[BUILD] God's Box 'Humpback' - 8hp Eurorack Multimode VCF

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Monobass
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Post by Monobass » Tue Jun 19, 2018 1:43 pm

It doesn't matter what position it's set in, just leave it. Centre Frequency is basically cutoff frequency.
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danfastlikeflan
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Post by danfastlikeflan » Thu Jun 21, 2018 3:13 am

Could I replace it with a resistor? I would love to have a switch on the front for the resonance overload header on the back.

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Re: [BUILD] God's Box 'Humpback' - 8hp Eurorack Multimode VC

Post by jakokrull@gmail.com » Fri Aug 17, 2018 9:50 am

Help - the filter does not function. LP and BP outputs have only noise coming out and HP and N produce a clean output signal with no filtering applied. Any suggestions? I have checked all the solder points and they seem solid.

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templar
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Post by templar » Sun Aug 19, 2018 10:17 am

jakokrull@gmail.com

maybe post some pictures of your build?

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JP8
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Post by JP8 » Wed Oct 24, 2018 3:48 am

As a replacement for the Nichocon Gold caps I can only find 16v in small size instead of the suggested 25v. I’d guess that the maximum power on the caps would be 12v, but I’m not sure. Is this difference significant? Can I use the 16v capacitors?

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Post by jstck » Sat Dec 22, 2018 4:03 am

I'm about to buy a kit for one of these and was just making sure I had all the parts required, and got a bit confused by the potentiometers. More specifically, the two "tall trimmer" pots. In the BOM, they are listed as B50K pots (CV1 and CV2), but from what I can gather from the schematic they correspond to R24 and R35 which are listed there as B10K. There are no 50k pots to be found anywhere in the schematic, and no other 10K pots in the BOM other than R25 (cutoff frequency knob).

Which one should I use? They're both just voltage dividers for incoming CV signal (and are mixed, together with R25 signal, via 100K input resistors) so I guess either should work in some fashion, but what is the reason for the disparity?

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Post by rosch » Sat Dec 22, 2018 4:34 am

10k will draw more current but will be less affected by noise. you could even use 100k for voltage divider. that's just generally speaking, haven't looked at the particular schematics

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Post by jstck » Sat Dec 22, 2018 9:13 am

These are the schematics I could find, the cutoff frequency input section is in the top left:

https://thonk.co.uk/documents/gbox/hump ... pboard.png

The value of those potentiometers will of course determine the input impedance, where both 10K and 50K are within reason (though I would prefer higher for these as I would probably use one for "note tracking"). I'm guessing though that the input would be have more nonlinearity to it if the potentiometer value gets close to that of the mixer input resistor.

There are other discrepancies though between the schematic and the BOM; The schematic has a 1K pot/trimmer, R32, after the cutoff frequency mixer op amp, which is not mentioned or visible anywhere else. And if the BOM matches what's currently being sold, I guess the schematic is just a bit off. Does anyone know of a more accurate schematic somewhere?

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Post by JP8 » Sun Dec 30, 2018 7:55 am

I finished my build. First it didn’t work. I only got a soft sound passing through without any filter action. So I took it apart, resoldered all joints and double checked the headers as suggested in this thread. I also replaced all the ICs. I put it back together but still no change. The frequency knob seems to act like a volume pot...

Any help would be appreciated. Picture of the build enclosed.

Cheers,
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Last edited by JP8 on Wed Jan 09, 2019 5:58 am, edited 1 time in total.

boork
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my build sounds great but is missing the crazy resonance(?)

Post by boork » Sun Jan 06, 2019 3:33 pm

hi folks,

I just finished a build of humpback using a new thonk kit, and everything on it more or less works - lowpass is lowpass, highpass is highpass, CV works, etc., sound comes out of it filtered, and sounds very good... the weird thing is it just isn't very resonant. Definitely won't self oscillate, and that is even with the jumper on (there's practically no resonance at all when off).

I also notice when I try basic sweeps, I get no change from closed to about 1o'clock, then from 1 to full clockwise I get a nice sweep (true of both the highpass and low, and I assume of the notch and band although I haven't checked w scope).

So I'm guessing I swapped some thing(s) in the build, but I don't know where to look. Tried making sense of the schematics, but they're over my head right now, sad to say. Anyway, was wondering / hoping someone might have some hints on where to focus my troubleshooting / start looking, before I sorta just go over the entire thing (?)

(Right now it sounds really nice, and I don't mind it, but I'd love to get that howl out of it if I can)

Thanks much!

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Post by honeyb » Tue Jan 29, 2019 3:15 pm

Just ordered two kits for this, but ran into a snag-- Mouser doesn't stock the 2n3819 transistors. "silicon N-Channel JFET designed for RF amplifier and mixer applications" Unless you order in batches of 5000 ....

