CEM3378 + AOUT_LC Noize problem

Testing/Troubleshooting
1

yesterday i finished my CEM and my AOUT_LC module.

so far everything is working fine, i can control the CEM with my MB and the filter works.

but ii’ve got a noise problem.

when i controll the filter with a normal CV pot, there is no noize at all,

but when i connect the AOUT to the midibox sid, i get some high frequency noize like this :frowning:

apparently the noise starts when i connect the gnd and or the 5V power line from the sid to the AOUT.

the silence in the middle of the audio file is when i disconnect the midibox from the AOUT_LC.

the AOUT_LC is powered by the midibox (+5V )

and an internal PSU for the +/-12V

so long,

julian

2

Yuck!

Ok.. the noise is definitely coming from the core, but is it coming from the power or is signal coupling from the IC control signals..  >:(

I don’t think 74HC595s mind if you do couple of tests and leave inputs/power floating *grin*

(IE. You could try removing control signals coming from the core and leave only power from core coming to 74HC595 and then see if the noise is still there..)

Moebius

3

it’s coming from the power.

i removed the control signals coming frome the core.

the noiz also starts when the aout isn’t connected to the sid and i just connect the ground from the sids audio out to the ground of the audio in from the cem (but in this case only very silent).

no noize if i connect the sid directly to the amp

best,

julian

4

i’ve made further testings…

if i controll the filter of my modular synth with the AOUT voltage, no additional noize appears.

but when i connect the sid audio as well to the filter, suddendly the CV becomes quite noisy -> the cut of freq is jittering.

so long,

julian

5

Hi Julian,

what happens, if you connect the ground and +5V line of the AOUT_LC module directly with your PSU (or port J2) instead of CORE::J6? Especially for the ground line this makes sense (the PSU ground pin should also be used as starting point for the ground for the CEM module - starlike wiring!)

Best Regards, Thorsten.

6

If i use the ground and +5V from the internal PSU, the AOUT_LC produces some kind of random voltage or very noizy CV voltage,

if i control a filter with that it sounds like the CV is modulated with noise. the more i open the filter, it becomes noisier :-/

i use this PSU, modified to deliver as well +/- 5V

http://www.synrise.de/diy/supply/schaltplan.htm

so long,

julian

7

Do you hear the same noise, if J1:Vs, SO, SC and RC are connected to ground, and Vd to +5V

(in other words: all digital input pins connected to ground)

Did you stuff the jumpers at J3?

What happens, if you remove the TL072, and control the CEM directly with the 12bit output (-> Pin 3 of the TL072 socket)

Best Regards, Thorsten.

8

the jumpers are connected. I can also controll my modular system filter now without any problems or noise.

also the CEM is fully controllable via the midibox. so the CVs are working, but in combinmation with the CEM i’ve got the noise

but even if the 2 CV outputs of the AOUT_LC module are not connected to the CEM, I hear the noise as soon as i connect the sid to the AOUT.

Aout and CEM share ground and +/-12V.

the noise appears as soon as i connect the +5V  coming from the SID. havent put the digital lines on ground yet, but disconnected them all and just connected the 5V from the sid. (i will try putting them on ground now)

so long,

julian

9

What happens, if the SID output is not connected to the CEM input (clamp CEM audio input via 1k resistor (or so…) to ground)

Best Regards, Thorsten.

10

it makes no difference if the sids audio out is connected to the filter…

i build the filter and the aout in an extra box, with normal audio plugs, so i can disconnect the sid whenever i want, od connect other hardware.

nothing is connected to the CEM but

+12V internal PSU

-5V internal PSU

and a OpAmp at the output powered with +/-12V internal PSU

ground

the only connection between SID and AOUT is the +5V line

(also tried it with ground connected to SID, makes no difference)

AOUT is connected to

+/- 12V internal PSU

GND

I can make a quick drawing if it helps.

julian

11

The goal should be to determine, if the noise is comming from the power lines between MBSID and filterbox, or from the digital lines. Yes, a connection diagram would help

Best Regards, Thorsten.

12

ok, now with volume all turned up at my amp, i hear the same noize even if the SID isnt connected to AOUT… but really really silent

as soon as i connect the sid it gets loud

When i use the 5V from the internal PSU the noise is gone (no difference if i connect sid to aout or not)

so i would say its the powerline…

julian

13

Alright - so you could power the AOUT_LC in this way. Only ground and the digital lines need to be connected with the core - does it help?

Best Regards, Thorsten.

14

problem when i don’t use the +5V from the core the AOUT_LC produces semi random CVs :frowning:

this is the way i have connected everything rigth now.

no other interconnections made

15

Then I think that the problem is the ground line.

Let it like it is (means: use +5V of the internal PSU), but re-route the ground within your MBSID.

The jack of your audio out, the core and the SID module must be grounded starlike from a single point - best: from the C64 PSU ground (if used), or from the ground at J2 of the core module (if core is stuffed with 7805)

Another point is, that the interconnections between AOUT_LC and core should be as short as possible (0.5m is already very critical). A shielded cable like used for MIDI could improve the results

Best Regards, Thorsten.

16

i reduced the noize… its not absolutely gone but not so dominant as before…

i just removed the GND connection to the audio in :-o

tomorrow i’ll have a closer look.

thank you very much for the help so far!

julian