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KORG R3 effects issue

 
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desordenado



Joined: 20 Oct 2015
Posts: 7

PostPosted: Tue Oct 20, 2015 10:38 am    Post subject: KORG R3 effects issue Reply with quote

Hello,

I recently bought a secondhand Korg R3. Got it for low price because it has an issue which I was hoping to be able to repair and was looking for some help or advise on how to solve it.

The problem is with the effects section. When certain effects are enabled, typically modulation or delay effects, I randomly get something that sounds like clipping noises. The synth serial number is around 7K, so in theory does not suffer from the tempo issue that has been discussed already here. It also does not seem to be an issue on the analog output, as that would happen always and not only for patches with certain effects.

I saw people mentioning about the power supply being flaky:
http://alfredoblogspage.blogspot.com.es/2015/01/korg-r3-internal-switching-regulator.html

So that might be a good guess (certain effect taking too much power and causing issues on the regulator which affects the processors or memory). Does that sound like a good theory?

Anyways, the synth even without the effects is awesome, love it. I have been having a lot of fun with it.

Gorka
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voip
Platinum Member


Joined: 27 Nov 2014
Posts: 1585

PostPosted: Tue Oct 20, 2015 7:15 pm    Post subject: Reply with quote

It is possible for some combinations of effects on synths to cause overload. I don't know how much this affects the R3. That will depend on the circuit, particularly the amount of headroom designed into the internal signal paths. The possibility of unintended distortion is mentioned in the manual in relation to the resonance control.

The service manual can be downloaded and checking for a flaky PSU is not too difficult with a multimeter, if you can work out where to test. If you're not confident about doing it, ask someone who has some electronics experience. Even without a multimeter, the signs may be there, such as flickering LEDs, or the system rebooting for no reason. Also check that the power input connection is sound and that wiggling it around a bit doesn't cause the LEDs to flicker, or cause rustling sounds in the audio outputs.
.
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desordenado



Joined: 20 Oct 2015
Posts: 7

PostPosted: Tue Oct 20, 2015 8:33 pm    Post subject: Reply with quote

Thanks voip for your suggestions,

[quote]It is possible for some combinations of effects on synths to cause overload. I don't know how much this affects the R3.
[/quote]

Understand, but it does not seem to be the case here. Issue happens with the factory presets and completely randomly. You would expect the overload to happen more or less similarly every time you repeat the same key presses and that does not happen in my case, for me it is completely random.

[quote]The service manual can be downloaded and checking for a flaky PSU is not too difficult with a multimeter, if you can work out where to test. If you're not confident about doing it, ask someone who has some electronics experience. Even without a multimeter, the signs may be there, such as flickering LEDs, or the system rebooting for no reason. Also check that the power input connection is sound and that wiggling it around a bit doesn't cause the LEDs to flicker, or cause rustling sounds in the audio outputs.
[/quote]

There are no other signs of flaky power supply. I do have some electronics knowledge and did a quick check on the different power rails, but they seemed to be fine (voltages were in the right values), not sure if there is anything else I need to check.

Also checked with a cheap scope to see if there were spikes when the issue happened, but did not see any (not sure if they were no spikes or the scope is too cheap to show them correctly).

oh, I did run the internal test from the service manual and that returned no errors.
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voip
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Joined: 27 Nov 2014
Posts: 1585

PostPosted: Tue Oct 20, 2015 10:05 pm    Post subject: Reply with quote

OK, if the power supplies are ruled out, you need to look elsewhere. If the problem seems to be intermittent, it could be a dry solder joint somewhere, or an issue with one of the devices on the circuit board(s) handling the signals. Dry joints are often vibration sensitive.

Much of what happens in the R3 is in the digital domain, with just a handful of components handling analogue signals. If the effect is one of clipping, and clipping can clearly be seen on the scope, it might be worth looking at the analogue side of things from the D/A to the outputs. If the effect is more one of distortion caused by the signal level fluctuating wildly, rather than clipping, then it might be worth looking at the digital signal chain, RAM, CPU, effects processor. Rather more specialised test gear is required for this. The lack of errors from the internal test probably rules most of the digital circuitry out. Is the same sort of distortion seen on signals originating at the audio inputs to the R3. Are both channels affected simultaneously and equally when the distortion appears?

The answers to these kinds of questions should help to narrow down the source of the problem.
.
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desordenado



Joined: 20 Oct 2015
Posts: 7

PostPosted: Wed Oct 21, 2015 7:56 am    Post subject: Reply with quote

[quote]If the effect is one of clipping, and clipping can clearly be seen on the scope, it might be worth looking at the analogue side of things from the D/A to the outputs[/quote]

I feel it is happening in the digital domain, because once it happens I can also hear it in the repeats of the delay effect. If it was analog side issue I would only hear it once, as the DA is after the delay.

