Squealing Op Amps - Vocoder Band Pass Filter

[@Zadster]

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...

[@SpeccyMan]

This is definitely the kind of thing I'd like to see more of in your videos. My passion for electronic music is second only to my passion for electronics. My one major project idea would be to combine the two and build an analogue synthesizer if I can stop being distracted by micro-controller projects and building quadcopters. :-)

[@matambale]

Must say, your vocal impression of a narrow bandpass filter centered at one kilohertz was worth the price of admission.

[@smbrown]

Just shared your channel on Facebook.... I was watching previous vocoder episode on New Year's Day when you went live... really enjoying your projects.

[@danielaunspach6312]

A possible use for your "Repaired Shania Twain" AND a bonus post bag video in one go! A definite thumbs up!

[@paulsengupta971]

I don't think that Shania Twain thing needs an additional bandpass filter... :-)

[@pileofstuff]

Great to see this project front-n-center again. I remember being a subscriber to ETI back around that time frame. I wonder if I still have any of the issues stashed away somewhere. Hmmm...

[@nrdesign1991]

Very simple and understandable explanation on how a vocoder works!

[@JulianIlett]

Thanks - I was hoping that explanation made sense :)

[@DogRox]

boy, that brings back a lot of memories. I remember a long time ago back in the 80s when Peavey Musical Instrument comp. sent me a whole bunch of schematic diagrams of quite a few of their amplifiers ranging from the Backstage to the Bandits to the Renown. I actually built the Backstage amp, and I went through the same process what you're going through to build the equalizer circuit. Of course it was a completely different circuit but the principles are the same. :-)

[@robwgeorge]

That was great. I've heard all of the words before but never was able to put them into context. One suggestion...get a frequency generation app for you phone an feed that into these filters. I believe that would showcase the filtration capabilities when moving the frequency above and below the threshold of the filter? Could also help adjust that tiny potentiometer.

[@joinedupjon]

alternatively you could get a spectrum analyser phone app (or audacity on PC), feed the filter white noise on the IP and look at the OP, with any luck it'd appear the same as the appropriate published graph and if not you could hopefully tune it up fairly rapidly. If you've not heard what a completed vocoder sounds like, it was used pretty extensively on the single 'O Superman' by Laurie Anderson... afaik vocoder was originally a form of analogue data compression to multiplex several speech channels down a phone line - but took off as a musical effect cos it sounds so weird.

[@akarshagarwal4516]

oh my good. julian you seem to follow your new year resolutions. :)

[@JulianIlett]

to the letter ;)

[@dentakuweb]

I'm loving these vocoder videos.

[@danielninjageeknz]

Yay, the return of the vocoder!!

[@richardbmw320]

Glad you have got on with this project again, looking forward to seeing it progress

[@momsazombie1]

Look forward to seeing and hearing this progress.

[@rodneyjaygarrett]

I really appreciate your videos. I always learn watching your videos.

[@JulianIlett]

Thanks Rodney :)

[@mrjohhhnnnyyy5797]

You didn't give me a chance to survive that kilohertz attack - I rushed to the volume control, but by the time I was there, I was hurt :D

[@sonodrome]

Excellent! Great to see you back on the vocoder project again :) maybe you could try playing white noise through it

[@drkastenbrot]

one fun thing used a lot in modern bass music is vocoding the carrier with itself. basically feeding the same signal into microphone and signal input.

[@JulianIlett]

+drkastenbrot I'll have to try that

[@nickpelov]

If you need 14 of those you can order PCBs. I ordered for a site (I can check which one it is if you are interested) $10 for 10 pcs 10x10 cm boards, shipping - about $19 and you get $10 off first order so it'll cost you $19. You have to fit it to 10x5cm board and you have to cut the boards in half by yourself because they don't offer that for the proto PCB service. If you use SMD parts 0805 you can fit it in 5x10 cmd board and you'll have 20 of them.

[@DantalionNl]

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~

[@Screamingtut]

love you building vids

[@rich1051414]

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.

[@jameslamb4573]

JIE Radiophonic Workshop! I hope by the time you've finished with the vocoder you'll produce your very own theme, think Dr Who and you can't go wrong. Please give R2-D2 a "real" voice.

[@2010craggy]

It's a great looking retro electronics project this one, but I did baulk looking at the filter PCB and its schematic diagram in the original article for this project..... I guess you could build each band pass and synth filter separately though, then add (or piggy back) them onto a bigger motherboard for neatness using pin strip and header sockets at the end perhaps instead of 28 individual modules and an accompanying birds nest of wiring to link them all in parallel with the signal source and signal output paths?

[@jonathanagnew9291]

hi Julian nice video , it would nice to see the frequency response on oscilloscope and see the response of the filter.

[@EngineMismanagement]

Looking good, a bit of attenuation on the input would have been nice though.

[@christopherlange4475]

sounds like a old wax drum player. awsome

[@DAVIDGREGORYKERR]

I wonder if you quadruple the frequency so that it can drive a Johnson Counter to drive a Tayloe mixer driven by audio phasing circuit to generate the I/Q signals so the units works as a Ring Modulator that will generate LSB/USB modulation signals which give you some interesting modulation outputs when you feed your voice or music through the unit. frequencies that might work would be between 4-40khz.

[@raymondheath7668]

I think the TL071 or TL074 would work great

[@tinplategeek1058]

Julian, you need to warn people not to listen using ear phones. Or tell them to turn it down at the appropriate part.

[@tenlittleindians]

I want more!

[@scarholmen]

This pot sounds like resonance.

[@PhantasmNZ]

Great video - like others I'd love to see the output on a scope (FFT) or spectrum analyser from a white noise input - particularly as you adjust the pot - do you have a scope? Also why don't you take the opportunity to design some simple PCBs (you could use the free KiCad for example) for these rather than proto board - you could either order finished professional boards or (better in my opinion as a vid) do some home PCB etching (toner transfer?) to show what can be done on a budget. These repetitive projects really lend themselves to spending a bit of time on a pcb. Cheers! Steve (New Zealand)

[@drkastenbrot]

PhantasmNZ the pot must be adjusting the highpass part of the bandbass, so it gets a bit brighter and narrower

[@rimmersbryggeri]

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.

[@johnhamilton1953]

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?

[@jezisvole]

...still waiting for you to sing like Cher :-)

[@genial6589]

Can you show the waves of input and output on a oszi, please?

[@anthonyj777]

Very interesting :)

[@DanTheMiddleagedMan]

very interesting project, julian! but it sure looks like a ton of work. Will we hear you singing a song if everything is finished? ;)

[@JulianIlett]

Certainly will. But I won't be singing, I'll be speaking. The vocoder will make me sing :)

[@jeffmerlin2580]

Can you make a video on how this filter actually works?

[@jstro-hobbytech]

Did you finish this or did the solar obsession get rid of this along with the mail bags? Haha I kid. I love vocoders

[@Slider2732]

Listening at around 14:00 I can imagine that submarines are actually playing Bach !

[@rich1051414]

The pinging of a submarine is a microphone that is amplified and band pass filtered to remove all the frequencies not interesting. You are not far off.

No oscilloscope to take a look at the output?

[@nrdesign1991]

in a pinch, you can always use the soundcard

[@LemoUtan]

Have you a 'scope which does an FFT to check resonance? And was there any significant DC component? If the analysis and synthesis filters are to be identical, what tolerance for Rs and Cs would be necessary?

[@JulianIlett]

I was thinking I might test and select the capacitors when building the final unit.

[@michelfug]

Can I ask what the difference is between the green ground and the black 0V wire? Isn't such a black wire also called 'ground'?

[@joinedupjon]

+Michel Fugers it's quite normal to have two supply rails +ve and -ve with respect to 0v (ground) in op-amp circuits... so the output can vary +ve or -ve of 0v . Eevblog has some decent op-amp tutorials if you'd like a refresher

[@okuryazar260]

Hi. could you make a video how a filter design?

[@tysseng]

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?

[@JulianIlett]

Wow, I had quite a struggle finding that resistor. I'm not sure - I'm tempted to say 220k. I'm going to put all the filter specific capacitors and resistors in turned pin sockets so I can fit them last.

[@tomlamerton2818]

unlucky jullian

[@tartrazine]

Julian, when you've polished off the vocoder project why not make the ETI modular analogue synthesiser from the 70s? 😬

[@JulianIlett]

Modular synths really appeal to me - especially the one's without a keyboard - 'cos I can't play keyboard.

[@tartrazine]

KZbin content = success you said recently, and I agree wholehertedly. "life" is the same... I remember as a teenager seeing this synth in ETI in the 70's, but having made various kits with varying success, despite loving the idea, I knew I would never make this thing work. It was bound to need tweeking I could nver doo, let alone soldering it together properly. It is plain YOU could make a lot of the parts even if it tooks years to complete. The various bits of a true analogue synth (MOOG) are all fascinating, and for today's audinece, fascinating I would think in a retro sort of way. Go-on Julian, do it! Make even more headphone-screeching noises! :)

[@neslin99]

What are little those round connectors near 0:13 and 10:07 called? P.S Thanks for all your videos. They've taught me a lot.

[@-yeme-]

if you mean the sockets, theyre single in line (SIL) turned pin sockets, they usually come as a strip 40 long and you trim them to size. if you mean the plugs/wires going into them, theyre just the wires sold as breadboard links

[@neslin99]

Yeah, the sockets. Thanks for the help, managed to find some. :) It's sometimes a little bit hard to figure out the names of all the different connectors.

[@d0d0uk]

3:27. Jimmy Saville was 1khz.

[@StreuB1]

Headphone users, RIP.

[@petti78]

Not all headphone users have them on too loud at all times.

[@Anvilshock]

Yeah, good riddance to those incompetent maggots who are stupid enough to ignore a clear, spoken warning, and would now need your condolence, genius.

[@andymouse]

this rings a bell is this from ETI ? electronics today international

[@JulianIlett]

Yeah, ETI September 1980

[@juniorocicat9573]

Julian, project idea, redesign this unit using a micro and dsp chips.

[@gandsnut]

My thought exactly... I appreciate the heck out of Julian undertaking this approach, as it will provide plenty of process and result info. Maybe some other YT'er has done a vocoder with a SBC engine.

[@_who_cares_1123]

Hey Julian, can you give me the eBay link for that Boxes? They are Awesome! Thanks

[@Adamcz95]

I would like to know too, I need to extend my storage space and this looks perfect!

[@ThatGuy-nv2wo]

www.ebay.com/itm/-/172113708463 maybe cheaper elsewhere. Try using the search box at the top you muppet.

[@JulianIlett]

I just put a link in the description :)

[@KJW648]

Julian use US Ebay, UK Ebay from china is cheaper... www.ebay.co.uk/itm/10pcs-Anti-static-SMT-SMD-Kit-Lab-chip-Components-Screw-Storage-Box-Case-/222143952797?hash=item33b8cfb79d:g:zkUAAOSwepJXVNmV 10=£4.74

[@_who_cares_1123]

Thanks to all.

[@marekcoufal570]

what about robot build?

[@Jeff121456]

a signal generator and spec analyzer would reveal what that pot is adjusting. But that would be boring. Blow something up.

[@rich1051414]

Quite obviously, it controls the gain of the input stage.

[@Klonkiller361]

MY EARS ARE BLEEDING

[@Anvilshock]

Deservedly so. You had your warning.

[@elfbier8935]

This screams for a function generator and an oscilloscope to see what exactly goes on.

[@JulianIlett]

I'd probably get results similar to those in the magazine article (figure 4 - filter frequency response curves).

[@TheDutyPaid]

Arduino project, real time KZbin subs count with data logger.

[@weirdscix]

Do you have a link for those containers please Julian?

[@MusicalBox]

If you look closely, you can read the words WEN TAI on the boxes Julian received. A search on Google using these words will give you lots of links to where you can buy them.

[@weirdscix]

Okay thanks a lot MusicalBox :-)

[@Anvilshock]

5:55 - more plastic boxes, in different colors and sizes, available here: www.ebay.co.uk/itm/1-50pcs-Electronic-Component-Parts-Plastic-Case-Laboratory-Storage-Box-SMT-SMD/141912228583

[@setSCEtoAUX]

Sounds like Radiohead.

[@TKomoski]

VOCODER Awh ...

[@desertdave]

HIGreat project, I remember making may of these electronics projects as a kid many years ago now, i got the full parts kits from a company called Powertran Cybernetics, they seem to be long gone now, my best project was a synth called Trancendent2000 developed by Tim Ore, i had many hours fun in my bedroom lab building that project, I think he had a hand in the design of this project as well, Does your scope not have a FFT function so you can compare the input and output spectrum ?, that would be a good experiment, please note we do have the TL081 Op Amps as well as others like the dual version on our ebay shop here,www.ebay.co.uk/itm/1-x-Texas-Instruments-TL081CP-Op-Amp-3MHz-8-Pin-PDIP-/322320719283?hash=item4b0bcfddb3:g:dEgAAOSwo4pYINHf , if you send me the address and I will get you a pack of them over to you, i am pleased your doing electronics full time now, i would love to start sending you some electronics parts to help you out with your experiments, keep up the great work, Dave

[@smbrown]

Link to the boxes, not sure this same seller but same product www.ebay.com/itm/10pcs-SMT-SMD-Kit-Lab-chip-Components-Screw-Storage-Box-Case-/172113708463?hash=item2812c6c5af:g:WtwAAOSw9N1Vj7pc

[@JulianIlett]

Yep - that's the one I bought :)

[@tomlamerton2818]

you weren't first

[@ElmerFuddGun]

What are you? 5? 6? Grow up! No one cares who was first!!!

[@krishna34674]

No one cares that you think that no one cares who was first!!!

[@jelletje8]

tru

[@tomlamerton2818]

first

[@SatyajitRoy2048]

First to see the shit !

[@TKomoski]

Looks Daunting to me, but I have utmost connnfiiiidennccee ... Reply