Pan Galactic Ghetto Blaster

The name Pan Galactic Ghetto Blaster comes from "Teenagers From Outer Space", an RPG by Ross Talsorian games. It is, of course, a play on "Pan Galactic Gargle Blaster" from "The Hitchikers Guide to the Galaxy" by Douglas Adams.

I do a lot of swing dancing and wanted a "portable" stereo that would play music loud enough for dancing to outside, and which also had a large enough battery to play said music for a reasonable length of time.

Since I already had almost all of the pieces lying around, it would be trivial (or so I thought) and cost me almost nothing, to put them together into a self contained unit. I took the Zapco 75W/ch amp that I used to have in Ricercar (my '85 Honda Wagon) and started from there. To make a long story short, I've spent far more than the estimated nothing, and a lot of time, but I've got a pretty cool setup. There are still a couple of bugs to work out, but it seems to kick out enough sound at full tilt boogie to dance to outside about 5 yards away (or half that if you are right next to a busy road).

Standardizing on the Anderson 75A connectors, I can power the unit off the internal battery, or off an external source. I can plug the battery charger directly into this battery, or into other batteries. I can even take the battery clamps, connect them to the battery rather than feeding the system and use it to jump start a car.

Of course, by the time you get done cramming all this electronics and a 35 AH gelcell (think motorcycle battery) into a large aluminum toolbox, it's not light. It weighs about 60 pounds.

Progress on 16 April 2002 .
03 May 2002 .
05 May 2002 .
The smoketest on 07 May 2002 .
charging the pggb.
packed and ready to go.
outdoor trials. Using my Zapco amp and preamp, I was able to hear the unit over hwy 9 traffic from 25 yards away. If there were no traffic going by, I could hear it reasonably well from about 80 yards up the road.

13 May 2002: The PGGB is now operational.

I am not too pleased with the current noise floor. The noise level is worst when running the CD player off of the internal battery. If the CD player is plugged into 110 for power, it works just fine. This noise seems to be caused by ground loops.

14 May 2002 . In order to deal with the groundloop related noise issue, I needed to modify the input selector. I also wanted to move the power supply, and while I had things apart, I could fix the fans, oh, and move the filter caps ... And in order to get to one thing, I had to take something else out, and that meant I needed to take the battery out to trim the battery mount ... you get the idea. All of a sudden, I had it back down nearly to bare metal. The input 12V filter was all that was left in the box. It should go back together a lot cleaner than the first assembly. I won't be grounding to the box anyplace, unless anything grounds through its case, which I doubt.

19 May 2002

I spent yesterday completely rewiring the boombox, making sure that nothing was grounded that shouldn't be, signal wires weren't running next to ground wires etc. When I fired it up it alternately sounded awesome, and horrible. I finally said "fuck it, it's probably something to do with the amp". Mind you this amp was the motivation for the project. I've been wanting to do something like this for nearly 10 years, when I took the amp out of my Honda.

I spent my morning and early afternoon going from shop to shop checking out amps. There was one, a bit bigger than I wanted, at Fry's for $100, that looked like it would do the job. At circuit city, I found one a bit smaller, similar specs, for $50, but when I asked if I could look at the box, the salesdroid refused, so I left. Continuing the peevesome process at shop after shop, I found a Rockford Fosgate 200S that was significantly smaller in the critical dimension than the others, and in the right power range too. They were asking $250 for it, which was a bit more than I wanted to spend. When he dropped the price to $200 I bought it. Interestingly, the salesman tried to talk me into the 150S, which was $50 cheaper, but I figured that I was so deep into the project, I might as well spend a bit extra and get something with the power the system was speced for.

Redoing the box to work with the RF, took some creative engineering, but I've got it back together. It doesn't seem to be quite as powerful as the old Zapco, or sound as good as the Zapco did, when it worked right, but it's not intermittently flakey.

Of course, as soon as I mentioned that I had bought an amp to a friend, he said "You should have said something, I've got a couple of 40W amps you could have".

One of these days, I'd like to dissect the old Zapco and see what the problem is. Thinking that the lack of output might be in the gain of the input signal, I tried using the preamp from the zapco, but got lots of annoying hiss. The same annoying noisefloor that I'd been hassling with.

I noticed last week that my portable CD player is way too prone to skipping, so I'll need to get a better one this week.

I'm sure that the majority of the money I spent on this project was "infrastructure and waste". I bought lots more crimpers, bolts and nuts than I used. I also bought lots of tools, saws for cutting the plexiglass, new drill bits, nice crimpers. There were a few things I got that ended up not working out, and some extra supplies that I ended up not needing, but I decided to spend the extra $10 here and there so I wouldn't find myself needing it 20 minutes after the hardware store closed.

Mounting LEDs in the panel proved to be incredibly peevesome. I suspect that there is some nifty trick that I'm missing because soldering to the leads is such a pain. As it is, I don't have an indicator LED on the cooling fan switch.

