My oscillators are bullies

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Putte
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My oscillators are bullies

Post by Putte » Mon Oct 19, 2020 12:58 pm

I´m celebrating ten years of 5U modular ownership in December. A long time, but also a decade that past quickly. So fast that I missed to check on a few basic things about modulars. Warming up and tuning oscillators, for instance. Now, to begin with, these are my oscillators:
-7 Dotcom Q106CRS
-2 Dove audio WTF oscillators
-2 krisp1 MU-S-VCO
-2 krisp1 MU-TZ-VCO
-3 Corsynth C104 Oddyssey (1 bought second hand)

They are arranged in pairs, except for three of the Q106s and the Oddysseys. This is also how I use them, two or three together for different patches. Anyway, in an early stage, can´t remember the details of when or by whom, I was told to let the osc:s warm up for about ten minutes. So, this is standard procedure, Before I tune in A4=440Hz. Another perhaps important thing is that there normally passes two to five days between the sessions.

Sometimes, when I start the modular, all three Q106s are almost perfect in tune, after several days. Could be, about -0,3Hz or so. The thing is, they all are. This also goes for the Oddysseys and the others. Other times, they can be -/+ 4-5Hz. In that case, they all are either 4 or 5 Hz down or up. It´s like they´re collaborating in detuning, when I´m gone. The Three Oddysseys are an even bigger mystery. After ten minutes, they can all be down to 433Hz. I tune them, but after a while, they´re up at 443Hz, all three of them. I´ve tried to extend the time before tuning. Doesn´t help. It´s like they deside not to react to the warming up time, waiting for me to adjust them, and then they warm up (and detune up a few Hertz). My oscillators are bullying me, at least when they´re three together!

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Re: My oscillators are bullies

Post by Dave Peck » Mon Oct 19, 2020 1:54 pm

I have found that I need to wait a lot longer than ten minutes to ensure that all of my oscs are stable. This is partly due to the circuitry within the oscs warming up to normal operating temp, and partly due to the way the large linear power supplies inside the various cabinets gradually warm up the insides of the cabinet, which has a direct effect on the osc tuning & tracking stability.

I was just recently reminded of this a few days ago when I did my twice-a-year 1V/OCT tracking calibration on all of my oscs. I was a bit impatient and started calibrating the oscs a bit too soon, maybe about 15 minutes after powering up the synth. And by the time I got the last osc done, the first oscs were now out of tune and out of cal because they had not yet reached a completely stable operating temp when I had started. I had to go make some coffee and kill some time for another 30 minutes and start over.

But once they DO reach stability, the tuning and the 1V/OCT tracking are rock solid.

Putte
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Re: My oscillators are bullies

Post by Putte » Mon Oct 19, 2020 2:46 pm

Okey, not sure I have that time, but I´ll try to wait a bit longer from now on.
Perhaps I should squeeze in all oscillators in the two power supply cabinets then?

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Re: My oscillators are bullies

Post by Thalassa » Mon Oct 19, 2020 2:53 pm

Hi Putte ,
If you have your equipment in a room that you are nor using for a few days, and you turn on all your equipment the room temperature will change with the time and that will affect your VCOS, Also you need to wait for the temperature inside the modular cabinet to be constant ( the PSU and the modules will warm up the cabinet ). In general you should wait more than 10 minutes for the C104 to warm up, in my measures the it needs more or less 30 minutes.

I made this graphic for the C104 long time ago, You can see that in the beginning it ramp up from 440 to 442,7 ( maybe it even was higher before the 15 minutes) and from that moment it goes down to 440hz again . As you can see after 45 minutes the oscillators only detune 2 cents of semitone in more than 2 hours ( 5 cents from 30 minutes to 2 hours).

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Re: My oscillators are bullies

Post by Dave Peck » Mon Oct 19, 2020 4:15 pm

Putte wrote:
Mon Oct 19, 2020 2:46 pm
Okey, not sure I have that time, but I´ll try to wait a bit longer from now on.
Perhaps I should squeeze in all oscillators in the two power supply cabinets then?
Do you have some cabinets that do NOT have power supplies in them? (i.e. powered from another cabinet, or from some other external P/S device). That might be better. Less overall temp change in a cabinet with no internal P/S.

