Electronics


   The 1975 ~ 1979 “Flashbox 200” (an historic electronics project). {R.I.P.}


Light Control Board

      This beast of a lighting system was my pride and joy in the mid 70's. I designed and built the entire lighting system. Controller, cables, lamp housings, everything. Twenty channels of techno-savy applied to hard rock in the age of disco. I had to do something to keep Rock alive right? That was an awful time for popular music. So many great local bands went under then.

Features.


      Inside it features two separate hi-power color organs I built from SW Technical Products kits, each handling (4) 600-watt channels, and a Thermin kit (also from SWTP) to drive the frequency and volume for them as a hands free way of changing color and brightness. Kind of looked like I was playing "Air Bongo's" at times. I could always tell when someone was getting near the light and sound boards during breaks. The Thermin would act as a motion detector and flash the stage lights. There were also the white plexiglass piano-like keys I made to play the lamps manually or use for hitting spotlights. The system had a rack of buss fuses, one for each lamp channel, an internal pre-amp so I could use a room mic to drive the organs if needed, and a big analog AC ammeter on top, front and center so I could prevent tripping a house breaker.

Construction.


      Particle board covered in brown naugahyde and faced with a sheet of transparent blue plexi-glass. The top design was laid out in pencil on the protective paper covering of the new plastic sheet and then traced carefully with a razor blade. Pealing off the larger areas leaves a protective pinstripe outline for the arrangements. Spray-paint it matte black and then peeled off the remaining striping makes a Tron-like outline for everything with a little back lighting.

      Each of the white plexi playing keys were hand made, the edges scraped smooth and the hook end formed by heating with a hot air blower and pressing into a wood form I had carved. The keys snapped onto a curved steel rod and were secured with inexpensive and replaceable rubber bands for tension. Crude but effective. Of course with the color organs in there I could set the light show to autopilot itself with a monitor signal from the sound system and fetch a drink. By setting up organ channels for singer spotlights I could have it fire up a spot any time a singer said anything in front of their mic. It worked perfectly and I used the heck out of it many years before it finally succumbed to the ravages of being loaded brutally into the bass players van too many times.

Flash Box 200 Construction       Unfortunately I have no pictures from shows, or the lamp housings I made. Working in a sheet metal shop I rolled and spot welded 20 of them all together. They were really great looking, with cooling fins on top and bottom, tapered front snoots with gel clips and gel frames, vented light dam back end plates with porcelain lamp sockets. Everything hooked up with wire harnessing I armored by pulling the wires through two 50' coils of aluminum flex-cabling (ten channels each). Really just a coffee-can lighting system but still, very cool and easy to set up.


Electronics, Amp and Effects Repairs

      Much of my repair work has been in the realm of on-the-spot emergency work with no documentation. Performance magic where a player sets up for a turn on stage and is surprised to find a dead rack or some other equipment failure. If I am on a set there is no question who they want. So far I have always found a repair and made the time slot.

Failure Prevention.

      Almost without exception, most failures with electronic equipment are in the front end power supply for a device, or the output power stage. These are the places where the parts get larger, heavy and thus, expensive. Designers and manufacturers try to save money on expensive parts and specify very close to design tolerances before going into production. A good illustration of this principle is with the old television sets. Ever wonder why the back of the cabinet never goes all the way back to square up and cover the back end of the picture tube? Always that big hump in back. It's not to make it fit in the corner of the room. It's because if it costs another dollar to make a larger box, and they sell a million sets, it would cost them another million dollars. Saves a lot of money and consumers don't really care. Money is saved wherever it can be saved.

      Another problem is cropping up with more designs coming from overseas. The designers there are designing first for 240v supplies. Then modifying the power supply to work with 120v for USA domestic sales. This works well enough under ideal circumstances, but produces a problem when power fluctuates on our 120v service. Lightening strikes and car crashes trip power off a lot more often here than overseas and we see a big surge when it is turned back on. When the power goes out in my home, I immediately think about what is plugged in and "live". Designs set to tolerances for 240v and then converted to 120v operation doubles the percentage of fluctuation on the components due to the effect of amperage going up when voltage drops on AC circuits, where as amperage goes down when voltage drops in a DC circuit. In other words a seven volt shift from 240v is a change of 3%. A seven volt shift from 120v is a change of 6%. If components tolerances are at 5% . . . . . This is why you have replaced your DVD player twice now already, and given up on your VCR player, because it won't read the remote right anymore. The front controls on the machine still work ok, but the lightweight brains inside have been scrambled by lots of little voltage twitches over time. These machines would still be working if the front end was still set for 240v and they where used on a 240v grid. Your computers have good power supplies, but not your consumer entertainment electronics. Things that draw very little power are the most vulnerable to spikes.

