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

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m (Analog audio voltage levels)
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See also:
 
See also:
 
* https://en.wikipedia.org/wiki/Line_level#Nominal_levels
 
* https://en.wikipedia.org/wiki/Line_level#Nominal_levels
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====Audio device differences====
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{{stub}}
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In audio, you have microphones, pickups, consumer line level, professional line level, headphones, speakers, and more.
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Each of these types is associated with their own voltage level and impedance.
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{{comment|(Note: current is negligible on most signal interconnections, but is relevant for speakers and headphones, and some microphones)}}
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You get mentions of low-Z and high-Z (Z referring to impedance) - but these depend on context.
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For example, guitar pickups are low impedance in their own context, the PC line-in is high impedance in their own context -- but the actual values are approximately equal, which means a lot of signal loss, and therefore bad quality sound.
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You ''could'' remember what will and won't work, which is simpler.
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Or you could understand why, which lets you fix things.
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Note that it is often sensible to reason from the side of the connection you ''cannot'' change (can be source or load), to figure out what must happen on the way or at the other end.
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Remember the quick-and-dirty rule that a sound input's impedance should be approximately ten times that of the sound source's output impedance:
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* Too little load impedance means too much current drawn from the source, which will make the source's circuit distort, and possibly overheat and break.
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* Too much load impedance means too little load on the source, meaning that little (voltage) signal makes it out of the source to the load, meaning you may hear less than you were expecting, the noise floor and interference matter more.
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Many cases can be solved with a ''direct box'' / '''DI box''' / '''Impedance-matching adapter''',
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which seems to typically be a transformer with high impedance on the input side.
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(should also eliminate hum. In fact, hum isolators are often even simpler, namely 1:1 transformers{{verify}})
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'''When tying together wires''', you're also playing with impedance:
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* Multiple high-impedance audio sources to one load (multiple sound sources on one line-in)
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** ...e.g. using a splitter cable to put two sources on one line-in
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** will work in that it won't damage your load
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** but the impedances of your sources can interact with interesting results.
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* One source to multiple loads:
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** e.g. one line out to two line ins
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** e.g. two headphones on one headphone out
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** usually okay, but more than a few will start loading your source's output amp
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http://www.deltamedia.com/resource/impedance.html
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http://psg.com/~dlamkins/lamkins-guitar/music/article/all-about-pickups-and-impedance
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http://hyperphysics.phy-astr.gsu.edu/hbase/audio/imped.html
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http://www.sengpielaudio.com/calculator-voltagebridging.htm
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http://gaussmarkov.net/wordpress/thoughts/input-and-output-impedance/
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====Plugs's relation to balanced/unbalanced, voltage levels, etc.====
 
====Plugs's relation to balanced/unbalanced, voltage levels, etc.====

Revision as of 02:38, 17 March 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


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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 electrets give, which is what most of these are
computer sound cards have
a voltage bias for electret mics - as those 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 in here 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 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 pro line(verify) level 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

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

Connectorwise:

  • XLR3 is pro mic level, and always balanced
and mono, because one signal requires a differential pair.
if you want to carry stereo over XLR, use two cables. But in most cases the device will have 6.3mm for balanced line instead.
  • 6.3 mm input jacks are typically pro line level
TRS is balanced, see notes on that above.
TR is unbalanced, often instruments, which is often lower level (but close enough(verify))
when a device instead uses these for mic in, aux, or controllers like pedals, they will be marked as such (or switchable)
  • mixer outputs are often 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.


6.3 TS versus TRS

  • 6.35mm (1/4") TRS is typically
mono and 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.
  • 6.35mm (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. In on the same socket they usually mark it if they do (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, high load)



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

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

V+ and V- is aspecific. 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: