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).

The Carbon CC is finally back in stock.  I’ve had a couple of them sitting around for weeks now as I just can’t get Alps RK50’s to put in them.  I have an order with Alps directly but something is holding up production.  I overpaid for two RK50’s just to get them so the price of the amps had to be increased a bit.  The Carbon CC is the ultimate statement of the Carbon, with an improved power supply, larger chassis, pure silver signal wiring and an upgraded attenuator.  While I was waiting on the RK50’s I ordered a 48 step attenuator so one Carbon CC has that installed.  Otherwise it is identical to the RK50 version but also a bit cheaper.

Price:  The RK50 version is sold out but I hope I will get more of them soon.  Alps quotes me late October but I hope to get more sooner

             5900$ plus shipping for the 48 step attenuator version

Here is my take on the BHSE, single chassis amp measuring just about 33cm deep with the volume knob. There were two of these amps under construction for a while of which this is the latter unit. This a full blown BHSE running at 20mA per tube and with the +/-400V power supply built into the chassis. It’s a tight fit but it all works nicely though the transformer can hum a tiny bit as it is suspended from the top panel. There is no hum present in the headphone output though.

The amp will shipped with a matched quad of JJ EL34’s and all the adjustment for the tubes is made through the top panel of the amp. I don’t endorse tube rolling at all but it’s a good idea with any BHSE amp to monitor how the tubes are doing from time to time. The amp can be set to either 117V or 230V via an internal switch. There is just one of these amps and I won’t build any more for a while at least.

Price: 5500$ plus shipping

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.

The silver Carbon is back in stock!

Price:  4600$ plus shipping 

All new black KGSSHV Carbon.  This has been a long, long time coming and fraught with endless issues but it is finally here.  First batch is only 4 amps and they are a little bit more expensive due to the extra steps needed to make them.  They are now back in stock with no shortage of units.

Price: 4800$ plus shipping

 

I have the mini KGSSHV’s in stock now.  This is a new version with a redesigned power supply.  The basic topology is the same but with a new layout for better thermal performance and more capacitance to improve performance.  Uses my signature orange power led which looks stunning on the black front panel.  The silver units are sold out and I won’t build any more.  Standard mini specs so they run at +/-400V and the current through the output stage is set at 10mA so it runs pretty warm.  It uses the 2SA1968 current sources which gives a more stable circuit with a slightly sweeter tone.

Price:  3100$ 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

The ongoing progress of designing a cheap KGSSHV continues and they are now up to the fourth version.  No changes on the inside now, just a different chassis to see what works for this project.  First few units are all black but I’m working on a silver version as well.

Now it has the new power supply and new transformer fitted. I’ve had one of these running 24/7 since early in June with excellent results. This is a KGSSHV in every way but with steps taken to cut costs without sacrificing performance. Basically, it runs at a slightly lower voltage (+/-360V) but is a 2SA1968 KGSSHV through and through. It is a great amp and I’m one step closer to building these in larger numbers to ease the entry to high performance electrostatic sound.

Price: 2300$ plus shipping

The silver version of the “cheap” KGSSHV is now ready.  Same as the black one above but with a silver front panel in a natural finish.

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

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 11.07.2018

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