Noise Toaster AREG issues

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Spheremonger
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Noise Toaster AREG issues

Post by Spheremonger » Mon Feb 08, 2021 11:31 am

Hi. Pretty new to all this, so after learning a bit of theory and doing a couple of other projects I thought I'd build a Noise Toaster as a way of learning more. On the whole it went well, but I have an AREG problem I just can't work out: with LFO Mod depth turned down, VCO, VCA and filter all switched to AR I just get a constant tone. AR Mod on the VCO causes a change of pitch but nothing else seems to happen. The repeat/1 shot switch and the attack and decay pots don't do anything and the push button momentarily increases the pitch but does nothing else (I'm guessing this is the one part that's working by sending extra voltage to the oscillator). Pin 14 on the op amp isn't showing anything so I replaced it just in case - no joy.
As far as I can tell all components are functioning and the wiring is correct, but I'm obviously wrong about something here.
If anybody who knows the NT can give me any advice on this, it would be greatly appreciated.
Thanks

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Bodo1967
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Re: Noise Toaster AREG issues

Post by Bodo1967 » Tue Feb 09, 2021 3:05 am

Does the AREG as such work as it should when checked at the "ARG" test point, i.e. does it go up and down again, or does it just go up and stay there (just to make sure - if I understood you correctly the latter is the case here)?

If in doubt, you can check this with an oscilloscope or even a DVM at test point "ARG". Best set the AREG gate mode to "repeat" to do so, as this saves you triggering it manually over and over again. If in doubt whether this switch is actually working, you may hardwire it for testing purposes. Voltage at the "ARG" test point should go up and down once upon pressing the "manual gate" pushbutton when the switch is set to "manual gate", or cycle as an LFO when the switch is set to "repeat". Best set it to rather fast values (pots turned down) for testing with an oscilloscope, as it is then easier to watch; do not set it too fast when testing it with a DVM so it has time to react.

Check the manual gate/repeat switch for proper function with a continuity tester (personal experience: I encounter faulty toggle switches every now and then).

If it does not go up and down but stays up (from your post I take it that's the case here) I'd double check the FET (Q9; 2N5457) and its direct environment first.
If it does oscillate, proceed to the next switches (selectors for the VCO and VCA modulation sources).
... why buy it for $100 when you can build it yourself for $150?

Spheremonger
Learning to Wiggle
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Joined: Mon Feb 08, 2021 10:31 am

Re: Noise Toaster AREG issues

Post by Spheremonger » Tue Feb 09, 2021 10:21 am

Hi, thanks for the help.
So, definitely no oscillation at ARG. I've gone through the components and re-flowed the solder joints as some of them looked a bit patchy, but other than the button not doing anything now there's no change. Switches and wires all seem ok. I've tested everything in circuit as much as I can but I think I might have to resort to removing things to check (I might have a dodgy JFET but I can't get a stable reading in circuit).
As far as I can tell, the lfo is still driving the oscillator... should that be happening? Its possible (or probable) that I'm misunderstanding the circuit, but if the oscillator is set to AR, the lfo mod depth is at zero and the AREG is set to manual, shouldn't there be silence until the button is pressed?
Thanks again for the help, I'm learning a lot from it not working, so I guess that's a good thing.

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Bodo1967
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Re: Noise Toaster AREG issues

Post by Bodo1967 » Wed Feb 10, 2021 2:51 am

Spheremonger wrote:
Tue Feb 09, 2021 10:21 am
So, definitely no oscillation at ARG. I've gone through the components and re-flowed the solder joints as some of them looked a bit patchy, but other than the button not doing anything now there's no change. Switches and wires all seem ok. I've tested everything in circuit as much as I can but I think I might have to resort to removing things to check (I might have a dodgy JFET but I can't get a stable reading in circuit).
Try to monitor the g(ate) pin of the JFET. It should react to manual triggering even in case of a faulty JFET, but it won't cycle (that won't happen if the op amp output U2-D pin 14) isn't fed back to the input via the maual/repeat switch).
Spheremonger wrote:
Tue Feb 09, 2021 10:21 am
As far as I can tell, the lfo is still driving the oscillator... should that be happening? Its possible (or probable) that I'm misunderstanding the circuit, but if the oscillator is set to AR, the lfo mod depth is at zero and the AREG is set to manual, shouldn't there be silence until the button is pressed?
The VCO as such will work all the time. The VCO isn't set to AR; that switch just selects whether you want the VCO to be modulated by the AREG or not (VCO frequency change similar to that by the LFO - if you set the AREG to repeat or cycling mode, it works as a second LFO with adjustable - by the attack and decay settings - shape).

The block diagram right at the beginning may also help understanding the structure of this little box :D. Also, the "Make: Analog Synthesizers" book featured in the upper left corner of the home page is also a good read. It describes the Noise Toaster very thoroughly and in detail, and has a lot more to offer - including Ray's never ending humor. I have it at home myself and can definitely recommend it.
... why buy it for $100 when you can build it yourself for $150?

Spheremonger
Learning to Wiggle
Posts: 3
Joined: Mon Feb 08, 2021 10:31 am

Re: Noise Toaster AREG issues

Post by Spheremonger » Wed Feb 10, 2021 2:38 pm

Ok, got it. I'll try that. Thanks for the help

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