Hot DCO Discussion!

Discussions about anything analog, digital, MIDI, synth technology, techniques, theories and more.
User avatar
StepLogik
Expert Member
Expert Member
Posts: 1492
Joined: Fri Dec 29, 2006 4:16 am
Gear: Gauntlets of Ogre Power, Vorpal Sword, Chain Mail +3, Ring of Invisibility, Staff of the Magi, Boots of Speed
Location: Boston, MA

Post by StepLogik » Sun Sep 09, 2007 2:32 pm

great post, bitrex!

the juno-60 is very similar in design. i've never fully understood the process, but your post clears it up considerably.

User avatar
Automatic Gainsay
Synth Explorer
Synth Explorer
Posts: 3962
Joined: Wed Feb 14, 2007 12:22 am
Real name: Marc Doty
Gear: Minimoog, 2600, CS-15, CS-50, MiniBrute, MicroBrute, S2, Korg MS-20 Mini, 3 Volcas, Pro 2, Leipzig, Pianet T, Wurli 7300, Wurli 145-A, ASR-10, e6400.
Band: Godfrey's Cordial
Location: Tacoma
Contact:

Post by Automatic Gainsay » Sun Sep 09, 2007 7:23 pm

This is one of the most authoritative, informative, and interesting threads I've ever read on VSE.
‎"I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question." -Charles Babbage
"Unity and Mediocrity are forever in bed together." -Zane W.
http://www.youtube.com/automaticgainsay

User avatar
gs
Active Member
Active Member
Posts: 350
Joined: Sun Sep 19, 2004 6:10 pm
Location: USA

Post by gs » Mon Sep 10, 2007 9:47 pm

bitrex, thanks! you are the bomb.

BTW, I didn't create this thread, but it was spun-off by a moderator from another discussion. My inquiry just so happened to lead off this discussion and a new thread for it.... :shock:

I guess it now all comes down to semantics...

You see, I have run into similar people with bitrex's knowledge, who still consider those DCOs to be "a hybrid concept" because they insist "the core of the DCO is still digital". They go by what the core does (the oscillation itself) and not what happens afterward... DACs and all notwithstanding.

Nevertheless, as bitrex pointed out...
the AUDIO signal from a synth like the 106 is not coming out of a digital to analog converter.
Therefore it's agreed, the signal created by DCOs is analog because it is a signal created without the use of DACs for the audio.
Kurzweil PC3, Yamaha MOX8, Korg Z1, Alesis Ion, Alesis QS8.2, Kawai K3M

User avatar
micahjonhughes
Active Member
Active Member
Posts: 703
Joined: Fri Mar 09, 2007 4:27 pm
Location: Chicago

Post by micahjonhughes » Mon Sep 10, 2007 11:15 pm

bitrex wrote: The square waves then go on to the 3 waveshaping ICs, MC5534s, each of which is responsible for 2 voices and is on the 3 voice boards. The output square wave is basically applied to an internal op amp that provides PWM, and the sub oscillator is provided by just a flip flop that divides the incoming square wave by 2. The sawtooth is generated by a constant current source charging a capacitor, which is discharged through a transistor switch turned on and off by the incoming clock.
If I'm reading this correctly, it seems that most of the Juno waveforms (pulse and sub) are just the processed output of a digital (quartz) clock. Only the saw wave is using the clock for timing.

Earlier on there were claims that there was a major difference between this method and the new Dave Smith oscilators. Any info on how they differ?

User avatar
gs
Active Member
Active Member
Posts: 350
Joined: Sun Sep 19, 2004 6:10 pm
Location: USA

Post by gs » Tue Sep 11, 2007 8:44 pm

micahjonhughes wrote:Earlier on there were claims that there was a major difference between this [Juno-106 DCO] method and the new Dave Smith oscilators. Any info on how they differ?
Well it looks from what bitrex wrote, the saw waves on the Juno operate on the same principal as DSI, using a charge/discharge capacitor (but timed by a digital clock), but the Juno square/pulse waves are just the processed output of the clock/counter. From what I understand, ALL the DCO waveforms on the DSI synths use the charge/discharge method.
Kurzweil PC3, Yamaha MOX8, Korg Z1, Alesis Ion, Alesis QS8.2, Kawai K3M

User avatar
adamstan
Active Member
Active Member
Posts: 511
Joined: Tue Aug 22, 2006 2:56 pm
Real name: Adam
Gear: Yamaha 2xDX7II|QY-70|PSR-S750|PSR-2000|TYROS|Electone D85|Electone E50
B5 DIY polysynth
KORG Poly61
Vermona DRM
Solton Programmer 24
LEMA EDD-5
Location: Poland
Contact:

