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

Here is a Stax SRM-717, by far the best amplifier Stax have ever made.  They were a licensed version of the KGSS circuit with some tweaks which have not aged well.  What I did is remove all those mods Stax did to the circuit and take it back to the KGSS.  This removes the overly warm nature of the stock and also allows me to increase the output power by 25%. 

This unit had been recently serviced by Stax and they had replaced all the electrolytic capacitors so no need to do that again.  It is very close to mint condition and looks close to new.  It can be set to any voltage before shipping it out. 

Price: 2300$ plus shipping 

Here is something very rare, a Stax SRA-14S.  This was the successor to the SRA-10/12S from the 70’s and is a large upgrade in every way.  The preamp is pretty great and the earphone section is an upgraded version of the SRM-1 Mk2. 

This unit I found in Japan without the external power supply and I just had to have it.  This may be the most difficult product Stax have ever made in terms of servicing but I just like it so much.  Now the external power supply isn’t one really, it’s just a transformer and some rather crude standby circuit as all the actual power supplies are inside the main chassis.  So I did the most logical thing, I sacrificed the add in bay on the back and put a nice custom made R-core transformer there.  The umbilical spot was fitted with an IEC socket and it even has a built in voltage selector now. 

All of the wear items have been swapped out and all moving contacts (of which are many) have been treated with Deoxit. It’s condition is fair, the front panel looks nice but there are some marks on the back cover.  The replacement transformer can be switched to either 115V or 230V using the internal voltage selector. 

In terms of sound, this was the best amp Stax had at the time and it holds up well today.  They are very rare as I believe only about 300-400 were ever made as it was very expensive, around 200000Yen back in the 80s’. 

Price: 2200$ plus shipping

Here is another rare one, the SRM-T1W.  This rare beast uses the SRM-T1S main circuit board but adds more inputs, a passive preamp output and adjustable bias for the left most output socket.  I doubt more than 500 of these were ever made compared to the T1 and T1S which were made in the thousands. 

With this one I’ve done all of my usual T1/T1S/006t mods to the it, added a CCS to the tubes section, replaced all capacitors and upgraded the bias supplies to modern standards.  I’ve also treated all the moving parts with deoxit. 

The amp is in pretty good condition, some patina on the front panel and marks on the back but nothing too bad.  Operationally it is excellent and it can be set to any voltage before shipping it out. 

Price: 1900$ plus shipping

Here is a pretty recent SRM-007tA that I’ve modified to use 6S4A tubes and they are driven by a CCS.  This is a huge step up in performance over the stock unit.  This makes it a mini KGST, a lot of power in such a relatively small chassis. 

This unit is pretty much flawless in appearance and feels very close to new.  It can be set to any voltage before shipping out. 

Price: 2500$ 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 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

Here is a stock SRM-252S I got recently with some headphones and have no use for.  Looks pretty much new and comes with the original box.  It will also come with my replacement power supply so it can be easily used anywhere in the world. 

Price:  350$ plus shipping

Stock Stax SRD-7 Mk2 adapter in fair condition.  There are some marks on the front and also on the painted cover but nothing too bad really.  These are pretty rare now so I left it in stock form and it makes for a very simple way to power electrostatics, both Pro bias and normal bias sets.  Nothing really to go wrong in these and they are universal in terms of input voltage so they can be used anywhere.  

Price: 430$ plus shipping

Stax SRM-1 Mk2 in pretty good condition given this is an early unit.  Some marks on the front and the back painted panels but it is to be expected of something this old.  I went through the unit and replaced all the electrolytic capacitors plus I replaced the output transistors as they were looking a bit scruffy.  The replacements are far better in performance as well so the amp is upgraded a bit with this.  As with most other SRM-1 Mk2’s, it can be set to any voltage before shipping it out. 

Price: 420$ plus shipping

The forgotten Stax SRM-3 amp, the first real upgrade from the SRM-1 Mk2.  Lovely little amp and a clear step up from the SRM-1 Mk2 and this one I’ve gone through and replaced all the electrolytic capacitors so it should be good to go for the next 20 years.  It is in fairly good condition and it can be set to any voltage before shipping it out. 

Price: 460$ 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 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 second 006tS amp.  Fully modified with a CCS and in very good condition.  No original box with this one and it can be set to any mains voltage.

Price: 1500$ 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 14.01.22