Symetrix 528 Peculiarities

[flintstone mop]

My recent purchase of a Kenwood TS850 committed me to have to RE-purchase a Symetrix528E. And I USED to own an Inovinics 222 also.....typical of me to USED to own.
The time owning a Flex SDR 1000 got me to experiment with the Mic. audio and found out that the parametric EQ settings of the Symetrix were really messing up the sound of the mic and nice large positive peaks. So, I disabled the EQ from the Symetrix and it was like night and day for better audio and more pos. peaks. The Edirol outboard sound card was capable of providing phantom power so, I bypassed the Symetrix altogether. And a little more positive peaks and better sounding TX audio.
That is the only thing I miss about the Flex radio TX audio. Apparently there is some magic taking place in the software/radio that makes it so good.
Ok, the story is getting into buzzard mode...sorry
The TS850 is an easy radio to modify for "DC to light transmit audio" Shielded wire to pin 1 on the AN612 balanced modulator and you're done.
So back on line with a Symetrix and fighting with those parametric EQ settings. And the result was just ok audio and miserable looking modulation on the 'scope. Experimented with reversing audio phase and it got even worse.
Bad memories return about the parametric EQ and so I DISable it and connect the Symetrix output INTO my DBX 1531 15 band graphic EQ. And I have returned to heaven!! Huge audio peaks and nice full sound. Less hassle fighting with over-modulation.
I look at the PDF for the Symetrix looking for any info on how the EQ works. Is it like a Dorrough unit? Or the Inovonics 222? multiband EQ compressor/limiters? Each band has its own compressor and you can even adjust the ratio!!! I'm assuming broadcast limiter, as in Negative peak limiter??
Nothing shows me that there is any type of processing, like a compressor for each band in the 528E. In fact, the compressor is BEFORE the EQ circuits and then it goes to the output section.
The Dorrough unit and Inovonics and CRL have compressor'/limiters for their EQ and then it goes into more processing before it is output to your transmitter.
What could I be doing wrong with my Symetrix that is screwing up TX audio so much when I am utilizing it's parametric EQ???
Why is it like night and day to see more positive peaks and nicer audio, using a graphic EQ?
Thanks for reading. A little baffled but made improvement to better sound and schwangin the munkey.
Fred

[N2DTS]

It sure pays to experiment and try different things.
As far as I know, the 528 is for PA use, to level things somewhat and to correct for bad microphones, like all the other non broadcast stuff.
The broadcast stuff is designed to make radio sound loud without over modulation, a much different job.

Phase shift is likely why you see what you see.
And I often have much different results with switching the phase of the OUTPUT, not just the microphone.
The 528 is likely balanced output and you can switch the phase there also.

I have an ultra voice that I use mostly as a mic preamp these days, and I noticed that turning on or off a section reverses the phase on the output.
Its got a downward expander, a compressor, and EQ, a tube sound (never used it), and a de esser.
The downward expander works very well, the compressor is ok but not real fast, the eq seems ok, the de esser seems to do nothing, but maybe I can not hear it working.
 

[W3GMS]

My recent purchase of a Kenwood TS850 committed me to have to RE-purchase a Symetrix528E. And I USED to own an Inovinics 222 also.....typical of me to USED to own.
The time owning a Flex SDR 1000 got me to experiment with the Mic. audio and found out that the parametric EQ settings of the Symetrix were really messing up the sound of the mic and nice large positive peaks. So, I disabled the EQ from the Symetrix and it was like night and day for better audio and more pos. peaks. The Edirol outboard sound card was capable of providing phantom power so, I bypassed the Symetrix altogether. And a little more positive peaks and better sounding TX audio.
That is the only thing I miss about the Flex radio TX audio. Apparently there is some magic taking place in the software/radio that makes it so good.
Ok, the story is getting into buzzard mode...sorry
The TS850 is an easy radio to modify for "DC to light transmit audio" Shielded wire to pin 1 on the AN612 balanced modulator and you're done.
So back on line with a Symetrix and fighting with those parametric EQ settings. And the result was just ok audio and miserable looking modulation on the 'scope. Experimented with reversing audio phase and it got even worse.
Bad memories return about the parametric EQ and so I DISable it and connect the Symetrix output INTO my DBX 1531 15 band graphic EQ. And I have returned to heaven!! Huge audio peaks and nice full sound. Less hassle fighting with over-modulation.
I look at the PDF for the Symetrix looking for any info on how the EQ works. Is it like a Dorrough unit? Or the Inovonics 222? multiband EQ compressor/limiters? Each band has its own compressor and you can even adjust the ratio!!! I'm assuming broadcast limiter, as in Negative peak limiter??
Nothing shows me that there is any type of processing, like a compressor for each band in the 528E. In fact, the compressor is BEFORE the EQ circuits and then it goes to the output section.
The Dorrough unit and Inovonics and CRL have compressor'/limiters for their EQ and then it goes into more processing before it is output to your transmitter.
What could I be doing wrong with my Symetrix that is screwing up TX audio so much when I am utilizing it's parametric EQ???
Why is it like night and day to see more positive peaks and nicer audio, using a graphic EQ?
Thanks for reading. A little baffled but made improvement to better sound and schwangin the munkey.
Fred

