Making tremolo pedal go faster

[RaistMagus]

Hi guys, first post here!  : )

I have a T-Rex Tremster tremolo and I want to increase the maximum oscilation speed. I wonder if I can just replace the speed pot with another value or if I could add a resistor somewhere. I could not find a schematic of this pedal so I'd like to learn more before I start messing with it. 

Any ideas? 

[Kipper4]

Hi and welcome.

This sort of mod is quite a common request. My (name) tremolo pedal is too fast, won't do helicopter fast,too slow,not slow enough.

Fortunately for you there's only a couple of designs that are used as lfo in pedal building.
Mostly I suspect because they are cost effective and require a small footprint on a pcb.

A good place to start would be acquire a cheap meter.
Then when you crack the back off of the box, you could observe the parts and report back.
Maybe take some pics and share, were a friendly bunch and will encourage you to learn stuff so that your knowledge will soon have a momentum of its own.
There will be times of confusion and doubt, we've all been there.
Especially when you first hold the probes one in each hand and feel like some kind of Dr Frankenstein .
You've got this.
Swapping out a pot may potentially be a solution. More information will defo help though.
Happy journey. I hope you enjoy your time here.

[antonis]

Then when you crack the back off of the box, you could observe the parts and report back.
Maybe take some pics and share

Cracked, observed, reported back, pics taken & shared..



Now what, Rich..?? 
(unfortunately couldn't find any shematic/diagram for locating LFO circuit, which should be somewhere around op-amp but..)

[Kipper4]

Well. Wasn't expecting that.
What s that thing? Got me there Antonis.

[antonis]

 
(just a pic found on web..)

IMHO, (+) input should be connected to a junction of two resistors with one of them also connected to OUT and the other to Vref..
Also, (-) should be connected to a junction of a resistor and a capacitor with the cap also connected to OUT and the resistor to a pot (or trimpot) also connected to OUT  with the first resistor also connected to the positive plate of an electro cap & a resistor going to some bias voltage..
(just a rough guess...)

[Passaloutre]

I came across this article when investigating my own tremolo mods: https://mimmotronics.com/blog/talk-theory-to-me/tttm4/

Perhaps it will help you figure you're out as well.

[Mark Hammer]

Analog tremolos will use one of a small handful of simple LFO circuits.  The single common principle that many of them work on is that the rate of one or more capacitors charge up is governed by one or more variable resistances; with higher resistance values translating into slower charge-up time.  The ideal is to increase the speed range at the top end (i.e., fastest speeds) without sacrificing too much at the low end (slowest speeds), or "dialability" (i.e., unintentionally squeezing useful speeds into a small range of pot rotation that makes it hard to replicate a speed you like).

One of the things you will often (though not always) find is that the pot used for setting speed/rate is in series with a fixed resistor.  The fixed resistor sets maximum speed, and the pot simply reduces speed from there.  So, if the circuit used a 500k speed pot in series with a 4k7 fixed resistor, one could drop 4k7 down to 3k3 to widen the speed range at the fast end, and/or use a 1meg pot to widen the speed range at the low end.

Since the speed will depend on how fast one or more caps charge up, replacing the cap/s with a smaller value will shift the entire speed range upwards, without having to do anything to the various resistances involved.  So, if speed depends on charging up a 100nf (.1uf) cap, then dropping the value to 47nf will make the fastest obtainable speed twice as fast.

Note that big drops in cap value will push the LFO into the audio range, where the circuit will start to sound more like a ring modulator.  So, for example, if 100nf maxed you out at 6hz, 47nf would get you just under 13hz, and 33nf would get you just over 18hz where it would begin to have a hint of "elastic band" to it.  Using 22nf would now push the max speed up to just over 27hz, which would have a definite "boinginess" to it.

[ElectricDruid]

You could maybe find the LFO cap by connecting another cap of similar value to the cap under test to each electrolytic cap in turn - I wouldn't solder it, just touch the leads to the connections of the one on the board. Turn the LFO up to 'fast' for starters. Parallel caps like that doubles the value, so if the rate drops to half, you've probably found the LFO cap.

Once you've found it, you can desolder it and reduce its value by whatever proportion you deem appropriate. Or mess with the resistors instead, like Mark suggested. Be aware some LFO designs lose amplitude as the frequency increases. I *doubt* they used such a circuit in a tremolo, but you never know (In a chorus, it actually helps).

[antonis]

Just be sure about right polarity for electros or some tsif-tsaf-tsouf might occur..
(also, discharge test capacitor prior to each one connection..)