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Author Topic: Any DIY EQ interest?  (Read 40606 times)

bblackwood

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Any DIY EQ interest?
« on: July 10, 2004, 03:05:12 pm »

I've been toying with the idea of building a very simple passive (LC) broadband peaking EQ and am wondering if this would be something you guys would be interested in doing online as a collaboration. I'm contemplating a boost only EQ that's fixed bandwidth (pretty broad bandwidth) and having only two bands (perhaps three), low (possibly mid) and hi. Probably only have two or three freqs per band and would utilize switches throughout.

This kind of project is relatively simple, and while many of us have several EQs in our rack, would be a nice chance to get your hands a little dirty, so to speak, while making something that sounds good and can be used everyday.

What do you think? Is this something in which you'd be interested in participating? If there is enough positive response, we'll do it online together, otherwise, I'll simply post what I do and you guys can do whatever you wish...
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Brad Blackwood
euphonic masters

Viitalahde

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Re: Any DIY EQ interest?
« Reply #1 on: July 10, 2004, 03:35:56 pm »

No need now for this kind of an EQ.. Got the passive EQ done and Sontec clone in a few months - next year I'm going for a Klein&Hummel UE-100 tubed eq.

But if you want, I could still hop in the project and offer some ideas..? What are yer plans for the gain make-up? I suggest something discrete.. Joe Malone at JLM audio has a new op-amp (JLM99v) that some at TheLab have tested and reported to sound exteremely beautiful with tight low end and silky mid range. The sucker can take over +/-30v rail voltages too..

I also have the switching thing in my passive eq I like - and I could share that with you if you want. Basically, it allows you to use each band in either stereo (left controls only) or dual mono (L&R controls) mode. Simple to do with rotary switches, requires a lot of wiring though. But I think it does a great thing to the workflow.
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Jaakko Viitalähde
Virtalähde Mastering, Kuhmoinen/Finland
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OatBran

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Re: Any DIY EQ interest?
« Reply #2 on: July 10, 2004, 04:56:58 pm »

  Definitely keep us updated on the forum, please.  I'd love to see some schematics, pictures, and parts lists as well.  This is something I would consider doing myself.  What kind of price range are we talking when all is said and done?  Will this EQ you make be something you will use in your process?  Are you making this out of a need that you have to fill?  Thanks.
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Gold

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Re: Any DIY EQ interest?
« Reply #3 on: July 10, 2004, 05:13:37 pm »

Viitalahde wrote on Sat, 10 July 2004 15:35

next year I'm going for a Klein&Hummel UE-100 tubed eq.



A friend of mine has a pair of those. They sound very very good. I think each channel is five or six rack spaces. Impressive. They are very clean sounding. It ain't no Massive Passive. That sounds like a very worthwhile project for a mastering studio.

Brad,
I don't really need an EQ like that and I have a number of other things I'm working on.
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Paul Gold
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doughiggins

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Re: Any DIY EQ interest?
« Reply #4 on: July 10, 2004, 07:35:29 pm »

yes
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doug

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Re: Any DIY EQ interest?
« Reply #5 on: July 10, 2004, 09:18:54 pm »

I'd be very interested, especially if you could find a schematic for a Universal Audio 550. Then couple it with a transformerless tube make up stage. Whadda ya say?
Dave

Viitalahde

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Re: Any DIY EQ interest?
« Reply #6 on: July 11, 2004, 05:05:44 am »

Gold wrote on Sat, 10 July 2004 22:13

Viitalahde wrote on Sat, 10 July 2004 15:35

next year I'm going for a Klein&Hummel UE-100 tubed eq.

A friend of mine has a pair of those. They sound very very good. I think each channel is five or six rack spaces. Impressive. They are very clean sounding. It ain't no Massive Passive. That sounds like a very worthwhile project for a mastering studio.


Yeah, they look really worthy - and complicated. That huge Fairman EQ is based on these. But this is a future project, first I need the basic devices..

More about the passive EQ project

I once tried those AC line filter blocks - on audio. They're building blocks that have a low pass filter composed of inductors and capacitors, and they come in different values. Normally ment to filter all the crap out of incoming AC.

I honestly think that these could be very well used in a passive eq design with carefully calculated impedances and a lot of testing. I remember I tried them in hi-pass configuration too. They sounded pretty good. The great thing here would be that they're readily-available, shielded and easy to use if a good design came up for them.

