Author Topic: Harmonic tremolo  (Read 734 times)

Mark Hammer

Harmonic tremolo
« on: September 10, 2019, 03:16:02 PM »
After hearing so many nice examples of it in use recently, twelve years late, I finally got around to making the solid-state emulation of the Fender Pro harmonic tremolo that RG whipped up in 2007 ( http://www.geofex.com/FX_images/FakeFenderVib2.pdf ), using the layout from MarkM (thank you, both).

Harmonic tremolo is like warm chocolate pudding or a good massage or a deep hot tub.  You just want to move right in and live there.  I don't know why I waited so long to move in.  There are chords that sound pretty good on their own, but sound absolutely luscious with a bit of this sauce.

That said, the circuit, as built and as good as it sounds, doesn't have as much of a range of intensity as I might like.  I'm thinking two things.  First, because I used unselected 2N5952 JFETs, I'm wondering if the biasing is appropriate for achieving maximum modulation depth.  Second, I'm wondering if it would be appropriate to add a bit more modulation by swapping the 4k7+5kpot arrangement for 3k6+5kpot+1k2-to-ground.

If you have experience with the circuit, let me know what you think.  I'm going for a pudding swim.

PRR

Re: Harmonic tremolo
« Reply #1 on: September 10, 2019, 05:21:51 PM »
Change D1 D2 to a trim-pot wired for zero to 10k.

Set Depth to minimum.

With trim at zero the circuit has high gain. When you increase trim resistance, gain drops, then stays constant. (You have biased the JFETs from full-on to full-off.) Leave it there at the edge of minimum gain.

Short R27. This will give more Depth than you can need. Figure how much you can stand. Unshort R27 and try 3k, 2k, 1k so Depth goes as high as useful and no more.

Re-check trimmer and Depth interaction.

I don't know why D1 D2. They don't seem to be proper temperature compensation for a JFET, and temp should not be a real issue. Measure your trimmer and install a fixed resistor.

Mark Hammer

Re: Harmonic tremolo
« Reply #2 on: September 10, 2019, 06:08:52 PM »
Dropped R27 to 3k9 and that pretty much did the trick for me.  No other changes needed. Thanks for your help.  Appreciated.

Groovenut

Re: Harmonic tremolo
« Reply #3 on: September 11, 2019, 11:42:48 AM »
After hearing so many nice examples of it in use recently, twelve years late, I finally got around to making the solid-state emulation of the Fender Pro harmonic tremolo that RG whipped up in 2007 ( http://www.geofex.com/FX_images/FakeFenderVib2.pdf ), using the layout from MarkM (thank you, both).
Mark,
Where did you find the MarkM layout?

Thanks!
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Mark Hammer

Re: Harmonic tremolo
« Reply #4 on: September 11, 2019, 03:42:13 PM »
Here: https://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Vibrato+LAYOUT.png.html

The PnP layout is here: https://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Vibrato+TRANSFER.gif.html

Just a reminder to those who are as easily distracted by the forum threads as I am, there's a wealth of stuff available if you follow the Layouts Gallery link at the top of the screen.

pinkjimiphoton

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Re: Harmonic tremolo
« Reply #5 on: September 11, 2019, 04:10:02 PM »
just as a headsup, if anyone wants a kit, google zeppelin design labs quaverato.
this is the best of all the harmonic trem circuits i tried, it absolutely nails the brownface trem. almost sounds like a perfectly phasey univibe at some settings.
i didn't add the midi add on to mine. its especially sweet in that it has tap tempo, and the kit is perfectly thought out.

from continuously variable wave form to switchable latch/momentary bypass to in/out of phase settings, its really amazing.

comes with everything, including roll-your-own vactrol, and the how-to manual makes it even plausible for an absolute beginner to nail it first time. best written build doc i've ever seen... i can't praise this project enough!

that said, i pulled it off my live board cuz i barely ever used it. but its definitely a keeper!!

thanks for the layout links mark, been wanting to build this a long time... i will talk to phil and dino about a layout if RG says its cool to put on deadendfx.

listen loud. blaze one first:
https://drive.google.com/open?id=0BzMJxNNgY3_yc0JNd0VqdmNIWEk

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Mark Hammer

Re: Harmonic tremolo
« Reply #6 on: September 11, 2019, 06:41:48 PM »
I don't think the schematic indicates so, but I used a reverse-log dual-ganged 100k pot for rate.  I'm guessing there are a lot of folks building or producing Uni-Vibe clones.  Pots like that are not traditionally easy to source, but not any more.

reggy1

Re: Harmonic tremolo
« Reply #7 on: September 15, 2019, 07:52:16 PM »
Hi Mark Thought I would see what this sounds like, so have etched a board and am currently populating it.
Could you clarify a couple of cap-related matters, pls?
Schematic has +'ive of C9 electro going to R24, -'ve of C15, and Q9. The layout has it the other way around, with C9 -'ve going to those points. Which option is correct, and, does it matter?
Schematic shows C10 as an electro, while layout has it as a film. Again, does it matter in this context?
I can (just) read a schematic enough to be dangerous. :icon_lol:
Thanks

PRR

Re: Harmonic tremolo
« Reply #8 on: September 15, 2019, 11:33:46 PM »
> Schematic has +'ive of C9 electro going to R24

Correct. (Top of R24 is about plus 2V, top of R24 is zero.)

Output cap is builder's choice. If polar, put + to Q4.

reggy1

Re: Harmonic tremolo
« Reply #9 on: September 16, 2019, 12:08:02 AM »
Thank you.