Korg/ARP Odyssey. LFO Envelope retrig problem.

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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby Broadwave » Sun Oct 11, 2015 8:32 am

I got a call from Ian @ UK Korg Tech - He did a check against an original Odyssey they had, and have agreed that the LFO retriggering is "Different" - Apparently, out of the thousands that have sold so far, I'm the only person to have brought it to Korgs attention :shock:
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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby marinedalek » Sun Oct 11, 2015 10:31 pm

Yep. The behaviour in the Korg reissue manifests this way, just to clarify: If you hit a key while the LFO is in the first half of its cycle, it correctly generates an trigger pulse as the LFO retriggers. If however you press a key when the LFO is in the second half of the cycle (square LFO LOW when assigned to Osc 1 pitch), no trigger is sent to the envelope. As the AR envelope just treats the LFO as a gate, it's not affected by this flaw.

I can also confirm that the square wave has to be "tuned" for 50% purity on my Korg Rev1 rather than keeping the slider full down, on both oscillators. From checking an FFT analysis of the pulse, the 50% point seems to alter through the pitch range of the oscillator, making me wonder if there's either leakage of pitch CV into the pulse width CV, or some capacitative coupling or wave symmetry issue with the saw waveform that the pulse is derived from. The control seems to be calibrated such that pulse width is correct at the lowest frequency possible on the oscillator, then as the frequency increases you must adjust the control to achieve the same pulse width. Not ideal considering the noticeable change in timbre across even a couple of octaves, and given David Friend's insistence on super-accurate oscillators. Even at 50% there are some low-level even harmonics present (50% pulse should have none) which may well be crosstalk from the sawtooth output, or some asymmetric distortion somewhere in the signal path of the synth.

There are various other quirks that I haven't taken time to characterise yet, such as changes in the amplitude of the AR envelope depending on the position of the ADSR repeat switches. I get the feeling that that section of the Korg version has been modified, perhaps to facilitate injection of the MIDI/Keyboard interface's signals, without proper attention paid to signal flow and loading of signals.

Another quirk in the same vein (i.e. possibly related to the implementation of MIDI) is the "trick" you can perform by connecting CV OUT to CV IN, achieving monophonic operation of the synth even when holding two keys on the keyboard. The original ARP schematics don't allow for this type of operation. In the original circuit, when a jack is connected to CV IN, the CV goes to Oscillator 1, but the interval between Osc 1 & 2 is still set by the interval between held keys on the keyboard. Thus if no keys or one key only is held on the keyboard, Osc 1 & 2 play in unison if tuned together, but when a second key is held Osc 1 tracks the CV input, while Osc 2 tracks CV In + the keyboard interval. The new design does not do this, because the analogue interval derivation part of the synth has been replaced with digital control and this CV+interval behaviour was not emulated.

I'm sure the two bigger differences (ADSR Retrigger and CV + interval for osc 2) can be rectified with relatively straightforward mods, but the subtler ones may require more careful analysis of the circuit behaviour. I'm not sure that the CV / square wave issues are annoying enough for me to mod them, but the ADSR retrigger is probably enough to push me over the edge into pulling out a soldering iron, unless of course Korg offers a manufacturer modification for the error. (ha!)
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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby Broadwave » Mon Oct 12, 2015 6:02 am

@marinedalek

Thanks for the reply & info - So I'm not going crazy after all ;)

I'll probably buy another at some point, once the "novelty" value has worn off they and start appearing on ebay. I've taken a look at some detailed pics of the PCB, and it pretty much seems to follow the original schematics - a bit of reverse engineering might be in order, although I'm concerned about how many layers there may be on the PCB.

I suspect the keyboard circuitry is completely different, but it shouldn't be too much hassle to add an opamp here and there to correct the CV out (mix the vib, bend etc. to the basic key CV). The LFO/ADSR retrigger, in theory, is a simple fix too - I did notice that the LFO reset perfectly with each key press, but I'm still not sure why it's mistriggering the ADSR so badly.
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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby bochelli » Mon Oct 12, 2015 11:28 am

In England at least there seems to be plenty offered for sale all 3 versions , mostly fully boxed with little use, I sense they were bought and not wanted, they will soon be for sale lower , as to mods on the new ones does this not simply go against the purchase intention ?
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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby tomorrowstops » Mon Oct 12, 2015 12:30 pm

Ugh. I'm glad I've avoided grabbing one. So that's two for two, Korg. The totally unrealistic level of noise in a bunch of the MS20 minis that they've completely brushed under the table ("But the original was noisy!" - Bullshit!) is equally ridiculous.

