More work on the ETI Vocoder project. Building and testing the 1kHz band pass filter.
ETI Vocoder constructional project reproduced with permission from Wimborne Publishing Ltd. http://www.epemag.com
ETI Vocoder constructional project reproduced with permission from Wimborne Publishing Ltd. http://www.epemag.com
Did you finish this or did the solar obsession get rid of this along with the mail bags? Haha I kid. I love vocoders
Must say, your vocal impression of a narrow bandpass filter centered at one kilohertz was worth the price of admission.
1khz is a particularly annoying frequency, yet a very common one to use to test an amplifier xD It's like an out of tune wind chime or something. Sounds like a flat C, but I could be wrong.
The feedback is because of the circuit. The input and output feedback are capacitively coupled. It is designed to cause feedback ringing. If you notice, there is an intentional redundant 15n capacitor on the positive feedback of the second op amp. That is causing the ringing. I assume this is to cause a slower decay when a frequency falls in range.
I want more!
I remember the ETI vocoder well. Along with the Cortex computer, they were THE big electronics projects from my childhood. I remember making the PCB for the power supply, and populating it with all the passives, but it never got any further (I was 11, okay…) I don't think I was totally sure what it did exactly, but it had so many control knobs and flashing lights! I even persuaded my dad to take me to the Breadboard electronics exhibition (that was the name of the exhibition, it wasn't just breadboards) in London where I bought an absurd number of 741s and 555s. For an electronics nerd like me in 1980, this stuff was heaven! Still is really…
Hi Julian – I have recreated most of the PCBs for the ETI vocoder as dual layer cards. However, I found a possible error in the parts list for channel 1 – in the schematics on page 65, R34 is 10k, but in the parts list on page 66 it is 220k. Any idea which one is correct? Since R34 is the only difference between the speech and excitation LP filters, maybe R34 was originally in the same position as R33 (and thus 220k), but then they moved it (space issues on the board maybe?), changed the value to keep the filter the same and forgot to update the parts list?
Julian, when you've polished off the vocoder project why not make the ETI modular analogue synthesiser from the 70s? 😬
Look forward to seeing and hearing this progress.
…still waiting for you to sing like Cher 🙂
Very simple and understandable explanation on how a vocoder works!
Hi. could you make a video how a filter design?
This is probably a total noob question, but is the pot linear or log? Also, if a circuits specs don't specify lin or log is one type assumed over the other?
you can verify the frequency spectrum of the bandpass filters output by using a microphone jack on the pc and a program such as sdr# to analyse the output. Since the capacitors have a certain tolerance the exact bandpass is probrably gonna be a bit off with such a program you could tune it up and get it perfect in line~
Thos modular boxes what are they calles and how do you get them. We had them in my old workplace but they bought them when they were in china.