Badly distorted CD audio on Quadra 650/800

[lobust]

I have a Quadra 650 board converted to a Q800 and installed in my Q800 chassis, with the original caddy loader cd rom drive.

System audio on the internal speaker seems to be working completely normally, games etc. all sound fine.

Last night, for no particular reason I thought I'd put an audio cd in there and play it. Just through the internal speaker, it sounded awful - terrible distortion as there's way too much gain. The distortion remains regardless of the volume.

I kind of assumed the audio passthrough was digital from the drive to the logic board and amplified on the logic board. Is there in fact analogue audio circuitry on the drive? I know @Branchus has stated clearly that all these drives need recapped, but I (again...) kind of assumed that was for actual drive function...

 

[This Does Not Compute]

IIRC machines from that era still used analog audio passthrough from the optical drive. You should have a separate, smaller ribbon cable between the optical drive and motherboard for this. I'd definitely suspect there's something wrong with the audio circuitry on the drive itself if other sounds from the motherboard are normal.

 

[MacKilRoy]

Download Astarte CD-Copy 2.0.x from Macintosh Garden, and use it to extract the audio from a CD as a test. Play back that audio in software, and it will be completely digital. This would verify that your CD is good, and being read properly, etc.

Astarte CD Copy:

https://macintoshgarden.org/sites/macintoshgarden.org/files/apps/ASTARTECDCopy2.03e.sit_.bin

Play it back using SoundEdit:

https://macintoshgarden.org/sites/macintoshgarden.org/files/apps/soundedit16.sit

 

[lobust]

Download Astarte CD-Copy 2.0.x from Macintosh Garden, and use it to extract the audio from a CD as a test. Play back that audio in software, and it will be completely digital. This would verify that your CD is good, and being read properly, etc.

Astarte CD Copy:

https://macintoshgarden.org/sites/macintoshgarden.org/files/apps/ASTARTECDCopy2.03e.sit_.bin

Play it back using SoundEdit:

https://macintoshgarden.org/sites/macintoshgarden.org/files/apps/soundedit16.sit

I'll give that a go if purely for the fun of it, but I should clarify that the drive seems to work perfectly otherwise - I have installed os's from it multiple times in the course of getting this old beast functional!

I guess recapping the drive is a fine job for the weekend too!

 

[MacKilRoy]

I'll give that a go if purely for the fun of it, but I should clarify that the drive seems to work perfectly otherwise - I have installed os's from it multiple times in the course of getting this old beast functional!

I guess recapping the drive is a fine job for the weekend too!

The test allows you to verify that the Mac reads audio from the CD just fine and plays it back to you through the same speakers, just digitally. If you have no issues, it’s your analog cable /connector (or the drive needs a recap).

 

[lobust]

Recapping the drive did indeed cure the issue, no more distortion!