Reply
 
Thread Tools Display Modes
  #1   Report Post  
Posted to rec.audio.high-end
Dave Cook Dave Cook is offline
external usenet poster
 
Posts: 15
Default Active vs. passive pre-amp

Out of curiosity, I hooked up my DAC directly to my amp just to hear
what it would sound like without going through my preamp. The DAC is
fed by a Squeezebox Touch, so I can use it's digital volume control
for attenuation. I was rather shocked how much more vibrant and
involving the sound was. It does make me wonder what the benefit of
all that electronics in a pre-amp really is. So I'd like to try
going passive with something like a stepped attenuator.

Is there anything I should know about the downside of going passive?
It does sound like there might by some loss of bass, though I'd like
to narrow this down with whatever measurements I can do with my
voltmeter and SPL meter.

My typical "serious" listening level is about -20dB (relative to unity
gain). A low level recording might require the volume to be raised to
-15dB or so. So I don't think I'll have any problems with having
enough gain.

Equipment, all connected with XLR cables, is as follows:

DAC: Cambridge Audio Azur 840C. Output impedance: 50 Ohm. This
seems to have a pretty beefy power supply for a CDP/DAC.

Pre-amp: BAT 3iX, Output impedance: 1000 Ohm

I also have BAT's VK-42SE solid state amp on loan, but it still seems
too smooth and laid back for my speakers, which are already laid back.

Amp: BAT VK-250
150W @ 8 Ohm
Input impedance: 100K Ohm. Should be any easy load?
Gain: 26 dB

Speakers: Vandersteen Quatros, not very efficient but an easy load for
the amp.

  #2   Report Post  
Posted to rec.audio.high-end
Trevor Wilson[_3_] Trevor Wilson[_3_] is offline
external usenet poster
 
Posts: 139
Default Active vs. passive pre-amp

"Dave Cook" wrote in message
...
Out of curiosity, I hooked up my DAC directly to my amp just to hear
what it would sound like without going through my preamp. The DAC is
fed by a Squeezebox Touch, so I can use it's digital volume control
for attenuation. I was rather shocked how much more vibrant and
involving the sound was. It does make me wonder what the benefit of
all that electronics in a pre-amp really is. So I'd like to try
going passive with something like a stepped attenuator.

Is there anything I should know about the downside of going passive?


**Given the low output impedance of your DAC, your findings are hardly
surprising. The high output impedance of your preamp was likely causing the
problems you cited.

It does sound like there might by some loss of bass, though I'd like
to narrow this down with whatever measurements I can do with my
voltmeter and SPL meter.


**If you keep the passive attenuator as low as practicable impedance-wise,
you should enjoy excellent results. I'd start with a 1,000 Ohm pot and see
what happens.


My typical "serious" listening level is about -20dB (relative to unity
gain). A low level recording might require the volume to be raised to
-15dB or so. So I don't think I'll have any problems with having
enough gain.

Equipment, all connected with XLR cables, is as follows:

DAC: Cambridge Audio Azur 840C. Output impedance: 50 Ohm. This
seems to have a pretty beefy power supply for a CDP/DAC.

Pre-amp: BAT 3iX, Output impedance: 1000 Ohm

I also have BAT's VK-42SE solid state amp on loan, but it still seems
too smooth and laid back for my speakers, which are already laid back.

Amp: BAT VK-250
150W @ 8 Ohm
Input impedance: 100K Ohm. Should be any easy load?
Gain: 26 dB

Speakers: Vandersteen Quatros, not very efficient but an easy load for
the amp.


..**I suggest you search out an active preamp which exhibits a nice low
output impedance. IME, such preamps can be blameless, sound-wise and equal a
passive attenuator in terms of distortion.


--
Trevor Wilson
www.rageaudio.com.au

  #3   Report Post  
Posted to rec.audio.high-end
Audio Empire Audio Empire is offline
external usenet poster
 
Posts: 1,193
Default Active vs. passive pre-amp

On Sun, 17 Oct 2010 09:11:21 -0700, Dave Cook wrote
(in article ):

Out of curiosity, I hooked up my DAC directly to my amp just to hear
what it would sound like without going through my preamp. The DAC is
fed by a Squeezebox Touch, so I can use it's digital volume control
for attenuation. I was rather shocked how much more vibrant and
involving the sound was. It does make me wonder what the benefit of
all that electronics in a pre-amp really is. So I'd like to try
going passive with something like a stepped attenuator.


