phillymatt53
Well-known member
Well, Barry!.... I had no idea that you were/are into such console stuff too.
OK, here's the thing about consoles, and what I did to modify mine....
Yes, modifying the changer, and thus making it sensitive with a magnetic cartridge takes some design work.
My console's Garrard 3000 is a nice changer, and was designed with a light-tracking Pickering/Stanton magnetic cartridge, has a synchronous motor and a heavy cast platter.
The speakers, particularly the woofers, are in close contact with the changer and are going to be prone to feedback/distortion from cabinet vibrations.
That sorbothane isn't the answer in that case, because woofer vibrations travel all through the cabinet.
The answer to this problem is electronics...
Here's the only possible and effective solution....
There is a relatively simple electronic circuit called a Sallen-Key filter, installed after the RIAA preamp, and the main control preamp of the system.
It uses a pair of TL072 IC chips, one for each channel, for stereo.
A handful of small capacitors, and a couple resistors, built in a shielded little box the size of a pack of smokes, and of course using a small DC power supply.
This filter sharply filters out any frequencies below a given/designed frequency.
In my console, I designed it to "kill" or block any audio below 27Hz, which is just above where the annoying woofer vibrations start to shake the console and changer.
Because there's really nothing worth hearing "down that low" in frequency to worry about in the first place.
And the results are, absolutely no more feedback, even at loud volumes that shake the house windows.
It doesn't have any sonic effect on the music you would hear, there is still plenty of bass above 27Hz, because most bass that songs have is above that, around 30-40Hz and up to150Hz.
Initially, before I built the filter, the changer would visibly start shaking on it's spring mounts at fairly loud levels, skipping grooves, and those 12 inch woofers would "bottom out" and distort.
The additional benefit of the filter is eliminating that nasty rumbling, popping, and overloading the amplifier, which actually robs the amp of its power due to the stress on it.
So it's a win-win success and I'm pleased with the results.
I've even made another the Sallen-Key filter for my custom jukebox stored out in my garage. - the vintage "Golden Oldies 45" changer needed it.
That juke's got FOUR 10" woofers and a 200 watt amp!
It's used for outdoor BBQ's and neighborhood gatherings and gets cranked up sometimes. The neighbors a block away heard that thing during the 4th of July BBQ's.
That Jukebox was a labor of love, took me 3 years to finish from scratch.
I've got pics of it if anyone is interested.
