my q is too tight

djgout · Post by **djgout** » Sat Jan 26, 2008 3:01 pm

okay. so yeah, i'm trying to figure out some eq design to modify the q of my yamaha m1532 desk. it's a cool desk with 2520 style discrete opamps on the pre stage and then some cooler old ICs in the rest of the circuit. it's absolutely yamaha's take on an API. the only problem is it was designed as a live desk. so the Q of the eq's is very narrow, like for the fight with feedback.

from what i've been able to understand reading the art of electronics filter chapters and some more stuff online and staring at a 550a schematic for a few hours i think that i'd like to set the q to be about an octave.

i believe by the attatched schematics of the eq section and frequency response graphs that i'd need to change the 560Rs in the output to the frequency caps.....but i'm not totally sure. can anyone help me figure this out?

Thanks

justin

RodC · Post by **RodC** » Sat Jan 26, 2008 4:41 pm

I believe you are correct. I wonder if you could put a pot in there (1K) and make a sweepable Q??

digitaldrummer · Post by **digitaldrummer** » Sat Jan 26, 2008 6:55 pm

I was just hoping to reply with "that's what she said!"

RodC · Post by **RodC** » Sat Jan 26, 2008 7:21 pm

digitaldrummer wrote:I was just hoping to reply with "that's what she said!"

lol, that joke never gets old! Well, I guess it does according to my wife...

RefD · Post by **RefD** » Sat Jan 26, 2008 8:28 pm

RodC wrote:
digitaldrummer wrote:I was just hoping to reply with "that's what she said!"
lol, that joke never gets old! Well, I guess it does according to my wife...

is that what she said?

err..

brianroth · Post by **brianroth** » Sat Jan 26, 2008 10:31 pm

That looks like a variation of a gyrator:

http://en.wikipedia.org/wiki/Gyrator

Bri

b3groover · Post by **b3groover** » Sun Jan 27, 2008 12:37 am

brianroth wrote:That looks like a variation of a gyrator:

Shut yo' mouth!

The Scum · Post by **The Scum** » Sun Jan 27, 2008 12:43 am

Yup. Gyrator indeed.

Read this for some applicable background:
http://forsselltech.com/downloads/desig ... esign2.pdf

To summarize (at least in Fred's circuit) - the Q is determined by the ratio of the two caps. Playing with the R might vary the center frequency, as well as the available cut/boost.

This is one of those circuits where a little SPICE will take you a long way towards understanding how the component values interact.

djgout · Post by **djgout** » Sun Jan 27, 2008 10:56 am

hmmm. SPICE would be nice....does it go well with a MAC and cheese?

thanks for the point in the right direction guys.

The Scum · Post by **The Scum** » Sun Jan 27, 2008 2:15 pm

A quick google search turns up hits (I was searching for "spice simulation mac").

It turned up this:
http://www.macspice.com/
That looks interesting, but I can't test it on my PC.

I use the freeware LTSpice/SwitcherCAD from linear.com...if you've got any of the programs that lrt you run windows apps, it's worth a try.

widdly · Post by **widdly** » Sun Jan 27, 2008 6:58 pm

You can put a resistor between the 50k wiper and the capacitors. That will lower the Q but will also lower the max boost/cut available. It wont effect the center frequency though. Might be worth a try if the amount of boost/cut is pretty high.

Message Board

my q is too tight

my q is too tight

Who is online