4301p compressor question...

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JAY X

Well-known member
Joined
Jan 9, 2009
Messages
683
Hi!

Trying to build the THAT 4301 compressor... based on design note 115 (fully adjustable compressor).
And i thought to add  the led bargraph compression indicator  (design note 112).

After looking at both schematics i think it is possible to make the compressor meter connection (with its buffer U4A 4558) to the inverting node of U2C 4301p, with a 20k in parallel to R16 (30k1), in the schematic of DN115. But i'm not sure... :p  I placed the 20k resistor in series....buff.

attached is a schematic.

Thank you for your help!

Jay x

 
> to the inverting node

Virtual Earth. Essentially ZERO volts for any condition.

The logical tap is the pole on SW3A. However this is in the middle of various 10K and 30K resistors. It will NOT like the 20K loading of the U4A meter input.

Since U4A is half a chip and the other half does not seem to be used, set up the other half as a unity gain hi-Z buffer.
 
Note that the CV at pole of the switch (where is where, as PRR says, you want to tap into the CV) will go from being positive a couple hundred mV when there is no signal to negative a couple hundred mV when there is gain reduction. So if you want the leds to be on and then turn off as there is more gain reduction, you need a non-inverting buffer and the led circuit needs to ignore negative swings (which it does).
 
HI All!

Thanks for your answers, they helped a lot!.

Now i have the plan to build a 500 module... and as there will be some relays, i planned to power them with the +15v rail but with a dedicated gnd return just for relays. The same idea for the vumeters, (LM3914/15)... so to not mix in the same circuit the gnd returns of leds and relays...

Another problem/question, is the maximum separation between PCB cards in a 1 unit wide  500 module...¿any idea/number?
My plan is to stack the top card upside down...

Last but not least... the 500 edge connector has pins on both sides... so it seems that it does not matter where you keep the contact pin (top or bottom) as far there is only one...¿right?

¡¡Have a happy new year!! :)

JayX
 
JAY X said:
Another problem/question, is the maximum separation between PCB cards in a 1 unit wide  500 module...¿any idea/number?

The width of a module, which also defines the spacing between the card edges, is 1.5", although the actual mechanical width of the front panel is slightly less to the modules fit next to each other.

My plan is to stack the top card upside down...

So you'll have a "main" module board, with daughtercards stacked onto it?

Last but not least... the 500 edge connector has pins on both sides... so it seems that it does not matter where you keep the contact pin (top or bottom) as far there is only one...¿right?

The prudent designer puts the contacts on both sides of the edge connector.
 
Andy Peters said:
The prudent designer puts the contacts on both sides of the edge connector.

Hi andy!...

mmm.. why?  ¿maybe because not all 500 edge cards on every 500 rack out there has contact pins on both sides of the pcb female connector?

 
JAY X said:
Hi andy!...

mmm.. why?  ¿maybe because not all 500 edge cards on every 500 rack out there has contact pins on both sides of the pcb female connector?
Twice as many chances to make a good connection, lower resistance, etc.  (BTW I hate edge connectors).

JR
 
Hi JR. Ok. I take note.

I have a question regardin RFI protection in the 500 board. Given the fact that RFI protection is more usual at the connectors...¿is it necessary at the pcb?. This would imply a trace to the pin1 of the  500 pcb edge...just guessing.... ??? among other subtle details... :p

Thank you very much!

Jay x

 
JAY X said:
Hi andy!...

mmm.. why?  ¿maybe because not all 500 edge cards on every 500 rack out there has contact pins on both sides of the pcb female connector?

If you don't plate on both sides of the edge connector, the pins on the mating connector will eat into the material where you didn't plate.
 
JAY X said:
Hi JR. Ok. I take note.

I have a question regardin RFI protection in the 500 board. Given the fact that RFI protection is more usual at the connectors...¿is it necessary at the pcb?. This would imply a trace to the pin1 of the  500 pcb edge...just guessing.... ??? among other subtle details... :p

Thank you very much!

Jay x
Sorry I have zero experience with 500 modules, nor much interest.

Good luck, somebody here probably does.

JR
 
JAY X said:
I have a question regardin RFI protection in the 500 board. Given the fact that RFI protection is more usual at the connectors...¿is it necessary at the pcb?. This would imply a trace to the pin1 of the  500 pcb edge...just guessing....

I suppose it depends on the backplane and lunchbox enclosure. Pins 1 of all of the connectors should be bonded to the chassis at entry point, and that's also the best place to locate the RFI protection parts.
 
Hi Andy!

Ok. it is clear that  there should be RFI protection in the backplane of the 500 rack.
Then, on the compressor pcb board near the input/output pins of the edge connector, it could be optional...

 
Hi All!

¿Does anyone know the GAIN pot value of the schematic? it is not drawn...Maybe 10k, 20k or 50k? In different design notes from THAT corp, i saw 10k or 50k... 

thanks a lot!

Jay x
 
iprovlek said:
Do you planning to do 500 series comp Jay!?

¡YEAH! 8)

I'm currently trying different front panel layouts for the pots... with right angle pots... or vertical mount pots... to accomodate all the switches and knobs...it is the most difficult part...

Jay X
 
Hi!

Finally i will use LM3914 for gain reduction meter, and LM3915 for input/output vumeter. But i have a little doubt about the db range used in compressors regarding in/out signal levels, as different makers  show varying levels.

Any comment is wellcome!

Jay x
 
JAY X said:
Finally i will use LM3914 for gain reduction meter, and LM3915 for input/output vumeter. But i have a little doubt about the db range used in compressors regarding in/out signal levels, as different makers  show varying levels.

You already have an RMS to dB converter inside of the 4301, so you really just need a way to scale and display the control voltages. In a feedforward compressor, the RMS detector measures the input level and produces a voltage scaled in dB per volt. Then, some other part of  the circuit generates a control voltage signal to do the gain reduction. Similarly, in a feedback compressor, the detector measures the output level, and additional circuitry generates a control voltage.  So, in either case, with some simple addition and subtraction of these control voltages, you could display input level, gain reduction, or output level.

You do need some way to display these voltages, but you don't need the log conversion that the LM3916 provides, since you already have that. Further, the 3916 will not  help you to display the gain reduction amount, which is useful as well. I'm not sure what you could use for the voltage display, but some quad op amps connected as a comparator with a resistor ladder might work well.
 
Hi!

The Lm3914/3915 are still available: http://www.banzaimusic.com

To Monte McGuire:

For the gain reduction meter i use an LM3914, linear, connected with a buffer to the pole of SW3A (dn115) as suggested by PRR.

I did not mentioned the LM3916, but the LM3915. The Lm3915, in my design monitors the input/output levels from the card edge pins of the 500 compressor board. But thanks to  your post,  there is clearly another way to do what i did. I have to study it ;) I will post a schematic asap.

Jay x
 
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