      So. . . Unplug, or kill the power switch on the power strip to your entertainment center unless you are using it.

Rechargeable Batteries.

      There is no value in Ni-Cad or lithium rechargeable batteries ( in musical equipment ). Don't use them in musical gear. And you may as well throw the 9-volt rechargeable's in the garbage right off the shelf. Even in other applications the 9-volt rechargeable's only take about three or four full charges before they suffer complete failure, (in my experience). Spendy little buggers too! Save these batteries for your shaver, kid's toys and home flashlights. And remember to deep cycle them and re-charge them frequently or they'll die then too. It's called exercising the battery and they like it. Lead-acid batteries are different in construction and don't like to be depleted. Deep-cycle Lithium-Ion/NiCad batteries but keep Lead/Acid batteries fully charged to prevent oxidization of the surface of the plates.

      A big difference between alkaline or lead/acid batteries and Ni-Cad or lithium batteries is how they act when they are depleted in a rack with others. A depleted alkaline or lead/acid battery looks like a conductor in circuit, so any other good batteries in the rack will still pass. A depleted lithium or Ni-Cad rechargeable will look like an open circuit after its death, so any other batteries in the rack that may still be good, will still not be able to see a circuit. So if just one rechargeable battery in the rack dies, the power goes down. The result is catastrophic in a performance situation. They die so suddenly that stage people think something else went wrong and waste time looking for the wrong problem. Rechargeable batteries don't work very long, die suddenly with no warning, the armed forces won't use them anywhere, and they will disappoint a musician on stage. It doesn't matter what you make a battery out of. It will require strip mining someplace for the raw materials to make any of them, so there is no environmental difference between a battery you throw away because it is dead (alkaline) or one you throw away because is doesn't work (lithium or Ni-Cad rechargeable). Let's pray for better technology to get this bug out of the way. On stage you need a warning window at at least thirty minutes before a battery fails completely.

Old Tube Amps.

      The secondary side of the power transformer on most old tube amps is rarely fused, and this creates a potentially bad situation. It's fine as long as the amp is used and used frequently. One of the things that can go wrong over time with old tube amps is when they sit around a long time, (a year) without being powered up. The large filter capacitors on the secondary rectification side dry out and pop suddenly when power is applied. If these caps pop, they short. If they short, they in turn take out the power transformer secondary side and anything else that heats up between them. A blown ten dollar cap can take down a two or three hundred dollar power transformer needlessly since there is no fuse watching the current flow on the transformer secondary side. A fifty-cent item is missing. I know, some would say it might trip needlessly and interrupt a performance. So, put in a slow-blow and make the value high enough so you at least have the transformer protected from a major power sucking shorted capacitor. The fuse doesn't even have to be accessible. If it pops, it is just telling you the amp is going down for service anyway. Just put a couple in-line with the capacitor pairs the next time you are in the amp.

Capacitor Reforming.

      There is a process to re-form old capacitors and it requires a varistat or variable AC voltage transformer. In an amp with solid state rectification diodes in it, all the tubes are removed from the amp and the amp is plugged into the varistat. Power is brought up slowly over days or weeks to work up the dialectic film in old capacitors. The aluminum oxide layer is maintained every time the capacitor is used. The capacitor uses a tiny amount of current called leakage current to maintain this oxide layer. They can heal themselves slowly if the voltage increases till they reach working voltage again. It is a risk to buy a fine old tube amp from a pawn shop and just turn it on first thing. You may destroy it needlessly. There are also circuit designs for auto reforming. A device that monitors current flow, automatically adjusting the voltage to a cap to achieve re-forming quicker and without supervision. This requires the cap to be removed for reforming and is best if you are inventorying old parts. Never use a variable AC transformer when driving anything that has an AC motor in it's design. Variable speed AC motors use phase shifts to produce different speeds. Not voltage changes.

A simple schematic for an automatic capacitor reforming circuit is here.
http://electrojumble.org/reforming.htm

Another clear perspective on capacitor reforming.
http://www.angelfire.com/electronic/unworthiness/Restore_cap.html  

The Compiled List of Tube Specs. Relevant To Guitar Amps.


Click for a larger view.

