My Pinbot's MPU board died and was not worth repairing due to multiple issues. I replaced it with a Rottendog System 11a MPU reproduction board. I'm grateful they make these, but the sound on Pinbot is now pretty messed up and I'm not the only one with issues. Specifically, the Speech and Sound (digitized audio) of the robot and certain explosions is not SUPER loud. In fact, if I try to adjust the music track to a normal volume, then the speech is so loud it is on the verge of blowing out the speakers - no exaggeration. Even if I turn the volume knob all the way down, the speech is still too loud.

I've heard no solutions from others, so my first step was to adjust R15, the 100k ohm trimmer pot on the Speech and Sound board. I turned it all the way down and there was a big improvement, but the speech is still way too loud. The trimmer pot only turns 1/4 turn - there's no more adjustment available.

So my plan is to replace this 100k ohm trimmer with a 200k one, from Mouser electronics.

http://www.mouser.com/Search/ProductDetail.aspx?R=3310C-001-204Lvirtualkey65210000virtualkey652-3310C-001-204L

So my question - does anyone see a problem with this approach? Has anyone had this issue? Are there alternative solutions?

Both Rottendog and the retailer The Pinball Wizard didn't have any advice to offer.

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My original 11A MPU was repaired by a respected professional, but when it fried a second time, he deemed it ready to be scrapped, so it was. I agree there's sound issues on the Rottendog System 11 board. I tried this board in Swords of Fury, which I think is 11B. It had the same issues as Pinbot, which is the digitized sound (call outs, explosions..) are super loud while the syth background music volume is normal. It needs to be balanced out between the two. On Pinbot the R15 pot on the sound board seems to have a big, positive impact on the problem, but it just does not have enough resistance at 100K ohms to totally make the problem go away. I'm going to try replacing it with a 200k ohms pot that is on order from Mouser. I will report back if this does the trick. Outside of this, the Rottendog Sys 11 MPU is a good working board and a relatively good price. Nice to have at least this option on the market. The Kohaut option is no longer available.
It's now the only new board option I'm aware of. I'd say if someone needs to replace their Sys 11 MPU, they should always go for a good condition used original board first. But those are hard to find. : (

Well in case anyone ever replaces their MPU 11A or 11B board with a Rottendog and has the same sound problem, here's the fix. I replaced with 100k ohm potentiometer on the speech board with a 250k ohm one. It helped - but not enough. Still too loud. So I had to upgrade to a 500k ohm potentiometer. That did the trick. The speech and explosions are now roughly the same volume as the music. But, I had to turn the pot all the way to maximum resistance (lowest volume) of 500k ohms. So whatever is going wrong with the Rottendog sound, it takes at least 500k ohms to balance it out. I don't know if anybody else has dealt with this but that's my solution. The Pot, form Mouser Electronics, is rather large, but solders in with it's two pins to the board without difficulty. This fix also eliminates most of the background "buzz" sound coming from the Rottendog board. Wish Rottendog would provide a fix for this. I tried this board on Swords of Fury, Sys 11B, and it had the exact same problem.

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Yes. It was it has been the same issue for me and basically the same fix. The sound was intolerable and probably on the verge of damaging some hardware. Difference is that I put the pot on the board instead of in the wire. The sound is not perfect but decent now. I previously tested this Rottendog board in Swords of Fury which is Sys 11B. Same damn problem with the digitized sounds. Probably as you pointed out, one of the resistors in the schematic are not what's on the board and Rottendog missed this. What gets me is they have not supported customer complaints and several suppliers now refuse to even sell the 11A-11B daughter board system from Rottendog. I think the 11C games are okay though, as they don't use the daughter board.

But I was also told by someone this week that Rottendog just sold their business to someone else. Perhaps that entity will make improvements. There's just a ton of System 11 games out there and many burned up boards. We need alternatives and the Kohaut boards are not being made as of January 2017. : (

Can you post some good pictures of your sound board in the back box? It is the small board in the upper left side of the box.

This thread has some additional ideas that are based more on modding the audio wires instead of the board. :

https://pinside.com/pinball/forum/topic/calling-all-williams-system-11-sound-gurus-having-volume-issues