HELLO!

My, my, it has been a while.

The fault is entirely mine. I've been immersed in the doings of Rochambeau Musical Apparatus for the past couple/few years now and it has sort of locked my time away from this particular avenue of sharing. While I will admit that what I am doing with RMA is in and of itself blog-worthy from a content point of view, it is also a deeply personal journey through mis-applying engineering, empirical education, and general mayhem and I have decided that my process functions better outside the spotlight and on my terms.

I want to stress that this is not due to overt secrecy; if anyone has any questions regarding any of the RMA designs or specific builds I should be somewhat easy to find.

At any rate, I have a back log of personal projects still and I will endeavor to publicize them when I feel doing so adds value to our pool of knowledge. Now without further ado:

The Akai MPC2000xl I purchased new in the spring of the year 2000 had lost function of the note variation slider. This appears to be, based on my perfunctory google search, a relatively common problem. Replacement parts are easy to find through branded supplier sites, but I'm a skinflint so when I happened upon a webpage that outlined opening up the slider and cleaning it out I naturally took that road first.

Are there twigs in there?

Full disclosure: my studio environment has at times been substandard in regards to environmental control. We're talking basements, uninsulated sheds, and a warehouse space in which the only source of heat was a tube amp and an engine block cooling off after my drive home from work. Swings in temperature and humidity are hard on gear, and the necessity of fixing stuff has delivered me to where I am today. Anyway, the slider contacts were indeed swamped with muck. A little isopropyl gently applied was in order...

..ah. Well then. It's an easy task to clean metal; it's quite challenging to grow it back into shape. And no, bending the corroded tines of the wiper outward a little bit in order to regain contact proved fruitless.

So, as I mentioned before, you can simply punch a couple keywords into a search engine and locate a specific replacement for this part with ease. I found them ranging from $10 to $15 USD before shipping, which, while far from outlandish did not strike me as the most effective solution.

I regularly order parts from Mouser for RMA, so it stood to reason that by looking for the part in generic terms I could skip at least one generation of mark-up. The criteria is 10K linear dual gang 45mm throw with a particular PCB footprint. I found my match here at Mouser for $1.83 before shipping.

Here's a PCB side shot indicating the solder joints that need to be removed for extraction. The blue pads are structural and two of the lower pads connect to nothing and can be ignored (at least in my machine).

Removal of the failed component was a breeze with my iron and a plunger type solder sucker.

Look at that! A single sided PCB with through hole wire jumpers.

New part drops right in, and soldered right up.

It's alive!

I didn't go into tear down of the MPC because while I am guilty of not having looked it up, I'm ASSuming there are numerous excellent information stores you can find regarding that. I do need to qualify my fix with the following:

THIS IS NOT A DEAD STOCK REPLACEMENT.

Functionally my machine works again, but the slider I used A) will not accept the stock slider cap (I may drill my cap out to attain a fit, but this is risky because the shaft of the new slider is larger in both non-height dimensions and there is not a lot of material to work with) and arguably more important B) the new slider has a center detent.

Since this is my machine I do not mind the center detent (in fact, I kind of like it) but I should note that at centered position my machine reads a +8 in the +/-120 range, so electrically it is not centered when physically centered.

For those reasons I would recommend the OE parts for client based work, but I'm happy with my fix.

Took in the new Baktun with some long overdue recording yesterday.

I'm still not clear of the underbrush in regards to the Otari, but it performed very well on tracks 3 & 4 yesterday, proving that continued hammering is warranted. But, this post is not about the tape machine.. in setting up to record I decided to utilize the long neglected Eventide H3000. I discovered forthwith the fact that the soft keys had entered into the realm of unresponsiveness, robbing me of the ability to edit patches and really use the instrument.

That simply would not do. Guts up.

I have some number of gaps in memory, as in the manual references patch programs at certain numbers that for all intents are inaccessible on this machine. Seeing as how I can still construct whatever I want, I'm ignoring that right now. The H3000 sounds good, and is a capable effector (honestly, if the digital vs analog sound quality debate comes up I'll point to this thing as the STFU card, and I am of analog bias). Anyway, I'm not here to talk about the selective memory either.

I just find it interesting that ROM doesn't fit the socket, and am curious about the empty socket to the right. No matter...

When I bought this it was inoperable. It would power up briefly, then the relays would click into bypass and everything dimmed out. The cause of this was the plug depicted here. Addressing conductivity at this connector brought the unit back to life. So yeah, I'm always on the lookout for rack mount Eventide gear that exhibits those symptoms, even though I just gave away the thousand dollar fix.

Anyway, back to the soft keys. Pull the bottom cover and this is the access. Spray liberally with residue free contact cleaner while tapping the switch. Allow complete evaporation, reassemble & enjoy your fully responsive instrument!

Dusting off the PA since it's going to see some use this fall, and I'd really like to dodge the last minute cram if at all possible.

While I was tooling about that corner of the garage I figured I'd give the pile of dead speakers a more thorough examination so I can start chewing on my plan for them as well. Enter a Cerwin Vega 154FM that was beaten into submission at Eugene Noise Fest 2007. If I had to wager a guess, I would say it was during The Sunken.

Which led me to this observation. Furthermore, clamping a battery lead onto that little sliver of wire confirmed that everything else was intact and functioned as normal.

Upon removal of the dustcap, which is a two layer fabric mesh over aluminum assembly, I was greeted with less than optimal news. Judging from the concentric creases, it would appear as if the tinsel fell out to prevent the voice coil from punching through the cone.

The eyelets that tie the tinsel to the voice coil wires are on the verge of punching through as well, observe the discoloration of the VC lead terminating into the empty eyelet, that'll be explained in a moment.

Due to the weakened cone structure, the voice coil assembly and immediate surrounding area could close up to the aluminum dustcap when the speaker was in it's positive excursion. This effectively shorted the output of the amplifier across the dustcap, producing the spalling seen here and heating the joint up enough to cause the solder to flow, whereupon that connection acted as a fuse and opened up eliminating further damage.

Repairing the electrical connection was easy. Reinforcing the integrity of the cone to avoid repeating the failure, however, resulted in the plastic surgery disaster seen here.

I'm not ashamed of this, it is ugly and I would not endeavour to recreate this, but honestly this driver has been sitting around awaiting a recone for 5 years, and if this botch-work quilt of a fix extends the use of an otherwise trashed object, I'm all for it. I realize that with the pooled glue splints the delicate nuances of whispering sweet lower mids have been pounded into the bog, but since this is a piston being deployed in the 40 to 100 hertz range that wouldn't have come up anyway.

So, the other night we sat down to watch some Dr. Who (final stretch of the Key To Time arc in the Tom Baker era) and lo and behold, the television, a Sony Bravia KDL-32M3000, was broken.

Neil nails it at 0:37. "No more telly.."

Actually, the symptoms were highly diminished brightness with a murky red hue, the images on the screen would essentially pulse: movement by an actor would be jerky, as if watching them through a strobe light with a sort of blur between frames. It was a lot like REALLY bad animation, running dark and murky reddish images at roughly 4 frames per second. It was, put simply, unacceptable.

Suspicious that it might be the source, I went to change inputs, only to observe the sluggish response with the menu windows as well, certainly not a source problem.

Since I'm not really super keen on the whole disposable culture thing, running out and buying a new TV isn't really high on the list. In searching the model family I learned this is a very common failure mode. I pretty much followed the following tutorial, and figure I may do someone a favor with clear and legible pictures.

I took to muting the sound, as there is no narration..

I had initially planned on testing voltages between these two points, but faced with the level of disassembly I decided to just go for it. The LCD was bought new in 2007, easing my apprehension a little.. sort of a nothing to lose now project.

All those circuit boards hanging off the back? They need to be removed. Disassembly down to the LCD section is a few layers deep, I took some pictures along the way in case I had to reference anything on reassembly. The entire process was not to bad, but I've certainly been inside simpler devices.

10 ohms, tied into wire runs each end and about to be encapsulated with yellow heat shrink.