Tube Scecifications

      This chart shows all the numbers I have collected as they relate to tube pinouts and electrical ratings. It saves a lot of space on the wall and covers the most common tubes used today. It is not much trouble to re-arrange the wiring for another tube type as long as you are aware of the needs of your output transformer and don't over power your output in doing a conversion. To figure that out, you will need to compare the specifications. I use this list.


 

A 9 Volt On-Board Battery Monitor.

      Click for a larger view.
Battery Low Indicator thumb pix

      The 9v battery monitor can be assembled from common SM components to a very tiny size and incorporated into almost anything that uses a 9v battery. I usually build it on the LED leads and use that mounting to support everything.

The light blinks on, and then quickly goes off when the power is switched on. If it blinks on and then goes out quickly, than that tells you the battery is good and strong. If it blinks on and then goes out slower than usual, then the battery is starting to go down, but you will be just fine for the evening performance. If it blinks on and stays on than you can expect low battery operational problems.

The trim pot in the design allows you to set the voltage threshold for yourself, so you have control over the point at which the circuit trips to full on indication. After you establish the setting you prefer you should measure its value to ground and the replace the whole pot with a close value of resistor and making the assembly even smaller. I found 4.4k worked to produce a 7.5v threshold. This thing draws no real power and will not drain a battery any faster than usual.

The Flex-Tapes in a Parker Fly Classic Guitar.

      Click for a larger view.
Parker Flex Tapes

      The flex-tapes in the first Parker Guitars were an almost mandatory step in the application and evolution of modern design techniques and technology's. With new technology coming out almost every day it makes people get all exited about what can be done and they just go out and do it, without even pausing to consider whether they should, or what will happen if it fails to perform as expected. I must admit I love technology but there are practical issues to think of before throwing a new idea into production.

      Unfortunately using flex-tapes in a guitar cavity resulted in a completely unserviceable design for the working world of the guitar player. I simply needed to tighten a loose pot and was very surprised when the tape simply tore like aluminum foil at the slightest stressing. I was even holding the back of the pot at the time and it did not get turned more than 15 degrees.

      I scraped down to the traces and patched over the three torn circuits with resister leads, and immediately began reverse engineering the entire guitar in anticipation of more problems with light weight components in what would be a heavily used guitar. I was going to reproduce these tapes and these drawings are to scale, but I decided to abandon the tapes in favor of point-to-point traditional wiring.

A Reverse-Engineered Full Schematic of the Parker Fly Classic Guitar.

                  Click for a larger view.
Parker Fly Schematic

      Maybe my own work will help you some day. This is a schematic of one of the very early fly guitars. The newer Parkers have gone back to more traditional wiring and changed a lot of things since this issue was made. There are more out there though, so if you have one these older Parker guitars, this drawing will be of value. I have looked for full schematics and never found one that really got down to it. So here is the whole original design, reversed engineered and laid out for you.

      I have completely removed all the flex tapes from mine, made modifications to remove the master volume pot entirely as the function is redundant to the stacked volume pots for piezo and electric pickups which are placed much more out of the way. I also removed the red mono/stereo button switch, wired a new and sturdier stereo output jack. Wired it mono output, using the traditional ring-to ground for power switching with plug in. I removed the piezo/ elect. selector since the blend is controlled and isolated in the on-board pre-amp already. I don't use stereo output, so that goes in favor of a simple and solid plug connection. I would use a pedal if I want volume swells so the little finger reach of the master volume is not desired as much as swing space for strumming. Of course my work is entirely reversible so as to allow the restoration of a true classic, (assuming it had new flex-tapes to rebuild it with). Anyway, here is the research on what is going on inside. You can decide what you want to accomplish with it.

An American grammar re-processing of the French article on modifications to the Marshall JMP-1 Preamp

A clear translation with component ID's and grid references keyed to the popular 6-sheet Marshall JMP-1 schematic. Plus other additional notes of interest to anyone looking to design their own mod's for their JMP-1.
    Click the graphic "Le Plan Marshall" link below.


JMP-1


And the JMP-1 Schematic and main-board photos to go with it.

The 6 sheet JMP-1 Schematic - PDF -


Photo showing both sides of the JMP-1 main-board - JPG -


This work has resulted from my study's to understand how to mod a Marshall JMP-1 pre-amp to my satisfaction. My goal is to achieve the sound I probably could get paying for mod's. My transformers are quiet enough so replacing old caps for better, clipping in a couple changes to the tone circuit, and re-working the design logic on the effects loop should 'bout cover what I need. Wish me luck, and I will update here later with my results. Enjoy...

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