Ambika w/ SVF voicecards - Glitchy sounds and strange audio behaviors?

I’m testing my Ambika with 6 SVF voicecards.

Resonance problem when filter is switched to HP mode (the LCD screen gets less luminous - OSC are set to none, no modulations on the filter except turning the editing knob and playing different notes):

When playing several notes together, the sound tends to clip/glitch internally (the clipping/glitch does not come from a saturated recording):

I’ve read in other topics that it could be a voicecard DAC problem. Any ideas or suggestions ?

Thanks for your help.

Hédi K.

Just checked, there are 5 different 4052s @ reichelt, the one you want is is the MOS 4052 as its the one with Vdd up to 18V. But i guess i wouldn’t like to eat at Reichelts Kantine anyway…

a 74HC4052 istn a CD4052 just like an aubergine isn’t a zucchini… you should always use the Cap the Quartz is specified for.

@fcd72: You wouldn’t it at the Reichelt Company Restaurant then :slight_smile: when I ordered 74hc4052 from them 2 years ago, I got CD4052s - that’s why I listed this reference on the Reichelt BOM in the first place.

The noise is 50 Hz motorboating due to a weak power supply. It is consistent with the screen going dimmer (not enough current…). But it is not clear to me why this happens only in BP mode. Which power supply do you use? Do you have the same problem with less voicecards? Is it specific to a particular voicecard? Can you make this problem (50 Hz ring modulation) appear in other circumstances?

When developing a polysynth there’s a trade-off between ensuring that the synth will never clip under any circumstances - and use signal levels which will be most of the time too low (-> noise!) ; or use signal levels which are reasonable for everyday use but which might occasionally clip. I have chosen the latter to get the best signal/noise ratio. If you prefer the former, change the 10k resistor above the resistor network by 4.7k or 6.8k. Or you can just lower the volume of the part you are playing…

Thanks Olivier. My PSU, bought today, is supposed to be rated for a max 660 mA. I will get it changed for a bigger one (1 A). I will check it later tonight with just one voicecard.

Hédi K.

After several tests, the “50 Hz motorboating” appears each time I’m switching to an other filter type (BP or HP, it doesn’t matter). I’ve put my Ambika in mono mode and only activated one voicecard, still the same problem. I definitely will change my 600 mA PSU to a bigger one.

About the clipping problem, I will check it later.

Hédi K.

I’ve changed my PSU for a 9V AC 1A this morning. Still the same problem with the strange behavior when changing the filter’s type and still clipping while playing with a lot of factory patches.

The crystal I’ve used for the MoBo is sourced at Reichelt and is not from the same brand as the ones provided in the voicecards difficult to source parts pack that I’ve bought at MI shop at the end of last December. Can it be the source of my problems … ?

Thanks for your inputs.

Hédi K.

The clipping problem is not related to the PSU, see my explanation above. You either need to reduce the volume of the part, or if it is not an acceptable solution to you, change the 10k resistor above the resistor network to 4.7k or 6.8k.

As for the supply problem:

  • Remove all voicecards except one.
  • Try removing the 4052 (no sound will go through) and check that the display is still affected when you change filter modes.

Understood for the clipping problem :wink: I will try the resistor’s swap later.

Before reading your last message, I’ve left only one voicecard. No problem when switching between filter’s types. Added a second voicecard, still fine in different filter’s types. Added a third one, then the problem started again.

BTW, it seems that with the new PSU the is working nicely now.

Last test following your advice. I’ve removed all voicecards except one, removed the 4052 IC. No problem with the display when changing filter’s type, but then no sound.

… ???

From your last message I thought that the problem went away. Can you explain what is the problem now?

Olivier. Sorry for not being that clear. The LCD screen is now OK but there is still this “50 Hz motorboating” noise when switching filter’s type. From my yesterday’s tests, it seems to appear after stacking 3 voicecards and more - it seems to be fine with just 1 or 2 voicecards. Just to be more precise, I’ve first plugged only 1 voicecard and added other one up to the problem appears.

I don’t really know where to look for ?

Thanks in advance for your help and advices.

Hédi K.

If you have a scope, can you scope the +8V ; -8V ; and +5V lines to find which one is getting weaker?

maybe it’s in the 3th voicecard you used? Did you try puting only this 3th one in?

try it with every combination of voicecards possible, it’s maybe just one voicecard that is causing your problem?

I can’t scope at home but I have a friend how has one at his work. I will ask him.
I will also try to swap and check again different voicecards’ combinations.

Thanks for your inputs.

Hédi K.

I will have an oscilloscope during this weekend and will scope what Olivier has advised.

What I suspect is that the +8V and -8V rails are not straight lines but have dips/gaps because of the excessive current consumption. A potential solution is to either increase the power supply voltage (at the risk of overheating); or the capacitance of the rectifier (might be worth adding a 2200uF on the empty slot).

What I don’t understand is why enabling the BP/HP mode suddenly raises the current consumption. Maybe one of the voicecards has a short on one of the MCU pins toggling the 4052? Or something wrong with the level shifter?

(Sorry for the late reply, 4 hours ago I saved this as a draft instead of posted)

I’ve just re-check and re-heated all solder joints for the PSU on the MoBo and tried different combination of 3 voicecards.

  • In 1-2-3 ports’ combination, the 4052 IC on all 3 voicecards was getting very hot ? … hotter than the dissipators in the PSU circuit.

  • In 1-3-5 ports’ combination, the 4052 IC on voicecards 1-3 was getting very hot ? … still hotter than the dissipators in the PSU circuit.

ICs getting very hot are not a good sign ? :frowning:

Hédi K.