MFOS Noise Toaster DIY Troubleshooting

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MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Thu Jan 23, 2020 1:08 am

Hi Wigglers,

ive built the Noise Toaster out on stripboard, both using my own layout and a layout ive found online.

Both builds exhibit the same problem. The AR Gen will not apply to the VCF cutoff. Also, the top LFO shape will also not apply to the cutoff whereas the square wave will.

The ARGen is working fine when applied to VCO pitch, or VCA, and LFO is working fine on VCO pitch. So I know the AR is looping and triggering. But it will not apply to VCF cutoff. It works correctly in both manual and repeat mode when applied to VCO.

At this point ive done two complete builds with different layouts, have replaced all front panel controls and rewired the panel 3 times. Im confident its not a layout or build problem.

Heres the confusing bit. Using the trigger button will activate the ARgen to correctly mod the VCF. But it will not work in repeat mode. So I know the signal path, VCF and ARGen function but for some reason it will not activate the VCF cutoff in repeat mode.

The only thing i havent replaced is the 2N5457s. Would fake transistors that arent putting out the correct values fail to trigger in this way? How can I test this?

Are there any other tests I can perform to get the ARGen to loop in VCF mode? Any help is massively appreciated.

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Thu Jan 23, 2020 8:33 pm

Quick bump.

Any and all theories about what might be causing this issue is very welcome.

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by guest » Fri Jan 24, 2020 4:02 am

can you give a link to the stripboard layout youre following? and maybe put up some pictures of the build?
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Re: MFOS Noise Toaster DIY Troubleshooting

Post by Bodo1967 » Fri Jan 24, 2020 4:09 am

Do you have an oscilloscope so you can monitor the signal path? That would be very valuable as to find out where the problem actually lies.
... why buy it for $100 when you can build it yourself for $150?

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Fri Jan 24, 2020 5:21 am

guest wrote:
Fri Jan 24, 2020 4:02 am
can you give a link to the stripboard layout youre following? and maybe put up some pictures of the build?
Thanks for the reply. Heres one of the layouts which i know is verified as working. Im pretty satisfied its not a build or layout issue as Ive gone over the schematics and layouts many times. Ive resoldered every joint and replaced every component between builds except the 2n5457. Of course its possible, but prob unlikely.

I should prob point out that Ive got a whole rack of diy stripboard modules that work perfectly, so im pretty experienced with troubleshooting diy builds. I am very much a builder and have very little theory, so this has got me stumped though.

Ive also built it out with my own completely different layout and got exactly the same result. This leads me to think the transistors might be at fault.

http://electro-music.com/forum/topic-68 ... highlight=

This is what I know:
- Envelope works perfectly when applied to vco mod, and vca. It repeats and triggers manually, and the attack and decay knobs work perfectly.
- VCF also works perfectly for the square LFO shape, but not the shaped waveform. All LFO waveforms apply to the VCO and respond as expected.
- ARGEn triggers VCF perectly in manual mode, so the circuit path is working. It just will not trigger it in repeat mode.

Id love some theories about how this is actually possible.

Would an out of spec tranny produce this result? What would make the VCF cutoff not respond to a working AR signal? The same signal when applied to VCO works fine.

Does anyone have a Noise Toaster they can provide some voltage readings on the ARGen output points so I can compare?

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Fri Jan 24, 2020 5:25 am

Bodo1967 wrote:
Fri Jan 24, 2020 4:09 am
Do you have an oscilloscope so you can monitor the signal path? That would be very valuable as to find out where the problem actually lies.
What are you specifically suggesting?

The signal path checks out according to the schematic, and by continuity tests. The same AR signal works fine when applied to vco, just not vcf. The LFO also works when applied to VCF.

So the ARGEN output just stops dead when it hits the VCF.But the exact same cable connected to VCO works. The ARGEN signal just seems to disappear when hitting the cutoff. Connecting it directly and bypassing the switches does nothing.

