Beginner confused with BOM

[oobs]

Hi all. I just got my soldering set together, and I have made two pedals from a kit earlier. Now I am looking at the Sabbath Distortion but I am a bit confused with the rather simplistic BOM.

• Resistors: should I buy carbon or metal film ones? Does it matter?
• Same with capacitators, can I order whatever fits the number?
• Semiconductors: I found the rest but the BOM says BC184 and what I have available is BC184C NPN?

Thanks in advance!

 

[PunchySunshine]

Hi all. I just got my soldering set together, and I have made two pedals from a kit earlier. Now I am looking at the Sabbath Distortion but I am a bit confused with the rather simplistic BOM.

• Resistors: should I buy carbon or metal film ones? Does it matter?
• Same with capacitators, can I order whatever fits the number?
• Semiconductors: I found the rest but the BOM says BC184 and what I have available is BC184C NPN?

Thanks in advance!

Congratulations on joining the solder sniffers club!

Resistors: I use metal film. You can use carbon if you want that "old school mojo".
Capacitors: Look at the footprint on the board. If it's rectangle, use film caps. If it's a circle, use electrolytic. Generally speaking...if the value in in (N) than it's a film cap and if it's in (U) than it's electrolytic.
Semiconductors: You "should" be fine with the BC184C NPN that you have, but I'm sure someone that is much more knowledgeable than myself can speak to this point with authority.

 

[tegendemuur]

The letters at the end semiconductor names tell you things about how it has been packed for distribution and tells you if its consumer or industrial grade (the latter usually can stand higher temperatures, and tends to be slightly more expensive). For our purposes, if the initial letters and numbers are the same, you're fine... What the letters at the end mean specifically can be found in datasheets.

Then again, as with many things, these seem to be suggestions and manufacturers might do their own oddball things once in a while. Though I don't seem to have encountered these myself, I am sure examples can be brought up by others here...

 

[Erik S]

Build reports on the forum are a great resource. When in doubt on component sourcing, my first step is always to search by the pcb name and see what other people used.

 

[Fama]

To add to the other comments:

For electrolytic caps (and maybe some other caps too, but less commonly - I think mylar caps might be one, they're usually an "alternative" for film box) you need to keep the voltage rating in mind too. Your best bet is getting 25V or 35V (or even 50V) rated electrolytic caps, but size increases along with the rating, so for smaller sizes (like 1uF up to maybe 100uF?) you can easily get 35V or even 50V caps which will be fine in every common pedal, but for higher values than that you really need to look at the size and pick the one that fits. 6x11mm is a pretty common size that fits pretty much everywhere, and if there's a larger value it usually has more space on the PCB too.

Also to add to the rule that nF is going to be film box, uF is going to be electrolytic, and pF is going to be ceramic - but 1uF could be either electrolytic or film box, you need to check what specifically is called for. Also tantalum is an option, but I'm not very well versed in it.

For semiconductors, like others said you can usually ignore the extra letters in the end, but do verify you're buying the DIP-8 package and not surface mount version (unless you want/need surface mount, of course), and for some specific ones like charge pumps the full letter name could be important (at least the ICL7660SCPAZ comes to mind, you want the S there).

 

[oobs]

Wow, that was a fast information overload

Thanks all!

 

[CheapSuitG]

Lots of great advice, especially the build reports.

One thing to add, buy spares.

Nothing worse than breaking or cooking a component and having nothing to replace it. Or worse, losing one. I dropped a diode on the floor, spent 20-30 minutes searching for it, couldn’t find it. Asked the wife for help, spent another half hour and nothing. It was then that I knew legends of the component thief trolls was true.

 

[z2amiller]

Regarding the transistor, the letter at the end of the transistor often indicates the gain range of the transistor.

Manufacturing transistors is somewhat inexact and the gain can have a pretty large range of values. Manufacturers
will do 'binning' where they test parts from each batch and sort them into ranges. So for example, the
"plain" BC184 will have a gain (hFE) between 240 and 900. But some manufacturers will sort those into
BC184B (240-450 gain) and BC184C (450-900 gain). See https://www.jameco.com/Jameco/Products/ProdDS/2277551.pdf
for an example of a datasheet where they call this out.

 

[oobs]

Regarding the transistor, the letter at the end of the transistor often indicates the gain range of the transistor.

Manufacturing transistors is somewhat inexact and the gain can have a pretty large range of values. Manufacturers
will do 'binning' where they test parts from each batch and sort them into ranges. So for example, the
"plain" BC184 will have a gain (hFE) between 240 and 900. But some manufacturers will sort those into
BC184B (240-450 gain) and BC184C (450-900 gain). See https://www.jameco.com/Jameco/Products/ProdDS/2277551.pdf
for an example of a datasheet where they call this out.

Thanks,this is interesting! So would I be well advised to buy a few of them and test which falls on the lower end and which on the higher? Can that even be tested? And how big would the practical difference be in a pedal?

 

[z2amiller]

Thanks,this is interesting! So would I be well advised to buy a few of them and test which falls on the lower end and which on the higher? Can that even be tested? And how big would the practical difference be in a pedal?

If the BoM doesn't specify, it's probably fine. You could socket the transistor if you _really_ wanted to try to tune it, but
for most pedals, something in the general vicinity of the gain range will be fine. There are some designs where it's important
to have one transistor with less gain than the other, for example, but in those cases the BoMs just specify different transistors
with different gain ranges. Some fuzz pedals in particular tend to be more particular about their transistor selection.

If you're interested in measuring the gain, there's are some pretty cheap testers like the FNRISI LCR-P1 or these
Generic LCR-T1s.

re: buying a few of them, that's generally not a bad idea in any case, if for no other reason that they're cheaper in quantity
and buying more stuff amortizes shipping. But not necessarily because you want to try a bunch of them out.

One place where you might need to buy a bunch of transistors to test is for phasers - when you're making a XC Phase,
for example, you need to test and match the JFETs so they all have very similar parameters, or buy an already matched set.
(for JFETs, you need to match Idss and Vgs rather than hFE)