Audio FAQ

Q: What does the letter at the end of OPAMP model mean such as OPA627AU, OPA627BU, OPA627BM, OPA627SM?
A: The first letter, ‘A’,’B’,’S’ means ‘OPAMP Grade’ and the quality is better in following order.
‘A’ < ‘B’ < ‘S’
The second letter, ‘U’,’M’,’P’ means ‘package type’.
P: DIP type
U: SMD(SOIC-8) type
M: Metal Can type(It protects against the noise and electricity)
Therefore the SM type is the highest price as the best sound quality.

Q: I want to upgrade the Operational Amplifier (OPAMP) chips. What do you recommend?
A: We highly recommend the Texas Instruments / Burr Brown OPA2134PA. These OPAMPs are readily available from To install the new OPAMPS...
1. Take note of the direction of the existing OPAMPs.
2. Use a common chip puller (available at Radio Shack) to remove the old OPAMPs.
3. Carefully insert the replacement OPAMPs facing the same direction as the old ones.

Q: What is S/PDIF?
S/PDIF stands for 'Sony/Philips Digital Interface'. It's a protocol that is used to transfer digital signals without quality loss between two digital devices such as DAT-, MD- or DCC-recorders and also soundcards. Originally it was invented to support 20bit resolution at fixed samplerates like 32, 44.1 or 48kHz. Most consumer soundcards are transfering only 16bit data while pro audio cards now often support 24bit resolution. To transfer the signal, either an electrical/coaxial cable with one RCA connector for stereo or an optical cable (usually Toslink) is used. Most soundcards with optical S/PDIF interface use Toslink connectors. These connectors (invented by Toshiba - that explains the name) are also called 'square connectors' in some situations.

Q: What are the maximum cable lengths for digital connections?
A: Optical Toslink connections with high quality cables can be relativly long - up to about 30m there are no real problems. It is not easy to get cables with that length however. For coaxial connections, it is important to use high quality 75ohm cables. They can be relativly long then as well. If you want to use normal audiocables for digital connections, you should be careful with the length - depending on the quality, cables with more than 1m could already cause trouble.

Q: Can different type of cables change the signal quality (digital transfers)?
A: No. If the connection works (and you get a fine audible signal), the quality is always the same. If you use a cable that can't be used for digital signals, you will get loud noise or no signal at all.

Q: What is AC-3? I heard that AC-3 is transfered via S/PDIF but how can multiple audio channels be transfered when S/PDIF only supports two?
AC-3 is an encoded signal (also known as"'Dolby Digital" and "5.1") that is created with special ultra high end equipment (usually in professional audio/video/TV studios) and then saved in digital data files - for example on a DVD. The encoded signal can be transfered via S/PDIF but it is not a normal audio signal. This means that a special AC-3 decoder (often built-in in HiFi amplifiers) is needed to playback the separate channels. Software DVD players can also decode AC-3 streams on a PC.

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