Friday, March 6, 2015

Modifying the Joyo Tremolo to Demeter Tremulator specs

The Joyo Tremolo is a "pretty good" tremolo out of the box for under $30, pleasant and traditional tremolo sound.  It is also very close to the Demeter Tremulator ($200) and can pretty easily made to sound almost exactly the same.

First a review of the build quality.  Everything is PCB mounted except for the footswitch, which is connected on a 6-conductor ribbon cable which is extremely fragile and easy to damage when working the parts around.  Be very careful with these tiny wires, they snap almost by themselves.

The PCB is pretty weak, I had several pads lift when re-working parts, so be as gentle as you can when doing the re-work.  This is not a pedal to work on over and over, it will fall apart.  Like the Behringer and Alesis compressors in some of my recent posts, this is not a product that's been built to last or really even be repaired.

Luckily the enclosure is pretty solid, the jacks are standard quality, not the worst, and the footswitch is a pretty standard 3PDT as well.  It seems like if you can get the work done and get it back together, it might last a while.

I really like this after the mods, it sounds exactly like Radiohead stuff with the Tremulator.  In my mind this is what a pedal tremolo should ideally sound like--excellent.

This is the video where I got these ideas from:
http://youtu.be/aB5xV99VXKI He also has a square to triangle wave shape pot mod that I skipped.  I found one more improvement on his mods as well, he didn't change the rate pot to Demeter value.  Without this mod the rate pot has a very bad range.

MOD LIST:
C5 - Change to 4.7 uF **non-polar**
R16 - change to 33K
C6 - remove 220pF cap
Rate Pot - change to 500K B or C taper
Optoisolator Bias Trim Pot - adjust to deepest setting for full silence on maximum intensity.  Or back it off if you like that gentle sound.  I like the dramatic deeper one, sounds more like a Tremulator to me.

R16 is right between diode 3 and the IC next to it.

C6 is the maroon colored film cap code "221" next to the diodes.

C taper, Anti-Log, is a really good sweep on the rate knob.  B taper, linear, is Demeter spec and would probably be fine too, I used C.  So did Bajaman on his Trembulator.

I also had to drill around the power jack a bit to enlarge the hole since my rate pot was a bit thick and moved things around slightly when reassembled.

And then I put some fancy Demeter/Marshall style knobs, looks great sounds great!  I built a Tremulator from scratch, gave it to a friend, have missed it ever since, finally got one back in my collection for minimum investment...very satisfying.  And that's a cool mean dog graphic too.




13 comments:

  1. hello! i just finished this mod, and it works out real nice! thanks!

    one question, my rate range changed such that i have much more "fast" level of rate, but also much less "slow" level of rate. i'm wondering if i did something wrong...otherwise it is awesome! let me know what you think - thanks!

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    1. If you did the full mod I recommended, a 500K "C" taper pot (anti-log, reverse audio taper) gives a very good sweep on the knob.

      I'm not sure what you did but I can say for sure, if the slowest sound is slow enough for you and not too slow, and the fastest sound is fast enough for you, then you can bring the "A" "B" and "C" taper into the equation which will give the exact same speeds at maximum and minimum control settings, but will "spread" the speeds out this way or that way depending on where you want or need more or less control.

      If it doesn't get slow enough for you, you might want to use a different pot value altogether. I haven't tried it but maybe a 1 Meg pot would get really slow. Was that the original Joyo value? I can't recall. You could also add a resistor in series with the rate pot to slow down the fastest and slowest rates at the same time, I think. Personally I don't have much use for the slower speeds, but I do like going helicopter fast sometimes, so the 500K "C" is just right for me.

      I believe the Tremulator is tuned a little faster (what I want) and the stock Joyo speeds are tuned slightly slower. If you prefer that you might want to switch back some of the values in the Joyo stock direction.

      Also double check your work and component values. And thanks for the comment! I'm so glad someone got something out of this blog, I'm chuffed.

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    2. I first switched out to a 500K "C" anti-log taper pot, but it just didn't seem to have any range at all, then i switched to a 1M "B" taper, and i got a nice range back. i also tried a 1M "C" anti-log taper, and again no range at all.

      i went back and checked the Joyo pot, and it is a 500K pot - do you know what yours initially came with?

      i do like where it currently is at - sound and range wise, but i'm just getting into this circuit stuff, so my brain just wants to know how all of this works...so, i'm trying to figure out why i lost the "ultra" slow speeds. does it have to do with the resistor or capacitor modifications? or do you have any insight on why i'm having (what seems to me) unusual reactions with "no sweep" using anti-log pots?

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    3. check out this or any article on pot taper:

      http://www.resistorguide.com/potentiometer-taper/

      I'm not an expert on tremolo circuits, but if you look at the "Loop" on the LFO section of the schematic, I believe the delay time is set by the total amount of series resistance in the loop. That would be the speed pot, and probably some of the other resistors in that section. Most likely the "tremulator mods" altered some of these values. I would recommend to experiment and see what you find. A breadboard, or some alligator clips, might come in handy for quickly substituting parts.

      It's also possible that you might have messed something up, because if you follow my guide "to a T" it should work perfectly.

      Good luck!

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  2. any chance you added an anti-pop resistor in the circuit? my joyo trem is popping when activated and not great for quiet ambient moments.

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    1. I have not no, but that's simple enough. Use a 1 MegaOhm resistor from signal in to ground, or signal out to ground, as needed. This will discharge any capacitors on the input or output so there's no pop when switching. Should not change the sound of the pedal at all.

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  3. Hello,

    does C5 have to be a elco? i replaced mine with a ceramic, and now all the pedal does is generate a single tone, which i can control the pitch through the rate control. weird thing being it's always audible, not only when the pedal is turned on.

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    1. That is very strange, I am not sure what's going on there! I would stick to the regular type/value I guess, hopefully no problems with sticking to the schematic.

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  4. Hello, just got to your mod.
    I have that tremolo pedal, except its Harley Benton and not Joyo what is the same.

    I didn't understand some of your explainantions (eg: about the bias trimpot, mine is 20k by default, already turned all the way up, can i change it for bigger value?)

    The Intensity potentiometer is a 50k one by default, can i change it to something bigger for something more square wave like?
    maybe you could add a picture of the PCB with legend pointing to the resistors etc you are acting on? i might be really noob friendly <3

    i made a post on fsb trying to get some help on this, dunno if i can put the link here http://www.freestompboxes.org/viewtopic.php?f=33&p=258911

    thanks for sharing all your work!

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  5. Hopefully the FSB guys can get you sorted out. The Bias trim pot controls the brightness of the LED inside the optoisolator. I think a bigger value will probably just make it dimmer, decreasing the depth, or intensity of the tremolo effect. If you are going for the "hardest" sound you probably turn the trim pot all the way down, for the brightest LED setting inside the optoisolator. You may want to take a look at some other tremolo circuits like the Tremulus Lune to see how they accomplish the different waveforms like square and triangle. Just spitballing here, hope I am not totally off base! good luck.

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  6. Does it still suck the volume when the intensity is increased?

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    1. I haven't noticed that. But if you did find this to be the case, You could probably bump up the gain on the output op amp.

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