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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
New person needs help with noise toaster
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Allison



Joined: Apr 23, 2013
Posts: 6
Location: Washington, Dc

PostPosted: Wed May 01, 2013 7:05 pm    Post subject: New person needs help with noise toaster Reply with quote  Mark this post and the followings unread

Hello,
I'm just getting into DIY synth... I have a technical background, but most of the work I do these days is on a computer, and I haven't built anything since grad school. Here's my problem.

My end goal is to build a drone synthesizer, with a few VCOs, filters, and a simple mixer. I've been working with the noise toaster design for its relative simplicity. Thus far, I've built the expo converter and the ramp core of the VCO. I've left out the inputs from the LFO and ARG, as well as the sync (C6 and R24). For ease of testing, I've used two different lm324s just so I can see what I'm doing. The only substitution I've made is an MPF102 instead of the 2N5457. I also used a 1N4148 diode.

My problem is that the frequency of the output sawtooth is way too high, and I only get a change in frequency over about 1/3 of the pot. The frequency ranges between 17-44kHz, which obviously isn't terribly useful. If I replace C2 with a .01uF cap, it shifts to 2kHz-16kHz. I can increase my range a bit more by increasing R2, but I feel like I'm missing a fundamental problem here. The other issue is that the peak-to-peak voltage for the output varies with the frequency, which is also problematic.

Does anyone have any troubleshooting hints? I figured this might be an obvious problem for someone with more experience.

Thanks!!
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Allison



Joined: Apr 23, 2013
Posts: 6
Location: Washington, Dc

PostPosted: Thu May 02, 2013 7:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

I should note that I will be happy to post any schematics or measurements... If anyone would be kind enough to help....
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elmegil



Joined: Mar 20, 2012
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Location: Chicago
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PostPosted: Thu May 02, 2013 9:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

I haven't built a Noise Toaster, but I've built a Soundlab Mini Synth and troubleshot another. They not identical VCOs but somewhat similar, particularly the FET for the frequency control.

Have you looked at the waveshape? That might give you some clues.

Have you built this on a breadboard? If not I'd recommend re-checking for shorts/solder bridges.

Are your transistors matched?

Triple check R3 to be sure it's what's supposed to be there. I had frequency issues with the SLMS when I had incorrect resistors in the same sort of place (R56), and initially I tried to solve that with a cap the same way you have.
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diablojoy



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PostPosted: Thu May 02, 2013 9:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

hi and welcome
try removing the mpf102 from the circuit and rechecking the oscillator cores frequency with out it.
while the MPF102 shares the same pin out as 2n5457 there are slight differences also because you havent completed the rest of the sync circuitry it may be effecting things

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Allison



Joined: Apr 23, 2013
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Location: Washington, Dc

PostPosted: Fri May 03, 2013 7:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi - and thank you!

How vital is transistor matching for this? Mine are not. I thought it was just important from a temperature stability perspective... But I don't know what I'm talking about.

I think the problem is with my exponential converter. I've tried putting the portion of the circuit in a simulator, just so I can figure out how it works, and it doesn't seem to be behaving like I expect - I'll post a link later. I really appreciate the advice!
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elmegil



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PostPosted: Fri May 03, 2013 8:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

The matching is involved in how the expo converter works. I have not yet grokked expo converters in fullness, so I can't explain, but you might give it a shot.

Ian Fritz has a great article about a pretty simple method that you can throw up on a breadboard to do matching:

http://home.comcast.net/~ijfritz/projects/transmat001.pdf
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bubzy



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PostPosted: Fri May 03, 2013 10:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don't recommend throwing up on breadboard Very Happy
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elmegil



Joined: Mar 20, 2012
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PostPosted: Sat May 04, 2013 6:10 am    Post subject: Reply with quote  Mark this post and the followings unread

bubzy wrote:
I don't recommend throwing up on breadboard Very Happy


Sounds like the voice of experience Wink
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Zodiak



Joined: May 20, 2007
Posts: 245
Location: Gillingham, Kent UK

PostPosted: Sun May 05, 2013 8:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello, looking at the schematic I doubt that the transistor matching will cause your problem, indeed unless you are going to use it to play melodies I don't think you need to bother. Smile

The lack of sync circuit link shouldn't make a difference either, most of the time you will probably have it switched out anyway.

The missing feed from the ARG and LFO shouldn't make much odds either.

(1) Check that U1 pins 3 12 and 10 are all at half the battery voltage.

(2) The try measuring the voltage between UC1 pin 8 and pin 10, assuming a 9V battery it should vary from about 90mV to -150mV. If not then check out everything to the left of U1 on the schematic.

I haven't really worked out how the exp convertor works, so next I would remove U2 and U3 to see if that helps. After that its down to checking the components one by one Crying or Very sad

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Allison



Joined: Apr 23, 2013
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PostPosted: Sun May 05, 2013 5:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thank you!! I have a lot of things to work with now... as soon as my 3 kids under 5 leave me alone long enough.

Working this out on the simulator, I think I do need the feed from the ARG (or, rather, a resistor tied to the virtual ground as input into the summer...)

Have you guys ever used these online simulators? They are seriously awesome. Here's a link to the expo converter... that is working as predicted now.

https://www.circuitlab.com/circuit/z6u3d9/noisetoaster-expo-converter/
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elmegil



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PostPosted: Sun May 05, 2013 7:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have tried circuit lab, but I'm not terribly clear on how the simulations are intended to work.

I use this one a lot: http://www.falstad.com/circuit/

It simulates pretty much real time, but doesn't let you save your work, so it's mixed.
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Zodiak



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PostPosted: Mon May 06, 2013 4:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Allison wrote:
Have you guys ever used these online simulators? They are seriously awesome. Here's a link to the expo converter... that is working as predicted now. /

I haven't tried that one, but I agree they can be invaluable, especially in a situation like this so you can compare voltages on the simulator to the ones you are getting to find a problem. Smile

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jukingeo



Joined: Oct 24, 2007
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Location: The dark side of the moon

PostPosted: Sat Sep 07, 2013 5:56 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
bubzy wrote:
I don't recommend throwing up on breadboard Very Happy


Sounds like the voice of experience Wink


Hmmm, good words to live by. In addition, I don't recommend baking or eating your BREADboard either.
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autowitch



Joined: Nov 19, 2011
Posts: 10
Location: Denver, CO

PostPosted: Sun Oct 06, 2013 6:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

jukingeo wrote:


Hmmm, good words to live by. In addition, I don't recommend baking or eating your BREADboard either.


So, that's what I've been doing wrong!
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