Boy do I missing working someplace with a well stocked electronics shop.

Next week, my Ramsey PH16 powermeter kit should arrive. If I can, I'll wire it up to do double duty measuring battery voltage, though I suspect it won't work too well for that.

Like so many projects, if I'd known what I was getting into, I wouldn't have started it, but by the time I realized that I shouldn't have started it, I was so deeply committed that I might as well finish it.

As peevesome as the whole process was, it's a pretty cool system. It's got reasonable power, and it sounds pretty clean. I've got three cig lighter power jacks in it (switched off the main switch). I've got a high intensity red led on the end of a wire, independantly switched, that can be used to read CD cases when using the system in the dark. I can plug "home" speakers in either instead of, or in parallel to the internal speakers.

I also now have a good selection of 12V power options using the anderson power connectors. I ended up getting a Triplite 25A 13.8V power supply, that will plug in, plus a nice little smart gelcell charger. I've got a cigarette lighter to anderson adapter I made so I can power my boombox off of almost any car, giving me a car stereo that easily swaps from car to car, or the ability to plug said battery charger into any car via the cig. lighter.

What would it cost to make one just like it, now that I know what I need an how much? I don't remember exact prices, and there are a lot of little things like crimp connectors, nuts and bolts, wire and such that I basically stocked up on, which now would only cost me a few buck in supplies, but cost me a bit to buy the boxes of 100 so I could get them cheaply:

5 hinges for shelves
10 3/4" angle aluminum 10 Plexiglass
10 cpu fans
10 handles for case sides
15 12V switches
15 Anderson connectors
15 LEDs
15 ground loop isolator 20 "banana jack" speaker connectors
20 Input source selector
20 cig. lighter sockets
25 Ramsey ph 16
50 toolbox
70 35 AH gel cell
60 6x9 internal speakers 200 Amplifier

This works out to a bit under $600. It doesn't count the 25A triplite power supply for running it off of house current ($140), the charger for the gel cell ($30), the anderson connectors for them ($7 each).

Should I have done it? Probably not. If someone were to pay me roughly my cost for the first one, would I sell it and make a better one? Without hesitation.

21 May 2002
I solved the gain problem by getting another CD player. The new one puts out a much higher signal level. On the drive home I noticed distortion, buzzing and other unpleasantries, when I turned the volume up. Early on, Gary Helbig told me that I'd need to get dynamat for it, so I bought some on the way home.
At one point this afternoon, I had noticed that one of the channels from the first of the four inputs was dead. Visual inspection showed this to be a busted trace on the input selection circuit board, which I was able to fix.
I hooked the oscilliscope up to the amp output to see if I could see major clipping of the signal. What I discovered was that if I cranked it at full for any length of time, the system would cut out, as if it was hitting it's protection circuitry. Further research showed that it would cut out if I was using the internal speakers: Jensen XS1692, coaxial 6x9 speakers rated at 4 Ohms. However when I hooked up my Klipsch Heresys, also rated at 4 Ohms, it behaved just fine.
With the Heresys, I was seeing intermittent peaks of about 20V, and consistent peak amplitudes of 14V. Applying (V^2)/R for peak power, that gives me 400/4 or about 100W peaks. Applying ((0.707*V)^2)/R that gives me about (9.9 ^2)/4 or about 25 watts RMS continuous, well within the ratings of the system.
Unfortunately, the system cuts out at amplitudes far below this with the Jensens. The case is getting a bit, but not exceptionally warm, and turning on the fans, which blow across the circuit board, does help a bit. I've written to Rockford Fosgate to ask them about how the protection circuitry works.
In addition to installing dynamat to all the various bits of open sheet metal, I also secured the various plexy panels so that they would not rattle and buzz. I also took an old blanket, tore and cut it into small bits which I stuck in ziplock sandwhich bags and tossed in the box to prevent resonance.

22 May 2002

It turns out that the problems with it shutting off were caused by insufficient cooling. I bought two hard disc cooler units (each with two fans bigger than the ones I had originally used) and installed them in the end of the box so that they'd blow along the whole length of the amp. I then drilled air exit holes in the back of the box along the other side of the amp to encourage airflow through the amp. It works.

Cranking the scope up to 500uSec/division I can actually see clipping on the output. I adjusted the amp so that my old phillips CD player (the one that doesn't have as high of output levels) will just barely drive it into clipping. It makes me wonder of the new Radio Shack CD player has enough output gain to drive my old Zapco Amp without the preamp. I'll have to experiment in all of my free time.

I went to connect up the PH16 last night and noticed that the negative side of both inputs were tied to ground. Had I connected it to the amplifier, I would have had a direct short across the negative output rails. This would have been what is technically known as "a bad thing". I talked to Ramsey today and they suggested 4 ceramic caps on the inputs, one each L+, L-, R+ and R-.

I've got a whole bunch more photos I need to upload. Oh well, I've been too busy working on it. With luck, all the critical features will be operational tonight.

