I am working on a home-made/designed EQ. I have decided on the filters I want. The filters are Not the issue.
Connecting them in some logical way is the problem. The type of EQ I am closest too in filter selection would be a parametric with a strange filter for the top end. and a low cut.
I have studied many schematics but they vary quite a bit and without owning many EQS I am not sure which style of connection is the best.
I've looked a lot at Orban, Calrec, Moog, Harrison, API, Neve, and others , focusing most on schematics which shed
light on opamp based designs without inductors
Surprisingly, with all the filter books I have (and books on pro audio too) not a single one of them covers the process of
integrating Low, Low Mid, Hi Mid and High into some kind of summing structure. They usually just show you what Low Mid and a high mid, and a low shelf look like individually. Maybe I am overthinking this and all it takes is summing the different filters outputs into one opamp like you would do designing a simple mixer. But I would be (happily) surprised if that was all it took.
So -questions
1. One setup I have looked at seems to involve a balanced in which then sends a feed to the first filters gain pot. the wiper of this pot enters the LOW sections filter input. one side of the pot then attaches to the next Gain pot (this goes to Low Mid) etc etc
the OUTS of all the EQS then connect to the Inverting input of staggered opamps (inverting in) so Low goes to one opamp, this feeds into the next opamp which then has LOW MID plug into its inverting input, etc
I assume you always want to start with the lower bands feeding into the higher?
2. but are there other ways? I know in graphic eqs some designs use just one opamp and have all the filters connect to its summing point. But is this problematic? I am wondering if there are other ways. Self talks about a RTF setup where your curves always go back to flat outside of the range you are interested in. But he only shows how to do this for a LOW, HIGH setup (more of a tone control setup than a parametric eq----but maybe there is no difference?)
Id also love to find out more about fixed Q options or gain dependent Q. (I have read the Api Q changes as you increase amplitude)
But once again, I can't find any info on these except in schematics. I am torn between trying to design an EQ that is just
a typical parametric, or one that uses more of a API style of pre-chosen frequency points. I have never owned an API eq but I have tried them and of course I have used the plugins (not the same I know but I like having the choices narrowed)
One problem is determining the best CHOICE points. And of course this adds the cost of switches, etc. Unless of course I just use pots that are set to a much smaller range of frequency choices....
sorry thinking out loud here
I know this is asking many things.
any info appreciated
also if anyone knows of ANY books which cover this (Self comes closest in Small signal audio) in detail, I sure would be happy. Or an article online.
I have all the typical filter books. Lancaster, Self, Berlin, Valkenburg, Jungs Audio book, etc.
but maybe there are great articles online I need to read
THANKS SO MUCH FOR ANY HELP
Connecting them in some logical way is the problem. The type of EQ I am closest too in filter selection would be a parametric with a strange filter for the top end. and a low cut.
I have studied many schematics but they vary quite a bit and without owning many EQS I am not sure which style of connection is the best.
I've looked a lot at Orban, Calrec, Moog, Harrison, API, Neve, and others , focusing most on schematics which shed
light on opamp based designs without inductors
Surprisingly, with all the filter books I have (and books on pro audio too) not a single one of them covers the process of
integrating Low, Low Mid, Hi Mid and High into some kind of summing structure. They usually just show you what Low Mid and a high mid, and a low shelf look like individually. Maybe I am overthinking this and all it takes is summing the different filters outputs into one opamp like you would do designing a simple mixer. But I would be (happily) surprised if that was all it took.
So -questions
1. One setup I have looked at seems to involve a balanced in which then sends a feed to the first filters gain pot. the wiper of this pot enters the LOW sections filter input. one side of the pot then attaches to the next Gain pot (this goes to Low Mid) etc etc
the OUTS of all the EQS then connect to the Inverting input of staggered opamps (inverting in) so Low goes to one opamp, this feeds into the next opamp which then has LOW MID plug into its inverting input, etc
I assume you always want to start with the lower bands feeding into the higher?
2. but are there other ways? I know in graphic eqs some designs use just one opamp and have all the filters connect to its summing point. But is this problematic? I am wondering if there are other ways. Self talks about a RTF setup where your curves always go back to flat outside of the range you are interested in. But he only shows how to do this for a LOW, HIGH setup (more of a tone control setup than a parametric eq----but maybe there is no difference?)
Id also love to find out more about fixed Q options or gain dependent Q. (I have read the Api Q changes as you increase amplitude)
But once again, I can't find any info on these except in schematics. I am torn between trying to design an EQ that is just
a typical parametric, or one that uses more of a API style of pre-chosen frequency points. I have never owned an API eq but I have tried them and of course I have used the plugins (not the same I know but I like having the choices narrowed)
One problem is determining the best CHOICE points. And of course this adds the cost of switches, etc. Unless of course I just use pots that are set to a much smaller range of frequency choices....
sorry thinking out loud here
I know this is asking many things.
any info appreciated
also if anyone knows of ANY books which cover this (Self comes closest in Small signal audio) in detail, I sure would be happy. Or an article online.
I have all the typical filter books. Lancaster, Self, Berlin, Valkenburg, Jungs Audio book, etc.
but maybe there are great articles online I need to read
THANKS SO MUCH FOR ANY HELP