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 top of the line Carbon CC.  I’ve given up on the Alps RK50 volume controls as I just can’t get them in the quantity that I need so for now on the Carbon CC amps will use the best volume controls TDK offers, 4CP-2500.  Otherwise the amps are the same as they have been for the last year or so.  Same upgraded power supply, 99.99% pure silver signal wiring, improved transformer plus the TDK pot.

Price: Out of stock while I work on building a new batch

After weeks of waiting on parts, the new batch of the Carbon is finally ready.  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 with all the power you could ever need.  It has a lot of detail, huge and expansive sound stage and the best bass I’ve heard from an electrostatic amp.

With this new batch, the internals of the amp remain the same except all the Carbon’s now have a custom made TKD volume control.  I was running low on the Alpha pots so all the new unit will have TKD pots.  The front and back panels are now also different with a shiny, black electroplated finish plus some slight changes to the design.  These two changes bump the price up a bit but were necessary due to Covid obliterating my supply chain.

Price: 5100$ 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.

After many years of not changing the KGST at all, I finally altered the chassis layout a bit so it better matches my other amps.  Small updates to the boards and circuit as well but nothing major.

Price: 3000$ plus shipping

Finally ready is the new version of the KGSSHV.  It’s really the first major change to the circuit in over a decade as I wanted to tie together the old KGSSHV performance with the warmer and more forgiving sound of the KGSS Klassik.  All of the transistors have been changed in this version plus a number of other changes and all the heatsinks are now onboard to make it more similar to the KGST in looks.  I did add the second output socket as it might help some users who want to use two sets at the same time.

The KGSSHV has been going strong for over a decade now and is the best solid state amp we’ve ever designed outside of the Carbon, which was heavily based on the KGSSHV.  This one is warmer and more forgiving than the original design which suits the modern Stax models better as they are on the bright side.

Price: 2750$ plus shipping

Here is a new amp I have been working on for a long time as a counter design to the normal amps I do.  The design brief I had in mind was all tube signal path, warm sounding and using easy to find tubes.  Well that led me down a rabbit hole of 4 completely different designs which all were built and tested until I settled on this one.  This took years and what started off as an amp to suit the 009’s sort of morphed into a general purpose tube lovers amp.  So this one is in many ways similar to the older tube designs of what Stax did in the 60’s, the Sennheiser HEV90 and others but with modern twists.  This amp uses two ECC83’s and two ECC99 tubes and a fully regulated power supply and custom transformers.  Lots of nice caps in the signal path and high spec input wiring.  Sound is nice and mellow sounding but with plenty of presence and power.

The chassis is a bit wild but I had these in stock so why not use them.  The amps can be used at either 115V or 230V and are fitted with RCA inputs and a passive RCA loop output.

Price: 3200$ plus shipping

The Octave V2 is my attempt at a lower power solid state amps so here I drew inspiration from the Stax SRM353X and all the previous Stax 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 small chassis 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.

Now we are on the third batch of these and I made some updates.  The biggest change is a new larger chassis so it can dissipate a bit more power.  The output socket is now my new Teflon unit and the amps are all fitted with an internal voltage selector.  Performance is slightly improved over the older versions but by no means a huge leap.

Price: 1340$ plus shipping

This will be the quarantine special as these amps have been planned for a few years but I never had the time to finish the build until now.  Lockdown does have that effect…  This is the TT or Tiny Triode.  This is call back to some of the first amps I designed and built and one I really like to this day.  The core circuit is just about as simple as you can build an electrostatic amp, just two active elements per phase with one film cap in the middle.

The tubes used are a 6N2pi for the front end (NOS ones from the USSR) and the ever popular 6CG7 for the outputs.  The power supply is the same as in the Octave V2 with the regulated bias supply and a built in voltage selector.  Quality parts used through out, especially the volume control which is the super nice TKD 2CP-601.  Power levels are on par with the Octave V2.

Price: 1150$ plus shipping

People have been asking for years to do some transformer boxes (or energizers) to drive electrostatic headphones and here they are with a brand new version.  Over the years I’ve accumulated a large number of Stax 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 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 no issues with using bridged amps. A common ground will turn them into smoke right quick so I would never set it up like that.  The boxes can be set for either 117V or 230V with an internal switch.

The latest version now has a new chassis design to be more inline with my other amps, R-core power transformer and numerous other improvements.

Price: 820$ plus shipping

Along with the new SRD-7 boxes, I’ve built a couple of units with Lundahl transformers.  These are custom made transformers which offer excellent performance and more transparency compared to the Stax transformers.  They are also lower in ratio so you need a higher power amplifier (more voltage really) to get the same volume levels as the Stax transformers.  Now the lower ratio plus how these are wound means they have much lower internal capacitance so more detail, better bass, more treble control and all that.

Compared to the regular SRD-7 a few other items have been upgraded as well, better internal wiring, solid aluminum feet and a high grade of power transformer.

Price: 1300$ plus shipping

Page updated 10.10.2021