DAC/Amp Basics

The gist of it

Besides your headphone there are two more very important links in your audio chain that determine the quality of the final sound.

1.) DAC: is an acronym for Digital to Analog Converter. It is the chip inside your device that receives the digital bit stream from your hard drive and converts the ones and zeros into an analogue waveform. This waveform is then send at line level to the amplifier for, well who would have thought, amplification.

2.) Amp: The audio amplifier receives the processed audio signal from the DAC and amplifies it (ideally) with minimal distortion. This allows the listener to achieve a comfortable listening volume and adjust the loudness depending on the headphone’s power requirements.

DO I NEED A DAC/AMP?

Yes, you absolutely need both! But chances are pretty high that the DAC and Amp in your phone or PC are totally fine. All consumer headphones are designed to be used with portable devices and desktop computers. Only pro audio equipment and more expensive enthusiast grade headphones absolutely require dedicated amplifiers.

I have a DAC with a 3.5mm output, can I hook up my headphones?

A common error is to connect plugs and sockets together just because they fit. Don’t assume audio level based just on the type of plug being used. The same type of plug can be used for different purposes (and different audio levels). DACs output an audio signal at line level which will not drive headphone correctly.

Rule of thumb: If you spend more than $150 on your headphones it is time to think about the rest of your audio chain.

The different In- and Output options of the headphone world

Tip [Ring (Ring)] Sleeve aka. TS / TRS / TRRS

TS = Mono: Most often use 6.3mm connectors to transfer analog audio from Pre-Outputs to powered speakers.

TRS = Stereo: Any headphone that doesn't have an inline mic or controls

TRRS = Four Conductor: Any headphone with inline mic or controls, rarely used for balanced stereo w/o controls.

This type of connector is "the" audio jack everyone knows and loves, except some phone manufacturers.

The jack comes in different sizes which are used for different applications:

  • 2.5mm: When manufacturers want to mess with you.
  • 3.5mm: For every piece of personal audio equipment ever.
  • 6.3mm: A very sturdy and robust connector used in studios and other professional fields.

Stereo 4pin XLR or dual mono 3pin XLR

4 pin XLR proved to make more sense than 2x3pin connectors as it's an easier, less cumbersome implementation.

Pin 1 is L+ (left positive), Pin 2 is L- (left negative), Pin 3 is R+ (right positive), Pin 4 is R- (right negative).

Nearly all balanced headphone amps use this configuration.

Male 3.5mm connector variants

Male 4pin XLR connector

Analog output options on a Questyle CMA400i DAC/Amp

Common digital input connections (from Source to DAC):

The presence of one or more of the following connections is a give-away that you have a DAC in front of you.

USB:

Is used for data and power input. Cheapest and easiest way to get your precious audio data out of your PC or phone. High quality DACs usually have a separate power input because if a USB connection transfers data and power it may cause issues if the source USB root from the PC is of poor quality.

Optical aka. SPDIF / TOSLINK:

  • S/PDIF = Sony/Philips Digital Interface Format - a digital format for the transmission of uncompressed stereo audio
  • TOSLINK = Toshiba Link - a standardized optical fiber connector system

Only transfers data, not power. This connection ensures a 100% clean input to the DAC. But a DAC with optical input must also feature a dedicated power supply from an electrical outlet.

S/PDIF is a type of digital audio interconnect used in consumer audio equipment to output audio over reasonably short distances. The signal is transmitted over either a coaxial cable with RCA connectors or a fibre optic cable with TOSLINK connectors.

USB Type A-B Cable

Optical TOSLINK Cable

Coaxial RCA Cable

Analog inter-connections (from DAC to Amp or between Amps):

These connections come into play once the DAC has done its job and it is time to transfer the processed signal from the DAC to the amplifier or headphone.

Unbalanced RCA (Cinch):

Can be found on almost every consumer DAC or Amplifier. An unbalanced cable consists of two connectors with two conductors each, connected by two wires inside the cable—a signal wire and a ground wire. Inside the cable itself, the signal wire is typically in the center of the cable with the ground wire surrounding it. The ground wire serves two functions—it carries part of the audio signal and serves to shield the main signal wire to some degree from outside interference from noise such as the hum from lights and transformers, as well as RF (radio frequency) interference that comes from TV and radio transmissions. It does a decent job of rejecting noise, but unfortunately, the wire itself also acts like an antenna and picks up noise.

Balanced 3pin XLR:

A balanced cable, by contrast, has three conductors in the connector and three wires in the cable. Two signals wires plus a separate ground wire. As in the unbalanced cable, the ground wire still surrounds the signal wires and is used as a shield against interference. The signal wires both carry a copy of the signal, but the two copies are sent with their polarity reversed. If you sum two signals that are identical but are reversed in polarity, the signals cancel out, leaving you with silence.

The receiving gear will flip the inverted signal back into its original orientation. But because both copies of the signal picked up the same noise as they traveled along the cable—and that noise is identical on the two wires in the cable—flipping the polarity of what arrives at the receiving gear will produce the original signal intact and noise which now has reversed polarity.

Summing that gives you a welcome result: signal that’s preserved and noise that’s canceled.

Unbalanced RCA Cable

Unbalanced 6.3mm TS Cable

Balanced XLR Cable

Full Size XLR next to XLR Mini

Digital and Analog in/output options on a Questyle CMA400i DAC/Amp

Different types of output signals:

  • Line-Output - Fixed:

The most common and important output on any DAC, it sends a fixed analog (usually -10dBV) signal to the Amplifier. Line output only carries very low current and should / can not really be used with a headphone.

  • Pre-Output - Adjustable:

A type of output that can be most often found on DAC/Amp combo units. This adjustable output lets you change the signal strength via the amp's volume knob. A perfect use case for this type of output is connecting a set of powered loudspeakers to an amplifier. A pre-output is often features a "mute relay". This mean inserting a headphone connector to the amplifier will mute the connected speakers. Removing the headphone from the output will resume playback via the pre-out.