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Title: Symmetrix 421-M Opinions? Post by: WBear2GCR on October 23, 2012, 08:46:07 AM Any one have experience or opinions on the Symmetrix 421-M?
It seems to be the sort of unit that is used in live performance to keep mic levels sounding even and natural. Also this one has a mic pre built in, which is handy. Someone on ebay has a boat load of them: http://www.ebay.com/itm/390410444656?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 (http://www.ebay.com/itm/390410444656?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649) I did pick one up... have yet to try it out. _-_-bear Title: Re: Symmetrix 421-M Opinions? Post by: Jim KF2SY on October 23, 2012, 09:14:24 AM This reviewer likes his -uses it for AM. http://www.harmonycentral.com/products/95588 Title: Re: Symmetrix 421-M Opinions? Post by: W1DAN on October 23, 2012, 02:32:19 PM Hi Bear:
Have not used one of these, but looked at the schematic. The mic amp might be a little noisy and has a little RFI filtering. On the good side, this uses the dbx 2150a VCA and 2252 detector, both IC's I am very familiar with as I home-brewed a 3 band compressor/limiter using these chips in the 1990s. The compression and limiting should be pretty smooth, but do not expect the limiter to be super tight on small peak overshoots. The filters should help for AM, but all ham AM needs some pre-emphasis too. I put in an offer for a couple of the units. 73, Dan Title: Re: Symmetrix 421-M Opinions? Post by: WBear2GCR on October 23, 2012, 03:35:45 PM Yeah Dan, Ha ha... coupla units! ;D Where did you find the schematic? I don't recall if it is in the manual or not, I think I downloaded that a while back. One idea on the mic pre is to use some better ICs... that should drop the noise, but I doubt that the noise is much of an issue for us, unless one uses a low output mic. Overshoot on the limiter? Don't care at all, have the 3 diode limiter in the modulator and I like my positive peaks... more interested in keeping the levels up if I back off the mic a bit... plus the free mic preamp makes it easy to plug in a "fancy" mic. Gotta rig up a PTT though. _-_-bear Title: Re: Symmetrix 421-M Opinions? Post by: KZ5A on October 23, 2012, 03:37:33 PM I have one in use presently and like it quite well. As mentioned, it does need to be used with an EQ.
Title: Re: Symmetrix 421-M Opinions? Post by: WBear2GCR on October 23, 2012, 05:37:29 PM Oh? What does it do to the sound? Mud? How about with a D 104 w/source follower? _-_-bear Title: Re: Symmetrix 421-M Opinions? Post by: W1DAN on October 23, 2012, 08:27:03 PM Hi Bear! AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Most audio that does not have some pre-emphasis will sound dull through a receiver that has any roll-off (and most do). You know that! Your idea of a D104 is a good one. Give that a shot, and I bet the healthy level the D104 puts out will hide any mic preamp hiss. And your diode clipper is just the ticket! Schematics are here: http://support.symetrix.co/s.nl/ctype.KB/it.I/id.397/KB.4374/.f I did order two from the seller (for stereo if needed). As you, I will use it as a preamp with metering and phantom power. It will be easier than my ATI mic preamp. Thanks for posting the link to the seller! 73, Dan |