Sega Audio Amp Distortion [SOLVED]

[dj_yt]

I'm working on getting the audio in my OutRun cabinet up to scratch.

I have two original Sega audio amps (839-0035). I also have two working Sega OutRun PCBs. Last time I ran the PCBs through a Supergun, they sounded fine. I do need to reconfirm this.

Both Sega amps 'work'. However, I'm pretty much convinced they both work equally badly.

No matter what combination of PCB and amp I use, the sound is slightly distorted and crunchy. It's quiet even with the volume turned right up. I also tried two volume pots to make sure that wasn't causing problems.

My questions:

- Should I recap the amp as the first step?

- Is it reasonably to assume poor amplification and/or distortion would be the result of a capacitor problem? My assumption is yes!

dj_yt2015-07-02 22:07:31

 

[dj_yt]

I solved the problem.

I hadn't connected the 50 pin amp plug which has the MUTE and GND connections to the audio amp. I had assumed that these were only needed to send a mute signal to the amp, but no, they are actually needed for proper earthing. There is a very quiet pulsing you can hear when the audio is fully off, but I can live with that for now. I'll hold off on recapping the amp for another day.

Has anyone had audio improvement changing the giant 22000mf 25v capacitor on the base boards of these machines?

dj_yt2015-07-02 22:17:20

 

[cmonkey]

Surely it won't do any harm to recap the audio amp? Those caps are probably nearly 30 years old now. Have you got an ESR meter that you could measure their capacitance with? My OR audio suffers from the same quiet pulsing as yours and I'm going to recap mine soon for good measure (and maybe even renew both amps at the same time).

 

[Gaming Heaven]

my Outrun also pulses just the same, maybe this is normal?!

 

[dj_yt]

Surely it won't do any harm to recap the audio amp? Those caps are probably nearly 30 years old now. Have you got an ESR meter that you could measure their capacitance with? My OR audio suffers from the same quiet pulsing as yours and I'm going to recap mine soon for good measure (and maybe even renew both amps at the same time).

Both channels sound the same. Both amps amps sound the same. If they were wildly different (or sounded bad) I'd do it straight away as this would indicate something amiss.

I will recap the spare amp for good measure, but I don't think it will make a huge difference right now, beyond future proofing the amp.