New Pedal: Purr Vibrato

About frickin’ time! I announced this new Vibrato pedal at NAMM 2018. Now it’s time for NAMM 2019, and Purr is finally available and in stock at Vintage King.

Why so long? As soon as we finalized the prototype and designed the new circuit board, a crucial part suddenly became unavailable. ARGH!

It took forever to track down an acceptable substitute. But we finally did, and I’m thrilled with the results. I hope other guitarists dig it too.

Hey, if you’re going to NAMM 2019 in Anaheim next week, please stop by and say hi. Especially since since I’ll be sharing a booth with my my friend James Trussart, creator of some of the loveliest guitars ever conceived. We’ll be in Hall D at Booth 3942.

It’s too early to say whether guitarist will dig the Purr pedal. But at least someone I know is excited about the new release!

10 comments to New Pedal: Purr Vibrato

  • Terry Relph-Knight

    Sounds purrfect. Any reason why you didn’t fit a switch to mix direct and vibrato signals to get chorus? Purrhaps you wanted to keep it purrely vibrato.

    • Joe Gore

      Because it’s sort of chorus-y sounding already? This will probably sound like hogwash to someone with your tech expertise but … vibrato is just WEIRD. The word “fragile” keeps coming to mind. With trem, the effect is obvious, regardless of rate or depth (at least at, say, rates over 2Hz or so and at reasonable depth) and the parameters aren’t very interactive. With vibrato (or at least, analog optical vibrato) even modest rate and mix alteration can make the effect seem to evaporate. I think it’s more about psychoacoustics than actual acoustics. But I’ve always found it difficult to “tune” vibrato, whether it’s analog or digital.

  • Sabrina

    Wow, the stereo sounds surprisingly “normal”. I would’ve thought having one ear vibrato’d and one dry would be more jarring.

  • Mark Hammer

    Unsynced stereo vibrato sounds even better. I made myself a stereo faux Magnatone with independent LFOs for each “side” and it sounds AMAZING. You owe it to yourself to whip one up, Joe. I don’t know what you’re using to set speed. I used the classic LFO circuit found in the old Electronics Australia tremolo and many amps. A dual-ganged pot was used to adjust speed, so that both LFOs could be made faster or slower at the same time. The aperiodic nature of the vibrato, however, is what makes the magic.

    The analogy I use is that of regular vs harmonic tremolo. Regular tremolo, even of the tube bias variety, sounds nice for a while but it eventually gets tiresome. Harmonic tremolo, on the other hand, you can leave on all afternoon. Same with this stereo vibrato. Your Purr sounds great as is. But I promise you that if you made a stereo one for yourself, you wouldn’t turn it off for days. The only down side is that you need two amps, or a stereo amp with stereo send/receive.

  • Mark Hammer

    In posting something on a related thread on the diystompbox forum, something occurred to me. Normally, because of how human hearing works, small changes in pitch, like the Purr and Magnatone produce, are very difficult to detect when the modulation rate is very slow. But that’s because the slight pitch change is compared to itself a moment ago. And if the change occurs slowly, that’s not enough of a change to be heard. But if you have a *stereo* unit, the pitch of one side is compared to the pitch of the other side, and THAT can be easily heard, even when the modulation depth is modest, and the rate slow.

    Yet one more reason to make a stereo unit.

    • Joe Gore

      Hi Mark — I’d love to hear your pedal. I’m quite familiar with stereo vibrato, having gone through a Magnatone collecting phase around the turn of the century. (They all broke, of course.) It’s a lovely tone, but I can’t say that I find the true stereo effect more dramatic than the faux-stereo one. Where I wound up with Purr is 100% subjective — for me it has the right amount of “noticeability” to sound attractive for long passages of music, though I’m sure every guitarist would have a different sweet spot. I spent approximately 200 years fiddling with all the part values surrounding leg 2 of the LDR. At least it felt like 200 years.

  • Mark Hammer

    Hi Joe – I don’t think the true stereo is more dramatic or noticeable. It’s just more immersive.

    And not to beat it to death, but my inspection of the Magnatone amp schematics shows that they never used independent LFOs; only opposite-phase outputs from a single LFO such that the two channels were counterswept, with one always being sharp when the other was flat. Unsynced independent LFOs removes the predictability.

    I’m sure you have more than one Purr kicking around, and have a splitter somewhere. And I know you have more than one amp. Run a different Purr to each amp, with their rates roughly the same, and let me know what you think. Maybe I’m hearing something that isn’t there, and maybe not.

    And yes, getting an LDR to provide JUST the right degree of modulation depth and right sweep feel is an art in itself. Though not using an LDR, one of the things that made the old Boss CE-1 so desirable was that they used a different LFO waveform for the Vibrato than they did for the chorus. I’m going to have to hunker down and learn how to program wavetables in the little mini-Arduinos I bought. In particular, I need to learn how to program in LFO waveforms whose shape changes with speed. Some things need a different waveform for faster speeds than for slower ones. Electro-Harmonix built that into the early-issue Small Stone with a very simple design twist. Certainly one of the quirks of LDRs is that they can differ in how they respond to quick changes of illumination, introducing a sort of automatic reduction in modulation depth with increasing LFO speed. As a “one-knobber”, I gather you exploited that aspect…after 200 years of experimentation. If I can learn how to master Arduinos, I might be able to get them to do that adjustment automatically, and more reliably.

    On a side note, after a number of e-mail exchanges, I persuaded Tom “Electric Druid” Wiltshire of the possibilities of harnessing his StompLFO chip to a one-shot waveform generator. So consider a one shot waveform that ramps upwards at some predetermined rate, dictating the modulation rate and depth of a sine wave Hit a momentary switch, and the modulation gets both faster and more intense, etc. Tom was persuaded and now produces a one-shot PIC controller; https://electricdruid.net/one-shot-event-generator/

  • This pedal sounds gorgeous. Of course, the two-amp wet/dry setup sounds amazing. Solid and moving, as it should.

    But dude. Your playing is painful. As in, creates feelings. Of beautiful, painful, lovely sounds. I love your playing.

    I’m new to pedal building (one boost under the belt and I want to take on the world…), and got pointed here because of your generosity with posting guides. I look forward to more of your tone, sonic and linguistic. Many thanks.

    • joe

      Thanks, Ted, for such generous compliments. Much appreciated. Hey, having built one functioning booster, you are officially over the hump! What’s your next project?

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