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 :

BajaTrembulatorschematic01

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.

 gffgd

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.

44412

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

http://www.freestompboxes.org/viewtopic.php?t=300

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