Frequently Asked Questions, Technical Notes and Support
F.A.Q.
Here is a list of Frequently Asked Questions regarding our rack mount mixers and mixer/amplifier units.
What is a "Source"?
A source is stereo or mono program material such as an AM/FM Tuner, CD Player, Video Player, MP3 player etc. "Source" is a source of program material
Mono or Stereo?
Does your application call for a mono or stereo setup? Most often in installation applications such as restaurants, clubs, bars, schools, and churches; the outputs are configured in mono because a stereo image is usually lost anyway and stereo music does not sound good if you can really only hear one side. All Rolls mixers and mixer/amplifiers either have a stereo/mono feature, or are configured for mono operation only. Rolls products give you the choice for your particular environment.
What is Phantom Power for, and how much do you need?
Phantom power refers to a device that is not powered by a power cord or battery or a conventional power supply. Usually it is part of the connecting cable to the device and a powered device appears to have no external power or "phantom power". A "Condenser" type microphone requires power in order for it to work. Many have places inside the microphone for batteries. All condenser microphones should operate on Phantom Power which is simply a voltage that runs from the mixer down the microphone cable and to the microphone. This eliminates the hassle of changing batteries. All Rolls mixers and mixer/amplifiers provide phantom power.
You may have heard an old industry standard voltage for phantom power of 48 volts. While this may be true, most condenser microphones will operate on 9 to 12 VDC of phantom power. Rolls mixers and mixer/amplifiers use 12 to 48 volts depending on the model #. With phantom powered Mic's the important thing for proper operation is usually current, not voltage. Even though the phantom voltage of a Rolls product may be 12V the circuit is made to deliver the same current (amps) as a 48V system. It is important to note that very few devices still have to have 48 volts in order to draw enough current.
How much amplifier power do I need?
The amount of amplifier power needed for your application will largely depend on the size of the room you're putting the sound into. Obviously, larger rooms require more amplifier power. A small board room is fittingly powered by a simple PA71 if a single microphone and single source needs to be amplified to a small speaker. However, large banquet rooms or ballrooms may require large or even multiple amplifiers to be sufficiently powered. For large applications, this decision should be left to a qualified professional only. This is usually a difficult question that can only be answered by a sound contractor. Some people just get a huge amplifier and speakers thinking they will just turn it up to the level they need. But, besides being dangerous, this can lead to many "bad sound" problems associated with the particular venue being used. If "good sound" was just a matter of size and power, there would be no small equipment.
How do I choose between a using a separate mixer and amplifier, or a mixer/amplifier combo unit?
An important factor in your application may be space; specifically rack space. The Rolls Mixer/Amplifiers were designed with this in mind. The MA1705 and MA2355 require only a single rack space, and the MA2152 uses two rack spaces. Compare this to three or even more rack spaces taken by individual mixers and amplifiers. Once again though, necessity will make the determination. A separate Mixer and amplifier is usually desirable if size, budget and user expertise are not a consideration.
Technical Notes and Support
Bellari VP129 Tube Preamp humming problem
If the VP129 is not properly grounded, it will cause a hum or buzz in your audio system. If you are having a hum or buzz problem, try connecting the turntable ground to your receiver ground, and not the VP129 grounding post.
RS79b S/N 0326XXXX lost presets + Expanded AM
We have discovered a problem when the RS79b uses 9Khz AM centers. When we included the diode D11 to expand the AM, the 9Khz presets are not remembered. What this means is if you want expanded AM and are using 10Khz centers you need D11 in. If you are a part of the world that uses 9Khz AM centers and the unit is the serial # series shown above, you need to cut D11. This diode is located in a tricky to find spot under the display housing. This is an illustration of how fixing one problem can cause another.
We currently ship all 120V units with D11 installed and as of 15Dec03 all 220V units ship without D11
MX56s Revision
All MX56s units with serial #'s that are less than 0230XXXX have a
problem with the headphone/line out. This is only the &s" units. R16
and R23 should be 10 ohms, not 10K. The 10K ohms give very low output
with the headphones and if the other outs are used with the headphone,
they will be very low also. Please return the unit to the dealer for
repair or call Rolls for an RA.
Burned Out Display on the RS78 or RS79:
To Repair - This is an easy repair; the entire display is not burned out, the back light bulb is. All you need to do is replace it. The bulb is readily available at any electronics store.
RS79b Display locked up problems
The update for the RS79b tuner is to solder a 9.1V zener diode in location ZD3 on the RS79’s main P.C.B.
1. Remove lid. This can be done from the top of the unit remove all eight screws on the top only.
2. Locate ZD3. It is in the middle of the P.C.B. it is labeled in white ink on the top of the board the actual part is just below and to the left of the white lettering.
3. After locating the diode do not remove it just solder the 9.1V zener diode (1N5239B) in parallel with the existing diode.
Parallel is to match the black line on the new diode with the black line on the old diode and solder the new diode on the top of the other.
How to Change the Resisters on the RA62 to Make More Power Available:
Replace R101, R102, R201, R202, R301, R302, R401, R402, R501, R502, R601, R602, with 10 Ohm Resistors.
MX442 Oscillator Fix:
Some people feel the 400Hz oscillator sine wave is not pure enough. The fix we have for this is replace Q2 with a J113 or equiv.
FET, remove R49 and put it where R50 was (this leaves a blank space at R49 and you have an extra 100K res). The FET is not a
pin for pin replacement, connect the gate to the B pad, the drain to the C pad and the source through a 3.3K res to the E pad.
Also connect a 10UF cap across the 3.3K res. If the oscillator level seems too low replace R18 and R19 with 220K res. If
oscillation does not occur with these values or if you wish us to do this no charge update, please call 801 263 0366
for an RA#. Units shipped after Nov 1999 already have this update.
MX422 METER RESPONSE
We have received several calls from customers stating that their MX422 meters are not responding. The reasons for this, are that customers aren't setting the input gain properly, setting the output PAD when necessary, and don't understand the function of the meters.
The MX422, like all mixers, operate at their best with a maximum input gain. This means turning up the input Trim control until the signal is just below clipping. Doing so also provides the most operating headroom within the mixer, and the best noise performance.
The meters on the MX422 indicate output level, and are located just before the LINE / -30dB PAD switch. If the user connects the MX422 Outputs to a mixer's Mic input for example, the actual output level of the 422 will need to be much less so that the mixer's Mic input is not over driven. Thus, the MX422 -30dB PAD switch should be pushed IN. The meters will still be reading the appropriate output level.
MX422 Field Mixer Meter Response
The meters are set at the factory for a 0 indication of a 0 dbv output
level. Non responding meters is caused by only one thing, not enough level from
the output amp. To correct this please verify the following. Start with the channel and master at center positions. Make sure the monitor switch is out.
- Turn up the trim control to the point where the meters read the level you desire.
- If this causes too much output from the output jacks, push in the attenuator button near the output jacks.
- Fine tune the level you want with the channel and master controls.
Finally, if the Pro standard of 0 dB is too hot for you, there are trim pots for each meter inside the unit that can be adjusted down to a 0 indication of about -10dBv.