The crackling sound when you crank Iron Maiden is most-likely clipping of the on-board amp that is not up to the task of driving the JBL speakers. Fun fact: There is no standard for audio output (and mix levels?) levels between each Stern release. That can cause problems like this.
The solution? Use the line level output and hook up a small, inexpensive external amplifier in the head.
This took a while to round up because my first efforts were using the specs in the Iron Maiden manual. Silly me. The line out CN5 connector specs in the Iron Maiden manuals are wrong. This thread has the RIGHT specs for CN5, including two versions of the connector.
THESE INSTRUCTIONS ARE SPECIFIC TO IRON MAIDEN. The Line Out has changed all over the place on the Spike/2 boards, so the details need to be adapted for other Spike/2 machines.
The built in amplifier on Iron Maiden LE shows strain when paired with the JBL Studio speakers, clipping when the volume is turned up into the 30s or so. The solution? Get a cheap external amplifier that can drive the JBLs better. To do that, you need to use the Line Out connector on the Spike/2 board. Pro/Premium owners can also upgrade their speakers AND amplifier to get sound better than the LE comes with.
I'm still waiting for parts to finish the Pro/Premium conversion, which I'll add to this when they come in, but I have the information and parts for the cable that adapts the pinouts to an RCA cable you plug into the amp, which you then plug into your existing LE JBL speakers. So let's get that info out!
To make the adapter, you need an RCA cable (I grabbed one out of my abandoned wires box):
a connector housing (this is the 6 pin version) - Digikey Part number 281838-6
some molex pins - Digikey part number 0016020087
and some shrink tubing (not pictured, harbor freight has variety packs)
There are TWO kinds of boards in the Spike/2 Iron Maiden run. Both have a CN5 connector, but one has a 6 pin CN5 and one has a 7 pin CN5 because the woofer output was added. You first need to figure out what kind of board you have. Look at the area below the CPU on the Spike/2 main board. The area highlighted in this picture is the revision:
Revisions 520-7031-01A, B, C, D or 199-7031-00A have a 6 pin CN5 connector and the pins are arranged like this:
Revisions 520-7031-01E or 1997031-00C have a 7 pin CN5 connector (7th pin for a line out woofer), and the pins are arranged like:
Revision 199-7031-00B was never produced, according to Stern.
So, cut the RCA cable, leaving about 18 inches from the cut to the RCA ends of the wire:
Separate the wire halves for about 2 inches, then strip the insulation off each one. On each wire, you'll have a "loose" insulation wire and another, smaller insulated wire inside. Twist the copper "loose" wire so it's in one piece on each of the wires.
Twist the two copper wires together and put some xtra-small shrink tubing over it (not shown), leaving a little bit of the copper peeking out the end. Shrink the tubing over the copper (ground) lead.
Cut a piece of small shrink tubing and slide it out of the way on the RCA wire so it's there for later (copper wire does not have small shrink wire on it in this pic):
Crimp the molex pins on the Left (white), Right (red), and copper lead. These pins are SMALL. I used a magnifying glass.
The two (legs) on the top and bottom of the connector FACE the CN5 connector, so they should be pointing right if you have the connector vertical in your hand.
In that orientation, plug the red into the top, white next, then the copper lead in the 3rd position from the top. They should "click" and you should not be able to tug them out. Slide the shrink tube up so it's snug against the connector and shrink it to the wires.
Your adapter is done, and you're ready to plug it into the Spike/2 board in the backbox. Turn off the machine and plug it in, like so:
Then plug the RCA connectors into marked L/R input jacks on the back of the Pyle amp you got from Amazon (https://www.amazon.com/gp/product/B0071HZ5LE) :
Then make a speaker cable adapter to plug into your JBL speakers (or just desolder the existing connector and solder the speaker wire straight to the speakers, noting the striped wire is +/red if you have naked copper speaker wire) and connect those wires to the output clips on the pack of the Pyle amp. You are good to go at that point. Make sure the amp volume is ZERO when you initially turn the machine back on, then slowly increase it until you get the level you want. This amp can overdrive the JBL speakers, so you won't be able to run it at max.
For the Pro/Premium conversion to better 5.25" speakers, you need to get the following parts (I got them from Terry at PinballLife - they take a LONG TIME and cost about $100 total, shipped):
2 x 515-1941-00 - speaker plate with threaded posts spaced for larger speakers
2 x 545-1046-02 - hard plastic red trim piece that goes around each new speaker
2 x 626-5113-00 - soft foam gasket/spacer
8 x 254-5000-01 - small plastic standoffs
These parts are pictured in the exploded drawing on page 40 of the LE manual.
Having completed the Pro conversion now - pictures to come - I would recommend ONLY doing it if you play your maiden at high volumes where it DOES sound AWESOME with this conversion. However, at low location-friendly volumes, it makes a difference, but it's very subtle (mostly cleaner highs).
Now that this project is done, how about these projects?
Reinforce the crappy Stern leg plates so the newer cabinet wood doesn't split at the corners:
Replace the noisy stock spike power supply fan with a much quieter one:
Fix mid-game Spike resets:
Fix your LEDs and LED Flashers in spotlights so they don't pop out unexpectedly: