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 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: 5100$ plus shipping

Now this is a rare beast and the first one I’ve ever seen, a balanced SRM-1 Mk2.  There were rumors that these existed (as the amp can accept a balanced input) but no further info was out there until this one showed up.  It was in rough condition but I cleaned it up, fixed a flaw with the circuit in one channel and updated it a bit too.  I also replaced all the capacitors, cleaned the volume control and other regular maintenance.  The voltage selector on the back was also broken so I glued it together again.

Aside from the balanced input, this is a standard SRM-1 Mk2 PP (two pro bias outputs, better resistors and better output wiring).  The condition of the chassis is ok but not great.  The amp was covered in tape residue when it arrived but I managed to clean it off.  It has the voltage selector on the back so it can be set to any voltage.

Price: 670$ plus shipping

Ahhh the Jade 2 amp.  Me owning this and exposing how shockingly bad its build quality is has caused Hifiman to loose their cool but now I just need to get rid of it.  The amp is what you would expect from Hifiman but I did some changes to it so it’s at least now safe to use.  I cleaned up the internal wiring, made sure it is properly earthed and replaced all the no-name capacitors with proper units.  I also redid a lot of the soldering as one capacitor just fell off the PCB.

Sound wise this is pretty thick sounding with not a lot of extension.  Uninvolving also springs to mind but it could be messed with and improved greatly.  I just don’t need any more projects so I’m offering it up for a lot less than retail.

Price:  400$ plus shipping

Here is one I thought I’d never sell but then again, I never use it. So this is a Stax SRA-7S which as the first popular Stax amplifier and designed for the SR-1. This was back in 1967 so before even the SR-3 or SR-X mk1 was released. It’s an all tube design and quite small for the amount of circuitry that is in it. So I got this amp from Japan and it has been completely rebuilt. The only original parts in this as the chassis, output sockets, tube sockets, amplifier PCB and the original tubes as they all measured good. The rest is all new and improved. There is a thread on head-case.org where I documented the lengthy rebuild process but basically when I got the amp it was 100V only and the power supply was basic to say the least. There was also no place to put the improved power supply so the first thing I did was to scrap the phono input as it took up so much space and was terrible to begin with. The transformer was scrapped and a new unit from Hammond was installed with the +300/+600V power supply from the Octave. The amplifier board was completely rebuilt with far better parts and moved further away from the transformer.

I really went to town here though as everything else was changed and upgraded. The front panel markings were peeling off when I got the amp so I cloned them and had my laser shop etch them onto the same plate once I had cleaned off all the old labels. The back panel RCA sockets had not aged well so I replaced them with new gold plated Neutrik sockets and redid all of the input wiring. There was a new input switch fitted plus a new volume control and balance pot, both Alps RK27. The power and mono/stereo switches were also both replaced with new units from Japan plus one output was converted to Pro bias output to make it more modern.

This amp has one unique feature which Stax stopped adding in the 70’s… it has a tone control. Basically this is a switch which has 4 settings and it increases the amount of series resistance there is inline with the output of the amp. Now the stock configuration was odd as it treated just one half of the push pull output so when I rebuilt it, it’s done right with matched sections for each output phase. Finally the amp was fitted with new feet, a proper power cable with strain relief and the top cover was powder coated. Last but not least…the knobs used on these are still being made in Japan so I custom ordered new ones as the old ones were unsightly.

The prices for these amps are crazy in Japan now even with tatty samples hitting 1000$ or more. I paid way too much for this one and the rebuilt was…insane so that explains the high price. I also kinda don’t want to sell it but that’s how it is… 😉

Price: 1500$ plus shipping

Last updated 22.08.19

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