Tremolo, anyone?

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[Not sure if this should go here or in the OT forum. Ended up here, anyway..]

 

Suppose you've taken up playing the electric guitar again after several years of almost no activity. I am looking over the collection of "effect pedals" I have, and have decided you want a really good tremolo.

 

[Let's just clear out the possibility of confusion here. The correct meaning of a tremolo is something along "a periodic variation in the volume". NOT a periodic variation of the frequency - the correct musical term for the latter is "vibrato".  "Tremoling" is rocking the volume control, "vibrating" is rocking the tuning. (Never mind the tuning-altering mechanic device om e.g. Fender guitars called a "tremolo arm". That should have been a "vibrato arm", but the wrong term was used and got stuck.)]

 

So, I might be interested in building my own tremolo.I speculate that this kond of effect should be one of the simplest do get working (as compared to e.g. effects using phase shifted signals (phaser, flanger, chorus), or exploring saturated components (fuzz, distortion) or moving bandpass filter (wha-wha)).

 

Basically, what I think I need is a circuit that attenuates the signal, and where I can control that attenuation. Specifically, the attenuation should vary periodically over time. 

 

I'd like to control

- Period (think 0 to perhaps 50 Hz)

- "Magnitude", i.e. maximum attenuation

- Waveform (nice sine wave, triangular, sawtooth ramping up or down, square...)

 

The typical box you buy has three knobs for these.

 

The signal should ideally be altered as little as possible - i.e. setting attenuation to zero should produce an output signal ideally identical to the input signal.

 

It seems most projects I've found isolates the waveform generation from the "attenuator" by e.g. a LED/LDR pair, so that supply/ground noise etc generated in the block that generates the waveform does not leak over into the signal that is attenuated.

 

Could I buy one instead? Of-course, but

 

1) I'd like to control the speed with a pedal that I already have (for those of you into these kind of things, it would work as an "expression pedal") - buying an expression-enabled box and the expression pedal ends up somewhere around $300-500..

 

1b) There are other effects I'd like to have that is not easy to build yourself, and where it pays off to buy quality stuff (curious? E.g a "compression effect box".)

 

2) Trying something like this will hopefully be fun

 

The waveform-generator could be a specific circuit, or an AVR that PWMs a signal that is filtered. If an AVR I'd need help with the filter as well, but doing it this way opens interesting possibilities. Example: When frequency increases attenuation could be decreased - so that you could go from a lo-freq very perceptible tremolo, up through something more staccato-like with the staccato eventually disappearing ending up with a clean signal.

 

I could envision something similar at the other end. Lowering the frequency below some threshold the thing goes into clean signal.

 

I'm sure there are a lot of interesting experiments I could do. Programming the thing will be up my alley. I am asking for your help with the analog hardware parts. 

I know there are a lot of people knowing the ins and outs of analog electronics. That is certainly not my field of expertise.

 

Any thoughts?

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A photofet H11F* series "variable resistor/analog switch" could be employed.  One opamp for photofet control plus another photofet in feedback form linear isolated control.

LDR's are kinda slow - good for level regulation but not for modulation.

Perhaps analog balance modulator/multiplier/mixer could be an alternative; nevertheless, there will be no insulation between signal and control.

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This almost begs for a DSP to be used.  And there are so many to choose from.  The TI TMS320xxx series is worth a look at FWIW.

 

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

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Well, another approach would be a DDS to generate whatever modulation you want, (sin, ramp, sawtooth, etc.), AND at whatever frequency you want.

One chip and this part is easy.

 

Then consider feeding it into an analog devices voltage controlled amplifier.  Some have digital inputs, not what you want.  Some have analog inputs, exactly what you want.

 

Add a couple op-amps to buffer, adjust gain, offset, etc., and it all comes together nicely.

 

JC

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LDRs are the classic solution. Find some old fender amp circuits and you'll see a CdS cell and a lightbulb.