Yes, This is something that most audiophiles all seem to try at some point. I
once built a preamp that had one transistor (as a buffer) and a hand-full of
passive parts per channel after trying the bypass test you just did. This was
before digital though. My source components were an Otari MX5050 half/track,
15ips tape deck (which I still have), a stand -alone phono preamp (don't
remember the brand), and a Scott 4310 AM/FM Stereo tuner (which I WISH I
still had). When I replaced my (expensive, for the time) Crown IC-150 preamp
with it I too was amazed at the sound **. That started me thinking about the
number of active stages in a piece and how they affect the sound. Eventually,
I went to all-tube amplification because the tube circuits are generally
simpler than solid-state circuits.

Is there anything I should know about the downside of going passive?
It does sound like there might by some loss of bass, though I'd like
to narrow this down with whatever measurements I can do with my
voltmeter and SPL meter.


Passive preamps can work and well, but you have to have to be careful. Some
source components will have higher output impedances than others and their
sound can end-up being compromised by the variable-load placed upon them by
the volume control. That's why I advocate a "semi" passive approach where an
emitter follower (in bipolar transistors) or a common-drain (in FET circuits)
precedes the volume control which is just before the output (an op-amp like
the National LM49710 can be used too, but this makes the circuit more
complex).

My typical "serious" listening level is about -20dB (relative to unity
gain). A low level recording might require the volume to be raised to
-15dB or so. So I don't think I'll have any problems with having
enough gain.

Equipment, all connected with XLR cables, is as follows:

DAC: Cambridge Audio Azur 840C. Output impedance: 50 Ohm. This
seems to have a pretty beefy power supply for a CDP/DAC.

Pre-amp: BAT 3iX, Output impedance: 1000 Ohm

I also have BAT's VK-42SE solid state amp on loan, but it still seems
too smooth and laid back for my speakers, which are already laid back.

Amp: BAT VK-250
150W @ 8 Ohm
Input impedance: 100K Ohm. Should be any easy load?
Gain: 26 dB

Speakers: Vandersteen Quatros, not very efficient but an easy load for
the amp.


Don't know, of course, how handy you are around a soldering iron but what I
would do, if I were you, is to go to:

http://www.dact.com/html/passive_preamp.html

And try their passive attenuator. Make it simple, just one input, a volume
control, and an output and plug each of your sources into it one at a time
and see how it works. If none of your source components is loaded-down by the
volume pot, then you can safely go buy (or build) yourself a switchable
version.

You might also take a look at:

http://www.stereophile.com/solidpreamps/54/index.html

Some of Corey Greenberg's points about passive vs, buffered control stages
are well taken (if you can stand his too-cute-by-a-mile writing style),
although his design puts the volume potentiometer BEFORE the buffer stage
which seems to be elementary purpose defeating to me. If you decide to build
Greenberg's circuit, keep in mind that this article was written almost 20
years ago. I'd replace the spec'd PMI BUF-03AJ milspec op-amp with the
aforementioned LM47910N from National. It should drop right-in with no
circuit modification required. Just make sure that when you wire it, you
change the pinout to suit the Natty part's mini-dip configuration. PMI isn't
even in business anymore and I don't think the BUF-03AJ is available.

Good luck.

** Makes one wonder. If all amps and preamps have NO sound of their own, as I
have seen many people here advocate, then how come there is such a difference
between NO active preamp and any active one?

  #4   Report Post  
Posted to rec.audio.high-end
Dave Cook Dave Cook is offline
external usenet poster
 
Posts: 15
Default Active vs. passive pre-amp

On Oct 17, 2:52=A0pm, "Trevor Wilson" wrote:
**Given the low output impedance of your DAC, your findings are hardly
surprising. The high output impedance of your preamp was likely causing t=

he
problems you cited.


Well, the pre-amp and amp are both BAT gear, so I assume the sound is
what BAT was aiming for. Also the 100k Ohm input impedance of the amp
seems like it should be an easy load for the pre (few amps, mostly
tube amps, have a higher input impedance.) The bass is excellent, but
the pre has an overall dark sound that doesn't work well with the
already laid back Vandies.

.**I suggest you search out an active preamp which exhibits a nice low
output impedance. IME, such preamps can be blameless, sound-wise and equa=

l a
passive attenuator in terms of distortion.


The BAT SS pre that I have on loan has an output impedance of 200 Ohm,
which still seems a little too "smooth". Maybe I'll try some semi-pro
gear like Bryston.

