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Stax SRM-Xh Review (Electrostatic Headphone Amp)

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amirm

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Is there a particular reason the amp itself is not measured but just the amp-headphone combined?
Yes, two reasons. First, I could not find my bloody DIN plug. :) This unit has been sitting here since February so wanted to get it out.

Second was the aggravation. I measured the last one as you state. Massive argument broke out that the 200 K impedance of the Audio Precision was too low and was putting too much burden on the amp. I actually showed later using an acoustic test like this that my measurements were correct and the impact there was negligible. Still, I was in no mood to start all that over so decided to just jump to acoustic test which no one can complain about.

If I had found the plug, I was going to build a high voltage voltage divider to create a higher impedance load but per above, I could not.
 
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SoundsGood2Me

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Thank You Amirm!
Stax are still a unique product, and deserve respect
Thank evolution that we now have Planar Magnetic
A current-hungry version of EStats
 

Ata

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You should try a KGSSHV amp or the KGSSHV-Carbon amp, the difference is night and day compared to any of the Stax amps, which are all inadequate to drive the SR-007s. Add some bass EQ and all the Stax amps completely fall apart at anything above background music levels, while the KGSSHV designs don't struggle with this at all.

These amps may be better but the pricing needle moves in the wrong direction! :eek:

For that kind of money I'd buy the recently reviewed DCA Stealth or similar, pair it with a TOTL SMSL or Topping stack or similar and call it a day, with spare change at hand.

By the way, with my setup, which has the lowest end solid state Stax amp, I don't have an issue with bass or loudness. Must be a sensitivity difference between the SR-L300 and SR-007 then.
 

soundwave76

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I was also curious to compare the top headphone models to my Stax. So I bought the HD800S, applied eq and… no comparison, Stax beat them hands down in my ears. DC Stealth comparison is tempting :)
 

johnnyx

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What is the mystery surrounding electrostatic energisers? High voltage power supplies and high voltage amplifiers aren't that mysterious in themselves. Has anyone built their own?
 

John_M

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I wonder if you could compare the frequency response at a higher dBSPL? There are numerous people in the "electrostat community" (if such a thing exists) who claim that, unless you buy an amp with the power of a nuclear reactor, it won't drive the bass properly (especially with the SR-007).

The frequency response graph doesn't seem supportive of these claims, although I'm not a technical expert so may be getting this wrong, and in any event the response might be "ahah but the volume is low so it's not showing the effect of an underpowered amp."
 

John_M

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Also, this could almost be used as a review of the SR-007 in the headphones section. Pretty much what was expected - it's going to get criticised for non-Harman compliance in the bass region but has very low distortion. :) (And query how much distortion is coming from the amp rather than the headphones).
 
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Also, this could almost be used as a review of the SR-007 in the headphones section. Pretty much what was expected - it's going to get criticised for non-Harman compliance in the bass region but has very low distortion. :) (And query how much distortion is coming from the amp rather than the headphones).
Yes but I want to spend a bit more time to see if I can optimize the cup placement on the ear. I did some of that here but like to spend a bit more time to do it.
 
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I wonder if you could compare the frequency response at a higher dBSPL? There are numerous people in the "electrostat community" (if such a thing exists) who claim that, unless you buy an amp with the power of a nuclear reactor, it won't drive the bass properly (especially with the SR-007).
In my case my amps all get distorted before I can get any good sensation of bass so they may be right. :) When I test the SR-007 by itself, I will try to get all three SPLs measured.
 

John_M

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Thanks for the replies - looking forward to seeing one or more Stax headphone reviews...
 
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Amirm, It would be interesting to see how one of the better transformer box adapters, (one in good condition) like a STAX SRD-7Mk2 or SRD-7PRO driven by a good quality amplifier measures, as I have no shortage of what sounds like, very clear undistorted power, which could easily cook my SR-L700's if I'm stupid.

I would assume the S/N ratio and distortion (and probably to a lesser degree, the frequency response) measured has more to do with the speaker amplifier driving the 2 passive left/right transformers.
My guess is that the SRD transformer adapter probably outperforms the dedicated STAX made amplifiers,
But there's only one way to find out.
 

the_brunx

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would love to see topping and co create some electrostat amps for stax and sennheiser he-series. the amp is the weak link for these headphones. an A90 amp for electrostats..
And actually all they need for a quick example is to get a transformer box circuit like the SRD7 pro driven by an A90 amp into one chassis.
 
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And actually all they need for a quick example is to get a transformer box circuit like the SRD7 pro driven by an A90 amp into one chassis.
The A90 is a Headphone amplifier / preamplifier, although powerful for a head amp, it wasn't designed, nor would it have enough power to drive speakers, (it has no speaker terminals).

