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How Do I Determine A Power-Amp's Input Impedance?
I have a Perreaux 3400B power amp (the 'B' stands for Balanced).
It's a modified version of the 3400 (http://www.perreaux.com/files/080-3400.pdf), which was specially configured with XLR inputs, so it could be used in a recording studio environment. (I was told this sub-line was specifically made for Hit Factory) - It has both XLR and RCA inputs on the back and you must chose with a little toggle-switch. Problem is, the amp has been out of production since 1995, there was no manual published for it and the Perreaux engineers I contacted simply don't remember what the input impedance was. I am not an electrical engineer, but I do have a digital multimeter at my disposal and I'm pretty good with a soldering iron. Q1: Is it possible to take a measurement with the tools I have, that will answer my question? If so, please give as detailed instructions as you can. Q2: Since the 3400 is rated at 47kO, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Help much appreciated, Clytemnestra rec.audio.pro rec.audio.tech |
#2
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How Do I Determine A Power-Amp's Input Impedance?
Probably the same. You could put a resistor (ex. 47k) in series with the
input, and apply a sine-wave input. Measure voltage across the resistor, and across the amp input. The ratio of the two (AC) voltages will tell you the impedance relative to your resistor. Could vary at different frequencies, though. I'm not sure how you'd measure input impedance for the balanced input. Maybe one of the engineer types around here could help......and, I suppose, correct me if my little measurement scenario has holes in it. :-) I suspect it would be a multiple, like 1/2 or twice the value, etc. Mark Z. (repair tech, not engineer) -- Please reply only to Group. I regret this is necessary. Viruses and spam have rendered my regular e-mail address useless. "Clytemnestra" wrote in message ... I have a Perreaux 3400B power amp (the 'B' stands for Balanced). It's a modified version of the 3400 (http://www.perreaux.com/files/080-3400.pdf), which was specially configured with XLR inputs, so it could be used in a recording studio environment. (I was told this sub-line was specifically made for Hit Factory) - It has both XLR and RCA inputs on the back and you must chose with a little toggle-switch. Problem is, the amp has been out of production since 1995, there was no manual published for it and the Perreaux engineers I contacted simply don't remember what the input impedance was. I am not an electrical engineer, but I do have a digital multimeter at my disposal and I'm pretty good with a soldering iron. Q1: Is it possible to take a measurement with the tools I have, that will answer my question? If so, please give as detailed instructions as you can. Q2: Since the 3400 is rated at 47kO, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Help much appreciated, Clytemnestra rec.audio.pro rec.audio.tech |
#3
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How Do I Determine A Power-Amp's Input Impedance?
Probably the same. You could put a resistor (ex. 47k) in series with the
input, and apply a sine-wave input. Measure voltage across the resistor, and across the amp input. The ratio of the two (AC) voltages will tell you the impedance relative to your resistor. Could vary at different frequencies, though. I'm not sure how you'd measure input impedance for the balanced input. Maybe one of the engineer types around here could help......and, I suppose, correct me if my little measurement scenario has holes in it. :-) I suspect it would be a multiple, like 1/2 or twice the value, etc. Mark Z. (repair tech, not engineer) -- Please reply only to Group. I regret this is necessary. Viruses and spam have rendered my regular e-mail address useless. "Clytemnestra" wrote in message ... I have a Perreaux 3400B power amp (the 'B' stands for Balanced). It's a modified version of the 3400 (http://www.perreaux.com/files/080-3400.pdf), which was specially configured with XLR inputs, so it could be used in a recording studio environment. (I was told this sub-line was specifically made for Hit Factory) - It has both XLR and RCA inputs on the back and you must chose with a little toggle-switch. Problem is, the amp has been out of production since 1995, there was no manual published for it and the Perreaux engineers I contacted simply don't remember what the input impedance was. I am not an electrical engineer, but I do have a digital multimeter at my disposal and I'm pretty good with a soldering iron. Q1: Is it possible to take a measurement with the tools I have, that will answer my question? If so, please give as detailed instructions as you can. Q2: Since the 3400 is rated at 47kO, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Help much appreciated, Clytemnestra rec.audio.pro rec.audio.tech |
#4
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How Do I Determine A Power-Amp's Input Impedance?
