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 Elliott Sound Products ESP's Guide to Purchasing Components 

Rod Elliott
Page Created 16 October 2007

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Purchasing components is a recurring question both on the ESP forum and via e-mail. It seems that most people buy exactly (or as close as possible to) the number of parts needed for a particular project. While this may seem to be sensible, as a hobbyist, you need parts to be able to experiment - either with the design you are currently working on or to prepare for the next project.

With high-cost parts such as big power transistors, large electrolytic capacitors and transformers, it is normal to purchase what you need and no more. To do otherwise can be very costly, and any left-over parts may never get used for the typical hobbyist.

With small and cheap parts such as small signal transistors, resistors and small capacitors, having a stock of these in your parts drawers is an excellent way to ensure that many projects will not require you to buy any of these small parts at all, and others give you the opportunity to add new values to your stock. In general, it is better to stay with the more common values - obtaining a usable stock of every resistor in the E48 series (48 values for each decade) becomes expensive. The E12 series will cover most projects, but are rather limiting if you need accurate filters for example.

The number of parts you collect will depend on how much experimentation you want to do - if you expect to build many experimental circuits in your quest for knowledge (or audio nirvana) then you will need more parts than someone who only builds the occasional project.

Experimentation in particular is one of the best ways to learn how circuits work. You will learn a great deal by building simple projects then figuring out why they work ... or not. When things don't work, you often learn more than you would if they do, because you have to figure out what is wrong. While building projects that you actually need is rewarding, experimentation is the thing that will teach you far more than any website or book ever can.

The list below is intended as a general guide only - it may not suit some, but it will give you an idea of the parts that are most likely to be useful. For experimentation, you do not need the "best" parts. Pure snake-oil-filled capacitors may be specified for some projects (none on my site though), but for experimentation they are not needed at all. A few bipolar electrolytics will suffice for all the higher values (1uF and above).

It is worth getting 1% metal film resistors though, if only because it allows you to populate your next project from your own stock. This can save a great deal of aggravation, and many projects can then be completed with the purchase of very few additional parts. It is unrealistic to try to maintain stock of everything though, as it can become very expensive.

My recommendations are shown below. The number of parts can be varied up or down depending on your own expectations and/or specific requirements, but in general the parts and quantities suggested are a good start.


Resistors

As the most common electronic part known, there is almost nothing that can be built without resistors. 0.5W metal film resistors can often be purchased in packs of 8 or 10, and there are some values that are far more comon than others. Some you can ignore complelely unless a project calls for them, and when that happens, that is your opportunity to obtain some for your own stock. In general, most ESP projects use the E12 range (12 values per decade). Many circuits call for E24 or even E48 values, but this is often just to make the circuit appear more "accurate" somehow, or to make it appear "special". Few circuits really need E24 or E48 values, with the possible exception of filters that require accurate tuning frequencies. There are exceptions of course, but they are less common that you might imagine.

The list below consists only of E12 values. Very low and very high values are not common, and a small few will cover most requirements. The majority are in the middle range ...

ValueCommentsQuantity
Below 10 OhmsNot common10 of a few values ¹
10, 15, 22, 33, 47, 68 OhmsSmall range usually sufficient20-50 of each value
100 OhmsThese are fairly common50
150, 220, 330, 470, 680 OhmsSmall range usually sufficient20 of each value
1k, 1k2, 1k5, 1k8, 2k2, 2k7, 3k3, 3k9, 4k7, 5k6, 6k8, 8k2Full E12 range recommended20-50 of each value
10k, 12k, 15k, 18k, 22k, 27k, 33k, 39k, 47k, 56k, 68k, 82kFull E12 range recommended20-50 of each value
100k, 150k, 220k, 330k, 470k, 680k, 1MegSmall range usually sufficient20-50 of each value
Above 1M OhmsNot common10 of a few values ¹

1 - "A few values" is not very helpful, but I must leave this to the individual. Some people will find these values very useful, others not at all.

It's usually a good idea to include a few higher power resistors as well. Common values are 0.1, 0.22 and 0.47 Ohms (all 5W) and perhaps a few values between 100 ohms and 1k in 1W. These are just handy to have around, and are by no means necessary for quick test circuits for line level applications. As with any generalised recommendations, it depends a lot on what you are doing.


Capacitors

Caps are the next most common electronic part, and there are few projects that don't use them. Standard MKT style "boxed" polyester caps are the most useful, because they have standardised pin spacings and have very good performance - despite spurious claims that may be made by the "magic component" proponents. There are also a few ceramic values that are very common, as well as some electrolytic and bipolar electrolytic types.

As with resistors, very low and very high values are not common, and a small few will cover most requirements. The majority are in the middle range ...

