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 Forum index » DIY Hardware and Software » Musical Interfaces
HELP - baby 8 sequencer
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sfshrimp



Joined: Jun 07, 2017
Posts: 3
Location: San Francisco

PostPosted: Wed Jun 07, 2017 11:08 am    Post subject: HELP - baby 8 sequencer
Subject description: Having a problem making it work
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Hi, I'm an electronics newbie, and am trying to build a version of the baby 10 sequencer (see schematic) with a 555 timing chip and 4017 decade counter to control a 555 oscillator. I'm having some problems getting mine to work fully - all the LEDs light up in sequence, I am able to reset the chip to change the number of steps, and I can change the tempo, volume, and make sound come out.

The problem I am having is that certain steps are making tones I don't want. If turn down all the pots to zero - the first and last steps always make a different tone, as well as step 5. Example: if I make the sequence 8 steps long - tone 1,5,8 will be make different tones than all the rest.

I checked the diodes, tried replacing them, doesn't change anything. Same with putting a different pot in the place of 1,5,8. The pots I am using are 10K (for v3-12), a 470K trim pot for tempo control. Scratching my head on why I can't get this to work. I also noticed that the pots don't control a huge range of octaves, not sure if this is a limitation of the 555 chip. Any ideas on how to fix? This is starting to drive me nuts because it should be a simple circuit. Evil or Very Mad



Schematic:

https://hackadaycom.files.wordpress.com/2016/01/complete_sch.png
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Grumble



Joined: Nov 23, 2015
Posts: 699
Location: Netherlands
Audio files: 20

PostPosted: Thu Jun 08, 2017 4:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
The pots I am using are 10K (for v3-12),

This is your problem right there!
You are using pots to low in resistance, because of this, the voltages across the diodes and leds (which are very temperature sensitive! ) become an important variable in setting the CV that controls the frequency of LM555 U1.
Besides that: Since the potmeters VR3-12 control the frequency of U1 and since the value can only vary between 0 -10k instead of the original 0-470k you can imagine that the frequency range will be less than original was intended.
I bet you had to change the capacitance of C3 to get some frequency in the audible range??
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sfshrimp



Joined: Jun 07, 2017
Posts: 3
Location: San Francisco

PostPosted: Thu Jun 08, 2017 11:22 am    Post subject: Reply with quote  Mark this post and the followings unread

I changed c1 to 1uf and c3 is a 10uf electrolytic cap. When c1 is the .01uf cap like in the schematic you barely hear anything, its like a very washed out, high frequency tone. I have some 470k trim pots but have had problems getting those to function also, they are the small three pin type that are surface mount. I tried substituting various other pots in place of thr 10ks but it doesnt seem to change anything except make the control range on the knob very tiny, which maybe points to some other problem? For example i tried a 50k pot and a 1m pot. Can i change the timing resistor to gwt the 10k pots to work? I am using the 1k resistors in the schematic
Currently.... thanks for your help!!!
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sfshrimp



Joined: Jun 07, 2017
Posts: 3
Location: San Francisco

PostPosted: Thu Jun 08, 2017 7:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Grumble wrote:
Quote:
The pots I am using are 10K (for v3-12),

This is your problem right there!
You are using pots to low in resistance, because of this, the voltages across the diodes and leds (which are very temperature sensitive! ) become an important variable in setting the CV that controls the frequency of LM555 U1.
Besides that: Since the potmeters VR3-12 control the frequency of U1 and since the value can only vary between 0 -10k instead of the original 0-470k you can imagine that the frequency range will be less than original was intended.
I bet you had to change the capacitance of C3 to get some frequency in the audible range??


So I tried what you said about replacing the 10K pots with the 470K trim pots I have, and it didn't work unfortunately. I made a short video showing what is happening. The video shows the 10K pots, but the result is similar. The reset of the decade counter makes two steps, and it sounds like a "dee doo" , "dee doo" ambulance kind of thing.

Here's the link to the video:
https://vimeo.com/220878777/748e404ef0

Diode is in middle, output from 4017 on left, and right pin is ground.
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electrotech



Joined: Apr 24, 2013
Posts: 32
Location: Ayrshire Scotland

PostPosted: Fri Jun 09, 2017 2:12 am    Post subject: Reply with quote  Mark this post and the followings unread

I agree with 'Grumble' about the value of the pots.
Also, the schematic diagram doesn't show any decoupling capacitors across the supply rails to each '555.
These are essential with bipolar '555s to ensure that the circuit works as intended.
I'd use a 10-47uF electrolytic between pins 1 & 8 on each one.

Andy
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