GX1 HP/LP 12dB filter in 4HP euro format

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oldcrow
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GX1 HP/LP 12dB filter in 4HP euro format

Post by oldcrow » Mon Feb 13, 2017 11:58 pm

Hey folks,

The original GX1 HP/LP filter I did for 5U in 2004 I am spinning in DIY for eurorack. To keep it simple I am using jumpers to set the filter as HP or LP as well as the full or half-tracking. The concept is to use two units as a pair of filters with the first set as HP half-tracking, and the other as LP full tracking. I will order up test PCBs and panels. More later --Crow :guinness:

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Post by GryphonP3 » Tue Feb 14, 2017 1:36 am

What is the difference between the CV and FM jack? CV is calliberated for good tracking and FM has the attenuverter? I wonder if people may prefer a mode switch over one pf the two CV input jacks.. we can always use an external mixer to mix cv inputs, but having the mode switchable only via jumpers behind the panel would really bug me personally. Thats a major function to miss out on from the front.

Maybe it wont bug others as much as me? I look forward to it anyway. Love all your circuits and ideas.

After a little more thought about your suggestion to use a pair, I guess thats not too much trouble. 8hp for a LP/HP filter is totally reasonable, with the option to have one 4hp semi switchable vcf is pretty generous.
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Post by oldcrow » Tue Feb 14, 2017 1:47 am

FYI I will still build the 5U version for anyone interested. :sb:

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Post by oldcrow » Tue Feb 14, 2017 1:58 am

The original GX1 filter potted modules weren't really meant for "good tracking." :goo: You can get pretty good tracking using 1% parts (same for BPF) since I use better transistors and a real CV summing front end. The original NE modules were passive summing.

I want to use a switch for HP/LP, but keeping things to 4HP makes it tricky. The NE10400 and NE10500 were hard-wired to be LP & HP, so I figured I would do the same for this edition. I'll tinker with it in the CAD.

Crow
/**/
GryphonP3 wrote:What is the difference between the CV and FM jack? CV is calliberated for good tracking and FM has the attenuverter? I wonder if people may prefer a mode switch over one pf the two CV input jacks.. we can always use an external mixer to mix cv inputs, but having the mode switchable only via jumpers behind the panel would really bug me personally. Thats a major function to miss out on from the front.

Maybe it wont bug others as much as me? I look forward to it anyway. Love all your circuits and ideas.

After a little more thought about your suggestion to use a pair, I guess thats not too much trouble. 8hp for a LP/HP filter is totally reasonable, with the option to have one 4hp semi switchable vcf is pretty generous.

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Post by GryphonP3 » Tue Feb 14, 2017 4:12 am

oldcrow wrote:The original GX1 filter potted modules weren't really meant for "good tracking." :goo: You can get pretty good tracking using 1% parts (same for BPF) since I use better transistors and a real CV summing front end. The original NE modules were passive summing.

I want to use a switch for HP/LP, but keeping things to 4HP makes it tricky. The NE10400 and NE10500 were hard-wired to be LP & HP, so I figured I would do the same for this edition. I'll tinker with it in the CAD.

Crow
/**/
GryphonP3 wrote:What is the difference between the CV and FM jack? CV is calliberated for good tracking and FM has the attenuverter? I wonder if people may prefer a mode switch over one pf the two CV input jacks.. we can always use an external mixer to mix cv inputs, but having the mode switchable only via jumpers behind the panel would really bug me personally. Thats a major function to miss out on from the front.

Maybe it wont bug others as much as me? I look forward to it anyway. Love all your circuits and ideas.

After a little more thought about your suggestion to use a pair, I guess thats not too much trouble. 8hp for a LP/HP filter is totally reasonable, with the option to have one 4hp semi switchable vcf is pretty generous.
A pair of these wouldn't be bad :) look forward to seeing this project come to life. I'll order a phaser set too when these come out, I think :bananaguitar: I'm well chuffed with the bandpass filter now that you discovered its issue. Sounds so good, and I'm very impressed with your clever diagnosis.
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Post by Randy » Tue Feb 14, 2017 7:01 am

I'm interested!

