[Neil Gould]

RANT
Every now and then, I look at new amp offerings to cover the "what-if"
scenario that my aging BGW amps will need to be replaced. I'm finding fewer
and fewer amps in the under 100w/ch range. Also, the newer amps either have
horrid THD (1%... really?!) or exorbitant pricing. Or both. Have speakers
really become so inefficient that one needs 300w/ch???
/RANT

Any suggestions for decent, reasonably priced amps?

--
best regards,

Neil

[Arny Krueger]

"Neil Gould" wrote in message
...
RANT
Every now and then, I look at new amp offerings to cover the "what-if"
scenario that my aging BGW amps will need to be replaced. I'm finding
fewer
and fewer amps in the under 100w/ch range. Also, the newer amps either
have
horrid THD (1%... really?!) or exorbitant pricing. Or both. Have speakers
really become so inefficient that one needs 300w/ch???
/RANT

Any suggestions for decent, reasonably priced amps?


The Behringer A500 is a good usable ca. 125 wpc amplfiier with profressional
and consumer inputs and outputs.

Don't confuse ratings with actual performance. If you haven't heard there is
a power war out there, and people will resort to all kinds of stupidity to
make it seem that their power amps have more power than the competitions.
This has reached its nadir with ratings systems such as PMPO, 1% THD, etc.


In fact juat about any good SS power amp will have less than 0.1% THD 20-20
KHz if you don't clip it. This may require shaving a few dB off of its
advertised power rating. Just about every power amp you see with X watts @ Y
wpc and 1 % THD will have 0.1% THD or less (usually far less and often down
below even 0.01%) at say 0.8 to 0.9 times Y wpc.

For example Behringer may on some days say that the A500 produces 500 wpc,
but after using one for a few years and testing it on the bench I think of
it as a 125 wpc (8 ohms) power amp. For another example, Behringer now
sells a power amp they call the EP4000 which internally seems identical to
one they called the EP2500.

This is not just about Behringer or just modern power amps. IME there was a
similar situation with the ca. 1980s QSC USA 850 and USA 900 just to bring
up a case that I actually have personal experience with. There were two
notable differences - the advertised power ratings and one was inverting and
the other was not. IOW they changed it from inverting to noninverting by
means of trivial changes to its input buffer circuitry. I think they
switched the wires going to pins 2 and 3 on the XLR jacks... ;-)

[Scott Dorsey]

Neil Gould wrote:
RANT
Every now and then, I look at new amp offerings to cover the "what-if"
scenario that my aging BGW amps will need to be replaced. I'm finding fewer
and fewer amps in the under 100w/ch range. Also, the newer amps either have
horrid THD (1%... really?!) or exorbitant pricing. Or both. Have speakers
really become so inefficient that one needs 300w/ch???
/RANT

Any suggestions for decent, reasonably priced amps?


This is for PA applications or recording? Smaller amplifiers are drying up
in both markets, mostly because powered speaker systems have started to take
the market over.

If it were me, I'd just get the BGWs rebuilt. But then, I'm using a 1961
model studio monitor amp, which I got in 1978 and which sounds just fine.

For PA use, the QSC RMX series isn't bad, but you're still dealing with RoHS
issues.... I'd feel more secure with a properly maintained old BGW....
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Neil Gould]

Scott Dorsey wrote:
Neil Gould wrote:
RANT
Every now and then, I look at new amp offerings to cover the
"what-if" scenario that my aging BGW amps will need to be replaced.
I'm finding fewer and fewer amps in the under 100w/ch range. Also,
the newer amps either have horrid THD (1%... really?!) or exorbitant
pricing. Or both. Have speakers really become so inefficient that
one needs 300w/ch??? /RANT

Any suggestions for decent, reasonably priced amps?


This is for PA applications or recording? Smaller amplifiers are
drying up in both markets, mostly because powered speaker systems
have started to take the market over.

If it were me, I'd just get the BGWs rebuilt. But then, I'm using a
1961 model studio monitor amp, which I got in 1978 and which sounds
just fine.

For PA use, the QSC RMX series isn't bad, but you're still dealing
with RoHS issues.... I'd feel more secure with a properly maintained
old BGW.... --scott

The BGW amps are driving my home audio & studio speakers, and even the 50wpc
model never gets driven beyond 20% or so of its capability.

I've had QSC amps, and in fact used to be a dealer (also for BGW, Crown,
Altec, JBL, etc.) but that was quite some time ago ('70s). I hope they're
better now than they were then!