Johan, in your abscence there was a discussion with slow_rider regarding tremolo. Bob got fired up regarding the 'confusion' with the term tremolo which Google explained just like you did.

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@Jim: I'm usually the guy going "if you can do it in software then go for that rather than hardware", but for this one wants to mess as little as possible with the signal (e.g. most good pedals boast "true bypass" when un-engaged). One wants as few A/D/A conversions as possible in the signal chain. I'll save those for where they make most sense (e.g. google "T C Electronic Flashback" - amazing thing.)

 

@several: I have enough projects for two to three remaining lifetimes. DSPs are out, if not absolutely necessary. E.g. learning VHDL and FPGAs have been in the queue for  10 years now.

 

@Kas: Can you quantify "slow"? I imagine I won't ever have to go over 50 Hz. (E.g. listening to mains power is just a hum...) Perhaps not more than 25 Hz. I'm willing to experiment before finalizing. I am trying to modularize the problem:

 

* A circuit that attenuates a signal depending on some control input, probably by varying that inputs voltage. A transistor is probably out since the input should be isolated from the control signal. On this I need help.

 

* something reading user inputs (pots, switches) and generating the control signal. ATM this, in my head, is an AVR using A/Ds for reading pots and PWMing the control signal. I am confident all the way here except for a filter to smoothen the PWM into a nice(r) 0-50 Hz signal.

 

* The isolation of the parts, if not intrinsic in some of the above.

 

Thanks for the comments and keep'em coming!

 

Side note for the nerds: I pulled out my Boss CS1 compressor from the wayback storage. Fine on the Fenders, awful on the Gibson. Single coil v/s humbucker thing? No matter the setting(s), it Stuka-dived during the "attack phase". Ideally you'd like all or most of the attack untouched, but then some or a lot of added sustain. I'm drooling over compressors that does a mix-in of the original signal - they're kind of expensive [*] so that's another reason for building the tremolo myself...

 

[*] I play  left-handed - "true southpaw" - and have acquired a few really good guitars over the last ten years (LP Studio, US Stratocaster, Mexico Tele and a remarkably good Ibanez semi-acoustic (think ES175)). From $600 (Tele) to $1100 (LP) per item. When the price of ONE stomp box reaches a quarter of what I paid for each guitar I get uncomfortable..

 

Now to search out the tremolo/vibrato discussion thread mentioned above..

 

[EDIT: Fixed typos. Added some more blah-blah..]

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Last Edited: Wed. Mar 18, 2015 - 08:39 AM
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Found the tremolo/vibrato thread hinted at above. Seems to me Bob is just as correct as I am on the tremolo thing. Amplitude variation. I'm kind of losing Bob when he introduces the Lesley but I think I read him to be correct there also. He also points out that Fender introduced a tremolo effect in their amps - there it is a tremolo following the correct definition. Variation in amplitude.

 

It's the fender guitars that have a so called "tremolo arm", a mechanical arrangement which as it's prime effect "tunes the guitar momentarily up/down when you wiggle the arm" - for hundreds of years the term for this in music notation is "vibrato".

 

When a singer does vibrato it is primarily a slight periodic variation in frequency. accomplishing that (inevitably?) introduces some tremolo also but the prime objective is the frequency variation. On a side note to that: I have difficulty appreciating some opera for the exact reason that some singers put on too much vibrato. In my ears it's +/- several full notes. (OTOH, what e.g. Mr Blackmore does, typically at the end of some solos during "The One True Golden Purple Era" ('69-'73 Blackmore, Gillian, Glover...)" is remarkable, +/- A LOT and exquisite! 

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"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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I only had to Google once to become aware of the anomaly. I think the Kiss 'destroyer' album has a scratch in it, i might have to bump the needle.

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Lesley cabinets introduce both vibrato and tremelo, in my judgement.

 

Four legs good, two legs bad, three legs stable.

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This almost begs for a DSP to be used. 

If that's the case I cannot help but notice that the original BeagleBoard and the BeagleBoard-xM have an OMAP processor (but not the BeagleBone's). The OMAP is a Cortex A8 and a TMS320C64+ DSP in the one CPU.

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I'd think a beaglebone with a 1GHz cpu would be more than enough to do some audio processing. There's probably an open source effects array.

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I would think you could do all that with an AtMega of some stripe and a multiplying DAC for the attenuator.

 

Greg

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So, Johan. Looks like you're going to have to use ADC and DAC. The forum members won't let you go down the analogue route...

 

Four legs good, two legs bad, three legs stable.

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There's a good overview of ANALOGUE VCA options here...

 

http://sound.westhost.com/articl...

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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[OT RANT AND WHINE]

O-fer-son-of-spaghetti-monsters-sake! I HATE that this forum software does not retain the form contents if you happen to back out and then go forward again. When does this happen? When you have scrolled up in the thread to check who posted what (and in the process has made the edit box lose focus) and then you scroll down and want to erase the last word you wrote - but you do not realize that there is no caret, the editor has no focus but rather the surrounding page and in that context pressing backspace means "Navigate to previous page".

 

Apart from the lists here still being flawed to the point of being useless, this is one of the worst things with the new forum incarnation.

 

Next best thing to retaining the contents, would be a dialogue box "You have contents in the post editor that has not been posted. Do you really... blah-blah, yadda yadda...?" That's not rocket science to implement..

[/OT RANT AND WHINE]

 

So I'll retype... Here goes:

 

Gentlemen! While I will follow with interest your discussions of the A/D/A path I will not go down that trail. It's just not going to happen. My cry for help was ideally so that someone would give me a turnkey solution to the parts where I'm not proficient so that I could go along with the parts where I am proficient.

 

Please do continue the discussions re A/D/A and DSPs.

 

But please, do discuss also the simplest possible solutions to a "VCA" (new term learned!). I thank Brian for the link above and will study with interest. A quick browse makes me think that the things in there are still too complicated, since the 'A' is for both "Amplification" and "Attenuation".

 

I'm initially satisfied with "Attenuation".

 

What would be some simplest possible analogue hardware implementations for a "VCA" if it's only "Attenuation"? How would you keep this galvanic isolated from the AVR that is creating the voltage waveform"?

 

I did some searching for Fender amp schematics, but they all seem to have tubes involved in their amp tremolos [*]. I would be very happy if I could get away with not playing with 400 or so Volts...

 

 

[*]Which they seem to call "Vibrato" ... arrrggghh! it's a good 20 years since I played a Twin Reverb, and I didn't recall that. My current amp is a Fender Blues Junior III - excellent but no tremolo. No I didn't own that Twin Reverb, because then I still would have it. I borrowed it for 4 weeks of practice and a hobby / private party gig. Lovely thing, but not mine. Alas...

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"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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If I were you I'd check out the suggestions that have been made re. LDRs and LEDs. I expect you can use the LDR in the feedback leg of an op-amp circuit. Although it may be too slow.

The page that Brian Fairchild linked to seems to be a very good starting point.

Four legs good, two legs bad, three legs stable.

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+1

 

LDR's are slow in the high impedance ( = low light ) area. But if you use them in, let's say, 5k to 100 Ohm, they're quite responsive. Responsive enough IMO for tremolo.

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Imagecraft compiler user

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LDR's are kinda slow =

IIRC bandwidth is limited by hundreds Hz; would have concerns, indeed, about bandwidth dependency upon resistance and temperature.

Just see that photofets as huge improvement over LDR's.

Would agree with pure DSP approach advice; contemporary components, nevertheless, would allow designing of a compact analogue tremolo modulator, leaving fun of embedding for the control part.

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LDRs ought to be perfectly fine for ALC application. You are looking for audible changes in amplitude not a VHF mixer.

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I get tremolo every time my mortgage repayment is due every month.....

 

The tremolo generator I built circa 1966 for my friend used a transistor as amplitude control, nowadays a FET may be better.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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If I were you I'd check out the suggestions that have been made re. LDRs and LEDs. [...] The page that Brian Fairchild linked to seems to be a very good starting point.

I am trying to read them, but please realize that for anything but basic DC analogue stuff I am an ignorant idiot. Which can be excellently demonstrated by...

 I expect you can use the LDR in the feedback leg of an op-amp circuit. Although it may be too slow.

Even these two sentences are above my level of knowledge. You might as well have spoken in Urdu or Gaelic or so.. "feedback leg of an op-amp"? I kind of know what you're talking  about but only superficially. BTW "leg"? Would that be "loop"? The "Although it may be too slow" is a warp-speed leap into another part of the galaxy. I do not know what is implied here (too slow for what?). And I do not understand what that statement was based on. I'm not at that level..

 

Please think of me as a software guy who is comfortable with digital at "low frequencies", but completely ignorant beyond that. When people around me start talking about time- and frequency-domains, things to consider when signals are "high frequency" or similar stuff I transform into a living question-mark. ATM the page that Brian linked to is to me what the Hieroglyphs where to humanity before the Rosetta stone.. (Note that I e.g. fished for hints re a filter to smoothen a PWMed signal to "something smoother". Designing a decent first- or second-order filter might be something many of you do for breakfast. For me that is a quite complicated matter.)

 

I learn new programming languages with ease. I do not fear C++ template programming. Others might find such things complicated, or even extremely difficult. For me it is analog electronics beyond basic high school level that is hard - to the point where I deem it a black art..

 

Another example is the Hackaday entry that Bob linked to. I am more or less lost. I can not even judge if it actually is a tremolo, or rather something else. If I go on the overall description only, it is not a tremolo. "Phase effect" has nothing at all to do with tremolo. The formulation "an RC filter that acts like a tone control" is not fitting for a tremolo. I am not knowledgeable enough to understand the schematics - so I can not check if my interpretation of the intro description is correct or not.

 

Similarly for the stuff Brian linked to: Does any of those circuits do something akin to what I want? I lack the knowledge to tell..

 

Just to remove any confusion: I want an automated "effect" corresponding to if I would wiggle the volume knob on the guitar up and down. At the very least I want to be able to control the frequency with which I wiggle the volume know, and how much I wiggle it. I would also like to have some kind of control of how one wiggle "looks" (from low to high "instantaneously" and then stay a while there and then down to low again instantaneously. I.e. a square wave. And then a sine wave. And then..)

 

(Returning to the Hackaday stuff: ) A variable periodic tone control is not tremolo. A phase effect is not a tremolo. 

 

I might have been overly naïve when I hoped for some simple circuit that could attenuate my guitar signal from a varying voltage control signal.

Basically I tried to do the despicable "groveling for a cook-book solution" blush , but it didn't work. Probably for a good reason. I will read, (try to) think/understand and re-do the cost/benefit analysis for make v/s buy, and get back here eventually.

 

If this requires me to get acquire substantial knowledge on op-amps, time/frequency-domain stuff etc then the "buy" will come out winning. The prime objective here is not learning analog electronics (although I would be happy for that as a spin-off side effect). The prime objective is learning more about playing the guitar.

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"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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You could try a multiplying DAC controlled by an AVR

 

http://www.analog.com/media/en/t...

http://www.analog.com/media/en/n...

 

Page 13 bipolar 4 quadrant operation:

http://www.analog.com/media/en/t...

 

Also have a look for "programmable gain amp " PGa

 

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http://www.clarkhuckaby.com/NewVibe/CloseLookVibe.html

Disregard the valve circuitry. You can see the ldr side is pretty simple. Instead of a neon, use a led.
I don't know if you can still buy CdS cells (ldr) in europe due to the cadmium in the cadmiun disulphide cell. In the olden days, a popular cell was the orp-12.