Different frequencies might be problematic though.. But as an idea I think it's worth checking out.
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Jaakko Viitalähde
Virtalähde Mastering, Kuhmoinen/Finland
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malice

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Re: Any DIY EQ interest?
« Reply #7 on: July 11, 2004, 05:15:50 am »

I'm game with that brad, should be interesting and we could learn from this

malice

TomW

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Re: Any DIY EQ interest?
« Reply #8 on: July 11, 2004, 09:09:44 am »

Hi Brad and all!!!

Been a long time lurker, great forum here - I'm learning a lot but still just a novice with a keen interest in mastering...and DIY Audio.

I find this topic very interesting - I was planning a passive Pultec styled-eq similar to Viitalahde's, Class-A make-up etc, more frequencies than the original but then...

I read Fred Forssell's paper on a passive EQ topology and evolution. Maybe it gets a little more complicated than the thing you're thinking about Brad but its worth a read.

http://www.forsselltech.com/schematics/EQ1A.PDF

The paper with this provides some interesting ideas.

http://www.forsselltech.com/Evolution%20of%20an%20EQ%20Desig n2.pdf

I would be interested in developing this topology to make a 4-band EQ with passive low and high bands with some discrete opamp gyrators for the 2 mid bands.

http://www.forsselltech.com/schematics/Gyrator1.htm

What do people think?? There would be many options for discrete opamps, although its not really a totally passive eq.

Cheers Tom
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bblackwood

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Re: Any DIY EQ interest?
« Reply #9 on: July 11, 2004, 10:55:26 am »

Well, I'm still deciding on the details, but do know that it will be:

  • LCR based filters (possibly buffered between each stage)
  • buffered input (like a simple OPA604 input amp)
  • two band, 'boost' only
  • variable 'Q' in the LF section, possibly fixed 'Q' on top
  • solid state throughout
  • simple - I don't want this to be some huge task with lots of ways to screw it up. Keep it simple and let it sound good. If we all enjoy it and like the way this works out, we'll look into doing more complex DIY circuits in the future.


I'm going to start hammering out some of the details and will be posting a little more soon enough, starting with a general block diagram in the next few days...

Anyone else interested?
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Brad Blackwood
euphonic masters

D Harris

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Re: Any DIY EQ interest?
« Reply #10 on: July 11, 2004, 11:01:32 am »

Sounds like fun, sign me up.
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Dave Harris
 Studio B Mastering

bobkatz

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Re: Any DIY EQ interest?
« Reply #11 on: July 11, 2004, 11:07:52 am »

bblackwood wrote on Sun, 11 July 2004 10:55

Well, I'm still deciding on the details, but do know that it will be:

[*]two band, 'boost' only




I'm interested in this, too, Brad. But why boost only when it is so easy to design a cut into the circuit? In fact, in passive EQ, cut is real easy to design.

Make up gain....  I vote for a 990 style footprint, since there are so many discrete amps that can be plugged into the socket. There's an issue of output coupling cap, though most following devices are far less susceptible to DC offset problems than people think.
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bblackwood

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Re: Any DIY EQ interest?
« Reply #12 on: July 11, 2004, 11:12:08 am »

Bob, the thinking is to keep it as simple as possible. Cut may be implemented, but I want this to a fun and easy project to get people's DIY feet wet. I'm flexible, but I don't want this to grow into the passive EQ design I did a few years ago that was going to require a 4Ru box, custom inductors, etc.

Also, I haven't even asked them yet, but I imagine I'll be bouncing some of these designs off some of my more astute designer buddies who do this stuff in their sleep (and who's names are easily recognizable in the pro audio design world)...

990 footprint idea is golden, Bob. Good idea.
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Brad Blackwood
euphonic masters

Viitalahde

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Re: Any DIY EQ interest?
« Reply #13 on: July 11, 2004, 11:52:41 am »

bblackwood wrote on Sun, 11 July 2004 16:12

990 footprint idea is golden, Bob. Good idea.


It's actually easy to design a layout that can take both normal 8-pin IC's and 990 footprint. My Sontec PCB's designed by Fabio Bauman are like this..
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Jaakko Viitalähde
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grock5

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Re: Any DIY EQ interest?
« Reply #14 on: July 11, 2004, 12:06:09 pm »

Something based off the early cinema/langevin stuff would be cool.

Make-up gain could be provided externally.

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