1176 ae 2:1 ratio. Need some help calculating resistor values

Hi, i want to modify my pair of diy mnat 1176 rev D to have the same ratios as the 1176ae.  2:1 4:1 8:1 20:1  So no more 12:1 ratio but a new 2:1 ratio.  Here's a drawing with what i think are the right resistor values.  I would be pleased if someone could double check my changes.  Or maybe if someone have the 1176ae schematic!  To resume how i have done it :  R19 is now the sum of R19+R20 to get the 8:1 on the button where the 12:1 was. R20 get the previous R21 value to get the 4:1 in place of where the 8:1 was.  The new values of R21 and R22 are taken from Igor 's 2:1 ratio on his 1176 51x.  Same logic for the second side of the switch.
Hubert

I would also like to modify my Hairball to a 2:1 and a slow 10ms attack.

The value on the schematic on my previous post are good to get the 2:1 ratio.  Don’t know about the slower attack.  It do sound somewhat slower at the 2:1 ratio

Sounds good. The ratio mod is more important, but slow attach would have been nice.

Have you had it confirmed yet?
I can’t read schematics just yet. Still a noobie here.

Yes confirmed, I still have the mod on my 2 1176 and it’s working really well

YLab said:

I would be pleased if someone could double check my changes.  Or maybe if someone have the 1176ae schematic!  To resume how i have done it :  R19 is now the sum of R19+R20 to get the 8:1 on the button where the 12:1 was. R20 get the previous R21 value to get the 4:1 in place of where the 8:1 was.  The new values of R21 and R22 are taken from Igor 's 2:1 ratio on his 1176 51x.  Same logic for the second side of the switch.
Hubert

Click to expand...

The values look good based on putting them in a spreadsheet. The left sets a voltage divider to reduce the signal at higher ratios. The right changes the threshold to change the point where compression kicks in. If you haven't read the 1176 manual it explains the circuit quite a bit. Basically the design changes the threshold with the ratio to maintain about the same level of compression.

Both set a voltage divider. If you plot them (divider vs ratio or threshold voltage vs ratio) they are both linear. So to make 2:1 you just want to extrapolate out, which is what your values do. Only issue is the threshold for 2:1 should be a little past -10, but you can't do that because the voltage supply for the threshold is -10

If it seems the threshold needs to be a little more accurate, you *could* change the zener (CR9) from 10v to 12v and recalculate the threshold divider to get the right voltages. 

MiamiBoy said:

I would also like to modify my Hairball to a 2:1 and a slow 10ms attack.

Click to expand...

Attack pot is 25k. Get a larger value pot and try it.  But I'm not sure how slow you can make it realistically.

The manual says the attack goes from 10 microseconds to 0.8 ms (800 microsecs). The timeconstant of a compressor comes from the RC circuit of the sidechain. Simple explanation is a capacitor at the gain control element is charged through the attack pot (25k) and drained through the release pot (5M).  The larger the attack pot, the slower the control voltage and compression. However, the attack and release interact in a simple RC sidechain. If you make the attack pot to big, the release pot is draining the control voltage as you are trying to charge it. Stock values of release/attack is 200. Make them too similar and it'll be anemic.
You could also make the capacitor bigger to slow it down. The problem is maintaining the very fast attack that the 1176 is known for, while allowing for slower times as well.
Perhaps consider a different compressor for slow attack, as there are sidechain modifications that some compressors have to make long attack possible, i.e. SSL

Good stuff, dmp.
Thanks a lot