Dave Cook

  #5   Report Post  
Posted to rec.audio.high-end
Arny Krueger Arny Krueger is offline
external usenet poster
 
Posts: 17,262
Default Active vs. passive pre-amp

"Dave Cook" wrote in message


Out of curiosity, I hooked up my DAC directly to my amp
just to hear what it would sound like without going
through my preamp. The DAC is fed by a Squeezebox Touch,
so I can use it's digital volume control for attenuation.


There seems to be no reason for addding anything else to the signal path if
this is the entire system.


I was rather shocked how much more vibrant and involving
the sound was.


Something is not what it seems here.

While the BAT 3ix preamp is not any good technican's idea of a good
general-purpose preamp by virtue of its poor performance into low impedance
loads (Please see
http://www.stereophile.com/tubepream...at/index4.html and frequency
response curve when driving a 600 ohm load), it should be OK for driving
your BAT VK-250 power amp due to its high input impedance. Of course, it may
have subtly failed in some non-obvious way except that it sounds bad.


It does make me wonder what the benefit
of all that electronics in a pre-amp really is.


In this system the BAT 3ix represents something that could possibly go awry
when it is completely unecessary as in an utterly simple system like this.

So I'd like to try going passive with something like a stepped
attenuator.


What is wrong with just using the digital attenuator in the DAC?

The most likely fault would be excessive noise when you turn its volume
down. Can you report on this?

There is a lot of audiophile myth and misapprehension about digital volume
controls, but a properly designed digital volume control can have many
practical and sonic advantages over common analog attenuators. For one
thing, channel balance of the digital volume control is likely to be
near-perfect, even at low volumes.







  #6   Report Post  
Posted to rec.audio.high-end
Dave Cook Dave Cook is offline
external usenet poster
 
Posts: 15
Default Active vs. passive pre-amp

On Oct 18, 7:12=A0am, "Arny Krueger" wrote:

your BAT VK-250 power amp due to its high input impedance. Of course, it =

may
have subtly failed in some non-obvious way except that it sounds bad.


Yeah, the 3iX is rolled off in the bass going into a 10K Ohm Bryston,
but is fine with the 100K Ohm BAT amp.

I suspect it's just doing it's job, though: sounding dark and laid
back to compensate for "detailed" audiophile gear in the rest of the
chain.

The BAT VK-42SE, an SS unit, is less dark sounding, but still sounds
smooth and laid back.

One thing, though, the mid-bass going direct does seem a little soft
compared to going thru one of the pre-amps. I've measured output from
the amp with sine tones and a voltmeter, and there doesn't seem to be
any problem in the bass, though. Not sure what the pre-amps are doing
to get a fuller bass sound.

What is wrong with just =A0using the digital attenuator in the DAC?

The most likely fault would be excessive noise when you turn its volume
down. =A0Can you report on this?


The noise from the DAC is much lower than from the 3iX, which is
already pretty low for a tube unit. It's the difference between
having to have my ear right on the tweeter to hear any noise vs.
having to be a few inches away to hear it.

The Squeezebox volume control is also 24-bit, so I'm not worried about
eating into the bottom 16 bits. I never seem to need more than 15-35
dB of attenuation.

  #7   Report Post  
Posted to rec.audio.high-end
Dave Cook Dave Cook is offline
external usenet poster
 
Posts: 15
Default Active vs. passive pre-amp

After trying direct for a few days and trying a couple other preamps
borrowed from my dealer, I find I still prefer the sound of going
direct for everything but the mid-bass, where all the active pre-amps
have more authority and texture. Going direct is not only cleaner
sounding, but instruments sound more natural and it feels more like
you are in the room with musicians. The actives also perhaps have a
wider soundstage, but I don't find the effect all that natural.

Dave Cook

  #8   Report Post  
Posted to rec.audio.high-end
Audio Empire Audio Empire is offline
external usenet poster
 
Posts: 1,193
Default Active vs. passive pre-amp

On Tue, 19 Oct 2010 18:57:50 -0700, Dave Cook wrote
(in article ):

After trying direct for a few days and trying a couple other preamps
borrowed from my dealer, I find I still prefer the sound of going
direct for everything but the mid-bass, where all the active pre-amps
have more authority and texture. Going direct is not only cleaner
sounding, but instruments sound more natural and it feels more like
you are in the room with musicians. The actives also perhaps have a
wider soundstage, but I don't find the effect all that natural.