Hi Fred,

The 528E is designed as a mic processor intended for broadcast use.   Its an averaging gain riding compressor that level things out so you don't have to watch the VU meter on the board as much.  It certainly was never designed to do what an Optimod or similar other processors will do.  Lots of studios used the 528E's as a microphone processor to boast levels and to control levels.  Its not a multiband processor.  It looks at the entire audio chunk and then either increases gain or decreases gain depending on the settings.  It also has a downward expander which is nice if you have lots of background noise.  My preference when used on SSB is to run the downward expander since I dislike blower noise on a SSB signal.  On AM a little bit of blower noise does not bother me and for that reason never use the downward expander on AM.  I have used the 528E for many years with very good success.  In fact I like it so much that I bought a second one a few years ago to use in another station.  My favorite EQ settings are not from the 528E's parametric EQ.  I have gotten the parametric EQ close but not exact to that which I can get from my graphic EQ which is a ART 341.  The 528E seems pretty much bullet proof from an RF susceptibility perspective.  With my setup I typically modulate about 120% positive and control the negative peaks with the Inovonics 222 negative peak limiter.  That is required since the 528E is no where near fast enough to be a negative peak limiter and also it was never designed to do that function in the audio chain.
The 528E does not do asymmetrical limiting or gain control .  So it will limit both the positive and negative peaks.  About the only way you will get extended positive peaks is to either use less compression and adjust the compression ratio or use a negative peak limiter and clip the negative peaks to allow more positive peaks to modulate the transmitter.  That's usually not a great solution since hitting the negative peak limiter that hard really starts to effect the sound.

Joe, GMS             

[flintstone mop]

I guess eyes get tired of long blogs and got tired reading after the second paragraph.

There seems like there is no explanation why, when I disable the parametric EQ on the 528E, and EQing with a plain Jane graphic equalizer gives me a larger modulation envelop and more positive peaks.

One of those goodies that slipped out of my hands cuz I figgered I would never need them again.
USED to have an Inovonics 222, Dorrough DAP 310 and a Urei BL-40 Modulimiter..not too smart..

Fred

[N2DTS]

Phase rotation is a guess..

[steve_qix]

I use a 528-E at Rattlesnake Island.

It is very helpful to change the "order" of the various stages.  There are 1/4 inch plugs in the back to accomplish this.  Make the compressor the last thing before the output stage.

It should be:  MicPre -> Parametric EQ -> Compressor -> Output stage.  There may be some other stages in there - I forget exactly and the 528-E is at the Island now, so I can't look at it, but you get the idea.

I do have a graphic EQ as well that's inserted into the chain ahead of the parametric EQ, but you can still do well with just the parametric.

Equalization definitely changes the phase of your audio, and in fact you may find you need to flip the phase to get it right after EQing.  Just experiment.....

Regards,

Steve

[flintstone mop]

Yes Steve!!!
Exactly what I found with the 528E. BUT flipping the phase made things worse. Slightly more pos peaks and the 'Scope trace didn't look very nice. My voice looks like the preferred Christmas tree on its Right side (pointing to the right in the 'Scope, when the EQ is good. The REA mod monitor meters displayed larger pos peaks. The 'Scope trace was the final word, though.
And that is a nice peace of info about re-arranging the order of processing in that box. I never thought of doing that.
I might give that a try. Right now reports of the TX audio are very good and I will let it be for now. I am giving up some loudness without a Peak Negative Limiter (for AM) and adjusted my modulation not to hit more than 95% neg. Positive peaks are schawngin' easily towards 120%. The DBX166A is a peak limiter/compressor, but when the Peak Stop light blinks it starts cutting back on the entire audio waveform, because it is not an AM limiter for radio.
Fred

[steve_qix]

Yes Steve!!!
Exactly what I found with the 528E. BUT flipping the phase made things worse. Slightly more pos peaks and the 'Scope trace didn't look very nice. My voice looks like the preferred Christmas tree on its Right side (pointing to the right in the 'Scope, when the EQ is good. The REA mod monitor meters displayed larger pos peaks. The 'Scope trace was the final word, though.
And that is a nice peace of info about re-arranging the order of processing in that box. I never thought of doing that.
I might give that a try. Right now reports of the TX audio are very good and I will let it be for now. I am giving up some loudness without a Peak Negative Limiter (for AM) and adjusted my modulation not to hit more than 95% neg. Positive peaks are schawngin' easily towards 120%. The DBX166A is a peak limiter/compressor, but when the Peak Stop light blinks it starts cutting back on the entire audio waveform, because it is not an AM limiter for radio.
Fred

The Christmas tree pointing to the right is a perfectly normal pattern, and is generally indicative of audio with a good low end and not too much phase shift after the audio processor.  It is sometimes called the "class E pattern", and in fact my audio looks just like this.

The actual shape of the scope pattern is not nearly so important other than looking for obvious clipping or spikes - things like that .  If the meters show more positives than negatives on the mod monitor - that's the most important thing.

[KQ6F]

I've consistently received good audio reports using the 528E.  However, I use it only for EQing (de-esser and expander/compressor both turned off).  For asymmetrical limiting and audio bandwidth control I use the Inovonics 222 with the NRSC low-pass filter modified for 5kHz bandwidth.  This was accomplished by changing  the ten 3300nf caps in the filter circuit to 5600nf.  This was a simpler mod than the published one that requires changing out 26 components.  I ran my version past Inovonics guru Jim Wood and he blessed it.

BTW, for maximizing positive modulation peaks the Voice Symmetry button on the 528E should be OUT.

Rod