23 May 2002: Upgraded the cooling fans

28 May 2002
I took the pggb to Baycon last weekend. As it turned out there was a swing dance on Friday night that was starting just as I showed up. As I wandered in during the class, Alex, the teacher, commented on the pggb and mentioned that he couldn't get his stereo working. So in its first public appearance, it was put immediately to work providing music for a dance.

I got lots of positive comments on it over the weekend, both on appearance and sound quality. People were especially appreciative of Saturday night when I was towing it around behind me while wearing my purple zoot suit and fedora. I did some sound level tests, like getting into a stereo war with the goth party and it acquitted itself well. At one point on Saturday night I went onto the party patio with it, and turned the volume up a bit so that it could be heard over the goth party at the other end. People cheered and told me to turn it up louder and louder. This was about the time that Harlan Ellison decided to call the cops about the noise and earned me the privilege of being the first person for him to berate on his tour of the party floor.

Unfortunately, I didn't get any pictures of the pggb at Baycon.

- WRTBD 02-05-21

I need to make a splitter of the 4.5 volt power supply so that I can run both CD players at the same time.
I need longer extensions, at least for the signal out of the CD player, so that I can put the PGGB in my back seat of the van, and have the CD player up on the console.

- WRTBD 02-05-20

My Ramsey Ph-16 peak hold meter showed up just as I was leaving for work. I need to figure out what I want for input ranges and how to wire them in. I'll also probably want multiple input sources:
Battery Voltage
Input Power
Input Signal
Amplifier Output

I'll also probably want to be able to send the input signal to rca jacks, either for hooking up to a scop, or another amplifier.

I'm not sure if my lack of output is input signal or amplifier output. I'd like to find a 12V mixer/preamp to use.

- WRTBD 02-05-13

Mount the input source selector switch to plexiglass rather than aluminum tied to the chassis.
Set the am/fm cassette up as an external unit that I can plug in the same as I would a portable CD player. Mounting it in the unit just isn't feasible.
Connect one of the panel switches to a white LED mounted on the cover for reading CD covers at night. Could possibly use an extra bright red LED so as not to trash night vision.
Move the power supply for the amp away from the other electronics. Make longer cables from the PS to the filter capacitors. Possibly add some shielding for the power supply.
Maybe put some aluminum shielding under the plexi near where the cig lighter power outputs are.
Get a triplite 12V/15A power supply that can charge lead acids or power the system off of wall current.

- WRTBD 02-04-15

LED lights in lid for seeing what you're doing when spinning tunes in the dark. Use red LEDs
Mount a car stereo in it (to the left of the battery) for cassette and radio.
would need an antennae mount.
connectors for external speakers
need narrow spade lugs about 3/16"
switching speakers from internal to external:
Use banana jacks mounted to plastic plate and just plug whichever
set of speakers is appropriate in.
Do we need more holes for speakers?
clean flash and burrs
use old toolbox for external power
should just spend the $100 for the triplite power supply
Get some BIG gelcells or try to ressurect my 7AH gelcells
able to mount ac inverter in powerbox
Put anderson connectors on
jumper cable set
Car battery charger (can plug into jumper cables)
external power box
little gel cell
power into the pggb

Where do we need fuses?

Mount battery last when assembling the system
don't need power relays if we use anderson 1300rbp connectors
schematics
mount handles on sides
get handles for side of power box
3.5" chest handles V175 - national
Can I use a multipin molex for the controller board?
can't use nuts to space speakers need metal tubing that will fit
around #10 bolts.

no holes on bottom
rubber feet on bottom?
can we do this without holes?
Should we turn the fans on with a switch?
with a temp sensor on the amp fins?
with both in series? parallel?

cdplayer charger
110v out use inverter plugged into cig lighter jack.
cig lighter plugs
meters and indicators
I'd like to have led vu meters.
I'd like to have a voltage meter, could just use banana jacks and
plug in a dvm when I want it.
power connectors
Use the Anderson power products connectors, $8 for a pair at hdb
capacitor mounts
need to be mounted to side.
get picture of dolly/stepstool for carrying
get big pnuematic tires for dolly
mount powersupply with fuse at top rather than bottom
how do we want to carry the gelcell charger in it?
Make a plastic plate to:
direct airflow over the amp
cover hotlead of gelcell
mount the speaker banana plugs to
mount the power switch to
mount the fan switch to
mount rca inputs for signal sources to
mount signal source switches to
(can we use pots and fade in the signals?)
mount cig lighter outlets to

Can I get sound working on the vaio, and use it as MP3 source?
Would need to rip my CDs
External hard drive for storing CDs
could get it working under windows


need connectors (lugs) to connect to amp.
Make sure that wires to the plastic plate are long enough that we can
pull plate out far enough when working on it
Test the 12V Power supply for the cd

drill holes for:
air exhaust from amp
mounting handles
mounting capacitors

Pictures to get:
dolly
old gelcell collection

I'm not the only one doing this:
LaBomba