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Post by teebeehex » Tue Feb 14, 2017 4:20 pm

Does it need to be 4hp? You could build a dual in 8-10hp with switches instead of jumpers.

Or.. keep the single design and have a second 8-10hp panel available for those who want to make the expanded dual :)

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Post by oldcrow » Tue Feb 14, 2017 7:37 pm

I think I will do both a 4HP unit and an 8HP panel. Same filters, except 8HP would have the filters with default jack and switch connections to use as a GX1 pair. 4HP PCBs first, though. :sb:
teebeehex wrote:Does it need to be 4hp? You could build a dual in 8-10hp with switches instead of jumpers.

Or.. keep the single design and have a second 8-10hp panel available for those who want to make the expanded dual :)

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Post by GryphonP3 » Tue Feb 14, 2017 7:53 pm

teebeehex wrote:Does it need to be 4hp? You could build a dual in 8-10hp with switches instead of jumpers.

Or.. keep the single design and have a second 8-10hp panel available for those who want to make the expanded dual :)
That seems like a lot of extra work/production for him for a small group who would prefer a dual panel over two singles. I think most people would like the 4hp design, and there is mot much benefit to using a single 8-10hp panel over a pair of 4hp panels. Switches only make sense to me if you are using a single filter. If you have two, why do you need to switch them? You already have a LP+HP. If you cant bring switches to the front of the 4hp panel somehow, I would say to leave it as is. I would personally prefer a switch to the two CV inputs (leave the one with attenuverter, and have it calibrated to track 1V/oct @ full CW) or keep it the way it is and get a pair if you need both HP+LP. The switch would make a single 4hp module much more appealing anyway, if that is the main focus. It seems like Crow designed it with a pair in mind though.

Again, maybe I'm wrong about what people want :despair:
oldcrow wrote:I think I will do both a 4HP unit and an 8HP panel. Same filters, except 8HP would have the filters with default jack and switch connections to use as a GX1 pair. 4HP PCBs first, though. :sb:

Nice! If you can do both, I'm sure people would appreciate it!
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Post by oldcrow » Tue Feb 14, 2017 8:32 pm

My primary goal is the flexibility of the filter as a module in a modular system, so having as many options tangible as possible is part of that goal. I have to balance this with making it economical enough that more than 5 people would buy in. :goo:

In the 4HP module sitting in the CAD, I am debating removing the CV jack in favor of the mode switch. This leaves the reversing FM control to set the tracking (which is not a bad thing). Tradionally I like having a fixed CV input and a modulation CV input but...well, we'll see. :guinness:

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Post by oldcrow » Wed Feb 15, 2017 6:08 pm

So here is my plan for the GX1 HP/LP filters. I will use the same filter board for both the 4HP individual filters and the 10HP filter pair. The idea is to use the filter boards as plug-in cards into the "filter couple host," sort of like how I do the crOwBX. When used as a plug-in card, you leave the pots and jacks off the filter boards and instead use three 4-pin right-angle board headers to plug each filter into the back of the host:

ImageImage

Two short 6-pin IDC cables are needed to connect the mode switches to the filters. I will probably include those for folks who buy the 4-board (3 PCB, 1 PCB-panel) set. On the host board is the option to use two resistors/jumpers to bridge the power across so that only one power cable is needed. More later, when I have actual boards in hand. :guinness: :guinness:

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Post by Isaiah » Thu Feb 16, 2017 3:56 am

Please tell me those are M3 mounting holes on the host PCB... :hihi:

It'd be great if you could squeeze some mounting holes onto these smaller Eurorack PCBs for those of us who like these smaller PCBs but use bananas or build in 4U. (Perhaps within the footprint of one of the minijacks?)

Perhaps we could expect an all-in-one GX-1 voice (since you already have the VCO153, GX-1 VC-BPF, GX-1 HP/LP-VCF)?
Though I'd hate to distract you from the CSR-15! :love:

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Post by oldcrow » Thu Feb 16, 2017 4:32 am

Those mounting holes are for (optional) angle brackets to hold the filter cards in place. The front panel (not done yet) always uses holes for 3mm fasteners.

