Difference between revisions of "Electronics project notes/Device voltage and impedance, audio and otherwise"

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m (Analog audio voltage levels)
m (On microphone impedance)
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Consumer mics used to all be high impedance,  
 
Consumer mics used to all be high impedance,  
which is fewer components, so cheaper,
+
because that's cheaper to make and noise isn't much of an issue on a one-or-two-meter cable.
but the impedance means it's more susceptible to noise with cables longer than a meter or two.  
+
  
 +
This stuck around in habits, including PC sound cards to this day.
  
  
  
''Most'' modern pro mics have an output impedance in the 150..250 Ohm range,
+
''Most'' modern pro-audio mics have an output impedance in the 150..250 Ohm range,
so that they're impedance-bridging with a mic amp, which typically have an input impedance in the 1.2k .. 3kOhm range.
+
so that they're impedance-bridging (factor 5 to 10) with a mic amp, which often have an input impedance of around 1.2k and almost always in the 1..3kOhm range.
  
The low impedance also means you can use longer cables with less bother
+
The low impedance also means you can use longer cables with less bother -- if used  balanced+differential-style. (Which with XLR wiring to XLR mic inputs is basically a given).
: ...if [[balanced cables]] and interpreted differential-style. Which with XLR wiring to XLR mic inputs is basically a given).
+
  
  
For higher-impedance mic elements, it also implies adding a transformer in the mic to get to expected impedance.
+
For higher-impedance mic elements such as the actual capsule inside most dynamic micrphones,
e.g. most dynamic mics have transformers, apparently also largely to increase the voltage to mic levels (while not making the impedance higher than practical).{{verify}}
+
you'll need adding a transformer in the mic to get to expected impedance.
 +
 
 +
Most dynamic mics have transformers, largely to increase the voltage to mic levels, while not making the impedance higher than practical{{verify}}.
 +
 
 +
 
 +
Low impedance ''also'' means it takes some energy, which is ''very-roughly'' why condenser mics are powered and dynamic ones only are better for louder things.
  
  
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Notes:
 
Notes:
* These are "the nearest category" style ratings, not exact figures. It wily vary per microphone
+
* Marked numbers are often "nearest category" ratings, ''not'' exact figures.
 +
: It will vary per microphone design
  
* impedance varying with frequency somewhat is part of its frequency response
+
* and also vary over its frequency response
  
* not using typical bridge-style impedance ratios will alter its frequency response
+
* not using typical bridge-style impedance ratios will ''alter'' its frequency response
: this is strangely common - strange in that most people do not quite understand how/why, just that.
+
: this is strangely common - strange in that most people do not quite understand why it does or how much, just that.
 
+
* 50 Ohm is basically an obsolete standard
+
  
 +
* 50 Ohm is basically an obsolete standard. As is 600, mostly.
 +
: So low is often around 200.
  
  
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There are also some modern ~600-ohm mics out there.
 
There are also some modern ~600-ohm mics out there.
  
It seems that microphones may also be marked with their designed load impedance.
+
It seems that some microphones are marked with their designed load impedance.
600 Ohm suggests this{{verify}} and this seems to be some of the confusion.
+
600 Ohm is sometimes this{{verify}} and this seems to be some of the confusion.
  
  
  
 +
Modern mics (pro and consumer) are intended to be loaded impedance-bridge style, so with an impedance rougly ten times as high
  
 +
...more roughly than in bridging in general - loading e.g. a dynamic microphone more than that (e.g. factor five) also seems common enough, despite that this loads the microphone itself enough that it will e.g. drop out the highs.
  
 +
And regularly ''because'' of that: it makes for a warmer/darker sound.
  
Modern mics are intended to be loaded impedance-bridge style, so with an impedance rougly ten times as high (more roughly than in bridging in general).
+
However, loading it more yet tends to also drop the lows, which just sounds tinny. {{comment|(also levels decrease, but you can often gain that back up)}}
  
Loading it more than that (i.e. with lower impedance) also seems common enough,
 
despite that this loads the microphone itself that it will drop out the highs.
 
And often ''because'' of that: it makes for a warmer/darker sound.
 