Dave Cook


This midbass "authority and texture" of which you speak is LIKELY a loading
issue.

  #9   Report Post  
Posted to rec.audio.high-end
Arny Krueger Arny Krueger is offline
external usenet poster
 
Posts: 17,262
Default Active vs. passive pre-amp

"Audio Empire" wrote in message

On Tue, 19 Oct 2010 18:57:50 -0700, Dave Cook wrote
(in article ):

After trying direct for a few days and trying a couple
other preamps borrowed from my dealer, I find I still
prefer the sound of going direct for everything but the
mid-bass, where all the active pre-amps have more
authority and texture. Going direct is not only cleaner
sounding, but instruments sound more natural and it
feels more like you are in the room with musicians.
The actives also perhaps have a wider soundstage, but I
don't find the effect all that natural.


This midbass "authority and texture" of which you speak
is LIKELY a loading issue.


I'd further speculate that it is due to the active preamps introducing a
high pass filter effect in the lower bass.

The wider soundstage may be due to the active preamps adding a little
channel imbalance.


  #10   Report Post  
Posted to rec.audio.high-end
Dave Cook[_2_] Dave Cook[_2_] is offline
external usenet poster
 
Posts: 4
Default Active vs. passive pre-amp

On 2010-10-20, Audio Empire wrote:

This midbass "authority and texture" of which you speak is LIKELY a loading
issue.


Going into a 100K Ohm load on the BAT? That's as about a low a load
as you can find in an SS amp. The output impedance of the DAC is
around 50 Ohm, giving a 200:1 ratio.

I should mention for completeness that the Vandersteen Quatros require
a high pass filter (6 dB/octave, -3dB@100 Hz) before the amp. The
Quatros built-in amps then compensate. This hp filter always needs to
be adjusted for the input impedance of the amp. I think it should be
transparent to the source, but maybe it's not. I don't know how to
measure the input impedance at the hp filter.

Dave Cook


  #11   Report Post  
Posted to rec.audio.high-end
Dave Cook[_2_] Dave Cook[_2_] is offline
external usenet poster
 
Posts: 4
Default Active vs. passive pre-amp

On 2010-10-20, Arny Krueger wrote:

I'd further speculate that it is due to the active preamps introducing a
high pass filter effect in the lower bass.


Seems possible. I've checked with a voltmeter and some sine tones,
and the BAT VK-42SE (the solid state one) did seem to drop a little in
voltage from 200 to 1000 Hz, but I'm not sure I should trust that the
voltmeter's VRMS input is accurate at these frequencies.

The wider soundstage may be due to the active preamps adding a little
channel imbalance.


I don't see how that would make the soundstage wider in both
directions rather than just shift it. Maybe it was just a volume
effect. I'll try more careful level matching. I can't do any AB
testing as everything requires cable swaps.

Dave Cook
  #12   Report Post  
Posted to rec.audio.high-end
John Stone[_2_] John Stone[_2_] is offline
external usenet poster
 
Posts: 2
Default Active vs. passive pre-amp

On 10/19/10 8:57 PM, in article , "Dave Cook"
wrote:

After trying direct for a few days and trying a couple other preamps
borrowed from my dealer, I find I still prefer the sound of going
direct for everything but the mid-bass, where all the active pre-amps
have more authority and texture. Going direct is not only cleaner
sounding, but instruments sound more natural and it feels more like
you are in the room with musicians. The actives also perhaps have a
wider soundstage, but I don't find the effect all that natural.


It seems strange that there would be such a difference. Modern high quality
preamps should be transparent. Are you doing any level matching when you are
doing your comparisons? Level shifts will account for the vast majority of
audible differences in such tests. If it's just subjective testing where you
are swapping cables and listening, you have an awful lot of variables there,
including considerable expectation bias.
I've done these types of tests recently myself, using a switched bypass
arrangement around the preamp, along with exact level match between the
bypass and the preamp itself. Another person, whom I can't see, does the
switching. Set up this way, all differences completely disappear. I'm using
a Pass Labs XP20 preamp feeding an electronic crossover.
But I've tried this with other setups, and the results were the same.

  #13   Report Post  
Posted to rec.audio.high-end
Dave Cook Dave Cook is offline
external usenet poster
 
Posts: 15
Default Active vs. passive pre-amp

On Oct 20, 7:21=A0pm, John Stone wrote:

It seems strange that there would be such a difference. Modern high quali=

ty
preamps should be transparent.