I also have a Yamaha power amp driving my guitar rig, but it is no match for
the BGW in terms of performance or accuracy, so I agree that I'll probably
just rebuild the BGWs when they need it.

--
best regards,

Neil

[Neil Gould]

Arny Krueger wrote:
"Neil Gould" wrote in message
...
RANT
Every now and then, I look at new amp offerings to cover the
"what-if" scenario that my aging BGW amps will need to be replaced.
I'm finding fewer
and fewer amps in the under 100w/ch range. Also, the newer amps
either have
horrid THD (1%... really?!) or exorbitant pricing. Or both. Have
speakers really become so inefficient that one needs 300w/ch???
/RANT

Any suggestions for decent, reasonably priced amps?


The Behringer A500 is a good usable ca. 125 wpc amplfiier with
profressional and consumer inputs and outputs.

Don't confuse ratings with actual performance. If you haven't heard
there is a power war out there, and people will resort to all kinds
of stupidity to make it seem that their power amps have more power
than the competitions. This has reached its nadir with ratings
systems such as PMPO, 1% THD, etc.

Yes, this power-play isn't a new phenomenon. But, when one can't find decent
specs for realistic levels, what is there to go by? Low noise... low
distortion levels... very flat response are must-have performance
characterists. One of the things I like about my BGWs is that they're low
noise... you can't tell whether they're on or off unless there's an input
signal or you stick your head in the cabinet and listen to the toroidal
power transformer. ;-)

--
best regards,

Neil

[Arny Krueger]

"Neil Gould" wrote in message
...
Arny Krueger wrote:
"Neil Gould" wrote in message
...
RANT
Every now and then, I look at new amp offerings to cover the
"what-if" scenario that my aging BGW amps will need to be replaced.
I'm finding fewer
and fewer amps in the under 100w/ch range. Also, the newer amps
either have
horrid THD (1%... really?!) or exorbitant pricing. Or both. Have
speakers really become so inefficient that one needs 300w/ch???
/RANT

Any suggestions for decent, reasonably priced amps?


The Behringer A500 is a good usable ca. 125 wpc amplfiier with
profressional and consumer inputs and outputs.

Don't confuse ratings with actual performance. If you haven't heard
there is a power war out there, and people will resort to all kinds
of stupidity to make it seem that their power amps have more power
than the competitions. This has reached its nadir with ratings
systems such as PMPO, 1% THD, etc.

Yes, this power-play isn't a new phenomenon. But, when one can't find
decent
specs for realistic levels, what is there to go by? Low noise... low
distortion levels... very flat response are must-have performance
characterists.

Perhaps for your peace of mind. However, for transparent reproduction all of
the above need only meet fairly reasonable specs.

One of the things I like about my BGWs is that they're low
noise... you can't tell whether they're on or off unless there's an input
signal or you stick your head in the cabinet and listen to the toroidal
power transformer. ;-)

True of a lot of modern equipment. It helps to not have cooling fans.

[Neil Gould]

Arny Krueger wrote:
"Neil Gould" wrote in message
...
Arny Krueger wrote:
"Neil Gould" wrote in message
...
RANT
Every now and then, I look at new amp offerings to cover the
"what-if" scenario that my aging BGW amps will need to be replaced.
I'm finding fewer
and fewer amps in the under 100w/ch range. Also, the newer amps
either have
horrid THD (1%... really?!) or exorbitant pricing. Or both. Have
speakers really become so inefficient that one needs 300w/ch???
/RANT

Any suggestions for decent, reasonably priced amps?


The Behringer A500 is a good usable ca. 125 wpc amplfiier with
profressional and consumer inputs and outputs.

Don't confuse ratings with actual performance. If you haven't heard
there is a power war out there, and people will resort to all kinds
of stupidity to make it seem that their power amps have more power
than the competitions. This has reached its nadir with ratings
systems such as PMPO, 1% THD, etc.

Yes, this power-play isn't a new phenomenon. But, when one can't find
decent
specs for realistic levels, what is there to go by? Low noise... low
distortion levels... very flat response are must-have performance
characterists.

Perhaps for your peace of mind. However, for transparent reproduction
all of the above need only meet fairly reasonable specs.

Not just for peace of mind... I've not had to buy a monitor amp in quite
some time, so it is likely that there may be things out there that would be
more than satisfactory. My rant was based on the difficulty in finding one
by reading the published specs and knowing that there isn't some place
nearby where I can audition them.

One of the things I like about my BGWs is that they're low
noise... you can't tell whether they're on or off unless there's an
input signal or you stick your head in the cabinet and listen to the
toroidal power transformer. ;-)

True of a lot of modern equipment. It helps to not have cooling fans.