Bork bork bork! Seems you can still get ldrs - http://se.farnell.com/advanced-photonix/norps-12/light-dependent-resistor-1mohm/dp/327700

Last Edited: Thu. Mar 19, 2015 - 11:45 AM
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You lost me Ossi..

 

I'm sure it's my ignorance, but I fail to see where a DAC applies. My input signal IS analog. I do not want to convert it to digital and then DACing it back again. I am seeking an analog solution to attenuating it. I.e the attenuation should be controlled by another analog signal (probably voltage).

 

In my head I still have the sketch below. It seems to me to be a straight forward approach with things nicely modularized. Everything from the top down to, but not including, the filter I am fully confident with.

 

- I need help determining the order and value details of the filter. Once we get into the details of the signal I assume there will be lots of people that does such before breakfast.

 

- I need there to be a galvanic isolation somewhere after the filter so that noise etc from digital switching does not leak into my guitar signal. It might be intrinsic to the attenuator or a separate stage. I don't know. I am not knowledgeable enough.

 

- I was hoping there would be some straight forward solutions/patterns/whatever re the attenuator. Something "simpler" than an amplifier.

 

As an alternative I might be willing to simply see if there exists a potentiometer that can be controlled digitally and that really goes from (very close to) zero Ohms up to some reasonable value. If this is a possible route I can experiment "hands on" with classic pots to determine the value needed for enough attenuation. All this assuming the pot is wired to form a voltage divider.

 

I expect such experiments to take on the order of a few evenings. Learning op-amps I would asses to weeks to months. DSPs months to year(s?).

 

As I said before - I enjoy if you sprinkle DSP and op-amp talk here. I will read it and learn what I can. It will be a pleasant "side effect" in the thread.

 

But I am looking for the "simplest possible solution". Staying analog all the way for the signal proper. If you know something that makes this practically impossible then please tell me and try to explain why.

 

Here's the inside of my brain:

 

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No guarantees, but if we don't report problems they won't get much of  a chance to be fixed! Details/discussions at link given just above.

 

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

Last Edited: Thu. Mar 19, 2015 - 12:10 PM
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With a multiplying DAC you would multiply your analog guitar signal by a digital value (equal to the gain)

coming for example from an AVR running a slow DDS sine generator.

 

Multiplying-Dac:  Uout=Uin*DACvalue

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Looking around the web, there are some simple circuits that simply use the LDR as one side of a resistive divider. I'd build the AVR side of thing first, and try a simple divider. If you want to take it further at that point, then look at more complicated voltage control amplifier circuits.

I can't help feeling that a multiplying DAC would let you hear the steps(depending on how many bits you use). For a relatively slow control signal I'd have thought PWN via an LPF would be more suitable, and use a lot less wiring. I'd still go for the fastest PWM you can achieve, as it should make the LPF easier(if you're planning simple passive RC filtering). There is an online LPF for PWM calculator around somewhere.

May have been this:

http://sim.okawa-denshi.jp/en/PW...

 

There is also info online about cascading passive RC LPFs.

I believe active filters are much better, but the last two times I've done filtered PWM I couldn't afford the power for an opamp.

 

Don't take any of this as gospel, I really don't know what I'm talking about. Just ideas.

 

 

 

Four legs good, two legs bad, three legs stable.

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 I really don't know what I'm talking about

That's ok. Worse is that I really don't know what you're talking about. My ignorance and low level of knowledge makes most of what you say pass way above my head.

 

Eg Ossis latest: He is talking about a (multiplying) DAC, so the input by definition is digital. But he also says that the input to this DAC is a sine wave. That's analog in my world. I'm sure it's me and my ignorance, but it just does not add up in my head. Ossi knows something I don't. Or thinks I can make an assumption or seeing some background/foundation (that surely is quite reasonable), but I'm not able to do/see that so everything just seems weird.

 

NOW do you see what level I am at, guys? (As I said earlier - if you want to talk programming I'm Your Huckleberry. Analog, not at all so. Quite the opposite, in fact.)

 

So, again...

 

What would be the absolutely simplest solution for an attenuator controlled by a voltage? (I was hoping for something like one transistor, a LED/LDR arrangement or something similar). No-one goes down that route. Why? Not possible? Or not "sexy" enough?

 

No, I'm not even able to set up a resistor in "an analog environment". That's how low a level I am at regarding analog. When we talk to absolute noobs re programming or embedded we often go to the absolute basic level. Talk to me that way about analog, 'cause that's where I'm at...

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In a multiplying DAC the the voltage, that the DAC usually uses as reference voltage, is not fixed, but may be a varying (guitar) signal.

A DAC usually multplies the ref-voltage with the digital signal. In a multiplying DAC even bipolar fast varying (ref-) voltages are allowed.

Se the app note from Analog Devices I gave in my first post!

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Johan,

 

if you don't fancy getting the soldering iron out...

 

http://www.profusionplc.com/pro/...

 

 

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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That price is hard to beat. Good catch, Brian smiley

 

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Johan Wrote:

Eg Ossis latest: He is talking about a (multiplying) DAC, so the input by definition is digital. But he also says that the input to this DAC is a sine wave. That's analog in my world. I'm sure it's me and my ignorance, but it just does not add up in my head. Ossi knows something I don't. Or thinks I can make an assumption or seeing some background/foundation (that surely is quite reasonable), but I'm not able to do/see that so everything just seems weird.

Take a look at this brief tutorial.  It may help.

http://www.analog.com/media/en/n...

 

As John said, do not take it as gospel.  But these folk know what they are doing.  There's some other real good PDF's in their knowledge base on this as well. 

 

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Johan,

 

Did I miss a requirement to use a processor? A quick google for 'tremolo effect analog circuit' produces dozens of the wee beasties... including this digital(ish) one: http://www.bonf.net/2008/03/08/c...

 

Neil

 

 

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Kit tremolos.

https://www.google.com/search?num=50&newwindow=1&site=&source=hp&q=kit+tremolo&oq=kit+trem&gs_l=hp.1.1.0j0i22i30l9.2517.7043.0.12769.8.8.0.0.0.0.143.824.5j3.8.0.msedr...0...1c.1.62.hp..0.8.818.f1Ip4Z7U-Ic

 

2 examples I looked at had enough info to build your own without the kit. One was optical.

 

Search for diy tremolo and tremolo schematics for lots of ideas

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Bob hit the nail on the head, but no-body noticed! 

Nice

 

 

 

Jim

 

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Yes, but one could still replace the 555 with a DDS so that one can feed it a square wave, sine wave, ramp, sawtooth, or whatever one wants, at whatever frequency one desires.

 

JC

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If Johan still wants to do things on an AVR then Profusion also have some eval boards for VCAs.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Although I know Johan wants to stay in the analog realm, I have to say that if I were looking at this I'd probably want to use a DSP. Or, for audio purposes, I reckon an XMega(or a SAM4S for me, as I am pretty familiar with it)would probably have enough horse power. There are so many other effects that could be added at a later stage once you move into the digital domain.
 

Four legs good, two legs bad, three legs stable.

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Bob hit the nail on the head, but no-body noticed!

If you a referring to the Hackaday thing, it might be nice. But it's not a tremolo, as I understand the description of that item.

 

There are so many other effects that could be added at a later stage once you move into the digital domain.