Probably the same. You could put a resistor (ex. 47k) in series with the
input, and apply a sine-wave input. Measure voltage across the resistor, and across the amp input. The ratio of the two (AC) voltages will tell you the impedance relative to your resistor. Could vary at different frequencies, though. I'm not sure how you'd measure input impedance for the balanced input. Maybe one of the engineer types around here could help......and, I suppose, correct me if my little measurement scenario has holes in it. :-) I suspect it would be a multiple, like 1/2 or twice the value, etc. Mark Z. (repair tech, not engineer) -- Please reply only to Group. I regret this is necessary. Viruses and spam have rendered my regular e-mail address useless. "Clytemnestra" wrote in message ... I have a Perreaux 3400B power amp (the 'B' stands for Balanced). It's a modified version of the 3400 (http://www.perreaux.com/files/080-3400.pdf), which was specially configured with XLR inputs, so it could be used in a recording studio environment. (I was told this sub-line was specifically made for Hit Factory) - It has both XLR and RCA inputs on the back and you must chose with a little toggle-switch. Problem is, the amp has been out of production since 1995, there was no manual published for it and the Perreaux engineers I contacted simply don't remember what the input impedance was. I am not an electrical engineer, but I do have a digital multimeter at my disposal and I'm pretty good with a soldering iron. Q1: Is it possible to take a measurement with the tools I have, that will answer my question? If so, please give as detailed instructions as you can. Q2: Since the 3400 is rated at 47kO, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Help much appreciated, Clytemnestra rec.audio.pro rec.audio.tech |
#5
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How Do I Determine A Power-Amp's Input Impedance?
Probably the same. You could put a resistor (ex. 47k) in series with the
input, and apply a sine-wave input. Measure voltage across the resistor, and across the amp input. The ratio of the two (AC) voltages will tell you the impedance relative to your resistor. Could vary at different frequencies, though. I'm not sure how you'd measure input impedance for the balanced input. Maybe one of the engineer types around here could help......and, I suppose, correct me if my little measurement scenario has holes in it. :-) I suspect it would be a multiple, like 1/2 or twice the value, etc. Mark Z. (repair tech, not engineer) -- Please reply only to Group. I regret this is necessary. Viruses and spam have rendered my regular e-mail address useless. "Clytemnestra" wrote in message ... I have a Perreaux 3400B power amp (the 'B' stands for Balanced). It's a modified version of the 3400 (http://www.perreaux.com/files/080-3400.pdf), which was specially configured with XLR inputs, so it could be used in a recording studio environment. (I was told this sub-line was specifically made for Hit Factory) - It has both XLR and RCA inputs on the back and you must chose with a little toggle-switch. Problem is, the amp has been out of production since 1995, there was no manual published for it and the Perreaux engineers I contacted simply don't remember what the input impedance was. I am not an electrical engineer, but I do have a digital multimeter at my disposal and I'm pretty good with a soldering iron. Q1: Is it possible to take a measurement with the tools I have, that will answer my question? If so, please give as detailed instructions as you can. Q2: Since the 3400 is rated at 47kO, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Help much appreciated, Clytemnestra rec.audio.pro rec.audio.tech |
#6
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How Do I Determine A Power-Amp's Input Impedance?
