Monday, February 28, 2011

How do you blow a five amp fuse while something is off, and has been powered off for a while?

I don't know, hopefully I'll find out. Otherwise I'm sort of dead in the water. But yeah, getting a little ahead of myself here. I tore down the rack as built since it was sort of tip happy with the bulk of the 556 bolted in.

Flowers anyone?

Not as nice as having it bolted directly to the floor, but stable enough to freestand the populated rack.

Repositioning everything in order to bolt in a rack that can carry the weight of the 556 during installation (and removal).

Alignment has become a bit off, three screws in.

Anyway, I fired the scope up, pulled up four traces and, having nothing to measure powered it back down again. Half hour later the lights in the house dim briefly while the distinguished sound of arcing occurs. One of the mains fuses has opened on the scope.

Of course, I can't look at it while it's bolted in (without contortion, anyway), so out it will come, again. Thinking about a decent lightweight solid state scope at the moment.

Friday, February 25, 2011

Winter, with its cooler temperatures, has chased me away from the uninsulated hell hole that is supposed to be my bench. I picked up an open frame server rack earlier this week, allowing vertical orientation of junk in the utility room (a welcome change).

With the inclusion of my scope, I can proceed with a bit more power in some of these piled up projects. However, with something in the neighborhood of 100 pounds hanging 24 inches out the ass end of this piece of equipment, my attempt at an installation pictured here has become little more than a mock-up. I need to tear this down and fortify the base (which is being helped on the balancing act by tube amps and bungee cords) in order to reach a comfortable level of structural integrity.

Atop the dual beam scope (each "side" being loaded with dual trace preamps for four simultaneous traces on the screen) are a General Radio 1192 and a Heathkit IB-1101 frequency counters. I look forward to deploying real tools again, and hope this will fertilize these chronicles.

Monday, February 21, 2011

Having cut a swath of days to establish a system with which to record, I crawled through some of the obvious contenders for needing a bit of attention, built some cables and generally focused on foundation work so the actual recording process would be a breeze.

This process culminated with firing up my road worn TOA RX-212 mixing board, only to be greeted with a "GZZZZZZZZZ" mechanical buzz accompanied by dimly lit clip LEDs (which I attempted to capture above). It sounds like a starved AC relay that is opening and closing in sync with the 60hz wall voltage.

This desk has seen a lot of abuse. It was water damaged when I bought it in the late 1990s, and has since then been gigged. This unit has face planted onto asphalt after a show, bounced around in the back of a pick-up truck, van and Volkswagen. Clearly it's not a delicate high end flower for the studio, but aside from the occasional necessity of physically hitting it to wake a channel up or being hit with a huge bout of crackle at the lowest travel of some of the sliders this mixing board has been a solid element of my [view] set-up for a long time. All the idiosyncratic nuances meshing very well with experimental sound.

Here's evidence of the aforementioned water damage along channel PCB alignment fence, though the points where the aluminum shielding has dissolved points to a mystery.

Gutshot! All the benefits of independent channel strips without the ease of removal. The ribbon distribution cable was replaced with point to point solid core wire pulled from a length of CAT-5 in (IIRC) 2002, the stock header/ribbon connector system having decayed into a patina'd bluish mess that had given up on its original purpose, that of passing electrons. This modification, while saving the day in terms of functionality, has elevated pulling the channel cards for repair into a PITA nightmare realm. Should I have to dig back into the channels for anything I'll probably replace the connection blocks with something similar to stock, since I've grown beyond just thinking about what I have on hand that will make something work in the space of nine years. I've also grown beyond the notion of upgrading all the ICs, but that's beside the point.

Centered here is the rectification and voltage regulation board. I expect I'll be plucking that out of there and rebuilding it, should my suspicion of insufficient or dirty power be confirmed.

Over all, I like this board a lot (for its application). The fact that TOA designed interchangeability between the RX-208, RX-212 and RX-216 is apparent with the almost modular design, which is close enough to be annoying that it's housed within a monolithic control surface. On the other hand, had they gone the extra mile and built the enclosure to be modular, mine probably would have long ago stopped working and fell to pieces.

Sunday, February 20, 2011

Built several balanced XLR cables yesterday using some Molex power supply cables I had plucked some years ago from the trash (E-Waste bin is the preferred nomenclature these days).

Cable was originally purposed for power feed to rugged computers, the sort mounted on a forklifts, etc. Three conductor 20ga in a woven shield. I've seen tighter weaves but I've also seen worse, the ~ eight foot lengths don't seem to pick up hum so far, but my testing has been cut short by some equipment malfunction.

Next up...

Saturday, February 19, 2011

The Autogram AC-8 is well on its way to being up and running.

My intent is to situate the AC-8 as master summing console in the studio, freeing up the other desks for branch/sub-mixes or abuse, depending on unit and project. This was a weak attempt at trying to induce some sort of saturation, I don't think I got anywhere near the headroom threshold. The Program/Audition outputs offer support of two independent stereo pairs.

Here's the input/output connectivity block. The good people at Autogram have uploaded user manuals for this era of gear here: this goes a very long way in clearing up what is what. Pictured is channel 3A input (red wire) and Program output.

I've pulled all the active stages per channel out (slotting those into the AC-6) and populated all the stereo channels with 1:1 600 ohm interstage transformers. I believe this means that the functional block above is the only active electronics each channel passes through.

Schematic for the MXA-1 mix summing stage is above and the LA-1 line amplifier stage is below.

These stages share PCB artwork, clearly there are only minor differences between the two. Since I have the luxury of having a complete quartet of spares (sitting in the AC-6) I'm thinking about rebuilding these stages, upgrading components where I can and eliminating redundant or unnecessary parts (the caps on input/output for example). As it stands now though, the desk is super quiet and full sounding and justifies the 38 by 20 inch footprint it consumes.