Even some amps without cooling fans create hum or hiss through the speakers
when no signal is fed to them. I have a fairly modern Yamaha "100wpc" power
amp that does this, and it's OK in my guitar rig since it's a lot less noisy
than the other instrument amps, but I wouldn't use it for a monitor amp.

--
best regards,

Neil

[Arny Krueger]

"Neil Gould" wrote in message
...
Arny Krueger wrote:
"Neil Gould" wrote in message
...

Yes, this power-play isn't a new phenomenon. But, when one can't find
decent
specs for realistic levels, what is there to go by? Low noise... low
distortion levels... very flat response are must-have performance
characterists.

Perhaps for your peace of mind. However, for transparent reproduction
all of the above need only meet fairly reasonable specs.

Not just for peace of mind... I've not had to buy a monitor amp in quite
some time, so it is likely that there may be things out there that would
be
more than satisfactory.


My rant was based on the difficulty in finding one
by reading the published specs and knowing that there isn't some place
nearby where I can audition them.

Auditioning power amps is about as much fun and as useful as watching paint
dry.

One of the things I like about my BGWs is that they're low
noise... you can't tell whether they're on or off unless there's an
input signal or you stick your head in the cabinet and listen to the
toroidal power transformer. ;-)

True of a lot of modern equipment. It helps to not have cooling fans.

Even some amps without cooling fans create hum or hiss through the
speakers
when no signal is fed to them. I have a fairly modern Yamaha "100wpc"
power
amp that does this, and it's OK in my guitar rig since it's a lot less
noisy
than the other instrument amps, but I wouldn't use it for a monitor amp.

Yes, it still pays to look at specs like SNR. and you are right - finding
that spec is not always easy. SNR can be more of an issue when people buy
amplfiiers that are excessively powerful given their speakers and their
listening situation.

[Neil Gould]

Arny Krueger wrote:
"Neil Gould" wrote in message
...
Arny Krueger wrote:

[...] It helps to not have cooling fans.

Even some amps without cooling fans create hum or hiss through the
speakers when no signal is fed to them. I have a fairly modern Yamaha
"100wpc"
power amp that does this, and it's OK in my guitar rig since it's a lot
less noisy than the other instrument amps, but I wouldn't use it for a
monitor
amp.

Yes, it still pays to look at specs like SNR. and you are right -
finding that spec is not always easy. SNR can be more of an issue
when people buy amplfiiers that are excessively powerful given their
speakers and their listening situation.

And, we arrive at the beginning of the circle... ;-) Most current-day amps
are excessively powerful for use with efficient speakers.

How is SNR computed when there's no S, just N? ;-) There are some things
that contribute to SNR that are not as objectionable as audible 60Hz hum and
HF hiss.

--
best regards,

Neil

[William Sommerwerck]

And, we arrive at the beginning of the circle... ;-)
Most current-day amps are excessively powerful
for use with efficient speakers.

I think people are confusing power output and gain. Gain has more of an
effect on the audibility of system noise than does power output.

[Les Cargill[_4_]]

William Sommerwerck wrote:
And, we arrive at the beginning of the circle... ;-)
Most current-day amps are excessively powerful
for use with efficient speakers.

I think people are confusing power output and gain. Gain has more of an
effect on the audibility of system noise than does power output.



But power output and gain seem to be related, especially
for the same input signal.

--
Les Cargill

[William Sommerwerck]

I think people are confusing power output and gain.
Gain has more of an effect on the audibility of system
noise than does power output.

But power output and gain seem to be related, especially
for the same input signal.

Nope. It's the opposite. Most power amplifiers (consumer and professional)
have a voltage gain of 26dBv. This allows amplifiers to be mixed (as when
using electronic crossovers) without having to worry about adjusting the
amplifiers' gains.

[Neil Gould]

William Sommerwerck wrote:
And, we arrive at the beginning of the circle... ;-)
Most current-day amps are excessively powerful
for use with efficient speakers.

I think people are confusing power output and gain. Gain has more of
an effect on the audibility of system noise than does power output.

Perhaps you can clarify the confusion that you see that leads you to think
that gain is important? Different speakers have different efficiencies, the
less efficient the speaker the more power required to achieve the same level
of audibility. Conversely, the more efficient the speaker, the less tolerant
of an amplifier's internal noise because that noise becomes audible,
regardless of the amp's gain factor.

--
best regards,

Neil

[Arny Krueger]

"Neil Gould" wrote in message
...
Arny Krueger wrote:
"Neil Gould" wrote in message
...
Arny Krueger wrote:

[...] It helps to not have cooling fans.

Even some amps without cooling fans create hum or hiss through the
speakers when no signal is fed to them. I have a fairly modern Yamaha
"100wpc"
power amp that does this, and it's OK in my guitar rig since it's a lot
less noisy than the other instrument amps, but I wouldn't use it for a
monitor
amp.

Yes, it still pays to look at specs like SNR. and you are right -
finding that spec is not always easy. SNR can be more of an issue
when people buy amplfiiers that are excessively powerful given their
speakers and their listening situation.

And, we arrive at the beginning of the circle... ;-) Most current-day
amps
are excessively powerful for use with efficient speakers.

How is SNR computed when there's no S, just N? ;-) There are some things
that contribute to SNR that are not as objectionable as audible 60Hz hum
and
HF hiss.

Usually the Signal level is presumed - either full output of the power amp
or some common reference level like 1 watt.

It turns out that the measured noise at the output of the amp may increase
signficantly as the power output goes up, because power supply ripple goes
up.

[Neil Gould]

Arny Krueger wrote:
"Neil Gould" wrote in message
...
Arny Krueger wrote:
"Neil Gould" wrote in message
...
Arny Krueger wrote:

[...] It helps to not have cooling fans.

Even some amps without cooling fans create hum or hiss through the
speakers when no signal is fed to them. I have a fairly modern
Yamaha "100wpc" power amp that does this, and it's OK in my guitar
rig since it's a lot less noisy than the other instrument amps,
but I wouldn't use it for a monitor amp.

Yes, it still pays to look at specs like SNR. and you are right -
finding that spec is not always easy. SNR can be more of an issue
when people buy amplfiiers that are excessively powerful given their
speakers and their listening situation.

And, we arrive at the beginning of the circle... ;-) Most
current-day amps
are excessively powerful for use with efficient speakers.

How is SNR computed when there's no S, just N? ;-) There are some
things that contribute to SNR that are not as objectionable as
audible 60Hz hum and
HF hiss.

Usually the Signal level is presumed - either full output of the
power amp or some common reference level like 1 watt.

Right... SNR always presumes there is a signal present.

It turns out that the measured noise at the output of the amp may
increase signficantly as the power output goes up, because power
supply ripple goes up.

Or not, depending on how PS ripple is being introduced into the signal.
Hiss, on the other hand, often varies with output power.

--
best regards,

Neil

[William Sommerwerck]

Auditioning power amps is about as much fun
and as useful as watching paint dry.

You still don't believe me when I say there are (or have been) amplifiers
with great specs that sound absolutely atrocious.

[William Sommerwerck]

"Neil Gould" wrote in message
...
William Sommerwerck wrote:

And, we arrive at the beginning of the circle... ;-)
Most current-day amps are excessively powerful
for use with efficient speakers.

I think people are confusing power output and gain. Gain has more of
an effect on the audibility of system noise than does power output.

Perhaps you can clarify the confusion that you see that leads you to think
that gain is important? Different speakers have different efficiencies,
the
less efficient the speaker the more power required to achieve the same
level
of audibility. Conversely, the more efficient the speaker, the less
tolerant
of an amplifier's internal noise because that noise becomes audible,
regardless of the amp's gain factor.

First of all, you're talking about speaker sensitivity. Obviously, the more
sensitive the speaker, the more the amplifer's internal noise will be
audible.

However, some of the system noise /precedes/ the power amplifier. The
audibility of such noise is influenced by the amplifier's gain.

As I'm writing this, I'm thinking... Maybe that's not right. Given a
higher-gain power amp, the gain on the mixer will be set lower, lowering the
noise from the mixer.

[Neil Gould]

William Sommerwerck wrote:
"Neil Gould" wrote in message
...
William Sommerwerck wrote:

And, we arrive at the beginning of the circle... ;-)
Most current-day amps are excessively powerful
for use with efficient speakers.

I think people are confusing power output and gain. Gain has more of
an effect on the audibility of system noise than does power output.

Perhaps you can clarify the confusion that you see that leads you to
think that gain is important? Different speakers have different
efficiencies, the less efficient the speaker the more power required
to achieve the same level of audibility. Conversely, the more
efficient the speaker, the less tolerant of an amplifier's internal
noise because that noise becomes audible, regardless of the amp's
gain factor.

First of all, you're talking about speaker sensitivity. Obviously,
the more sensitive the speaker, the more the amplifer's internal
noise will be audible.

However, some of the system noise /precedes/ the power amplifier. The
audibility of such noise is influenced by the amplifier's gain.