 
However, loading it more yet tends to also drop the lows,
 
which just sounds tinny.
 
 
If you like the frequency response, can accept a somewhat lower signal, and don't blow up anything, have fun with whatever amount of loading.
 
If you like the frequency response, can accept a somewhat lower signal, and don't blow up anything, have fun with whatever amount of loading.
(but know that it's not quite the intent. Also if you have the choice of using an EQ if you have it anyway, this may be better for SNR{{verify}})
+
(note that if you have an EQ on your mixer, that may be easier to control, and slighly better for overall SNR{{verify}})
  
 +
Don't expect the same from cheaper mics - e.g. the transformers in cheap dynamics tend to be smaller, so react differently{{verify}}.
  
For some condenser mics, higher-than-1:10-loading will start distorting (loaded FET?{{verify}}).
 
Which is sometimes done intentionally too.
 
  
 +
Condenser mics react differently, because you're dealing with the FET and not the capsure. Loading them more will more easily distort the signal -- which is also sometimes entirely intentional.
  
In all cases the exact response varies per microphone type, and components/design so can vary with model.
 
Also don't expect the same from cheaper mics - e.g. the transformers in cheap dynamics tend to be smaller, so react differently{{verify}}.
 
  
 +
In all cases the exact response varies per microphone type, and ''can'' vary with model due to the components/design used.
  
  
Some mic amps allow you to select their input impedance.
+
 
 +
Some mic amplifers allow you to select their input impedance.
  
 
This in part to work with a wider range of mic impedances,
 
This in part to work with a wider range of mic impedances,
 
yet many people will probably consider it a dark/bright sound setting.
 
yet many people will probably consider it a dark/bright sound setting.
 
 
  
  

Revision as of 17:29, 4 June 2018

This is for beginners and very much by a beginner. It's meant to try to cover hobbyist needs, and as a starting point to find out which may be the relevant details for you, not for definitive information.

Some basics and reference: Volts, amps, energy, power · Ground · batteries · resistors · changing voltage · transistors · fuses · diodes · varistors · capacitors · inductors · transformers · baluns · amplifier notes · frequency generation · skin effect


And some more applied stuff:

IO: wired local IO wired local-ish IO · · · · Shorter-range wireless (IR, ISM RF, RFID) · bluetooth · 802.15 (including zigbee) · 802.11 (WiFi) · cell phone


Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes

Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer

Audio notes: basic audio hacks · microphones · amps and speakers · device voltage and impedance, audio and otherwise ·

Less sorted: Common terms, useful basics, soldering · Microcontroller and computer platforms · Arduino and AVR notes · ESP series notes · Electronics notes/Phase Locked Loop notes · mounts, chip carriers, packages, connectors · signal reflection · pulse modulation · electricity and humans · Unsorted stuff


See also Category:Electronics.


Impedance and interconnection

Connecting two things

Output impedance is larger than the load's input impedance

Impedance matching

Impedance bridging

Audio

Analog audio voltage levels

...and impedances.

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)



Most audio levels are not so well standardized, and some have changed over time, somewhat quietly. So assume each can be a factor of two off and can require a little knob twiddling at least. (TODO: sort out peak versus RMS values)


  • phono input
on the order of a milliVolt, and seems to often be the not-yet-amplified output of phono cartridges
There are two common types:
Moving Magnet (MM) pickups give ~2.5mV,
Moving Coil (MC) give ~0.2mV
MC versus MM is one of those debates. Higher-end is usually MC, but quality also significantly depends on other factors.
phono pre-amps will amplify this to (typically) consumer line level (and impedance)
phono directly on line-level (or mic level) input as-is will be very too quiet (or if you manage to amplify it, very noisy)
avoid connecting non-phono and in particular line-level outputs to phono inputs, it may be possible to blow the preamp
impedance
cartridge output: varies, order of 500 Ohm or lower (verify)
phono amp imput: 47k Ohm


  • consumer microphone level
on the order of ~10mV (verify)
because that's the order of what ~1cm electret (FET output(verify))s give, which is what most of these are
computer sound cards have
a voltage bias for electret mics - as electrets are the typical mic you plug in
internal amplication to get it to the same level as line level. (Relevant mainly in that plugging line level into mic in will distort)
impedance
mic output - high-impedance microphones are typically cheaper, e.g. the common electret mic is often 1-2kOhm but some 10kOhm+ (verify)
PC mic in impedance: 1..10kohm (varied over time and with cards)