There are people spending little or very much time on doing such things. Those spending little time seems to get crap, hissing, hum, switching noise etc. Those spending a lot of time might get it right. Some of those who really get it right make a buck out of it. E.g. TC Electronic. I havent opened my Flashback, but everything indicates that it has a CPU and possibly a DSP inside. (It's re-programmable! By USB or by a smartphone app - hold the phone near the gutiar pickups and a signal is sent into the TCE boc with new parameters. Way cool, but I won't fall into that nerd-trap.. ;-)

 

I'm not planning to spen a lot of time on tinkering with home-made stuff. I want to PLAY. I want quiet, smooth, good effect boxes. I have been, and am, buying them. Latest was the wonderful TC Electronic Flashback. I bought myself free from hundreds of hours of tinkering to get something similar - it cost me about $200. More than well worth it.

 

The reason I was thinking about doing the tremolo myself was that it seemed like paying something like $150 for a working one was bad(ish) bang for the buck. And I'd love to slaughter my 30 y.o. crap wah-wha to make it an expression pedal for the "Rate" of a tremolo.

 

This is definitively not about having stomp-box/effect pedal building as a hobby. I want to get it over with ASAP so that I can play.

 

My hobbies re AVRs are in a completely different direction.

 

(It's akin to fixing something on the car myself when I realize I can save a lot of money not going to the mechanic. Not that I particularly enjoy un-mounting door panels and searching for electrical faults. It's just that when the mechanic takes on some such he might spend several hours, and at $50+ an hour.. One electric window fixed = money saved for one new guitar effect pedal or a set of new tubes for the amp, or ten sets of strings or 200 guitar picks or...)

 

@Rick: I will definitively study that in detail! (But tomorrow - this afternoon/evening there is this small matter of an uncle (by marriage) celebrating his birthday. His 100th.. :-)

 

@Neil: I have seen that one, but rejected it for some reason. Perhaps becauswe it's square on/off, nothing else [*] . A bit crude. (But it might be interesting for others to have a look. Take special note of the reference to Radioheads "Plant Telex" (sic, it's actually "Planet..."), but that is i) one remarkable song, and ii) one of the effects I'd like to be able to produce. (A side-side note is this mantra/rant we had in the '90: "There is heated debate on whether it's Oasis or Blur that is the best contemporary band. Remarkably, the answer is "Radiohead". Plus the fact that XTC where still active in the '90s..).

 

[*] Some "amplifying tremolos" seems to do square(ish) forms by raising the amplitude of e.g. a modulating sine wave and "clipping the tops". 

 

Thank you all! I have some reading to do tomorrow! Nice!

As of January 15, 2018, Site fix-up work has begun! Now do your part and report any bugs or deficiencies here

No guarantees, but if we don't report problems they won't get much of  a chance to be fixed! Details/discussions at link given just above.

 

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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Four legs good, two legs bad, three legs stable.

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I'd build the volume control part with a 9V battery, a pot, and a voltage divider with a 100K R and an N chan mosfet, not logic level. Hook the pot up to the gate, play the gitfiddle thru the resistor divider and crank the pot up and down. If it gets louder and softer, you are about 75% done. Replace carbon based pot turner with something electronic.

 

Imagecraft compiler user

Last Edited: Sun. Mar 22, 2015 - 03:11 PM
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I think you should go the analog route. Here's a reference circuit - it has some subtleties.

 

V9A is a phase shift oscillator. V9B is an inverting amplifier. The true and inverted signals are fed to opposite sides of the long tailed pair modulator V8, resulting in either the A side signal or the B side signal being dominant. Now these two signals come from a pair of RC networks, with different values, fed by cathode follower V7B, and the tremolo effect is not simply to turn the volume up and down but to favor one of these over the other.

 

I'm not suggesting you build this out of tubes - though I would - but some analysis of the RCs connected to V7B would probably help in getting that "classic sound". Note the date on this schematic, for classic status.