True, but I'm not concerned about the "front end"... my rant is about audio
amps.

As I'm writing this, I'm thinking... Maybe that's not right. Given a
higher-gain power amp, the gain on the mixer will be set lower,
lowering the noise from the mixer.

Exactly.

Furthermore, with a decent mixer or preamp, that's not much of an issue. You
can't hear whether my BGW-powered monitor system is on or off regardless of
the preamp settings, and that's a quality that I would like to be able to
replace.

--
best regards,

Neil

[Frank Stearns]

"William Sommerwerck" writes:

"Neil Gould" wrote in message
...
William Sommerwerck wrote:

And, we arrive at the beginning of the circle... ;-)
Most current-day amps are excessively powerful
for use with efficient speakers.

I think people are confusing power output and gain. Gain has more of
an effect on the audibility of system noise than does power output.

Perhaps you can clarify the confusion that you see that leads you to think
that gain is important? Different speakers have different efficiencies,
the
less efficient the speaker the more power required to achieve the same
level
of audibility. Conversely, the more efficient the speaker, the less
tolerant
of an amplifier's internal noise because that noise becomes audible,
regardless of the amp's gain factor.

First of all, you're talking about speaker sensitivity. Obviously, the more
sensitive the speaker, the more the amplifer's internal noise will be
audible.

However, some of the system noise /precedes/ the power amplifier. The
audibility of such noise is influenced by the amplifier's gain.

As I'm writing this, I'm thinking... Maybe that's not right. Given a
higher-gain power amp, the gain on the mixer will be set lower, lowering the
noise from the mixer.


It's the science (and sometimes art) of gain staging, where you take into account
many factors to optimize a complete *system* -- from the air striking a microphone
diaphragm, all the way out to the movement of a speaker cone -- and everything
between; ultimately to serve what it is you're trying to accomplish.

Sounds simple, but often it's not. To get an interesting taste for a portion of
this, see if you can find documentation for an audio console that shows internal
gain staging. Much of it is not nearly as clear-cut as you might expect.

Frank
Mobile Audio

--

[Scott Dorsey]

William Sommerwerck wrote:
Auditioning power amps is about as much fun
and as useful as watching paint dry.

You still don't believe me when I say there are (or have been) amplifiers
with great specs that sound absolutely atrocious.

There are plenty of those, and they are the result of measuring the wrong
specs.

My personal favorite example is the ST120, of course.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[William Sommerwerck]

You still don't believe me when I say there are
(or have been) amplifiers with great specs that
sound absolutely atrocious.

There are plenty of those, and they are the result
of measuring the wrong specs.
My personal favorite example is the ST120, of course.

I wish certain people would listen to the (now discontinued) Crown K1
switching amp. Fine specs -- horrible sound.

[Mike Rivers]

On 8/30/2012 7:38 AM, Arny Krueger wrote:

Auditioning power amps is about as much fun and as useful as watching paint
dry.

I always thought they were about the same. Back when I
didn't have any money (as opposed to now when I have it but
don't like to spend it) I built a couple of Southwest
Technical Products Tiger .01 amplifiers to drive my
monitors. The specs looked good and they got good reviews. I
was happy using them for several years and then one day my
friendly local dealer loaned me a Bryston. Although the
difference wasn't like night and day just listening to
music, what I found when I started mixing with that amplfier
was that I could hear the effect of much smaller changes in
EQ cut or boost with the Bryston than with the SWTP amplifiers.

I replaced the SWTPs with a Hafler DH220 that was nearly as
good as the Bryston at about 1/5 the cost. I'm still using
it 25 years later. It's probably time for a re-cap job,
da'ya' think?



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Mike Rivers]

On 8/30/2012 9:46 AM, Neil Gould wrote:

Perhaps you can clarify the confusion that you see that leads you to think
that gain is important?

What's important is not gain. You can't really legitimately
calculate gain anyway because you have volts going in and
watts going out. What's significant, and useful to know, is
the input sensitivity - how many volts in it takes to drive
it to full power out.



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[William Sommerwerck]

Perhaps you can clarify the confusion that you see that
leads you to think that gain is important?

What's important is not gain. You can't really legitimately
calculate gain anyway because you have volts going in and
watts going out. What's significant, and useful to know, is
the input sensitivity -- how many volts in it takes to drive
it to full power out.

Well... not really. Most amplifiers have the same voltage gain -- 20 times.
It doesn't matter the make or model -- put in half a volt and you get 10
volts out.

[Trevor]

"Mike Rivers" wrote in message
...
On 8/30/2012 9:46 AM, Neil Gould wrote:
Perhaps you can clarify the confusion that you see that leads you to
think
that gain is important?