Clytemnestra wrote:
It's a modified version of the 3400 (http://www.perreaux.com/files/080-3400.pdf), which was specially configured with XLR inputs, so it could be used in a recording studio environment. (I was told this sub-line was specifically made for Hit Factory) - It has both XLR and RCA inputs on the back and you must chose with a little toggle-switch. Problem is, the amp has been out of production since 1995, there was no manual published for it and the Perreaux engineers I contacted simply don't remember what the input impedance was. Do you have a schematic for it? The dominant issue is probably the input shunt resistor. It's probably reasonably high. Q1: Is it possible to take a measurement with the tools I have, that will answer my question? If so, please give as detailed instructions as you can. No, it's probably easier to work it out from the circuit. You can find the input resistance with the tools you have, but that may or may not be useful depending on the way the input is designed. Q2: Since the 3400 is rated at 47kO, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Probably not. Why do you care anyway? This isn't 1950 any longer, when everyone was doing constant-impedance lines for maximum power transfer. Today as long as the output Z is lower than the input Z, everything is fine. Unless you're mating to something with a transformer coupled output, of course. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#7
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How Do I Determine A Power-Amp's Input Impedance?
Clytemnestra wrote:
It's a modified version of the 3400 (http://www.perreaux.com/files/080-3400.pdf), which was specially configured with XLR inputs, so it could be used in a recording studio environment. (I was told this sub-line was specifically made for Hit Factory) - It has both XLR and RCA inputs on the back and you must chose with a little toggle-switch. Problem is, the amp has been out of production since 1995, there was no manual published for it and the Perreaux engineers I contacted simply don't remember what the input impedance was. Do you have a schematic for it? The dominant issue is probably the input shunt resistor. It's probably reasonably high. Q1: Is it possible to take a measurement with the tools I have, that will answer my question? If so, please give as detailed instructions as you can. No, it's probably easier to work it out from the circuit. You can find the input resistance with the tools you have, but that may or may not be useful depending on the way the input is designed. Q2: Since the 3400 is rated at 47kO, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Probably not. Why do you care anyway? This isn't 1950 any longer, when everyone was doing constant-impedance lines for maximum power transfer. Today as long as the output Z is lower than the input Z, everything is fine. Unless you're mating to something with a transformer coupled output, of course. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#8
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How Do I Determine A Power-Amp's Input Impedance?
Clytemnestra wrote:
It's a modified version of the 3400 (http://www.perreaux.com/files/080-3400.pdf), which was specially configured with XLR inputs, so it could be used in a recording studio environment. (I was told this sub-line was specifically made for Hit Factory) - It has both XLR and RCA inputs on the back and you must chose with a little toggle-switch. Problem is, the amp has been out of production since 1995, there was no manual published for it and the Perreaux engineers I contacted simply don't remember what the input impedance was. Do you have a schematic for it? The dominant issue is probably the input shunt resistor. It's probably reasonably high. Q1: Is it possible to take a measurement with the tools I have, that will answer my question? If so, please give as detailed instructions as you can. No, it's probably easier to work it out from the circuit. You can find the input resistance with the tools you have, but that may or may not be useful depending on the way the input is designed. Q2: Since the 3400 is rated at 47kO, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Probably not. Why do you care anyway? This isn't 1950 any longer, when everyone was doing constant-impedance lines for maximum power transfer. Today as long as the output Z is lower than the input Z, everything is fine. Unless you're mating to something with a transformer coupled output, of course. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#9
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How Do I Determine A Power-Amp's Input Impedance?
Clytemnestra wrote:
It's a modified version of the 3400 (http://www.perreaux.com/files/080-3400.pdf), which was specially configured with XLR inputs, so it could be used in a recording studio environment. (I was told this sub-line was specifically made for Hit Factory) - It has both XLR and RCA inputs on the back and you must chose with a little toggle-switch. Problem is, the amp has been out of production since 1995, there was no manual published for it and the Perreaux engineers I contacted simply don't remember what the input impedance was. Do you have a schematic for it? The dominant issue is probably the input shunt resistor. It's probably reasonably high. Q1: Is it possible to take a measurement with the tools I have, that will answer my question? If so, please give as detailed instructions as you can. No, it's probably easier to work it out from the circuit. You can find the input resistance with the tools you have, but that may or may not be useful depending on the way the input is designed. Q2: Since the 3400 is rated at 47kO, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Probably not. Why do you care anyway? This isn't 1950 any longer, when everyone was doing constant-impedance lines for maximum power transfer. Today as long as the output Z is lower than the input Z, everything is fine. Unless you're mating to something with a transformer coupled output, of course. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#10
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How Do I Determine A Power-Amp's Input Impedance?
