grounding, output noise, etc...
2015-06-04 by steve.welk@...
Ok, rather than hijack an earlier thread, thought I'd start a new one. Re: my recently revived polaris, I'd written...
...Anyway, only one question. When pushing my master volume up past ~ 1/3 full scale, it gets pretty noisy. I gather this is "normal". Was there ever a fix for this? Do dedicated analog voltages/ground from the power supply board help?
In a response on the thread, bkuris wrote...
I found that upgrading the opamp on the output board really improved the sound of these units after doing the well documented grounding change (which I can't remember but involved cutting a wire I believe). I can run them at full volume without worrying about hiss, bass sounds clearer and more like you would want from a synth... I can't remember the exact parts that I ordered but they were in the $3-$15 range, likely something from burr-brown (maybe a newer TI excaliber TL207x) that was well regrading in the DIY audio community. The change wasn't subtle. Next time I have a unit open I'll take a closer look. It isn't a difficult mod -- remove old chip, add socket, add new chip. I'm sure someone industrious could do a drop-in board instead...
...Anyway, only one question. When pushing my master volume up past ~ 1/3 full scale, it gets pretty noisy. I gather this is "normal". Was there ever a fix for this? Do dedicated analog voltages/ground from the power supply board help?
In a response on the thread, bkuris wrote...
I found that upgrading the opamp on the output board really improved the sound of these units after doing the well documented grounding change (which I can't remember but involved cutting a wire I believe). I can run them at full volume without worrying about hiss, bass sounds clearer and more like you would want from a synth... I can't remember the exact parts that I ordered but they were in the $3-$15 range, likely something from burr-brown (maybe a newer TI excaliber TL207x) that was well regrading in the DIY audio community. The change wasn't subtle. Next time I have a unit open I'll take a closer look. It isn't a difficult mod -- remove old chip, add socket, add new chip. I'm sure someone industrious could do a drop-in board instead...
Ok. I'd put a socket on my output board long ago... Think there's an LF347 op amp in there now... It may indeed have helped the overall sound quality over the LM348 - too long/too many beers ago for me to recall... Anyway - how about this well documented grounding change? What is it? The op amp may have improved sound quality, but I still get a lot of noise when the master volume is raised...
Thanks,
Steve