Dubka

DIY Harrison Filters?
« on: May 29, 2011, 12:46:21 PM »
For anyone who knows how or has schematics or whatever - how about a set of the famous Harrison HPF and LPF filters?

A 2u box of 8 would be amazing...   :)


dandeurloo

Re: DIY Harrison Filters?
« Reply #1 on: May 29, 2011, 01:33:06 PM »
Yes it would!  I love the Great River EQ's.  Dan nailed it!  Those filters are amazing. 


PROFESSIONAL CHASSIS AND FRONT PANELS FOR DIY PROJECTS: WWW.COLLECTIVECASES.COM

Dan Deurloo
www.collectivecases.com
www.risendrums.com

12afael

Re: DIY Harrison Filters?
« Reply #2 on: May 29, 2011, 01:57:18 PM »
this is a PCB that I did some time ago, I didn´t test this pcb but I built the filter together with the Nemek eq.



http://www.twin-x.com/groupdiy/albums/userpics/harrisonfiltersch~0.jpg


edit: build to built... verbal time...  ::)
« Last Edit: May 29, 2011, 11:26:36 PM by 12afael »
heavy metal is the law!!!

Dubka

Re: DIY Harrison Filters?
« Reply #3 on: May 29, 2011, 04:41:11 PM »
Wow!  That's great! 
It looks a perfect size for mounting a number of them too..
Does anyone have the means to prototype this circuit?
If so, we could be in business  :)

signalflow

Re: DIY Harrison Filters?
« Reply #4 on: June 01, 2011, 02:56:47 PM »
I just ordered some prototypes of a layout that I did for these should be here in 15 days.

-Casey
The shortest distance between two places is a nap.

jensenmann

Re: DIY Harrison Filters?
« Reply #5 on: June 01, 2011, 03:32:26 PM »
I´m very interested to get the PCB layout or PCBs if possible. I want to upgrade my liveconsole with HP/LP filter and this seems to be exactly what I´ve been looking for.
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

jensenmann

Re: DIY Harrison Filters?
« Reply #6 on: June 01, 2011, 03:36:45 PM »
Rafael, I tried to pm you, but your inbox is full. I´d be willing to check the PCB and prototype it if you guys want to share the layout.
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

12afael

Re: DIY Harrison Filters?
« Reply #7 on: June 01, 2011, 08:27:52 PM »
Jens check your email.
I`m happy to share the layout.

Rafael
heavy metal is the law!!!

Dubka

Re: DIY Harrison Filters?
« Reply #8 on: June 02, 2011, 11:48:01 AM »
I was thinking the pcb's might be best with the pots on the right hand side and HPF below LPF.
This would suspend the board vertically within the chassis so any number could be mounted side by side.
I'm picturing the front panel something like this...

X    LPF    LPF    LPF    LPF    LPF    LPF    LPF    LPF    X

X    HPF   HPF   HPF    HPF   HPF    HPF   HPF   HPF    X

(X = rackmount holes)

signalflow

Re: DIY Harrison Filters?
« Reply #9 on: June 09, 2011, 10:37:24 PM »
Raphel,

Did you end up preferring the linear pots or the rev log pots on this circuit?  Also did you end up scaling the resistors as mentioned in your nemek thread?  Or were you happy with the results as is?

-Casey
The shortest distance between two places is a nap.


12afael

Re: DIY Harrison Filters?
« Reply #10 on: June 10, 2011, 12:50:20 AM »
 Sorry Casey, I didn`t try with the revlog, it work well for me with linear pots. my second nemek is still waiting some free time.

I use dual 50K linear pots and TL074 so I think I didn`t scale the resistors.

Rafael
heavy metal is the law!!!

omeiko

Re: DIY Harrison Filters?
« Reply #11 on: June 10, 2011, 03:57:17 AM »
I couldn't get a smooth enough range with linear pots with that circuit. I made a board with opa604's and rev logs worked better for me.

-Okko

Marcocet

Re: DIY Harrison Filters?
« Reply #12 on: June 15, 2011, 11:17:52 PM »
Awesome. I'm very interested in a whole bunch of PCBs if and when you want to put together an order.

telefunk

Re: DIY Harrison Filters?
« Reply #13 on: August 07, 2011, 04:29:21 PM »
Just thought I should post:

HP/LP section of the Harrison 32C console EQ.

In my console the op-amps were originally HA-4605-5 but I use LME49470 nowadays, practically same as in the Great River 32c IIRC.

abbey road d enfer

Re: DIY Harrison Filters?
« Reply #14 on: August 07, 2011, 04:59:56 PM »
OK, so what's so special about these filters?
Well, you can see that the HP uses a follower with a gain of 2.
TYpically, a Butterworth filter based on a unity-gain follower (standard Sallen-Key) would need different values for the pot sections, the one going to ground being twice the one in the FB path.
The usual workaround is to use a follower with a gain of 1.414 (sqrt of 2) or 3dB with pots of equal value.
Apparently, they have gone a little further, which makes the HP filter a Chebychev with ca. 1.5dB ripple, that means that there is a 1.5dB hump just above the cut-off frequency, and the slope at cut-off is slightly higher than Butterworth. Cut the offending bass and boost just above, a nice trick.
The only drawback is that they have to deal with the additional gain, that they need to compensate somewhere (not a big deal anyway), as done by R1/R2 and IC1A.
For the LP, it is even simpler, the FB cap, which is usually twice the value of the one that goes to ground, has been increased by a factor of 2, giving the same C1.5 alignment. Cut the hiss and boost presence.
Nothing magic, but a proof that these guys at Harrisson know what they do, with real hands-on expertise.
« Last Edit: August 07, 2011, 05:07:03 PM by abbey road d enfer »
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

elskardio

Re: DIY Harrison Filters?
« Reply #15 on: October 17, 2011, 10:36:19 PM »
Hi Rafael,

Could you share your PCB layout please?

You can PM me!
Thank you
Gabriel


Marcocet

Re: DIY Harrison Filters?
« Reply #16 on: October 18, 2011, 12:21:28 AM »
Hey Gabriel

I haven't gotten to prototype the current pcb design yet. Things have been crazy here with studio construction. However I'm getting back on it and should hopefully have a final design available in a few weeks. I think we may offer boards as well if there's any interest.


nielsk

Re: DIY Harrison Filters?
« Reply #17 on: October 18, 2011, 09:49:47 AM »
What is special about these filters is how they interact with the EQ, not how they behave on their own....

elskardio

Re: DIY Harrison Filters?
« Reply #18 on: October 18, 2011, 09:56:10 AM »
Hey Marc,

I just finished building 16 preamps and none of them have a simple roll off.

I'm looking for a simple design to make 8 channels of HPF in a rack format.

Please let me know if you have any suggestion!
Cheers
Gabriel
« Last Edit: October 18, 2011, 09:59:45 AM by elskardio »

Re: DIY Harrison Filters?
« Reply #19 on: May 27, 2012, 01:26:08 PM »
Is it possible that I also get a PCB layout of the unit? I really appreciate it.

Jens check your email.
I`m happy to share the layout.

Rafael


 

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