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#1
Posted to rec.audio.tech
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how to remove bias voltage
Hello,
I came across the following problem which I would like to solve with your help. My brand new iRiver iFP899 provides a stereo line-in jack for connection to any kind of source providing line-in level for direct encoding. It can also be used as external mic input via settings in the menu of the player. I guess the jack input features so-called "plug-in power" which means that a few volts of bias on the mic input is injected, which can power some small consumer-type electret mics that don't have their own battery (although most do have batteries anyway). I measured the input and it provides about 3.15V (DC unloaded) for bias voltage. Funny enough, the bias voltage does not dissappear when I switch to "line-in" mode from "external mic" mode. Now I want to connect my hifi mixer to the device to record old vinyl records, CDs, whole real-time mixes etc. As soon as I plug the device into the mixer line-out output the VU meters overflow, i.e. they show full amplitude. I guess that is due to the "wrong direction" current travelling INTO but not OUT OF the mixer because of the bias voltage on the wire. What tricks can I use to couple the device to my mixer so the iRiver line-input DC bias does not reach the external source and does not affect it? Many thanks in advance and best regards Quinn |
#2
Posted to rec.audio.tech
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how to remove bias voltage
"Quinn Valente" wrote in message ... Hello, I came across the following problem which I would like to solve with your help. My brand new iRiver iFP899 provides a stereo line-in jack for connection to any kind of source providing line-in level for direct encoding. It can also be used as external mic input via settings in the menu of the player. I guess the jack input features so-called "plug-in power" which means that a few volts of bias on the mic input is injected, which can power some small consumer-type electret mics that don't have their own battery (although most do have batteries anyway). I measured the input and it provides about 3.15V (DC unloaded) for bias voltage. Funny enough, the bias voltage does not dissappear when I switch to "line-in" mode from "external mic" mode. Now I want to connect my hifi mixer to the device to record old vinyl records, CDs, whole real-time mixes etc. As soon as I plug the device into the mixer line-out output the VU meters overflow, i.e. they show full amplitude. I guess that is due to the "wrong direction" current travelling INTO but not OUT OF the mixer because of the bias voltage on the wire. What tricks can I use to couple the device to my mixer so the iRiver line-input DC bias does not reach the external source and does not affect it? Many thanks in advance and best regards First make sure you are not plugging a T/S plug into a TRS socket. They sometimes use the ring of a TRS socket for low voltage electrets (not strictly "phantom" in that case), and using an adapter cable with the ring unconnected will solve the problem. Otherwise you could try a suitable non polarised capacitor in series with the input. MrT. |
#3
Posted to rec.audio.tech
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how to remove bias voltage
Thanks, Mr. T!
I'm sorry but I don't know what you mean by T/S plug and TRS socket. The iRiver device has a miniature stereo jack which I connect via an adapter cable stereo jack -- cinch. How can I implement non polarised capacitor in series with the input? Which capacitor values are needed so that none of my audiosignal frequencies get lost? Regards, Quinn "Mr.T" MrT@home schrieb im Newsbeitrag u... "Quinn Valente" wrote in message ... Hello, I came across the following problem which I would like to solve with your help. My brand new iRiver iFP899 provides a stereo line-in jack for connection to any kind of source providing line-in level for direct encoding. It can also be used as external mic input via settings in the menu of the player. I guess the jack input features so-called "plug-in power" which means that a few volts of bias on the mic input is injected, which can power some small consumer-type electret mics that don't have their own battery (although most do have batteries anyway). I measured the input and it provides about 3.15V (DC unloaded) for bias voltage. Funny enough, the bias voltage does not dissappear when I switch to "line-in" mode from "external mic" mode. Now I want to connect my hifi mixer to the device to record old vinyl records, CDs, whole real-time mixes etc. As soon as I plug the device into the mixer line-out output the VU meters overflow, i.e. they show full amplitude. I guess that is due to the "wrong direction" current travelling INTO but not OUT OF the mixer because of the bias voltage on the wire. What tricks can I use to couple the device to my mixer so the iRiver line-input DC bias does not reach the external source and does not affect it? Many thanks in advance and best regards First make sure you are not plugging a T/S plug into a TRS socket. They sometimes use the ring of a TRS socket for low voltage electrets (not strictly "phantom" in that case), and using an adapter cable with the ring unconnected will solve the problem. Otherwise you could try a suitable non polarised capacitor in series with the input. MrT. |
#4
Posted to rec.audio.tech
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how to remove bias voltage
"Quinn Valente" wrote in message ... I'm sorry but I don't know what you mean by T/S plug and TRS socket. T/S is tip-sleeve, TRS is tip-ring-sleeve. The iRiver device has a miniature stereo jack which I connect via an adapter cable stereo jack -- cinch. Assuming it is actually a stereo input, that's unusual to have voltage. Microphone inputs are usually mono. Have you checked to see what accessories iRiver sell for this device? I'm betting you just need the correct lead. How can I implement non polarised capacitor in series with the input? Which capacitor values are needed so that none of my audiosignal frequencies get lost? You would need one on each channel hot input. Size will depend on the impedances, but at least 2 uF in most cases. MrT. |
#5
Posted to rec.audio.tech
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how to remove bias voltage
"Mr.T" wrote ...
