abs@ukc.ac.uk (A.B.Smith) (02/05/91)
Hi, I am currently building a number of audio circuits (pre-amps, effect boxes, that sort of thing) and the circuits I have don't specify the construction material of the capacitor. Could someone give me a few rules on what sort of capacitor I should select (ie. when should I use Ceramic, Mylar, Polyester, etc). I have a few basic books on electronic construction but they omit this sort of information. Could I use the same type throughout the circuit (except for the electrolytics) ? And can I use tantalum beads capacitors instead of electrolytics ? Many thanks, Andrew.
kludge@grissom.larc.nasa.gov ( Scott Dorsey) (02/06/91)
In article <64@owl.ukc.ac.uk> abs@ukc.ac.uk (A.B.Smith) writes: >I am currently building a number of audio circuits (pre-amps, effect >boxes, that sort of thing) and the circuits I have don't specify the >construction material of the capacitor. Four coupling capacitors in audio circuits (DC blocking caps), use polyester or polypropylene caps. They'll be a bit hard to find in large values, but the audio mail order places carry them and you'll be shocked at the improvement in sound over cheap electrolytics. For power supply caps, use good quality electrolytics. The high frequency types designed for switching supplies are good; they have low ESR which permits them to deliver a lot of current fast on demand, which is important for even small signal audio stuff. You'll find capacitors contribute a lot to the sound quality (and resistors contribute a lot to the noise figure). --scott
gsteckel@vergil.East.Sun.COM (Geoff Steckel - Sun BOS Hardware CONTRACTOR) (02/06/91)
In article <1991Feb5.185727.14775@news.larc.nasa.gov> kludge@grissom.larc.nasa.gov ( Scott Dorsey) writes: In article <64@owl.ukc.ac.uk> abs@ukc.ac.uk (A.B.Smith) writes: >I am currently building a number of audio circuits (pre-amps, effect >boxes, that sort of thing) and the circuits I have don't specify the >construction material of the capacitor. - For coupling capacitors in audio circuits (DC blocking caps), use polyester - or polypropylene caps. The `true believers' in audio wonderfulness would never use a polyester cap anywhere. In fact, they do have a large `dissipation factor' and apparently are somewhat nonlinear, as are `high-K' ceramics (with Z5U or Y5V tempco markings). I would recommend polystyrene or polypropylene film caps for wonderful coupling caps, or low-K (NPO) ceramic or mica caps for small values ( < 100 pF). They will be much larger physically and cost much more than the polyester caps. I don't think this distinction applies for bypass (shunting unwanted signals to ground). I'd use polyester for bypass type applications. A common trick is to bypass an electrolytic with a film capacitor of 1-10% the electrolytic's value to achieve good high frequency performance for bypass applications. Cost & size vs. religion is the tradeoff in this case. geoff steckel (gwes@wjh12.harvard.EDU) (...!husc6!wjh12!omnivore!gws) Disclaimer: I am not affiliated with Sun Microsystems, despite the From: line. This posting is entirely the author's responsibility.
kludge@grissom.larc.nasa.gov ( Scott Dorsey) (02/06/91)
In article <4193@eastapps.East.Sun.COM> gsteckel@east.sun.com (Geoff Steckel - Sun BOS Hardware CONTRACTOR) writes: I wrote: >> For coupling capacitors in audio circuits (DC blocking caps), use polyester >> or polypropylene caps. > >The `true believers' in audio wonderfulness would never use a polyester cap >anywhere. In fact, they do have a large `dissipation factor' and apparently >are somewhat nonlinear, as are `high-K' ceramics (with Z5U or Y5V tempco >markings). >I would recommend polystyrene or polypropylene film caps for wonderful coupling >caps, or low-K (NPO) ceramic or mica caps for small values ( < 100 pF). >They will be much larger physically and cost much more than the polyester caps. That's right. Make sure you buy only Wondercaps or some expensive foreign brand. Only polypropylene will do, and the harder they are to get, the better they are. Anyway, polyesters are usually quite fine capacitors for coupling, although at high voltages (in in working with tube gear), the polypropylenes have a good upper hand. Ceramics are bad news. Electrolytics in the audio path are bad news. Please return the rest of this discussion to rec.audio.high-end --scott
francis@cs.ua.oz.au (Francis Vaughan) (02/06/91)
In article <1991Feb5.211414.16831@news.larc.nasa.gov>, kludge@grissom.larc.nasa.gov ( Scott Dorsey) writes: |> In article <4193@eastapps.East.Sun.COM> gsteckel@east.sun.com (Geoff Steckel - Sun BOS Hardware CONTRACTOR) writes: |> I wrote: |> >> For coupling capacitors in audio circuits (DC blocking caps), use polyester |> >> or polypropylene caps. |> > |> >The `true believers' in audio wonderfulness would never use a polyester cap |> >anywhere. In fact, they do have a large `dissipation factor' and apparently |> >are somewhat nonlinear, as are `high-K' ceramics (with Z5U or Y5V tempco |> >markings). |> >I would recommend polystyrene or polypropylene film caps for wonderful coupling |> >caps, or low-K (NPO) ceramic or mica caps for small values ( < 100 pF). |> >They will be much larger physically and cost much more than the polyester caps. |> |> That's right. Make sure you buy only Wondercaps or some expensive foreign |> brand. Only polypropylene will do, and the harder they are to get, the better |> they are. |> |> Anyway, polyesters are usually quite fine capacitors for coupling, although |> at high voltages (in in working with tube gear), the polypropylenes have a |> good upper hand. Ceramics are bad news. Electrolytics |> in the audio path are bad news. |> There is a fairly well established precedence rule in selection of capacitors. This is based on minimising a number of factors. And is very much horses for courses. There are quite well established standards for defining these charateristics (including some MIL Spec ones). You can actaully measure the distortion produced by a capacitor in a simple test rig. With some dieletrics the results are not good. (> 1%). The distortion is often related to the input voltage (low volts, worse distortion) and shows some correlation with DA. All capacitors have a self resonant frequency, and capacitance tends to drop around here. Many designs seek to get this frequency as high as possible by lowering the inductance with suitable mechanical design. For audio work the critical parameters are distortion and dielectric absorbtion (DA). The best capacitors are PTFE dielectric. These are almost unobtainable in anything but very small values. The dieletric film is quite hard to make (it is hard to make without imperfections). PTFE has almost vanishing DA. The next favorite dieletric is Polystyrene. These are available in values up to the low nF without much trouble. DA is almost as good as PTFE. I have had no problems in replacing ceramic caps in audio circuits with styrocaps even though I was a little worried about stability in feedback loops. The next dielectric down is Polypropylene. Again nearly as good as Polystyrene. Available is quite large vaules (10mF) but big and not cheap. Most people I know use Roedenstein (SP?) caps here, Wondercaps are many times the price for no proven electrical advantage. Polyprops are available in 1% tolerances and are always the first choice for active cross overs and RIAA networks. They typicly have very good thermal charateristics too. (Low delta-C for delta-T) Next in line is Polycarbonate, bringing up the rear of the best dielectric group. Available in reasonable values, they are about 1/2 to 1/3 the size of Polypropylene for the same value and rating. They exhibit noticable greater DA than the others but are still quite good. Then comes Polyester. These capacitors exhibit something like 4 times the DA of the previous group. They are at least cheaper. Thermal charateristics are nothing wonderfull and they are mostly 10% or worse tolerances. Bad capacitors are high K ceramics (many thousands or time worse DA and distortion) electrolytics, and really bad are tantalums. Low K (NPO) ceramics are better but still much worse than any of the plastics. However sometimes there is no option if you need to tame instability. Tantalums really have no place anywhere near an audio signal. Leave them in power supply bypassing where they are really good. There are a few intersesting ways to improve electrolytics (and unfortunatly an electro is often the only way to get the Farads). The higher the voltage rating the better is one theory. Bypassing with plastics is a must. Bipolar (back to back electros) seem to be a bit better, and if they are biased with something approaching their working voltage things improve as well. (Hard to do, often the whole purpose is to get rid of a voltage offset, and the bias voltage must be very clean, or you ruin everything). Impeadances can be hard to work out too. Francis Vaughan
spp@zabriskie.berkeley.edu (Steve Pope) (02/07/91)
In article <64@owl.ukc.ac.uk> abs@ukc.ac.uk (A.B.Smith) writes: > > >Hi, > >I am currently building a number of audio circuits (pre-amps, effect >boxes, that sort of thing) and the circuits I have don't specify the >construction material of the capacitor. > >Could someone give me a few rules on what sort of capacitor I should >select (ie. when should I use Ceramic, Mylar, Polyester, etc). A few simple rules for audio circuits: (1) Always use an aluminum electrolytic as opposed to a tantalum in an audio signal path (this applies not only to coupling caps, but emitter bypass caps etc.). (2) Polypropylene or polystyrene are good choices for equalizers and such where some precision is needed. (3) Don't use a capacitor with high hysteresis (such as a ceramic) as a sampling cap in a sample/hold circuit. /steve
kludge@grissom.larc.nasa.gov ( Scott Dorsey) (02/07/91)
In article <10836@pasteur.Berkeley.EDU> spp@zabriskie.berkeley.edu.UUCP (Steve Pope) writes: >A few simple rules for audio circuits: > >(1) Always use an aluminum electrolytic as opposed to a tantalum >in an audio signal path (this applies not only to coupling caps, >but emitter bypass caps etc.). NO NO NO! Aluminum electrolytics are better than the tantalums, but they are still pretty bad. Use a plastic film capacitor (polypropylene is better, but polyester is okay). >(2) Polypropylene or polystyrene are good choices for equalizers >and such where some precision is needed. What does precision have to do with anything. Most of these caps are 5%. (Electrolytics have very poor tolerances, usually -10%, +50%, which is not the only reason to avoid them, but a good one). You can get high precision plastic film caps for eq circuits, but most plastic film caps aren't very high precision at all. >(3) Don't use a capacitor with high hysteresis (such as a ceramic) >as a sampling cap in a sample/hold circuit. Don't use it for anything. Throw it away. --scott
spp@zabriskie.berkeley.edu (Steve Pope) (02/08/91)
In article <1991Feb7.145212.24656@news.larc.nasa.gov> kludge@grissom.larc.nasa.gov ( Scott Dorsey) writes: >In article <10836@pasteur.Berkeley.EDU> I wrote: >>A few simple rules for audio circuits: >> >>(1) Always use an aluminum electrolytic as opposed to a tantalum >>in an audio signal path (this applies not only to coupling caps, >>but emitter bypass caps etc.). > >NO NO NO! Aluminum electrolytics are better than the tantalums, but they >are still pretty bad. Use a plastic film capacitor (polypropylene is >better, but polyester is okay). Mea culpa. I intended to say, IF the value needed is so large than an elecrolytic is the only choice, always use aluminum, never tantulum. Otherwise, don't use an electrolytic at all! > >>(2) Polypropylene or polystyrene are good choices for equalizers >>and such where some precision is needed. > >What does precision have to do with anything. Most of these caps are 5%. >(Electrolytics have very poor tolerances, usually -10%, +50%, which is >not the only reason to avoid them, but a good one). You can get high precision >plastic film caps for eq circuits, but most plastic film caps aren't very >high precision at all. Some equalizers and filters call for precision values. Seimens makes some nice 2% polypropylenes that are close to ideal. I've also seen people use dipped mica's which come n precise values but I'm not sure audio purists would agree with this. >--scott steve
dam@cs.glasgow.ac.uk (David Morning) (02/08/91)
kludge@grissom.larc.nasa.gov ( Scott Dorsey) writes: ]In article <10836@pasteur.Berkeley.EDU> spp@zabriskie.berkeley.edu.UUCP (Steve Pope) writes: ]>A few simple rules for audio circuits: ]> ]>(1) Always use an aluminum electrolytic as opposed to a tantalum ]>in an audio signal path (this applies not only to coupling caps, ]>but emitter bypass caps etc.). ]NO NO NO! Aluminum electrolytics are better than the tantalums, but they ]are still pretty bad. Use a plastic film capacitor (polypropylene is ]better, but polyester is okay). Where can I get 100uF emitter bypass or 10uF coupling polypropylene or polyester caps? Dave
kludge@grissom.larc.nasa.gov ( Scott Dorsey) (02/09/91)
In article <7709@vanuata.cs.glasgow.ac.uk> dam@cs.glasgow.ac.uk (David Morning) writes: >Where can I get 100uF emitter bypass or 10uF coupling polypropylene or >polyester caps? In the U.S., Madisound carries good 10 uF polypropylene, and DigiKey carries 10 uF polyesters from Panasonic that I use. If you need 100 uF emitter coupling caps for an audio circuit you have a different problem. --scott