TWIN PEAKS Tap Tremolo (Y.A.H.T: Yet Another Harmonic Tremolo)

[drolo]

After midwayfair and samhay's builds (http://www.diystompboxes.com/smfforum/index.php?topic=101722.0  and http://www.diystompboxes.com/smfforum/index.php?topic=102736.0) fueled my curiosity about the Harmonic Tremolo found in Fender Brown Face amps (and some others of that era), I wanted to try my luck at emulating it.



I also found inspiration in 2 circuits on GEEOFEX where R.G. had already laid out how to emulate the sound of the Harmonic Tremolo (or Vibrato as Fender called it)

Here:
http://www.geofex.com/FX_images/FakeFenderVib2.pdf

And especially interresting for me, here:
http://www.geofex.com/FX_images/P90-to-fenderPro.gif

A few words about the circuit.

After the Input buffer the signal is split to a LP filter (around 1.6kHz) and a HP filter (around 3.3kHz). I found these to work the best but they can be tweaked to one's liking of course. The Tone knob is able to pan between bass and treble. The signal of each filter goes through an Optocoupler's LDR and is summed at the output stage (U1B). The output stage has a trimmer that allows to adjust the overall volume.

The Optos are Vactec VTL5C1. One could use others, even home made ones. Anything can be tweaked to work when correctly biased. I chose them over others because they had the best response time with fast square waves.

The optos can be driven either in phase or out of phase. In phase, it produces a

"normal" tremolo effect, as both bass and treble are modulated at the same time.
Out of phase, you get the "Harmonic Tremolo" where it pans between the bass and

treble signal. I have added 2 additional modes, one with only bass

modulation/fixed treble and on with treble modulation/fixed bass.

To switch these modes, I found these very nifty compact 2P4T rotary switches that were a blessing in order to keep this build rather compact while having the rotary switch and pots PCB mounted.



I am using a TAPLFO PIC from Electric Druid, which is a very handy Tap LFO with multiple Waveshapes. Any other common LFO should work the same though. It would allow a much simpler layout an smaller box ;-)

The LFO's PWM signal goes through 2 inverting op amp stages to drive the Optos. The first one has a trimmer connected to the negative input that allows to apply an offset voltage to get the TAPLFO's signal (0-5V) centered around the half-supply bias voltage.

The 2P4T switch routes the LFO signal to the optos as explained above.

The biasing is easiest like this:
- Adjust the offset to get the LFO signal centered around the half supply voltage
- Adjust the 2 Opto's current with their dedicated trimpot to have the maximum swing without audible ticking.
- Adjust the volume on the Output stage.

If for example you get too much ticking, reduce the LED's currents and make up for the volume drop with the volume trimmer.

I went a bit overkill with the power supply as you can see. I may have been OK without the separate filtering on V2 but since I build everything on Perf and it was quite some work ... I did not want to risk having high frequency noise or LED ticking bleeding into the audio circuit...and having to start all over. When I first finished the perf, I had a strong high frequency whine but it all went silent when I boxed it up and used shielded wire for in and output.

Here is a small demo:

Thanks for all the people mentioned above and also others that inspired and educate me :-)

[midwayfair]

a) Sounds awesome, and I like a lot of stuff about the circuit, especially how you did the CV output section and the rotary.
b) The contest starts in two days and this isn't an entry!?

EDIT: What's the Offset trimmer do?

[drolo]

a) Sounds awesome, and I like a lot of stuff about the circuit, especially how you did the CV output section and the rotary.
b) The contest starts in two days and this isn't an entry!?

EDIT: What's the Offset trimmer do?

Thanks Jon!