I do have an oscope, so would love more info about what youre suggesting.

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by Bodo1967 » Fri Jan 24, 2020 5:31 am

feedbackl00p wrote:
Fri Jan 24, 2020 5:25 am
I do have an oscope, so would love more info about what youre suggesting.
I had considered it possible that the problem was located somwehere at the switches (faulty switch, miswiring, whatever). Apparently - from what I read in your previous post now - that seems not to be the case, however.
... why buy it for $100 when you can build it yourself for $150?

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by guest » Fri Jan 24, 2020 5:45 am

my first guess is a bad mod depth pot on the VCF. does the LFO rate indicator LED still blink when you have the LFO set to control the VCF? does this blinking change at all depending upon the waveform selected. for square wave, which does work, does the blinking change at all when you switch between VCF and VCO as its output destination?
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Re: MFOS Noise Toaster DIY Troubleshooting

Post by guest » Fri Jan 24, 2020 5:56 am

also, does the AR signal still control the VCA when its patched to control the VCF? or does it stop altogether? the thing thats odd to me, is that the square wave from the LFO can control it, but the other signals can not. the main difference in that signal is that its stronger. so its possible the JFET on teh VCF is just not biased correctly, or is bad, but its also possible that there is too smal of an impedance someplace at the input, and the signal is getting loaded down when connected. the latter would cause the signal to degrade, which would be noticed in other areas where that signal is sent.
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Re: MFOS Noise Toaster DIY Troubleshooting

Post by guest » Fri Jan 24, 2020 6:20 am

use your scope to take a look at the signals on the JFET. this is probably best done without audio going through the VCF. turn the mod pot full up. the source should be at 4.5V, with a bit of signal on it (10mV? maybe a bit more?), and the gate should be a bit under 4V, with +/-300mV signal or so.
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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Fri Jan 24, 2020 6:25 am

guest wrote:
Fri Jan 24, 2020 5:56 am
also, does the AR signal still control the VCA when its patched to control the VCF? or does it stop altogether? the thing thats odd to me, is that the square wave from the LFO can control it, but the other signals can not. the main difference in that signal is that its stronger. so its possible the JFET on teh VCF is just not biased correctly, or is bad, but its also possible that there is too smal of an impedance someplace at the input, and the signal is getting loaded down when connected. the latter would cause the signal to degrade, which would be noticed in other areas where that signal is sent.
Very intriguing. Ill test the AR controlling the VCA when patched to the VCF and let you know. Many thanks for the suggestion.

Do you happen to know if the trigger button bypasses the JFET? It seems important that the ARGEN will affect the VCF in manual, but not on repeat. Or is it maybe that its getting a full wack of BP power due to its direct connection to BP that is somehow being lost in repeat mode when applied to VCF?

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Fri Jan 24, 2020 6:26 am

guest wrote:
Fri Jan 24, 2020 6:20 am
use your scope to take a look at the signals on the JFET. this is probably best done without audio going through the VCF. turn the mod pot full up. the source should be at 4.5V, with a bit of signal on it (10mV? maybe a bit more?), and the gate should be a bit under 4V, with +/-300mV signal or so.
Thanks again, ill measure these.

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by guest » Fri Jan 24, 2020 6:36 am

yeah, thats the same as the LFO square wave - the signal under manual control is about 2x larger. so this again points to either a low impedance connection, or a poorly biased or broken JFET. the latter is more likely, as JFET parameters have a large variation, so it could easily not be biased correctly.
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Re: MFOS Noise Toaster DIY Troubleshooting

Post by EATyourGUITAR » Fri Jan 24, 2020 10:00 am

fake or damaged 2N5457 are very common. especially if you did not wear protection when handling your 2N5457. like guest said, they also have a lot of variation in manufacturing. you could switch to a different supplier and it would probably fix it regardless of which of these 3 scenarios you are in.
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Re: MFOS Noise Toaster DIY Troubleshooting

Post by emmaker » Fri Jan 24, 2020 12:58 pm

feedbackl00p wrote:
Thu Jan 23, 2020 1:08 am
Both builds exhibit the same problem. The AR Gen will not apply to the VCF cutoff. Also, the top LFO shape will also not apply to the cutoff whereas the square wave will.