"Quinn Valente" wrote ... The iRiver device has a miniature stereo jack which I connect via an adapter cable stereo jack -- cinch. Assuming it is actually a stereo input, that's unusual to have voltage. Microphone inputs are usually mono. Microphone inputs on small consumer devices like this are typically T/R/S 3.5mm stereo mini-phone with "plug-in power" (electret microphone bias voltage). Have you checked to see what accessories iRiver sell for this device? I'm betting you just need the correct lead. How can I implement non polarised capacitor in series with the input? Which capacitor values are needed so that none of my audiosignal frequencies get lost? You would need one on each channel hot input. Size will depend on the impedances, but at least 2 uF in most cases. I have a web page giving details of how to do this, including selection of capacitor value. It was written for people who want to connect professional microphones to consumer cam- corders, but the principles and circuit are the same for your application... http://www.rcrowley.com/CamAdapt.htm |
#6
Posted to rec.audio.tech
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how to remove bias voltage
In article , "Richard Crowley" wrote:
"Mr.T" wrote ... "Quinn Valente" wrote ... The iRiver device has a miniature stereo jack which I connect via an adapter cable stereo jack -- cinch. Assuming it is actually a stereo input, that's unusual to have voltage. Microphone inputs are usually mono. Microphone inputs on small consumer devices like this are typically T/R/S 3.5mm stereo mini-phone with "plug-in power" (electret microphone bias voltage). Have you checked to see what accessories iRiver sell for this device? I'm betting you just need the correct lead. How can I implement non polarised capacitor in series with the input? Which capacitor values are needed so that none of my audiosignal frequencies get lost? You would need one on each channel hot input. Size will depend on the impedances, but at least 2 uF in most cases. I have a web page giving details of how to do this, including selection of capacitor value. It was written for people who want to connect professional microphones to consumer cam- corders, but the principles and circuit are the same for your application... http://www.rcrowley.com/CamAdapt.htm I noticed the Camcorder usage. On most camcorders I have used, the input overloads on any loud sounds, like a band playing inside. My better Sony camcorder can handle large inputs without overloading, Well it does overload a few feet away from a concert speaker set. I also found a cassette unit I have overloaded. The gain controls are often in back of the preamp stage. So for anyone trying to mic something like this for loud sounds, I would recommend adding attenuating resistors before the input jack. For someone using a self powered electret mic with biased input jack, I'm not sure of the best route for that scenereo. greg |
#7
Posted to rec.audio.tech
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how to remove bias voltage
"GregS" wrote in message ... On most camcorders I have used, the input overloads on any loud sounds, like a band playing inside. My better Sony camcorder can handle large inputs without overloading, Well it does overload a few feet away from a concert speaker set. I also found a cassette unit I have overloaded. The gain controls are often in back of the preamp stage. So for anyone trying to mic something like this for loud sounds, I would recommend adding attenuating resistors before the input jack. Which doesn't always help since some camcorders have only automatic gain control with an aggressive AGC action that compresses everything to overload, even when the input signal voltage is reduced. My Canon does unfortunately. MrT. |
#8
Posted to rec.audio.tech
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how to remove bias voltage
"Quinn Valente" writes:
Hello, I came across the following problem which I would like to solve with your help. My brand new iRiver iFP899 provides a stereo line-in jack for connection to any kind of source providing line-in level for direct encoding. It can also be used as external mic input via settings in the menu of the player. I guess the jack input features so-called "plug-in power" which means that a few volts of bias on the mic input is injected, which can power some small consumer-type electret mics that don't have their own battery (although most do have batteries anyway). That's quite typical. I measured the input and it provides about 3.15V (DC unloaded) for bias voltage. Funny enough, the bias voltage does not dissappear when I switch to "line-in" mode from "external mic" mode. Funny thing. I think it hsould have dissapeared of that equipment were well designed. Now I want to connect my hifi mixer to the device to record old vinyl records, CDs, whole real-time mixes etc. As soon as I plug the device into the mixer line-out output the VU meters overflow, i.e. they show full amplitude. I guess that is due to the "wrong direction" current travelling INTO but not OUT OF the mixer because of the bias voltage on the wire. Quite possible. What tricks can I use to couple the device to my mixer so the iRiver line-input DC bias does not reach the external source and does not affect it? Suitable cpaacitors on the line to block the DC and pass the AC. Some capacitance calue that is 10 uF or higher (10 uF at 20 Hz is around 800 ohms, not much attenuation if input impedance is very many kilo-ohms). A plastic cpacitor would be best, but an electrolytic paraleld with 100 nF plastic capacitor should also work. Other option is to use an audio signal isolation transformer on the line connection. This transformer will not pass through the DC, but will pass audio signals nicely. The plug-in power is very limited in current, so I don't think that this DC on the deivce side would not cause any serious problems to transformer (expected 1-3 mA should nto saturate the core of most audio transformers I think). -- Tomi Engdahl (http://www.iki.fi/then/) Take a look at my electronics web links and documents at http://www.epanorama.net/ |
#9
Posted to rec.audio.tech
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how to remove bias voltage
"Mr.T" MrT@home writes:
"Quinn Valente" wrote in message ... I'm sorry but I don't know what you mean by T/S plug and TRS socket. T/S is tip-sleeve, TRS is tip-ring-sleeve. The iRiver device has a miniature stereo jack which I connect via an adapter cable stereo jack -- cinch. Assuming it is actually a stereo input, that's unusual to have voltage. There are many small portable recorders and video cameras with stereo microphone inputs with 3.5 mm stereo jack connector. The plug-in-power arrangement is quite commonly used in this field. Microphone inputs are usually mono. That's the case for the microphone inputs in PC sound cards. Have you checked to see what accessories iRiver sell for this device? I'm betting you just need the correct lead. How can I implement non polarised capacitor in series with the input? Which capacitor values are needed so that none of my audiosignal frequencies get lost? You would need one on each channel hot input. Size will depend on the impedances, but at least 2 uF in most cases. MrT. -- Tomi Engdahl (http://www.iki.fi/then/) Take a look at my electronics web links and documents at http://www.epanorama.net/ |
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