Hi,

I have a brand new OB-6 Module and noticed some strange issues.
Does anyone know if this behavior is known?

I tried to clear temperature tables [Manual]+[3], because I have read that it can solve problems. It didn't make a difference.

1. When turning on, a short pop and rising sound can be heard. The display shows the number 6, the rising sound stops immediately and the display shows 1.7.4. I am not sure if I had the ascending tone before clearing temperature tables.

2. Init patch. OSC 1 level or OSC 2 level turned up. Filter cutoff set to 0. Filter keyboard tracking set to Full. Notes from C#0 to Ab#0 can be heard. Filter opens surprisingly in this range. If filter cutoff is set to above 13 the filter stays closed as expected.

3. Init patch. SUB OSC level turned up only. Sync is set to on. XMOD Filter ENV to VCO 1 pitch. The SUB OSC jumps from one note to another sometimes.

Are all of the above mentioned issues normal behaviour?
Thank you for your help.

If you clear the tuning tables then you need to run the tuning routine at least once or the filters and oscillators will be way out.

Can't comment on 1 because I have everything muted when I power on my keyboard because the on/off pop is extremely loud. The display on mine flashes briefly and then shows the firmware version: yours is version 1.7.4.

2 is probably down to the fact you've wiped the tuning tables and haven't run the tuning again.

3 is normal: it's down to how the sub is generated and it can affect some voices more than others. On mine the pitch of the sub on one voice can jump around until the synth has warmed up and stabilised.

Thank you so much.
That's good to know.

2 Unfortunately, this was present before I cleared the tables. It is very strange and only happens when the cut off filter is set to 0.
3 Great that I'm not the only one. I have read that the sub can act strangely when sync is on.

Try running the tuning regularly as the synth warms up and every time you hear it drifting or the filters misbehaving. Hopefully when you've built up the tuning tables the problem will go away.

You could also check whether there's any sort of problem with the cutoff knob by setting the synth to output CC messages and recording the resulting MIDI in a DAW: look to see whether the value of controller 102 is at zero when the cutoff is set to zero.

Yes, thanks. I ran the tuning from low temp until it reached 49. I calibrated every 3 degrees until it reached normal temperature.

The filter only opens when filter keyboard tracking is set to full. And only notes from C#0 to Ab#0. When I lower the osc freqs from C2 to C1 and play the same notes again, (+ keyboard transposed one octave higher) the filter doesn't open anymore.

I have just checked everything again.
After recalibrating tables the strange sub osc behaviour is gone.
Before it really played an octave lower on some notes.
The filter problem is still there.

That's a bit worrying: is it across all the voices or just some of them?

It'd probably be a good idea to talk to Sequential's support: https://www.sequential.com/support/contact-support/ They're really helpful and will get the problem resolved for you.

Yes, that's not all that great.
It happens only on some voices. Not all.
I have found older threads about the exact same problem. One guy sent his synth back with the problem. They told him that it's a minor software problem. And that they will probably fix it with a software update in the future.

https://forum.sequential.com/index.p...ic,6207.0.html

I have also contacted the support. They told me that the filter behavior does not indicate a defect in the device.

That's really weird: I don't seem to have the problem on my keyboard (an early one with a serial number in the 700 range).

Let's hope they fix the cause of it in a future firmware update since, judging from the thread on their forum, it does seem to be an issue for a significant number of people.

I had a new OB6 Module and had a ton of problems. Two mod dest buttons were sticky and it took weeks of repeating a process instructed by Sequential to fix. Support were helpful but I never trusted the build quality after that as the buttons occassionly would get sticky again.

Also the tuning was wild, I'd run callibration several times and it would work but eventually it would drift, typically after switching it on the next day. Had quality issues with my Prophet 6 - USB port fell off and filter knob rubber worn down. I've had various analog synths for years and only my Sequential products have had such quality issues. Vermona, Electron, Roland (2nd hand Juno 106!) and even my Behringer synths have had far less hardware issues.

Maybe I've just been unlucky, and I still crave Sequential products as they look, sound and feel great but I just don't trust the build quality from my past experiences.

Yes, I have just received confirmation again from support that both sub osc and filter behavior is expected and that it varies between units and calibrations. They want to fix it in the future.

That‘s worrying and sad because the sound of the OB-6 is phenomenal. Did you have the tuning problems right from the start or did they come later? Yes, I also have an old MKS-80, sold a Juno 106 & Juno 60 a long time ago. The MKS-80 sound is still exceptional but I love the precise filters and envelopes of the OB-6. I think they sound a bit sluggish sometimes on the MKS.

Consider exchanging it (ideally you can try the new one before returning the current one).

I did consider to exchange it. I could return it until next week. The problem is that both the Prophet 6 module and OB-6 module are sold out in Europe. They will not be available again until next March...

Do not let you be treated like a fool.
Its astonishing how Sequential customer support tries to avoid to admitt any fault in order to prevent any action. Especially for European customers. Had enough experience. Its a shame for a premium brand.

I am really unsure what to do. I would need the synth and would have to wait until next year for another one... I didn't realize there were quality issues with so many units.
I figured I could live with the filter behavior, on the other hand, the synth costs a lot of money....
And on the other hand, the same problem may be present again on the next device or with other issues....

Check the sub consistency among all voices when hard sync is engaged and the slave oscillator detuned (classic hard sync sound). Also check the general noise floor, compare it to other synths, especially when using sustain levels at 50%, not 100%.

I had two OB6, both went back for different quality reasons. That was when the OB6 cost 1000 Euro less. I actually thought they would have improved. Support was helpful by offering me to send 6 new voice cards, but I wasn't really in the mood to open the synth. Personally, I developped a sort of zero tolerance with any serious fault, so stuff has to go back, no nerves left to fiddle around with problems which should have been resolved by the manfacturer, since the customer is not a cost-efficent quality control.

You've got a hard decision to make. If you like the OB-6 and the issue isn't causing any problems unless you deliberately go looking for it then you might choose to keep the synth. If it is noticeable in some sounds since the voices that have played notes in the range where the problem occurs continue to drone until shut off by the VCA envelope then you might want to return it.

The sub oscillator sync problem is a case in point: one of the factory patches deliberately uses the effect, and on my OB-6 one voice sounds noticeably different to the others when playing that patch. Since I don't use sync that much it never bothered me and I quickly forgot about the whole thing until it came up here and Sequential's own forum. At that point I discovered I also had the problem with another voice that alternated between the two sub behaviours at random while the synth was warming up. In the end I decided that, since I only experienced the issue on that one patch (which wasn't a sound I'd ever use), I just didn't care: it's an analog synth, there are going to be variations between voices thanks to component tolerances, so it's not going to be absolutely perfect.

"premium" in price only it seems.

Yes, but it's a bit of a pitty. They develop nice sounding synths for sure. And there isn't much of an alternative.

Its a shame for many that dreamt of owning a Sequential/Oberheim or Moog for years, may have saved up to buy it only to get it and its faulty or buggy

Well, if you want to exceed the usual simple sound, hard sync is a way to get a lot of different timbres. And not to be able to use the sub in that case is a serious restriction.

The problem arises because the sub is created with the slave oscillator. For Moog it is the other way round.

There is one "boring" behavior of the sub and one less boring. In a shop there was the less boring sub sync behavior for all voices, and I got a unit, the second one, where all voices had the more "boring" sounding configuration, at least consistent, but that unit had a high noise floor. The less boring behavior is when the sub makes a kind of step during a sync sweep. Behavior depends on whether the sub is restarted in phase like the oscillator or not.

Yes: it's something of a design flaw. If they'd done it the other way round the issue wouldn't exist. And if the sub wasn't so sensitive to the component tolerances it wouldn't be a problem. As it is, if you have voices that misbehave you can't use the sub on polyphonic patches that use sync.

Thank you, I did check the sub consistency.
I have found an older thread where you helped someone with exactly the same behavior:
OB6 sub osc
I have the same weird distortion sounds from the sub when sync is on (VCO 1/2 off)
The behavior is consistent across all voices.
I checked the noise floor and compared it to my other synths with volume to 100%.
MKS-80 -62dB
OB-6 -83dB (no difference with different sustain levels)
Slim Phatty -95dB

It really looks like a design flaw. Yes.
I have tested it a little more.
The sub is consistent with a kind of step down an octave and back up again across all voices.
I can imagine that the whole thing is still within a certain tolerance.
The weird distortion sounds from the sub when sync is on (VCO 1/2 off) only happens when both VCOs are set to C2. As soon as I switch VCO 1 to C# or above everything is fine again.
Anyway, my understanding is that no matter if digital or analog synth, when hard sync is used you should always avoid octaves and fifths between OSC 1 and OSC 2.

Thank you so much. That's really good to know. It seems that I have the less boring behavior with the sub

That's not a distortion. When the sub is reset in phase after each half cycle it simply disappears, because it is a square wave, and what you hear is a residual sound. Therefore, as VCO 1 approaches the same frequency as VCO 2, the sub strongly thins out and should vanish.

I believe that there are units where the sub is not reset at all.

Thank you that makes sense. And thanks for the explanation.
I think if the sub had also reacted differently across voices, I would have returned the synth...

You're OK then. One of my OB-6's voice cards doesn't do that, it remains at the higher octave all the time, and a second card only does it once the synth has fully warmed up.

The issue got noticed because one of the factory presets deliberately uses this 'feature' to introduce a delayed octave down to the sound. Some people found it didn't work on some of their voice cards, so playing the same note repeatedly to cycle round the cards would produce different results.

It's something so specific, and not an effect that I'd ever tried to exploit, that I just didn't care about it. Personally I could live without the other rather weird sounds the sub can produce when using sync, so I don't use it when using sync.