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elektrouwe
Joined: May 27, 2012 Posts: 143 Location: Germany
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Posted: Sat Aug 30, 2014 4:32 pm Post subject:
LC-tank bass drums Subject description: from theory to working circuit |
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I recently got a donation of some 100 small power transformers. Because I don't need so many power supplies, I wondered if I could use the primary winding as a big L, add a small C. in parallel and have it resonate in the audio range.
Pic.1 shows an LC-tank simulation : L is 20H, copper windings have 1Ohm and C is 100nF. As you can see it's a really mighty base drum with a decay time in the minute range ! Unfortunately a 20H coil with 1Ohm resistance needs a lot of windings with fat wire. Although I did not mind the 100kg weight and the size of a washing machine, I decided to continue experimenting with my transformers...
Ok, reality check : Pic.2 shows the simulation with measured data from the primary winding of my 1VA, 230V:6V transformers.
L is still 20H, but a size of 2x2x3 cm3 cries for thin wire: 2kOhm is a lot, and this leads to a bass burst of only 0.1 secs
Ok, we have to fight the 2k. I knew a circuit called "negative impedance converter" with the nickname NIC. It' made of a non-inverting amplifier with positive feedback.
Pic.3 shows the bad LC-tank from pic.2 with a NIC build with 1 opamp , 1 R for the positive feedback and a 100k potentiometer to adjust gain.
As you can see, the compensation works and let us control the damping between very short bass bursts (uncompensated) and oscillation (overcompensated) ! finding the narrow sweet spot with the pot. to get a nice 0.5 ..1 sec tone is not so easy, but I can accept it for such a simple circuit.
Last step was to realize it in Lunetta style : in pic.4 the opamp has been replaced by 2 inverting CMOS amps and a 3rd inverted is used for a 2nd distorted output than can be mixed with the clean sine of the LC-tank.
Have fun !
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L´Andratté
Joined: Sep 23, 2012 Posts: 150 Location: Hamburg, Germany
Audio files: 5
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Posted: Thu Oct 16, 2014 3:31 am Post subject:
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Hi electrouwe! That´s very
You could build a decent transformer gamelan with your stack.
Where´s your mentioned pic.4? I´d like to see it.
And hear it!
Curious how all that copper sounds |
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elektrouwe
Joined: May 27, 2012 Posts: 143 Location: Germany
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