Humble beginnings….

I thought the title was appropriate because while this build might not look like much, what comes after it is hopefully somewhat more impressive. It’s an external AC power supply (a.k. a. a transformer in a box 😀 ) for an upcoming version of Kevin Gilmore’s Dynahi SuSy (SuperSymmetry) balanced headphone amplifier (more info here).

The reason for making an external PSU isn’t grounded in any particular philosophical belief but simply in a lack of available space in an (already sizeable) amplifier chassis. The decision to make it an external AC PSU rather than an external DC PSU is a slightly philosophical one though – although heavily influenced by thoughts on practicality and versatility 🙂

This is 2x25VAC and it will eventually have a 2x30VAC identical twin for another project which also requires an external PSU – at least if it is to have any hope of fitting in a standard-sized stereo rack 😀

The chassis is as compact as I could reasonable make it and the output is fused via my fuseboard (link) and then fed to a 5-pin Neutrik XLR which has a few features I like for this application (solid, reliable, cheap, locking etc.)

Front panel, power switch and final wiring coming once the front panel layout for the amplifier itself is ready 🙂

High voltage…

Yes I am still here, but it’s another busy period for me at work so updates to the blog are correspondingly few and far between. As usual when I don’t have a lot of time for diy I still somehow manage to start up new projects. Even with less than 48 hours at home in a weekend, there’s still time to do a little soldering to relax and unwind 😀

Among the overdue projects I’ve managed to start up lately are some amplifiers for my Stax electrostatic headphones. This is actually more than a little overdue, because I haven’t had a Stax amplifier for nearly a year now and so the headphones I have aren’t getting any use which is a shame really.

The pile of half-assembled boards in the picture actually consists of the following designs, all by Kevin Gilmore:

– A pair of KGST tube amp boards and matching 350V PSU

– A mini-version of the KGSSHV amp and matching 400V PSU

– A version of the KGSSIC/“Carbon” amp and matching 400/450V PSU

Most of the boards were all acquired through various group-buys on the forums, but Kevin graciously keeps the Gerber files for all of his designs available for free download as well.

I’ve soldered more or less all the parts I have available, so still to do are:

1) Order remaining parts (working on that – since it’s also possible to do from hotels after work :D)

2) Figure out the mechanical stuff (mostly done, but still needs a bit of work – and some tools I don’t have regular access to)

3) Select and match a pile of semis (saving that one for a rainy day 🙂 )

4) Finish and test boards (as quickly as possible)

I’m not really used to high-voltage stuff so I am being extra careful with these boards. Just like when you move up in frequency, moving up in voltage means that things that were not previously issues suddenly become very important. Fortunately I have a working variac again (fixed after stupidly blowing a fuse in it a few weeks ago) which makes testing much easier – not to mention safer all round.

These aren’t the only Gilmore-designs I’m working at the moment by the way, but the rest involves much more pedestrian voltages 😀


A milestone is reached…

Here is one of the projects, if not the project, that gave this blog its name :). It’s the Gilmore Dynahi class A headphone amplifier. First published as a design by well-known headphone amplifier designer (and chemistry professor) Kevin Gilmore on head-fi in late 2003, the Dynahi was one of the most extreme headphone amplifier designs when it was published (Kevin has pushed the envelope a little bit since then, especially with some tube amps 😀 ). The amplifier runs in class A on +/- 30V regulated rails and dissipates around 20W/channel (plus around the same for the regulated PSU boards). If that isn’t enough, you can build it as a balanced configuration as well (often referred to back in the day as the “dynamite” :D). The design was quite common a few years ago but is now not seen very often, probably because most of the active components are very hard to find nowadays.

My boards are actually from one of the original group buys on head-fi, around 2004-2005. For the last year or so (ok, it may well be two or three…) I have had the amp boards populated with resistors and the PSU-board assembled without ICs mounted, but that is as far as it got. However, this weekend I finally managed to fabricate the required angle brackets, which meant I could start matching up and mounting the output transistors. This may not be the most entertaining part of a build (at least not for me), but there is a certain satisfaction to it anyway – especially after it is done 😉

The amp boards are now briefly tested and seem to be working fine, but the PSU is acting up a little and needs to be troubleshooted. Otherwise the next step is to design the casework – even with the substantial heat that this amp gives off I am still convinced that it is possible to fit it into a 1U case (just haven’t completely figured out how yet 🙂 )

Oh, and by the way: This also happens to be my 40th post here on the blog which also qualifies as some sort of milestone I guess 😉