Heres the confusing bit. Using the trigger button will activate the ARgen to correctly mod the VCF. But it will not work in repeat mode. So I know the signal path, VCF and ARGen function but for some reason it will not activate the VCF cutoff in repeat mode.

Noise Toaster Strip Board
Are you sure that the behavior isn't what's described in the Noise Toaster Strip Board with regards to mod pot and R44?

<edited changed Q8 S to Q8 G>
With a scope probe all pins on S6, R38 pin 2, Q8 G and Q8 D to see what's going on.

A number of transistors/FETs don't have standard pin outs. Get the data sheet for the FETs from the vendor that makes them and check that the FETs you used are in right?

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Sun Jan 26, 2020 8:25 pm

emmaker wrote:
Fri Jan 24, 2020 12:58 pm
feedbackl00p wrote:
Thu Jan 23, 2020 1:08 am
Both builds exhibit the same problem. The AR Gen will not apply to the VCF cutoff. Also, the top LFO shape will also not apply to the cutoff whereas the square wave will.

Heres the confusing bit. Using the trigger button will activate the ARgen to correctly mod the VCF. But it will not work in repeat mode. So I know the signal path, VCF and ARGen function but for some reason it will not activate the VCF cutoff in repeat mode.

Noise Toaster Strip Board
Are you sure that the behavior isn't what's described in the Noise Toaster Strip Board with regards to mod pot and R44?

<edited changed Q8 S to Q8 G>
With a scope probe all pins on S6, R38 pin 2, Q8 G and Q8 D to see what's going on.

A number of transistors/FETs don't have standard pin outs. Get the data sheet for the FETs from the vendor that makes them and check that the FETs you used are in right?
The FETS are in correctly according to the datasheet, i made that error earlier and updated all the layouts.

As far as I understand you should be able to repeatedly modulate the cutoff on any input with the repeating ARgen. If someone has a stock Noise Toaster can they please confirm this?

Many thanks for the probing suggestions. Im hoping to get back to this project tonight and go through my list of things to look at. Ill report back.

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Tue Feb 04, 2020 10:05 pm

Ok Ive finally found some time to knock off this project. Ill be replying separately to posters that have helped me directly.

Ive gone back to using my own modular layouts for ease of building and editing, attached.

Its a bit inefficient in terms of component use (ie 6 x LM324 instead of 2) but the whole build is about $25 from mouser including stripboard. The original idea was to use one of the existing mods that add patch cables as a way to build a battery powered drone box with multiple oscillators and lfos etc.

Its based on the schematics on the Make Electronics Analog Synth book, and on the slightly differently laid out schematics on the MFOS website.
Schem1
schem2

The front panel wiring and connections are exactly the same as here.

Current Issues:
- The ARG will not modulate the VCF in repeat mode. It does work when pushing manual button.
- The LFO will not modulate the VCF in anything other than the square LFO shape. Square LFO appears to modulate Cutoff correctly.
- ARGen repeat doesnt modulate VCA. Setting it to manual mode and pressing the button makes it work correctly.

Everything else works. The Argen and LFO shapes appear to modulate the VCO correctly.
Noise Toaster Collectedv2.png
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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Tue Feb 04, 2020 10:12 pm

guest wrote:
Fri Jan 24, 2020 5:45 am
my first guess is a bad mod depth pot on the VCF. does the LFO rate indicator LED still blink when you have the LFO set to control the VCF? does this blinking change at all depending upon the waveform selected. for square wave, which does work, does the blinking change at all when you switch between VCF and VCO as its output destination?
The led does still blink when its set to control the VCF.
Blinking doesnt appear to change based on waveform.
Blinking doesnt change when switching between VCF and VCO as output.

