SID & analog filter

MIDIbox SID
1

i’m again in the situation in which my SID 8580 don’t plays anymore… don’t know if its the sid itself or the PCB, but i think that it’s the sid and my pcb has definitely something wrong on it… it’s the second 8580 i fire…

imagine that since last week everything is ok… now you turn on and nothing plays!!! :frowning:

Ok, beside this sad informations…i didnt gave up the SID project, and  i’m trying to get more SIDs, now i have 3 6581 and 2 8580 but i dont’ know if they if are working or not (maybe someone wants to test them?! :wink: )

my next plan (on a VERY long timetable…) would be to build a 4 sid unit, but this time with at last one fuse before the main power supply… :slight_smile:

the question: i hear from your comment that 8580 are better then 6581, but i have more 6581… maybe i will combine 2 and 2 (if the 8581 are working…)

what about the cooperation between 4x6581 and an DIY anolgue filter (ex. the moog filter that throsten showed in another topic)??   do you think that the analog filter would “fatten up” the sound?

the main task would be to connect a CV out from the sid/core to the filter resonance and cutoff control… anyone has experience in this? how does it work?? it would also be nice to implement an analog filter control with, lets say, a simple pot, and build  a simple switch to choose from CV control or pot control.

once the filter is connected, how it is effectively controlled by MIOS?

i see that the CV module has 8 outputs, but i feel that only 2 are necessary, one for cutoff and one for resonance, am i wrong? in this case, only a max IC would be needed…

the natural extension to this would be to build both a lowpass and an highpass filter… in this case 4 CV out would be needed…

any thoughts on this mad plan??

after the construction of the sequencer i need more wires to be soldered!!! :smiley:

2

Hi,

(At this point of developement) AOUTs in a SID are the part of the modulation matrix, so CV are controlled from the modulation sources.

Unfortunately most DIY VCFs (for example that Moog ladder) do not implement resonance CV, but it’s really a simple matter (?!) of putting an OTA (or similar voltage controlled element) in the place of a resonance pot.

(Like U3 in: http://www.sowa.synth.net/poly/f_vcf.gif)

Most VCF have manual Filter control pot + CV inputs, so filters Cutoff frequency can be set with manual pot and then modulated with CV.

(For reference, check that Rick’s Moog ladder filter schematics: http://dropmix.xs4all.nl/rick/Emusic/Moog/

Resonance pot = P11, Emphasis.

Cutoff frequency pot = P8, Frequency

V/Oct CV input = KOV

TM/ENV = modulation inputs)

i see that the CV module has 8 outputs, but i feel that only 2 are necessary, one for cutoff and one for resonance, am i wrong? in this case, only a max IC would be needed…

Yup.. but I think that you’ll be wanting a filter per SID..

Bye, Moebius

3

Hi,

Unfortunately most DIY VCFs (for example that Moog ladder) do not implement resonance CV, but it’s really a simple matter (?!) of putting an OTA (or similar voltage controlled element) in the place of a resonance pot.

(Like U3 in: http://www.sowa.synth.net/poly/f_vcf.gif)

mmhhh… ad advanced design for me… :slight_smile:

anyway thanks for the info!

Yup.. but I think that you’ll be wanting a filter per SID..

interesting observation, indeed… i didnt thought by myself!!!

::slight_smile:

the design becomes complicate…

4

implement resonance CV, but it’s really a simple matter (?!) of putting an OTA (or similar voltage controlled element) in the place of a resonance pot.

You seem to know some things about implementing voltage control in (analog) circuits, moebius? I want to do this to the pitch contol of an analog kick drum and some other analog designs, i was first thinking of using a led+LDR but your tip about using OTA’s looks maybe more stable.

Do you know which method is faster/more stable, and do you have more info/links/etc. on the OTA as CV-input?

cheers,

marcel  

5

Illogik.. Sorry,

Been too lazy and scared to answer this kind of questions. :slight_smile:

OTA is definitely faster and more stable than LDR+Photoresistor (or Vactrol). With OTA’s people even realise filters that are V/OCT.. but you probably have seen all that.

But, what are you doing? Something to do with MR-808’s suggestion with 808’s bass drum? :wink: Could you be more specific?

Links:

http://www.physicsenterprises.andrews.edu/diy_archive/schematics/oakley/super.html

That Moog Transistor Ladder again. This time with resonance CV and bandpass output.. (and can be made to sound as weak as 303’s ;))

www.ele4music.com - using web.archive.org. (Those old pdfs with schematics don’t really seem to be online)

Some VCF’s with CV resonance..

I’m not sure, but I think that pitch control of a most the drum circuits floating on internet are not to be controlled on stabile v/oct manner,

Bye, Moebius

p.s. I am interested on this.. post any info you have!

