Audio Phaser, Electronics Today International, September 1976

Free online ressources on guitars, amps, effects, guitar technique and more. Dedicated to the fond memory of its founder SPeter Davidoff.
User avatar
modman
a d m i n
Information
Posts: 4888
Joined: 19 Jun 2007, 16:57
Has thanked: 4392 times
Been thanked: 2130 times

Post by modman »

PDF:
eti447.pdf
(390.24 KiB) Downloaded 224 times

eti447 1.jpg
eti447 2.jpg
eti447 3.jpg
eti447 4.jpg
eti447 5.jpg
eti447 6.jpg
Please, support freestompboxes.org on Patreon for just 1 pcb per year! Or donate directly through PayPal

User avatar
Lani
Solder Soldier
Information
Posts: 192
Joined: 22 May 2017, 11:57
my favorite amplifier: Bassman 5f6a
Completed builds: .....ummmm yeah. Too many to list.....
Location: Ithaca, New York
Has thanked: 133 times
Been thanked: 93 times

Post by Lani »

Ooooooh, I love the acid trippy traces with these old school designs.... Thanks Modman!!

User avatar
bmxguitarsbmx
Cap Cooler
Information
Posts: 510
Joined: 25 Mar 2010, 21:15
Has thanked: 700 times
Been thanked: 216 times

Post by bmxguitarsbmx »

This is an interesting circuit... I assume only an unbuffered cd4049 hex inverter would work here.

All INPUTS of hex inverters are shorted together, as per the note: 3,5,7,9,11,14 are shorted together and connected to the Voltage control.

Each Hex inverter OUTPUT controls a stage of the phase shift.

VCC(pin 1), VSS(pin 8), and NC(pin16) are connected to Vbias set up with the 10k + 15K voltage divider (6V).

VERY COOL! I didn't know you could do this. At first glance seeing the CD4049, I assumed it must be a PWM phase shift design. Any one else see one like this before?

User avatar
ppluis0
Diode Debunker
Information
Posts: 915
Joined: 14 Jul 2010, 18:33
Location: Argentina
Has thanked: 127 times
Been thanked: 299 times

Post by ppluis0 »

This reminds me another design using hex inverters:
viewtopic.php?p=288672&hilit=ampeg#p288672
Cheers,
Jose

User avatar
uncleboko
Cap Cooler
Information
Posts: 509
Joined: 25 Mar 2008, 20:19
Has thanked: 58 times
Been thanked: 41 times

Post by uncleboko »

Bad clicking from this circuit.

User avatar
bmxguitarsbmx
Cap Cooler
Information
Posts: 510
Joined: 25 Mar 2010, 21:15
Has thanked: 700 times
Been thanked: 216 times

Post by bmxguitarsbmx »

uncleboko wrote: 11 Jul 2022, 12:20 Bad clicking from this circuit.
You might be able to lower the noise by putting a capacitor across the power pins of IC8.

User avatar
cspar
Breadboard Brother
Information
Posts: 110
Joined: 29 Oct 2020, 21:26
Has thanked: 75 times
Been thanked: 67 times

Post by cspar »

bmxguitarsbmx wrote: 11 Jul 2022, 18:19
uncleboko wrote: 11 Jul 2022, 12:20 Bad clicking from this circuit.
You might be able to lower the noise by putting a capacitor across the power pins of IC8.
Since Vcc and Vss are both connected to the same Vb I'm not so sure about that working as you suggest.

Perhaps splitting c4 into smaller capacitors in parallel but scattered between the voltage divider and next to the ic inputs on the same rail might help?
"Just because the forgoing circuits have produced results there is no reason experimenting won't lead to added results." L. E. Darling, in his article containing the earliest published vacuum tube synthesizer circuit, Popular Science Jan 1920

User avatar
cspar
Breadboard Brother
Information
Posts: 110
Joined: 29 Oct 2020, 21:26
Has thanked: 75 times
Been thanked: 67 times

Post by cspar »

The first thing the signal does when it hits the board is straddle the lfo output...

Looks like it needs a better layout not just different filtering.
"Just because the forgoing circuits have produced results there is no reason experimenting won't lead to added results." L. E. Darling, in his article containing the earliest published vacuum tube synthesizer circuit, Popular Science Jan 1920

User avatar
Manfred
Tube Twister
Information
Posts: 1936
Joined: 04 Apr 2009, 23:42
Has thanked: 1668 times
Been thanked: 1344 times

Post by Manfred »

I have a PCB layout clone with SprintLayout6.0 in progress.