Remember I'm dealing with equipment with output impedances in a range
of ~ 50 Ohm to 1000 Ohm and with tube gear vs. solid state gear. I
do know that when I had the 1000 Ohm BAT 3iX hooked up to my Bryston
3B-SST amp (10K input impedance) I measured a drop in the bass
response below 100 Hz of at least 1dB from. the bass response with the
100K Ohm BAT VK-250 amp. The drop relative to the response with the
200K Ohm BAT VK-55 (a tube amp) was more like 2dB below 100 Hz.

Are you doing any level matching when you are
doing your comparisons?


No, but why can't I make one piece sound like the other just by
adjusting the volume?

I'm trying to set up now for some level matched tests with Room EQ
Wizard and my Radio Shack SPL meter. If I'm careful I think that
should be able nail down frequency response differences to within 0.1
dB or so.

Dave Cook
  #14   Report Post  
Posted to rec.audio.high-end
Dave Cook Dave Cook is offline
external usenet poster
 
Posts: 15
Default Active vs. passive pre-amp

On Oct 20, 7:21=A0pm, John Stone wrote:

It seems strange that there would be such a difference. Modern high quali=

ty
preamps should be transparent. Are you doing any level matching when you =

are
doing your comparisons?


I did some measurements with Room EQ Wizard. Levels are calibrated
with pink noise and log sweep is used for getting frequency response
(phase is also recorded, but I'm not sure what to do with that). I
think the error here in setting the calibration is at least 0.2 dB,
though. I plotted the relative level in dB between each device used
vs. going direct from the DAC to the amp.

http://www.mediafire.com/?spuun4alsdv5e

The devices a

Bryston 3iX tube pre-amp with 1000 Ohm output impedance
Burson Buffer, which is an active buffering device
Gryphon XT solid-state pre-amp with 50 Ohm output impedance

(I think I may have messed up the calibration when measuring the
Gryphon).

I don't know how to do octave smoothing with gnuplot, so you have to
eyeball the trends in the graphs. Maybe someone can suggest something
free that can do a better job plotting audio data and that can take
columnar data from a textfile. However, it seems pretty clear that
the BAT 3iX has a rising midrange and a falling treble.

I also tried measure the Vrms output from the amp with a voltmeter,
but mine does not seem to be accurate over 1kHz or so.

Dave Cook
  #15   Report Post  
Posted to rec.audio.high-end
Audio Empire Audio Empire is offline
external usenet poster
 
Posts: 1,193
Default Active vs. passive pre-amp

On Thu, 21 Oct 2010 21:31:33 -0700, Dave Cook wrote
(in article ):

On Oct 20, 7:21=A0pm, John Stone wrote:

It seems strange that there would be such a difference. Modern high quali=

ty
preamps should be transparent. Are you doing any level matching when you =

are
doing your comparisons?


I did some measurements with Room EQ Wizard. Levels are calibrated
with pink noise and log sweep is used for getting frequency response
(phase is also recorded, but I'm not sure what to do with that). I
think the error here in setting the calibration is at least 0.2 dB,
though. I plotted the relative level in dB between each device used
vs. going direct from the DAC to the amp.

http://www.mediafire.com/?spuun4alsdv5e

The devices a

Bryston 3iX tube pre-amp with 1000 Ohm output impedance
Burson Buffer, which is an active buffering device
Gryphon XT solid-state pre-amp with 50 Ohm output impedance

(I think I may have messed up the calibration when measuring the
Gryphon).

I don't know how to do octave smoothing with gnuplot, so you have to
eyeball the trends in the graphs. Maybe someone can suggest something
free that can do a better job plotting audio data and that can take
columnar data from a textfile. However, it seems pretty clear that
the BAT 3iX has a rising midrange and a falling treble.

I also tried measure the Vrms output from the amp with a voltmeter,
but mine does not seem to be accurate over 1kHz or so.

Dave Cook


Check E-bay for a used HP 400E Audio voltmeter. They're generally available
cheap. I bought one last year off of E-bay for $15 sans power cord.



  #16   Report Post  
Posted to rec.audio.high-end
Audio Empire Audio Empire is offline
external usenet poster
 
Posts: 1,193
Default Active vs. passive pre-amp

On Thu, 21 Oct 2010 21:30:58 -0700, Dave Cook wrote
(in article ):

On Oct 20, 7:21=A0pm, John Stone wrote:

It seems strange that there would be such a difference. Modern high quali=

ty
preamps should be transparent.


