Harrison Ford Filter Feeler

[straypacket]

I've got two channels wired up, powered, and ready to go. 

I'm seeing that the input pads are marked

 +       -
 o   o   o

So, (naturally?) I assume that the unmarked middle pad is ground ... but,  while testing the wiring on the inputs I'm noticing that the input pad marked negative (rightmost input pad, when looking from the top of the board) is tied to ground - and the middle input pad seems to be where the negative input is tied to the ICs.

Am I missing some basic Ohm's-Law-ish principle, or is the board mis-labeled?

I searched within the thread for "input ground" and "negative ground" but didn't turn up any info.

 

[emrr]

The input pads are mislabeled. 

 

[emrr]

Are these boards turning out 25-2K75Hz HPF and 160-20kHz LPF like the current Harrison/Great River product?  I really can't make out the legend on the case in any pictures, and don't find that info anywhere in the thread, only G-Sun's comment that his appear to show:

65-4k Hz, and the highcut goes from 14k-125Hz.

Did some cypherin', calculator says 31.6-4K8 and 133-17K ranges.

 

[dmp]

This appears the most common circuit found in a google search.

These pcbs are exactly the circuit in this Harrison 3232 schematic with input/output ICs. Looking at the HPF/LPF sections of the attached schem confirms this.
Not sure what the Great River is but I don't think this project was ever intending to be a clone of it.
Finding a good picture of a 3232 channel strip would be a good reference for labeling.

i.e.
http://www.uaudio.com/blog/bruce-swedien-harrison-32c/

 

[dmp]

Also, follow up to the last post, Dan's front panel uses the same freq labeling as the original..

And by the way, Smart Studios had a Harrison for awhile in the '80s and I heard the these HP LP filters were really special. They were very good to allow for layering of tracks.
I'm looking forward to finishing them. Someday soon I hope.

 

[emrr]

The optional circuit is what I referred to in what you quoted.  The Great River is done in conjunction with Harrison and appears to be a reissue. 

Did some cypherin', calculator says 31.6-4K8 and 133-17K ranges.

Curious if anyone other than G-Sun has measured their build.  The math says different on the frequency range.  I assume source drive Z changes the math, which I assume is based on 0R source. 

 

[dandeurloo]

The great river eq's are killer!  I have used them many times and love them.

I just thought I would add that to this thread.

 

[dmp]

Anybody have a Mouser part number for the switch caps that work with Dan's front panel?
The ones I ordered are too big. You'd think I'd be able to measure...

 

[dandeurloo]

I posted this in the thread somewhere already. 

P/N: S111-004BLACK - Knobs
P/N: C110BLUE - End Cap
P/N: RED - End Cap

I ordered these parts from Selco.  Selco is the same place I am ordering my knobs and caps for the Sontec EQ I just built. 

 

[dmp]

Thanks - but I meant the push button bypass switch. The caps I got are a little too big for the holes in the front panel

I've ordered from selco several times. They have great service and seem to be able to get any sifam knob you might need.

 

[dandeurloo]

Oh, I got those from CAPI!

http://classicapi.com/catalog/product_info.php?cPath=22_117_55_91_95_144&products_id=117

 

[dmp]

Cool thanks

 

[straypacket]

Regarding Selco orders:  Dan, are you ordering in large quantities?  They told me there was a $50 minimum...

 

[jimkeaney]

Hi guys, I've had one of these pcb's kicking around for a while. I bought it hoping to make a guitar pedal out of it. Anyone have any ideas on what components/etc I'd have to replace/manipulate to make it a guitar friendly impedance?

 

[dandeurloo]

Regarding Selco orders:  Dan, are you ordering in large quantities?  They told me there was a $50 minimum...

I just did them for this and my Sontec EQ.

 

[12afael]

jimkeaney : you don`t need the the balanced input and output, replace r1 for a cap and r2 for a 1M. that should be enough.

 

[Esoterimix]

Does anyone have 2-4 pcb's (assembled or not) for the Harrison Ford Filters? I'd be interested in getting my hands on a few of them... Feel free to e-mail me if you have extras: [email protected]

Thank you in advance! I gotta say, being new to this community, it's nice to see so many people involved and communicating... All the help has been great thus far. p.l.u.r.

 

[tonycamp]

Hi fella's,

i scanned the whole thread, i'm wondering, roughly, how much is the build for 8 channels, i'm thinking of going for it.

thanx
T

 

[emrr]

Dudes, am I crazy or is this thing +6 in both bypass and on?  It is!  (that would be +7.5 at the Chebychev ripple points)

on:
INA134 (unity) -> R1/R2/IC1A (-6) -> HPF (+6) ->LPF (unity) -> DRV134 (+6) = +6dB

bypass:
INA134 (unity) -> DRV134 (+6) = +6dB

Put INA137 or THAT1246 in the input to have unity throughput. Or am I crazy? 

I can't quite believe it got missed, but I sure don't see it addressed anywhere in the thread, or the related threads. 

 

[emrr]

Here's a bit of esoterica for all to consider.  When coupled with INA137 or THAT 1246 (-6 dB).

DRV134: unity gain driving 600 ohms.  +0.7 dB driving 10K.
THAT1646: unity gain driving 10K.  -0.7 dB driving 600 ohms. 

In other words, both are +6 dB parts characterized for different loads, even though they are considered interchangeable. 

May make a difference to you, may not.  Important to grasp that a hard bypass of either system is still not likely a matched gain comparison.