Amplifiers

Can I use a mixture of different amplifiers in my system?

You can mix different POPE Professional power amplifier models in your system with no problem as all POPE Professional power amplifiers have very similar gain settings. There may be complications if POPE Professional power amplifiers were to be mixed with other brands in an audio system and this may also compromise sonic performance.

Can I power more than one set of loudspeakers from one amplifier?

POPE Professional amplifiers are primarily designed to drive only one pair of loudspeakers (4ohms). Driving more than one set of loudspeakers means that the amplifier will work harder than normal and this may cause it to overheat. No harm should come to your equipment if this happens, as POPE Professional power amplifiers and integrated amplifiers incorporate sophisticated protection circuitry that will temporarily shut down the amplifier as a safety measure. It is usually possible to drive more than one set of loudspeakers; however, it is advised that certain precautions are taken to minimize the possibility of problems arising. These include:

1. Evaluate the combined input impedance of the loudspeakers: the lower the combined impedance, the harder the amplifier will have to work. For example, two sets of 4 ohm speakers in parallel equals a combined impedance of 2 ohms.
2. Be aware of your volume setting, the type of music being played and the length of time for which it is played. For example, playing aggressive music at volume 95 for 2 hours will work the amplifier much harder and heat it up much more than playing relatively tranquil music at volume 15.
3. Is the amplifier well ventilated? Poor ventilation and/or airflow around the amplifier does not allow generated heat to escape and overheating may occur.
4. Keep ambient temperature in the vicinity of the amplifier low if possible. The warmer the air around the amplifier, the hotter it will become as it also generates its own heat.

The secret, when driving more than one set of loudspeakers, is to maximize the favorable factors (good ventilation, sensible volume levels, favorable combined speaker impedance etc).

Should I daisy-chain multiple amplifiers or connect them in parallel?

There are no sonic differences between either the daisy-chained or parallel method. Daisy chaining would be necessary if you are using more power amplifiers than you have outputs from your pre-amplifier. The signal line input is directly connected to the line output of the same amplifier and therefore in the daisy-chain method, it is not critical which amplifier is connected to the output of the pre-amplifier, provided that the treble power amplifier is connected to the treble input of the loudspeaker and the bass power amplifier is connected to the bass input of the loudspeaker.

What are the benefits of multiple amplifiers?

When multi-amping, separate amplifiers are connected to the loudspeakers drive units or sets of drive units. This technique not only provides more power, but also results in better control of the drivers and reduces any possibility of interaction between the drive units. The result is a significant improvement in performance and is also the interim step before Active configuration.

Please note – it is vital that the links at the rear of a POPE Professional loudspeaker are properly configured before multi-amping to prevent possible damage to the power amplifiers. If you are in any doubt, please contact your retailer.

Can I connect a mixer with balanced outputs to a power amp with unbalanced inputs?

Yes. In fact there is a way to connect them, which gives you most of the hum cancelling you'd get if both units were balanced. Here's how it goes:

If the mixer has XLR outputs and the amp has ¼" inputs, use a balanced patch cable with a female XLR at one end and an TRS (stereo) ¼" male jack at the other. Modify it as follows:

1. Remove the ¼" TRS plug,
2. Solder on a standard mono ¼" plug as follows; - tip wire to tip tab, ring and sleeve wire (shield) to sleeve (ground) tab (alternately you can just modify the wiring inside the stereo plug,
3. Mark that cable with some tape to indicate that it's the one for this application.

If the mixer has XLR outputs and amp has screw terminals or phono (RCA) connectors, use a balanced female XLR - to - ¼" male TRS cable and remove the ¼" plug. If you need to install an RCA plug, solder the tip wire to the tip of the RCA and solder the other wire plus the shield wire to the RCA's jacket (ground). If the amp has screw terminals, attach the tip wire to the positive (+) screw and the other two to the negative (-) screw. If it doesn't work, the most likely problem would be how the mixer's XLR output pins are wired so be prepared to unsolder and re-solder a connection or two at the XLR end of the cable.

{Note: The standard balanced XLR wiring (here at Yorkville and with most companies) is pin 1=ground, pin 2 = positive (+), pin 3 = negative (-) }

If both the mixer and the amp have ¼" connectors, it's best to use a balanced TRS-TRS patch cord modified as follows; (1) Remove one of the ends, (2) Replace it with a standard mono ¼" plug soldering the tip wire to the tip tab and the other two to the ground tab (the longer of the two). (3) Mark the mono-plug end with some tape so that in future you'll know this is the cable for this application and that the mono end goes into the unbalanced jack.

