Woofer wiring on a Rock-Ola 490/494 from a newbie

TonyJ · by **TonyJ** » Fri Jun 24, 2016 6:22 pm

New to the board and have dabbled in restoring tube radios and Victrola machines the past few years and was asked by a friend to look at a family jukebox that hasn't worked for awhile. She had two issues with it - the first was that after a record played, the gripper wasn't picking the record up and would stack a new record on top of the old. Did some searching and found that lubrication was most likely the issue and successfully took care of that with some SAE 20 oil. The second issue was that she said that woofers were blown as there was no bass coming from the machine. In looking at the wiring diagrams they had and how the woofers were wired, I found that someone had connected both the left and right speaker feeds to the same terminal on the audio distribution terminal and corrected that and brought them to life. Needless to say they are ecstatic and told me this morning they listened it to it for 2 hours last night after I left.

However, not having touched a jukebox before, this woofer wiring arrangement where the woofer is fed from the "hot" sides of the left and right audio is strange to me. It would appear to me that it gives a "center channel" effect only. Is this common with most jukeboxes? To my ear, the bass was a bit lacking. I'm sure the amp is in need of rebuilding as there is some AC hum from filter caps that are probably in need of replacing. But even so, with the volume I could get from the upper speakers, the woofers just didn't seem to be as punchy and wonder if it's partially due to that "center channel" wiring configuration and the design of that model? Also, the right upper speaker didn't have quite the brilliance the left did and curious if that could also be an amp or crossover issue. Which I also noticed on the schematic, the right upper speaker appears to be wired out of phase also.

Sorry for the long post, this is new to me and enjoyed getting this at least playing in the state it's in for her. Of course, now I want a juke, always wanted one as a kid. Wonder if that will push my wife over the edge with the radios and Victrolas already living in our house...

by **Ron Rich** » Fri Jun 24, 2016 11:06 pm

Tony,
I don't know about that model RockOla, but they did do some "weird wiring", on some coin operated phono's.
Another brand (Seeburg), used a "minoralizer" ( 500 mh choke), on most all of their solid state amps., in the bass section. Is it possible that RockOla did the same, and the former person that worked on that system found one channel "bad" ? Therefore he hooked all speakers to one side to hide that fact ?? --And yes--that amp does need attention, now, before you loose an output transformer !
Ron Rich

TonyJ · by **TonyJ** » Mon Jun 27, 2016 3:52 am

Thanks for the feedback. Both channels are working, although the right channel seems to be lacking some highs and the treble slide switch doesn't appear to have any effect. Next time I get out there I'll figure out if that's the amp or speaker itself. I've told them we need to pull the amp soon and have it rebuilt and they are on board with that. Are there any preferred places to have that done? I've found a few on the net, but if there are one or two that are recommended, I'd like to use their services. Thanks!

by **Ron Rich** » Mon Jun 27, 2016 8:59 am

Hi Tony,
If I were looking for someone to rebuild that amp--I'd axk all potential re-builders how many of them have you rebuilt ?? Ron Rich

Rob-NYC · by **Rob-NYC** » Tue Jun 28, 2016 3:27 am

......this woofer wiring arrangement where the woofer is fed from the "hot" sides of the left and right audio is strange to me. It would appear to me that it gives a "center channel" effect only. Is this common with most jukeboxes?

This was/is common in Rowe-AMI machines. It reduces rumble and the chance of acoustic feedback from the out of phase signals from the pickup. Rock-Ola seems to have adopted it for similar reasons. It requires that either the pickup be wired out of phase or a phase inversion ckt be incorporated into the machine' s preamp.

As for the hum, if it is 120Hz it indicates either failing filter caps or excessive load on the power supply. In either case the amp needs service before it can be safely used.

viewtopic.php?f=3&t=6428

Here is a schematic of the general wiring and amp schematic:
http://elektrotanya.com/rockola_model-4 ... nload.html

Rob-NYC