Bajaman trebulator , modification

Ok, I had this tremolo for quite some time now and I haven’t really enjoyed it since. The sound seemed too much choppy and squary (if this is a word) . Actually, it was !  A quick oscillscope view showed me that the ouptut driving the led was a nice round square wave .

the part that we’re interested in is the final stage of the oscillator :


The square wave can be  be easily explained by the X5 op amp gain stage before it (LF351). This can be an easy fix. As the oscillator outputs a nice sinewave with a reasonable amplitude the need of amplification is moderate. Beside if the amplification is bigger than needed , you saturate the op-amp (hence the square). I think that a simple X2 gain stage is more than enough (fig1)

Adding  a switch to select the waveform between square and sinus (fig2) could ba a nice idea. Driving an op-amp into saturation to create a squarewave is a nice thing as well , it avoids the ticking noise of a comparator based oscillator.


You may think that we can get rid of this op amp and connect the oscillator directly into the LED  but my tweaks made me think that a buffer is still required to not load down the oscillator (which will stop at lower frequencies). The use of  a pot to increase the gain could also be nice  but I didn’t find this really efficient and useful.

I also added a gain boost circuit at the end of the circuit to access a volume control on the panel (with a nice boost if needed) . Once again, it’s really simple juste an op-amp gain stage. This can , of course, be substitued for a JFET  or any kind of amplifier. VR is the bias voltage made of the two 100K resitor coupled by the 4u7 cap.


Anyway, this is a rather short post but I think it may intersest readers who want to build a simple tremolo .


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