  • consumer line level
on the order of ~300mV (~310mV RMS, ~440mV peak, 0.9V peak-to-peak)
also sometimes known as -10dBu (mostly in situations that also do +4dBV pro levels)
but has varied somewhat over time.
I've seen amplifiers with a sensitivity of 250mV, older ones with 150mV
Some recent devices are moving to higher voltages - amps may choose to deal with up to 1V, or 2V in the case of DVD, Bluray(verify) (perhaps in imitation of pro line level?)
when the the other end is not aware, you may need to attenuate the output, and/or keep the amplification low, to avoid distortion.
impedance
line in impedance is often ~100 Ohm. Possibly higher, up to 1 kOhm
line out impedance is often ~10 kOhm. Possibly higher, up to 1 MOhm


  • professional microphone level
order of 10mV.
Can be ~1mV, can be ~200mV (in theory more but this is atypical)
more varied designs, and possible amplification at the mic, means more variation with design and per use
(e.g. dynamic mics are somewhat intentionally low, to be able to deal with the louder things)
...so you will need that gain knob
impedance:
mic output: most are (higher) in the 50..200 Ohm range, with deviations (see more notes around here)
mic preamp/mixer input: order of 1..2kOhm


  • professional sound line level
the standard also known as +4dBV means 1.2V RMS (1.7V peak, 3.4V peak-to-peak) (verify)
with some variants a little higher and lower, so think 1V order of magnitude


  • instrument level has no standard
...but is often somewhere between mic and line level
output impedance
pickup impedance is often quite high (see also notes below on pickup impedance)
input to a mixer will typically need a direct box (a.k.a. DI) to convert to typical impedance
the exception is guitar amps, which expect high impedance, basically because they expect directly connected pickups


Less standard / more varied:

  • headphone level
roughly commercial line level, but less of a standard - can be higher.
using headphone out for line out is safe (because the voltage is the same, and line ins have higher impedance)
driven by amps with an impedance of roughly 4Ohm in that it has enough power enough to drive a ~30-60Ohm headphone (with a few milliamps(verify)
headphones are often around 30-60 Ohm
there are ~4Ohm, but you reakky woudn't plug those into everything (likely to distort)
there are 250Ohm-600Ohm headphones, but these need their own preamp (the idea here being that you can design for slightly better THD with less load on the amp)
  • Car audio tends to be on the order of 2V, sometimes 4V (verify)
so a headphone amp can be a good cheat to connect consumer-level things to this
  • consumer speaker wires
The voltages are proportional to the amplifier's/speaker/s ability (and relate to be).
For ~100W speakers you'll see up to a few dozen volts
a tiny desktop speaker may be <1W (verify)
impedance
speaker load is often 8 or 4 Ohm (sometimes 2, sometimes 16)
amplifier output impedance is typically very low, say 0.1 Ohm (this is also why the whole 'match your speaker impedance exactly to your amp impedance' thing is nonsense in a literal sense -- but with lower-impedance speakers you should limit how much you turn up the volume, because the maximum sensible power output happens earlier - and above that you get both distortion (THD increases with load) and risk of damage)
  • pro speaker wires
not really a thing. Most speaker cables are either
XLR-connected: carrying line signals to active speakers
Speakon-connected: already-amplified signal to a passive speaker
TS: already-amplified signal to a passive speaker. (Sometimes avoided to avoid smoky mixups, then typically Speakon instead)
Note these are different from TS instrument cables, basically in that instrument cables use a thinner core-and-shield and these are beefer and not shielded (just 2-lead stranded(verify))


See also:

Audio device differences

Balanced audio / pro audio

Plugs's relation to balanced/unbalanced, voltage levels, etc.