Clyt,
My first question is why you even want to know the input impedance. It's surely high enough to not be an issue when driving it from any resonable preamp. That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. Even easier is to use a potentiometer instead of a fixed resistor. I'd start with a 100K variable resistor and adjust the sine wave oscillator to put out one volt. Then move the voltmeter to the amp's side of the resistor and adjust the resistor until you read 0.5 volts. The amp's input impedance is whatever the resistor's value is set to. If you can't get it down to 0.5 volts try a 500K variable resistor instead, then repeat. --Ethan |
#11
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How Do I Determine A Power-Amp's Input Impedance?
Clyt,
My first question is why you even want to know the input impedance. It's surely high enough to not be an issue when driving it from any resonable preamp. That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. Even easier is to use a potentiometer instead of a fixed resistor. I'd start with a 100K variable resistor and adjust the sine wave oscillator to put out one volt. Then move the voltmeter to the amp's side of the resistor and adjust the resistor until you read 0.5 volts. The amp's input impedance is whatever the resistor's value is set to. If you can't get it down to 0.5 volts try a 500K variable resistor instead, then repeat. --Ethan |
#12
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How Do I Determine A Power-Amp's Input Impedance?
Clyt,
My first question is why you even want to know the input impedance. It's surely high enough to not be an issue when driving it from any resonable preamp. That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. Even easier is to use a potentiometer instead of a fixed resistor. I'd start with a 100K variable resistor and adjust the sine wave oscillator to put out one volt. Then move the voltmeter to the amp's side of the resistor and adjust the resistor until you read 0.5 volts. The amp's input impedance is whatever the resistor's value is set to. If you can't get it down to 0.5 volts try a 500K variable resistor instead, then repeat. --Ethan |
#13
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How Do I Determine A Power-Amp's Input Impedance?
Clyt,
My first question is why you even want to know the input impedance. It's surely high enough to not be an issue when driving it from any resonable preamp. That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. Even easier is to use a potentiometer instead of a fixed resistor. I'd start with a 100K variable resistor and adjust the sine wave oscillator to put out one volt. Then move the voltmeter to the amp's side of the resistor and adjust the resistor until you read 0.5 volts. The amp's input impedance is whatever the resistor's value is set to. If you can't get it down to 0.5 volts try a 500K variable resistor instead, then repeat. --Ethan |
#14
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 09:16:15 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: My first question is why you even want to know the input impedance. It's necessary to know in order to correctly adjust some dip switches on the crossover control unit for an Infinity Modulus sub/sat system. Here is the relevant passage from the owners manual: http://home.nyc.rr.com/acidrock212/infinity-ecu.jpg That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? Clytemnestra |
#15
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 09:16:15 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: My first question is why you even want to know the input impedance. It's necessary to know in order to correctly adjust some dip switches on the crossover control unit for an Infinity Modulus sub/sat system. Here is the relevant passage from the owners manual: http://home.nyc.rr.com/acidrock212/infinity-ecu.jpg That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? Clytemnestra |
#16
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 09:16:15 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: My first question is why you even want to know the input impedance. It's necessary to know in order to correctly adjust some dip switches on the crossover control unit for an Infinity Modulus sub/sat system. Here is the relevant passage from the owners manual: http://home.nyc.rr.com/acidrock212/infinity-ecu.jpg That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? Clytemnestra |
#17
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 09:16:15 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote: My first question is why you even want to know the input impedance. It's necessary to know in order to correctly adjust some dip switches on the crossover control unit for an Infinity Modulus sub/sat system. Here is the relevant passage from the owners manual: http://home.nyc.rr.com/acidrock212/infinity-ecu.jpg That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? Clytemnestra |
#18
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How Do I Determine A Power-Amp's Input Impedance?
