Amplifiers for electrostatic headphones

Here is a rundown of any products I have in stock at any given time.  Given the demands of my day job I do not accept orders ahead of time, I just sell what I’ve built.  This also works better with the more experimental nature of what I do as we are always coming up with new designs and/or changing older ones. Feel free to contact me at spritzer@mjolnir-audio.com if you are interested in any item here.  I will reply to every mail so if you haven’t received a reply within 24 hours then feel free to send me another email.  Email gets lost all the time, it is flagged as spam or something like that.  All prices in US dollars (USD).

While I wait for balanced Alps RK50 volume controls I built two single ended only Carbon CC amps.  These are the same as the regular Carbon CC, same upgraded power supply, 99.99% pure silver signal wiring and improved transformer.  On top of that these have new old stock Penny+Giles RF15 stereo volume controls and WBT Nextgen rca sockets.  Performance wise this is exactly the same as the balanced version but with the added benefit of RCA inputs for those with single ended sources.  This has been requested often over the years so why not build a couple to try it out.

While working on these I’m also building balanced amps which just lack the RK50 attenuators.  I hope to get some of them in November so the amps will be ready to be finished then.

Price: 6500$ plus shipping for the RCA version

 

It’s finally here, the KGSSHV Carbon.  This is the first electrostatic amp in the world to use SiC FET output devices which are as close to triodes as transistors can get.  The original design concept for this amp was born to tame the rough top end of the SR-009 but it grew from there to become the best solid state amplifier we have designed. Right up there with the BHSE and the T2 as the best amps of their kind all the power you could ever need, a lot of detail, huge and expansive sound stage and the best bass I’ve heard from an electrostatic amp.  Kevin and I are very proud of this one.  The Carbon design requires heatsinks which are at least three times the size of the KGSSHV mini so it was a real challenge to make the amp this compact.   It did require a new power supply design so I tweaked the KGSSHV mini design a bit to fit the Carbon better plus it has a vastly oversized transformer.

Price:  4600$ plus shipping 

The KGSSHV Carbon is also available in black.  It is identical to the silver units but the extra steps needed to make the front panel black add a bit to the cost.

Price: 4800$ plus shipping

 

Now the KGST is finally available again.  This amplifier has been called the mini BHSE and it is a fitting name.  This is a hybrid amplifier and the circuit is similar to the BHSE in many ways.  The power supply is similar and so are the first two amplifying stages.  The main difference is with the tubes used and how they are used.  The KGST uses the tube in a more traditional nature but with the same constant current source as the BHSE.  The tubes used are the 6S4A and they handle the output directly with no extra stages needed.  There are no external heatsinks and the tubes are fully enclosed in the chassis.

Sound wise they are very similar but the KGST is warmer and more forgiving making it a better match to the SR-009.  Like the BHSE it runs very warm so it needs a lot of air to breath.  Similar to the KGSSHV this one has a servo which monitors and corrects the output so warmup is less of an issue.

Price: 3000$ plus shipping

I realized late last year that I’ve been building KGSS amps for over 15 years and wanted to do something to mark the occasion.  Now I could just have made them like in the old days…massive boxes with not a whole lot in them but nahhh…that wouldn’t be fun.  I wanted to do something difficult so the age old question popped up into my head, how small could I possibly make a classic KGSS amp?  Well…here is the answer, pretty damn small.  So this is the standard KGSS circuit from 1999 but with some small changes such as output resistors to make it safe to use, better output devices  but that’s about it.  I also wanted to make it as authentic as is possible so it uses the same 2SK389 input fets as the original (now obsolete) and it had to have a real Stax socket as that was what we used back in the day.

To say that these are difficult to build would be an understatement.  Just to make the amplifier PCB for an amp this complex, to fit these heatsinks, was a massive project and then cram all this in there.  The amp is just 27cm deep (with the knob), 21cm wide and 7.5cm tall with quite a lot less internal room so yeah… pretty difficult.  Standard XLR sockets for the inputs but no room for the loop out sockets so they were left out.  There will only ever be a handful of these amps built so one run and I’m done.  I don’t think I can build any smaller than this so the smallest high performance Stax amp out there.  🙂

I added a picture with the SR-007BL Mk1 to make it all period correct and to show how tiny the amp is next to the phones.

