Sluckey Inspired MOSFET Tremolo

[2deaf]

mwelch55 asked on the More Tremolo Thread if a MOSFET could be used instead of a triode for Sluckey's Tremor-Lator.

Whereas the -1.5V or so bias created by the LED of the VTL5C1 is good for a 12AX7, it puts an LND150 firmly in "off" mode.  So you can't simply replace the Source circuit with a VTL5C1 LDR in a MOSFET LFO.

The VTL5C1 LDR will work if you place the LED in series with the Drain resistor and leave the Source circuit alone.  It will also work if you configure the MOSFET LFO as an AC-coupled Source Follower with the LED as the tail.

 

[mwelch55]

Thanks 2deaf.  I'll give that a try.  If I make a PCB for it, I can make it small and probably fit into most amps.

[finkaudio]

Hi,


was this idea ever done in hardware? Now that I have the Trem-O-lator running, it would be nice to add this spin-off to other amps that got no tube leftover or free up 2 tubes. A small board can be easily made :-)

Best regards

Karl-Heinz

[sluckey]

I think 2deaf had it breadboarded. Hopefully he'll chime in.

[2deaf]

was this idea ever done in hardware?

I put it in this amp.  Works great.

[finkaudio]

...thanks a lot for sharing!

Best regards

KH

[DummyLoad]

a PCB. not sure it'll work, but if 2deaf's schema is correct, then no reason it shouldn't unless i transposed an error.

dims, are 2.5"L x 2.25"H so it should fit on the inside of the control panel of most chassis. PCB generated from netlist of attached schematic. 

--pete

[DummyLoad]

single sided board - makes building simpler for home fabrication.

dimensions are 2.25" x 2.5"



--pete

[finkaudio]

Hi Pete,


did you try it out? I did and found it not as "fluid" as the tube version. Looked a the waveform and it was very asymmetric and not very well balanced. I finally moved to a Neon bulb and that made a smoother  tremolo to my ear. Don't get me worng - the version that 2deaf made was working, but I personally wanted it a bit smoother

I tried a Fender roach and also a homemade duo with a single Neon lightbulb and an LDR that was more on the lower resistance side. Black hot shrinking tube made it a perfect replacement. Both versions did work fine.

Here is what I changed:



The output pin goes to the Intensity potentiometer. I used 22nF instead of the 2x10. The version of 2deaf was too fast in my setup (or for my taste)

My board is soldered on the back of the two potentiometer - let me know if you want a photo.

I'm still thinking, there must be a way for a nice Tremolo with a sinusodial function. Both, the LED and the Neo bulb version have a more ON/OFF nature. So a Bias wiggling version is not a bad idea, but the oscillator itself is already somewhat out of shape 

Best regards

KH

[DummyLoad]

KH, i have not tested this circuit. interesting observations. i will try to test later in the week and reply.


--pete

[DummyLoad]

some scope shots of four LDR types - The o-scope probe is connected to the LDR resistor that's connected to a LED for a visual. The distortion I suspect is the switching noise from the LDR LED. Of the four LDRs tested, I think that the NSL-32SR3 has the best symmetry. The NSL-32SR3 is also the device that's the biggest pain to deal with physically, the LED leads are very short and a smaller diameter then all of the other LDRs. All the Luna NSL series have a painted dot to indicate the cathode (-) lead of the LED.

I have not tried either of the Luna NSL-xx device beyond the simple test on a breadboard. I will give them both a spin in the 3 tube reverb + tremelo posted in the tube amp forum and update in the week. 

https://lunainc.com/wp-content/uploads/2016/06/NSL-28.pdf
https://lunainc.com/wp-content/uploads/2016/06/NSL-32SR3.pdf

VTL5C3

https://www.dropbox.com/s/4dnju0q1trydlnz/20200731_133736-VTCL5C3.mp4?dl=0

NSL-28

https://www.dropbox.com/s/i2gnodrgkawuo62/20200731_134105-NSL-28.mp4?dl=0

VTL5C1

https://www.dropbox.com/s/wwekh07flw1cha7/20200731_134504-VTL5C1.mp4?dl=0

NSL-32SR3

https://www.dropbox.com/s/yzlu7tgeplgdwz9/20200731_134831-NSL-32SR3.mp4?dl=0

--pete

[finkaudio]

Hi Pete,

very good information :-)

I tried to find the specs and what I noticed is that obviously there is a difference between On and off....means attack and release time. Those couplers have been used for limiters in the past!

The NSL-32SR3 has identical attack and release time and so it's not a surprise that the signal looks more symmetric. I just ordered those NSL-32SR3 to test them with the original schematic.

Again, thanks!

ATB KH