Remember I'm dealing with equipment with output impedances in a range
of ~ 50 Ohm to 1000 Ohm and with tube gear vs. solid state gear. I
do know that when I had the 1000 Ohm BAT 3iX hooked up to my Bryston
3B-SST amp (10K input impedance) I measured a drop in the bass
response below 100 Hz of at least 1dB from. the bass response with the
100K Ohm BAT VK-250 amp. The drop relative to the response with the
200K Ohm BAT VK-55 (a tube amp) was more like 2dB below 100 Hz.

Are you doing any level matching when you are
doing your comparisons?


No, but why can't I make one piece sound like the other just by
adjusting the volume?


That IS level matching. It must be as close as possible, preferably within 1
dB or less. Even a small level mismatch will make the two sources sound
different even if they really aren't different. The problem is that the ear
can detect a tiny level difference as a "difference" even if one cannot
identify that difference as being a difference in volume.

I'm trying to set up now for some level matched tests with Room EQ
Wizard and my Radio Shack SPL meter. If I'm careful I think that
should be able nail down frequency response differences to within 0.1
dB or so.


You'd be better off to use an audio voltmeter across the speaker wires to
match source levels using tones on test CDs or an audio oscillator (Behringer
sells a cable tester with a built-in 2 tone oscillator that puts out either
400 Hz or 1KHz at "0" Vu, -10 Vu, or -50 Vu. The cable tester is $30 most
places and is battery powered. Pretty handy thing to have around). The Radio
Shack meter is simply not accurate enough to level match to the degree
required for this type of test. You want accurate electrical level parity,
not SPL parity.
  #17   Report Post  
Posted to rec.audio.high-end
Arny Krueger Arny Krueger is offline
external usenet poster
 
Posts: 17,262
Default Active vs. passive pre-amp

"Dave Cook" wrote in message


On Oct 20, 7:21 pm, John Stone wrote:


Are you doing any level matching when you are
doing your comparisons?


No, but why can't I make one piece sound like the other
just by adjusting the volume?


I'm trying to set up now for some level matched tests
with Room EQ Wizard and my Radio Shack SPL meter. If
I'm careful I think that should be able nail down
frequency response differences to within 0.1 dB or so.


Measurements in the acoustic domain are notoriously unstable.

I also tried measure the Vrms output from the amp with a voltmeter,
But mine does not seem to be accurate over 1kHz or so.


Most general use voltmeters are that way. Their major purpose in life is
measuring 50 or 60 Hz power.

Just use a 400 Hz test tone!


  #18   Report Post  
Posted to rec.audio.high-end
Audio Empire Audio Empire is offline
external usenet poster
 
Posts: 1,193
Default Active vs. passive pre-amp

On Sat, 23 Oct 2010 10:36:51 -0700, Arny Krueger wrote
(in article ):

"Dave Cook" wrote in message


On Oct 20, 7:21 pm, John Stone wrote:


Are you doing any level matching when you are
doing your comparisons?


No, but why can't I make one piece sound like the other
just by adjusting the volume?


I'm trying to set up now for some level matched tests
with Room EQ Wizard and my Radio Shack SPL meter. If
I'm careful I think that should be able nail down
frequency response differences to within 0.1 dB or so.


Measurements in the acoustic domain are notoriously unstable.

I also tried measure the Vrms output from the amp with a voltmeter,
But mine does not seem to be accurate over 1kHz or so.


Most general use voltmeters are that way. Their major purpose in life is
measuring 50 or 60 Hz power.

Just use a 400 Hz test tone!



It's better than acoustic . Besides, absolute accuracy is not important here,
anyway. What's important is RELATIVE accuracy. I.E. that the meter read
EXACTLY the same for all of the units under test with the same 400 Hz TONE,
and that the scale can be sufficiently expanded to get the outputs as close
one another as possible.
  #19   Report Post  
Posted to rec.audio.high-end
Arny Krueger Arny Krueger is offline
external usenet poster
 
Posts: 17,262
Default Active vs. passive pre-amp

"Audio Empire" wrote in message

On Sat, 23 Oct 2010 10:36:51 -0700, Arny Krueger wrote
(in article ):


"Dave Cook" wrote in message


I also tried measure the Vrms output from the amp with
a voltmeter, But mine does not seem to be accurate over
1kHz or so.


