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This is part three of a three part series on DIY synth building. If you're brand new to electronics I strongly recommend you watch them in order! 
Part 1: <a href="http://casperelectronics.com/finished-pieces/omsynth-minilab/omsynth-video-tutorials/video-1-oscillators/">Oscillators</a>
Part 2: <a href="http://casperelectronics.com/finished-pieces/omsynth-minilab/omsynth-video-tutorials/video-2-sequencers/">Sequencers</a>
Part 3: LoFi sampler and voltage controlled filter.  

This is a super cool little looper/sampler project based around the ISD1820 "voice recorder" IC. It's dirty and clicky and generally crappy but I've found it to be a surprisingly endearing circuit to play with. Just after filming the tutorial I realized it could also be used as an equally crappy but totally effective low pass voltage controlled filter! An unexpected feature of a cheap voice recording chip. I've put info on that <a href="http://casperelectronics.com/finished-pieces/omsynth-minilab/omsynth-video-tutorials/voice-recorder-based-voltage-controlled-filter/">here</a>.


For this project you will need:

-<a href="https://www.ee.iitb.ac.in/uma/~wel/wel12/Components%20Records/digital%20ic%20datasheet/cd40106.pdf">CD40106</a> Schmitt trigger IC
-<a href="http://www.intersil.com/content/dam/Intersil/documents/cd40/cd4020bms-24bms-40bms.pdf">CD4040</a> Binary counter/clock divider IC
-<a href="http://www.tuxgraphics.org/npa/outdoor-doorbell/ISD1800_datasheet.pdf">ISD1820</a> Voice recording IC. These may be hard to find in shops, but a quick ebay search will give you lots of options. 
-1k, 10k, 100k, 1M resistors
-100k potentiometers
-0.1uF, 1uF, 10uF capacitors
-a breadboard or two
-a 5volt power supply or 9volt battery with a 5volt regulator like the L78L05
-lots of jumper wires
-alligator clips and some kind of metal objects to clip to in order to make a touch panel for controlling the pitch of the sample. 


<strong>BUILDING A BASIC SAMPLER</strong>
First we'll start with the most basic sampler circuit. This is taken almost directly from the <a href="http://www.tuxgraphics.org/npa/outdoor-doorbell/ISD1800_datasheet.pdf">ISD1820 data sheet</a>. I've added:
-extended range on the pitch control 
-line in 
-stereo headphone output 
<em>basic ISD1820 circuit</em>
<a href="http://casperelectronics.com/wp-content/uploads/Simple-Sampler.png"><img src="http://casperelectronics.com/wp-content/uploads/Simple-Sampler-460x326.png" alt="Simple Sampler" width="460" height="326" class="alignnone size-large wp-image-2200" /></a>

<strong>ISD1820</strong>
First a note about the ISD1820. This is not a "good" sampler chip... The sound quality is bad, there's a moment of silence when the sample loops and, most annoyingly, it clicks when the sample starts. These things can't really be avoided (with the exception of the clicking which can be addressed with some fancy/maybe not worth it/ footwork). But despite all this I have found it to be genuinely fun to play with and depending on what you are recording, it can actually be a pretty useful little sampler. On the plus side, this is as cheap and simple as DIY samplers get. I would say this is about as simple as audio circuits in general get, which counts for something. And I'm happy to find that the chip is quite flexible allowing wide pitch control range and modulation options (touch control, CV control, light sensors, potentiometers), and some interesting amplitude control options.  
<strong>
Circuit details:</strong>
-R4,R5,C3 & C4 condition the mic input so it works. 
-R1,R2<r3 and C1 buffer and attenuate an external signal. Its necessary to dramatically lower most signals to avoid strong clipping. Use lower value resistors on the input for quieter signals and higher value for louder ones. 
-C5 on the record button help "debounce" the signal and minimizes false triggers. The record input can become quite finicky once you start adjusting the pitch above and below "normal" settings. The debouncing cap wont fix it but it will help. 
-"play gate" and "play trig" are two different inputs to play the sample. "play gate" will play the sample as long as the input to that pin is high (5 volts)> "play trig" will run the sample for its duration as soon as it recieves 5 volts at the pin, regardless of how long the pulse is. Both are useful but I primarily use the "play trig" input. 
-C10, R6 and R7 make up an output buffer and dual mono signal splitter. This allow you to connect the signal to a stereo headphone jack that you can use with stereo and mono plugs. This can also be done by simply connecting the signal to the left and right lugs of the jack. The problem with this is that plugging a <strong>mono</strong> cable into a stereo jack shorts the left output to ground. So if the signal is connected to left and right it will work with headphones but if you plug in a mono jack it will short out the audio signal. The two resistors solve this issue. 
BUT adding these means you cant add the speaker in series with the jack (common configuration that lets you use the jack as a speaker switch). To do this you can use the schematic below. The downside of this is that you will only get the signal in the right ear of your headphones. 
<em>mono output with in-line speaker</em>
<a href="http://casperelectronics.com/wp-content/uploads/speaker.png"><img src="http://casperelectronics.com/wp-content/uploads/speaker-460x237.png" alt="Speaker" width="460" height="237" class="alignnone size-large wp-image-2201" /></a>

<a href="http://casperelectronics.com/wp-content/uploads/basic-sampler-w-line-in.jpg"><img src="http://casperelectronics.com/wp-content/uploads/basic-sampler-w-line-in-460x540.jpg" alt="Basic Sampler W Line In" width="460" height="540" class="alignnone size-large wp-image-2198" /></a>

ADDING MORE PITCH CONTROL
