Hi,
Good parts?
Well I wouldn't think there would be a standard answer other than what perhaps fits the criterias set for a circuit
If the circuit has high voltages carbon comp resistors can take higher voltages than metalfilm of same size.
The difference can be over 400V's.
Carbon Comp resistors have more noise than metalfilm due to impurity in the materials and the CC's can also pick up moisture and this shows up as random noise.
Metalfilm resistors have lower noise due to purer materials, but require larger sizes in high voltage circuits to withstand voltage.
Metalfilm resistors go into short circuit while CC's go into open circuit when overloaded beyond.
CC's have sturdier mechanic structure than MT's and can thus absorb vibrations to a greater extent, while this is a minor issue as resistors can be mounted in several ways.
MT's have tighter tolerances than than CC's and thus deviate less from stamped value.
There are also carbon film resistors and those have lower noise than CC's but higher than MT's and also go into open circuit when overloaded and have looser tolerances than MT's
Resistors become many components at high frequencies ( beyond human ear)
This is important in for instance radiotransmitters and recievers et.c
Generally inductances and capacitances and other 'ghost' components that show up in a resistor at VHF are of no significance at audio frequencies.
Now a circuit like an amplifier of sorts behaves one way in the audio range and in another at frequencies higher than human hearing allows. This can be of great importance in poweramplifiers that can self destruct
from oscillations if safety measures are not taken but that is a whole other subject.
Anyway back to resistors, if a 9V treblebooster is built on a pcb I'd see no reason not to use MT resistors
for reasons of minimizing noise as I'd view that as the most important aspect and there would be no mechanical issues or high voltages or risk for short circuit.
I might have another view if the resitors sits in a powersupply or highvoltage poweramp et.c
Capacitors:
the one thing often overlooked with capacitors is the actual value and ability to hold the value in audiofilters, and it may be the singular important thing in a circuit.
Some filter circuits like Biquad, Twin T Notch et.c et.c really rely on tight tolerances and in for instance the TTN
this sets both the Q and the depth.
1% types or better are generally prefered in filters
Ah, now a capacitor may sit between the collector and base of a transistor...............now there's also a ghost component known as Miller capacitance that is created within the transistor and is amplified by the gain of the transistor. The cm, is found in the datasheet of the transistor and is easily computed, and it sits then in parallell with the external capacitor and the combined value of those is then amplified..........
Now some capacitors can be microphonic- depends on the circuit
Generally capacitors don't generate noise -unless they are cheap elko's in which case noise can be generated.
In old guitarpedals one can use freezerspray to detect such a noisy cap and it is done by freezing one cap at a time and listening to the output for changes in noise-if there is a change when freezing one cap that cap is faulty.
Capacitors that are used frequently stay healthy and lifetime for an Elko can be at least 30 years if it is constantely used.
Check capacitor datasheet provided by most capacitor manufacturers for further information on lifetime expectancy as this depends on type and what voltage is applied.
However if you find an old tubeamp in a barn somewhere be vary that old elkos dry up- in some cases one can restore such caps, but that would likely only be an option if there is no mechanically suitable replacement.
Capacitors also have a set of ghost components and thus come into play and become important again at high frequencies above human hearing and wether it affects again depends on what happens in the circuit at such high frequencies
Uh, I think this must be all for this time as capacitors is a huge subject, but I'd say for guitarpedals I would not see any reason for using other than polyester or polypropylen capacitors that are small, mechanically stable and can take most cleaning substances, and there are these days fine low noise elkos, however the really small ones may have shorter lifetime depending on the circuit type, while in guitarpedals that would be........well not really something to worry about
Of typical interest in a circuit would be mechanical stability also with capacitors
Ah, but one more thing so those old germaniums- the 'pop corn' trannies those do have a lot of inherent noise and also this pop corn noise that stems from impurities in the materials and usually very low gain.
There would as I see it only be two things of interest when looking at a transistor like for instance OC44 in a treblebooster for guitar and those would be the low ft and possibly distortionlevels.
Right, well then this with potentiometers...............now since musicians sometimes operate potentiometers with their feet it would be nice if the whole shaft wouldn't protrude the potentiometerbody during such circumstances.
Some pots have a flange others one can like MXR put a relief washer on.
The lifetime of potentiometers is defined in the specifications for the potentiometer and so is noise.
Some pots are sealed and that is a good feature in guitarpedals since little particles can enter the box via input and output jacks
A pot is a mechanical part and a mechanically sound one with good lifetime expectancy may cost a little.
Buying parts in just one or two or for just one pedal can be really expensive but parts in bulk gives reasonable prices.
The parts you'd pay for in a commercial guitarpedal would bethe mechanic structure and the mechanical parts.......
Have fun
BJ
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