The offending ribbon connector is the largest PITA of this process. After gingerly scuffing the insulation layer with some sandpaper I folded it up and secured it with some 3/4" blue masking tape so I could solder with impunity. A bit of liquid flux was added to the partially scuffed pad to assist soldering (I feared going deeper due to the incredibly small traces, so once I visually observed a bit of metal I stopped).

With the pre-tinned wire I essentially placed the wire over the pad and directed heat from the top side. Took the better part of a second at 600f. Once that contact was made it was returned to its relaxed position and secured with tape.

The actual voltage feed I want is on the left, but the pads are close & small enough that my tinning one incurred a little crosstalk to the other.

Not what I would call a structural solder joint, that's what the tape & shroud is for..

Overall view.

While I had it apart I took a moment to admire the elliptical full range drivers that are stock in this thing. Not that the driver struck me as magnificent, just that the shape is neat enough to imagine several dozen of these in a line array configuration. No expectations...

Rainbow artifacts aside, the picture looks as good as new.

Received my ON-Semi MJ21195/96 power transistors for the Soundcraftsmen power amplifier late last week and slapped them in over the weekend. In a wholly unscientific manner I opted on the MJ21195/96 because the response curves tapered in a gradual manner and the ramp up to roughly the 50% current output appeared peppier. Plus they were cheaper, by 57 cents each. If the amp sounds like shit when I'm done, exploring the other output devices is within my capabilities.

That would, naturally, only happen after a recap and some other tweaking the good people at audiokarma.org have spoken of.


This, and a pair of pliers to grab and twist the shaft, is how I reached the rear screws without tearing this thing completely down.


As I wrote a while back, the rebranded TO-3 transistors were less than informative in regards to determining which of the 2SB554/2SD424 pair carried which cryptic alpha-numeric stamp. Direct measurement to determine the orientation of "diodes" on surviving devices was the simplest route to identification, here we see the unobtanium "5A" PNP (2SB554) being replaced with current production devices.

Replacement surgery went well, next up looks to be replacing the differential pair to shed some DC offset on the outputs, but before I go that far I aim to secure a copy of the service literature on this amp to assist in avoiding any pitfalls. Why yes, I probably should have had that from the beginning.

Recapped the B+ power supply of my 1973/4 Fender Princeton last night. This is the amp that had sat in a shed for a while and sounded anemic as hell in a raspy farting through a cork wall sort of way. The main problem was not a failing speaker as the seller thought, but a lifted ground reference in the phase inverter section that proved a simple fix. The amp was far from done, needing the logical next step: removal and replacement of 37 year old electrolytics.


Since the overall amp is so compact, I faceplanted the cabinet and used the upper rear baffle railing as my chassis stand.


Here's the original equipment, a Mallory axial 20MF hailing from the 43rd week of 1973 and a Mallory 40-20-20 multi-section can cap built in the 29th week of 1973 (you'll just have to trust me on that one).


Can caps that tie to the chassis require a nice solid structural solder joint that completes ground and secures the cap to the amp. For this, liberal application of heat is a thousand times better than trying to remove and replace a chassis pool with an underpowered or small iron. Here's the 100 watt Weller I use for chassis work in comparison to the variable temp iron I use for all other component grade work.


Of course, with a behemoth hot iron, all of its benefits in this single application are detrimental in every other way. Shifting of existing components that would otherwise be untouched is crucial; I've smelled enough melting plastic already, thanks.


This tab got the desoldering treatment, I'm about to bend the tab up and free this joint. The joint on the opposite end proved easier to just heat and rotate the can, shifting that tab out of the pool. Then it's just a matter of bending the remaining tabs up and dropping the old can out.


Ancient (remember, electronic eras pass faster than those of humans) solder flux reminds me of cerumen, and it too is generally undesirable when built up and can take multiple passes to get clean. Above shot is after a single scrub/soak pass of isopropyl, and yes the good people at Fender put that flux there in the first place. I have a few cotton swab heads full of the stuff if any collectors are interested.