What's important is not gain. You can't really legitimately calculate gain
anyway because you have volts going in and watts going out.

You're kidding right? The volts going out is EASILY measured, and therefore
the gain, usually at no load, but also any other impedance you wish to
choose.


What's significant, and useful to know, is the input sensitivity - how many
volts in it takes to drive it to full power out.

Most decent amplifiers are voltage limited so full power out depends on load
impedance, gain and "input sensitivity" are directly related anyway.

Trevor.

[Mike Rivers]

On 8/30/2012 4:27 PM, William Sommerwerck wrote:

Well... not really. Most amplifiers have the same voltage gain -- 20 times.
It doesn't matter the make or model -- put in half a volt and you get 10
volts out.

Really? I didn't know that. Even the ones with a "gain"
control? I take it that's with the output unloaded, which
doesn't do anyone any good other than to post a fact on a
newsgroup.

So that means that if I put +20 dBu into any amplifier, I'll
get out 155 v? But you got me curious. I have a Hafler
DH-220 within lifting distance of the bench, I put in 0.5v
RMS and got out 10 v RMS, unloaded. I didn't try it under
load, but I'm guessing that at about 100 watts rated power
output (not sure about that, just a good guess) something's
going to clip if you feed it from a nominal +4 dBu source
and expecting that it has 20 dB of headroom.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Mike Rivers]

On 8/30/2012 6:56 PM, Trevor wrote:
"Mike wrote in message
What's important is not gain. You can't really legitimately calculate gain
anyway because you have volts going in and watts going out.

You're kidding right? The volts going out is EASILY measured, and therefore
the gain, usually at no load, but also any other impedance you wish to
choose.

Gain is the ratio of two of the same thing. Sure, you can
measure the voltage gain, but without knowing that the
amplifier acts as a pure voltage source and is capable of
maintaining a given voltage into any impedance from open
circuit to its rated impedance, you don't really know what
the output voltage under real working conditions is.

What's the value of knowing the voltage gain of a power
amplifier unless you know it's load-independent? I'll admit
that some practically are.

Most decent amplifiers are voltage limited so full power out depends on load
impedance, gain and "input sensitivity" are directly related anyway.

Related, yes, but they aren't the same. When you divide
watts by volts, you don't get gain, just like when you
divide apples by oranges, you don't get a fraction of an apple.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[PStamler]

Yeah, most power amps made in the last 25 years have voltage gain of about 20x with the level pots wide open and 8 ohms loading the output. Most solid-state amps are pretty much load-independent, which means that the voltage gain of 20x will hold for reasonable loads (i.e. 4-16 ohms).

Doing the arithmetic, a power amp with a gain of 20x will put out (mumble, mumble) about 75W when you feed it with a +4dBu signal and drive an 8 ohm load. So you won't get 20db of headroom out of it unless the amp is rated at 750W into 8 ohms. In fact, with a 110W/ch amp like the Hafler DH-220, it'll clip at about +7dBu in. (Ignoring issues of balanced vs. unbalanced signals -- pretend there's a 1:1 transformer in line with the amp's input.)

That's why consumer-type power amps can be problematical in pro operations, and why pro power amps usually have input level controls to attenuate the signal. Turn the effective gain of the power amp down, using the input level control, and you get an amp that can take a +24Bu signal from a console without clipping.

Peace,
Paul

[PStamler]

Er, make that 7500W of power for 20dB of headroom over 75W. Sorry, momentary brain glitch.

Peace,
Paul

[Neil Gould]

Mike Rivers wrote:
On 8/30/2012 6:56 PM, Trevor wrote:
"Mike wrote in message
What's important is not gain. You can't really legitimately
calculate gain anyway because you have volts going in and watts
going out.

You're kidding right? The volts going out is EASILY measured, and
therefore the gain, usually at no load, but also any other impedance
you wish to choose.

Gain is the ratio of two of the same thing. Sure, you can
measure the voltage gain, but without knowing that the
amplifier acts as a pure voltage source and is capable of
maintaining a given voltage into any impedance from open
circuit to its rated impedance, you don't really know what
the output voltage under real working conditions is.

You can easily measure the voltage under real working conditions, so you can
know it. ;-)

What's the value of knowing the voltage gain of a power
amplifier unless you know it's load-independent?

Voltage is the important factor for audio amps, because that is what
speakers require to move the diaphragm. The speaker's load resistance and
efficiency determines how easily the amp can supply the signal voltage gain,
so the amplifier's watts (power) mainly "guarantee" the voltage needed to
deliver the signal gain to the speakers. ;-)

Thinking in terms of dB adds an unnecessary level of abstraction to the
topic, IMO, but the math works anyway.