The SRD-7Mk2, SRD-7Pro were designed to connect to the speaker outputs of a poweramplifier or integrated Amplifier, I think somewhere between 15 to 50 watts RMS per Channel, into 8 ohms would be required for adequate drive and headroom, when connecting to an SRD transformer box and Stax electrostatics.

If Toppings JohnYang designed an amp at a reasonable cost, say $700 to $800 or there abouts, I'm sure there would be a market for it, as Stax headphones are reasonably priced when compared to similar quality Dynamic / plannar headphones, it's the expensive amps / energisers that discourages people from trying Stax headphones.
But I personally would love to see a well designed modern version of the old SRD transformer boxes, for about $350 max, then make my own choice of desktop amp to drive it.
 

the_brunx

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The A90 is a Headphone amplifier / preamplifier, although powerful for a head amp, it wasn't designed, nor would it have enough power to drive speakers, (it has no speaker terminals).

The SRD-7Mk2, SRD-7Pro were designed to connect to the speaker outputs of a poweramplifier or integrated Amplifier, I think somewhere between 15 to 50 watts RMS per Channel, into 8 ohms would be required for adequate drive and headroom, when connecting to an SRD transformer box and Stax electrostatics.

If Toppings JohnYang designed an amp at a reasonable cost, say $700 to $800 or there abouts, I'm sure there would be a market for it, as Stax headphones are reasonably priced when compared to similar quality Dynamic / plannar headphones, it's the expensive amps / energisers that discourages people from trying Stax headphones.
But I personally would love to see a well designed modern version of the old SRD transformer boxes, for about $350 max, then make my own choice of desktop amp to drive it.
No, you don’t need that much! 15 to 50 watts into 8 ohms to drive SRD7 pro?? Where do you get this info? I still have a user manual from a normal bias transformer and it says 5 watts as requirement and keep in mind you need way more power to drive normal bias transformers (+headphones) as opposed to pro bias because of lower polarization voltage. Pro bias requirements will be way lower. The A90 even borderline A30pro is enough. In fact more than enough to be potentially harmful at full blast if fed properly
 
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No, you don’t need that much! 15 to 50 watts into 8 ohms to drive SRD7 pro?? Where do you get this info? I still have a user manual from a normal bias transformer and it says 5 watts as requirement and keep in mind you need way more power to drive normal bias transformers (+headphones) as opposed to pro bias because of lower polarization voltage. Pro bias requirements will be way lower. The A90 even borderline A30pro is enough. In fact more than enough to be potentially harmful at full blast if fed properly
My understanding is that the bias supply is for the actual electrostatic charge, 230 volts on older models and 580 volts in newer Pro Bias models.

I thought that the fluctuating music +/- signal is seperate to the 580 volts bias supply, and that it also requires quite a lot of voltage to drive the headphones to an acceptable volume, often 300 to 500 volts rms on the Stax amplifiers
The SRD Pro bias boxes have two passive step up transformers about 25 to 1 to increase the speaker amplifiers weaker output signal to the electrostatic headphones higher voltage requirements,
Most speaker amplifier usually put out 15 watts as a minimum, that's where I get my assumption from, mine are driven by a 26kg Crown Studio Reference 2 (360 watts rms into 8 ohms) with the left/right pots turned down to about 9 o'clock (about quarter turn and power available) for a good range on my dac as my main volume control, I'm sure it's putting out something like 20 watts at least.

But if a Headphone amplifier can drive the SRD then I stand corrected, I'm assuming the 4 pin xlr headphone output is what you connect the SRD to by using a diy adapter or is it connected to the rear left right pre outs ?
 

the_brunx

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My understanding is that the bias supply is for the actual electrostatic charge, 230 volts on older models and 580 volts in newer Pro Bias models.

I thought that the fluctuating music +/- signal is seperate to the 580 volts bias supply, and that it also requires quite a lot of voltage to drive the headphones to an acceptable volume, often 300 to 500 volts rms on the Stax amplifiers
The SRD Pro bias boxes have two passive step up transformers about 25 to 1 to increase the speaker amplifiers weaker output signal to the electrostatic headphones higher voltage requirements,
Most speaker amplifier usually put out 15 watts as a minimum, that's where I get my assumption from, mine are driven by a 26kg Crown Studio Reference 2 (360 watts rms into 8 ohms) with the left/right pots turned down to about 9 o'clock (about quarter turn and power available) for a good range on my dac as my main volume control, I'm sure it's putting out something like 20 watts at least.

But if a Headphone amplifier can drive the SRD then I stand corrected, I'm assuming the 4 pin xlr headphone output is what you connect the SRD to by using a diy adapter or is it connected to the rear left right pre outs ?
Yes, with XLR. It works great.

Your volume pot is logarithmic, won’t be surprised if you are outputting way less than 5 watts at 9’oclock setting

The bias voltage goes into the membrane the signal voltage goes into the plates. Higher bias voltage higher sensitivity.
 
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