6

This intrests me but is far beyond my current abilities. Is there an easy way to add some more filtering and or DSP to each of the 4 sid units so that each could be controled independantly and simultaneously? Several people have suggested just and external multi-effects unit but most of them you can only adjust 1 channel at a time not all 4. I was hoping there would be something I could add inline to the audio out before mixdown to output from the sidbox.

Another thing that I just was thinking about whic h I haven’t searched to see if it has been answered yet was, is there a sugested mixer circuit for the 4 stereo chanels down to 1 stereo channel? I know there are tons of schematics on the net so I asked for the suggested one.  

Another thing, how hard would it be to implement a LFO that ping-pongs the 8 mono chanels to a stereo out with a switch for L/R/Ping-Pong so you can select where the channel is going?

7

hey moebius,

i’ve seem to have forgotten this topic, found it when i was searching the forum for info on “voltage control”.

As for what i’m doing/planning; a lot…

I’ve almost finished the mbseq, but the encoders don’t work well, i guess i have too messy wiring so i’m making pbc’s for the encoders/buttons/dins to clean it up.

Then i’ve also finished soldering the mbcv application (waiting for lcd and hoping for shx8 support in mbcv application ;)) this i want to build together in a midi controlled box containing analog sounds/modules;

  • A 909 style kick with distortion and dedicated 24 dB/Oct VCF (thanks gbeth!) kick plans/pcb pattern from j.schmitz; http://www.analog-synth.de/synths/tr909/tr909.htm ; the kick-velocity, -trigger(converted gate from mbseq) the vcf cutoff(and hopfully some kick controls; pitch, attack/decay) are going to be controlled by mbseq/cv.
  • A cynare drumsynth from www.csg.synth.net (cheap pcb’s available!!); the trigger, gate, vcf cutoff (and hopfully the pitch) controlled by mbseq/cv
  • A mono(noise)synth with the sn76477, have to make/find/adapt a design for this so this is only a idea right now.
  • A VCF with simultaneous HP/BP/LP inputs(!) (also from cgs.synth.net.) with dedicated envelope generator (to filter cutoff); vcf cutoff cv and envelope gating by mbseq/cv
  • 2 stand alone (VC)LFO’s and another envelope generator.
  • whatever still fits inside the box next to the above!?  ;D(modulation matrix as described at;http://monopole.ph.qmw.ac.uk/~thomas/synthdiy/patchpanels.htm?? like these      things or maybe this “voltage controlled” (vactrol!) delay; http://home.comcast.net/~sbernardi/elec/og2/og3_echo.html )

                             

I hope to get the mbseq working properly before the end of the month, then i’ll start testing the analog modules (probably first the kick and the VCF) with the MBCV application.

In the mean time i’ll start reading up on the OTA/voltage control subject (thanks for the links), i want to try this out; since i don’t really need a nice 1V/Oct cv input; i just want to make some funtions (externally) controllable so i can make control sequences.

When i have some results with this i’ll be happy to share them with you (but don’t expect too much ;)).

As for iceberg; i haven’t made anything like the ideas your talking about but i suggest you look at the cgs.synth.net web site, there are a lot of small analog synth modules that are voltage controlled (lfo’s, filters, audio (panning)mixers etc.). You can order cheap ($5-$20) pcb’s and there is good info/support for building the modules; i think you can accomplish the things you want!

cheers, and good luck building to all!

marcel

8

i found a PCB and schematic for a korg ms20 filter (both highpass and lowpass). i have  korg ms20 at home at i think it’s quite good… and also the highpass filter can add a tremendous power in the low range once you increase resonance!

the only problem is that i don’t want to build 4 filters (2HP, 2LP)… so i think i will be summing the 2 sids (yeah, finally i decided to build only 2, wiht 6581) with an opamp (with gain) and send the signal directly to the filter.

but i will also leave the option to use the 2 sids in stereo thru a bypass of the opamp and, moreover, let the filter to be used also with an external signal (so to be used also as a standalone FX unit), with another series of bypass…

what do you think about this design?

9

hey bosone,

the only problem is that i don’t want to build 4 filters (2HP, 2LP)… so i think i will be summing the 2 sids (yeah, finally i decided to build only 2, wiht 6581) with an opamp (with gain) and send the signal directly to the filter.

you dont have to build 4 filters; a lot of diy VCF are “variable state”; meaning you can switch the same filter between LP/BP/HP, + i think you’re going to be much happier when you have a filter per SID, but thats only my opinion.

If you do it like this, you can make 2 filters and leave out the mixer (or put it after the filter outputs).

if you can etch your own pcb’s; here is a variable state filter that works for sure (i’ve buildt this one)+ it’s quite small + the parts are easily obtainable;

http://www.musicfromouterspace.com/analogsynth/statevariablefilter.html

cheers,

marcel

10

the powerfulness of the ms20 is that you can use them in series… i thought to do the same…

however, in the schematic that i found, changing from HP to LP is a simple matter of changing the pinning of a capacitor… so it could be a good idea to implement