There are at least 2 methods to properly setting system gains. One is by using an oscilloscope. The other method involves using a digital multi-meter.
The idea here is to use ALL of the available "dynamic range" of each electronic device in the system. In other words, we want all components to "clip" at the same time. This way, each unit is used at its maximum possible level BEFORE distortion. By doing this, we can maximize performance and most importantly, MINIMIZE noise. Note: We are minimizing noise, not eliminating it. All we need to do is lower the noise level below what we can hear. There is noise in every audio system. In a properly designed and installed system, the noise is just not audible. This goes for good home hi-fi systems, home theaters and professional recording studios. We want to get the HIGHEST voltage level through the system and make all final level adjustments at the AMPLIFIERS. The goal is to have the system play at its highest output level with the amplifier gain controls as low as possible.
- CD with test tones (The CD MUST have an "all bits high" track) or a signal generator. An "all bits high" track is one that is recorded at the maximum digital level allowed. This will give you a reference for the "loudest" CD you could ever encounter.
- Oscilloscope or DMM with resolution to two decimal places.
OSCILLOSPCOE AND DMM METHOD
- Disconnect all speakers from the amplifiers.
- Turn all amplifiers on, and set all gains to the same position (about 1/2).
- All amplifiers must be fed simultaneously from the same signal source.
- Set the Oscilloscope Volts / Division setting to 1 volt. Set the Time / Division to .1 mS. Set the DMM range to read up to 20 volts AC.
- Touch the oscilloscope probe the center pin of the RCA(s) coming from the signal source. Set the source level control to the maximum unclipped setting; or to the maximum input voltage allowed by the amplifier(s). Make a note of this level on the source unit. When using a DMM, clipping cannot be observed as with the oscilloscope. You will have to approximate the maximum unclipped AC output voltage from your source. Check with the manufacturer for a reference voltage to stay at or below.
- Set the Oscilloscope Volts / Division setting to 10 volts (20 volts for 1000 watt plus amplifiers). Set the Time / Division to .1 mS. Set the DMM range to read up to 100 volts AC.
- Connect the signal source to the amplifier(s) and bring the level up to that which was established in step #6.
- Touch the Oscilloscope probe to the amplifier speaker terminal. You will have to check each terminal marked "bridged" or "mono" on stereo amps, or a single terminal on true mono amplifiers. Place the DMM leads in parallel with the output of the amplifier.
- Adjust the gain on each amp to just below clipping. Clipping will be obvious as the peaks of the waveform on the Oscilloscope screen begin to flatten out. Check with the manufacturer for a reference voltage to stay at or below.
As a secondary procedure to double-check the gain matching on mono amplifiers being used in bridged pairs. This should be done after all of the above steps have been completed.
- Set your DVM to DC volts on a 0-20 volt scale.
- Place one probe on appropriate speaker terminal of each amplifier in the bridged pair.
- Bring the level up to that which was established in the above step #6.
- You should read very close to ZERO volts.
- At this point, you can fine-tune the gains on the pair(s) of bridged amps to get this DC reading as low as possible.
- If you have multiple bridged pairs of amps, the DC readings should match.