Rush LE DIY Audio Upgrade
One of the first things I noticed when I got my LE was how lousy the audio was. I’ve spent enough time tweaking Stern Spike 2 audio to know that the fundamental problem is the underpowered built-in audio amp. The same amp is used to power the $2 paper cone speakers in the Pro and Premium.
I am generally happy with the quality of the Kenwood speakers on the LE. I’m not looking to turn this into a high end piece of audio equipment - and I like the look and low profile of the Kenwoods. You can certainly swap out the speakers and go with a higher end amplifier, but I don’t personally feel that is necessary. If you want to read more about other aftermarket speakers, I suggest this really great thread: https://pinside.com/pinball/forum/topic/improving-sound-quality-the-diy-route
NOTE: There are several commercial options available for upgrading your Spike 2 audio. I’ve never used any of them, as they cost more than I’m willing to pay. I also like doing things myself when I can. If off the shelf upgrades are more your style, then they are a great option and will surely sound better than factory.
High level steps:
1. Hook into the line level outputs for Left, Right, and Subwoofer using a simple breakout cable attached to CN5 on the Spike 2 CPU board
2. Build a speaker adapter cable (or just solder directly to the speaker lugs)
3. Add a small externally powered amplifier to the backbox to handle Left and Right channels and output to the Kenwood factory speakers
4. Run the Subwoofer line level output to an external powered subwoofer (e.g. Polk PSW10 or Klipsch RSW-12)
5. Adjust the Audio settings through the menu system
Rough cost:
1. Amp ($50)
2. Cables and connectors ($25)
3. Subwoofer (shared w/ another machine, so counting half the cost here) (~ $100 for Klipsch, ~ $60 for Polk) - these often go on sale and that can lower this cost. The Klipsch was $159 on Amazon yesterday.
1.0 Line Level Output Cable
I first learned about the CN5 connector from PinMonk 's excellent writeup on improving Iron Maiden audio: https://pinside.com/pinball/forum/topic/replacing-on-board-amp-with-external-amp-for-iron-maiden#post-4439126
CN5 is a 7 pin connector on the CPU board that has line level outputs for Subwoofer, Right, and Left channels. This is the same connector that the Stern headphone adapter uses. You can buy adapter cables from some of the commercial audio upgrade companies, but it is simple enough (and much cheaper) to make your own. I already owned a decent crimp tool - which is highly recommended.
The 7 pin housing has a .100” (2.54mm) pitch and requires female crimp pins (you need one housing and four pins). Here are some sample housings/pins that will work:
https://www.mouser.com/ProductDetail/TE-Connectivity-AMP/1375820-7?qs=vmWJZJgp01vfG7%2F6tp8xJw%3D%3D
https://www.mouser.com/ProductDetail/TE-Connectivity-AMP/1375819-3?qs=vmWJZJgp01uV4n%2F4EuVitA%3D%3D
The amp that I used has RCA inputs for L and R, so I used a 3 foot 3x Male-Male RCA A/V cable.
https://www.amazon.com/gp/product/B00BDYL93Y
I cut off the three connectors on one end and stripped them to attach the pins (all grounds connected to one pin) and insert those into the housing. Note that my connector and pins are a bit different from the ones I linked above.
The pinout on the connector, starting from the top, are as follows:
7 - Sub out
6 - R out
5 - L out
4 - Ground
3 - R in (not used)
2 - L in (not used)
1 - Ground
The Red and White RCA connectors are for Right and Left - the Yellow is for the Sub. I will be using a 10 foot RCA extension cable to extend the Yellow cable to the line level input on my external sub.
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Inner conductor insulation colors are a bit confusing- Yellow RCA: Green, Red RCA: Red, White RCA: Yellow
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NOTE: Since we are completely bypassing the internal amp on the CPU board, you can unplug the speaker and sub cables from the bottom left of the CPU board (CN1 and CN4). I just tucked them under the edge of the board to get them out of the way. You definitely want to do this if you are using an external sub, as we don’t want anything driving the crappy cabinet speaker (which is more of a mid range speaker as opposed to sub).
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2.0 Speaker Adapter Cable
I wanted this mod to be reversible, so I created an adapter cable that attaches to the 4 pin Molex speaker connector used to connect the factory speakers to the CPU speaker level outputs. I already had one of these connectors in my connector stash, but you can order these from Mouser (you need one housing and four pins):
https://www.mouser.com/ProductDetail/Molex/03-06-1044?qs=th8CuLdcYnn3SuU5k7nxNQ%3D%3D
https://www.mouser.com/ProductDetail/Molex/02-06-1103?qs=359VwiUTsp0rVi3UDduwvw%3D%3D
I took 2 short lengths of speaker wire, attached the pins on one end and stripped the other end to run to the speaker terminals on the back of the amp. Alternatively, you could just unsolder the speaker wires from the Kenwood speakers and solder new speaker wire that you will attach to the external amp.
I used inexpensive 18 gauge speaker wire from Amazon that I bought a spool of years ago.
3.0 External Amplifier
There are a lot of options here, and I’ve tried several of them ranging from $10 to $80 but I REALLY like the price/performance of this $44 Class T amplifier that comes with a 5A power supply:
https://www.amazon.com/gp/product/B077Z7DBRT
I plugged the power supply into the 120v utility port in the lower right of the backbox. Some people may not like this as it is always powered, but that doesn’t bother me. The amp and power supply can be secured using 3M command strips.
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4.0 Subwoofer Output
I used a 10 foot RCA extension cable (Male - Female) to give me plenty of room to connect to the Yellow RCA cable and out the bottom of the cabinet to the external sub. I share a single sub between two pinball machines (they have separate L and R inputs and you can use either one).
https://www.amazon.com/Extension-Cable-Stereo-Female-Connectors/dp/B07NP6G82J
Getting the RCA cable out of the cabinet can be a bit tricky. There are vent holes at the bottom rear of the cabinet (you’ll need to raise the playfield to get to them) and they are covered with a mesh screen that is stapled in place. I usually pry out one of two of the staples and use a flathead screwdriver to pry the mesh up and give enough room to run the RCA cable through one of the holes.
5.0 Audio Settings Adjustment
Before powering on the machine, you should set the volume level of the amp and sub gain around mid level. Also center the treble and bass adjustments (if any) on your amp. The sub cutoff should be set to allow as high frequencies as possible (generally this is completely clockwise on the Low-Pass knob).
After powering up the machine, go into Settings - Utilities (UTIL) - Set Audio Levels (VOL). Make the following adjustments:
1. Volume: 25
2. Backbox Speaker Type: 4 ohm
3. Cabinet Speaker Type: 4 ohm
4. Audio Filter: None (very important!)
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Now you can adjust the volume knob on the amp and sub to comfortable levels - maybe a bit louder than normal. Adjust the treble and bass knobs on the amp to taste - I ended up leaving mine pretty close to center. You then have lots of room to drop the volume on the pinball machine below the baseline level of 25.
If you try this, please post your results and let me know how it went. This is now the best sounding machine in my collection.