#66 Audient iD22 teardown

Despite having hoped to nab an Audient interface for some time now, only quite recently did i manage to get my hands on one. Since i'm a cynical... [ahem] person, after having heard several notable(?) audio engineering channels over on Youtube ranting and raving about these, and the "Audient console preamps", and the "discrete JFET DI" and whatnot, my curiosity was indeed itching to see if and how the reality lives up to all the hype and marketing. 

#60 MOTU 8M teardown

Well, this one's a "biggie" - i had been lusting after one of these for a few years now, but the price was (and technically still is) on the prohibitive side, retailing at ~$1300-1500, depending where you look. Fortunately though, i've been stalking eBay off and on for one of these, and a used one happened to pop up just the other week, on auction. To my amazement and delight, despite there being at least 6 other "watchers", i was fortunate enough to win it for the opening bid, ie. about half the price of a new one.

#57 Apogee Ensemble Firewire pt.2 - the repair

I was considering making the previous post about the repair as well, but once the teardown part of it was done, i decided it had gotten long enough already, so here's the testing and (hopefully) repair of it, separately.

#55 Focusrite Scarlett 2i2 (1st gen) teardown & modding

I had fiddled with one of these a couple years back, but here's another chance to take a look inside a (1st gen) Focusrite Scarlett 2i2, their second-smallest USB audio interface of the range.

#49 Joyo ZoMBie, part two - analysis and repair

It took the best part of an evening and a couple hours the next day, but i managed to lift the schematic for the whole preamp board. I also recreated the board, but that was mostly for sanity-checking. I used all the same component designators, but didn't bother measuring all the dozens of small ceramic caps, because there's only SO far i'm willing to go...

#47 Joyo ZoMBie guitar amplifier teardown

My bandmate got his hands on this Joyo ZoMBie about a week or two back; it was sold as faulty. No idea how or why, but there's something dicky with the tone control - on some power-ups it works fine, but sometimes quits working (ie. sounds like the setting got stuck at some random point along the travel of the knob), no matter how much you twist it. Power cycling sometimes helps, but inconsistently, and even if it does, it just "gives up" again, sooner or later.

#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).

#21 SM Pro Audio TB202 dual tube preamp / channel strip modding & upgrade

<Further developments can be found in parts two, three and four>

I'll admit, this was a bit of a lucky catch, in that it was mistakenly listed in the wrong eBay category, but one i "stalk" for good deals on certain faulty bits of audio gear. It was up for auction, there didn't seem to be much demand for it, and i ended up winning it for a mere 21 euros. About as much as the shipping for it ended up costing, oddly enough.

But still, even for some 40-odd bucks, not a bad little unit. Two channels, a (bare-bones-ish) compressor on each (1.5-10:1 ratio, 1ms/5ms attack, 500ms/1500ms release, at least according to the specs in the manual), as well as 3-band EQ (80Hz shelving / 1.8kHz bell / 8kHz shelving), and there's a tube / valve involved in the circuitry as well. If nothing else, i figured it would do nicely as a bass DI (or even an overdriven preamp, once some internal re-wiring is figured out and done).