 

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In about 2 Month the new starterkit CY8CKIT-059 will be available for $10. Wait for it. On-chip ADCs & DACs and many DMA possibilities

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re "In about 2 Month the new starterkit CY8CKIT-059 will be available for $10. Wait for it. On-chip ADCs & DACs and many DMA possibilities"

 

Having followed this interesting thread i got the feeling that most of the replies simply neglected Johan's main arguments: getting the project done fast so that he can move on playing his guitar, no ADC/DAC in the signal path, and a simple advice for a device that can control the amplitude to create a tremolo effect.

 

Given these requirements, the above suggestion fails in almost every argument! :-) But i'm sure Johan doesn't need an advocate to stress his points!

 

BTW, @Johan: did you think of actually applying your analog signal to the reference input of an D/A converter? That way your analog signal would not get disturbed by any conversion process, and you would simply control its strength by applying the wanted attenuation factor via the digital inputs of that D/A converter.

Einstein was right: "Two things are unlimited: the universe and the human stupidity. But i'm not quite sure about the former..."

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No, not Behringer. My experience with other Behringers is not good.

 

@peret: Just looking at that schematic takes me close to just buying the thing instead.. (many moons ago me and a mate built a tube amp (the "P1", if you know it). That was fun - for a complete tube amp. But for something as simple (in my mind) as a tremolo...

 

Has anyone, apart from Bob who is closest to the "as simple as possible" that I am after, looked at my sketch above of what is in my head. Any reactions to that?

As of January 15, 2018, Site fix-up work has begun! Now do your part and report any bugs or deficiencies here

No guarantees, but if we don't report problems they won't get much of  a chance to be fixed! Details/discussions at link given just above.

 

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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I was hoping someone would stick the 4 parts I listed in my message into a protoboard and see if it worked. I think its easy to make a lo freq oscillator. I think every tremolo I've ever heard was a sin wave.  A square wave tremolo isnt a concept I can imagine.

 

Imagecraft compiler user

Last Edited: Fri. Mar 27, 2015 - 12:59 PM
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Yes, I looked at it, and commented that you should build the AVR part, and then build a simple LED/LDR based divider as a starting point. I also opined that smoothed PWM would be much simpler than feeding 12 - 16 bits of parallel into a multiplying DAC or a digitally controlled attenuator or etc.

 

Four legs good, two legs bad, three legs stable.

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K.I.S.S

 

Sine only. 3 transistors. No optical. Point to point wiring Kit. $44. Or build it on a breadboard with parts you already have.

 

http://www.modkitsdiy.com/sites/modkitsdiy.com/files/product_files/the_trill_tremolo_schematic_1.pdf
 

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JohanEkdahl wrote:

Has anyone, apart from Bob who is closest to the "as simple as possible" that I am after, looked at my sketch above of what is in my head. Any reactions to that?

I looked at it, but it seems very far indeed from "as simple as possible". ADCs on the pots, PWMs, filters, software .... "simple" is doing it with five transistors. And do not go the LDR route. Those circuits are awfully noisy.

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For me, simple is feeding your guitar through your pc soundcard and running an effects program. Phasing, flanginging, chorus, reverb, looping....

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I'm pretty certain there are iPhone apps(probably Android as well).

 

Four legs good, two legs bad, three legs stable.

Last Edited: Thu. Mar 26, 2015 - 07:40 AM
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Talking of "music processors" (were we?) I was just window shopping the other day and stumbled upon these:

 

https://www.teenageengineering.c...

 

https://www.teenageengineering.com/_img/54e1e47d8fc4190300737af7_512.jpg

 

The most interesting thing on that page (for a nerd like me) was:

  • Silabs EFM 32 gecko mcu
  • Cirrus logic DAC

I did a bit of reading but couldn't really determine if "EFM 32 Gecko" was designed specifically as a "music processor" or just happened to be a rather good choice for this kind of thing.

 

This probably doesn't fall into the "simple" category though! ;-)

Last Edited: Thu. Mar 26, 2015 - 10:36 AM
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The efm32 is not really a firebreather in terms of performance, but those pocket operators sound real good. Not my bag though.