Reinventing the wheel!

Stompboxes circuits published in magazines, books or on DIY electronics websites.
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modman
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Post by modman »

borislavgajic wrote:I missed that video...........great :applause:
pitty that we could not see mictesters schematic.......it is not nice to prommis, and then nothing...... :|
People should promise less and just do it (as Nike says)... but still some interesting ideas in this thread.
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borislavgajic
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Post by borislavgajic »

I agree with you Johan..... :thumbsup
.....but if I want to be honest, mictester shared a lot of hes stuff here, and I am gratefull.......just wanted to see that schem too (:blackeye )

Boris

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MicMicMan
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Post by MicMicMan »

I didn't try it yet, (I'm planning to do so, but I'm very busy at the time)...
But there certainly is a clue looking at the Ne555 datasheet by Texas Instruments : there is a PWM Generator schematic in the applications .

Assuming your CV control is included between 1/3*Vcc and 2/3*Vcc you can get a clean,0% - 100% PWM signal right at the 555 output (read the datasheets!).
How would you ensure that you get the CV input voltage included between 1/3*Vcc and 2/3*Vcc then? Well... Using another 555 chip! The capacitor is always charging and discharging within those threshold. You then need a buffer between the two 555, since the CV input of a 555 needs a low input inpedance : any op-amp would do the job. There, you got a pretty simply generated PWM signal with a triangle-like response.
The problem here is that you don't have a depth control. Maybe some dividers with a pot and resistors would do the trick, but I'm not quite sure. Also, the triangle would be severely distorted that way. It must be possible to improve the response of that small system I just described using transistors as intensity generators (the thing to look at is "generating a triangle signal using a ne555 chip"). I'm not an expert and can't be sure though.

Anyone thinks he understood that I said and wants to come up with a schematic? Or even a Spice simulation?
I should provide it for sure, but if someone is a bit less busy than me... well... you're welcome.
:horsey:

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Post by HEAD »

Sorry folks, but I just had to: bump! :)

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Post by earthtonesaudio »

MicMicMan wrote:I didn't try it yet, (I'm planning to do so, but I'm very busy at the time)...
But there certainly is a clue looking at the Ne555 datasheet by Texas Instruments : there is a PWM Generator schematic in the applications .

Assuming your CV control is included between 1/3*Vcc and 2/3*Vcc you can get a clean,0% - 100% PWM signal right at the 555 output (read the datasheets!).
How would you ensure that you get the CV input voltage included between 1/3*Vcc and 2/3*Vcc then? Well... Using another 555 chip! The capacitor is always charging and discharging within those threshold. You then need a buffer between the two 555, since the CV input of a 555 needs a low input inpedance : any op-amp would do the job. There, you got a pretty simply generated PWM signal with a triangle-like response.
The problem here is that you don't have a depth control. Maybe some dividers with a pot and resistors would do the trick, but I'm not quite sure. Also, the triangle would be severely distorted that way. It must be possible to improve the response of that small system I just described using transistors as intensity generators (the thing to look at is "generating a triangle signal using a ne555 chip"). I'm not an expert and can't be sure though.

Anyone thinks he understood that I said and wants to come up with a schematic? Or even a Spice simulation?
I should provide it for sure, but if someone is a bit less busy than me... well... you're welcome.
:horsey:

I must have subconsciously internalized this info because this is about exactly what I did in my "analog PWM generator" circuit. The main difference is I used a CD4093 instead of two 555s. (link)

A depth control can just be a pot referenced to the midpoint of the supply, as I've drawn in the linked-to schem above.

Note: it does distort the (already imperfect) triangle to have the depth pot, so buffering and/or current sources would help.
rocklander wrote:hairsplitting and semantics aren't exactly the same thing though.. we may need two contests for that.

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Post by MicMicMan »

you're absolutely right, that's why I've been interested in reading your thread.
I've already tried to generate, and simulate, a PWM signal with its carrier at around 50khz in order to ensure that the thing is perfectly silent even when plugged in standard audio devices (according to shannon's theory), for a phaser using 4060 chips.
The problem I encountered is that at such speed, and at 9v dc power, the tl074 is not a reliable enough device. I found out that the lm318 chip would perhaps do the job well, when used as a comparator.

Another thing I've had some thoughts about recently, is that the carrier waveform doesn't need to be a nice triangle, but just needs to be somehow symetric, as long as its frequency is a lot above the one of the LFO it's meant to carry. A 555 with a current source (for the LFO) and a buffer (for impedance matching purposes, since the CV entry of the 555 really needs a low impedance input) would probably solve this problem nicely. I'll give it a shot this afternoon.

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Post by HEAD »

mictester wrote: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!
Hi mictester,

don't want to bother you nor demand you to post these files. But I'm still very interessted and would be thankfull if you would come up with this somehow, sometime. I guess I wouldn't be the only one. ;)

Cheers
Helge

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Post by mictester »

HEAD wrote:
don't want to bother you nor demand you to post these files. But I'm still very interessted and would be thankfull if you would come up with this somehow, sometime. I guess I wouldn't be the only one. ;)

Cheers
Helge
Okay. I've been incredibly busy, but I'll get the scribbles on here later this week.
"Why is it humming?" "Because it doesn't know the words!"

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Post by HEAD »

mictester wrote:
HEAD wrote:
don't want to bother you nor demand you to post these files. But I'm still very interessted and would be thankfull if you would come up with this somehow, sometime. I guess I wouldn't be the only one. ;)

Cheers
Helge
Okay. I've been incredibly busy, but I'll get the scribbles on here later this week.

Cool! Thanks in advance! I'm realy looking forward to this. :applause:

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Post by Björn »

I wish my weeks were as long as mictester's are...

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Post by CodeMonk »

He left.

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borislavgajic
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Post by borislavgajic »

CodeMonk wrote:He left.
........right....._? :D

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Post by ppluis0 »

Mictester SAYS that left to participate in FSB, but looking at his profile reveals that him visit us today at 08:26.

Perhaps at some thread he can regain interest in writing again.

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Post by HEAD »

I still hope that he regains some interest.... :(

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Post by diagrammatiks »

smd ldr photocoupler arrays.

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Post by Blitz Krieg »

did this work?

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Post by Nocentelli »

modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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