ValueCommentsQuantity
100, 120, 220pF 50V ceramicPower amp Miller caps, etc.10 of each
100nF 50V multilayer ceramicOpamp Bypass20-50
1, 1.5, 2.2, 3.3, 4.7 nF MKT PolyesterFairly common20
10, 15, 22, 33, 47, 68 nF MKT PolyesterSmall range usually sufficient10 of each value
100 nF MKT PolyesterVery common20
220, 470 nF MKT PolyesterNot very common but useful5-10 of each value
1, 4.7, 10, 22 uF Bipolar electrolyticVery useful10 of each value
10 uF 63V ElectrolyticVery common10-20
22, 47, 100, 220, 1000 uF 35V or 63V ElectrolyticCommon & useful5-10 each value

A few higher value electros are always useful if you need to experiment with power supply applications. 4,700uF/63V is a good value, and has a high enough voltage for most circuits. If more capacitance is needed, you can simply parallel the 4,700uF caps. As your test and experimentation stock, it doesn't matter if the caps are rated at well over the voltage you are using.


Semiconductors

There is a bewildering array of different types, having different characteristics, voltage, gain, bandwidth, etc. They are the mainstay of many simple circuits, and it is useful to have a few on hand. For many general purpose circuits, the following will allow you to verify that a design works, but you may not be able to use high voltages or currents, or get the best performance. Some devices (like the MC4558) are simply useful to have around to experiment with, even though they may never make it into any project.

The following is my recommendation, and I use them regularly (as shown in many projects) ...

TypeCommentsQuantity
BC549 NPN Small signal transistor30V, low noise, high gain10-20
BC559 PNP Small signal transistor30V, low noise, high gain10-20
BC546 NPN low power transistor80V general purpose10-20
BC556 PNP low power transistor80V general purpose10-20
BD139 NPN Medium power80V GP driver transistor10
BD140 PNP Medium power80V GP driver transistor10
TIP35C NPN 125W 100VRugged, GP high power5
TIP36C PNP 125W 100VRugged, GP high power5
TL072 GP JFET opampGood performance in most circuits5-10
MC4558 GP, Very cheapHigh performance opamp5-10
1N4148 Small signal diode100V, 100mA10-20
1N4004 400V 1A power diodeImmensely useful20-50
555 GP timerJust handy to have2-5

GP = General Purpose

Depending on your requirements, you may also want to include a few zener diodes (12V and 15V are useful values). These allow you to test opamp circuits without bothering with fully regulated supplies. You may wish to include a few MOSFETs as well, such as MTP3055 or IRF540 - these are cheap, and will work fine for general experiments.


Where To Purchase?

Unfortunately, this is not a question I can answer. In Australia it's easy enough, because we have suppliers that I know and have dealt with. Elsewhere, I can only cite a few companies that I know of, but have probably never dealt with. ESP customers come from all over the world - there are very few locations where ESP boards have never been ordered, especially within the Americas, Europe, the United Kingdom and Asia-Pacific (even parts of the former Soviet Union).

Ultimately, it is up to the individual to find a supplier for the various parts needed. Since I do not have any paid advertising on my site, I am reluctant to advertise specific suppliers anywhere - there are simply too many and they are too diverse. Some specialise in large quantities but will sell in ones and twos, others can sell small quantities but will be unable to supply larger orders. Some sell in large quantities only. On-line sellers come and go, and it's impossible to keep up with who has what and for how much.

As noted in several places on my site, I don't make recommendations for suppliers, nor will I attempt to give cost estimates for projects, experimentation stock or anything else. The prices vary considerably from one supplier to the next, and it's simply impossible to try to maintain any estimates for a worldwide market.


Conclusions

None of these recommendations are absolutes - many hobbyists will decide on more or fewer of any given part. There may also be favourite values/parts that have been omitted. The idea of this short article is to provide a guideline for those starting out, to ensure that they have enough general purpose parts to experiment.

As each project is built and parts are ordered, order a few extra of anything that's cheap. Add these to your collection, and before long it will be possible to make up a good part of many projects using your own stock, ordering only the devices that are particular to the project.

Occasionally, you will see common parts offered by your supplier at bargain prices. Be careful - bargain power transistors may be fakes! For most passive parts, low power semiconductors, diodes and the like, it can be very economical to purchase 100 or so if the price is right. As long as it is something you are likely to use or can adapt to your experiments, bargains can be a great way to build up your basic stock of experimentation parts.

While buying parts in 100 or 1,000 lots is economical for small manufacturers, it rapidly becomes far too expensive for hobby projects, and there's no point having thousands of something if you will never be able to use them all. While I may have 20,000 resistors and perhaps a few thousand transistors, ICs, etc. on hand at any given moment, I do short run production jobs as a result of consultation and design work. It would be very foolish of me to have to purchase a few parts just to be able to test a design. For example, every new project or revised PCB layout is built and tested before sale to ensure there are no mistakes. If a mistake is found, then I am able to offer a solution, rather than scrap an entire shipment of PCBs.


 

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Article created 16 Oct 2007