Clytemnestra wrote:
On Sun, 11 Jan 2004 09:16:15 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: My first question is why you even want to know the input impedance. It's necessary to know in order to correctly adjust some dip switches on the crossover control unit for an Infinity Modulus sub/sat system. Here is the relevant passage from the owners manual: http://home.nyc.rr.com/acidrock212/infinity-ecu.jpg Frankly, this exceprt makes the gear seem to be expensive junk. That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? You have the right idea, but it gets even worse. Many multimeters measure AC voltage accurately only at line frequencies, ie, 50 to 60 Hz. You'll probably need an oscilloscope to perform the test Ethan suggests. Clytemnestra -- ================================================== ====================== Michael Kesti | "And like, one and one don't make | two, one and one make one." | - The Who, Bargain |
#19
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How Do I Determine A Power-Amp's Input Impedance?
Clytemnestra wrote:
On Sun, 11 Jan 2004 09:16:15 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: My first question is why you even want to know the input impedance. It's necessary to know in order to correctly adjust some dip switches on the crossover control unit for an Infinity Modulus sub/sat system. Here is the relevant passage from the owners manual: http://home.nyc.rr.com/acidrock212/infinity-ecu.jpg Frankly, this exceprt makes the gear seem to be expensive junk. That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? You have the right idea, but it gets even worse. Many multimeters measure AC voltage accurately only at line frequencies, ie, 50 to 60 Hz. You'll probably need an oscilloscope to perform the test Ethan suggests. Clytemnestra -- ================================================== ====================== Michael Kesti | "And like, one and one don't make | two, one and one make one." | - The Who, Bargain |
#20
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How Do I Determine A Power-Amp's Input Impedance?
Clytemnestra wrote:
On Sun, 11 Jan 2004 09:16:15 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: My first question is why you even want to know the input impedance. It's necessary to know in order to correctly adjust some dip switches on the crossover control unit for an Infinity Modulus sub/sat system. Here is the relevant passage from the owners manual: http://home.nyc.rr.com/acidrock212/infinity-ecu.jpg Frankly, this exceprt makes the gear seem to be expensive junk. That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? You have the right idea, but it gets even worse. Many multimeters measure AC voltage accurately only at line frequencies, ie, 50 to 60 Hz. You'll probably need an oscilloscope to perform the test Ethan suggests. Clytemnestra -- ================================================== ====================== Michael Kesti | "And like, one and one don't make | two, one and one make one." | - The Who, Bargain |
#21
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How Do I Determine A Power-Amp's Input Impedance?
Clytemnestra wrote:
On Sun, 11 Jan 2004 09:16:15 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: My first question is why you even want to know the input impedance. It's necessary to know in order to correctly adjust some dip switches on the crossover control unit for an Infinity Modulus sub/sat system. Here is the relevant passage from the owners manual: http://home.nyc.rr.com/acidrock212/infinity-ecu.jpg Frankly, this exceprt makes the gear seem to be expensive junk. That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? You have the right idea, but it gets even worse. Many multimeters measure AC voltage accurately only at line frequencies, ie, 50 to 60 Hz. You'll probably need an oscilloscope to perform the test Ethan suggests. Clytemnestra -- ================================================== ====================== Michael Kesti | "And like, one and one don't make | two, one and one make one." | - The Who, Bargain |
#22
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How Do I Determine A Power-Amp's Input Impedance?
Here are three "definitive" answers...
One Since the 3400 is rated at 47k, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Yup, absolutely. The 3400B version almost certainly "piggybacks" the balanced input on top of the 3400's design. It's highly unlikely they would have changed the unbalanced input. Two Regardless of the amp's input impedance, you're still going to have to LISTEN to the system and decide whether it SOUNDS right -- as Infinity's instructions point out. Set the DIP (not dip) switches to the 47k position, and spend time listening to a wide range of program material. Then try the 70-80k position and the 26-40k positions to see what, if any, differences you hear. Basically, you're listening for a proper blend between the woofer and the satellites, and the "right" amount of energy in the 140Hz region. These characteristics are affected by both the crossover frequency (as set by the DIP switches) and the woofer level. Three Borrow a third-octave analyzer. If you live in the Seattle area, I'd be happy to stop by and set it up for you, for the cost of mileage and a free lunch. Just don't start prophesying, okay? |
#23
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How Do I Determine A Power-Amp's Input Impedance?
Here are three "definitive" answers...
One Since the 3400 is rated at 47k, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Yup, absolutely. The 3400B version almost certainly "piggybacks" the balanced input on top of the 3400's design. It's highly unlikely they would have changed the unbalanced input. Two Regardless of the amp's input impedance, you're still going to have to LISTEN to the system and decide whether it SOUNDS right -- as Infinity's instructions point out. Set the DIP (not dip) switches to the 47k position, and spend time listening to a wide range of program material. Then try the 70-80k position and the 26-40k positions to see what, if any, differences you hear. Basically, you're listening for a proper blend between the woofer and the satellites, and the "right" amount of energy in the 140Hz region. These characteristics are affected by both the crossover frequency (as set by the DIP switches) and the woofer level. Three Borrow a third-octave analyzer. If you live in the Seattle area, I'd be happy to stop by and set it up for you, for the cost of mileage and a free lunch. Just don't start prophesying, okay? |
#24
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How Do I Determine A Power-Amp's Input Impedance?
Here are three "definitive" answers...
One Since the 3400 is rated at 47k, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Yup, absolutely. The 3400B version almost certainly "piggybacks" the balanced input on top of the 3400's design. It's highly unlikely they would have changed the unbalanced input. Two Regardless of the amp's input impedance, you're still going to have to LISTEN to the system and decide whether it SOUNDS right -- as Infinity's instructions point out. Set the DIP (not dip) switches to the 47k position, and spend time listening to a wide range of program material. Then try the 70-80k position and the 26-40k positions to see what, if any, differences you hear. Basically, you're listening for a proper blend between the woofer and the satellites, and the "right" amount of energy in the 140Hz region. These characteristics are affected by both the crossover frequency (as set by the DIP switches) and the woofer level. Three Borrow a third-octave analyzer. If you live in the Seattle area, I'd be happy to stop by and set it up for you, for the cost of mileage and a free lunch. Just don't start prophesying, okay? |
#25
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How Do I Determine A Power-Amp's Input Impedance?
Here are three "definitive" answers...
One Since the 3400 is rated at 47k, is it a safe assumption that the 3400(B) is similarly rated, when used through the RCA inputs? Yup, absolutely. The 3400B version almost certainly "piggybacks" the balanced input on top of the 3400's design. It's highly unlikely they would have changed the unbalanced input. Two Regardless of the amp's input impedance, you're still going to have to LISTEN to the system and decide whether it SOUNDS right -- as Infinity's instructions point out. Set the DIP (not dip) switches to the 47k position, and spend time listening to a wide range of program material. Then try the 70-80k position and the 26-40k positions to see what, if any, differences you hear. Basically, you're listening for a proper blend between the woofer and the satellites, and the "right" amount of energy in the 140Hz region. These characteristics are affected by both the crossover frequency (as set by the DIP switches) and the woofer level. Three Borrow a third-octave analyzer. If you live in the Seattle area, I'd be happy to stop by and set it up for you, for the cost of mileage and a free lunch. Just don't start prophesying, okay? |
