eightstring

R.G.: Before reading your posting, I finally understood that the driver needs a magnet.However the driver still only pull and not push. In the begining I thought a frequency divider or a dc shift was needed to avoid "attraction rectification". Dc shift is energy consuming. The answer was simple!. A magnet is the same as a dc shift but with no energy consuming. The magnet is used to bias the coil attraction and make it entirely positive (or negative, depending the placement). This explains why lead reversing or magnet polarity reversing did actually change the sound of the strings in your cases.

onelastkiss I said the coil can only pull and cannot push. Imagine two magnets,in north/south polarity they attract each other (what i call pull), in south/south or north/north polarity the repel each other (what i call push). Now imagine an electromagnet,a battery,and a piece of iron or steel. In a polarity the electromagnet will attract the iron, but in the reverse polarity it STILL will attract the iron.Thus the only option is to attract or not to attract,to pull or not to pull. The iron piece is not a magnet, it can be only attracted. The string is the piece of iron and the sustainer driver is the electromagnet. Well, when you send a ac signal to the driver,the negative cycles will pull just like the positive ones,so the the attraction force will look like the output of a bridge rectifier.Making the cycles to be twice as fast. Because of this,the string fundamental can be only driven with half of its frequency, and also is possible to drive the string with a high frequency modulated to half the frequency of the string.I previosly read in the thread someone talking about a patent talking about using a 40khz tone to drive the strings. sorry I made a drawing but I have no webpage and cannot post it. You told the hex drivers had problems with trying not to drive adjacent strings. Anyways the problem should be less than a single big driver,isn't it? ansil: I think transformers are lame because they have a lot of problems,when managing wide bandwidth or high frequencies,but sure someone can go with it. For higher impedance drivers I had I mind something like these: http://www.geofex.com/circuits/+9_to_-9.htm and or http://www.geofex.com/circuits/+9_to_33.htm Simply higher voltage available. (98% efficiency).

Hi , I'm new to this thread. I had the idea to build a diy sustainer for a couple of years. In jan '05 I build a sustainer circuit, it didn't work ,the last stage had little power and sucked out batteries fast,and the strings didn't move,but the signal conditioning work was good.I though the notes should be shifted 90º degrees and they did. Since then I think the driver is the most important thing to build and optimize. I have been experimenting with pure tones with my sound card (has a powerstage that never burns!) (old isa soundblaster16). For the A string (110hz) i need a tone of 55hz to drive the fundamental. for the other notes, i always need half the frequency of the string to drive it. This is because the coils cannot push steel,only can pull it (with negative or positive current) then the atraction is RECTIFIED.This converts a 55hz tone in a 110hz tone with harmonics. To drive a string with its own frecuency i think you need to have a entirely positive or negative signal (to avoid attraction rectification), or use a somewhat complex cmos frequency divider to obtain a one octave less tone. I saw your are using a rather simple amp circuit (sorry i read just 20 pages of the thread).How can you drive the fundamental of a note? I have achieved to drive to fundamental tone of the A string (110hz) with a 1000hz and 2000hz tones (amplitude modulated at 55hz), 4000hz moved little. The coil (a small one with just 1.3 ohms) did get too hot with a 55hz tone but with 2000hz*55hz it just got warm and moved just a bit less. I'm trying to guess the size of the coil, the gauge of the wire, nº of turns etc. For a same size of coil there can be many versions: thick wire and few turns , and thin wire and many turns. The latter is going to have more inductance, but more resistence also.In principle it's a matter of the voltage available to drive it. The second needs more voltage, the first more current. But the second one has more inductance and can filter high notes (and may need too high voltage for a battery), the first may send the energy straight to heat.In an AC transformer, the primary has a inductance that stops the 50hz/60hz frequency with imaginary impedance.When the secondary is loaded , it somewhat sucks the primary magnetid field letting more current to pass. A driver should be like that,aimed at the string probable frequency. I also think that (although i would like a small driver) a big driver should be more efficient, because a "upscaled" version of a coil may have the same inductance (same turns) but less resistance (being more optimal). What do you think?.