Freq Central module assistance required pls ( VCF + VCA)

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Dude163
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Freq Central module assistance required pls ( VCF + VCA)

Post by Dude163 »

Hi everyone, for my 50th bday I bought a nice set of FC PCBs and some custom panels from a friend to start up eurorack again , just a basic setup to use with my Elektron Analog 4

SYSTEM X : 2 VCO , 1 VCF , 1 ENV , 1 VCA and 1 Vogue VCF



Long story short, the VCF and VCA do not work, Ive tried every permutation to get sounds out of them, and I also was able to use teh same setup and get sounds through the vogue so the setup is workable

I built them up carefully and took my time ( about 2 months, waiting for parts also !) Im not very knowledgable with electronics and im terrible at diagnostics beyond, checking chips orientation, cold solder joints/shorts


I just took some photos of them if that may help, is there something very obvious Im overlooking?





thanks in advance

Robert T.Image
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Dude163
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Post by Dude163 »

Forgot to mention, the 10k resistor on the VCA is on the back, I couldnt desolder the holes as they got filled in by an error
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ringstone
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Post by ringstone »

Did you source your LF351 from Tayda? I and numerous other people have found that they received non-working versions of these chips recently from that source - we had a big Frequency Central group buy here in Australia.

Cheers
Blair
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Dude163
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Post by Dude163 »

First off. Thank you !

Yes I did get them from tayda. And they are used in both of these modules !

Did you get a replacement from tayda ? Or from another source ?

Cheers.

Robert T
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SMonk
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Post by SMonk »

Dude163 wrote:First off. Thank you !

Yes I did get them from tayda. And they are used in both of these modules !

Did you get a replacement from tayda ? Or from another source ?

Cheers.

Robert T
Try replacing the lf351's with TL071. It worked for me in my SystemX VCF (but my VCA still doesn't work, for some reason).
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teebeehex
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Post by teebeehex »

It seems that most people who have built the FC ADSR have ended up swapping out the 351 for a TL071. r a TL071.

The build thread for this is here:
https://www.muffwiggler.com/forum/viewt ... c079cea4fc
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Dude163
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Post by Dude163 »

Hmm I dont have any TL071s, I have some 72s, would that work ??
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ringstone
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Post by ringstone »

Dude163 wrote:Hmm I dont have any TL071s, I have some 72s, would that work ??
That's a definite no, TL072 is a dual op-amp and TL071 is single. They have different power pins (which I found out when I inadvertently swapped the TL071 and TL072 on one of my Miss10 boards!).

LF351 seems to be getting a bit rarer now but I notice Banzai seem to still have some. TL071 will definitely be easier to get hold of though.

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Blair
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Dude163
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Post by Dude163 »

Thanks!
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billsship
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Post by billsship »

I replaced my lf351 with an 071 and that reversed the cutoff, but it didn't affect the sound. I would reflow all the joints, and check to see if you have soldered everything. I have methodically built modules before, no sound, and then found a resistor leg that hadn't been soldered.

Good luck!
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Post by ClausF »

Dude163 wrote:Hmm I dont have any TL071s, I have some 72s, would that work ??
For those issues and for bug-fixing a short look in the data sheet or at least at the pinout (just google TL071 or TL072) would be helpful. With the pinout you know, at which pins you have to expect +12V and -12V and you can check at your soldered PCB (without chips) if you have there what you expect. One of the tests I always do after soldering....
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Dude163
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Post by Dude163 »

Ok Ill do a quick google on how to use a multimeter :(
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Dude163
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Post by Dude163 »

Ok replaced the LF351s with TL071s

VCA : Works 100%
ENV: Now works 100 % ( before only INV did)

VCF : Nothing, not a peep, time to go multimeter


So to fix that I should check continuity? or should I power it on and check for V ?
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Dude163
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Post by Dude163 »

I think I found the problem :(

I used BC557s for 3 of the 4 2N5485s , time to desolder and get to work
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sixty_n
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Post by sixty_n »

Hope you get it sorted.

If you block the holes up when desoldering (I always do) I find the safest way to clear them is using a miniature drill bit (0.6 mm or so) in a pin vice
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Dude163
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Post by Dude163 »

FIXED!!!!
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ringstone
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Post by ringstone »

:banana:
bournio
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Post by bournio »

Glad you got it sorted! Always check pin outs for things, it saves hassle!

I had a non functioning ENV and VCF, but I've just replaced the LF351s with TL071s and all is good.
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Dude163
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Post by Dude163 »

Well teh main lesson is :

dont try soldering 6 PCBS with 6 kids under 11 running around the house :()
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bournio
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Post by bournio »

That's pretty good advice! I'm surprised you got any components soldered!
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