Most general use voltmeters are that way. Their major
purpose in life is measuring 50 or 60 Hz power.

Just use a 400 Hz test tone!


It's better than acoustic.


Far better. There really is no such thing as 0.1 dB accuracy or resolution
with acoustic measurements. Have someone else walk round the room, or simply
wait for the air currents and temperatures to redistribute themselves, and
you will measure a different number.

Acoustic measurements with pure continuous tones haven't been used by
professionals for decades. The first refinement was to start using swept
tones, and the second refinement was using spectrum analyzers to measure
artificially generated noise.


Besides, absolute accuracy is
not important here, anyway. What's important is RELATIVE
accuracy. I.E. that the meter read EXACTLY the same for
all of the units under test with the same 400 Hz TONE,
and that the scale can be sufficiently expanded to get
the outputs as close one another as possible.


Agreed. Matching is of the essence, not absolute frequency response.

Most cheap digital voltmeters are already a dB or more down at 1 KHz. But
they can generally be used for comparisons up to about 10 KHz or more. The
frequency response of DVMs is not always specified. I have two DVMs - a
Fluke and a Protek, that are flat within a few tenths of a dB up to 20 KHz.
The rest are not really audio instruments, but I could and have used them
for level matching.

Good frequency response is actually a distraction when you are metering the
power line and batteries, which is what most people use DVMs for.


  #20   Report Post  
Posted to rec.audio.high-end
Audio Empire Audio Empire is offline
external usenet poster
 
Posts: 1,193
Default Active vs. passive pre-amp

On Mon, 25 Oct 2010 07:09:55 -0700, Arny Krueger wrote
(in article ):

"Audio Empire" wrote in message

On Sat, 23 Oct 2010 10:36:51 -0700, Arny Krueger wrote
(in article ):


"Dave Cook" wrote in message


I also tried measure the Vrms output from the amp with
a voltmeter, But mine does not seem to be accurate over
1kHz or so.

Most general use voltmeters are that way. Their major
purpose in life is measuring 50 or 60 Hz power.

Just use a 400 Hz test tone!


It's better than acoustic.


Far better. There really is no such thing as 0.1 dB accuracy or resolution
with acoustic measurements. Have someone else walk round the room, or simply
wait for the air currents and temperatures to redistribute themselves, and
you will measure a different number.

Acoustic measurements with pure continuous tones haven't been used by
professionals for decades. The first refinement was to start using swept
tones, and the second refinement was using spectrum analyzers to measure
artificially generated noise.


Besides, absolute accuracy is
not important here, anyway. What's important is RELATIVE
accuracy. I.E. that the meter read EXACTLY the same for
all of the units under test with the same 400 Hz TONE,
and that the scale can be sufficiently expanded to get
the outputs as close one another as possible.


Agreed. Matching is of the essence, not absolute frequency response.

Most cheap digital voltmeters are already a dB or more down at 1 KHz. But
they can generally be used for comparisons up to about 10 KHz or more. The
frequency response of DVMs is not always specified. I have two DVMs - a
Fluke and a Protek, that are flat within a few tenths of a dB up to 20 KHz.
The rest are not really audio instruments, but I could and have used them
for level matching.

Good frequency response is actually a distraction when you are metering the
power line and batteries, which is what most people use DVMs for.



Yep. But like you say, good frequency response or accuracy are not important
here, but repeatability is. Still, in all, I consider my E-Bay purchase of an
HP-400E to be about the best $15 I ever spent on audio (and my Behringer
cable-tester box with the built-in 400 Hz and 1KHz oscillator was the best
$30 I ever spent on an audio device - BTW, If you don't have one, American
Musical Supply is selling these puppies fro $21! )

Reply
Thread Tools
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Active vs Passive monitors muzician21 Pro Audio 39 June 1st 09 01:16 PM
Passive or active bi-amping (aka active operation) Jerry High End Audio 56 August 29th 06 12:28 AM
passive or active crossovers smoove Car Audio 7 June 10th 05 07:21 AM
active or passive sub? simon Audio Opinions 1 May 6th 05 06:38 PM
subwoofer-passive or active and more... s.pl Tech 5 October 17th 04 11:25 PM


All times are GMT +1. The time now is 10:19 AM.

Powered by: vBulletin
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 AudioBanter.com.
The comments are property of their posters.
 

About Us

"It's about Audio and hi-fi"