

Plainly you're going  down this path one way or another.

Well, I have not made up my mind, yet.

I try to keep my health and deal safely with electricity. I also aim to maintain the integrity of expensive devices - in particular for those Stax products that I only would have on loan. Due to Covid restrictions it will be more like months rather than weeks until I can start with it afterall.

So, if you have comments on anything hazardous (either on health or product inegrity) in my description above when manipulating a Stax extension cable, please let me know. Maybe someone also comes up with an easy way to match volumes with high precision. Thank you!

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13 hours ago, Playmusic said:

So, if you have comments on anything hazardous (either on health or product inegrity) in my description above when manipulating a Stax extension cable, please let me know. Maybe someone also comes up with an easy way to match volumes with high precision. Thank you!

For the Stax amps with two outputs, all the corresponding pins are connected in parallel. Assuming your selection only contains such amps, just plug your multimeter's probes into the correct receptacles and you're done. 

If you still need to go with your idea with the extension cable, I think you'll only need to expose the bare wire enough so you can get the probes to contact it, so drilling a small hole with 1mm diameter would be sufficient. If you don't want to ruin a 100$ cable, just buy a pair of clamp test probes for your multimeter and attach them to the pins of the headphone plug and insert it as far as possible - it should still make proper contact. You'll need to be careful, and ensure that the probes you buy can actually wrap around the pins.

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10 hours ago, naiy8oaY said:

For the Stax amps with two outputs, all the corresponding pins are connected in parallel. Assuming your selection only contains such amps, just plug your multimeter's probes into the correct receptacles and you're done. 

That sounds very promising if I understand it correctly.

Let us consider the case that the unloaded output voltage is 100 V (for one channel) and that the loaded output voltage is due to the output impedance of the amplifier 80 V. So, when the headphone is plugged into one receptacle then the voltage at the unused receptacle is also 80 V which I can easily measure. (I found some diagrams on Stax wire configuration on the internet.)

Is my understanding also correct that when another headphone is plugged into the second receptacle in parallel (with the same settings, in particular for volume control) the output voltage would drop, but still be equal for both receptacles?

10 hours ago, naiy8oaY said:

[...] drilling a small hole with 1mm diameter would be sufficient. If you don't want to ruin a 100$ cable, just buy a pair of clamp test probes for your multimeter and attach them to the pins of the headphone plug and insert it as far as possible - it should still make proper contact. You'll need to be careful, and ensure that the probes you buy can actually wrap around the pins.

Thank you very much for pointing out the simplification with the 1 mm hole. This was exactly my wish for posting in this forum that someone would point out a simplification which was not obvious to me.

And the ide with the clamp test probes is even better concerning cost and process. I now found the probes below which look suitable. spacer.png

Thank you very much for your excellent feedback. I would give two likes if I could.

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This looks like another fine product of Ho Chi Minh City.

There certainly seems to be a lot of big caps. God knows the 

creative ways they are trying to kill us with now.

 

carbonclone.thumb.jpg.fd5a3a01c38c8ce60c73781409e13de1.jpg

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10 hours ago, Spychedelic Whale said:

@Playmusic

I don't get it.

If you are afraid you are choosing an costlier amp just because it has higher SPL, then just lower the volume on more expensive one and if you think the less expensive amp now sounds better, then your wallet thanks you. 

He wants to (somewhat) objectively determine which of the amps is actually the best. To accomplish this, he absolutely has to level match them pretty precisely, and using a multimeter to do so is actually a very good choice. Otherwise the amp that is even slightly louder in the comparison will appear to sound better, masking any minor differences that may actually exist.

 

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On 3/23/2021 at 12:48 PM, Playmusic said:

That sounds very promising if I understand it correctly.

Let us consider the case that the unloaded output voltage is 100 V (for one channel) and that the loaded output voltage is due to the output impedance of the amplifier 80 V.

Stax Headphones behave essentially like a capacitor. DC resistance is probably multiple Mega Ohm. Assuming you stay within the current (and voltage) driving capabilities of the amp, things should get complex, but I wouldn't expect a change even remotely as large as you postulate.

On 3/23/2021 at 12:48 PM, Playmusic said:

So, when the headphone is plugged into one receptacle then the voltage at the unused receptacle is also 80 V which I can easily measure. (I found some diagrams on Stax wire configuration on the internet.)

That's accurate at least within the measuring accuracy you're going to get with an off the shelf multimeter. 

On 3/23/2021 at 12:48 PM, Playmusic said:

Is my understanding also correct that when another headphone is plugged into the second receptacle in parallel (with the same settings, in particular for volume control) the output voltage would drop, but still be equal for both receptacles?

As above, if the combined capacity (etc.) stays well within the capabilities of the amps, I wouldn't expect much of a change.

On 3/23/2021 at 12:48 PM, Playmusic said:

Thank you very much for pointing out the simplification with the 1 mm hole. This was exactly my wish for posting in this forum that someone would point out a simplification which was not obvious to me.

And the idea with the clamp test probes is even better concerning cost and process. I now found the probes below which look suitable. spacer.png

Thank you very much for your excellent feedback. I would give two likes if I could.