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Re: My oscillators are bullies

Post by kindredlost » Mon Oct 19, 2020 4:55 pm

Ahh, just throw a heavy chorus delay on the final output and you won't notice these things anymore.
:sarcasm:

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Re: My oscillators are bullies

Post by cornutt » Mon Oct 19, 2020 5:29 pm

Sounds like you might have a case of parasitic sync. This can happen if the power supply or distribution isn't up to the job. I'll let someone who is more knowledgeable about power supplies chime in.
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Re: My oscillators are bullies

Post by Dave Peck » Mon Oct 19, 2020 6:47 pm

kindredlost wrote:
Mon Oct 19, 2020 4:55 pm
Ahh, just throw a heavy chorus delay on the final output and you won't notice these things anymore.
:sarcasm:
Ha! Actually you make a point. I have sometimes wondered if I really need to be going to all of the hassle of ensuring all of my oscs have perfect tracking over seven octaves when I nearly always end up intentionally detuning them to create a massive buzzing wall of sound and then only use a couple of octaves on any one patch...

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Re: My oscillators are bullies

Post by KSS » Mon Oct 19, 2020 11:52 pm

One thing I never see mentioned in threads like this is the *very* simple way to speed up the process. Play. Your. Synth.

Preferably at high pitches and using as many modules as possible. Don't forget to include your analog filters, which also have temp sensitive expos for reasonably decent pitch tracking.

High ptiches put more current through the temperature sensitive part of the circuit and heat it up faster. High module usage gats the inside of the case warmer sooner. Even if you don't want to actually play the thing while it's out of tune, set up a patch and let it run with the mixer channel or output amp off. If you have a sequencer, usin it to run the synth during warmup. Every gigging musician should be doing this already.
Last edited by KSS on Wed Oct 21, 2020 1:55 am, edited 1 time in total.

Putte
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Re: My oscillators are bullies

Post by Putte » Tue Oct 20, 2020 12:30 pm

Well, I´ve got one krisp1 Overdrive II and one Deep Equinox phaser. Perhaps they can sweep away all possible chances of sensing oscillators being out of tune.
Another idea, since the studio is close to work. I could stop by in the morning, and turn on the modular. It should be well warmed up by 5 pm.
To answer the question about power supplies. There are six cabinets (2x11U each). Two of them have QPS1s inside. One has two and the other three Q106s. The three Oddysseys are in one of the two top cabinets, far from the power supplies. So are the two MU-TZ-VCOs, next to Another pair of Q106s. That quartet is very stable, at the most 0,2-0,3Hz off.
No, it just seems I need more patience after turning on the power supplies. Luckily, there are other machiines to give some attention and love meanwhile. Another thing I should do quickly, is to fill the four remaining empty U:s. They´re obviously leaking warmth! There´s a lesson for us all, fill all empty spaces as fast as possible.
Thanks, Thalassa, for that graphic. It explains a large part of the mystery I´ve experienced.

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Re: My oscillators are bullies

Post by oldgearguy » Wed Oct 21, 2020 4:21 am

In the old days, we had a timer to know when the MiniMoog and others were stable enough to tune -- the lava lamp.

Once the lava inside started to loosen up and flow then we knew the room temperature and gear were stable for tuning.
(joking a bit but not joking. If the room was cold the lava lamp took longer to start moving).

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Re: My oscillators are bullies

Post by kindredlost » Wed Oct 21, 2020 8:01 am

that's hilarious oldgearguy!

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Re: My oscillators are bullies

Post by hamildad » Wed Oct 21, 2020 8:08 am

reminds me of the story within the Harald Grosskopf Synthesist liner notes, of him having to point an anglepoise lamp at the innards of his minimoog to keep the temp stable in his freezing flat in Berlin in the 70s.

I always think of this, when I inwardly complain about some little problem with recording or working with analogue synths...
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Re: My oscillators are bullies

Post by Sideshow » Fri Oct 23, 2020 4:15 am

oldgearguy wrote:
Wed Oct 21, 2020 4:21 am
In the old days, we had a timer to know when the MiniMoog and others were stable enough to tune -- the lava lamp.

Once the lava inside started to loosen up and flow then we knew the room temperature and gear were stable for tuning.
(joking a bit but not joking. If the room was cold the lava lamp took longer to start moving).
Maybe that's why I like bringing lava lamps for my gigs :cloud:
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Re: My oscillators are bullies

Post by josaka » Fri Oct 23, 2020 4:44 am

on one hand we have this thread about getting stuff to stay in tune...
on the other hand the very same folk are going mad about getting the new STG oscillators..
which purposefully go out of tune.. I dont get it..

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Re: My oscillators are bullies

Post by oldgearguy » Fri Oct 23, 2020 6:24 am

josaka wrote:
Fri Oct 23, 2020 4:44 am
on one hand we have this thread about getting stuff to stay in tune...
on the other hand the very same folk are going mad about getting the new STG oscillators..
which purposefully go out of tune.. I dont get it..
Fair point. For me, it's not so much the out-of-tune that bothers me. It's more the tracking errors across the octave(s) that is annoying.
That's partly why I have 2 VCOs from the same manufacturer in my setup - they tend to track consistently once calibrated so even if there's a slight out of tune-ness with an oscillator, they are both tracking the notes played consistently.

It's a hassle for me when 2 VCOs don't behave similarly across the span that I'm playing/sequencing way more than a note or two being slightly sharp or flat. So the STG oscillators (when they arrive) will most likley be used as a pair and I will enjoy getting the slight wobble in them as well as having them track very well across the octaves.

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Re: My oscillators are bullies

Post by Putte » Sun Jan 10, 2021 11:36 am

The problem remains, but this weekend I´ve tried to do some more troubleshooting. First, the problem in short:
1)I tune in an A/440hz, which usually means I have to adjust down from about 442-443hz
2)After a minute or two, the oscillators are down to 429-432hz, so I turn them up 8-10hz
3)Another few minutes later, the oscillator are out of tune, about 443-447hz
4)This can go on for ever - when tuning them down, they soon go to somewhere around 430-433 again

Just to be clear, yesterday to modular was on for about four hours, and in the end I still had this problem. So, today I troubleshooted, and noticed a few parametres:
-This problem only concern oscillators played with keyboard (as opposed to sequencers), which only is done with my dual diy keyboard (keybed-Doepfer MKE - Kenton Pro solo II - modular (see picture))
-The lower keybed is connected to three Q106:s, and they are fine. The top keybed goes to three C104, and they´re the ones bullying me, or so I thought…..
-I first exchanged one of the C104s for a Q106, which behaved just like the others. It detuned quickly, why I started to suspect this isn´t a oscillator problem.
-So I switched keybeds (the CV and gate outputs on the Pro solos), and the problem also switched - the three Q106s went out of tune instead. Okay, so this issue can´t be related to the oscillators, right?
-Between every change and switching I did, I practised a little bit of soloing on both the keybeds, and I think I maybe even heard the detuning, from one tone to another. This thing seemed to happen fast, and it could be related to the change of keys.
-So, I tuned the three C104s all over again, and put a small weight on the A/440hz key. For about ten minutes, the oscillators didn´t go out of tune at all. Removing the weight and playing for a while, and they soon did.
-The problem could come from the MKE or the Pro solo, but both keybeds have identical signal chains. The last thing I tried, was the multiples. Both CV first go to two different re-synthesis multiples, so I moved the ones in the failing signal chain to the other. During the few minutes I had left, before I hade to leave, it might have worked, at least a bit.

I´m thinking this issue could be caused by too long cables from Pro solo to modular (16 feet), perhaps in combination with non active multiples. But keys, MKE, Pro solo are cables the very same from both of the keybeds to the modular.
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Re: My oscillators are bullies

Post by Dave Peck » Sun Jan 10, 2021 3:40 pm

From the description, it sounds like this may be an issue related to the internal Sample & Hold circuitry in one of the keyboards. Possibly a capacitor needs to be replaced.

Some analog CV keyboards use an internal S/H circuit that is triggered with each note played to maintain the voltage after the key is released. This is necessary because once you let the key up, there's no actual connection and no pitch CV voltage signal any more, but you need the pitch CV to stay at whatever the last voltage was so that the last note played will continue to hold at the correct pitch. If this S/H circuit isn't working really well, it's output voltage can 'droop' over time, or in some cases can randomly fluctuate up & down.

One way to tell if this might be happening - after letting the oscs warm up for quite a while, connect the suspect keyboard to any osc and play a fairly high note which will send a fairly high DC pitch control voltage to the osc. Patch the osc direct to an output, no filter, no VCA, so it drones constantly. leave the synth alone for maybe ten minutes - don't touch the keyboard. Then, play THE SAME NOTE on the keyboard again while listening to the osc. If you hear the osc pitch suddenly jump up or down slightly, it indicates that the pitch CV had drifted and is being suddenly corrected when you press the key again, and the control voltage being sent to the osc is the problem, it is NOT the osc.

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Re: My oscillators are bullies

Post by Zifor » Sun Jan 10, 2021 3:50 pm

Just an idea , but would it make sense to have a heat sensor in the cabinets with some sort of fan to regulate temperature? (Bar of course stabilising your oscillators digitally - easiest way).
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Re: My oscillators are bullies

Post by Elahrairah » Sun Jan 10, 2021 9:16 pm

Zifor wrote:
Sun Jan 10, 2021 3:50 pm
Just an idea , but would it make sense to have a heat sensor in the cabinets with some sort of fan to regulate temperature? (Bar of course stabilising your oscillators digitally - easiest way).
The heat sensor won't measure the side of each circuitboard properly. Just playing the thing for 15 minutes should do the trick.

I've only had problems in the first minute of turning on a cold circuit.

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Re: My oscillators are bullies

Post by Grumble » Mon Jan 11, 2021 2:13 am

Thalassa wrote:
Mon Oct 19, 2020 2:53 pm
Image
That first peak can also be caused by moist (speculating...) as we all know that moisture conducts electricity and when your synth warms up, the moist evaporates (magically disappears)....

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Re: My oscillators are bullies

Post by Putte » Mon Jan 11, 2021 1:50 pm

Dave Peck wrote:
Sun Jan 10, 2021 3:40 pm
From the description, it sounds like this may be an issue related to the internal Sample & Hold circuitry in one of the keyboards. Possibly a capacitor needs to be replaced.

Some analog CV keyboards use an internal S/H circuit that is triggered with each note played to maintain the voltage after the key is released. This is necessary because once you let the key up, there's no actual connection and no pitch CV voltage signal any more, but you need the pitch CV to stay at whatever the last voltage was so that the last note played will continue to hold at the correct pitch. If this S/H circuit isn't working really well, it's output voltage can 'droop' over time, or in some cases can randomly fluctuate up & down.

One way to tell if this might be happening - after letting the oscs warm up for quite a while, connect the suspect keyboard to any osc and play a fairly high note which will send a fairly high DC pitch control voltage to the osc. Patch the osc direct to an output, no filter, no VCA, so it drones constantly. leave the synth alone for maybe ten minutes - don't touch the keyboard. Then, play THE SAME NOTE on the keyboard again while listening to the osc. If you hear the osc pitch suddenly jump up or down slightly, it indicates that the pitch CV had drifted and is being suddenly corrected when you press the key again, and the control voltage being sent to the osc is the problem, it is NOT the osc.
This a double MIDi keyboard. There is no S&H in it. The only S&H even remotely related is the dotcom in the upper left cabinet.

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Re: My oscillators are bullies

Post by Dave Peck » Mon Jan 11, 2021 2:23 pm

Putte wrote:
Mon Jan 11, 2021 1:50 pm
Dave Peck wrote:
Sun Jan 10, 2021 3:40 pm
From the description, it sounds like this may be an issue related to the internal Sample & Hold circuitry in one of the keyboards. Possibly a capacitor needs to be replaced.

Some analog CV keyboards use an internal S/H circuit that is triggered with each note played to maintain the voltage after the key is released. This is necessary because once you let the key up, there's no actual connection and no pitch CV voltage signal any more, but you need the pitch CV to stay at whatever the last voltage was so that the last note played will continue to hold at the correct pitch. If this S/H circuit isn't working really well, it's output voltage can 'droop' over time, or in some cases can randomly fluctuate up & down.

One way to tell if this might be happening - after letting the oscs warm up for quite a while, connect the suspect keyboard to any osc and play a fairly high note which will send a fairly high DC pitch control voltage to the osc. Patch the osc direct to an output, no filter, no VCA, so it drones constantly. leave the synth alone for maybe ten minutes - don't touch the keyboard. Then, play THE SAME NOTE on the keyboard again while listening to the osc. If you hear the osc pitch suddenly jump up or down slightly, it indicates that the pitch CV had drifted and is being suddenly corrected when you press the key again, and the control voltage being sent to the osc is the problem, it is NOT the osc.
This a double MIDi keyboard. There is no S&H in it. The only S&H even remotely related is the dotcom in the upper left cabinet.
Got it. But there is still a midi to CV converter between the keyboard and the modular, and that could be the source of the issue based on your description of how the problem follows the keyboard rather than following the osc. I suggest trying that same experiment I described anyway, to see if the analog voltage output from the midi to CV converter is working correctly or if it is drooping/drifting after a few minutes.

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Re: My oscillators are bullies

Post by Putte » Mon Jan 11, 2021 2:34 pm

Right, I will try that as soon as I get a chance. Its not so mich that it follows the keyboard, as the Pro solos.
They are, by the way, set to the exact same settings, as are the two MKE.

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Re: My oscillators are bullies

Post by Elahrairah » Wed Jan 13, 2021 8:04 pm

Grumble wrote:
Mon Jan 11, 2021 2:13 am

That first peak can also be caused by moist (speculating...) as we all know that moisture conducts electricity and when your synth warms up, the moist evaporates (magically disappears)....

If there's two transistors performing the linear-to-exponential, they will push in different directions, and a spike like that would be one warming up sooner than the other.

Need more datapoints between them to see if it's wobbling or spiking.

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