Thursday, February 17, 2011

February is turning into a bad month for progress on the repair/build front.

When I first secured this blog (sometime in 2006) my intent was to review some of the repurposed equipment I use. I shot that idea down, so as to avoid tempting the rarity index from pushing these devices into a price bracket beyond my means. ((I realize that notion hinges on enough people actually giving a shit about what I do, but I feel it's a forgivable cautious motivation none the less)) So, this page lay dormant for a while until the repair log theme surfaced; meanwhile it would seem as if holding my enthusiasm at bay did nothing to ward off the upward creep in value of these units I enjoy working with.

I'm still a bit wary, though as tooling (slowly) progresses to the point at which scratch manufacturing of these systems is possible, I foresee a more forthcoming flow of information. Free information is what divides us from the animals.

There also remains the notion of trade secret, espoused by the protective artist. That with knowledge of the ingredients, one's edge or advantage is lost. I've more or less crawled beyond that juvenile framework upon which so many have hung a delusional veneer of originality to conceal the regurgitated processes within. In short, different people produce different compositions when seated at a given set-up, assuming of course that said set-up has the inherent potential to overstep the ruts carved by one trick ponies.

Naturally, I mean none of my marginally vitriolic language above to be focused on any one individual or group, why give such individuals weight with which to work? No, universal truths should be shared by all, equally. The balance of beneficial and detrimental facts being an oft times ugly meter of the position of things. Reality, if you prefer..

Monday, February 07, 2011

I think my picture to words ratio is tilted toward STFU today.

Wheatstone/Audioarts A32 broadcast console, an over all angle. Minimal clutter lending weight to the 100mm sliders, the wood is a nice touch too (though appears somewhat tainted by greasy DJs).
Modules from left to right: 4x MM-20, 12x SL-20, 2x blank, LS-6, blank, SC-20. CR-20 & OM-20.

MM-20 is the microphone preamp, the input transformer has been wiped clean of any identifying marks. Socketed NE5532N are found throughout the desk, I believe the SN74LS00Ns situated beneath the Penny Giles slider support logic switching and illumination of the front panel controls. Input, output and power feed are hidden somewhere in the forest of pins on those ribbon connectors.

I expect the PGM & AUD buttons control those yellow box relays seen above.

The SL-20 is much like the MM-20, minus the transformer and with an additional dual op-amp, which is sensical because this stage is stereo whereas the MM is mono.

Same stripped down features, but in... ((STEREO))

LS-6 is pretty self explanatory (forgive me, I'm going to go ahead and explain it anyway). It performs Line Selection, from 6 choices. From what and to where, however, are still shrouded in mystery. It's also around this point where I stopped being comfortable pulling the modules out, since it is no longer so clear what is what in the final sections.

SC-20; Studio Control, looks to house the talk-back circuitry and routing to the studio.

CR-20; Control Room loses the TB control, as the operator typically does not require supporting electronics to talk to themselves, and adds headphone amplification.

OM-20; your guess as to what the O stands for is as good as mine. This houses master level and VU meter trim and timer control (which will come in handy if I'm ever trying to record and bake at the same time).

The PSU was naturally absent upon purchase, as was a loom with 29 DB-25 connectors (that's 725 connections, in case you were curious and yet slow in the math).

The switches also seem to be a weak point in the design. I love mechanical indicators, but these are less than crisp in their response, the A/B input plungers also need help to actuate between up and down. The only PGM & AUD switches in the on position are the ones next to the holes.

Upper shelf component selection aside, complexity has worked against this desk in the span of 20 years. The Autogram AC-8 which is almost 10 years older, has the potential to be a far more user friendly and upgradeable desk.

Sunday, February 06, 2011

This past week has been one obstacle after another on the electronics front. Old vehicles, learning software and a mass of other trifling happenings has pushed me off the map for a bit. Though, on a somewhat superstitious mumbo-jumbo front an illustration has been drawn regarding the delay of gratification cultivating a proportionally larger boon for the field which had so recently been repressed.

I went hunting for a home stereo preamp yesterday, armed with a budget figure based on a locally advertised unit carrying more modern features than I need but at roughly 10% of the mid 1990s MSRP. Then I happened on a couple of broadcast mixing consoles, an Autogram AC-8 and a Wheatstone A-32, which more or less derailed my hunt for a preamp, having consumed, to the dollar my established budget.

I'm running through the AC-8 in this installation as I am somewhat familiar with this beast, already having it's smaller sibling the AC-6. Typical broadcast console interface, a mixer refined to the barest of features, routing switches and volume controls.

One of my favorite things about old radio mixers is the ease of access they afford the technician. These were often designed with 100% up time and field repairs in mind, the Autogram/Rockwell stuff exemplifies this by confining the various stages into cans that can plugged and unplugged in seconds while another channel is active.

From the upper left of the picture on the base chassis: input terminal blocks; output stages left and right program, mono and left and right audition; amplifier and power supply board and output terminal blocks. The front panel modules are two MPA-1 microphone preamps, one for each input channel which is set to mono via the configuration switch next to the empty sockets, followed by five stereo channels of MT-1 socketed interstage audio transformers and a pair of IA-1 variable gain op-amp modules.

With the exception of the microphone preamp and op-amp modules, all the routing and level controls are passive. Two pair of balanced input wires terminate to an input selection switch which feeds the module, a stepped attenuator and an output routing switch.

Large, low loss connectors to impede the 600 ohm line as minimally as possible.

Here's a gutshot of the MPA-1 microphone preamp module from the AC-6 I took 6 years ago. Input transformer at bottom feeding the active circuitry.

Here's the innards of an MT-1 module, a Triad A-67J.

More fixing stuff and less showcasing on the horizon, once I climb through that Wheatstone unit..