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How can I design these improvements for the crackle box?
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amundsen



Joined: Jun 02, 2009
Posts: 11
Location: Brussels, Belgium

PostPosted: Wed Feb 28, 2018 8:13 am    Post subject: How can I design these improvements for the crackle box? Reply with quote  Mark this post and the followings unread

Hello,

I would like to build a crackle box (kraakdoos) with a line output.

I plan to start from this schematics from EAM.se.

There was a discussion on that topic previously but the guy who said he'd try to connect a line output over an opto-isolator never reported back if it worked and all the people on this thread seem to have left the forum (the topic is more than 10 years old...).

Also, I'd be interested to power the circuit from a wall adapter rather than from a battery. Obviously the choice of the battery in the original design was based on safety considerations. But there are other circuits which imply the electric connection of the user as a resistor (resistive touchscreens for instance) and no one has been killed by such circuits. So I guess it's possible to protect the user, but how? I was thinking about an isolation transformer but is it the right solution? Is there a better one?

Thank you in advance.
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Grumble



Joined: Nov 23, 2015
Posts: 727
Location: Netherlands
Audio files: 21

PostPosted: Wed Feb 28, 2018 8:22 am    Post subject: Reply with quote  Mark this post and the followings unread

I would take a potentiometer (10k -100k is ok) and connect it over the loudspeaker, the runner is your output, wile the point of the speaker not connected to the capacitor will be your "ground"
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LFLab



Joined: Dec 17, 2009
Posts: 470
Location: Rosmalen, Netherlands

PostPosted: Wed Feb 28, 2018 11:02 am    Post subject: Reply with quote  Mark this post and the followings unread

I recently did a cracklebox:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

I do not think safety is directly an issue with using a wallwart adapter (if done safely), but I do think that since the cracklebox takes advantage of "less than optimal" behaviour of the opamp, source impedance of the PSU is a key aspect of the sound. To this end I made a provision to put a resistor in series with the supply. If you are using an external supply, I'd also do that.
As for a line out, I also read that thread so I think I am going to use a microphone if I want to record, rather than a line out. I think this will add some expressiveness, especially in the volume, because that does not vary much when playing the touch surfaces.

Let me know (via PM) if you want a PCB, I have a few left.

Here's first trial:
https://youtu.be/08GPv87Wfn4
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amundsen



Joined: Jun 02, 2009
Posts: 11
Location: Brussels, Belgium

PostPosted: Thu Mar 01, 2018 2:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello,

@Grumble: I don't understand the meaning of "runner" in this context. Can you explain please?

@LFLab, one question: is there any specific reason for you to use styrofoam capacitors or is it simply because you have them in your supply?

Regarding your plan to use a microphone, I like the ides of changing the volume by miking but don't you fear to loose all the lower frequency range you could have with a line ourput compared to the limited range provided by a tiny speaker?
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LFLab



Joined: Dec 17, 2009
Posts: 470
Location: Rosmalen, Netherlands

PostPosted: Thu Mar 01, 2018 5:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, I just used whatever, was planning to use el cheapo ceramics.
You make a good point on the low end, I used a tiny speaker for the first build, and it definitely needs something bigger, else it is just squeaks.
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amundsen



Joined: Jun 02, 2009
Posts: 11
Location: Brussels, Belgium

PostPosted: Thu Mar 01, 2018 5:12 am    Post subject: Reply with quote  Mark this post and the followings unread

By the way I have assembled this kit which is nice because you don't need the 709 op-amp but I think there's no proper impedance adaptation on the minijack socket because I got no signal when used as line output whereas I have something when connecting headphones.
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LFLab



Joined: Dec 17, 2009
Posts: 470
Location: Rosmalen, Netherlands

PostPosted: Thu Mar 01, 2018 6:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Interesting, would like to see the schematic.
However, I do think you need an old opamp to accurately replicate the behaviour (although the rakit does make nice noises). On the original cracklebox, you can just use the signal which goes to the speaker (just disconnect speaker), but apparently, the speaker (and enclosure presumably) does add a certain "je ne sais quoi".
Nice kit though, I do think you need a speaker which is bigger, mine was bigger than what's in the kit, and the original had a proper speaker from Visaton.
They no longer have the kit on the website:
https://www.mijnwebwinkel.nl/winkel/steim-webshop/a-45371328/products/cracklebox/
Pity, should have noted the type of speaker. But it was basically a small broadband speaker 2.5" or so.
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Grumble



Joined: Nov 23, 2015
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PostPosted: Thu Mar 01, 2018 7:36 am    Post subject: Reply with quote  Mark this post and the followings unread

amundsen wrote:

@Grumble: I don't understand the meaning of "runner" in this context. Can you explain please?

"runner" is the connection of the potentiometer that "runs" along the resistor when you turn the shaft.

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amundsen



Joined: Jun 02, 2009
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Location: Brussels, Belgium

PostPosted: Thu Mar 01, 2018 7:51 am    Post subject: Reply with quote  Mark this post and the followings unread

Grumble wrote:
amundsen wrote:

@Grumble: I don't understand the meaning of "runner" in this context. Can you explain please?

"runner" is the connection of the potentiometer that "runs" along the resistor when you turn the shaft.


Okay! Thanks for the info. I couldn't find it on the Web.
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LFLab



Joined: Dec 17, 2009
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PostPosted: Thu Mar 01, 2018 9:08 am    Post subject: Reply with quote  Mark this post and the followings unread

"wiper"
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Grumble



Joined: Nov 23, 2015
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PostPosted: Thu Mar 01, 2018 11:00 am    Post subject: Reply with quote  Mark this post and the followings unread

head banging monitor

In Dutch this is called the loper (translate: runner)...

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amundsen



Joined: Jun 02, 2009
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Location: Brussels, Belgium

PostPosted: Fri Mar 02, 2018 12:31 am    Post subject: Reply with quote  Mark this post and the followings unread

LFLab wrote:
Interesting, would like to see the schematic.


I think it's simply a reproduction of the 709's internal schematics (see attachment).


LM709.jpg
 Description:
Schematics of the LM709 (from TI)
 Filesize:  44.81 KB
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This image has been reduced to fit the page. Click on it to enlarge.

LM709.jpg


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LFLab



Joined: Dec 17, 2009
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PostPosted: Fri Mar 02, 2018 1:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, that's what I saw on their website as well, I do wonder if that captures all of the interesting behaviour (well, it'll probably add some of it's own Smile ).
Regardless, 709's are really not that hard to get.
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