About the contest, I had not really considered participating, especially with all the great builds I see around here ... Also I thought the entries had ended already ... :-/ since I posted this today, i guess I'm disqualified ..:-D

The offset trimmer is an idea I got from here:
http://www.geofex.com/FX_images/Panning%20LEDs.pdf

Without it, the first inverter would turn the 0-5V signal into a squashed 4.5-8.5V signal, and the second inverter again something like 1.5-4.5V. Very hard to bias and not clean at all.
The offset helps to shift the incoming voltage to ideally be centered around 4.5V so the first inverter puts out 7-2V and the second inverter, the exact inverted signal (in theory...) 2-7V. That way the signal does not hit the power rails of the OPamp and gets processed without being distorted.

[moosapotamus]

Nice work! Yeah, sounds awesome!

~ Charlie

[drolo]

Thanks Charlie :-)

On a more cosmetic note, I printed some graphics on matte/transparent sticker paper with a monochrome laser printer. I had done it previously with nice results when the design involved only fonts and simple shapes without any grayscales. With this one, as it incorporated a photo in the background (the Twin Peaks red room  )  it ended up looking like, pardon my language, smeared poo ...

Obviously my printer (a HP 1010) is not suited for photo prints but does any one have any tricks on how I can prepare the image to have the best results? reducing image depth? Dithering? Some moiré pattern?

[mistahead]

Thanks Charlie :-)

On a more cosmetic note, I printed some graphics on matte/transparent sticker paper with a monochrome laser printer. I had done it previously with nice results when the design involved only fonts and simple shapes without any grayscales. With this one, as it incorporated a photo in the background (the Twin Peaks red room  )  it ended up looking like, pardon my language, smeared poo ...

Obviously my printer (a HP 1010) is not suited for photo prints but does any one have any tricks on how I can prepare the image to have the best results? reducing image depth? Dithering? Some moiré pattern?

Just go for half toning methods, they're the most impacting/forgiving at the same time for pretty much every type of "fiddly printing".

[drolo]

Just go for half toning methods, they're the most impacting/forgiving at the same time for pretty much every type of "fiddly printing".

True, it did look better on a test I made. But in the end I decided to go with a simpler design without images:



Usually I never label my own pedals as I always remember what button does what. I guess I just wanted to go fancy for once... :-)

[deadastronaut]

excellent tremolo/build...

love that bass/treble blend too...

[Valoosj]

Wow  (I'm speechless)

[kaycee]

Oh! My! That is supurb, what a lovely sounding tremolo, very 

Great project there, maybe you could get someone to make some boards for it? I'm sure you'd shift a few, me for one, sounds so nice and all those features, brilliant stuff!

[samhay]

Nice job. The blend control is a nice touch and works very well. How did you settle on the 3.3k crossover frequency?
The dual LDR approach is similar to Bajaman's Vibotrem (other forum), but you use it to maximum effect with the 4 mode selector, which is very cool and lets you A/B(/C/D) the harmonic tremolo vs normal tremolo properly.

[drolo]

Oh! My! That is supurb, what a lovely sounding tremolo, very 

Great project there, maybe you could get someone to make some boards for it? I'm sure you'd shift a few, me for one, sounds so nice and all those features, brilliant stuff!

I wouldn't mind having some done ... I just don't know anyone who does that or how to go about submitting the idea ... to whom ... If you have any tips, let me know ;-)

Speaking of boards, here is how it looks like inside:





It's the first time I tried a split board with controls on a daughterboard. It allows to cram in a lot more stuff :-)
Initially I had tried to draw a doublesided PCB and have it etched but it was getting too complex for my poor PCB skills, plus I just could not wait the ordering time and perfed away instead ;-)

[drolo]

Nice job. The blend control is a nice touch and works very well. How did you settle on the 3.3k crossover frequency?
The dual LDR approach is similar to Bajaman's Vibotrem (other forum), but you use it to maximum effect with the 4 mode selector, which is very cool and lets you A/B(/C/D) the harmonic tremolo vs normal tremolo properly.

Weird that I had not come across Baja's project when I was researching about this ... It's a very similar approach.
I had tried the LDR's to ground/bias like he has but was not getting enough chop so I put them in series instead. The effect was much more pronounced.