Post by adamstan » Tue Sep 11, 2007 9:31 pm

gs wrote:
micahjonhughes wrote:Earlier on there were claims that there was a major difference between this [Juno-106 DCO] method and the new Dave Smith oscilators. Any info on how they differ?
Well it looks from what bitrex wrote, the saw waves on the Juno operate on the same principal as DSI, using a charge/discharge capacitor (but timed by a digital clock), but the Juno square/pulse waves are just the processed output of the clock/counter. From what I understand, ALL the DCO waveforms on the DSI synths use the charge/discharge method.
It's the same in Juno, and in Prophet (and in my beloved Siel Opera) - capacitor with current source is used to create sawtooth wave. The square wave is obtained by feeding sawtooth into comparator - its other input is fed with voltage responsible for PWM (In Juno, these two circuits - integrator and comparator are inside the MC5534 chip). You can see it clearly looking at Siel Opera schematics, as waveshaping circuit is 'discrete' (built from opamps and transistors) BTW - as timing of sawtooth wave is still determined by the clock, and opamps are very fast, the way of obtaining square wave (comparing sawtooth vs PW voltage OR processing of clock signal directly) makes no difference. Actually, when I think about it, there's no simple way to obtain PWM without using the sawtooth or triangle wave as an input to comparator.
Man with a tape recorder | Living in the '80s ;-)

User avatar
micahjonhughes
Active Member
Active Member
Posts: 703
Joined: Fri Mar 09, 2007 4:27 pm
Location: Chicago

Post by micahjonhughes » Tue Sep 11, 2007 9:58 pm

adamstan wrote:
gs wrote:the Juno square/pulse waves are just the processed output of the clock/counter.
It's the same in Juno, and in Prophet (and in my beloved Siel Opera) - capacitor with current source is used to create sawtooth wave. The square wave is obtained by feeding sawtooth into comparator
Just to clarify are you disagreeing with Bitrex's explanation or our interpretation?

I understand how the comparator could be used to give the pulse wave. I was actually trying to figure out how the pulse width could be varied if the square wave was based on the clock output.

Is it safe to believe that fully analog oscilators work the same way but with a non digitally produced clock (from some oscillating circuit)?

User avatar
adamstan
Active Member
Active Member
Posts: 511
Joined: Tue Aug 22, 2006 2:56 pm
Real name: Adam
Gear: Yamaha 2xDX7II|QY-70|PSR-S750|PSR-2000|TYROS|Electone D85|Electone E50
B5 DIY polysynth
KORG Poly61
Vermona DRM
Solton Programmer 24
LEMA EDD-5
Location: Poland
Contact:

Post by adamstan » Tue Sep 11, 2007 10:09 pm

micahjonhughes wrote:Just to clarify are you disagreeing with Bitrex's explanation or our interpretation?
In Juno, square wave from 8253 is fed into MC5543, which performs integrating, and produces square with PWM. I'm not sure, how the chip works, however, as you say
I was actually trying to figure out how the pulse width could be varied if the square wave was based on the clock output.
I can't imagine how could it perform PWM without using the sawtooth.

micahjonhughes wrote:Is it safe to believe that fully analog oscilators work the same way but with a non digitally produced clock (from some oscillating circuit)?
In 'pure' VCO, the capacitor is discharged by the comparator, after voltage reaches a certain value - therefore by varying charging current (you do this by apllying different CVs), you vary charging time, and thus frequency.

In DCO's we are discussing, capacitor is discharged by the pulse from digital clock. The whole waveshaping circuitry is in most cases the same in both designs.

So I think, the answer can be "YES" - in the way described above ;-)
Man with a tape recorder | Living in the '80s ;-)

User avatar
nathanscribe
VSE Review Contributor
VSE Review Contributor
Posts: 2889
Joined: Fri Aug 11, 2006 1:03 pm
Location: The right side of the Pennines
Contact:

Post by nathanscribe » Wed Sep 12, 2007 4:28 pm

Actually, the Juno (6 and presumably 60 too, which is what I think we're talking about) creates its PWM wave by feeding the sawtooth into one input of a comparator, and a multiplexed CV (from the PW mod section) into the other. It's an MC14051 analogue multiplexer.

User avatar
adamstan
Active Member
Active Member
Posts: 511
Joined: Tue Aug 22, 2006 2:56 pm
Real name: Adam
Gear: Yamaha 2xDX7II|QY-70|PSR-S750|PSR-2000|TYROS|Electone D85|Electone E50
B5 DIY polysynth
KORG Poly61
Vermona DRM
Solton Programmer 24
LEMA EDD-5
Location: Poland
Contact:

Post by adamstan » Wed Sep 12, 2007 4:43 pm

nathanscribe wrote:Actually, the Juno (6 and presumably 60 too, which is what I think we're talking about) creates its PWM wave by feeding the sawtooth into one input of a comparator, and a multiplexed CV (from the PW mod section) into the other. It's an MC14051 analogue multiplexer.
Thanks for that info. I was looking at Juno 106 schematics, and it uses just MC5543 for whole waveshaping - it includes integrator, comparator, and even flip-flop for SUB-OSC.
Man with a tape recorder | Living in the '80s ;-)

Post Reply