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 07:34:09 -0800, "Michael R. Kesti"
wrote: Clytemnestra wrote: On Sun, 11 Jan 2004 09:16:15 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: My first question is why you even want to know the input impedance. It's necessary to know in order to correctly adjust some dip switches on the crossover control unit for an Infinity Modulus sub/sat system. Here is the relevant passage from the owners manual: http://home.nyc.rr.com/acidrock212/infinity-ecu.jpg Frankly, this exceprt makes the gear seem to be expensive junk. Here's a clue - it is...................... That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? You have the right idea, but it gets even worse. Many multimeters measure AC voltage accurately only at line frequencies, ie, 50 to 60 Hz. You'll probably need an oscilloscope to perform the test Ethan suggests. Very true. And of course, he doesn't need to know the input impedance, so long as it's more than say 10k ohms. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 07:34:09 -0800, "Michael R. Kesti"
wrote: Clytemnestra wrote: On Sun, 11 Jan 2004 09:16:15 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: My first question is why you even want to know the input impedance. It's necessary to know in order to correctly adjust some dip switches on the crossover control unit for an Infinity Modulus sub/sat system. Here is the relevant passage from the owners manual: http://home.nyc.rr.com/acidrock212/infinity-ecu.jpg Frankly, this exceprt makes the gear seem to be expensive junk. Here's a clue - it is...................... That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? You have the right idea, but it gets even worse. Many multimeters measure AC voltage accurately only at line frequencies, ie, 50 to 60 Hz. You'll probably need an oscilloscope to perform the test Ethan suggests. Very true. And of course, he doesn't need to know the input impedance, so long as it's more than say 10k ohms. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 07:34:09 -0800, "Michael R. Kesti"
wrote: Clytemnestra wrote: On Sun, 11 Jan 2004 09:16:15 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: My first question is why you even want to know the input impedance. It's necessary to know in order to correctly adjust some dip switches on the crossover control unit for an Infinity Modulus sub/sat system. Here is the relevant passage from the owners manual: http://home.nyc.rr.com/acidrock212/infinity-ecu.jpg Frankly, this exceprt makes the gear seem to be expensive junk. Here's a clue - it is...................... That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? You have the right idea, but it gets even worse. Many multimeters measure AC voltage accurately only at line frequencies, ie, 50 to 60 Hz. You'll probably need an oscilloscope to perform the test Ethan suggests. Very true. And of course, he doesn't need to know the input impedance, so long as it's more than say 10k ohms. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 07:34:09 -0800, "Michael R. Kesti"
wrote: Clytemnestra wrote: On Sun, 11 Jan 2004 09:16:15 -0500, "Ethan Winer" ethanw at ethanwiner dot com wrote: My first question is why you even want to know the input impedance. It's necessary to know in order to correctly adjust some dip switches on the crossover control unit for an Infinity Modulus sub/sat system. Here is the relevant passage from the owners manual: http://home.nyc.rr.com/acidrock212/infinity-ecu.jpg Frankly, this exceprt makes the gear seem to be expensive junk. Here's a clue - it is...................... That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? You have the right idea, but it gets even worse. Many multimeters measure AC voltage accurately only at line frequencies, ie, 50 to 60 Hz. You'll probably need an oscilloscope to perform the test Ethan suggests. Very true. And of course, he doesn't need to know the input impedance, so long as it's more than say 10k ohms. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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How Do I Determine A Power-Amp's Input Impedance?
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How Do I Determine A Power-Amp's Input Impedance?
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How Do I Determine A Power-Amp's Input Impedance?
