AC coupling caps...

R

Ricky

Guest
Typically, an AC coupling cap is driven from a low impedance source and only the load needs to be factored into the frequency equation. But when the cap is on the input, is it typical to factor in the expected source impedance, or assume a worse case of low driving impedance?

I have a design with 600 ohm differential audio inputs and I keep seeing a different response on the input and output. I finally realized this was because my input simulation used a low impedance drive, but the output included the output impedance and the load impedance. Duh!

So, do I need to beef up the input caps to handle a low impedance driver? Or, I guess I\'m asking, what is typically expected of the frequency response at the input? Is it typically for a rated driving impedance or for all source impedances?

Not much point in asking my customer. He has indicated that the various test gear this will be connected to is all over the map on this. That\'s one reason why setting a dBm level on the test gear output does not give consistent voltages measured at the interface. I don\'t expect he will know much more about the user equipment this will be connected to.

The 47 uF input caps required for worse case are a bit on the large size and the voltage rating is limited. I\'d prefer to use 33 uF caps if practical..

I guess this caught me by surprise. I thought I had completed this design, but I moved the input caps to a slightly different point in the circuit, and things changed a lot.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209
 
On Monday, 24 April 2023 at 18:51:16 UTC+1, Ricky wrote:
Typically, an AC coupling cap is driven from a low impedance source and only the load needs to be factored into the frequency equation. But when the cap is on the input, is it typical to factor in the expected source impedance, or assume a worse case of low driving impedance?

I have a design with 600 ohm differential audio inputs and I keep seeing a different response on the input and output. I finally realized this was because my input simulation used a low impedance drive, but the output included the output impedance and the load impedance. Duh!

So, do I need to beef up the input caps to handle a low impedance driver? Or, I guess I\'m asking, what is typically expected of the frequency response at the input? Is it typically for a rated driving impedance or for all source impedances?

Not much point in asking my customer. He has indicated that the various test gear this will be connected to is all over the map on this. That\'s one reason why setting a dBm level on the test gear output does not give consistent voltages measured at the interface. I don\'t expect he will know much more about the user equipment this will be connected to.

The 47 uF input caps required for worse case are a bit on the large size and the voltage rating is limited. I\'d prefer to use 33 uF caps if practical.

I guess this caught me by surprise. I thought I had completed this design, but I moved the input caps to a slightly different point in the circuit, and things changed a lot.
Click to expand...

The design choice of whether it stays in spec for off impedances is yours alone. If the customer is using it in all sorts of situations, keeping it in spec under a wide range seems wise. Indeed it seems wise even if the customer is not. But only you choose your specs/price tradeoff. For rock bottom price consumer products that\'s more likely to be \'sod it, this is cheaper, to hell with the customer\' not so much for pro gear.
 
On Monday, April 24, 2023 at 5:56:16 PM UTC-4, Tabby wrote:
On Monday, 24 April 2023 at 18:51:16 UTC+1, Ricky wrote:
Typically, an AC coupling cap is driven from a low impedance source and only the load needs to be factored into the frequency equation. But when the cap is on the input, is it typical to factor in the expected source impedance, or assume a worse case of low driving impedance?

I have a design with 600 ohm differential audio inputs and I keep seeing a different response on the input and output. I finally realized this was because my input simulation used a low impedance drive, but the output included the output impedance and the load impedance. Duh!

So, do I need to beef up the input caps to handle a low impedance driver? Or, I guess I\'m asking, what is typically expected of the frequency response at the input? Is it typically for a rated driving impedance or for all source impedances?

Not much point in asking my customer. He has indicated that the various test gear this will be connected to is all over the map on this. That\'s one reason why setting a dBm level on the test gear output does not give consistent voltages measured at the interface. I don\'t expect he will know much more about the user equipment this will be connected to.

The 47 uF input caps required for worse case are a bit on the large size and the voltage rating is limited. I\'d prefer to use 33 uF caps if practical.

I guess this caught me by surprise. I thought I had completed this design, but I moved the input caps to a slightly different point in the circuit, and things changed a lot.
The design choice of whether it stays in spec for off impedances is yours alone. If the customer is using it in all sorts of situations, keeping it in spec under a wide range seems wise. Indeed it seems wise even if the customer is not. But only you choose your specs/price tradeoff. For rock bottom price consumer products that\'s more likely to be \'sod it, this is cheaper, to hell with the customer\' not so much for pro gear.
Click to expand...

With \"pro gear\", why would the source impedance not match the load? This is one of the issues the original design struggled with. There\'s not enough head room in the power supply voltage for an op amp to drive both an output impedance and the input impedance at the level desired. I came up with a synthetic output impedance circuit, which used a 12.1 ohm resistor to look like 50 ohms. This provided enough margin to get 7.5V output from a 12V supply (I was lucky to find a very good op amp for this circuit too). Rev 3 of this board supports multiple voltage levels and in/output impedances, including no termination on the input. So I trimed out some of the \"fat\" in the output stage and no more synthetic impedance. That\'s ok, because they backed off on the output voltage drive. It\'s looking pretty good if I can fit it all on the board. The impedance selections require several new analog switch chips.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209
 
Ricky wrote:
===========
With \"pro gear\", why would the source impedance not match the load?
Click to expand...

** The two almost never match - ie have the same value.
The aim is always to transfer signals from the source into the load with as little loss of voltage as possible.
Equal value matching would degrade the s/n ratio or cause active sources to distort their output signals trying to drive too low impedance.
A ratio of 1:10 or more is acceptable in most coupling situations, while making accurate level measurements may need higher ratios.
So input coupling caps need to be sized to cater for a near zero source impedance.

FYI, microphones used in pro audio may have rated output impedances from a few ohms to 600 ohms and can be active - the actual signal may come direct from a voice coil or via a small transformer or an active circuit built inside the mic.


..... Phil
 
On Tuesday, 25 April 2023 at 03:17:48 UTC+1, Ricky wrote:
On Monday, April 24, 2023 at 5:56:16 PM UTC-4, Tabby wrote:
On Monday, 24 April 2023 at 18:51:16 UTC+1, Ricky wrote:
Typically, an AC coupling cap is driven from a low impedance source and only the load needs to be factored into the frequency equation. But when the cap is on the input, is it typical to factor in the expected source impedance, or assume a worse case of low driving impedance?

I have a design with 600 ohm differential audio inputs and I keep seeing a different response on the input and output. I finally realized this was because my input simulation used a low impedance drive, but the output included the output impedance and the load impedance. Duh!

So, do I need to beef up the input caps to handle a low impedance driver? Or, I guess I\'m asking, what is typically expected of the frequency response at the input? Is it typically for a rated driving impedance or for all source impedances?

Not much point in asking my customer. He has indicated that the various test gear this will be connected to is all over the map on this. That\'s one reason why setting a dBm level on the test gear output does not give consistent voltages measured at the interface. I don\'t expect he will know much more about the user equipment this will be connected to.

The 47 uF input caps required for worse case are a bit on the large size and the voltage rating is limited. I\'d prefer to use 33 uF caps if practical.

I guess this caught me by surprise. I thought I had completed this design, but I moved the input caps to a slightly different point in the circuit, and things changed a lot.
The design choice of whether it stays in spec for off impedances is yours alone. If the customer is using it in all sorts of situations, keeping it in spec under a wide range seems wise. Indeed it seems wise even if the customer is not. But only you choose your specs/price tradeoff. For rock bottom price consumer products that\'s more likely to be \'sod it, this is cheaper, to hell with the customer\' not so much for pro gear.
With \"pro gear\", why would the source impedance not match the load?
Click to expand...

IME it mostly doesn\'t. Why would it really?
It\'s app dependant of course.
 
On Wednesday, April 26, 2023 at 6:23:13 PM UTC-4, Tabby wrote:
On Tuesday, 25 April 2023 at 03:17:48 UTC+1, Ricky wrote:
On Monday, April 24, 2023 at 5:56:16 PM UTC-4, Tabby wrote:
On Monday, 24 April 2023 at 18:51:16 UTC+1, Ricky wrote:
Typically, an AC coupling cap is driven from a low impedance source and only the load needs to be factored into the frequency equation. But when the cap is on the input, is it typical to factor in the expected source impedance, or assume a worse case of low driving impedance?

I have a design with 600 ohm differential audio inputs and I keep seeing a different response on the input and output. I finally realized this was because my input simulation used a low impedance drive, but the output included the output impedance and the load impedance. Duh!

So, do I need to beef up the input caps to handle a low impedance driver? Or, I guess I\'m asking, what is typically expected of the frequency response at the input? Is it typically for a rated driving impedance or for all source impedances?

Not much point in asking my customer. He has indicated that the various test gear this will be connected to is all over the map on this. That\'s one reason why setting a dBm level on the test gear output does not give consistent voltages measured at the interface. I don\'t expect he will know much more about the user equipment this will be connected to.

The 47 uF input caps required for worse case are a bit on the large size and the voltage rating is limited. I\'d prefer to use 33 uF caps if practical.

I guess this caught me by surprise. I thought I had completed this design, but I moved the input caps to a slightly different point in the circuit, and things changed a lot.
The design choice of whether it stays in spec for off impedances is yours alone. If the customer is using it in all sorts of situations, keeping it in spec under a wide range seems wise. Indeed it seems wise even if the customer is not. But only you choose your specs/price tradeoff. For rock bottom price consumer products that\'s more likely to be \'sod it, this is cheaper, to hell with the customer\' not so much for pro gear.
With \"pro gear\", why would the source impedance not match the load?
IME it mostly doesn\'t. Why would it really?
It\'s app dependant of course.
Click to expand...

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209
 
On Wednesday, April 26, 2023 at 5:23:30 PM UTC-7, Ricky wrote:
On Wednesday, April 26, 2023 at 6:23:13 PM UTC-4, Tabby wrote:
On Tuesday, 25 April 2023 at 03:17:48 UTC+1, Ricky wrote:

With \"pro gear\", why would the source impedance not match the load?

IME it mostly doesn\'t. Why would it really?
It\'s app dependant of course.

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.
Click to expand...

In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency.
Matched, the response is flat.

Microphone cords are the only really long audio wires where it matters, in most
cases.
 
On Thursday, April 27, 2023 at 3:49:13 AM UTC-4, whit3rd wrote:
On Wednesday, April 26, 2023 at 5:23:30 PM UTC-7, Ricky wrote:
On Wednesday, April 26, 2023 at 6:23:13 PM UTC-4, Tabby wrote:
On Tuesday, 25 April 2023 at 03:17:48 UTC+1, Ricky wrote:

With \"pro gear\", why would the source impedance not match the load?

IME it mostly doesn\'t. Why would it really?
It\'s app dependant of course.

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.
In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency.
Matched, the response is flat.

Microphone cords are the only really long audio wires where it matters, in most
cases.
Click to expand...

C+ You need to show your work. ;)

Why does this only matter for mic cords? According to what you\'ve posted, it simply has to do with wire length. Signals are distributed over cables other than from mics and to speakers. In particular, in telephony work, very long wires are used, driven from active sources driving electronic loads, so all impedances are added intentionally.

In this particular case, the signal comes from somewhere in a building, routed digitally over a network to another building, then routed as analog again to somewhere in that building. Lots of long, analog wires.

I was going to say I\'ve only been asked to handle two input impedances, but there\'s also \"high\" impedance mode. However, in that case, the low frequency response is much better, far below 20 Hz, because the caps are feeding into 36k impedance, rather than 300 or 50 ohms.

The only reason to bump the input cap values is to handle the case of low driving impedance. Not a big deal. I can get caps to fit the same footprint in either case. I\'ll get with the customer to find out exactly what is needed. In some ways, I try to be an overachiever with this sort of stuff. I still need to find room for all these components.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209
 
torsdag den 27. april 2023 kl. 17.25.19 UTC+2 skrev Ricky:
On Thursday, April 27, 2023 at 3:49:13 AM UTC-4, whit3rd wrote:
On Wednesday, April 26, 2023 at 5:23:30 PM UTC-7, Ricky wrote:
On Wednesday, April 26, 2023 at 6:23:13 PM UTC-4, Tabby wrote:
On Tuesday, 25 April 2023 at 03:17:48 UTC+1, Ricky wrote:

With \"pro gear\", why would the source impedance not match the load?

IME it mostly doesn\'t. Why would it really?
It\'s app dependant of course.

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.
In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency.
Matched, the response is flat.

Microphone cords are the only really long audio wires where it matters, in most
cases.
C+ You need to show your work. ;)

Why does this only matter for mic cords? According to what you\'ve posted, it simply has to do with wire length. Signals are distributed over cables other than from mics and to speakers. In particular, in telephony work, very long wires are used, driven from active sources driving electronic loads, so all impedances are added intentionally.

In this particular case, the signal comes from somewhere in a building, routed digitally over a network to another building, then routed as analog again to somewhere in that building. Lots of long, analog wires.

I was going to say I\'ve only been asked to handle two input impedances, but there\'s also \"high\" impedance mode. However, in that case, the low frequency response is much better, far below 20 Hz, because the caps are feeding into 36k impedance, rather than 300 or 50 ohms.
Click to expand...

can\'t you put the caps after the shunt resistance?
 
On Thursday, April 27, 2023 at 12:29:25 PM UTC-4, Lasse Langwadt Christensen wrote:
torsdag den 27. april 2023 kl. 17.25.19 UTC+2 skrev Ricky:
On Thursday, April 27, 2023 at 3:49:13 AM UTC-4, whit3rd wrote:
On Wednesday, April 26, 2023 at 5:23:30 PM UTC-7, Ricky wrote:
On Wednesday, April 26, 2023 at 6:23:13 PM UTC-4, Tabby wrote:
On Tuesday, 25 April 2023 at 03:17:48 UTC+1, Ricky wrote:

With \"pro gear\", why would the source impedance not match the load?

IME it mostly doesn\'t. Why would it really?
It\'s app dependant of course.

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.
In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency..
Matched, the response is flat.

Microphone cords are the only really long audio wires where it matters, in most
cases.
C+ You need to show your work. ;)

Why does this only matter for mic cords? According to what you\'ve posted, it simply has to do with wire length. Signals are distributed over cables other than from mics and to speakers. In particular, in telephony work, very long wires are used, driven from active sources driving electronic loads, so all impedances are added intentionally.

In this particular case, the signal comes from somewhere in a building, routed digitally over a network to another building, then routed as analog again to somewhere in that building. Lots of long, analog wires.

I was going to say I\'ve only been asked to handle two input impedances, but there\'s also \"high\" impedance mode. However, in that case, the low frequency response is much better, far below 20 Hz, because the caps are feeding into 36k impedance, rather than 300 or 50 ohms.

can\'t you put the caps after the shunt resistance?
Click to expand...

Yes, that\'s where they had been. In fact, they had been much smaller, because of the higher impedance of the amp circuit. But there\'s a 50 ohm termination and I was uncomfortable with the idea that it only takes maybe 4VDC to drive it past its rating. I thought adding the cap would prevent that. It started in the leg with the 50 ohm resistor, but that does things with the low end frequency response, because of the rising termination resistance. It was moved in line with the input. The 50 ohm mode is single ended, so now the circuit is a bit asymmetrical. I added the same cap to the other leg and it is now outside of both the 50 ohm termination and the 600 ohm termination. It is the 600 ohm mode where the low end frequency response is important.

Maybe I\'m over thinking this, or made a mistake previously in the power calculations. Running a half watt into a 600 ohm resistor takes 17VDC. That\'s not remotely likely. So if I make myself not worry about the apparent deformity in the low frequency input impedance in the 50 ohm mode, I can put one cap in line with the 50 ohm resistance to protect it from a 5VDC input, which is possible, even if unlikely. It\'s also only one part, instead of two, and because the low end response in this mode is not so important, can be a smaller value if needed.

Thanks for asking me about this. I must have munged the power calculation at some point, and thought the 600 ohm circuit needed protection too.

I have other things to do right now. I\'ll come back to this later.

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209
 
torsdag den 27. april 2023 kl. 19.44.11 UTC+2 skrev Ricky:
On Thursday, April 27, 2023 at 12:29:25 PM UTC-4, Lasse Langwadt Christensen wrote:
torsdag den 27. april 2023 kl. 17.25.19 UTC+2 skrev Ricky:
On Thursday, April 27, 2023 at 3:49:13 AM UTC-4, whit3rd wrote:
On Wednesday, April 26, 2023 at 5:23:30 PM UTC-7, Ricky wrote:
On Wednesday, April 26, 2023 at 6:23:13 PM UTC-4, Tabby wrote:
On Tuesday, 25 April 2023 at 03:17:48 UTC+1, Ricky wrote:

With \"pro gear\", why would the source impedance not match the load?

IME it mostly doesn\'t. Why would it really?
It\'s app dependant of course.

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.
In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency.
Matched, the response is flat.

Microphone cords are the only really long audio wires where it matters, in most
cases.
C+ You need to show your work. ;)

Why does this only matter for mic cords? According to what you\'ve posted, it simply has to do with wire length. Signals are distributed over cables other than from mics and to speakers. In particular, in telephony work, very long wires are used, driven from active sources driving electronic loads, so all impedances are added intentionally.

In this particular case, the signal comes from somewhere in a building, routed digitally over a network to another building, then routed as analog again to somewhere in that building. Lots of long, analog wires.

I was going to say I\'ve only been asked to handle two input impedances, but there\'s also \"high\" impedance mode. However, in that case, the low frequency response is much better, far below 20 Hz, because the caps are feeding into 36k impedance, rather than 300 or 50 ohms.

can\'t you put the caps after the shunt resistance?
Yes, that\'s where they had been. In fact, they had been much smaller, because of the higher impedance of the amp circuit. But there\'s a 50 ohm termination and I was uncomfortable with the idea that it only takes maybe 4VDC to drive it past its rating. I thought adding the cap would prevent that. It started in the leg with the 50 ohm resistor, but that does things with the low end frequency response, because of the rising termination resistance. It was moved in line with the input. The 50 ohm mode is single ended, so now the circuit is a bit asymmetrical. I added the same cap to the other leg and it is now outside of both the 50 ohm termination and the 600 ohm termination. It is the 600 ohm mode where the low end frequency response is important.

Maybe I\'m over thinking this, or made a mistake previously in the power calculations. Running a half watt into a 600 ohm resistor takes 17VDC. That\'s not remotely likely. So if I make myself not worry about the apparent deformity in the low frequency input impedance in the 50 ohm mode, I can put one cap in line with the 50 ohm resistance to protect it from a 5VDC input, which is possible, even if unlikely. It\'s also only one part, instead of two, and because the low end response in this mode is not so important, can be a smaller value if needed.

Thanks for asking me about this. I must have munged the power calculation at some point, and thought the 600 ohm circuit needed protection too.

I have other things to do right now. I\'ll come back to this later.
Click to expand...

if they mode is switchable, can you detect DC and switch 600 Ohm mode if it exceeds the 50 Ohm rating?
 
On Thursday, April 27, 2023 at 2:49:17 PM UTC-4, Lasse Langwadt Christensen wrote:
torsdag den 27. april 2023 kl. 19.44.11 UTC+2 skrev Ricky:
On Thursday, April 27, 2023 at 12:29:25 PM UTC-4, Lasse Langwadt Christensen wrote:
torsdag den 27. april 2023 kl. 17.25.19 UTC+2 skrev Ricky:
On Thursday, April 27, 2023 at 3:49:13 AM UTC-4, whit3rd wrote:
On Wednesday, April 26, 2023 at 5:23:30 PM UTC-7, Ricky wrote:
On Wednesday, April 26, 2023 at 6:23:13 PM UTC-4, Tabby wrote:
On Tuesday, 25 April 2023 at 03:17:48 UTC+1, Ricky wrote:

With \"pro gear\", why would the source impedance not match the load?

IME it mostly doesn\'t. Why would it really?
It\'s app dependant of course.

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.
In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency.
Matched, the response is flat.

Microphone cords are the only really long audio wires where it matters, in most
cases.
C+ You need to show your work. ;)

Why does this only matter for mic cords? According to what you\'ve posted, it simply has to do with wire length. Signals are distributed over cables other than from mics and to speakers. In particular, in telephony work, very long wires are used, driven from active sources driving electronic loads, so all impedances are added intentionally.

In this particular case, the signal comes from somewhere in a building, routed digitally over a network to another building, then routed as analog again to somewhere in that building. Lots of long, analog wires.

I was going to say I\'ve only been asked to handle two input impedances, but there\'s also \"high\" impedance mode. However, in that case, the low frequency response is much better, far below 20 Hz, because the caps are feeding into 36k impedance, rather than 300 or 50 ohms.

can\'t you put the caps after the shunt resistance?
Yes, that\'s where they had been. In fact, they had been much smaller, because of the higher impedance of the amp circuit. But there\'s a 50 ohm termination and I was uncomfortable with the idea that it only takes maybe 4VDC to drive it past its rating. I thought adding the cap would prevent that. It started in the leg with the 50 ohm resistor, but that does things with the low end frequency response, because of the rising termination resistance. It was moved in line with the input. The 50 ohm mode is single ended, so now the circuit is a bit asymmetrical. I added the same cap to the other leg and it is now outside of both the 50 ohm termination and the 600 ohm termination. It is the 600 ohm mode where the low end frequency response is important.

Maybe I\'m over thinking this, or made a mistake previously in the power calculations. Running a half watt into a 600 ohm resistor takes 17VDC. That\'s not remotely likely. So if I make myself not worry about the apparent deformity in the low frequency input impedance in the 50 ohm mode, I can put one cap in line with the 50 ohm resistance to protect it from a 5VDC input, which is possible, even if unlikely. It\'s also only one part, instead of two, and because the low end response in this mode is not so important, can be a smaller value if needed.

Thanks for asking me about this. I must have munged the power calculation at some point, and thought the 600 ohm circuit needed protection too.

I have other things to do right now. I\'ll come back to this later.
if they mode is switchable, can you detect DC and switch 600 Ohm mode if it exceeds the 50 Ohm rating?
Click to expand...

Seems like an unnecessary circuit when a simple cap takes care of it. That circuit will have a cap too, right?

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209
 
On Thursday, 27 April 2023 at 08:49:13 UTC+1, whit3rd wrote:
On Wednesday, April 26, 2023 at 5:23:30 PM UTC-7, Ricky wrote:
On Wednesday, April 26, 2023 at 6:23:13 PM UTC-4, Tabby wrote:
On Tuesday, 25 April 2023 at 03:17:48 UTC+1, Ricky wrote:

With \"pro gear\", why would the source impedance not match the load?

IME it mostly doesn\'t. Why would it really?
It\'s app dependant of course.

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.

In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency.
Matched, the response is flat.
Click to expand...

in some cases. In many there is no real world problem. It\'s app dependant.

Microphone cords are the only really long audio wires where it matters, in most
cases.
Click to expand...
 
whit3rd wrote:
---------------------
My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.

In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency.
Click to expand...

** You never lose low frequencies, only highs in both cases.
At frequencies much shorter than a wavelength, unloaded cables placel C across the source while ones shorted at the receiving end place L in series. At 20kHz, the wave is circa 15kms.

Microphone cords are the only really long audio wires where it matters, in most
cases.
Click to expand...

** Line level cables can be long too and long speaker cables are common outdoors for public events - normally run at low current at 70 or 100V rms max to keep copper losses low. Transformers are involved.


...... Phil
 
On Thu, 27 Apr 2023 15:21:33 -0700 (PDT), Tabby <tabbypurr@gmail.com>
wrote:

On Thursday, 27 April 2023 at 08:49:13 UTC+1, whit3rd wrote:
On Wednesday, April 26, 2023 at 5:23:30?PM UTC-7, Ricky wrote:
On Wednesday, April 26, 2023 at 6:23:13?PM UTC-4, Tabby wrote:
On Tuesday, 25 April 2023 at 03:17:48 UTC+1, Ricky wrote:

With \"pro gear\", why would the source impedance not match the load?

IME it mostly doesn\'t. Why would it really?
It\'s app dependant of course.

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.

In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency.
Matched, the response is flat.

in some cases. In many there is no real world problem. It\'s app dependant.

Microphone cords are the only really long audio wires where it matters, in most
cases.
Click to expand...

The differential impedance of a typical shielded twisted pair is
around 100 ohms... nothing like 600, much less 1200. Audio systems
are, usually, wildly mismatched.
 
John Larkin wrote:
-----------------------------

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.

In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency.
Matched, the response is flat.

in some cases. In many there is no real world problem. It\'s app dependant.

Microphone cords are the only really long audio wires where it matters, in most
cases.

The differential impedance of a typical shielded twisted pair is
around 100 ohms... nothing like 600, much less 1200.
Click to expand...

** No consequence in the audio band with the usual short (< 50m) runs involved.
Cable C is only 100 to 250 pF per meter.

FYI by far the most common mic impedance is 200ohms - not 600.

> Audio systems are, usually, wildly mismatched.

** Not when you know all the facts involved.



...... Phil
 
On Friday, 28 April 2023 at 04:14:05 UTC+1, Phil Allison wrote:
John Larkin wrote:
-----------------------------

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.

In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency.
Matched, the response is flat.

in some cases. In many there is no real world problem. It\'s app dependant.

Microphone cords are the only really long audio wires where it matters, in most
cases.

The differential impedance of a typical shielded twisted pair is
around 100 ohms... nothing like 600, much less 1200.
** No consequence in the audio band with the usual short (< 50m) runs involved.
Cable C is only 100 to 250 pF per meter.

FYI by far the most common mic impedance is 200ohms - not 600.
Audio systems are, usually, wildly mismatched.
** Not when you know all the facts involved.
Click to expand...

Wild mismatch is routine with audio. Knowing all the facts involved doesn\'t change that. Such mismatch is mostly not a problem.
 
On Friday, April 28, 2023 at 1:26:35 PM UTC-4, Tabby wrote:
On Friday, 28 April 2023 at 04:14:05 UTC+1, Phil Allison wrote:
John Larkin wrote:
-----------------------------

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.

In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency.
Matched, the response is flat.

in some cases. In many there is no real world problem. It\'s app dependant.

Microphone cords are the only really long audio wires where it matters, in most
cases.

The differential impedance of a typical shielded twisted pair is
around 100 ohms... nothing like 600, much less 1200.
** No consequence in the audio band with the usual short (< 50m) runs involved.
Cable C is only 100 to 250 pF per meter.

FYI by far the most common mic impedance is 200ohms - not 600.
Audio systems are, usually, wildly mismatched.
** Not when you know all the facts involved.
Wild mismatch is routine with audio. Knowing all the facts involved doesn\'t change that. Such mismatch is mostly not a problem.
Click to expand...

Except that it does impact the low end frequency response. That is the filter that, in general, uses a larger and a bit more expensive capacitor, so this would want to be minimized in consumer electronics. If the output impedance of the signal source would impact this response, they would need to make a decision as to how much they want to spend to accommodate the various signal sources. It\'s only pennies, but they count pennies in commercial gear.

--

Rick C.

--- Get 1,000 miles of free Supercharging
--- Tesla referral code - https://ts.la/richard11209
 
On Friday, 28 April 2023 at 22:24:52 UTC+1, Ricky wrote:
On Friday, April 28, 2023 at 1:26:35 PM UTC-4, Tabby wrote:
On Friday, 28 April 2023 at 04:14:05 UTC+1, Phil Allison wrote:
John Larkin wrote:
-----------------------------

My understanding is that impedance mismatch can cause issues of frequency response, such as the one I\'m seeing.

In a distribution system, with long wires, you match the source and/or the load with
the characteristic line impedance, because too LOW resistance makes the
wire an inductor, and too HIGH resistance makes the wire a capacitor.
High-Z you lose high frequency response, low-Z you lose low frequency.
Matched, the response is flat.

in some cases. In many there is no real world problem. It\'s app dependant.

Microphone cords are the only really long audio wires where it matters, in most
cases.

The differential impedance of a typical shielded twisted pair is
around 100 ohms... nothing like 600, much less 1200.
** No consequence in the audio band with the usual short (< 50m) runs involved.
Cable C is only 100 to 250 pF per meter.

FYI by far the most common mic impedance is 200ohms - not 600.
Audio systems are, usually, wildly mismatched.
** Not when you know all the facts involved.
Wild mismatch is routine with audio. Knowing all the facts involved doesn\'t change that. Such mismatch is mostly not a problem.
Except that it does impact the low end frequency response. That is the filter that, in general, uses a larger and a bit more expensive capacitor, so this would want to be minimized in consumer electronics. If the output impedance of the signal source would impact this response, they would need to make a decision as to how much they want to spend to accommodate the various signal sources. It\'s only pennies, but they count pennies in commercial gear.
Click to expand...

Ie it\'s a design decision that\'s trivial to make a nonproblem.
Or you can use it as a plus, trimming down on frequencies a nonideal speaker can do without.
 
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