{Note: The standard balanced ¼" wiring (here at Yorkville and with most companies) goes tip = positive (+), ring = negative (-), sleeve = ground }

{Additional notes: (1) This form of "trick" balancing works very well with one small exception; if you switch off the mixer but leave the amp on, you may hear some hum through the speakers. If so, it is because the balancing in the mixer, which is generally an active circuit these days, has also been switched off (naturally), ergo there's no more hum canceling. Just remember to switch off the amp too. Oh, and one other thing - if you hadn't already figured it out, these balancing tricks work for EVERYTHING; unbalanced mixer to balanced amp, balanced mixer to unbalanced EQ, or crossover, or compressor/limiter, effects units, etc., etc. }

Why is it not recommended to run a 2 ohm load on certain power amps when all these amp companies boast about their power ratings at two ohms? What do the professionals do to avoid running at 2 ohms (besides wiring the speakers differently)?

Many companies, we included, make both 4-Ohm and 2-Ohm power amps. Why not has anything but 2-Ohm amps? The problem with a 2-Ohm amp is, you HAVE to run it into 2 Ohms in order to get full power. But in most cases, especially club systems where there are only one or two main cabinets on each side of the stage, because nobody makes 2-Ohm cabinets, you need the ability to deliver full power to a 4-Ohm load. For Example Two 8 Ohm cabinets or one 4 Ohm cabinet per side. Actually, all POPE Professional power amps can either run into 2 Ohms, or have twins, which can.

And what do the pros do about 2-Ohm loads? It depends on the definition of "pro". The big touring rigs tend to favor 8-Ohm loads, 4 Ohms minimum. This is because delivered power losses over long cable runs are lower when the speaker impedances are 8 Ohms. They can become very high - 60% percent or worse (!) - into 2-Ohm speaker loads.

Feeling confused? Check out the power loss chart in our FAQ Cabling. Club pros, on the other hand, can contend with whatever loads they encounter principally because the speaker cables don't have to be so long hence the cumulative resistance doesn't get high enough to rob large amounts of power.

Is it ok to run only one channel on my amplifier and can I mismatch loads?

You may do both. Your amplifier can be loaded with a very wide range of speaker impedances. The minimum impedance is 2 ohms for stereo operation while it is 4 ohms for bridge mono operation. All POPE Professional amplifiers are designed to operate safely into infinite load impedances (no speakers). Loading arrangements from one channel to the next can vary in any way you wish. In fact, you can load one channel with a distributed voltage load, using an output transformer, and use the other channel to drive a direct low impedance load.

What is the difference between parallel and bridged mono modes?

The "Parallel" setting duplicates the effect of cross-patching the two inputs, using an internal switch to save the hassle of an extra cable. The two input jacks are connected together, so that a signal on either jack now appears in BOTH channels (therefore only a single signal should be connected). Each channel's Gain control regulates its volume as usual, and separate speakers are connected to each channel as usual. When using this mode, DO NOT combine the output of both channels into a single speaker; this is likely to damage the amp. The Parallel mode is useful when you want to drive several speakers with the same signal, but with two separate volume controls. Bridged Mono mode reverses the polarity of the signal going to Channel B, and matches its gain to Channel A. This makes the voltage between the two red speaker outputs DOUBLE the usual value, which allows several times the normal power to be delivered to a single speaker. This also increases the stress on the amp; this is not "something for nothing" but is a way to combine the 4-ohm ratings of both channels into a single 8-ohm load, or the combined 2-ohm ratings into a 4-ohm load. The Bridged mono setting is useful when you want to deliver the entire power of the amp to a single 8 or 4 ohm speaker.

How do I set my amplifier into the Bridge-Mono mode?

This depends on the amplifier you have. Generally, you will first turn the power off, set the bridge mono switch to the bridge position and attach your speaker wires onto the two red binding posts of each channel. It is then necessary to apply your input signal to channel one on your amplifier and adjust the gain as needed. For some amplifiers, the gain of channel 2 must be turned all the way down while others are required to be all the way up.

Where should the gain controls of my amplifier be set?

We recommend that the gain controls be set between half-way and fully up. The input sensitivity of POPE Professional amplifiers is at about 0dBV or (1Vrms). Amplifier gain controls set at a lower position require input signals to be set to a higher level to obtain suitable power levels. There are other noise and gain alignment considerations. Particularly with unbalanced input lines, the hotter your signal is at the input of an amplifier, the more noise propagation you will have into your amplifiers. Also, the gain structure of your system may become such that you will reach the maximum gain travel of a fader, at your source device, before obtaining expected power within your amplifiers.

What is the difference between Class AB, Class G, and Class H technology?

Actually we are describing two different aspects of amplifier output stages.

