Rickresource Rickenbacker Forum

Happyface wrote:When the PF 500 came out, some folks were complaining about how loud the fan is. Mostly bedroom warriors I'd guess. You won't be hearing it at a gig.

Glad to hear that it is working out for you!

ricnbacker wrote:...forgive me but whats a PA Amp?

ken_j wrote:

ricnbacker wrote:...forgive me but whats a PA Amp?

Public Address.

ricnbacker wrote:

ken_j wrote:

ricnbacker wrote:...forgive me but whats a PA Amp?

Public Address.

I knew that I have always heard them referred to as PA systems...not amps, thought it might be something else

ricnbacker wrote:

cjj wrote: All amps heat up as they are used, the more power they drive the faster they generate heat and unless that heat is dissipated fast enough, they will get too hot. Most amps are made to deliver a certain amount of power, but possibly not continuously, unless there is adequate cooling.

The Ampeg PF series, like many amps, rely on convection cooling, so if there's not enough free space around the amp heat sink (or if the ambient temperature is too high) they can get too hot, even running at less than full power.

This is one place where most PA type amps shine since they are designed to run at high power for extended periods. Most have fans to provide cooling since it's very difficult to ensure adequate cooling by convection alone. But then you have fan noise to contend with. A lot of modern PA amps have thermally controlled fans which only run when things get up to a certain temperature, and often speed up as the temp goes up. This way, the amp has no fan noise when things are quiet and only when pumping out a lot of power do the fans come on, but it's unlikely you'll hear them over the music...

"The Ampeg PF series, like many amps, rely on convection cooling" this head has a fan on it...and its always on. you think this one has a heat sink to? that could be better no?

forgive me but whats a PA Amp?

johnallg wrote: Like this: http://www.musiciansfriend.com/live-pow ... ifiers/qsc

cjj wrote: I was just reading from the manual:
http://www.ampeg.com/pdf/PF_heads_OM.PDF

Page 18 says, "The amplifier module is mounted on a large heatsink, which is cooled by convection where cool air is drawn through its fins, carrying heat away. In order for this convection cooling to work efficiently, it is important to provide adequate air space behind and to the side or above the amplifier."

It does mention on page 4 that is has a "Lightweight and fan-cooled switching power supply" which indicates to me that only the power supply is cooled by the fan, not the amplifier itself.

But, I'll admit I've never actually used (or even seen) one of these amplifiers, so I could be completely wrong...

ricnbacker wrote:fan cooled switching power supply....I guess thats the "class D" amp feature ???

cjj wrote:But, class D is a switching amplifier, which as Jeff said, has nothing to do with the power supply.

In a class D amp, the output transistors are either fully on or fully off instead of operating in the "linear" range. With modern MOSFET transistors, which have a very low ON resistance, this makes an amp extremely efficient since excess power is really only dissipated during the transition period (where the transistor is partially on, which is where most amp topologies run all of the time).

Class D amplifiers use a pulse width modulation method which varies the "on" time of the transistors to achieve differences in output level. If the frequency at which the transistors are switched is sufficiently higher than the signals being amplified it is a simple matter to design a low pass filter to "reconstruct" the analog signal at the amplifier output. This is very similar to the way an digital to analog converter works.

So, in a sense, this does make them behave in a digital manner since digital circuits typically operate in 2 states, on or off, but it's not really quite the same...

bassduke49 wrote:

cjj wrote:But, class D is a switching amplifier, which as Jeff said, has nothing to do with the power supply.

In a class D amp, the output transistors are either fully on or fully off instead of operating in the "linear" range. With modern MOSFET transistors, which have a very low ON resistance, this makes an amp extremely efficient since excess power is really only dissipated during the transition period (where the transistor is partially on, which is where most amp topologies run all of the time).

Class D amplifiers use a pulse width modulation method which varies the "on" time of the transistors to achieve differences in output level. If the frequency at which the transistors are switched is sufficiently higher than the signals being amplified it is a simple matter to design a low pass filter to "reconstruct" the analog signal at the amplifier output. This is very similar to the way an digital to analog converter works.

So, in a sense, this does make them behave in a digital manner since digital circuits typically operate in 2 states, on or off, but it's not really quite the same...

My head hurts.

jps wrote:

ricnbacker wrote:fan cooled switching power supply....I guess thats the "class D" amp feature ???

No, that is just a switch mode power supply, not the power amp topology. A SMPS can be used for any kind of power amp, not just Class D, which describes the topology of the power amp, and no, Class D is not digital! That's marketing BS.

bassduke49 wrote:

cjj wrote:But, class D is a switching amplifier, which as Jeff said, has nothing to do with the power supply.

In a class D amp, the output transistors are either fully on or fully off instead of operating in the "linear" range. With modern MOSFET transistors, which have a very low ON resistance, this makes an amp extremely efficient since excess power is really only dissipated during the transition period (where the transistor is partially on, which is where most amp topologies run all of the time).

Class D amplifiers use a pulse width modulation method which varies the "on" time of the transistors to achieve differences in output level. If the frequency at which the transistors are switched is sufficiently higher than the signals being amplified it is a simple matter to design a low pass filter to "reconstruct" the analog signal at the amplifier output. This is very similar to the way an digital to analog converter works.

So, in a sense, this does make them behave in a digital manner since digital circuits typically operate in 2 states, on or off, but it's not really quite the same...

My head hurts.