I almost have enough to make a proper GX-1 voice. I want to make a 4HP version of the GX1 VCO (not the same as the CS VCO) as well as the GX1 WSC (waveshape converter) and filter EG. All of this is to refine circuits for the CSR-15, btw. :sb:
Isaiah wrote:Please tell me those are M3 mounting holes on the host PCB... :hihi:

It'd be great if you could squeeze some mounting holes onto these smaller Eurorack PCBs for those of us who like these smaller PCBs but use bananas or build in 4U. (Perhaps within the footprint of one of the minijacks?)

Perhaps we could expect an all-in-one GX-1 voice (since you already have the VCO153, GX-1 VC-BPF, GX-1 HP/LP-VCF)?
Though I'd hate to distract you from the CSR-15! :love:

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Post by Isaiah » Thu Feb 16, 2017 4:52 am

oldcrow
:yay:

Please, don't let me distract you further! I'll try to be patient haha!
I'm just excited about the CSR-15 and a possible mini GX-1 voice.
Thanks for the information!

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Post by oldcrow » Thu Mar 02, 2017 11:02 pm

So far so good. here is the filter coupler with one filter card mounted. Cards that install to the coupler do not need pots or jacks but rather use three 4-pin right-angle headers as shown on the board in the middle. The board on the right shows how a single 4HP filter is fitted with panel pots and jacks in a very similar (ok, it is the same :hihi: ) manner as the GX1BPF. 4HP modules use jumper blocks to select HP/LP and tracking. Using the 10HP coupler host board provides switches for this along with everything else. (2nd pic). More soon! --Crow :sb: :goo: :sb:

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Post by teebeehex » Fri Mar 03, 2017 1:41 am

Not quite the implementation I was thinking of but... WOW!

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Post by oldcrow » Sat Mar 04, 2017 3:02 am

Dual filters mounted to host coupler. I'll get some audio demos done over the weekend. Production boards will have trimmers with side-adjust. Since the host board can bridge the power, only one board needs a power header.

More soon! --Crow
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Post by GryphonP3 » Sat Mar 04, 2017 7:09 am

Hell yeah! Put me down for one at least :) now i just need a VCO (or 3)
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Post by oldcrow » Mon Mar 06, 2017 4:40 pm

All finished. I will install in the cabinet and record an audio demo next. :sb:

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Post by oldcrow » Wed Mar 08, 2017 11:18 pm

Audio demos are here. Each demo except #4 have a dry and a Lexicon 224-flavored version.

http://www.cs80.com/modu/GX1HPLP/

The tone source is one Crowminius oscillator sawtooth.

Demo #1 is the filter pair in a 70% resonant HP->LP chain with the Crowminius Filter EG and an LFO moving things around. This is the sound of those "funny" buttons on a CS-80 which were brought over from GX1 patches. :sb:

Demo #2 is LP->LP, a bit more traditional 24dB/Oct response except with two 12dB/Oct filter section, each with its own frequency, resonance and tracking, can do some pole speading as shown by using the LFO to animate just the 2nd filter here.

Demo #3 is 24dB/Oct highpass, and is your de-facto screaming lead sound.

Demo #4 is a short verification the filters can in fact self-oscillate, though for good tracking the expo CV needs a bit of trimming.

More soon! :guinness: :guinness: :guinness:

Crow
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Post by LSuveg1 » Wed Mar 15, 2017 5:00 pm

Lovely demos -- I can't wait to build one of these! Watching for updates...

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Post by strange tales » Wed Mar 15, 2017 5:34 pm

Definitely interested in this. Please let me know when it's available!

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Post by Randy » Mon Apr 10, 2017 6:47 pm

Just wondering if there are any updates, or a potential release date?

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Post by Xtheunknown » Fri Jul 07, 2017 10:56 pm

Will these be available pre-built? If so, what is the price?

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Post by oldcrow » Mon Jul 10, 2017 2:11 am

I am a bit backlogged, but will try to get the DIY boards out before the end of the summer. --Crow

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