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Tue Feb 04, 2020 10:38 pm

guest wrote:
Fri Jan 24, 2020 6:20 am
use your scope to take a look at the signals on the JFET. this is probably best done without audio going through the VCF. turn the mod pot full up. the source should be at 4.5V, with a bit of signal on it (10mV? maybe a bit more?), and the gate should be a bit under 4V, with +/-300mV signal or so.
OK so the Gate (pin3) has 1.5v.

Neither the drain or source has any measureable voltage on them. This feels significant!

Just to add that the modules themselves are getting +4.2v and -4.15v. Without the front panel plugged in its at +4.4v/-4.4v.

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by guest » Tue Feb 04, 2020 11:12 pm

what are you using for your ground reference on this measurement? 1.5V is way too high if youre using signal ground. if youre using the battery/wallwart ground, then increase R44 to 220k and see if it makes a difference.
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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Wed Feb 05, 2020 5:10 am

guest wrote:
Tue Feb 04, 2020 11:12 pm
what are you using for your ground reference on this measurement? 1.5V is way too high if youre using signal ground. if youre using the battery/wallwart ground, then increase R44 to 220k and see if it makes a difference.
Im using the virtual ground of the psu module(4.5v). Im just measuring this with a multimeter as my scope currently has issues.

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Wed Feb 05, 2020 5:39 am

guest wrote:
Tue Feb 04, 2020 11:12 pm
what are you using for your ground reference on this measurement? 1.5V is way too high if youre using signal ground. if youre using the battery/wallwart ground, then increase R44 to 220k and see if it makes a difference.
Have changed R44 to 220k. Now the gate pin oscillates between 1v and 2v.

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Wed Feb 05, 2020 5:47 am

Something else Ive just noticed.

Turn unit on, vco to filter off, noise to filter on. Envelope set to repeat, VCF set to Areg.

The unit will sweep the cutoff once at the correct AReg settings as soon as I turn it on, then will stop. Ive verified this by changing the attack and decay settings, setting it to manual and listening to the envelope shaping the white noise, then turning the unit off and on again.

At startup it does sweep the cutoff once, but then stops.

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Re: MFOS Noise Toaster DIY Troubleshooting

Post by guest » Wed Feb 05, 2020 10:41 am

it sounds like a bad JFET, or R45 isnt soldered to BN. measure the voltage on either side of R45, and make sure its at -4.5V on the opposite end from the JFET. the JFET gate should never be more than 0.7V or so above the source, so 1.5V is way too much.
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Re: MFOS Noise Toaster DIY Troubleshooting

Post by feedbackl00p » Wed Feb 05, 2020 7:03 pm

guest wrote:
Wed Feb 05, 2020 10:41 am
it sounds like a bad JFET, or R45 isnt soldered to BN. measure the voltage on either side of R45, and make sure its at -4.5V on the opposite end from the JFET. the JFET gate should never be more than 0.7V or so above the source, so 1.5V is way too much.
OK so the BN side of R45 measures -4.3v and the JFET side measures about -.8v to -1.7v.

From what youre saying this points to a dodgy JFET? Is there any rig i can build to verify this? Ive been looking at transistor matching circuits but the theory is over my head.

What do you think about the behaviour of the argen sweeping the filter correctly once on startup, but then stops?

Also, is there any simple way to substitute a different FET? I spent several hours yesterday looking at substitutes and Im none the wiser. Ive seen several suggested replacements but Im not sure that they are applicable in the ways that matter.

Do you know of any source for 2n5457s? I bought mine off ebay, so i now assume they are a rebadged something else. Mouser has them, but they are $2 eah which seems ridiculous.

Anyhoo, thanks muchly for your help in getting to the bottom of this, its been really instructive.

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