Price:  2600$ plus shipping

Finally ready, the black version of the KGSS Klassik.  I built a larger batch of these than the silver ones and they are almost gone now.

Price: 2600$ plus shipping

Here is the current KGSSHV with all the latest improvements to the circuit.  This has been a long standing project to make a more affordable version of the KGSSHV while not minimizing the performance in any way. The chassis is a bit bigger than the now discontinued mini (240mm wide vs. 210mm) but it is still a small amp which packs a nice punch.  It is a KGSSHV 2SA1968 though and through and the main changes were to lower the rail voltages down to +/-350V and the most of the parts are SMD to make assembly easier.   It also uses a cheaper Stax socket but that’s it, the rest of the parts are the same as in all my other amps.  It is truly a non-compromise design and you really need to go up to the Carbon to improve on it.

The KGSSHV is available in silver only to simplify the production and has the same internal switch to select between 115V or 230V.

Price: 2300$ plus shipping

he Octave V2 is finally ready and this time around it is a solid state unit. I had some chassis left over from the V1 run so the challenge was to cram a high voltage amplifier into a chassis which is just 40mm tall. I would have placed the transformer on the outside but that would just have been silly… So here I drew inspiration from the Stax SRM353X and all the previous amplifiers of the same lineage. In many ways this is a simplified KGSSHV with the biggest change to the input stage as I removed the low voltage supplies which feed them. It is now fed off the high voltage rails directly to make it all a bit simpler and cut costs. This amp runs at +/-300V with a brand new power supply we designed, the main HV rails are unregulated but with really big capacitors so ripple is a non issue as the amp simply runs off the charge on the capacitors. Turn it off and the amp still runs for a few seconds… There are two regulated power supplies in there though, a small 12VDC supply for the front panel LED and a fully regulated +580VDC supply to run the bias.

The other major design constraint with this design was power and how much it could dissipate. The height really limits what I could do in terms of heatsinks so I can’t do full KGSS/KGSSHV power levels here but it is more powerful than the Stax amps. It’s also a warmer amp and can easily drive any of the Lambda series up to the SR-009. It is naturally fully balanced but works just as well with single ended sources via adapters. The pictures are really bad off this thing as we get so little natural light this time of year here in Iceland. I was shooting this with the sun directly on it and well…it highlights stuff that isn’t really there.  The knob is black and the socket doesn’t look so washed out.  🙂

Price: 1200$ plus shipping

As the stock of Octave V2’s is almost finished I made some more in a similar chassis style to the V3 power amp version.  Same price as above and I’ll offer them both until one version is out of stock.

Here is one in the same vain as the SRD-7 below though not a transformer but rather an electrostatic power amp.  So many of us have excellent amps which could act as preamps so something like this has been requested frequently over the years.  It can be used with most headphone amplifiers, preamps or even passive preamps.  It is an Octave V2 but with no volume control and only the XLR input sockets on the back.  It can also be used single ended with either XLR to RCA adapters or a special cable.

This is a nice and simple way for anybody with a good stereo or dynamic headphone system who wants to try electrostatics.

Price: 1100$ plus shipping

 

People have been asking for years to do some transformer boxes (or energizers) to drive electrostatic headphones and I finally relented. That lot sold out really quickly last year and I finally had time to build some moe.  Over the years I’ve accumulated a large number of SRD-7 transformer boxes, some of which I have converted to pro bias but most have been scrapped. The only things I saved were the transformers and the Stax sockets. So what I did here is to put the excellent SRD-7 transformers into a much better enclosure with my own bias supply to maximize their potential. On top of that the input to the transformers is protected from overload and the output has a clamp circuit so it can never damage the headphones connected to it. This is a fully passive circuit which only kicks in if the transformer peaks at roughly 550Vpp, 1100Vppss.  Any higher than that and you run the risk of damaging Pro bias headphones.

There is nothing here in the signal path except the transformers and the input protection circuitry. The left and right channels are also isolated so issues with using bridged amps. A common ground will turn them into smoke right quick so that is best avoided.

The boxes can be set for either 117V or 230V with an internal switch.  This is one of the many improvements over the first version and why these are a bit more expensive.

Price: 670$ plus shipping

 

 

Page updated 23.09.2018

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