Tremolo pedals.. or is it 'vibrato'?

[The Captain]

I used to have a silverface fender twin with a gorgeous built in 'vibrato' effect (ie depth/ intensity knobs, like the 'How soon is Now' guitar sound): Is a 'tremolo' pedal the same type of effect as this 'vibrato'? & can a low/ reasonably priced one (there are so many cheap ones, chinese made presumably thesedays) emmulate this sound to decent effect? Ive seen 'Behringer' (?)makes one for as little as $30, but having not played a pedal type ever- any ideas? cheers, Captain.

[Tom Phillips]

Fender called their effect "Vibrado" but it is really tremolo which is amplitude modulation not pitch change. So...yes the pedals make the same effect.

Check out the tremolo pedal reviews here http://www.muzique.com/trem.htm

Regards,
Tom

[Brad1]

From Wikipoedia:

"Confusingly, vibrato is sometimes referred to as tremolo, notably in the context of a tremolo arm of an electric guitar, which produces variations of pitch although true tremolo is a periodic fluctuation in the amplitude (rather than the frequency) of a sound. Conversely, the so-called vibrato unit built in to many guitar amplifiers produces what is known as tremolo in all other contexts."

Old Magnatone amps had vibrato where the pitch fluctuates. A Leslie will produce a bit of both, because the doppler effect is changing the pitch slightly, while also varying the volume as the horn spins.

Interestingly, I have found that the "Rotary" effect in a Yamaha DG-Stomp is a fairly decent Leslie simulator. It seems to do a bit to pitch and volume, it has an adjustable frequency split point, and you can set the speeds for the "top" and "bottom" rotor independantly, and control them with an expression pedal. The speeds ARE locked in their respective speed-ratio settings once set, (unless you send them some MIDI data to change them), but when you work the pedal, the thing ramps up and slows down over time, like a real spinning speaker (horn..baffle...whatever). Pretty cool actually, although I wish it had a bit more depth to it. It sounds better on a recording, or through headphones than it does through a couple of say, Vibro Champs. I'm assuming that is because the two amps aren't actually throwing the sound around the room, but emanating from their respective points, and something may be getting lost between and beyond them....which is weird, because it does sound kinda cool on a recording. Maybe the other instruments are masking the deficiencies?

Just something that popped into my head....

Like Tom said, tremolo is usually just amplitude, vibrato is mainly pitch...but MAY contain amplitude variance to some degree, depending on the effect.

Brad1

[David Schwab]

Fender called their effect "Vibrado" but it is really tremolo which is amplitude modulation not pitch change. So...yes the pedals make the same effect.

And oddly enough they called the vibrato bridge a tremolo!

Yes that effect is tremolo. The old Danelectro/Silvertone amps had real vibrato... it changed the pitch.

[Mark Hammer]

The real irony is that, while a trembling voice usually results in pitch wavering due to the irregular tension on the vocal cords, and talking while you hold onto a jackhammer (i.e., vibrating) results in cyclical variation in how much air you are able to move across your vocal cords (producing level variations), officially, "tremolo" refers to cyclical variation in level, while "vibrato" refers to cyclical variation in pitch.

This gets even more confusing when one adopts other methods of producing vibrato. For instance, ANY modulation pedal, whether time (flanger, chorus) or phase based (phase shifter, Uni-Vibe), produces pitch fluctuation when the "dry" signal is cancelled and only the modulated signal is used. However, in the case of the phase-shifter, one of the side-effects of this is also some volume fluctuation, even though the principal effect is that of pitch fluctuation. Easy to see how they get mixed up.

As David correctly notes, amps have varied widely in the methods used to produce the modulated effect they may have included. The oscillator that drove the fluctuation may have been identical, but what it controlled was sometimes different. In some instances, the oscillator drove a pair of phase-shift stages to produce pitch-change, whicle in others it was automatic volume fluctuation in the preamp, pure and simple, and in other instances was a bizarre amalgam of the two.

The manner in which tremolo is produced yields different-sounding effects. Some older amps produce tremolo by varying the bias of the power stage/tubes, while others produce tremolo by means of a photocell in the preamps stage. They sound different in a way that is hard to describe, except to say that the bias method sounds more like the tone "gives up". The Line 6 Tap Tremolo, has an optical and bias setting on it, and to my mind does a very nice job emulating the feel of tube bias. Whether it does so better than other commercial products, I cannot tell, but it sounds great to my ears.

An effect I am fond of is the "phasefilter" effect. This originated in a synth module conceived of and developed by John Blacet in the late 1970's , using 2 allpass (phase-shifter) stages in series with two lowpass stages. When this is combined with a dry/clean signal, it produces an effect that is a kissing cousin to phase-shifting, but sounds a little different (read review here: http://hammer.ampage.org/files/Device1-6.PDF ). When you have no clean signal added in, however, it takes on this incredible swampy feel which has a bit of tremolo, vibrato, and auto-wah wrapped up together. Highly recommended.

You can achieve this effect with any Small Stone phase-shifter, by simply rerouting two capacitors from the input of the phase-shift stage to ground. An example of how to do this is shown here: http://www.tonepad.com/getFile.asp?id=99 using the later issue Ross Phaser.

[The Captain]

Thanks all for very knowledgable answers. The link to the tests have made me plump for a danelectro 'tuna melt' (heavens above what were they on?) for a cheap as chips trial. Id love a vintage stop jobby, but funds wont allow yet.

Interestingly am I right in thinking the specific tremolo effect on 'How Soon Is Now' by The Smiths, was acheived using two silver style Twin reverbs sort of stereo panning type tremolo between the two?

[Don Doucette]

About 30 years ago my high school electronics teacher gave us a bunch of circuits to try in class, I kept most of the guitar related ones and discarded the rest. This is one of those circuits. Origin unknown and I don't ever remember building it but it is such a simple circuit with so few parts that it is worth trying. Some interesting mods to this circuit are possible, one is to add an additional 9v battery or reduce the value of R8, this will drive the circuit a little harder making for some interesting output.

So if you don't want to try a cheapo you can always try to build one first.

Don



B1, B2 - 9V Battery
C1 - .47µf Capacitor
C2 - 2.2µf capacitor
C3 - 4.7µf 25v electrolytic capacitor
C4 - .047µf capicitor
Q1 - 2N3904
Q2 - 2N3906
R1, R8 - 100KΩ 1/2W
R2 - 10KΩ pot
R3 - 2.7KΩ 1/2W
R4 - 3.3KΩ 1/2W
R5 - 560KΩ 1/2W
R6 - 500KΩ pot
R7 - 470Ω 1/2W
R9 - 4.7KΩ 1/2W
S1 - SPST foot switch

Q1, R2-R5 and C1-3 form a phase shift oscillator. Speed control R2 varies it's output frequency, which is coupled through C4, R6 and R7 to Q2. Q2 and R8 then amplitude modulate the signal in the line between the instrument and the amplifier. The amount of modulation applied is varied by depth control R6.

[The Captain]

Hey thanks- interesting.. do you have any pics of innards? I find schematics I can only interpret properly with a layout or idiot-pic for reference. Cheers Captain.

[Don Doucette]

As in my post... I have never built one before so there are no pics, however I did build one tonight, I need a case, stomp switch and a couple of pots to complete it. I'll pick them up tomorrow and when I'm done I'll let ya know how it sounds.

Don

[The Captain]

Ah yes I reread your post- iirc the Verbolo diy fender amp has similar thing in it, and changing the odd cap slowed/ increaced rate and stuff.. Id appreciate a gawp at a pic- all good stuff, cheers Captain.

[Mark Hammer]

I recognize that one from those assorted "99 Transistor projects" mags I used to buy on the newstands back in the day. Note that R1, R8/Q2 form a kind of virtual volume pot. R1 forms the input leg, and R8+Q2 form the ground leg. The junction of R1/R8 acts like the wiper of the pot. The oscillator voltage applied to the base of Q2 makes it act like a variable resistor. So the "pot" is 100k on one leg, and 100k plus some "mystery resistance" on the other leg. It will *always* attenuate the input signal just a bit, and the tremolo effect will variable attenuate below that as well.

So, the first "problem" with this circuit is signal loss, relative to bypass mode. The second problem is that it will load down everything. Consequently, it needs some sort of input buffer and output buffer, on each side of R1, as well as some means of bringing the level up to near bypass,

[Enzo]

Does this actually work? Just looking, I don't see how Q2 ever turns on. No DC bias to its base, and all the current through it comes from the signal. And with all that resistance, it needs to be a very large signal to overcome the junction drops in Q2. Or am I missing something?

And i can see how C1,2,3 and Q1 could make an oscillator, shouldn't Q1 have a collector load? AS it stands, it looks like it would send unused pulses of current through R9, but the signal going to the base if Q2 is just a cap sampling off the B+ rail. The only signal I see there is whatever sag on the batteries R9 can provide. SHouldn't C4 come off Q1 emitter? Or use the collector after adding a load resistor? Or am I missing something here too?

In fact, looking at the feedback loop, I don't see how the B+ will vary enough to send anything back around through the loop. In fact, what I would propose would be to break the line between S1 and C1 and add an appropriate resistor as the collector load. Then C4 makes sense, and the feedback loop makes sense.

Either I am an idiot or the circuit is funny. Please set me straight either way.

[puretube]

never trust a schematic on the web...

[Mark Hammer]

In this case, it was in print long before it was ever on the web. More than likely, sometime around 1976 or even earlier.

At the same time, there IS a naive mistaken assumption that because "it's on the web" that it lacks any errors whatsoever. I might point out that, while magazine projects in Elektor, Popular Electronics, et al often have/had erratums and addendums in the issue or two after a project was published, the schematics that would show up in large collections, whether these were any of the one-off magazine-style circuit collections I would buy at newsstands during the 70's, or things like the Rudy Graf circuit collections, often lacked any means of followup, or any sort of included commentary. My guess is that at no time during its lifespan, was the tremolo circuit in question accompanied by ANY commentary about the input/output impedance issue, and perhaps no one ever verified the correspondance between the circuit - as shown - and something that worked as intended. These things tend to take on a life of their own, with everyone who collects them and either posts them or slaps them into yet another "1001 circuits you can build in an evening" book assuming that the schematic is problem free.

As such, Ton's/Puretube's implicit advice to think twice and look over the schematic to verify functionality should be taken seriously. Doesn't mean the schematic is NOT correct, just that you shouldn't start by assuming that it is.

[R.G.]

never trust a schematic on the web...

I guess more to the point - trust but verify. And never trust a schematic you can't verify, at least to the point of understanding how it could work.

I don't see how Q2 ever turns on. No DC bias to its base, and all the current through it comes from the signal. And with all that resistance, it needs to be a very large signal to overcome the junction drops in Q2. Or am I missing something?

The circuit has other issues, as you mention. However, it is possible for the Q2 thing to work. The negative-half swing on the Q2 base could be big enough (if Q1 had a collector load... ) that it turned on Q2. Q2 would conduct even with small voltages on it's collector-emitter in the resistive region of its characteristic, which bipolars have but you don't hear much about.

In fact, I think it might give a rough-and-ready volume variation if Q2's collector was open, given that the two resistors R1 and R8 are 100K, making the maximum volume loss be 6db.

And never forget - it might just sound ... ugly... too.