![]() This is increased when feedback is applied. Even the TL071/2 has an input impedance of 1TΩ, with typical bipolar opamps only providing around 300MΩ or so open loop. The OPA2134 (or the single OPA134) has an input impedance of 10TΩ - and that is not a misprint. 9V alkaline batteries have a typical capacity of around 580mA/h, so with a load of ~10mA it should provide over 50 hours operation (including the LED). Be aware that the OPA2134 draws roughly double the supply current of a TL072, so battery life will be reduced. A single 9V battery is not advised for a TL072 because it is not designed for operation at less than 10V. While the OPA2134 is a fairly expensive opamp, they have much lower noise than the common-or-garden TL072. The three circuits are shown using a 9V battery and an OPA2134 (or NJM2068) opamp. Some players tune for C 1 (32Hz), but that's still easily accommodated with the circuits shown below. The circuit is simplified considerably for musical instruments, because response below 40Hz isn't necessary (the lowest note on a traditionally tuned double bass is E 1 - 41Hz). The circuits shown in the article/ project are intended more for a specialised bench amplifier, and aren't really suitable for musical instrument pickups. ![]() The general principles are discussed in some detail, but it can't be considered a 'true' project for several reasons.įor starters, the final circuit (shown in Figure 10 of the referenced article) requires the use of a 1GΩ resistor, and these are not easy to get and are expensive. The basic principles are discussed in the article High Impedance Input Stages / Project 161. I've also experimented with piezo transducers. However, there is an exception to the 'high impedance' rule that's covered later (charge amplifier)įor reasons that escape me, I've not described a piezo preamp before this, even though I have used piezo transducers in a number of projects developed for customers. While bipolar input opamps can be used, there will be a significant noise penalty. Almost without exception, this means a FET input, either JFET or FET input opamp. In most cases, the input impedance needs to be somewhere between 'high' (1MΩ or so) to exceptionally high (greater than 100MΩ). ![]() They can be used as pickups for various musical instruments, such as acoustic guitars, violins, cellos, double-bass (aka upright bass), ukuleles and mandolins (etc.), and also as accelerometers. I tried to play with the bridge placement to find a spot where the G string was louder, but the D string was losing volume, and the high E string was positioned too close to the edge of the fingerboard.Piezo transducers are common in a range of different areas. The two lower strings were much louder than the remaining strings and the G string was dead. ![]() Despite adding a custom JFET Tillman preamp, I add weird and unsolvable outcome. I was unhappy of the original piezo included in the guitar. This article is an update of the post I made about the mods I did to the Harley Benton Custom Line ResoKing guitar. New Piezo Transducer pickup – Artec PP-607 Ceramic PIEZO Pickup
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