--
best regards,

Neil

[Trevor]

"Mike Rivers" wrote in message
...
On 8/30/2012 6:56 PM, Trevor wrote:
"Mike wrote in message
What's important is not gain. You can't really legitimately calculate
gain
anyway because you have volts going in and watts going out.

You're kidding right? The volts going out is EASILY measured, and
therefore
the gain, usually at no load, but also any other impedance you wish to
choose.

Gain is the ratio of two of the same thing. Sure, you can measure the
voltage gain, but without knowing that the amplifier acts as a pure
voltage source and is capable of maintaining a given voltage into any
impedance from open circuit to its rated impedance, you don't really know
what the output voltage under real working conditions is.

Now your just being silly, measure it under the conditions *you* want if the
standard test conditions don't meet your specific requirements. IF the gain
varies under normal operating conditions, get it fixed or get a new
amplifier that meets your requirements, like not clipping at the required
output.


What's the value of knowing the voltage gain of a power amplifier unless
you know it's load-independent? I'll admit that some practically are.

Right, but it's irrelevant to the voltage or power gain for any given load.


Most decent amplifiers are voltage limited so full power out depends on
load
impedance, gain and "input sensitivity" are directly related anyway.

Related, yes, but they aren't the same.

Never said they were, but one can easily calculate the other given all
necessay parameters.


When you divide watts by volts, you don't get gain,

And why would anyone who understands anything at all about electronics want
to do that? Does that mean you don't?

Trevor.

[Mike Rivers]

On 8/31/2012 6:21 AM, Trevor wrote:

When you divide watts by volts, you don't get gain,

And why would anyone who understands anything at all about electronics want
to do that? Does that mean you don't?

That was my point.

But in the real world, power amplifiers are specified/rated
in watts. Loudspeakers are rated in watts of power handling
capacity and in mW in for dB SPL out. Of course it's easy
for someone who knows Ohm's Law to calculate the voltage at
rated power going into a static 8 ohm (or your choice) load.
But what does this mean to the person going into Guitar
Center to buy a PA system who wants to know "will this get
loud enough?"



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Neil Gould]

Mike Rivers wrote:
But in the real world, power amplifiers are specified/rated
in watts. Loudspeakers are rated in watts of power handling
capacity and in mW in for dB SPL out. Of course it's easy
for someone who knows Ohm's Law to calculate the voltage at
rated power going into a static 8 ohm (or your choice) load.
But what does this mean to the person going into Guitar
Center to buy a PA system who wants to know "will this get
loud enough?"

The honest salesperson will reply that there is no way to answer that
question, while the less-than-tech-savvy salesperson can answer "yes" or
"no", and be right most of the time. ;-)

--
best regards,

Neil

[William Sommerwerck]

But in the real world, power amplifiers are specified/rated
in watts. Loudspeakers are rated in watts of power handling
capacity and in mW in for dB SPL out. Of course it's easy
for someone who knows Ohm's Law to calculate the voltage
at rated power going into a static 8 ohm (or your choice) load.
But what does this mean to the person going into Guitar
Center to buy a PA system who wants to know "will this get
loud enough?"

Well, there are such things as constant-voltage distribution amplifiers. (I
think.)

http://en.wikipedia.org/wiki/Constan...speaker_system

The idea of rating a power amplifier on the basis of its power output might
seem perfectly logical, but it's not the only way to do it. Power-output
ratings are based on the fact that almost all vacuum-tube amplifiers are
operated in matched-impedance mode. * The output transformer has taps that
(nominally) match the speaker impedance.

Transistor amps come close to being constant-voltage. ** Consequently,
speaker drive ratings are more-commonly based on sensitivity -- how much
voltage is needed for a given acoustical output. There's no reason -- other
than initial customer confusion -- why we couldn't change to such a system.


* The Futterman being the obvious exception.
** McIntosh used to make transistor amplifiers with autotransformers to
squeeze all they power possible from the output stage.

[Les Cargill[_4_]]

William Sommerwerck wrote:
I think people are confusing power output and gain.
Gain has more of an effect on the audibility of system
noise than does power output.

But power output and gain seem to be related, especially
for the same input signal.

Nope. It's the opposite. Most power amplifiers (consumer and professional)
have a voltage gain of 26dBv.

But some amplifiers are 100 watt amps, and some are 1000 watt amps.
That's a delta in gain of ... 10dBV* into the same load.