Sounds like a bunch of cutting corners/lazy engineering to boost profit margins. I guess we all forgot we're dealing with a giant corporation looking after their own self interests!
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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby Broadwave » Wed Oct 14, 2015 7:15 am

bochelli wrote:as to mods on the new ones does this not simply go against the purchase intention ?


I guess it depends what on what the original purchase intention is. For the majority of buyers it'll just be to own a version of an iconic synth, and leave it at that (until they get bored with it and want the next latest must have synth - "Ohhh look, a JP-08! I wonder what I can sell to get one"). I can see ebay being flooded with them in 6 months time, so I'll bide my time ;)

But, If I can get a second hand one cheap enough, I'll mod the h**l out of it - correct the faults, put in I/O patch points and add aftertouch. I just didn't want to risk it with a brand new one.

EDIT - Has the word h**l been censored? h**l, h**l, h**l, h**l - Yup, I guess it has.
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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby bochelli » Wed Oct 14, 2015 1:19 pm

Broadwave wrote:
bochelli wrote:as to mods on the new ones does this not simply go against the purchase intention ?


I guess it depends what on what the original purchase intention is. For the majority of buyers it'll just be to own a version of an iconic synth, and leave it at that (until they get bored with it and want the next latest must have synth - "Ohhh look, a JP-08! I wonder what I can sell to get one"). I can see ebay being flooded with them in 6 months time, so I'll bide my time ;)

But, If I can get a second hand one cheap enough, I'll mod the h**l out of it - correct the faults, put in I/O patch points and add aftertouch. I just didn't want to risk it with a brand new one.

EDIT - Has the word h**l been censored? h**l, h**l, h**l, h**l - Yup, I guess it has.


Would not surprise one bit if someone has already made the changes inside one they own if you are not selling on does it matter its yours.
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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby haj » Wed Nov 04, 2015 7:39 pm

I'm watching this thread with interest even though I'm happy enough with current state of mine ;)
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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby Crystal20 » Thu Nov 19, 2015 11:45 am

No, sadly it makes no difference - an external trigger doesn't reset the LFO either, which I'm pretty sure it should, so that's probably a good place to start looking. I just hope Korg hasn't deviated too far from the original circuit - tracing it all back with SMDs is going to be a PITA, especially if it's a muli-layer PCB.
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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby marinedalek » Wed Nov 25, 2015 11:19 pm

All triggers reset the LFO - with the keyboard repeat problem it's actually the ADSR envelope that isn't being retriggered in 50% of cases.
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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby macdev » Sun Mar 26, 2017 1:20 am

Zombie thread!

I just got an ARP Odyssey and I found this bug pretty fast. I had no idea the unit had this problem. Ok, so how do we fix it? I'd like to keep it and fix it instead of selling it, although I could get a module. I would rather not take it apart until there's a definitive fix for this bug. The module and FS versions have this fixed.

I can see that when I press a key that the internal light flickers, so the unit got the event that a key was pressed. It's just that the ADSR isn't resetting.
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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby artilect99 » Sun Jul 01, 2018 6:07 am

Yeah sorry to bump a dead thread but has anybody made any further attempts to fix this issue? Someone mentioned above it being an easy fix with rewiring the LFO repeat switch and inverting the square wave LFO. Since my Ody is off warranty now I want to try fixing this behavior. Can anybody advise me?
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Re: Korg/ARP Odyssey. LFO Envelope retrig problem.

Postby Broadwave » Sun Jul 01, 2018 6:49 am

I gave up trying to reverse engineer the SMT components to sort the problem out... I ended up selling the Keyboard version and got the Module. Everything works fine, but the Square wave pulse width still changes as the frequency is raised - Definitely not a trait of the original Oddy, but it'll do.
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