[gefski]

I was wondering the same thing...had this crazy idea to purchase an SR-009 for Christmas and running it off my SRM1 MK2. Does this make sense?

Any chance of taking your amp to a meet and trying an 009 or even an 007? I listened to both at a meet this year, but they were driven by an Eddie Current. That setup was so popular that I didn't get a chance to try either driven by my SRM1 MK2 Pro. Had fun with lots of Lambdas though, and even a normal bias Sigma.

 

[miceblue]

Can anyone provide a summary of how e-stat amps work in Layman's terms? The prices range from $200-$6000, so I'm just curious to know what can be done inside of an e-stat amp to make the price range so large.

For normal headphone amplifiers you've got op-amps, output resistors and capacitors, different jacks, linear power supplies, etc. I'm not sure if op-amps are even used in e-stat amps as opposed to your Average Joe transistors.

 

[Currawong]

The problem as I understand it is the very high voltages required. Since a lot of electronics, such as TVs, have moved to much lower-powered solutions, the manufacture of a lot of high-voltage devices has ceased, making it harder to mass-manufacture amps. That means tube and transformer solutions.

 

[Evshrug]

Can anyone provide a summary of how e-stat amps work in Layman's terms? The prices range from $200-$6000, so I'm just curious to know what can be done inside of an e-stat amp to make the price range so large.

For normal headphone amplifiers you've got op-amps, output resistors and capacitors, different jacks, linear power supplies, etc. I'm not sure if op-amps are even used in e-stat amps as opposed to your Average Joe transistors.

I admit I haven't looked too much into it, so anyone feel free to correct my conjecture:

The older models came with transformer units that hook up to speaker taps... I think a dedicated e-stat amp is basically a speaker amp with a transformer (or maybe rated with the right voltage so it doesn't need a transformer) and instead of speaker taps it has Stax's proprietary plugs, so the headphones can plug right in. Apparently once they have enough power, e-stats are not very picky.

 

[cucera]

Well all current Stat amps are discrete direct driven high voltage amps. The only exceptions Luninare and Malvalve that are not so well regarded. For 200$ I would get an Stax 252 and for 6000$ A Headamp BHSE (my Choice). But there are quite a number of good choices between, and one even above.

 

[HemiSam]

I don't know if I'm posting in the right thread, so apologies up front if I'm in the wrong place.
 
I took a dive into electrostat hp's with the purchase of Koss ESP-950's along with the E/90 amp.  Been very much enjoying the detail, highs and mids since I purchased them a few weeks ago.  Currently revisiting my Led Zep collection...sounds great  I've not been listening to my other rig since then and have been looking at an amp upgrade for the e-stats.  The Stax SRM-1/MK-2 looks to be a good one based on several threads I have been reading through.
 
My question:  is this indeed a good choice for an amp upgrade without breaking the bank and if so, the Stax amps I have seen obviously have quite a few years on them.  Is there a trustworthy technician/elctronics store in the U.S. that specializes in tune-ups and restorations so I can have a purchased SRM-1/MK-2 refreshed to ensure I have a good working unit?  I would also ask the shop to modify the Koss extension cord with a Stax plug to allow me to use the ESP-950s with the upgraded Stax amp.  
 
Thanks for any thoughts/recommendations.
 
HS

 

[b0bb]

Can anyone provide a summary of how e-stat amps work in Layman's terms? The prices range from $200-$6000, so I'm just curious to know what can be done inside of an e-stat amp to make the price range so large.

For normal headphone amplifiers you've got op-amps, output resistors and capacitors, different jacks, linear power supplies, etc. I'm not sure if op-amps are even used in e-stat amps as opposed to your Average Joe transistors.

e-stat amps are differential, in simple terms it is a 4 channel amp while most dynamic amps are 2 channel amps, the part count is higher when all things being equal.
 
The estat circuit is a discrete opamp with active current source loads without the unity current buffer common in most dynamic headphone amps,.
 
High voltage transistors/mosfets are very expensive about 5-10x the cost, that is when you can buy them.
 
There are low cost units like the SRM252s but STAX had to keep the cost down and skimped on the power supply, The Koss ESP950 amp is another example of a reasonably priced unit and this one uses opamps as does the Sennheiser HEV70 companion amp to the HE60.
 
If you push aside the markup and fancy casework most of the cost is in the high voltage power supplies and the transistors.
The current KGSSHV's output stage needs 16 devices at about $5-$10 just for the transistor.
Good quality HV caps from Nichicon/Panasonic/CDE are about $5-10/piece and KGSSHV needs 8 of them.
 
The cost really starts to take off when you get to hybrid territory like the Blue Hawaii (BH/BHSE), a single EL34 tube can cost as much as $300 (Mullard XF2) and it needs 4 of them, the older version 1 of BH has a transistor current source requiring 28 transistors@$17/piece.
 
Then comes the options...
The Alps RK50 volume control is about $1000

 

[miceblue]

e-stat amps are differential, in simple terms it is a 4 channel amp while most dynamic amps are 2 channel amps, the part count is higher when all things being equal. High voltage transistors/mosfets are also very expensive about 5-10x the cost , that is when you can buy them.

There are low cost units like the SRM252s but STAX had to keep the cost down and skimped on the power supply, The Koss ESP950 amp is another example of a reasonably priced unit and this one uses opamps as does the Sennheiser HEV70 companion amp to the HE60.

If you push aside the markup and fancy casework most of the cost is in the highvoltage power supplies and the transistors.
The current KGSSHV's output stage needs 16 devices at about $5-$10 just for the transistor.
Good quality HV caps from Nichicon/Panasonic/CDE are about $10/piece and it needs 4 of them.

The cost really starts to take off when you get to hybrid territory like the Blue Hawaii (BH/BHSE), a single EL34 tube can cost as much as $300 (Mullard XF2) and it needs 4 of them, the older version 1 of BH has a transistor current source requiring 28 transistors@$17/piece.

Interesting explanation. Thanks for taking the time to write that!

So that means e-stat amps are technically balanced by nature, aren't they? A 4-pin XLR jack has L+/L-/R+/R- just like a 5-pin STAX plug, but the STAX plug needs the additional pin (or two) for the high-voltage bias for the speaker diaphragm.

For the SRM-252S you mentioned that STAX skimped out on the power supply (I'm guessing the wall wart that comes in the package?) in order to make it more affordable. If it was supplied with a proper power supply like from a linear power supply, how would the performance differ from other solid state amplifiers (like the KGHVSS)?

A lot of the more expensive e-stat amps have a tube output stage, is this mainly for voltage gain as an alternative to resistors? If so, that sounds like a mighty expensive alternative. >.>

 

[b0bb]

Interesting explanation. Thanks for taking the time to write that!

So that means e-stat amps are technically balanced by nature, aren't they? A 4-pin XLR jack has L+/L-/R+/R- just like a 5-pin STAX plug, but the STAX plug needs the additional pin (or two) for the high-voltage bias for the speaker diaphragm.

For the SRM-252S you mentioned that STAX skimped out on the power supply (I'm guessing the wall wart that comes in the package?) in order to make it more affordable. If it was supplied with a proper power supply like from a linear power supply, how would the performance differ from other solid state amplifiers (like the KGHVSS)?

A lot of the more expensive e-stat amps have a tube output stage, is this mainly for voltage gain as an alternative to resistors? If so, that sounds like a mighty expensive alternative. >.>

 
e-stat amps are balanced.
 
The SRM-252s output stage runs at  2mA, this limits the drive to power hungry phones like the SR009, the KGSSHV runs at about 10mA and the Blue Hawaii at 20-30mA
 
An internal inverter built into the SRM252 steps up the 12V to 550V with a max current output of 10mA
KGSSHV runs at 900-1000V and the Blue Hawaii at 800-900V
 
I have the 252S, replacing the wall wart with a fully regulated supply improves the performance when driving the SR-Lambda series(207,307,407,507) and the Sennheiser HE-60. It will drive the SR-009 if the volume is not turned up too high.
 
The linear amplifier part in the 252S is almost identical to the 323S except is current thru the stages is reduced. The 323S is like a simplified version of the KGSSHV.
The 252S does not use load resistors, it has an active current source like the 323S and KGSSHV, quite a nice design.
 
It also does not have any heatsinking so increasing the bias current will overheat the amp.
Replacing the cheap electrolytics in the 252 with high ripple Panasonics and Nichicon polymer caps will really wake it up.
 
Tubes are used to handle higher power at high voltages, the solid state silicon carbide high voltage transistors as just starting to become mainstream and I expect designs using these devices will start to show up in the commercial and DIY space in the coming years.

 

[b0bb]

A word of caution when substituting the 12V wall wart on the SRM-252S
 
The pinout on the 3.5mm power 12V plug is reversed, the outer sleeve is +12V and the inner sleeve is 0V.
 
Off the shelf 12V PSUs  usually have it the otherway, if this is is used it will blow the fuse soldered onto the board

 

[miceblue]

e-stat amps are balanced.

The SRM-252s output stage runs at  2mA, this limits the drive to power hungry phones like the SR009, the KGSSHV runs at about 10mA and the Blue Hawaii at 20-30mA

An internal inverter built into the SRM252 steps up the 12V to 550V with a max current output of 10mA
KGSSHV runs at 900-1000V and the Blue Hawaii at 800-900V

I have the 252S, replacing the wall wart with a fully regulated supply improves the performance when driving the SR-Lambda series(207,307,407,507) and the Sennheiser HE-60. It will drive the SR-009 if the volume is not turned up too high.

The linear amplifier part in the 252S is almost identical to the 323S except is current thru the stages is reduced. The 323S is like a simplified version of the KGSSHV.
The 252S does not use load resistors, it has an active current source like the 323S and KGSSHV, quite a nice design.

It also does not have any heatsinking so increasing the bias current will overheat the amp.
Replacing the cheap electrolytics in the 252 with high ripple Panasonics and Nichicon polymer caps will really wake it up.