Now it's ready for a new cap. I'm not concerned over the existing solder there and think of it as tinning for the new joint.


The replacement multisection is built by CE Manufacturing in the US, purportedly off the original Mallory tooling. In comparing parts side by side I find that very easy to believe, fitment was EXACT.


Somewhat hard to see, but the pull job here has a bulge in the center vent.

I bought the caps in reference to the schematic as opposed to referencing the actual amp, which is why the replacement multisection is a 20-20-20 as opposed to the 40-20-20 that was original. Frankly, I'm not overly concerned at the 20% drop in total capacitance of the power supply. It seems as if manufacturing tolerances of electrolytics tend to over build as opposed to under build, and I've heard people bellyaching about adverse effects that over capacitance has on tone. Seriously though, retrofitting a lower capacitance to follow the mid 1960s circuit isn't a life or death matter.


Here it is, ready to burn in slowly on a variac. I'm not in love with the recreation of the original joint at the head of the axial cap, but it seems solid enough and the other did last for 37 years just fine.. I only addressed the B+ caps for now as this is my amp and I expect to be in and out of it for a while; tinkering with the guts and getting it just right to my ear, so COMPLETE overhaul is less of a pressing issue. Once I've insured a solid electrical base, next step is to rotate through a pile of 10 inch speakers to find the best match for my practice and recording needs.

Ground Control, we have a problem.


In June of 2009 I purchased an early Grass Instruments S4 on eBay, well aware that it was in operational disarray. The seller simply tossed the open chassis into a box full of peanuts and dropped it onto a loading dock. Less than ideal shipping aside, I think that the majority of problems with this unit actually stem from poor storage. Which is the only reason I can comprehend for the fluorescent tube shards I've had to pick from its somewhat tacky guts.



Another selenium stack awaiting surgery, I think this makes five awaiting passage over the bench.


However, the interesting puzzle is nested in the wire wound precision potentiometers.


The resistive element is severed, rendering the pot useless. I have another wire wound pot that was floating around a parts bin with the same mode of failure, easy to spot the weak point of the design. With this unit, seeing as how the failure is nearly at the end of the travel, I'll probably take the easy way out and bridge the gap. The break in the parts bin unit is more centralized, so I expect a bridge would deliver an audible step. I'll continue to contemplate my options on that one.

I'm playing a set tonight, and for various reasons I don't want to drag out my full set-up, forcing my hand at a little improvisation. This has me surveying the piles in terms of what relatively compact devices will either produce or pass sound, the forefront contender being a Tektronix 106 square wave generator.


I've determined that the GenRad/Tektronix connectors will take a banana just fine, and since I have a chassis mount banana lug I can ground reference the signal output without resorting to stupidity. I'll consider bastardizing this unit with UHF connectors since they occupy the same sort of space and I can probably pull it off cleanly, otherwise I'll just leave them be. This of course is an eventual plan, and bears no relation to what I hope to do today.


Cracking the case to give it a visual reveals a quartet of 7189 tubes living in harmony with a variety of discrete transistors. Two days in a row now I've peeked at the guts of a tube/transistor hybrid, this one won't be getting the knife though, so I'll have to proceed with caution. Thankfully the transistors are socketed, so in the event that B+ has intermingled with the low voltage buss, part replacement will be a breeze.


Of course, it would appear as if I'm getting ahead of myself, since I'm not going to tackle this level of failure a few hours before a show. Evidently those General Electric electrolytics from 1968 have not fared well over the years. Here's a shot that captures the clear corrode through of the negative lead on that cap, and that murky brown glut is an erupting carbon comp resistor.


Once I find a bit of Tektronix silver solder I'll have a go at replacing this section, and all similar electrolytics. For the time being, I'll have to see if I can burn in my SKL 302 variable filter instead.



EDIT: at 80.9 volts AC mains input, the signal leg of output #2 was sitting at roughly +10 volts DC. Meaning we'll be seeing some more in depth gutshot of this unit as well (also meaning no one will be hearing any signal pass through this beast for a while yet). Here's an appetizer: