| Author |
Message |
Bonzi
Guest
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 Posted:
Sat Nov 12, 2005 5:42 am Post subject:
impedance questions with lynx one and old mic pre / headphon |
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I have 2 sets of headphones. The first set is the green aviation types
made by David Clark. They sound pretty good and really keep out
external noise. I measured the resistance (impedance?) of each speaker
to be 20k ohms. Perhaps this did not measure impedence?
My second pair is a little cheapy pair of philips phones that came with
a portable cd player. They measure at 20 ohms (not k ohms). I notice
the volume on the philips to be a little less than the green ones, but
not by much. I'm presuming this is attributed to the impedance.
I'm running out of a lynx one card directly into these headphones
(split off of my quested monitors via a 4pole switch). The specs on the
card say the lynx will run a load of 600ohms. My brain must not be
wired to understand impedence because it starts to hurt when I try to
understand it ;)
While the David Clark headphones are usable, the levels need to be
amplified. Any suggestions on something single channel for under $100?
How about these new portable BurrBrown opamp headphone amps the kids
are using with IPODS that come in little candy tins?).
Now here's a really dumb question I have (since I still can't seem to
get a practical understanding of impedance down). Why can't I just put
a resistor in series with each headphone speaker to raise the impedance
(resistance) to make it louder? I swear electronics makes no sense to
me.
That was headphones. Now to the mic pre stuff...
I'm using an old RCA mic preamp (BA-72) into the lynx one card. The
output source impedance of the RCA preamp is 600 ohms (it has a 150ohm
strappable setting). This is running into a 24k ohm load impedance on
the lynx card. Is this bridging? Is this good? Is there some special
ratio as far as bridging or is it just good to go low impedance source
into high impedance in general.
This impedance stuff is very non-intuitive for me. I keep digging for a
simple explanation only to find answers that give me no formula of
logic to use. How does more resistance in the load make something
louder? The only thing I can come up with is that this has to do with
hooking together 2 circuits (a source and a load) and each has it's on
capacitor based resistance (which is special in some way regarding AC
voltage such as audio).
I'm also considering setting up dpdt switches for the input and output
transformers on the RCA (input has 150 or 600 ohms and so does output)
so I can compare them.
Any suggestions out there in net land? Thank AOT
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Mike Rivers
Guest
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| Posted:
Sat Nov 12, 2005 6:42 pm Post subject:
Re: impedance questions with lynx one and old mic pre / head |
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Bonzi wrote:
| Quote: | I have 2 sets of headphones. The first set is the green aviation types
made by David Clark. They sound pretty good and really keep out
external noise. I measured the resistance (impedance?) of each speaker
to be 20k ohms. Perhaps this did not measure impedence?
|
No, it didn't, but if that's the DC resistance and there wasn't a
"mute" switch engaged, they would certainly be categorized as "high
impedance" phones. Most audio headphones have a DC resistance of less
than 100 ohms. Did you hear a click in the headphones when you
connected the meter? If not, you weren't measuring the phones, but
something else. Some of those aircraft headsets use connectors that
aren't standard in audio. Perhaps there's a David Clark web site that
has a wiring diagram. I didn't look, but you can.
Have you tried connecting them to a real headphone jack?
| Quote: | My second pair is a little cheapy pair of philips phones that came with
a portable cd player. They measure at 20 ohms (not k ohms). I notice
the volume on the philips to be a little less than the green ones, but
not by much. I'm presuming this is attributed to the impedance.
|
20 ohms is more like it. It depends on what's driving the headphones,
but as a rule, the lower the impedance, the louder the volume. But
that's also a function of the efficiency of the transducer.
| Quote: | I'm running out of a lynx one card directly into these headphones
(split off of my quested monitors via a 4pole switch). The specs on the
card say the lynx will run a load of 600ohms. My brain must not be
wired to understand impedence because it starts to hurt when I try to
understand it ;)
|
Take two Tylenol and call me in the morning. A source designed for a
600 ohm (or higher) load won't be very happy driving 20 ohm headphones.
Most of the voltage gets dropped across the internal impedance of the
card's output circuit and that leaves less voltage to drive the
headphones. While you can get some sound out of this combination and
you won't damage anything by connecting the "standard" phones to the
Lynx output, you won't get much volume either. They need to be driven
by a low impedance source, like a headphone amplifier (a low power
amplifier) or some other output that's designed to drive headphones.
If the Clark phones are indeed a significantly higher impedance, that's
why they sound louder when connected to the 600 ohm output of the Lynx
card. They put less load on the card's output circuit and therefore see
a higher voltage. On the other hand, they may be designed to work with
a higher voltage so they may not actually be louder. In any case, the
Lynx is not designed to drive headphones to a volume satisfactory for
most people so either will need some help.
| Quote: | While the David Clark headphones are usable, the levels need to be
amplified. Any suggestions on something single channel for under $100?
How about these new portable BurrBrown opamp headphone amps the kids
are using with IPODS that come in little candy tins?).
|
I dont' know what the kids are using with their iPods, but anything
that's intended to be a headphone amplifier will work. As to how much
volume you'll get from your headphones, nobody can predict that without
duplicating your exact setup. Find a kid with an iPod and try it.
| Quote: | Now here's a really dumb question I have (since I still can't seem to
get a practical understanding of impedance down). Why can't I just put
a resistor in series with each headphone speaker to raise the impedance
(resistance) to make it louder? I swear electronics makes no sense to
me.
|
Well, this isn't the place to learn it. You need to find a book (or I
guess anyone who thinks 'iPod" would rather find a web site) that
explains basic electricity and Ohm's Law. Forget "impedance" for the
moment and study DC circuits and how resistance, voltage, current, and
power are interrelated. The math isn't difficult at all. If you can do
arithmetic you can work it out. Impedance is like resistance but it
changes with frequency. Get the DC (no frequency) concepts down first.
| Quote: | I'm using an old RCA mic preamp (BA-72) into the lynx one card. The
output source impedance of the RCA preamp is 600 ohms (it has a 150ohm
strappable setting). This is running into a 24k ohm load impedance on
the lynx card. Is this bridging? Is this good?
|
Yes, and yes. My but you have a strange collection of equipment.
| Quote: | Is there some special
ratio as far as bridging or is it just good to go low impedance source
into high impedance in general.
|
Generally if the load impedance is at least 10 times the source
impedance, it's considered "bridging," though not many audio people use
that term any more. Today, most audio equipment is designed with an
input impedance of 20K ohms or more, and an output impedance of 100
ohms or less. If the Lynx is specified as being capable of driving a
600 ohm load, it probably has an acutal output impedance of 60 ohms or
lower.
| Quote: | This impedance stuff is very non-intuitive for me. I keep digging for a
simple explanation only to find answers that give me no formula of
logic to use. How does more resistance in the load make something
louder?
|
Adding more resistance to the load never makes anything louder. Forget
that concept.
Every source has some "source impedance" which is always in series with
the actual voltage source and the load. When you complete the circuit
by connecting a load across the output terminals (in this case, the
headphones), you have two resistors in series, driven by the voltage.
The voltage gets divided between those two resistors. Since the same
current flows through both resistors (that's the definition of a series
circuit), the higher resistance will have the higher voltage across it.
But this doesn't go on indefinitely. You need some power to move the
diaphragms, and that takes current. The higher the resistance in a
series circuit, the lower the current. There's an optimum value for
maximum power transfer but don't worry about that now. |
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Scott Dorsey
Guest
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| Posted:
Sat Nov 12, 2005 8:07 pm Post subject:
Re: impedance questions with lynx one and old mic pre / head |
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Bonzi <chainsawhalos@hotmail.com> wrote:
| Quote: | I have 2 sets of headphones. The first set is the green aviation types
made by David Clark. They sound pretty good and really keep out
external noise. I measured the resistance (impedance?) of each speaker
to be 20k ohms. Perhaps this did not measure impedence?
|
Resistance is impedance at DC. What you want to measure is impedance
around 1KHz.
In fact, the David Clark phones should be around 600 ohms impedance,
maybe a little higher.
| Quote: | My second pair is a little cheapy pair of philips phones that came with
a portable cd player. They measure at 20 ohms (not k ohms). I notice
the volume on the philips to be a little less than the green ones, but
not by much. I'm presuming this is attributed to the impedance.
|
The lower impedance means the headphones need higher _voltage_ for the
same amount of power, but lower _current_.
But in addition to this, these headphones probably need less power to
get the same amount of level, because they aren't as efficient as the
David Clark set. Aviation phones tend to be very efficient since they
don't need to produce much low end and often need to be turned up very
high.
| Quote: | I'm running out of a lynx one card directly into these headphones
(split off of my quested monitors via a 4pole switch). The specs on the
card say the lynx will run a load of 600ohms. My brain must not be
wired to understand impedence because it starts to hurt when I try to
understand it ;)
|
Okay, this means you don't want to use a pair of headphones that is
_less_ than 600 ohms, because the card can't provide enough current
to drive it.
| Quote: | While the David Clark headphones are usable, the levels need to be
amplified. Any suggestions on something single channel for under $100?
How about these new portable BurrBrown opamp headphone amps the kids
are using with IPODS that come in little candy tins?).
|
That might do it, but you still aren't going to be able to swing much
current with one of those. There is a cheap Behringer headphone amp
that seems usable, but there isn't much out there unless you want to
use a real power amp.
| Quote: | Now here's a really dumb question I have (since I still can't seem to
get a practical understanding of impedance down). Why can't I just put
a resistor in series with each headphone speaker to raise the impedance
(resistance) to make it louder? I swear electronics makes no sense to
me.
|
The _output impedance_ is a measure of how much current the device can
produce... that is, it can put enough current in to make a 600 ohm load
happy.
If you put a resistor in series with the load, you can make the output
jack see the proper load, which means your distortion will go down and
your frequency response might improve, but now you are losing more power
through the resistor.
| Quote: | I'm using an old RCA mic preamp (BA-72) into the lynx one card. The
output source impedance of the RCA preamp is 600 ohms (it has a 150ohm
strappable setting). This is running into a 24k ohm load impedance on
the lynx card. Is this bridging? Is this good? Is there some special
ratio as far as bridging or is it just good to go low impedance source
into high impedance in general.
|
This preamp has an output transformer. It _needs_ to see a 600 ohm
load. Put a 620 ohm 1W resistor between the two terminals so that
it sees a 600 ohm load. You'll find the top end sounds a lot less
brittle when the preamp transformer sees the proper load.
| Quote: | This impedance stuff is very non-intuitive for me. I keep digging for a
simple explanation only to find answers that give me no formula of
logic to use. How does more resistance in the load make something
louder? The only thing I can come up with is that this has to do with
hooking together 2 circuits (a source and a load) and each has it's on
capacitor based resistance (which is special in some way regarding AC
voltage such as audio).
|
I think there is a good description in the FAQ, actually.
| Quote: | I'm also considering setting up dpdt switches for the input and output
transformers on the RCA (input has 150 or 600 ohms and so does output)
so I can compare them.
|
Shouldn't be much difference, IF the load is correct for the output
you are using. That means 150 ohm shunt resistor for the 150 ohm
output, 600 ohm shunt for the 600 ohm output.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis." |
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Arny Krueger
Guest
|
| Posted:
Sat Nov 12, 2005 11:45 pm Post subject:
Re: impedance questions with lynx one and old mic pre / head |
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|
"Scott Dorsey" <kludge@panix.com> wrote in message
news:dl4sv7$ns9$1@panix2.panix.com
| Quote: | Bonzi <chainsawhalos@hotmail.com> wrote:
I have 2 sets of headphones. The first set is the green
aviation types made by David Clark. They sound pretty
good and really keep out external noise. I measured the
resistance (impedance?) of each speaker to be 20k ohms.
Perhaps this did not measure impedence?
Resistance is impedance at DC. What you want to measure
is impedance around 1KHz.
In fact, the David Clark phones should be around 600 ohms
impedance, maybe a little higher.
My second pair is a little cheapy pair of philips phones
that came with a portable cd player. They measure at 20
ohms (not k ohms). I notice the volume on the philips to
be a little less than the green ones, but not by much.
I'm presuming this is attributed to the impedance.
The lower impedance means the headphones need higher
_voltage_ for the same amount of power, but lower
_current_.
|
Umm, isn't is more like:
The lower impedance means the headphones need lower
_voltage_ for the same amount of power, but higher
_current_.
-or-
The higher impedance means the headphones need lower
_voltage_ for the same amount of power, but higher
_current_. |
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Paul Stamler
Guest
|
| Posted:
Sun Nov 13, 2005 12:47 am Post subject:
Re: impedance questions with lynx one and old mic pre / head |
|
|
"Mike Rivers" <mrivers@d-and-d.com> wrote in message
news:1131799368.270639.255470@z14g2000cwz.googlegroups.com...
| Quote: | I'm using an old RCA mic preamp (BA-72) into the lynx one card. The
output source impedance of the RCA preamp is 600 ohms (it has a 150ohm
strappable setting). This is running into a 24k ohm load impedance on
the lynx card. Is this bridging? Is this good?
Yes, and yes. My but you have a strange collection of equipment.
|
Actually the answer may be "Yes, and no." Yes, it's bridging, but it may not
be good; the RCA is probably set up for impedance matching rather than
bridging, and will be happier driving a 600-ohm load. (The transformer will
ring if the load isn't 600 ohms.) Level will drop (probably 6dB) but your
frequency response will be flatter.
Note that if I'm wrong and the RCA is designed for a bridging load, then
ignore everything I just said.
Peace,
Paul |
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Bonzi
Guest
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| Posted:
Sun Nov 13, 2005 1:43 am Post subject:
Re: impedance questions with lynx one and old mic pre / head |
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Thanks for responding Mike. Between you, Scott's, and Arny, I'm
starting to understand this better! This has generated some more
comments below:
| Quote: | Did you hear a click in the headphones when you
connected the meter? If not, you weren't measuring the phones, but
something else.
|
I did hear a clicking when I measured the dc resistanceonthe Clarks. It
was late last night. I just took another reading and it shows 2.3k ohms
on the Clarks (TRS connector). Quite a bit lower (a little closer to
the 600ohms Scott was thinking). I realize now that impedence is more
like variable resistance given different audio frequencies. So there is
probably some best median resistance (regarding maximum power transfer
I would guess).
| Quote: | 20 ohms is more like it. It depends on what's driving the headphones,
but as a rule, the lower the impedance, the louder the volume. But
that's also a function of the efficiency of the transducer.
|
So impedence by itself with power requirements in terms of current are
what I'm missing. It's more a combination of resistance and required
power which affects volume. But then quality is affected related to
maximum power transfer? Certain frequencies get resisted and their
respective volumes changed/affected given impedence mismatching.
| Quote: | Take two Tylenol and call me in the morning.
That helped! |
| Quote: | A source designed for a
600 ohm (or higher) load won't be very happy driving 20 ohm headphones.
Because it's going to have to put out more amperage (current) and it |
may do a sloppy/inaccurate job of it, if not just not supply the needed
current at all.
Less current = distortion
Less voltage = less volume?
| Quote: | Most of the voltage gets dropped across the internal impedance of the
card's output circuit and that leaves less voltage to drive the
headphones.
Kind of like a 9v battery has built in resistance? I'm digressing here, |
but I never understood this. Why not reflect the true output of the
battery at 2 volts or whatever it drops to as a result of it's internal
resistance... anyway
| Quote: | While you can get some sound out of this combination and
you won't damage anything by connecting the "standard" phones to the
Lynx output, you won't get much volume either. They need to be driven
by a low impedance source
Meaning a source that has a low impedance output (which means it |
expects a low impedance load)? Such an amp would have the capability of
putting out a strong current (volume) given low impedance loads
(meaning little resistance)? But the wattage from source to source will
vary regardless of it "being" a low impedance source? See my confusion?
It seems related to db where db is not a specific amount, but a ratio
between to volumes (well, one of those "db" terms. I'm not sure which
one dbV dbu dbm, anyways).
| Quote: | If the Clark phones are indeed a significantly higher impedance, that's
why they sound louder when connected to the 600 ohm output of the Lynx
card. They put less load on the card's output circuit and therefore see
a higher voltage.
This doesn't make sense to me. Higher impedance headphones would offer |
more resistance and thus you would have less current (ie. volume).
| Quote: | Forget "impedance" for the
moment and study DC circuits and how resistance, voltage, current, and
power are interrelated. The math isn't difficult at all. If you can do
arithmetic you can work it out. Impedance is like resistance but it
changes with frequency. Get the DC (no frequency) concepts down first.
I've kind of got ohms law down. I'm still working on it. I get confused |
because of things like theory vs. practical, inferior measuring
devices. I really need to get an oscilliscope and an ammeter to advance
my learning.
| Quote: |
I'm using an old RCA mic preamp (BA-72) into the lynx one card. The
output source impedance of the RCA preamp is 600 ohms (it has a 150ohm
strappable setting). This is running into a 24k ohm load impedance on
the lynx card. Is this bridging? Is this good?
Yes, and yes. My but you have a strange collection of equipment
So the high resistance on the input of the load is good because the |
source (the pre in this case) doesn't have to send as much current to
work correctly?
| Quote: | Adding more resistance to the load never makes anything louder. Forget
that concept.
got it. thanks. |
| Quote: | Every source has some "source impedance" which is always in series with
the actual voltage source and the load. When you complete the circuit
by connecting a load across the output terminals (in this case, the
headphones), you have two resistors in series, driven by the voltage.
The voltage gets divided between those two resistors. Since the same
current flows through both resistors (that's the definition of a series
circuit), the higher resistance will have the higher voltage across it.
But this doesn't go on indefinitely. You need some power to move the
diaphragms, and that takes current. The higher the resistance in a
series circuit, the lower the current.
great explanation. thanks. |
| Quote: | There's an optimum value for maximum power transfer but don't worry about that now.
yeah, I've heard of that. It must be difficult to pinpoint because of |
the variable resistance at different AC frequencies (audio). Ie.
impedance |
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Mike Rivers
Guest
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| Posted:
Sun Nov 13, 2005 2:00 am Post subject:
Re: impedance questions with lynx one and old mic pre / head |
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|
Bonzi wrote:
| Quote: | I just took another reading and it shows 2.3k ohms
on the Clarks (TRS connector). Quite a bit lower (a little closer to
the 600ohms Scott was thinking).
|
That's more like it.
| Quote: | So impedence by itself with power requirements in terms of current are
what I'm missing. It's more a combination of resistance and required
power which affects volume. But then quality is affected related to
maximum power transfer? Certain frequencies get resisted and their
respective volumes changed/affected given impedence mismatching.
|
Unless you're designing a filter, you want the impedance to be
relatively constant over the frequency range that you're working.
| Quote: | Less current = distortion
|
No direct relationship there.
| Quote: | Less voltage = less volume?
|
Well, sort of. But since voltage, current, and impedance are all
related, you can't generalize.
| Quote: | Kind of like a 9v battery has built in resistance?
|
Yes. There's some guitar player who says he can tell what kind of
battery is in his effect pedals by how they respond to the battery's
internal resistance.
| Quote: | Why not reflect the true output of the
battery at 2 volts or whatever it drops to as a result of it's internal
resistance... anyway
|
Because you don't know how much voltage will be dropped across thei
inernal resistance unless you know how much current is being drawn from
the battery. An ordinary voltmeter draws practically no current, so the
terminal voltage that you measure doesn't have any voltage drop because
of the internal resistance. A "battery tester" has a load that draws
current, so it can display the voltage across that known load. Usually
it's just a "good" range on the meter.
| Quote: | Meaning a source that has a low impedance output (which means it
expects a low impedance load)?
|
No. These days, a "low impedance output" means that it doesn't really
want to see a low impedance load, because it can't deliver much
current. A power amplifier (meant to drive speakers or headphones) has
an output impedance of a fraction of an ohm because it does have to
deliver some current to the speaker, but it still wants to be connected
to a speaker that's several times that impedance.
Things of the generation of your RCA mic amplifier, as Scott and Paul
pointed out) were designed to operate with matched output and input
impedances. There were almost always transformers at the output and a
transformer expects to see a known load impedance. But we don't design
gear like that any more. It's too expensive.
| Quote: | But the wattage from source to source will
vary regardless of it "being" a low impedance source? See my confusion?
|
You need to read up on Ohm's Law. Then it will all become clear. This
is basic science, not confusing magic.
| Quote: | I've kind of got ohms law down. I'm still working on it. I get confused
because of things like theory vs. practical, inferior measuring
devices. I really need to get an oscilliscope and an ammeter to advance
my learning.
|
It's not all that complicated. It all makes very good sense. |
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Bonzi
Guest
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| Posted:
Sun Nov 13, 2005 5:42 am Post subject:
Re: impedance questions with lynx one and old mic pre / head |
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| Quote: | Less current = distortion
No direct relationship there.
|
Right. I've been studying in between posts so I know what you mean. I
didn't realize that current is volume and voltage and current aren't
directly porportionate (it depends on resistance). You need more
voltage to get a little more current (volume) porportionate to
resistance.
| Quote: | Less voltage = less volume?
Well, sort of. But since voltage, current, and impedance are all
related, you can't generalize.
|
Got it (or getting pretty darn close :)
| Quote: |
Kind of like a 9v battery has built in resistance?
Yes. There's some guitar player who says he can tell what kind of
battery is in his effect pedals by how they respond to the battery's
internal resistance.
Why not reflect the true output of the
battery at 2 volts or whatever it drops to as a result of it's internal
resistance... anyway
Because you don't know how much voltage will be dropped across thei
inernal resistance unless you know how much current is being drawn from
the battery. An ordinary voltmeter draws practically no current, so the
terminal voltage that you measure doesn't have any voltage drop because
of the internal resistance. A "battery tester" has a load that draws
current, so it can display the voltage across that known load. Usually
it's just a "good" range on the meter.
|
Makes sense now. thanks.
| Quote: | Things of the generation of your RCA mic amplifier, as Scott and Paul
pointed out) were designed to operate with matched output and input
impedances. There were almost always transformers at the output and a
transformer expects to see a known load impedance. But we don't design
gear like that any more. It's too expensive.
|
That info sure helps.
| Quote: | You need to read up on Ohm's Law. Then it will all become clear.
I went back and looked at it and it makes much more sense now. Thanks |
again Mike! |
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Bonzi
Guest
|
| Posted:
Sun Nov 13, 2005 5:42 am Post subject:
Re: impedance questions with lynx one and old mic pre / head |
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|
| Quote: | Actually the answer may be "Yes, and no." Yes, it's bridging, but it may not
be good; the RCA is probably set up for impedance matching rather than
bridging, and will be happier driving a 600-ohm load. (The transformer will
ring if the load isn't 600 ohms.) Level will drop (probably 6dB) but your
frequency response will be flatter.
Note that if I'm wrong and the RCA is designed for a bridging load, then
ignore everything I just said.
|
Here's what the RCA BA-72a manual says:
=========================
Source Impedance: 150 or 600 ohms balanced or unbalanced, 37.5 ohms
unbalanced
Input Impedance:
Matching: Unloaded input transformer (input impedance higher than
source impedance for all frequencies (20-20kHz)
Bridging: Externally mounted bridging gain control required
(approx. 20k ohms input)
Load Impedance: 600 ohms when shipped (may be changed to 150 ohms
========================
I guess it doesn't mention bridging in terms of the output, only the
input. I'm going to try the output shunt this week. This pre can also
be jumpered for extra gain (assuming I don't overload it) to make up
after the shunt perhaps. We'll see.
I'm not really sure what it means regarding bridging the input. Do you
think it's saying that you could shunt it to 20k ohms and you'd want to
have a gain control? |
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Bonzi
Guest
|
| Posted:
Sun Nov 13, 2005 5:42 am Post subject:
Re: impedance questions with lynx one and old mic pre / head |
|
|
| Quote: | Resistance is impedance at DC. What you want to measure is impedance
around 1KHz.
|
This explains things. I don't imagine there is an AC ohm meter that can
output a 1kHz voltage and measure the resistance (ie. an impedance
meter?). Not that I would need one, just curious what tools are out
there.
| Quote: | In fact, the David Clark phones should be around 600 ohms impedance,
maybe a little higher.
|
As I mentioned in my response to Mike Rivers, I re-measured the
impedance (it was late last night when I initially read it) and it's
2.3k ohms (not 23k ohms) which is definitely closer to 600 ohms FYI.
| Quote: | I'm running out of a lynx one card directly into these headphones
(split off of my quested monitors via a 4pole switch). The specs on the
card say the lynx will run a load of 600ohms.
Okay, this means you don't want to use a pair of headphones that is
_less_ than 600 ohms, because the card can't provide enough current
to drive it.
|
I revisited the Lynx One spec
(http://www.lynxstudio.com/lynxonespecs.html). It's output impedance is
shown as 50ohms (unbalanced) or 100ohms (balanced), but it mentions
that it has the "capacity" to run slightly higher impedance loads (it
mentions 600ohms).
I'm taking this to mean that the Lynx would be capable of producing
more voltage needed by a higher impedance load. Any higher than 600ohms
and it wouldn't be able to produce enough voltage for a "typical" load,
perhaps. Anything lower than 50 ohms and it's saying that it may not be
able to supply enough current. If the card cannot supply enough
current, does that potentially hurt the card/computer power supply or
is it just harmlessly bottoming out?
| Quote: | The _output impedance_ is a measure of how much current the device can
produce... that is, it can put enough current in to make a 600 ohm load
happy.
|
Thanks. This cleared things up quite a bit.
| Quote: | If you put a resistor in series with the load, you can make the output
jack see the proper load, which means your distortion will go down and
your frequency response might improve, but now you are losing more power
through the resistor.
|
Great. Makes sense. Thanks.
| Quote: | I'm using an old RCA mic preamp (BA-72) into the lynx one card. The
output source impedance of the RCA preamp is 600 ohms (it has a 150ohm
strappable setting). This is running into a 24k ohm load impedance on
the lynx card. Is this bridging? Is this good? Is there some special
ratio as far as bridging or is it just good to go low impedance source
into high impedance in general.
This preamp has an output transformer. It _needs_ to see a 600 ohm
load. Put a 620 ohm 1W resistor between the two terminals so that
it sees a 600 ohm load. You'll find the top end sounds a lot less
brittle when the preamp transformer sees the proper load.
|
Interesting - I did notice the high end to be a little harsh. 620 vs.
600 ohms make a difference in the output shunt?
Regarding the input transformer, I've read various information
regarding running SM57's into preamps and ideal input impedances. This
RCA can be set for 150 ohms input. Wouldn't a lower input should be
better (as you would perhaps get a more accurate reflection of the
sound in the current since you would get more current for your voltage
(and thus a louder signal from the mic before amplification)? Black
magic time? Should I shunt the input up to 2k? Maybe even a variable
resistor pot and set it to taste.
Again, thanks Everyone for the great information!!!!! |
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Chris Hornbeck
Guest
|
| Posted:
Sun Nov 13, 2005 5:42 am Post subject:
Re: impedance questions with lynx one and old mic pre / head |
|
|
On 12 Nov 2005 17:26:45 -0800, "Bonzi" <chainsawhalos@hotmail.com>
wrote:
| Quote: | I've been studying in between posts so I know what you mean. I
didn't realize that current is volume and voltage and current aren't
directly porportionate (it depends on resistance). You need more
voltage to get a little more current (volume) porportionate to
resistance.
|
Many guys are more comfotable thinking of impedance/resistance
in terms of gear ratios.
Low gears on a car are high RPM-to-torque ratios.
Low impedances/resistances are high current-to-voltage
ratios.
High gears on a car are low torque-to-RPM ratios.
High impedances/resistances are low current-to-voltage
ratios.
Similar analogies can be made for fluid flows.
Pressure=Voltage=Torque.
Volume Flow=Current=RPM.
Not perxactly right, but close enough for duck season.
Good fortune,
Chris Hornbeck |
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Bonzi
Guest
|
| Posted:
Sun Nov 13, 2005 5:42 am Post subject:
Re: impedance questions with lynx one and old mic pre / head |
|
|
| Quote: | My second pair is a little cheapy pair of philips phones that came with
a portable cd player. They measure at 20 ohms (not k ohms). I notice
the volume on the philips to be a little less than the green ones, but
not by much. I'm presuming this is attributed to the impedance.
20 ohms is more like it. It depends on what's driving the headphones,
but as a rule, the lower the impedance, the louder the volume.
|
This makes perfect sense to me now. Thanks so much!!
| Quote: | But that's also a function of the efficiency of the transducer.
|
Right! Speaker efficiency. That's why, even though the green cans are
higher impedance, they are louder. Because they are more efficient!
| Quote: | I'm running out of a lynx one card directly into these headphones
They need to be driven
by a low impedance source, like a headphone amplifier (a low power
amplifier) or some other output that's designed to drive headphones.
|
I'm re-reading this post and now I see one key reason for my confusion.
When you just said "low impedance source" that means "a source that
could drive a low impedance". Amplifiers have 2 impedance measurement
(in and out). Mics and speakers have one. Brain feels better when it
understands...
| Quote: | If the Clark phones are indeed a significantly higher impedance, that's
why they sound louder when connected to the 600 ohm output of the Lynx
card. They put less load on the card's output circuit and therefore see
a higher voltage.
|
Are you saying that the card's output voltage fluctuates? I'm a little
confused here. I thought output voltage is static (and thus current,
whatever it is based on resistance). Does the card know how to provide
various voltages in order to provide some constant amperage? I've
avoided digital electronics. Can it do that? Maybe that's what I'm
missing?
I thought you provide a static (no pun intended) voltage and whatever
resistance there is determines what the current will be (and if there's
enough current, the load's will function).
