Need advise for a HPF

[JAY X]

Nothing complicated, just a single switch opamp based, HPF for a THAT 2181 VCA compressor. Slope: 6db/oct or 12db/oct? Cutoff Frequency: 80 or 100hz, or...? To avoid compressor pumping..¿what is the most usual/useful frequency?.

Jay x

 

[gyraf]

it all depends. What for exactly?

 

[Script]

Hmm, around there. Sometimes higher, sometimes lower. Depends on type of music,, application, mix or master, overall goal etc etc

Could build circuit and try different freq. Then put selection on toggle or rotary or make sweepable.

 

[JAY X]

It is for a channel compressor. Drums , bass, guitars, voices, etc... On the front panel i only have space left for a dpdt push switch...
The RND 535 seems to have a HPF tuned to 150hz..

I found an online filter calculator, for sallen-key 2nd order filters.
http://sim.okawa-denshi.jp/en/OPseikiHikeisan.htm

 

[Script]

Depending on circuit, it might be as simple as an RC filter.

Space for push switch = space for toggle ? Ugly?

On-Off-On toggle might give you 'flat' and two selectable frequencies.

Or try and find small(er) rotary?

 

[elskardio]

A simple RC filter before the side chain's detector is all you need.
Pick a single value for the film capacitor, then switch different resistor values to alter the frequency.
I personally like 100Hz and it's what I use on my VCA compressor.

 

[dmp]

A simple RC will be 6 dB/oct while the Sallen-Key is 12dB/oct. Though two RC stages can also be cascaded to give 12dB/oct (the CAPI VP28 does this to get the -6/-12 switch) . You can also use the Neve inductor based HPF for 12 dB/oct.
Prototype to see what you want.
My experience has been that a simple RC filter (-6 dB/oct) is sufficient for the sidechain of a bus compressor.
Typically there is a capacitor at the input of the detector. Usually it is large (47uF) to pass all frequencies. Changing that to a smaller size, will create the HPF. The 3dB corner frequency for a RC HPF is 1/ (2*PI*R*C). Since two capacitors in parallel add, you can use the switch to put a large capacitor in parallel with the small one to go from "HPF on" back to the "HPF off".

 

[JAY X]

Hi!

Ok!, good ideas around here!!. I like the 3pos toggle switch idea!.

My idea is to build a 500 series format mono compressor, and place also a stereo link switch. At this respect, i noticed two things.

Those compressors that don't have stereo link switch rely on the link switches of the 500 Rack to link the compressors sidechain.
But those compressors that have a stereo link switch, i'm not sure how do they "transmit" the SC signal to the following unit...

 

[dmp]

The rack still needs to be configured to connect the link pins - often a jumper - the stereo link switch simply turns it off/on from the front of the unit.

 

[Script]

I like the 3pos toggle switch idea!.

With a simple RC, as you have to ADD capacitance to lower the frequency (get flat), the smallest cap value (highest freq) is permanently in circuit -- sitting at the toggle mid (i.e. Off) position. Example:
On/Off/On
100/150/flat

 

[abbey road d enfer]

My fave is the "thrust" filter that has a 3dB/octave slope.

 

[JAY X]

The rack still needs to be configured to connect the link pins - often a jumper - the stereo link switch simply turns it off/on from the front of the unit.

Ok...so, the link bus in these racks, as it is a single line, acts as a send from the compressor that acts as the master unit, and as a receiver for the slave unit to be controlled.

 

[Newmarket]

A simple RC will be 6 dB/oct while the Sallen-Key is 12dB/oct. Though two RC stages can also be cascaded to give 12dB/oct (the CAPI VP28 does this to get the -6/-12 switch) . You can also use the Neve inductor based HPF for 12 dB/oct.
Prototype to see what you want.
My experience has been that a simple RC filter (-6 dB/oct) is sufficient for the sidechain of a bus compressor.
Typically there is a capacitor at the input of the detector. Usually it is large (47uF) to pass all frequencies. Changing that to a smaller size, will create the HPF. The 3dB corner frequency for a RC HPF is 1/ (2*PI*R*C). Since two capacitors in parallel add, you can use the switch to put a large capacitor in parallel with the small one to go from "HPF on" back to the "HPF off".

Yes. But the "47uF" cap is going to be an electrolytic (or it is going to be massive ) and I'd advise that the smaller value implementing the hpf should not be an electrolytic (or tantalum really).