*if it's 20, great - haven't stopped to think that all the way
through.


This allows amplifiers to be mixed (as when
using electronic crossovers) without having to worry about adjusting the
amplifiers' gains.



Makes sense.

--
Les Cargill

[William Sommerwerck]

Nope. It's the opposite. Most power amplifiers (consumer
and professional) have a voltage gain of 26dBv.

But some amplifiers are 100 watt amps, and some are
1000 watt amps. That's a delta in gain of ... 10dBV* into
the same load.

Gain is gain. It has nothing to do with power output.

[Trevor]

"Mike Rivers" wrote in message
...
When you divide watts by volts, you don't get gain,

And why would anyone who understands anything at all about electronics
want
to do that? Does that mean you don't?

That was my point.
But in the real world, power amplifiers are specified/rated in watts.
Loudspeakers are rated in watts of power handling capacity and in mW in
for dB SPL out. Of course it's easy for someone who knows Ohm's Law to
calculate the voltage at rated power going into a static 8 ohm (or your
choice) load.

MANY tests I see quote figures at 2.83 Volt output rather than 1W into 8ohm
already, since that's what they measure, and that's what anybody with a
voltmeter can measure. It's unlikely you'd really want figures for 1W into
4ohm etc. and not know ohms law!


But what does this mean to the person going into Guitar Center to buy a PA
system who wants to know "will this get loud enough?"

How many people "going into Guitar Center to buy a PA system" want to know
the amplifier gain though? Seems to me most don't understand gain staging or
they wouldn't just turn the power amp input level control to maximum as I
see so often.

Trevor.

[Mike Rivers]

On 8/31/2012 1:37 PM, William Sommerwerck wrote:

Gain is gain. It has nothing to do with power output.

Only if you specify that you're speaking of voltage gain,
which doesn't mean much to someone shopping for a power
amplifier.

What's important about knowing the sensitivity for a given
power output is that it helps you figure out how to match it
up with what's feeding it. Some amplifiers have a fixed
sensitivity, others have an input attenuator.

Suppose you have a mixer that claims (manufacturer, not me)
"+4 dB" output. Most mixers today have an LED ladder meter,
a dB scale with 0 around the middle. This usually represents
an output level somewhere between 0 dBu (0.775 v) and +6 dBu
(1.55 v) depending on the manufacturer, the model, whether
the output is differential or single-ended (or which one is
used if there are both) and the phase of the moon.

If you connect this mixer to a "gain of 20" amplifier, when
the meter reads zero, you'll be putting about 30 watts into
an 8 ohm load. This may very well be too loud. If the
amplifier has an input attenuator, this is the way to turn
it down to a dull roar. But if it doesn't, and you turn down
the master output level of the mixer, the meter will be down
in a portion of its scale where it won't be significant.
Plus, if you're feeding something else from that output,
like maybe a recorder, the level for that device is likely
to be off.

If the amplifier has a fixed voltage gain, you'll be posting
on a forum "How come I can't run the mixer above half scale
on the meter without blowing my ears off?" followed shortly
by "Why is my recording at such a low level? The PA is
plenty loud."

Not enough of this stuff gets sold to system engineers, so
you have to make enough information look like it's written
in the same language for gozoutas and gozintas in order for
the customer to have a clue.



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Mike Rivers]

On 8/31/2012 5:16 PM, Trevor wrote:


MANY tests I see quote figures at 2.83 Volt output rather than 1W into 8ohm
already, since that's what they measure, and that's what anybody with a
voltmeter can measure.

I've never seen a test like that, but then I can't remember
the last time I've seen a test/review of a power amplifier.
Maybe it's an audiophile thing. Are we talking about a
different market?

How many people "going into Guitar Center to buy a PA system" want to know
the amplifier gain though? Seems to me most don't understand gain staging or
they wouldn't just turn the power amp input level control to maximum as I
see so often.

They don't know better. But then some power amplifiers don't
have an input level control.





--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Arny Krueger]

"William Sommerwerck" wrote in message
...
Auditioning power amps is about as much fun
and as useful as watching paint dry.

You still don't believe me when I say there are (or have been) amplifiers
with great specs that sound absolutely atrocious.

Trying to be effective as a mind reader is fraught with difficulties, such
as you hve encountered with this statement.

If by 'great specs" you mean published specs, then geat specs mean
absolutely nothing. Why would a manufacturer publish a spec that makes his
product look weak?

There is a list of specifications that pretty well precludes bad-sounding
amplifiers, but I'm not sure that I've ever seen anybody actually put them
into their marketing blurbs.