I did a search for cold solder joints by tapping in the board in suspected componencts (power supplies, RAMs, processor) but could not find a place which will force it to happen

[quote]Is the same sort of distortion seen on signals originating at the audio inputs to the R3. Are both channels affected simultaneously and equally when the distortion appears? [/quote]

good points... will check that Crying or Very sad
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thehighesttree
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Joined: 18 Nov 2011
Posts: 584
Location: Canada East

PostPosted: Wed Oct 28, 2015 5:36 pm    Post subject: Reply with quote

Before you rip your R3 apart any further: try using an external sequencer's tempo and set your R3's clock to "Ext MIDI" (or "Ext USB" if you're using a USB cable), then "WRITE" twice to save it to your Global Settings. Once your connections are set up correctly and the tempo LED responds to external changes, you'll be able to confirm--if the issue persists--that it has nothing to do with the jumping tempo bug.

I know you've mentioned that you don't feel it relates to that, but tempo-synced (by default) LFOs like those in many of the FX are where you'll feel that bug the hardest. I say this because the delays generally allow "zippy" sounds to be produced when you sweep the delay time knob, which is cool live but sucks anytime your values are randomly shifting around. I have a faulty R3 and negate the issue by syncing to an external clock, but without this it tends to do the same sort of spasmoidal stuff with BPM-synced LFOs and effects; the tempo shifts and (being BPM-locked) the LFOs can't compensate, so they glitch and reset as they would if you changed the tempo manually, generating a brief, unpleasent s**t-tone as it resets the LFO and "zaps" the attached variable.

Hopefully you're in a situation where an external tempo isn't a dealbreker, and that this is the only issue with the machine! Given the symptoms you described, there's certainly hope that that's it. MIDI-slave it and let us know if that kills the issue!
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desordenado



Joined: 20 Oct 2015
Posts: 7

PostPosted: Wed Oct 28, 2015 9:10 pm    Post subject: Reply with quote

Thanks for the tip. I will try. External tempo would be OK for me (much better than ripping apart the synth).
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desordenado



Joined: 20 Oct 2015
Posts: 7

PostPosted: Thu Oct 29, 2015 8:19 am    Post subject: Reply with quote

I did a quick test configuring the clock for Ext MIDI, but without any actual MIDI device sending clock and I could still hear the noises. The external clock was definately well set cause Arpegiator stopped triggering as I did the change
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whirlwind_megaspeed



Joined: 21 Dec 2017
Posts: 1

PostPosted: Thu Dec 21, 2017 2:33 pm    Post subject: Reply with quote

I have a problem with an R3 I just bought that sounds _exactly_ like the one you described, did you manage to fix it? Or did you sell it to someone who sold it to someone who sold it... To me? Smile

I was figuring the glitch might come from a bad RAM chip, possibly the SRAM of the DSP. I didn't open it yet, but looking at the service manual things seem fairly well laid out, I might just try my hand at SMT soldering. I'll have to find something to practice on before, though...

There's also that DAC upgrade mod I was thinking about. We'll see.
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desordenado



Joined: 20 Oct 2015
Posts: 7

PostPosted: Sat Dec 23, 2017 9:52 pm    Post subject: Reply with quote

I did not manage to fix it and did not sell it either. I live with it. Bothers me, but it is OK, I am not a pro musician anyway.

I agree with you, the issue indeed looks like it could be from a bad RAM chip. If you manage to fix it, please let me know
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desordenado



Joined: 20 Oct 2015
Posts: 7

PostPosted: Tue Feb 06, 2018 4:46 pm    Post subject: Reply with quote

Mine has just developed another issue. It now randomly goes out of tune. You might be playing and suddenly you hear the pitch dropping (always seems to go down) and stay dropped. Have not investigated much on it as it is random, maybe I can still compensate it with the overall tune setting, but I think I will get rid of my R3.

The glitch in the effects was not bothering me much for the use I make of it, but detuning not good.

@whirlwind_megaspeed any luck with yours?
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X-Trade
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Joined: 14 Feb 2006
Posts: 6489
Location: Reading, UK

PostPosted: Mon Sep 03, 2018 11:37 am    Post subject: Reply with quote

desordenado wrote:
Mine has just developed another issue. It now randomly goes out of tune. You might be playing and suddenly you hear the pitch dropping (always seems to go down) and stay dropped. Have not investigated much on it as it is random, maybe I can still compensate it with the overall tune setting, but I think I will get rid of my R3.

The glitch in the effects was not bothering me much for the use I make of it, but detuning not good.

@whirlwind_megaspeed any luck with yours?


Pitch issues are usually down to a fault with the pitch bender.
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