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 08:01:38 -0800, "William Sommerwerck"
wrote: Yup, absolutely. The 3400B version almost certainly "piggybacks" the balanced input on top of the 3400's design. It's highly unlikely they would have changed the unbalanced input. Thanks, your response was the most helpful so far. Regardless of the amp's input impedance, you're still going to have to LISTEN to the system and decide whether it SOUNDS right -- as Infinity's instructions point out. That's precisely what I've been doing. It sounds quite good, but I hear a little cancellation at about 100 Hz. I'm trying to determine if it characteristic of this type of speakers system, or if something may be out of adjustment. Clytemnestra |
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 08:01:38 -0800, "William Sommerwerck"
wrote: Yup, absolutely. The 3400B version almost certainly "piggybacks" the balanced input on top of the 3400's design. It's highly unlikely they would have changed the unbalanced input. Thanks, your response was the most helpful so far. Regardless of the amp's input impedance, you're still going to have to LISTEN to the system and decide whether it SOUNDS right -- as Infinity's instructions point out. That's precisely what I've been doing. It sounds quite good, but I hear a little cancellation at about 100 Hz. I'm trying to determine if it characteristic of this type of speakers system, or if something may be out of adjustment. Clytemnestra |
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 08:01:38 -0800, "William Sommerwerck"
wrote: Yup, absolutely. The 3400B version almost certainly "piggybacks" the balanced input on top of the 3400's design. It's highly unlikely they would have changed the unbalanced input. Thanks, your response was the most helpful so far. Regardless of the amp's input impedance, you're still going to have to LISTEN to the system and decide whether it SOUNDS right -- as Infinity's instructions point out. That's precisely what I've been doing. It sounds quite good, but I hear a little cancellation at about 100 Hz. I'm trying to determine if it characteristic of this type of speakers system, or if something may be out of adjustment. Clytemnestra |
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 08:01:38 -0800, "William Sommerwerck"
wrote: Yup, absolutely. The 3400B version almost certainly "piggybacks" the balanced input on top of the 3400's design. It's highly unlikely they would have changed the unbalanced input. Thanks, your response was the most helpful so far. Regardless of the amp's input impedance, you're still going to have to LISTEN to the system and decide whether it SOUNDS right -- as Infinity's instructions point out. That's precisely what I've been doing. It sounds quite good, but I hear a little cancellation at about 100 Hz. I'm trying to determine if it characteristic of this type of speakers system, or if something may be out of adjustment. Clytemnestra |
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 09:40:22 -0500, Clytemnestra
wrote: That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? Sure - there are way to get test tones using either a CD player or a computer sound card output. http://www.esser.u-net.com/ttg.htm http://www.globalshareware.com/Mp3-Audio/Utilities-Plug-Ins/SigJenny-download.htm http://www.dogstar.dantimax.dk/testwavs/ The fact that your digital meter may not be well suited to measurements other than line frequency really don't matter much, as any error will be the same for the measurement of source voltage, dropping resistor voltage and voltage across the amp's input as long as you make these measurements at the same frequency. |
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 09:40:22 -0500, Clytemnestra
wrote: That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? Sure - there are way to get test tones using either a CD player or a computer sound card output. http://www.esser.u-net.com/ttg.htm http://www.globalshareware.com/Mp3-Audio/Utilities-Plug-Ins/SigJenny-download.htm http://www.dogstar.dantimax.dk/testwavs/ The fact that your digital meter may not be well suited to measurements other than line frequency really don't matter much, as any error will be the same for the measurement of source voltage, dropping resistor voltage and voltage across the amp's input as long as you make these measurements at the same frequency. |
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How Do I Determine A Power-Amp's Input Impedance?
On Sun, 11 Jan 2004 09:40:22 -0500, Clytemnestra
wrote: That said, you can determine the input impedance fairly easily by feeding a 1 KHz tone through a resistor, and measuring the voltage before the resistor and after. I appreciate the advice, but as I said before I only have a digital multimeter at my disposal. It sounds like I'd have to bench the amp and connect it up to a tone or sine wave generator to do what you suggest. Am I interpreting you correctly? Sure - there are way to get test tones using either a CD player or a computer sound card output. http://www.esser.u-net.com/ttg.htm http://www.globalshareware.com/Mp3-Audio/Utilities-Plug-Ins/SigJenny-download.htm http://www.dogstar.dantimax.dk/testwavs/ The fact that your digital meter may not be well suited to measurements other than line frequency really don't matter much, as any error will be the same for the measurement of source voltage, dropping resistor voltage and voltage across the amp's input as long as you make these measurements at the same frequency. |
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