There are probes with a U shaped hook at the end. If you find one that allows you to bend that hook into a shape that wraps around the pins of the plug, that would probably be ideal. You'd still have to make sure that the probe doesn't cause any shorts, so just measure on the second socket if possible.

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Thank you for you explanation on the electrical behaviour of the Stax amp + headphone.

10 hours ago, naiy8oaY said:

There are probes with a U shaped hook at the end. If you find one that allows you to bend that hook into a shape that wraps around the pins of the plug, that would probably be ideal. You'd still have to make sure that the probe doesn't cause any shorts, so just measure on the second socket if possible.

On the probes: I saw those very thin U-shaped hooks, but I thought they might slip during measurement and cause a short. The idea to bend them did not occur to me, but now that I know it, this is a very good option.

Some Stax amplifiers have only one receptacle (SRM-D50), so it is helpful to also have this option as a backup.

Thank you for your competent and generous feedback!

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This can end very badly!

You are dealing with very high, unforgiving voltage here, a small misstep can easily turn into a catastrophic disaster. 

I advise you to consider if you are willing and prepared to deal with such consequence before you continue to proceed down this path.  

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18 hours ago, mwl168 said:

This can end very badly!

You are dealing with very high, unforgiving voltage here, a small misstep can easily turn into a catastrophic disaster. 

I advise you to consider if you are willing and prepared to deal with such consequence before you continue to proceed down this path.  

Safety comes first. So, thank you mwl168 for sharing your concerns.

Injury/death are not acceptable options for me, so I made some precautions:

  • The measurement equipment is rated at 600 V CAT III.
  • I found seven sources for the Stax pin configuration (male/female) on the internet, so I am quite confident where bias, L+, L-, R+, R- are correctly identified.
  • A sine wave is generated on the left channel and null on the right channel. L+ is unmissable on the Stax connector and even if I was subject to a temporary confusion of left and right, I would measure L+ vs R+ without damage. The bias pin is further away and to be avoided.
  • The input to the amplifiers will be decreased before the test by 20 dB. So, the voltage on the left channel will be around 5 V.

If you have further suggestions on how to improve safety, please share.

I would like to seize the opportunity and bring up myself some questions on safety during regular operation of electrostatic equipment:

  1. During operation, the transducer is right next to the ear. Why are the high voltages not a concern?
  2. Some (non-Stax) amplifiers have receptacles where the golden-coloured metal inserts extend right to the white front of the receptacle. At least, this is what it looks on the product images. So, I wonder what happens if the amplifier is turned on, no headphone is connected, and a person comes close to the receptacle?
  3. What risks emenate from a micro break in a Stax headphone cable which is not immediately visible to the eye?

 

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On 8/8/2019 at 1:58 AM, kevin gilmore said:

Ok, the stax mafia has spent quite a bit of time with the kse1500

first the headphones are 200v bias. The kingsound must have been modified to lower bias voltage otherwise these headphones will eventually pop.

yes the kse1500/kse1200 is an extremely low power classAB amplifier with significant distortion. But great battery life. 

The kingsound is a chip amp driving transformers. Might actually sound better, but definitely not stax mafia approved.

A really good battery powered portable electrostatic amp is harder than you might think.

The stax d10 is another example that has issues.

Is there a teardown image you can share please? Also the charts for distortion measurements if it was measured. They have an odd choice for the dac chip too, cirrus 4272 in their other amps, not sure of this in particular. I couldn't find much information about the chip other than it being used in a few ADCs like focusrite Scarlett and Saffire pro 40. It doesn't seem to have much folklore around it either unlike say a Wolfson 8741.

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Does anyone know if the Stax SRM-D10 and the Shure KSE1500 / KSE1200 use similar amplifier circuitry?

I read somewhere that the SRM-D10 uses an Apex Microtechnology HV opamp. Perhaps this is also the case with the Shure units?

As Manueljenkin mentions above, there seems to be very little technical info available on the Shure amps and as well, the Stax D10.

An info would be very interesting and much appreciated!

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define similar. shure is 4 x discrete opamps made with 400v complementary bipolar parts. stax d10 is 2 x apex pa443 dual monolithic opamps made with 350v n-channel mosfets. stax d10 uses xmos 208 and ess dac. i don't remember what the shure uses. birgir has pictures of both should he desire to post them.

there is a guy in ukraine (i think) that is selling a shure clone for about $800 (no dac)

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Thanks Kevin. Very interesting!

Similar?.....Well they both use HV opamps, probably both with a lot of global feedback around them.

Birgir, if you could post photos, that would be great.

Best regards,

Doug (aka Linear)

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On 3/19/2021 at 11:17 AM, Playmusic said:

Taking a step back and a nap is always good advice. Thank you.

At the same time, my hearing is not good enough to differentiate in a shop environment between amplifiers without level matching the headphone. Before buying, I would like to be sure (to some extent) that I pick the right amplifier.

Measuring the unloaded voltage in a Stax plug output up to 50 V looks safe to me with a CAT III 600 V DMM. On the other hand, bare wires in some configuration for loaded voltage measurements look less safe - for me and the devices.

So, if anybody in this forum has ever tried to level match a single electrostatic headphone with several amplifiers for auditory comparison purposes then I would highly appreciate your feedback.

so,

test successful? User dead? inquiring minds need to know!!!

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