IDLE CURRENT: Class AB refers to the amount of idle current flowing in the outputs at zero output. Amplifiers have positive and negative output transistors which handle their respective halves of the output signal. They must "hand off" the output current to each other as the signal passes through zero. A "Class A" output stage begins to transfer current well above its "cutoff point", resulting in much current overlap. This eliminates any chance of "crossover distortion" but generates tremendous waste heat at idle, limiting the possible power of the amp. A "Class B" output stage attempts to make the transfer at exactly zero current, which is impossible to maintain perfectly and leads to "zero crossing distortion" (more commonly called "crossover distortion", a buzzy form of distortion most audible at very low levels). Class AB is the practical compromise--just enough idle current to ensure a smooth transfer between the positive and negative output transistors, without a wastefully high idle current.

POWER SUPPLY DESIGN. The other major source of waste heat, even in a class AB design, occurs at moderately high output powers. The output transistors drive the speakers by coupling a precise amount of audio voltage from the amplifier's "power supply", which is a steady reservoir of fixed voltage. Most of the time, the output transistors are called on to only deliver a fraction of the power supply voltage to the load, and the unused fraction is consumed as heat in the output devices. We can reduce the losses by providing two or more"tiers" of DC voltage, with "steering circuits" which draw from the lowest possible voltage supply. This way the waste heat in the outputs is reduced. A "Class G" design does this by using two different sets of output transistors, one coupled to the lower voltage and one to the full voltage. The signal transfers from the low to high voltage set as required. A "Class H" design uses additional circuitry to connect a single set of outputs to lower or higher voltage as required. Both approaches are capable of good results; the Class H can be designed for somewhat lower costs, especially in amps with more than two power supply "tiers".

Why POPE use SMT?

POPE Professional is always looking for ways to make amps smaller, lighter, and more affordable. "Surface Mount Technology" is a new miniaturized method of placing parts on circuit boards without the usual wire leads. SMT parts have small metal bumps which are soldered to pads on the top of the board. This saves 50-75% of the space consumed by "thru-hole" components using wire leads, and eliminates the extra cost of attaching the leads to the parts.

Is it possible to change the input sensitivity within your amplifiers?

In theory, yes, but only by changing certain resistor values, which requires opening the covers and exposure to dangerous voltages. This should be done only by qualified service personnel, or under the guidance of POPE Professional Technical Services.

POPE Professional MA & MAC Series amplifiers are having an option to change the sensitivity on the rear panel.

Should the fan in my POPE Professional amplifier run all the time?

Almost all POPE Professional amplifiers have 2-speed or variable speed fans that operate at low speed immediately upon power up. Two-speed fan designs reach the highest speed once a certain temperature is reached. Variable speed fans change rotation speed as amplifier operating temperatures change. The exceptions to this are the PE Series which are convection cooled amps. PE Series amps fans do not turn until a particular temperature is reached and from that point the fan speed varies with temperature.

Can I drive a 2 ohm load with my POPE Professional amplifier in bridge-mode?

The minimum rated impedance for an amplifier in bridge-mono is 8 ohms. A 4 ohm load is possible as this represents a 2 ohm per channel equivalent. Two ohm load precautions still apply, as it would with any amplifier, so supplemental cooling may be found necessary. It will also be important to watch for any impedance transients that arise from the speakers in use. Four ohm bridge-mono loading is the absolute minimum across the entire audio range (20Hz - 20kHz.)

Does your clip indicator represent true output clipping?

Yes, the LED is driven only when the amplifier output fails to track the input. This condition normally results only from clipping, which occurs when the power amp reaches either its voltage or current limit. The LED begins to become visible at 0.1% distortion, and reaches fairly full brightness at 1-10% distortion, which is clearly audible. Therefore the brightness corresponds to the likeliness of hearing the distortion.

The output voltage on my amplifier measures from 0Vdc to 0.3Vdc. Is this normal?

Small amounts of "DC offset" do not indicate a problem, although normally it should be less than 0.05 volts (50mv). At 0.3Vdc, we are dissipating 0.011 watts (11 mw) in an 8 ohm load which is clearly negligible. The 1400/USA 850/USA 900 models may measure several volts on the output if not loaded, but the voltage will promptly settle to zero if a normal load is connected.

I am getting a lot of hum and hiss from my system. Is there a quick way to tell if Answer: the amplifier is making the noise, or is it a problem with my system?

The fastest way to tell if the amplifier is the cause of the noise, is to disconnect the input cables from the amp. If the noise is still there, it may be the amplifier; if it's gone, it's a source device inducing noise into the amplifier. If after removing the input connectors from the amplifier you find the noise still present, it will then be necessary to determine if the noise is coming from the AC line. This further isolation may be helpful. Try relocating the amplifier using a different AC service, if the same level of noise is present, the amplifier is likely to be the cause. If the noise is lower, the AC service may be the cause.