Sorry to go on about impedance, but hopefully I won't be the only one
who finds this thread useful. |
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Mike Rivers
Guest
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| Posted:
Sun Nov 13, 2005 7:03 pm Post subject:
Re: impedance questions with lynx one and old mic pre / head |
|
|
Bonzi wrote:
| Quote: | They need to be driven
by a low impedance source, like a headphone amplifier (a low power
amplifier) or some other output that's designed to drive headphones.
I'm re-reading this post and now I see one key reason for my confusion.
When you just said "low impedance source" that means "a source that
could drive a low impedance".
|
No, I mean one with a low series inpedance inside the box (before the
terminals) that won't cause too much voltage drop at the terminals when
you connect it to a low impedance load. Ohm's Law and Seriec Circuits.
Think.
| Quote: | Amplifiers have 2 impedance measurement
(in and out). Mics and speakers have one. Brain feels better when it
understands...
|
That's because an amplifier has an input and an output each of which is
intended to be connected to a different kind of thing. Microphones have
only an output, speakers have only an input (unless you consider the
acoustic side as an input or output respecively).
| Quote: | Are you saying that the card's output voltage fluctuates? I'm a little
confused here. I thought output voltage is static
|
Yes. If you put a steady signal into and amplifier and measure the
voltage at the output terminals, the lower the load impedance you
connect to the output terminals, the lower the voltage you will measure
there. Why? Because the remainder of the voltage will be dropped across
the internal impedance and it isn't available, along with the current,
to do the work of moving the speaker cones. Ohm's Law. Series Circuit.
Think. |
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Mike Rivers
Guest
|
| Posted:
Sun Nov 13, 2005 7:07 pm Post subject:
Re: impedance questions with lynx one and old mic pre / head |
|
|
Bonzi wrote:
| Quote: | Sorry to go on about impedance, but hopefully I won't be the only one
who finds this thread useful.
|
I didn't realize you were going to be pushing this so far. I wrote a
three part article in Recording Magazine in the September, October, and
November 2003 issues complete with illustrations and examples. You
might want to order those back issues. Check at
http://www.recordingmag.com. You may have to make a phone call to order
them. |
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Paul Stamler
Guest
|
| Posted:
Mon Nov 14, 2005 12:42 am Post subject:
Re: impedance questions with lynx one and old mic pre / head |
|
|
"Bonzi" <chainsawhalos@hotmail.com> wrote in message
news:1131843247.173145.114440@z14g2000cwz.googlegroups.com...
| Quote: | I'm running out of a lynx one card directly into these headphones
(split off of my quested monitors via a 4pole switch). The specs on the
card say the lynx will run a load of 600ohms.
Okay, this means you don't want to use a pair of headphones that is
_less_ than 600 ohms, because the card can't provide enough current
to drive it.
I revisited the Lynx One spec
(http://www.lynxstudio.com/lynxonespecs.html). It's output impedance is
shown as 50ohms (unbalanced) or 100ohms (balanced), but it mentions
that it has the "capacity" to run slightly higher impedance loads (it
mentions 600ohms).
I'm taking this to mean that the Lynx would be capable of producing
more voltage needed by a higher impedance load. Any higher than 600ohms
and it wouldn't be able to produce enough voltage for a "typical" load,
perhaps. Anything lower than 50 ohms and it's saying that it may not be
able to supply enough current. If the card cannot supply enough
current, does that potentially hurt the card/computer power supply or
is it just harmlessly bottoming out?
|
No, you've gotten tangled again. Let's start fresh.
The Lynx is not designed to drive headphones -- that's where a lot of the
confusion is coming from. It's a *voltage-source*, a device designed to
drive an audio line, either semi-pro (unbalanced) or pro (balanced). It will
produce enough voltage to do that job, and enough current to support that
voltage (so to speak), provided the load impedance is 600 ohms or greater --
the load can be as high above 600 ohms as you want. If the load impedance is
below 600 ohms then you'll draw more current than the Lynx was designed for,
and it'll begin to distort. Ignore the output impedance of the Lynx; it
isn't all that relevant for the job it's designed to do. The Lynx was never
designed to transfer power, or to match impedances. It works on the
assumption that its load impedance will be significantly higher than its
source impedance.
What does this mean for your headphone project? It means the
higher-impedance Clark headphones will probably work decently with the Lynx,
and the lower-impedance headphones won't. You'd still be better off getting
a small headphone amplifier, though, and reserving the Lynx for the job for
which it was designed.
Peace,
Paul |
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