User avatar
bmxguitarsbmx
Cap Cooler
Information
Posts: 510
Joined: 25 Mar 2010, 21:15
Has thanked: 700 times
Been thanked: 216 times

Post by bmxguitarsbmx »

Yeah, I agree cspar. IC8 is where the clicking is coming from, so it's worth a shot.

With a fresh layout, running a RC filter to IC8 would be good. These oscillators can really pollute the circuit with pops with the square wave part.

I wonder if you could drop the open loop gain of IC8 with a high value resistor from output to inverting input to just limit how hard that squarewave hits.

User avatar
luix
Information
Posts: 49
Joined: 17 Mar 2009, 01:56
Has thanked: 3 times
Been thanked: 22 times

Post by luix »

In my experience that kind of LFO produce a current bump every time the waveform inverts and this bump is readily audible in output, to solve this problem I isolate the LFO opamp with a capacitance multiplier circuit, one transistor, one resistor and two or three capacitors 8)
you can find some of my creation on instagram @ luixanalogdevices

User avatar
ppluis0
Diode Debunker
Information
Posts: 915
Joined: 14 Jul 2010, 18:33
Location: Argentina
Has thanked: 127 times
Been thanked: 299 times

Post by ppluis0 »

bmxguitarsbmx wrote: 11 Jul 2022, 18:19
uncleboko wrote: 11 Jul 2022, 12:20 Bad clicking from this circuit.
You might be able to lower the noise by putting a capacitor across the power pins of IC8.
Hi pals,
I've seen in the Boss CE3 that there have added a 10 nF capacitor between the output and the inverting pin of the comparator that was not present in the previous designs.
I believe that it is to "round off" that transition of that square wave in some way.
In the diagram that appears above it would be equivalent to connecting a condenser between pins 2 and 6 of IC8

Cheers,
Jose

User avatar
cspar
Breadboard Brother
Information
Posts: 110
Joined: 29 Oct 2020, 21:26
Has thanked: 75 times
Been thanked: 67 times

Post by cspar »

Luix and Jose, both of your suggestions are great tidbits of information and good ideas worthy of mention.

IMHO, the purpose of the article is to introduce the cmos topology, not the lfo though.

To borrow a quote from a recent diy magazine article thread;
CheapPedalCollector wrote: 26 Jun 2022, 21:34 There are sometimes interesting ideas that may not be executed well, that can be expanded on. Other times they are just bad and fun novelties.
This one, as published, obviously is more of a proof of concept prototype than a finely tuned design.

If I went to build this I'd be inclined to put the lfo on a daughterboard and not be attached to a peticular design for it personally.

And also perhaps use dual op amps while adding the previous mentioned filtering adjustments on the phaser board to begin with.

I would expand on the prototype with a more flexible prototype.

There hasn't been a contest here in awhile. Having one where the entries are "original" designs that are based on a magazine article of the designer's choice would be a fun theme.

Thanks to Modman, as well as a few others, we have a bunch of them to choose from here on the site alone. :thumbsup
"Just because the forgoing circuits have produced results there is no reason experimenting won't lead to added results." L. E. Darling, in his article containing the earliest published vacuum tube synthesizer circuit, Popular Science Jan 1920

User avatar
modman
a d m i n
Information
Posts: 4888
Joined: 19 Jun 2007, 16:57
Has thanked: 4392 times
Been thanked: 2130 times

Post by modman »

cspar wrote: 13 Jul 2022, 17:12 Thanks to Modman, as well as a few others, we have a bunch of them to choose from here on the site alone. :thumbsup
And you must choose wisely according to your needs. I cannot repeat this enough: I am only posting these old magazine articles for reference and to open up discussion. Also to dispel that all was better back in the day: it wasn't... many of these projects contain errors that mostly go uncorrected, quite a few seems untested and those that work are often blatant copies. Some blatant copies contain copying errors... please please please handle with care.

If you want to build the best phaser project available, don't start here.

But at least now there is a central place on the web to discuss these errors, and anybody googling the titles of these articles won't have to start from zero when trying them out. Even though corrections are sometimes published, there is always the delay of at least a month. Another main reason to post them was to show (not argue) that electronic designs are not subject to copyright and nobody thought so in the 60s or 70s.
Please, support freestompboxes.org on Patreon for just 1 pcb per year! Or donate directly through PayPal

User avatar
luix
Information
Posts: 49
Joined: 17 Mar 2009, 01:56
Has thanked: 3 times
Been thanked: 22 times

Post by luix »

cspar wrote: 13 Jul 2022, 17:12 Luix and Jose, both of your suggestions are great tidbits of information and good ideas worthy of mention.
You're right, sorry! :oops:

Long time ago I've experimented a lot with phasers and I found that using a CMOS inverter as variable resistor is really tricky so I've abandoned the design and I've invested my time on modding and improving the MXR Phase 90, maybe I'll post my conclusion with sch&PCB in another topic.

I promise myself to study and try on a guitar phaser the circuit below, promise I never kept :mrgreen: :
cmos-vcr.gif
but I think that even if it works well the cost would be excessive for a guitar pedal.
cspar wrote: 13 Jul 2022, 17:12 There hasn't been a contest here in awhile. Having one where the entries are "original" designs that are based on a magazine article of the designer's choice would be a fun theme.
A contest would resurrect my guitar electronic passion but I'll stay out of my house till september so let's do it after summer :shred:
you can find some of my creation on instagram @ luixanalogdevices

User avatar
cspar
Breadboard Brother
Information
Posts: 110
Joined: 29 Oct 2020, 21:26
Has thanked: 75 times
Been thanked: 67 times

Post by cspar »

When I'm drinking my morning coffee and see that an old article has been posted, I take the design with a grain of salt and look at it like it's more of a crossword puzzle in the paper than as build instructions.

Although I speak for myself, it's apparent that I'm not the only one looking at the articles this way.
modman wrote: 14 Jul 2022, 09:29 I cannot repeat this enough: I am only posting these old magazine articles for reference and to open up discussion.
Modman, I understand the other very valid points that you brought up in the post with that quote and they are actually a part of my previous comment even though I didn't explicitly state them.

Perhaps that was obscured by my personal focus on the cmos topology over the "worthy of mention" lfo fixes that where suggested.

I'm not encouraging building stock magazine circuits nor even suggesting that you could mod this peticular design into something that would hold it's own against some of the better phaser designs available to the diy community.

It was my intention to bring general attention over time to the meat of your previous post, while also encouraging critical thinking and discussion of flaws and fixes across multiple threads.

To me, the idea of encouraging the diy community to publicly take old diy articles as inspiration for functional new diy designs would be a poetically beautiful tapestry that in the long run would help to put the articles in the proper context.
luix wrote: 14 Jul 2022, 12:58 A contest would resurrect my guitar electronic passion but I'll stay out of my house till september so let's do it after summer :shred:
I agree, my plate is pretty full right now with some tube stuff I'm working on and I would imagine more folks would participate if it was during the northern hemisphere fall/winter.
"Just because the forgoing circuits have produced results there is no reason experimenting won't lead to added results." L. E. Darling, in his article containing the earliest published vacuum tube synthesizer circuit, Popular Science Jan 1920

User avatar
bmxguitarsbmx
Cap Cooler
Information
Posts: 510
Joined: 25 Mar 2010, 21:15
Has thanked: 700 times
Been thanked: 216 times

Post by bmxguitarsbmx »

Another noise inducing part might be the 10k + 1k voltage divider before going into the phase shifter section. Dropping the S in the S/n signal to noise ratio. The last transistor stage contains the make-up gain. Kinda like a "de-emphasis, emphasis" design. The opposite of the "pre-emphasis, de-emphasis" strategy for lowering noise.

User avatar
Guilherme
Information
Posts: 47
Joined: 11 Jul 2007, 16:15
Has thanked: 5 times
Been thanked: 4 times

Post by Guilherme »

Maybe it's intended to keep the signal level low and minimize distortion, when using the mosfets as VCR.

User avatar
uncleboko
Cap Cooler
Information
Posts: 509
Joined: 25 Mar 2008, 20:19
Has thanked: 58 times
Been thanked: 41 times

Post by uncleboko »

Remember also that the editorial staff of both ETI and Hobby Electronics were apt to change guitar pedal circuits from those offered, which were working well, into something they wanted to see, cutting pay for original article authors.

User avatar
modman
a d m i n
Information
Posts: 4888
Joined: 19 Jun 2007, 16:57
Has thanked: 4392 times
Been thanked: 2130 times

Post by modman »

uncleboko wrote: 15 Jul 2022, 06:28 Remember also that the editorial staff of both ETI and Hobby Electronics were apt to change guitar pedal circuits from those offered, which were working well, into something they wanted to see, cutting pay for original article authors.
Maybe we should move this discussion to a separate caveat thread about the article. I, for one, don't know much about the background of these different magazines. I'd love to know more about that. I also kind of arrived at the conclusion of suspecting articles without authors of plagiarism.
Please, support freestompboxes.org on Patreon for just 1 pcb per year! Or donate directly through PayPal

Post Reply