My MFOS modular expansion box project (work in progress)

[Bodo1967]

not yet. maybe it got held up in customs. this happens sometimes (esp. with merch from England for some reason).

It does happen over here as well - the Synthcube shipment from this summer took almost 2 weeks to get through German customs in Frankfurt , and the Elby shipment with the CGS PCBs also took several (as in: more than six) weeks to get to me .

[Bodo1967]

Finished the MFOS VC-LFOs (I built two of them and put them behind one panel):







The YuSynth ADSRs (also two of them behind one panel) are also finished, and so is the MFOS 8 Stage Phaser.

Unfortunately I forgot to take pictures before placing them in the cabinet, and now I'm too lazy to get them out again .

There is actually some progress with the MFOS Wave Freaker:

"Part 2" of the circuit (i.e. the stuff on the second schematic - step wave, pulse wave and the sub oscillators) are now working.

However, what I get out of the analog switch (CD4066; U5 in the circuit) is weird. Looks to me like some bleedthrough (or whatever) from the comparators it is fed with:



The triangle bits are actually folded - but there's some square wave bits between them that don't belong there .

The signals at the inputs of the CD4066 look alright (clean triangle waves), but all the outputs look like the picture (and so does the output of U 6 (point "CC"). I ordered a few new CD4066 today since and see if replacing the chip leads to any improvement.

I'm nevertheless grateful for any ideas concerning this matter.

[Bodo1967]

Did you buy the transistor or the diode suprladder PCB from Oakley?

The transistor ladder filter. Needs troubleshooting though

[x] Done. It was a missing connection beteween the two center pads (ground) in the Dotcom style connection field (I didn't use connectors but hardwired it in the same way as with the other modules in this thread).

And another module is on the way : I ordered the Frequency Central "Klang Stadt"* wavetable oscillator on the weekend.

* German speakers would write "Klangstadt" (in one word) though ; this translates to "sound city".

[Bodo1967]

Frequency Central Klang Stadt and Dual 3 in 1 Audio Mixer are completed. The "Bouncing Ball" module is in its troubleshooting phase (there is an issue with two IC pins being accidentally swapped by the developer - result: 1 fried resistor and LM339 each ) and will hopefully be completed by the end of the week.

Most of the CGS modules are finished except for a couple of parts I'm still waiting for. Once these arrive, getting them ready to test (and troubleshoot if required) shouldn't take too much time.

[Bodo1967]

The "Bouncing Ball" module is in its troubleshooting phase (there is an issue with two IC pins being accidentally swapped by the developer - result: 1 fried resistor and LM339 each ) and will hopefully be completed by the end of the week.

One of the circuits (it's actually an AR generator that can either be used with external trigger, or as an LFO-like cycling AR envelope - you combine two of them in different modes to get the "bouncing ball" effect) is up and running, and the other one is finished except for a CD4053 which I ran out of stock, and which is on its way.

Most of the CGS modules are finished except for a couple of parts I'm still waiting for. Once these arrive, getting them ready to test (and troubleshoot if required) shouldn't take too much time.

Finished the "Modulo Magic" on the weekend; the Bin-N-Tic will probably be up next .

[Bodo1967]

There is actually some progress with the MFOS Wave Freaker:

"Part 2" of the circuit (i.e. the stuff on the second schematic - step wave, pulse wave and the sub oscillators) are now working.

However, what I get out of the analog switch (CD4066; U5 in the circuit) is weird. Looks to me like some bleedthrough (or whatever) from the comparators it is fed with:



The triangle bits are actually folded - but there's some square wave bits between them that don't belong there .

The signals at the inputs of the CD4066 look alright (clean triangle waves), but all the outputs look like the picture (and so does the output of U 6 (point "CC"). I ordered a few new CD4066 today since and see if replacing the chip leads to any improvement.

It's been a long time, but I took it off the shelf a few days ago and checked a few things. And yes, I had made a big mistake indeed.

There is a part in Ray's description where he says that mid bias should be 5.3 V. The voltage is adjusted with two resistors dividing 10V from a Zener diode. I had put in the actual values, but only had about 4.7 instead of 5.3 V. The big mistake, after having adjusted the other two bias settings 3 V above and below that level, was to think "never mind, it's the 3 V difference that matters". I hadn't considered and wasn't aware that the approx 0.6 V less would already create exactly this situation:

The reason we bias all of the outputs to be above ground is so we can use the CD4066 analog switch later in the signal processing. Since the CD4066 is powered by V+ and ground it's analog switches can only pass positive level signals. Negative level signals on the inputs of the CD4066 will turn on the parasitic protection diodes and cause havoc (and excessive current drain).

I then replaced R16 (180k) with a 500k trim pot and adusted it so I had 5.3 V at the output of U3-A.

Hm, not much difference in the wave.

Wait - perhaps the mentioned parasitic diodes weren't enough so save the poor analog switch. Try and replace it. And *bingo*. Now it works.

The best birthday gift I could make myself (it's really my birthday, I'm 55 today ).

[johnstilton]

Hey, its been awhile but you came back to it and figured it out AND learned something. Thats great!