#42 Presonus Audiobox 1818VSL - revisited and revived!

[Part one can be found right over here]

Through a mix of patience, persistence and good luck, i managed to get my grubby mits on another, fully functional Audiobox 1818VSL, for considerably less than the 1-2 pricey ones available on eBay in Europe.

#41 Focusrite Scarlett 18i20 (1st gen) teardown & repair(?)

A local friend bought this slightly battle-scarred Focusrite Scarlett 18i20 off a buddy of his. The reported issue was some random / intermittent noise affecting only the inputs. Time will tell if that was conveyed to me accurately, or if it's a more global issue. First thing's first though - having a wee little look-see on the inside.

#40 Fake "Beats" Bluetooth speaker teardown & mod

I got this handed in by a local friend the other day. It was apparently bought in Singapore a good few years ago, hasn't been used in quite a while, and i guess(?) the charging cable (slightly less usual mini-USB) got misplaced or something.

#39 M-Audio Profire 2626 teardown and repair

Ebay strikes again - this time, a pretty damn cheap (to acquire) M-Audio Profire 2626 Firewire audio interface. I maintain it's still the cheapest way, to this day, to get 24 inputs and outputs to and from a computer. Most other 1U (rackmount) interfaces will give you 8 mic preamps but only one bank of ADAT. The ones with two sets of ADAT I/O will cost you a pretty penny, though.

Either way, this was sold as "not detected by the computer", so my bet's on the Firewire chip being toast, "as usual". Can you see a pattern emerging here?

#38 Focusrite Scarlett 18i8 (1st gen) teardown

Yet another "sold as faulty" eBay catch - a nice little(?) Focusrite Scarlett 18i8 USB audio interface. Which turned out to actually have nothing at all wrong with it.

Admittedly, i went against the first commandment of teardowns (ie. "Don't turn it on; take it apaaaah't!.."), but only because it was the first troubleshooting step, and it used the same drivers as my Scarlett 18i6 "daily driver".

#36 TC Electronic Digital Konnekt x32 teardown and repair

We're having a "productive" period, as it turns out. This time around a TC Electronic Digital Konnekt x32 audio interface / digital patchbay is on the chopping block. Or on the operating table, rather - i do indeed hope to repair, rather than dismember and mutilate this thing.

I managed to catch this, along with a twin of its, for under $200 / 200e delivered, as a "job lot", both sold as untested / faulty. The first one was shown powered up and possibly working fine (several LEDs on the front panel being lit), so potentially fine, pending tests. This second one though, not quite so much - only the blue LED halo surrounding the power button lit.

#35 Focusrite Saffire Pro 24 DSP teardown and repair

Yet another sold-as-faulty eBay catch - a nice little Focusrite Saffire Pro 24 DSP Firewire audio interface. The listing said:

"I bought this online and it is not working or it is not compatible with my computer. My computer is not recognising this audio interface. So I am selling it as not working."

 Fine by me. The photo of the back showed the Firewire port as looking quite pristine, so it wasn't a case of connector-inserted-upside-down. And for the price i won the auction for, it was worth the gamble. A frontal photo did show it powered up, so at the very least, it wasn't dead.

#34 MOTU Traveler mk3 teardown and repair

Hunting for faulty stuff on eBay has been fruitful yet again: this time, a MOTU Traveler mk3 Firewire audio interface. The reported issue was by now, the "classic", dead Firewire.

A pretty comprehensive little package, with loads of features shoehorned into quite a compact package - 1RU thickness / height, but only about 80% of the width.

#33 Superlux R102 active ribbon microphone teardown & reverse-engineering

By sheer luck / accident, the other week i refreshed my Facebook main page (or "news feed" or whatever), and the first thing i saw was an ad from one of the trading groups i'm in, about a Superlux R102 (mk1) ribbon mic for sale, for a measly 30e (~$32). The seller was in a (sort-of-nearby) town i was headed to just a few days later, so i jumped at the chance. Immaculate shape, fully functional, retails for about four times as much - why not?

#32 M-Audio (Avid) Fast Track C600 teardown & repair

This little bugger, an M-Audio / Avid Fast Track C600, was listed as faulty on eBay - description said it would no longer power up, regardless of it being bus-powered or having its own external power supply connected. Got it shipped for 30eu / $30, so why not?

#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?

#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.

#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).

#19 Takstar / Gear4Music WPM-200 Wireless Monitor System part 3: transmitter mods

And at long last(?), we've reached the point where we take a look at the transmitter end of this wireless monitoring system. Not a whole lot to see on the outside, really: power switch, power LED, channel select rotary switch (1 to 6) on the front, and the DC input barrel socket and the 1/4" stereo input jack socket on the back.

#18 Takstar / Gear4Music WPM-200 Wireless Monitor System part 2: receiver mods

Ok, turns out i lied in the previous post, as this part 2 won't be about the transmitter - so sue me...

Either way, into the meat of it: upon some listening tests with music, it turned out the expanders were misbehaving just awfully. They made the volume jump up and down virtually all the time, in a very disconcerting manner - basically briefly increasing the volume (noticeably) upon every louder bass note (and only for the duration), and dropping back down in between.

I took apart one of the receivers, and lifted the schematic of the expander chip and the associated passives around it. Pretty much exactly what's in the datasheet of the TA31101, with the exception of having omitted the coupling capacitor going to the "Comp In" (pin 11), thereby turning the compressor side of the chip into another 1:2-ratio expander, just like the other half.

#17 Takstar / Gear4Music WPM-200 Wireless Monitor System part 1: receiver teardown / li-po upgrade

This "part one" will be dealing only with the WPM-200 receivers and the lithium-upgrade pertaining to them. The transmitters and subsequent mods will be dealt with at a later date.

Fine, i'll admit, i miiiiiiiight be ever so slightly guilty of the whole "if all you have is a hammer, everything around you looks like a nail" thing, what with these nifty little one-cell charger & protection boards, but hey - at least it kinda validates(?) my "stockpiling" of laptop and phone batteries along the years. Now, i finally have the excuse to put some of them to good use and all that...

During my UK eBay browsing sessions a month or two (or seven?) back, i happened to come across a few listings of faulty wireless monitor sets (transmitter & bodypack-receiver) from this British music gear retailer. A bit of googling later, revealed to be straight rebadges of Takstar WPM-200 sets - nope, they hadn't even bothered changing the model number. The one thing they might've customized, though, are the radio frequency ranges / channels (since there are different regulations on different continents, and so on).

#16 Cheap chinese BM700 / BM800 microphone modding / upgrade, part 2 (CK12 & K47 capsules)

<Continuation from part 1>

After quite a while, i "finally" got around to modding the other three BM800 mics i had. Just for the hell of it, i decided to make a matched triplet (to use as, say, three overheads on a big drum set).

I went with more of my modded-Schoeps boards, and matched components between them, as closely as i could (within reason, at least). Resistors were no big deal, and neither were the capacitors; one of those cheapo chinese ATMega328-based "component testers" helped with matching the JFETs and PNP transistors. No, i didn't necessarily care about the absolute values, just that they're the same (or as close as reasonably possible).