Metalizer Question / Help

bassculture · Joined: Jan 23, 2011 Posts: 22 Location: france

Just finished a Metalizer with a Soundtronics kit

My Metalizer seems to work perfectly BUT

I've noticed that when no signal, or too weak (Signal < 1v)
the metalizer output noise (brown / pink kind)

is this behaviour normal ?

bonzai · Joined: Apr 02, 2017 Posts: 7 Location: Germany

I have a similar question: I followed the pcb and schematics on http://yusynth.net/Modular/EN/METALIZER/ i.e. I've used mostly standard 5% resistors (just because I have a whole load of them left and want them to be gone) and only 1% metal film for the 15k and 150k.
For the big caps at the power connector I used 22uF.
The board is self-etched using Yves' original layout with no modifications.

The "problem" here is also, that I do hear some constant sound coming out, even if nothing is connected at all, but also when connecting something to the input.
I.e. even if the VCA controlling the input is completely closed, the metalizer is outputting some kind of "motorboating" or creaking sounds (if that's the right word), hard to describe...

Is this normal (I guess not) and if not: what could be the reason for that?
I've already swapped the 680nF for 1uF caps, with no effect...

Cheers,
bonzai

gabbagabi · Posted: Mon May 07, 2018 11:05 pm Post subject:

hi,
i can not test it, cos i did not built it

but if i look on the schematic
http://yusynth.net/Modular/Commun/METALIZER/Metalizer-sch.gif
i would start to investigate by desoldering the leg of R19, the one which is connectet to C3 and maybee use a crococlip to connect this leg to GND
then i would go with the scope (or audio probe) to the output of any stage C5 7 9 11 and check what is happening

bonzai · Joined: Apr 02, 2017 Posts: 7 Location: Germany

Hi!

Good idea, thanks! Will try that... Smile

gabbagabi · Posted: Wed May 09, 2018 2:35 am Post subject:

i would also be interested to know what the output amplitude of the vca is,
in comparisson to the input (with full CV/ Shape)

bonzai · Joined: Apr 02, 2017 Posts: 7 Location: Germany

Okay, did some measurements now:
pin 7: here I can see a square wave ~50mV peak to peak on top of a 1.2V DC signal
pin 8: ~300mV pp (DC offset also around 1V)
pin 14: ~2.5V pp
pin 1: ~5.1V pp

looks like the square wave starts at the first opamp stage (between R19 and C5) and then gets boosted up by the following stages. Funny: even if I remove the TL072 from its socket (ie no input, no modulation cv) I'll get that square wave...

UPDATE:
I tried again with my 2x9V block "PSU": the square signal is gone then, everything fine! So, it looks like maybe my PSU (it's a smpsu btw) is transferring some crap into the metalizer?!? Interesting, never seen that before. Will try that again with the psu in my other case.

UPDATE2:
better late than never: as I built a new skiff a while ago, I put the metalizer onto its SMPSU as the only module - no hum. But as soon as I connect other modules (Rings, Clouds and two other non-digital modules), the hum is back. So, to me it looks like the metalizer picks up noise from the rails.

By the way: looks like the PCB layout has a minor bug: the EURO power connector has wrong spacing, the two rows are too far apart. I had to bend the pins in a bit to make them fit...