#31 Warwick ProFET 5.1 bass amplifier teardown & maintenance

A local buddy just brought this German beastie in, citing a dicky DI output, and an unhealthy-sounding fan. Well, when i say "German", i mean the brand itself; as one might expect, it's "obviously" made in China, as it says on the back. But isn't nearly everything (else), anyway?

#30 Double Dock Day - HP HSTNN-I11X and Dell PR03X (USB 3.0) teardown

Right, so i had been on the lookout for a cheap docking station for my Dell Precision M4800 for a while, and the other week i stumbled across and ad on a local website about a clearance sale from a university - docking stations, laptop chargers, some desktops etc. When i finally got to their premises, instead of the $5-10 prices i expected, the guy there said i could have them for some coffee-change into the tip-jar, so i walked out with two PR03X's for a mere 40-50 cents or so - me happy!

The HP dock though, was about 15$, but came with a ma-HOO-sive 230W power brick, which is for another project; expect a teardown of the brick soon. Sadly the dock wouldn't fit my HP Elitebook 6930p (only the later xx40 Elitebooks), but that doesn't mean we can't take a peek under the skirts, and then resell it to make some of the money back, right?

#29 Tie-dyed acoustic panels

I know, it's a bit of an uncharacteristic topic for this (sort of a) blog, but despite the curve-ball thrown here, bear with me. It's for a good cause... As it were.

#28 Active full-range surround speaker project (BN96-12832 & TPA3118)

Since the "unofficial" theme of this blog seems to be repair, recycling and repurposing (more or less), i finally got around to getting knee-deep into this idea, which i started devising quite a while ago - a pair of "slimline" surround speakers.

Disclaimers:
 - No, these are not meant (or supposed) to be "hi-fi". More just for a bit of "ambient noise", if you will, for movies with 5.1 soundtracks. That, and possibly alternative monitoring for checking mixes.
 - No, these are not meant to go terribly loud. Due to, let's call them, physical constraints, they'll be placed at the corners of my sofa (right up against the wall, opposite the TV and the "mains"), so no huge SPL's are required.

#27 Samsung 5V 1A ETA0U81EBE USB travel charger

This one's a quickie, but i figured i might as well document it.

A friend passed me this a few weeks ago, not quite sure why. I don't recall it being mentioned as dead, only not-used. Either way, last night i wanted to charge the battery inside my modded M-Audio Fast Track, in preparation for a local gig next week. Upon plugging it into this thing, the power LED flashed up for an instant, then nothing. I figured it might not like the USB data lines being tied together, as they often are, in chargers; it powered on and worked well with another charger. But that prompted me to crack this one open.

#26 Cheap & easy DIY LED light panels

Recycling's all the rage nowadays, right? Right..? Well, either way, freebie raw materials for projects are always welcome, that's something i'm pretty sure we can all agree on. Now, i'm not admitting to be a hoarder, far from it, but i kinda-sorta couldn't bring myself to throw away the dead (read: cracked) laptop LCDs that i had replaced for various clients at work. And what with "finally" expanding this blog onto YouTube, i figured i'd need some extra lighting for the workbench. Catching my drift yet?

#25 Behringer ADA8000 "Ultragain Digital" revival

I got my hands on one of these Behringer Ultragain Pro-8 Digital a few months ago, as faulty (as in, totally dead) for about 50$ shipped. Having done some preemptive googling before going for it, i was expecting the transformer to be toasted. Sure enough, that's exactly what the problem was - one half of the center-tapped primary measured in the hundreds of kohm, so pretty much open-circuit (as opposed to the 50-odd ohms the remaining good half measured).

Initially i was planning on finding / getting a "drop-in replacement" toroidal transformer, ie. similarly sized physically and power-wise, but with less insanely-high secondary voltages. The stock one, according to some "inspection notes" i found online, seems to have had roughly 2x20VAC windings for the analog +/-15V (meaning the voltage regulators had to "burn off" uselessly much power / voltage), 12VAC for the 5V regulators, and a whopping 58VAC winding for the phantom power regulator. That's about a 50% overkill across the board. One can only wonder just what possessed them to spec the transformer quite like that, especially since it must've been a custom order - you'll rarely find retail units with more than two (identical) secondary windings, and when you do, expect to pay a pretty penny for'em.

#24 SM Pro Audio TB202 dual tube preamp / channel strip modding & upgrade, part 4

On the note of front panel switches, you might've noticed two extra ones, in the previous post (the part 3). One other idea had crossed my mind, already long before this second stage of modding. It took me a little while, but i managed to get my head around how to implement this. The idea was to be able to swap the order of the two processors in the signal path.

From the factory, as described in the "part one" post, the processing order is input - gain - tube - compressor - EQ - output. But in some cases, it can be desirable to have the EQ come before the compression stage. That way, one can attenuate certain frequency ranges that one would not want the compressor to react to (or conversely, boost ranges for the compressor to react to).

#23 SM Pro Audio TB202 dual tube preamp / channel strip modding & upgrade, part 3

Even before having received the thing, i had already started thinking of daisy-chaining the two channels. In the context of something like a bass preamplifier, for example, one would want a "clean" channel, perhaps with some heavy compression, in order to have a consistent signal (especially in the lower registers), as well as a "dirty" channel, with a high-passed signal having some distortion applied to it.

#22 SM Pro Audio TB202 dual tube preamp / channel strip modding & upgrade, part 2

Once the "adventures" from the previous post were completed, i proceeded to hook up one channel to my audio interface and feed some test-signals into it. This revealed a few things which didn't sit with me all that well.

First of all, the compressor didn't seem to be doing much of anything. No level reduction with the knob turned up to full (even with full input gain and clipping the snot out of the tube), the associated LED stayed green (instead of going red), nothing. A bit of oscilloscope-probing in the signal rectifier area quickly pointed out the issue - there was no real rectification going on. The signal coming out of that stage was still largely sinusoidal, albeit with a small kink at the zero-crossings. Well, that's no good...

Removing the diode in the signal-rectifier for testing didn't reveal anything, it measured as a normal 1N4148 both in and out of circuit. My aforementioned buddy pointed out that the arrangement they had used in this design, a "precision diode" circuit, was somewhat flawed as a concept, as is described in this link over here. I then proceeded to upgrade both channels to the "precision rectifier"circuit (see link above).