#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).

#20 SM Pro Audio TB202 power supply repair

<Some sort of continuation from another post>

Buuuuut that brings us to what might as well amount up to the proverbial "elephant in the room" - the power supply. No markings or label anywhere on it - if i didn't know any better, i could almost say it never had any (no adhesive residues or anything). Fortunately, it was held together with four Phillips-head self-tapping screws, so "disrobing" it wasn't unecessarily traumatic. That being said, what greeted my eyes, sort of WAS.

#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).

#15 Alesis io|26 repair & modding

So, i got my hands on one of these Alesis io|26 interfaces for pretty cheap (50 bucks delivered). "Of course", i bought it as faulty (can you see a pattern yet?), with the already "classic" issue of dead Firewire chip (the ubiquitous Texas Instruments TSB41AB2).

I went for it mainly for two reasons. First, because i knew it was based on the TC Applied Technologies Dice II chip, and as such, should have flexible enough mixing / routing options; second, due to the ADAT inputs available. The sort of "added bonus", one might say, were the gain adjustments for the 8 analog (mic/line) inputs.

#14 TC Electronic Studio Konnekt 48 "Dice II STD" replacement / transplant

A couple years ago i got my hands on a faulty one of these. Details of the revival process can be found over here; photos visible only for forum members though. Buuuuut since i'm in a good mood, OVER HERE you can find the link to a Google Drive folder with all the (relevant) photos i had posted on that particular thread - you're welcome...

The last issue i had to take care of, back then, was the (apparent?) shorting to ground that some of the I2S clock signal lines, coming out of the Dice II chip. Fortunately, it has several sets of these clock output signals in use, so between cutting a couple traces and adding some wire jumpers, i managed to put together and distribute a healthy set of clock signals to all the ADC & DAC chips that required them.

PS: It seems that the original link for the schematics of this unit is dead nowadays ("thank you", Music Group?), but for the sake of completeness and posterity, i've reuploaded it right over here.

#13 Fisher RS-1022 rehabilitation and bling-ification

So i had this old Fisher RS-1022 Studio Standard stereo receiver brought in, with one of the fuses in-line with the speaker outputs blown. Fair enough, that was easy enough to replace, they made it quite easy, with the fuseholders being mounted right on the rear panel. The clamps were nowhere near as elastic (or firm) as they might've once been, but with a pair of needle-nose pliers and a bit of creativity, that was no biggie.

Second issue, five of the six lamps that illuminate the tuning scale and the radio signal level were dead. In four of the dead ones, the fillament was attached only at one end, and in the fifth, it was attached at neither end. Interesting little lamps, 6.3v AC, 250mA, in a similar casing as 6x32mm glass fuses. Good luck finding replacement ones (which may very well just end up dying again anyway); these will get replaced with a few white LEDs recovered from a laptop display's backlight.

#12 Cheap chinese BM700 / BM800 microphone modding / upgrade (to say the least).

<Part 2 can be found right over here>

Last year, after hearing (or rather, after reading) about these cheapo BM700 / BM800 microphones, over on the GroupDIY forum, i decided to get a few myself. They were cheap enough (under 20 bucks a piece), and i figured they would, at the very least, make for reasonable enough donor bodies.

Some credit is due in no small part to Mr. Henry Spragens, whose microphone section on his blog served as a considerable portion of inspiration for this endeavour. Said blog is a fountain of knowledge, testing and ideas for anyone interested in condenser microphone modding or even building from scratch.