Tubes are used to handle higher power at high voltages, the solid state silicon carbide high voltage transistors as just starting to become mainstream and I expect designs using these devices will start to show up in the commercial and DIY space in the coming years.

Ah I see. You seem to be quite familiar with e-stat technology in general, so thanks for taking the time to chime in to this thread! : )

I have a linear power supply coming my way eventually, so I was hoping it would make a difference compared to the standard wall wart. Right now I'm using a Toyozumi Dengenkiki step-down transformer (my SRS-2170 unit is from Japan but I live in the USA), which has a power conditioning step in the box, but I wanted to see if a dedicated power supply would affect its sound at all. And yup, I am well aware of the inverted polarity of the DC input plug. Why did STAX have to use this design? It's literally the only electrical appliance that I have that uses such a DC barrel. D:

On the topic of current for e-stat headphones, what makes the SR-009 require more current than the SR-207 for example? I thought current was only needed to charge the stators and diaphragm.

 

[Chris J]

Ah I see. You seem to be quite familiar with e-stat technology in general, so thanks for taking the time to chime in to this thread! : )

I have a linear power supply coming my way eventually, so I was hoping it would make a difference compared to the standard wall wart. Right now I'm using a Toyozumi Dengenkiki step-down transformer (my SRS-2170 unit is from Japan but I live in the USA), which has a power conditioning step in the box, but I wanted to see if a dedicated power supply would affect its sound at all. And yup, I am well aware of the inverted polarity of the DC input plug. Why did STAX have to use this design? It's literally the only electrical appliance that I have that uses such a DC barrel. D:

On the topic of current for e-stat headphones, what makes the SR-009 require more current than the SR-207 for example? I thought current was only needed to charge the stators and diaphragm.

Even electrostatic panels need voltage and current to make them move.
As you know, Volts X Amps = Power.
The panels need power to do work, i.e. move air.
Fairly straightforward when you look at it that way.

 

[miceblue]

Even electrostatic panels need voltage and current to make them move.
As you know, Volts X Amps = Power.
The panels need power to do work, i.e. move air.
Fairly straightforward when you look at it that way.

Right, but the issue at hand is current. I thought e-stats primarily operate on voltages, not current.

P = VI sure but if I is small and V is big, you still get the same P as if V was small and I was big. 20-30 mA seems kind of small compared to the big V values used when talking about e-stats.

But maybe I'm wrong about this. 20-30 mA is sufficient for many dynamic driver headphones at reasonable volume levels at least.

 

[Chris J]

Right, but the issue at hand is current. I thought e-stats primarily operate on voltages, not current.

P = VI sure but if I is small and V is big, you still get the same P as if V was small and I was big. 20-30 mA seems kind of small compared to the big V values used when talking about e-stats.

But maybe I'm wrong about this. 20-30 mA is sufficient for many dynamic driver headphones at reasonable volume levels at least.

 
Ah, OK!
 
yes, 20-30 mA is quite bit for a dynamic headphone when you consider that drive voltage for a dynamic is typically on the order of the volt or two RMS.
 
So 20-30 mA is massive for an electrostatic driven at 10-100 Volts RMS!

 

[b0bb]

Ah I see. You seem to be quite familiar with e-stat technology in general, so thanks for taking the time to chime in to this thread! : )

I have a linear power supply coming my way eventually, so I was hoping it would make a difference compared to the standard wall wart. Right now I'm using a Toyozumi Dengenkiki step-down transformer (my SRS-2170 unit is from Japan but I live in the USA), which has a power conditioning step in the box, but I wanted to see if a dedicated power supply would affect its sound at all. And yup, I am well aware of the inverted polarity of the DC input plug. Why did STAX have to use this design? It's literally the only electrical appliance that I have that uses such a DC barrel. D:

On the topic of current for e-stat headphones, what makes the SR-009 require more current than the SR-207 for example? I thought current was only needed to charge the stators and diaphragm.

The 252s uses a 45x voltage multiplier to raise the 12V to 500+ V, it is not regulated or short circuit protected, if you put in 18V or more, the supply rails go up to 800V and the amp blows up.
 
STAX relies on the wall wart and switching of the polarity is to prevent the insertion of a random power supply with the same plug.
 
The SR-009's diaphragm is almost 2X the size of the SR-207, in order to maintain the same electric field strength it needs almost 4X the charge, assuming all else is equal.
Electric field strength is proportional to the charge per unit area, the bigger diaphragm the more charge is needed.
 
In a time-varying scenario such as a music signal, the amp has to move this charge in and out of the stators to change the electric field which causes the diaphragm to move.
The electric field strength is a 3dimensional measure of the lines of electrostatic force between the stators and diaphragm.
 
The bigger the diaphragm the more charge per unit time needs to be moved between the amp and the diaphragm to maintain the the same change in the electirc field.
 
The definition of electric current is the amount of charge moving thru a conductor per unit time, so the big phones with big diaphragms take more current to drive them.