Anyone have a good substitute which worked in their builds?

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Post by Pav » Fri Feb 01, 2019 2:45 pm

You could try banzai music in Germany ..their website is showing stock and will be able to order tiny quantities albeit delivery can be slow at times.
rgds Pav

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Post by JAO » Fri Feb 01, 2019 4:21 pm

honeyb wrote:Mouser doesn't stock the 2n3819 transistors.
Just grab them on ebay. Plenty available.

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Post by honeyb » Sun Feb 03, 2019 5:07 am

Working on the build right now. The board has several points which say "RX2 (see manual)"

But of course there is no manual...

Any idea what these connections are for?

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Post by Trashcan » Fri Mar 08, 2019 7:59 pm

HI, does anyone have the Mouser part no. for the trimmer, I misread something somewhere that lead me to think that it was not required... :bang:

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Mouser Part Numbers for TL071 and TL072

Post by workingklass0 » Fri Mar 08, 2019 10:37 pm

Hello all!

I am trying to compile a Mouser project list for this filter. However, I am a little bit confused about which TL071 and TL072 chips I should add. Any recommendations or suggestions? Thanks.

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Post by mutate » Mon Mar 18, 2019 12:20 pm

Finished my build and noticed the cutoff does not completely filter out all sound when turned fully counter clockwise (LP out). Wondering if anyone else noticed this on theirs?
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Post by muffdiver » Sun Jun 02, 2019 8:07 pm

Having some issues with my build. Seems like it's better since I swapped out CA3080 ICs. Also went though and replaced all ICs and 3819 Transistors. Not sure what to try next for troubleshooting...

Behavior:

Getting some response from resonance but the cutoff doesn't appear to be correctly closing. Cutoff acts more like a volume pot instead of the sweeping thru of frequency spectrum. Input and resonance appear to operate correctly. And I get expected behavior from CV in.

Let me know if anything pops out. I've gone thru and double checked resistor values but another pair of eyes could help.

Troubleshooting:
  • - Replaced all ICs
    - Resoldered joints
    - Replaced 3819 resistors
    - Checked capacitor values and orientation
    - spot checked resistor values.
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Post by mentalu » Mon Sep 30, 2019 3:43 pm

is there a panel file for this anywhere?

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Post by Monobass » Mon Sep 30, 2019 3:58 pm

mentalu wrote:is there a panel file for this anywhere?
PDF here - http://thonk.co.uk/documents/gbox/humpb ... 0panel.pdf

Panel is 128.5mm x 40.3mm
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Post by mentalu » Tue Oct 01, 2019 12:39 pm

@monobass

Thanks!

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Post by RNZN » Thu Oct 24, 2019 5:05 am

Hi there,

I´ve built the Filter and unfortunately it is not working properly. I pretty much have the same issue as described by others on Muffwiggler: @FrJK


LP and BP output is not working, there is no output coming at all. HP and N have output, but Cutoff and resonance seem to have no influence whatsover on the output. The input poti works and attentuates the volume of the input.

Other builds in this thread had the same issue and could be solved by replacing the trimmer on the front, resp. fixing bad connection between the boards. I tried both and made sure all sits tight.

Only thing different is I used BF244A instead of 2N3819, but should be equivalent according to: https://alltransistors.com/mosfet/crsea ... &caps=TO92

I also used on cutoff and input dual gang stereo potis, with the upper 3 legs just snipped off. Fotos of my build are attached.

Do you guys have any idea what the issue might be? I double checked all solderjoints, replaced the TL72/71 Ic´s, but still no chance.
Any help or idea what it could be would be most aprreciated.
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Post by synthetek » Thu Oct 24, 2019 7:03 am

RNZN wrote:Hi there,

I´ve built the Filter and unfortunately it is not working properly
Where did you get the CA3080s? They look like they are possibly fakes

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Post by primitivestreak » Sun Oct 27, 2019 2:45 pm

Hi all,

I've just built one of the new humpback kits from Thonk and have the same issue as other users here - no output from LP, BP and no cutoff/resonance response from HP.

n.b. This version of the kit doesn't have the trimmer, but instead uses two resistors.

In my case, I initially had the cutoff & resonance pots in the incorrect positions, (which ironically worked ok, albeit with limited range). Only once I rectified the mistake did the above problem occur.

I wondered if anyone had found a solution to this?

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Post by Funky40 » Tue Nov 19, 2019 11:09 am

i also just built the Humpback from the newest batch of full kits:

my problem: the BP out is dead !

everything else works fine ! sounds GREAT !


any tipps ? i guess i should replace some parts ?
any specific IC to look at first ?


( i should have spare CA3080s from my first DIY-Cat live somewhere lying around)
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