Rane RPM 26z User Manual

Page 5

Manual-3

Audio Connections

For each Input or Output Euroblock connector:

• Connect the (positive) audio line to the ‘+’ terminal.

• Connect the (negative) audio line to the ‘–’ terminal.

• Connect the cable shield to the ground terminal.

For those installations where the RPM 26z’s internal shield-

to-chassis connection causes interference, connect each shield

directly to the chassis PEM nut located above each Euroblock

connector, keeping the shield wrapped around the audio conduc-

tors as much as possible.

For optimum Electromagnetic Interference (EMI) immunity,

connect the shields at both ends of the cable. See the RaneNote

“Sound System Interconnection” for more information on system

connections and proper grounding practices.

Analog Input Stage

Each analog input uses a two-stage gain approach. The first stage

contains a variable gain preamp. The second stage contains a

Digital Trim control located immediately after the A/D con-

verter.

Input Clipping

If you’ve set the Analog Gain so the input stage is not clip-

ping, it is not possible to clip the A/D converter, since there is no

additional gain between the initial input stage and the A/D con-

verter. The Digital Trim control, located after the A/D converter,

can be set to clip the signal to your heart’s content, so adjusting

this trim to provide the hottest signal to the DSPs without clip-

ping is the most important step when setting up gain structure.

For this reason, a dedicated meter displaying the signal level be-

ing passed to the DSPs is provided in each Analog Input block.

If the DSPs are working with a clipped signal, the audio is (as

expected) distorted and none too pretty, but it is not a drastic,

damaging sound. And while it’s technically possible to write a

DSP algorithm to emulate the glorious clipping distortion of

vacuum tubes, it’s not particularly useful for an installed sound

system, where the DSP power could be put to better use remov-

ing that annoying 500 Hz feedback from the podium mic. Plus,

they don’t yet make DSP chips with gold-plated substrates for

those celestial highs and that moist, supple midrange.

Analog Output Stage

Each analog output also uses a two-stage gain approach, which

differs slightly from that of the analog input stage. The first stage

is a Digital Trim control located immediately before the D/A

converter. The second stage is an analog trim control located im-

mediately after the D/A converter. Attenuation is handled in the

analog domain, while boosting (when the incoming digital signal

is low) is handled in the digital domain. Boosting and attenuat-

ing using this two-stage approach helps maintain the RPM 26z’s

excellent noise performance.

Digital (AES3) Input

AES3 is a popular 2-channel (stereo) digital audio interface com-

monly found on professional digital audio equipment (digital

mixers, DAT machines, etc.). Each channel of the AES3 digital

stream is treated independently within the RPM 26z.

See the RaneNote “Interfacing AES3 and S/PDIF”, available

from Rane’s web site (www.rane.com/library.html), for more

information about interfacing consumer S/PDIF gear to the

professional AES3 standard.

Use the AES3 Input to:

• Connect from the AES3 Ouput of an RPM 88/44/22.

• Connect directly from the AES3 output of a digital mixer.

• Connect to an external A/D converter, effectively adding two

more analog inputs.

Incoming Sample Rate and Word Length

The AES3 input has a built-in sample rate converter capable of

accepting incoming sample rates up to 96 kHz. Sample rates ex-

ceeding the RPM 26z’s internal 48 kHz sample rate are automat-

ically downsampled. Word lengths up to 24-bits are accepted.

Control Connections

Versatile Input Port (VIP)

Eight logic input pins are provided, each capable of accepting

DC voltage between 0-5 VDC. VIP pins are used with contact

closure switches for Preset recall, or with potentiometers for

remote Level control. The functionality (Preset recall versus

control) of each pin is assignable as part of the Device Configu-

ration.

• The maximum allowable voltage on any VIP pin is 5.3 VDC.

• Use of twisted pair cable is recommended for better noise im-

munity.

• If an external device is used to generate a 0 to 5 volt signal,

connect the ground of the external device to the GND pin of

the VIP.

Preset Recall Using Contact Closure Switches

The minimum “low” voltage required to detect a contact closure

and change Presets is 2.5 V. Since the internal pull up is 100 kΩ

to +5 V, it is possible to calculate the maximum allowable cable

length, provided the wire resistance per foot (or meter) is known.

Example:

To be safe, let’s allow a maximum of 80 kΩ worth of cable

resistance. This value keeps the voltage divider formed by the

100 kΩ internal resistance and 80 kΩ cable resistance from

dropping below 2.5 V.

(5 V * 100 kΩ) / (100 kΩ + 80 kΩ) = 2.777 V

If the cable resistance is 30 Ω per 1,000 feet (305 meters)

(1,000 ft / 30 Ω) * 80,000 Ω = 2,666,666 ft (813 km)

Thus, you can only use 2,666,666 feet (505 miles) of twisted

pair cable before the Preset recall functionality becomes inter-

mittent (assuming the cable is properly twisted and not run

through excessive magnetic or electric fields).