Used and special one-off amplifiers

Time to split up the special’s page into two so one for headphones and another one for electronics.  Here I’ll list what my more unusual amplifier projects, used amplifiers that I’ve refurbished/rebuilt plus any other piece I’m selling.  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 or is flagged as spam.  All prices in US dollars (USD).

Here is the new Stax SRM-700t amp which I just had to get since I do so much work on these Stax tube units.  Turns out this amp uses the exact same circuit as the SRM-T1/006t/007t amps and it sounds pretty bad in stock form.  Thin and lifeless as is the norm with the stock Stax amps but I fitted this one with a constant current source and it completely transforms its performance.  Now it sounds alive and quite powerful, a huge step up from the stock unit.  This unit came from Japan and is pretty much new in every way.  Comes with the original box and can be set to any voltage prior to ship it out.

Price: 3500$ plus shipping

I have a couple of my older KGSSHV’s for sale.  I sent these out on loan for a project I was involved in that is finished so they were shipped back to me and I fully refurbished them, so they are good as new.  This is the regular version of the older last version of the KGSSHV but fitted with the newest PSU design.  Other than that these are regular KGSSHV’s and a great amp for most users. 

The only issue with them is they are very sensitive to any electrical issues, especially if the neutral and ground are not at the same potential.  Combat against it I’d have to fully rebuild the units so I’m just going to offer these at well below my cost with the caveat that they might need to be used with a power conditioner if the electrical supply is not up to snuff. 

Price: 1900$ plus shipping

 

This is a bit of unicorn, SRM-007t nr.4 in the world.  It is in very good condition so I just had to have it have look through it to see if anything had changed on the later units.  Turns out they god this right the first time so I replaced all the wear items and did my uses 007t mods, fitted a CCS and swapped the tubes out for 6S4A’s which makes this a mini KGST now.  Cracking little amp and it can be easily set to any voltage due to the voltage selector on the back

Price: 2300$ plus shipping

This is a an older 007t that has been fully refurbished, fitted with a CCS and the tubes changed to 6S4A’s which makes this a baby KGST.  Some light marks around the tubes on top but otherwise in very nice condition.  The amp can be set to any voltage before shipping it out. 

Price:  2000$ plus shipping

This is a late production Stax SRM-Xh that I’ve completely refurbished with new capacitors.  This the later bipolar version which is very similar to the later SRM-212 and 252.  It will come with my aftermarket PSU with either a US or Schuko plug. 

Price:  230$ plus shipping

This is a prototype Octave V2 which I was looking into but ultimately proved too hard to assemble.  This one has custom PCB’s to make it this small but all the performance of the normal Octave V2.  It has only RCA inputs  but is otherwise identical to the standard Octave.  It can be set to either 117V or 230V before shipping it out. 

Price: 950$ plus shipping

The following amps are all used Stax units which are based on the same circuit and have received similar modifications.  The main essence is how the tubes are being driven, the stock Stax amps use (to this day) resistors to drive the output tubes but what I do is remove those and fit a solid state constant current source (CCS).  What this does is almost eliminate the loss you get with the resistors so more power and more voltage swing which completely changes the amps performance.

This is one of the rare “gold” SRM-T1S units in pretty nice condition considering its age.  I’ve gone through it and done all of my usual mods, replaced all the caps etc. so it sounds better than new.  It has the same internal voltage selector as most T1/T1S units so I can set it to any voltage before shipping it out. 

Price: 1100$ plus shipping

This is a SRM-T1S in that lovely SR-Omega color.  This is a late production unit as it has the external voltage selector and has been fully refurbished and CCS modified as the other amps. 

Price: 1300$ plus shipping

This is the nicest SRM-T1 I’ve seen in years.  It is virtually flawless and even the transparent sticker on top of the front panel is intact (which it never is).  This one has been fully refurbished and then received my full mods and CCS and on top of that it comes with the special Stax branded tubes they did for the Lambda Signature back in 1987.  As with all other Stax amps, I can set it to any voltage prior to shipping it out. 

Price: 1300$ plus shipping

This one is the same as above but a bit of a rarity, as it is the 006t but with three Pro bias outputs.  Stax only made these for just over a year as they discontinued support for the Normal bias sets but the new 006tA wasn’t quite ready.  Their solution, just add the third Pro bias socket and the amp is now a bit odd.  🙂  Same performance and with the CCS mod, this amp can actually drive three sets at the same time.

Price: 1300$ plus shipping

It is in very good condition and sounds lovely as all these CCS modded amps do.  One odd thing is that this unit came with vintage EI tubes and they measure great so I left them in.  The amp can be configured to either 117V or 230V before shipping it out.

Price: 1400$ plus shipping

Here is a Stax SRM-006tS that I’ve converted to a CCS for the output tubes.  I also fixed the issue where one of the output resistors is bypassed on the PCB from the factory.  This is one of the newest units with a Japan only transformer (so 100V only) so I had a new transformer made and fitted to the amp.  The core is a bit bigger so the transformer runs a bit cooler.  There is an ever so slight mechanical hum from the transformer but it is very minor.  The amp looks pretty much like new and comes with the original box as well.

Price:  1500$ plus shipping

Here is a second 006tS amp.  Fully modified with a CCS and in very good condition.  No original box with this one but well packaged and it can be set to any mains voltage.

Price: 1500$ plus shipping

This is a small portable electrostatic amp out of China with a built in DAC.  It was sold together with a set of headphones and they use a propitiatory connector, not that I let that stop me.  I’ve fitted it with a Stax socket and adjusted the bias to the Stax standard as well. 

In a similar vein to the King Sound H3, this uses a regular Class D amp with transformers to step up the signal for the electrostatics.  The bias supply is a simple voltage multiplier run off a small PSU and this is a neat desktop or portable amp. 

400$ plus shipping

This is the King Sound M-03 portable electrostatic amp and the latest version at that.   In stock form it is not Stax compatible but I’ve fixed that.  This one is pretty much brand new and comes with the original pouch.  Neat little amp that works well once fixed.  It uses transformers to step up the output from a regular amp chip so it weighs a bit. 

Price: 400$ plus shipping

This is a transformer box I received with some DIY electrostatic headphones out of China.  In stock form it was pretty terrible but I’ve completely rebuilt it, added a teflon Stax output socket, nice binding posts and full output protection.  The bias supply is a pretty neat DC-DC converter so it takes a 12VDC input and the PSU is included.  The transformers in this is some China special but they sound pretty good and are very much oversized.  They also have a higher ratio than the Stax standard so you can get away with a lower powered amp to drive these.  Hard to put down a number but a powerful headphone amp with a lot of voltage swing should work well to push this. 

Since the stock box arrived with no markings at all I stuck one of my badges on the front of it and printed out some labels on the DYMO for the back.  These are just stick on so easy to remove. 

Price:  300$ plus shipping

 

Burson Conductor V2 which I was using as a preamp.  Very nice unit, sounds great and is a far better unit than the new Conductor amps.  This one doesn’t have the dac module so it is just a headphone/preamp. Can be set to either 115V or 230V.

Price:  600$ plus shipping

Here is an Audio-GD dac I’ve had for some years but I can’t remember which version this is.  It is filled with PCM1704 dac chips and very nice discrete parts.  The utter overkill in terms of design and parts quality which is the norm with Audio-GD and this one sounds great, I just never use it with a Denafrips Terminator in the house.  The dac was set to 115V when I got it but it was easy to convert it to 230V and I easily revert it back if needed.

Price: 600$ plus shipping

A completely original Stax SRA-8S preamp/amplifier from 1967.  This one is completely untouched and while it came from Japan the transformer does have a provision to run on 117V as well.  Simply move one wire and you are set.  Now this amp needs to be refurbished but I have so many that I just want to sell it.  These are super rare and a great match for anybody with a SR-1 set or even the super rare SR-2.

Price: 800$ plus shipping

Here is a DIY amp I got from Japan as a combo with some headphones I wanted.  The plan was to do something with it but I just don’t have the time so I’m offering it up for sale.  This is the classic Stax SRX amplifier and is very well made.  It comes with all of the tubes and a very nice Tango transformer.  Therein lies a problem though as the transformer is 100V only and no way to adjust that.  There are replacement transformers available from ISO/Tango and other Japanese firms but they are rather pricey. 

Still it would be a fun project for somebody as it can easily be swapped to CCS load for the output tubes and other mods. 

Price:  300$ plus shipping

Last updated 19.11.21