What is clipping? Why is it bad?Can you tell which of these statements are true and which are myths?

Clipping is bad for loudspeakers because it really heats up the voice coils.

Myth. Dynamic loudspeakers are notoriously inefficient; they turn well over 90% of the audio power put into them into waste heat instead of acoustical energy. A clipped signal does produce heat in the voice coil, but so does an unclipped signal, too.

A variation of this myth is that extra heating occurs because the voice coil and cone stop moving during the clipped portion of the audio waveform. This also is untrue; even if the instantaneous signal voltage stays the same for some short period of time, like a millisecond or so, the cone stays in motion because at frequencies above the loudspeaker’s resonance the voltage is an accelerative force.

Clipping at any power level is capable of damaging your loudspeakers.

Myth. Some may tell you that a clipped signal from even a very low-power amp will blow out a high-power loudspeaker driver, but that’s untrue. Picture a 50-watt amp driving a 500-watt (continuous) loudspeaker driver. Even if the amp is driven into very severe clipping, it will still put out less than 100 watts, and therefore will not be a threat to the loudspeaker (it probably will not sound good, though).

Try that with an amp rated at, say, 400 watts or higher, though, and the results may be very different. This is because an amp, when it clips, can usually put out much more power than it is rated for. Prolonged, sustained clipping may cause that amp to put more than 500 watts into the loudspeaker for some significant time and cause a thermal failure (melting) in the voice coil. On the other hand, in a system where the amplifier and loudspeaker are well matched (i.e., amplifier power is roughly equal to the loudspeaker's program power rating), very brief and occasional clipped peaks are generally harmless.

Clipping is bad for loudspeakers because it is DC.
Myth. A clipped signal is not DC. Even if the clipping is so severe that the waveform shape approaches that of a square wave, it’s still AC.

Even so, DC by itself is not necessarily dangerous for loudspeakers. In fact, a good way to check polarity of a woofer driver is to connect a small battery across it and see which way the cone moves for a given DC polarity; the amount of power dissipated is minuscule. However, a significant DC offset on an amplifier output is undesirable for several reasons: because it will dissipate power in the voice coil without producing any acoustical output; because it may cause the voice coil to travel out of the magnet gap, which would reduce the cooling; and because it shifts the driver’s at-rest position and thus makes the available excursion asymmetrical, reducing the overall safe excursion limits of the driver.

Clipping is bad for loudspeakers because the sharp corners rip up speaker drivers.
Myth. No.

Clipping is bad for loudspeakers because the amp may put out more power than you expect.

True. The real danger in clipping is that it could overpower the loudspeaker. Even an amp that may seem rated safely below the loudspeaker's power handling capacity might put out dangerous power levels if you are careless with allowing it to run into clipping.

In addition, severe clipping reduces the dynamic range because it quashes the peaks even as the average power in the output signal is elevated by excessive gain boost. Thus, there is often a temptation among inexperienced sound system operators to try to recapture some of the lost "punch" by pushing the levels even higher, which only makes the problem worse.

How do I choose the right amp?

Usually there is no one “right” amplifier, but instead several that will do the job as needed. Among them, you may wish to consider features, weight, future uses, price, and other criteria to make your selection.

First, choose your loudspeakers—for the sound quality and coverage you need—and then choose suitable amplification to drive them.

A general rule of thumb for choosing a suitable amount of amp power is to match the amplifier’s power rating to the loudspeaker’s program power rating. It doesn’t have to be an exact match—within about ±20% is fine. For example, if you have two 8Ω loudspeakers with a program power rating of 350 watts, then you could look for a two-channel amp rated at around 280 to 420 watts per channel into 8 ohms (PE 400, PM 600, MS 1000, MAC 3202 & MA 5200). An alternate approach, if you need only mono operation and will not need to add other loudspeakers, would be to choose an amp rated at about 560 to 840 watts into 4 ohms in bridged mono (MAC 3202).

The idea is that if you choose your amp this way and avoid driving it into significant clipping, your loudspeaker will be fairly safe from blowing out due to overpowering.

If the loudspeaker has no program power rating, then use about 1.5 to 2× its continuous (often called “RMS”) power rating as a target.

You’ve probably noticed that POPE Professional has many lines of power amps. If you buy your pro audio gear from dealers, music stores, or online retailers, you’ll find the general-purpose amps: PM & PE, MAC Series. The PE Series are basic entry-level two-channel amps, good for loads of 4 ohms or higher per channel. The PM Series amps are a line of two-channel amps that range from fairly low power (300 watts per channel into 8Ω) up to very high (2600 watts per channel into 2Ω). The MS Series amplifiers employ the high-performance lightweight power supply technology developed for POPE Professional’s renowned Light weight touring amps.

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