Connectorwise:

  • XLR3 is pro mic level, always balanced/differential, always mono.
mono, because one signal requires a differential pair.
if you want to carry stereo over XLR, use two cables (in practice, stereo is often about inter-device, and may well be two balanced 6.3mm TRS instead).
  • 6.3 mm is (typically) pro line level (6.35mm but people are lazy typers)
6.3mm TRS is balanced mono, see notes on that above.
or, sometimes, unbalanced stereo. This is an exception and will be noted.
6.3mm TR is unbalanced mono, often instruments, which is also often lower voltage levels (but close enough(verify))
when a device instead uses 6.3mm these for mic in, aux, or controllers like pedals, or stereo, they will be marked as such (or switchable)
  • mixer outputs are often two 6.3mm jacks (balanced, TRS)
  • RCA on a mixer are typically only used for phono in, or consumer in (aux)
so common mode. Ideally it's isolated (to avoid conductive ground loops)


On 6.3 TS versus TRS

  • 6.3mm (1/4") TRS is most typically mono and balanced/differential. A mixer input will often mark this as "balanced"
Tip and Ring is the pair, Sleeve is shield.
No, it's not stereo. And using a 3.5mm-to-6.3mm converter to plug in consumer line level will do Weird Things.
  • 6.3mm (1/4") TS - instrument cable
is mono, and not differential
Tip is signal, Sleeve is shield,
mixers tend to accept both TRS balanced and TS unbalanced. If on the same socket they usually mark it (e.g. "bal/unbal")
Note that unbalanced inputs are not always isolated, so connecting unbalanced things other than instuments could create common mode issues.
contrast with...
  • 6.35mm (1/4") TS - speaker cable - that is, amplifier-to-passive-speaker
basically a pair of thicker wires than instrument cable would use, and no shielding (it doesn't have to care at all because it's higher voltage, low-impedance load so coupling falls into nothing)



Things to avoid

On pickup impedance

Things that are't pure bridging

Other notes

On microphone impedance
On 600 Ohms, and impedance matching

DI

Impedance-matching adapter / impedance-matching transformer / line matching transformer

Digital logic voltage levels

An image search like this may be the simplest answer.


When, power-supply-wise, a distinctin is made between e.g. Vcc and Vdd, it's BJT and FET:

  • VCC - positive supply, BJT
  • VEE - negative supply, BJT
  • VSS - negative supply, FET
  • VDD - positive supply, FET

Which note, is referring to collector, emitter, source, and gate

V+ and V- is not specific.

https://en.wikipedia.org/wiki/IC_power-supply_pin



In the context of logic levels: (sorted from higher to lower voltage spans)

  • (VCC)
  • VOH - maximum output high
  • VIH - minimum input high
  • VT - theshold level, used in a few definitions, and applies to devices that transition at a given level(verify)
  • VIL - maximum input low
  • VOL - minimum output low
  • (Gnd)

Usually/ideally, boolean levels should be in VCC-VOH for high, and VOL-Gnd for low.


The VIH-to-VOH difference is the high noise margin (sometimes NMH), the VIL-to-VOL difference is the low noise margin (sometimes NML). These two mean that noise (or voltage drop) of about this magnitude won't disturb the boolean interpretation.


The VIL-VIH interval is usually not defined as either logic level (devices could choose one or the other).




Some voltage level systems:

  • TTL: O to 5V. Boolean levels: 0V~0.8V should be low, and 2V to Vcc should be high (where Vcc is ideally between 4.75V and 5.25V). More specifically:
    • VOL: 0.4V
    • VIL: 0.8V
    • VIH: 2V
    • VOH: 2.4V
    • VCC: 5V
  • LVTTL: 0 to 3.3V. Threshold levels identical to 5V TTL but VCC is 3.3V (so only the VOH - VCC interval is smaller)
    • VOL: 0.4V
    • VIL: 0.8V
    • VIH: 2V
    • VOH: 2.4V
    • VCC: 3.3V
  • CMOS: various levels, levels mostly relative to VCC. Variants include: (verify)
    • CMOS with VCC=5V
    • CMOS with VCC=2.5V
    • CMOS with VCC=1.8V
    • CMOS with VCC=1.5V
    • CMOS with VCC=1.2V
  • ETL
  • BTL
  • LVDS
  • PECL
  • RS232
  • RS485, RS422


See also: