Reinventing the wheel!
- mictester
- Old Solderhand
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I've been trying to get rid of the need for LDR or FET "variable resistors" in a phaser, and I wanted to avoid the noise and distortion of transconductance amplifiers (like in the Small Stone or Ropez). The problem with using LDRs is that you have to use quite some current to illuminate them, and if you use LEDs, the illumination against current isn't at all linear, and can give you a "dead band" where the LEDs are off unless you take steps to offset the oscillator voltage. With the FET approach, you have to match the FETs, and I can't be bothered to go through a big bag of transistors trying to find four, six or even eight with roughly the same characteristics!
A few years ago, I designed a "switched-mode attenuator" for an audio limiter (for broadcast use) that used FETs as switching elements across the audio path, and these were switched hard on and off with a pulse-width modulated squarewave. The pulse width was derived from the level of the incoming audio with a CMOS oscillator that had a mark to space ratio varying from 1 : 9 to 9 :1. This completely eliminated the need for matched components and gave great results, particularly as the audio was delayed by a time equivalent to the attack time of the limiter between the level sensing point and the attenuator. The switching frequency is well above the audio range (~40 kHz), so only a simple lowpass filter is needed after the attenuator stage.
I thought - "let's use PWM into some 4066 gates and use these as the "variable resistors" in a phaser". Two 4066s would allow eight stages! I used my same old CMOS PWM oscillator (at about 40 kHz) and a conventional chain of op-amps. It sounds great, and can be envelope swept too! I was really excited, and was about to put the thing on this board as a new way of doing things.....I then remembered the MXR Commande Phaser...... damn! There's nothing new under the sun!
However, despite my disappointment, I'll finish the PCB and Vero layouts and put the thing up here. Build it. You won't be disappointed. It's the best phaser I've ever tried!
A few years ago, I designed a "switched-mode attenuator" for an audio limiter (for broadcast use) that used FETs as switching elements across the audio path, and these were switched hard on and off with a pulse-width modulated squarewave. The pulse width was derived from the level of the incoming audio with a CMOS oscillator that had a mark to space ratio varying from 1 : 9 to 9 :1. This completely eliminated the need for matched components and gave great results, particularly as the audio was delayed by a time equivalent to the attack time of the limiter between the level sensing point and the attenuator. The switching frequency is well above the audio range (~40 kHz), so only a simple lowpass filter is needed after the attenuator stage.
I thought - "let's use PWM into some 4066 gates and use these as the "variable resistors" in a phaser". Two 4066s would allow eight stages! I used my same old CMOS PWM oscillator (at about 40 kHz) and a conventional chain of op-amps. It sounds great, and can be envelope swept too! I was really excited, and was about to put the thing on this board as a new way of doing things.....I then remembered the MXR Commande Phaser...... damn! There's nothing new under the sun!
However, despite my disappointment, I'll finish the PCB and Vero layouts and put the thing up here. Build it. You won't be disappointed. It's the best phaser I've ever tried!
"Why is it humming?" "Because it doesn't know the words!"
- ~arph
- Cap Cooler
Yes a few years ago I came across a pwm phaser in an electronics book. It was a modular one that had one audio/lfo board and could then be extended with additional boards with four stages each. I believe in the example they built a 24-stage phaser. I specifically recall that it had quite an interesting way of pwm generation. I'll see if I can find the schem. I have made some scans.
EDIT:
It is in a book called: Praktische filtertechniek, from Harry Baggen of Elektor.
It is from 1996.
I found the scan (photo actually) of the lfo section, but sadly not the phase section. It needs some work to make it more readable though.
EDIT:
It is in a book called: Praktische filtertechniek, from Harry Baggen of Elektor.
It is from 1996.
I found the scan (photo actually) of the lfo section, but sadly not the phase section. It needs some work to make it more readable though.
Last edited by ~arph on 20 Jul 2010, 07:54, edited 1 time in total.
In the quiet words of the virgin Mary: "Come again?"
- analogguru
- Old Solderhand
Information
Such a design has been published in the 80´s in the Elektor magazine and was sold such a phaser by MXR in the Commande series too (M-161). Schematic should be online in the web.
analogguru
analogguru
There´s a sucker born every minute - and too many of them end up in the bootweak pedal biz.
- Dirk_Hendrik
- Old Solderhand
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Take a look at the ADA phaser as well. Uses this principle as well.
- HEAD
- Resistor Ronker
Hi,
nothing new under the sun, ok. But at least this sounds quite interesting. I'm looking forward to this as I'm realy keen in phaser. Never heard or read about that way doing it until now. I guess now I've got some lecture to read while being burned lying at the lake.
Cheers
Helge
nothing new under the sun, ok. But at least this sounds quite interesting. I'm looking forward to this as I'm realy keen in phaser. Never heard or read about that way doing it until now. I guess now I've got some lecture to read while being burned lying at the lake.
Cheers
Helge
- Dirk_Hendrik
- Old Solderhand
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- borislavgajic
- Opamp Operator
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this is how it sounds
Boris
Hello!
found this at http://www.synthdiy.com/: 6stage Audio Phaser project 447 in Electronics Today International 1976.
I´m curious about the inventions of mictesters version
found this at http://www.synthdiy.com/: 6stage Audio Phaser project 447 in Electronics Today International 1976.
I´m curious about the inventions of mictesters version
- borislavgajic
- Opamp Operator
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I have build this one....it is nice project.... .but not PWM phaser.......
this one uses set of FET-s from 4049 chip
...some new idea from me...take 6 -8 - 12 potentiometers....dip them in canister with liquid V/2 .....move them dipper ,or get them out of liquid that is going to change resistance in every phaser stage.........it is simmilar to DeArmond tremolo pedals........
Boris
this one uses set of FET-s from 4049 chip
...some new idea from me...take 6 -8 - 12 potentiometers....dip them in canister with liquid V/2 .....move them dipper ,or get them out of liquid that is going to change resistance in every phaser stage.........it is simmilar to DeArmond tremolo pedals........
Boris
- mictester
- Old Solderhand
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It's a completely different principle - the ETI circuit is using the 4049 as FET "variable resistors". My approach uses CMOS switches driven by a high frequency (~40 kHz) Pulse Width Modulated clock, to vary the amount of signal passed to the virtual ground at each stage. This has a number of advantages, including no concern about the accuracy of the component values, low noise (though the latest version has companding to allow it to be used in a studio), and very low distortion. The use of the FETs as variable resistors will introduce both noise and distortion.dutom wrote:Hello!
found this at http://www.synthdiy.com/: 6stage Audio Phaser project 447 in Electronics Today International 1976.
I´m curious about the inventions of mictesters version
My approach is very economical, and doesn't use any unusual components or try to use any components in modes that they are not intended for! Using a 4049UB as variable resistors is quite a good approach, but it's a very noisy device, and susceptible to static discharges (unbuffered CMOS is notorious for getting fried by static!).
The latest version I've built uses a TL082 dual op-amp for the LFO, three TL074 quad op-amp packages (8 stages of phasing, input buffering and output low pass filtering (to get rid of any 40 kHz clock), and mid-rail supply filtering), a transistor PWM stage (a sort of clever monostable) and three 4066 CMOS ICs - two for the phasing stages and one for the bypass switching. I've just added level sensing for note-triggered phasing, using another dual op-amp, and I've also added companding circuitry for noise reduction (not that there was much to start with). The total component cost is <$30, and it's quite easily the best phaser I've ever heard!
When I'm fully happy with the design, and when I've built two or three more of them, I'll put the schematics and board layout up here.
"Why is it humming?" "Because it doesn't know the words!"
- HEAD
- Resistor Ronker
Uuuh, thank you well! Nice! Maybe I'll give it a try though the use of 8 single op amps is a bit.... outdated. Today we are lucky and are able to get our hands damn cheap on TL074 for example.dutom wrote:Hello!
found this at http://www.synthdiy.com/: 6stage Audio Phaser project 447 in Electronics Today International 1976.
I´m curious about the inventions of mictesters version
- mictester
- Old Solderhand
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The ETI circuit will be noisy and distorted (both functions of the way the components in the phasing stages are being used). Wait until I post my PWM phaser, and you can have low nois, low distortion and the deepest phasing you've ever heard!HEAD wrote:Uuuh, thank you well! Nice! Maybe I'll give it a try though the use of 8 single op amps is a bit.... outdated. Today we are lucky and are able to get our hands damn cheap on TL074 for example.dutom wrote:Hello!
found this at http://www.synthdiy.com/: 6stage Audio Phaser project 447 in Electronics Today International 1976.
I´m curious about the inventions of mictesters version
"Why is it humming?" "Because it doesn't know the words!"
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No reason to wait after MXR and Nelson have done it: https://www.diystompboxes.com/smfforum/ ... ic=76747.0
- HEAD
- Resistor Ronker
mictester wrote:The ETI circuit will be noisy and distorted (both functions of the way the components in the phasing stages are being used). Wait until I post my PWM phaser, and you can have low nois, low distortion and the deepest phasing you've ever heard!HEAD wrote:Uuuh, thank you well! Nice! Maybe I'll give it a try though the use of 8 single op amps is a bit.... outdated. Today we are lucky and are able to get our hands damn cheap on TL074 for example.dutom wrote:Hello!
found this at http://www.synthdiy.com/: 6stage Audio Phaser project 447 in Electronics Today International 1976.
I´m curious about the inventions of mictesters version
I try to, but I'm an impatient guy and I'm pretty bored by all the "yet another boutique TS" stuff looking for new approaches or challenges. I have some spare time at the moment and I would like to build something but couldn't find anything that attracts my attention until now (build so far about 60 pedals).
Cheers
Helge
- borislavgajic
- Opamp Operator
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so I was wondering......if optical phaser (fet , and ota based) are noisy and distorted comparing them to PWM.......why most famous phasers are Biphase ,mxr90,ross,bad stone,small stone...?
I can not wait to see mictesters design.... really would like to make one PWM based phaser....on YouTube ADA phaser was not that great sounding......or I am wrong...?
Boris
I can not wait to see mictesters design.... really would like to make one PWM based phaser....on YouTube ADA phaser was not that great sounding......or I am wrong...?
Boris
- mictester
- Old Solderhand
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"Nelson" might have a few good ideas, but the MXR circuit is really touchy, and often doesn't work properly unless to take a lot effort to select parts. I think I've done better!littleBloona wrote:No reason to wait after MXR and Nelson have done it: https://www.diystompboxes.com/smfforum/ ... ic=76747.0
"Why is it humming?" "Because it doesn't know the words!"
- borislavgajic
- Opamp Operator
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- mictester
- Old Solderhand
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That's not too far from what I've been doing. It looks like "Elektor" and I continue to think the same way!borislavgajic wrote:http://www.uni-bonn.de/~uzs159/allpass.png
http://www.uni-bonn.de/~uzs159/pwmgen.png
"Why is it humming?" "Because it doesn't know the words!"
- analogguru
- Old Solderhand
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yep, that´s the Elektor design from the mid-80´s I was talking about.
analogguru
analogguru
There´s a sucker born every minute - and too many of them end up in the bootweak pedal biz.
- borislavgajic
- Opamp Operator
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...soulpreacher,dynacomp,compulator
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EHX bassmicrosynth,EHX EnglishMuffin,Tube Phaser,springtubereverb ,greyDOD,FulldriveII mosfet,OCD,VOX repeat percussion,RingStinger,Meatball,12stage phaser.... - Location: Sombor , Serbia
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somebody made it? how does that phaser sounds?analogguru wrote:yep, that´s the Elektor design from the mid-80´s I was talking about.
analogguru
cheers
Boris