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PMC-300A




 
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W9BHI
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« on: March 07, 2014, 06:52:05 PM »

I have access to a PMC -300A  AM processor.
Anybody have any experience or opinions on this device?
I would like to use it with a Symetrix 528E on my T-368.

Thanks,
W9BHI
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K1JJ
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"Let's go hiking in the woods, Tommy!" - Yaz


« Reply #1 on: March 07, 2014, 07:01:42 PM »

I have access to a PMC -300A  AM processor.
Anybody have any experience or opinions on this device?
I would like to use it with a Symetrix 528E on my T-368.

Thanks,
W9BHI

I just bought one and set it up.  I also use a Symetrix 528E.  The PMC-300A is a very transparent unit that will independently let you set your negative peaks and positive peaks.  There is no limit on positive peaks like many other units.   It's early to say, but I like what I see and the audio reports today were excellent.

Being designed in the early 1980's it doesn't use menus and DSP, which is a plus for me. All analog. I especially like the two setting pre-emphasis it offers. I usually depend on my own EQ, but the middle setting added a nice upper high end brilliance to the audio. I usually don't use that stuff, but this is exceptional.

I would recommend giving it a try.  There are a number of  AMers here using them too, who may have comments.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
W9BHI
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« Reply #2 on: March 08, 2014, 10:29:21 AM »

Thanks,
I am going to get this unit.
Being that it is over 25 years old, I will probably replace all of the electrolytic type capacitors
Just as a precaution.

Don W9BHI
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W7TFO
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« Reply #3 on: March 08, 2014, 10:54:30 AM »

Circuit Research Labs, or CRL, as everyone calls it, was in my backyard of Tempe. Arizona back then.

Ron Jones (sk) owned the company, and with a crack team produced some of the most successful audio processors ever built.

The APP Audio Preparation Processor (an agc unit), the SEP Spectral Energy Processor (a multiband EQ unit), and the PMC Peak Modulation Controller (a tough limiter) made up a complete set that was used to beat boxes like the Optimod in many AM broadcast installations.

If you are lucky enough to find the other two units, you would then have a system that could not be beat for clarity, transparency, and punch.  They were designed to work as an integrated system.

It may not come without an electrical cost:  A station I was CE for back in '83 (KZZP) ran a vintage Bauer FB-5000 transmitter that sounded just fine, but the program director (read licensed psychotic) wanted it to dominate the band and sound very aggressive. 

I called Ron and he came over and made enough measurements to determine what was necessary to make that TX produce extreme modulation density without ever peaking 100% neg.

A custom package including a one-off tilt correction box was installed.  Man, what a difference it made on 1310 in Phoenix! Shocked

It all came to an end three months later when the boss found out a pair of 4-1000 modulators lasted all of two weeks before being just burnt flat dead. Tongue

The old box was put back as it was.  $$ ruled.

Experiment with your box to determine where the 'happy' spot is and don't push it too far...it can sound great without frying tubes for the sake of a couple dB loudness.

All the manuals are available online now from Orban , as the current owners of the CRL line:  http://ftp://ftp.orban.com/CRL/


73DG
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Steve - K4HX
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« Reply #4 on: March 08, 2014, 11:20:23 AM »

I run my with the following settings.

Front Panel
Process: 2
Density: Middle position
EQ:  FULL

Real Panel
Low Cut/Flat: Flat
EQ Freq: set to 1 kHz
Auto Clip/Standard: Standard

You can run the Process Control at the higher numbers but I've found the processing become more noticeable and a bit busy sounding at those settings. It will be LOUD though and these can be used if conditions are poor.

Get the manual and read it. It does a pretty good job in explaining how the box works and what each setting does.
 
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K1JJ
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« Reply #5 on: March 08, 2014, 12:56:58 PM »

I run my with the following settings.

Front Panel
Process: 2
Density: Middle position
EQ:  FULL

Real Panel
Low Cut/Flat: Flat
EQ Freq: set to 1 kHz
Auto Clip/Standard: Standard

You can run the Process Control at the higher numbers but I've found the processing become more noticeable and a bit busy sounding at those settings. It will be LOUD though and these can be used if conditions are poor.

Get the manual and read it. It does a pretty good job in explaining how the box works and what each setting does.
 

Very good info, tnx.  It's all in the setup and adjustments.  I found it is easy to get frustrated with it unless we spend the time trying different settings. But eventually the sweet spots are found.  Jeff / NBC was a great help.


I noticed that the overall sound is VERY much affected by how hard the input is driven with audio.  It comes down to the flashing light on the FRONT panel.  If it comes on once in awhile, the processing effect is very light. If the light stays on most of the time, there is a busy sound and the background noise comes way up.

Steve, on the 6K - 1 KHz knob on the back... do you have it fully clockwise? Or where is it positioned?


The density affects time constant for release and I hear little to no difference when I adjust it.

When the process control is turned up, the negative peak limiting seems to hold nicely while the audio gets busier. It took me some time to find the right combination.

For my needs:  All I want is to limit and set the  negative peaks at -95% ...  and provide a positive peak ceiling above which cannot be exceeded by rogue errors. (+130%)  My increased background noise results from a higher audio drive needed to increase positive modulation - and not from the desire to have a busy audio sound from compression, etc.  I am working hard to keep blower noise to an absolute minimum.


More tips and comments about the PMC-300A are appreciated!


BTW Don, I used to have a 1970's Durrough 310?  that had problems with old caps. I had to replace them.  I didn't replace any on this PMC-300A yet, but ya never know. Anyone have comments about doing this?   Not knowing exactly how the unit is supposed to perform on the bench, it is hard to determine which ones are bad without a shotgun approach, unless it is simple power supply hum.

T

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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
N2DTS
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« Reply #6 on: March 08, 2014, 10:45:13 PM »

I got mine fixed and on the air today, I had a shorted tantalum cap in the low pass filter section.
Once I got that fixed, the unit worked great, and I worked out the same settings as above, but use the auto clipping setting.

Audio reports were very good, I was told I sounded dense, and the audio did also...

The frequency pot on the back I just adjusted so it sounded like I had some nice highs, that sets the high frequency agc starting point (frequency).

I have a VX 2000 (ultra voice) as a mic preamp, noise gate, and basic EQ.
It seems to drive the pmc-300 well.
Its a good unit for voice, but the compressor built in is not fast enough for keeping the modulation under 100%.

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K1JJ
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« Reply #7 on: March 08, 2014, 11:19:17 PM »

.
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
N2DTS
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« Reply #8 on: March 08, 2014, 11:53:50 PM »

I was talking about the vx-2000, its really slow to attack.
The pmc-300 is better, and with careful adjustments of the input and output levels it seems to do ok.

If you set it at 90% negative and do not hit the input too hard, it seems to work.

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K1JJ
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"Let's go hiking in the woods, Tommy!" - Yaz


« Reply #9 on: March 09, 2014, 12:13:12 AM »

I'll take a closer look at the attack time. It may have been the 528E doing it.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed. 

Nothing like a new homebrew rig. Come into the shack, flip on the switches and everything works perfectly.

And, nothing like an old dog.
Steve - K4HX
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« Reply #10 on: March 09, 2014, 03:07:13 AM »

You'll want the front panel light to flash on the higher peaks only, unless you are going for BAs to the wall audio.

I have the pot set so that the boost starts at 1 kHz. I forget if that is CW or CCW.

The PMC 300 is driven by a DAP 310.
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