1.6 / 3.3kHz seemed like the most pleasing when I was breadboarding. Now that I read Baja's description and interesting analysis of the original circuit, I realize the original had the crossover much lower ...
Strangely, when comparing, my trem seemed to sound a bit like the vids of the actual amp I could find on youtube ...  perhaps a bit colder...

[samhay]

The Tremulus Lune and its spawn use an LDR in series like you have - this approach seems to be work well, so good choice.

There is a fairly wide sweet spot in the crossover frequency of my Anharmonic tremolo, so I guess the filter's corner frequency is probably not especially critical. Ultimately, it doesn't matter what the cutoff frequency is on paper as long it sounds alright - which yours does.

[midwayfair]

I get the sense that the crossover frequency needs to be different with each approach. The crossover the cardinal is all the way up at 7k, but it still sounded right next to the actual amp.

I'd say I'd give a layout a go, but my attempt to do Samhay's was a disaster. I suck at op amps. However, I do at least have a schematic with the tap tempo half if you want to use it. You'd just need to have the dry path done. They're separated pretty far on the PCB as well.

[moosapotamus]

I might give a PCB layout a go. Love the sound of this.

~ Charlie

[Valoosj]

I can have a go at a layout (doublesided, ready for a fab house) if you'd like. I've had some decent training with my latest project of getting the A/DA flanger in a 1590B ...
Just tell me which specifics you would like for your layout, such as pots mounted on pcb or tabs at the top, ... Any specifics you might have in mind.

Btw David, Vlaams of Waals/Flamand ou Wallon?

[drolo]

There is a fairly wide sweet spot in the crossover frequency of my Anharmonic tremolo, so I guess the filter's corner frequency is probably not especially critical. Ultimately, it doesn't matter what the cutoff frequency is on paper as long it sounds alright - which yours does.

Seeing the different corner frequencies used in different projects and the results, I guess you are right : )

[drolo]

I get the sense that the crossover frequency needs to be different with each approach. The crossover the cardinal is all the way up at 7k, but it still sounded right next to the actual amp.

I'd say I'd give a layout a go, but my attempt to do Samhay's was a disaster. I suck at op amps. However, I do at least have a schematic with the tap tempo half if you want to use it. You'd just need to have the dry path done. They're separated pretty far on the PCB as well.

Yeah the 7k left me wondering, but in your design it does work very good.

It's kind of you about the layout, but for now I am satisfied with my perf, as long as it does not fall apart. All my diy pedals are perf actually, never made a PCB. But I am getting better at making solid and clean builds. I am already working on a new project and don't feel like spending time with something that is done and behind me :-)

[drolo]

I can have a go at a layout (doublesided, ready for a fab house) if you'd like. I've had some decent training with my latest project of getting the A/DA flanger in a 1590B ...
Just tell me which specifics you would like for your layout, such as pots mounted on pcb or tabs at the top, ... Any specifics you might have in mind.

Btw David, Vlaams of Waals/Flamand ou Wallon?

Thats great :-)

Here is the perf layout I used:


Maybe that can answer some of the questions

pots mounted on the perf as well as the rotary switch. I used some miniature ones as pictured in my first post. But for convenience I guess people find the bigger lorlins or alphas more easily. (although these little rotaries are amazing and cost next to nothing http://www.befr.ebay.be/itm/300881322642?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649  it's a hell of a deal!) just that if you use the lorlins, you will need the pcb mounted pots with longer legs :-)

I tried at some point to draw a double sided PCB but I was having a hard time getting the microchip and led driver traces separate from the audio traces (but it was also the first time I was trying to design a double sided PCB I have to admit ...)

If you get to do it and people are interested, I guess we could have some printed. I have never had a PCB printed so if someone knows good places that are not too expensive for small runs...

BTW I am neither Walloon nor Flemish, I am a Portuguese that kind of stuck around after his studies in Brussels ;-)
I understand Flemish quite well, since I speak German, but I never got to learn to speak, really.