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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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TV speaker amplifier
Well, last night, I finished the first draft of the amplifier for my
bathroom tv speaker. Thanks for the advice earlier It works well** except for two problems. A) Allong with the TV sound, it blends in the strongest AM station in town. The amplifer module I bought just has 5 unshielded wires coming out of it, and for the input, I used 20 inches of lamp cord connnected to a 1/8" phone plug, which plugged into the earphone jack of the tv. I guess the fix most likely to work is to replace the lamp cord with co-axial shielded cable. Right? Or I could just wrap some kind of shielding around the wire that is there. Like heavy duty aluminum foil taped in place. Good idea. Easier becaue I wouldn't have to hunt for some shielded cable, or solder a phone little plug to the end. . B) It's probalby much too loud. I have to turn the tv volume down from a maximum of 50 to about 15. Then let it get amplifed again by the amp. I'm figuring the TV output has less distorition, and that using it at low volume which then gets amped by this thing introduces distortion. (Though I caouldn't tell because the AM radio was too much of a distraction.) The remedy for this seems to be to change wall warts. Right now I'm using a 12VDC, 500mA adapter, which I chose mostly because it was the first I saw in my box that had the end, the tip, cut off already. The spec says it can use 4.5 to 12VDC **I'm using a Kemo M031N monaural amplifier module that sells for about 8 dollars at MCM Electrronics. Rated at 3.5 watts. I'm glad I didnt' get the 8? wattt version that was about 13 dollars. It's "box" is open on one side but filled with some sort of hard filling. It has 5 unshielded wires coming out of one side. Two for the input. And two for the speaker plus two for the power, which share one negative wire. Which makes 5 total. I paid no attention to polarity, since it's a monaural output, but when I put in a shielded input, I could make sure that the shield is conected to what the instructions say is the ground, if it matters??? Unlike their drawing, I don't have the pot wired into the input, because the TV is 9 feet away from the bathtub. Rather it's in the wires that go to the speakers, from a 1930's record player, mounted above the tub (for the last 30 years.) . Thanks. |
#2
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TV speaker amplifier
A) Allong with the TV sound, it blends in the strongest AM station in
town. The amplifer module I bought just has 5 unshielded wires coming out of it, and for the input, I used 20 inches of lamp cord connnected to a 1/8" phone plug, which plugged into the earphone jack of the TV. I guess the fix most likely to work is to replace the lamp cord with co-axial shielded cable. Right? RIGHT!!! Story... Back in 1978 I was working at a hi-fi store in Pennsylvania. Around this time, fancy speaker cables and interconnects were becoming popular. One customer bought some Monster speaker cable, then called us to say that he had a hum problem. When I saw his system, I broke into uncontrollable laughter. He had attached RCA plugs to the Monster cable, and was using it as an interconnect! B) It's probalby much too loud. I have to turn the tv volume down from a maximum of 50 to about 15. Then let it get amplifed again by the amp. I'm figuring the TV output has less distorition, and that using it at low volume which then gets amped by this thing introduces distortion. (Though I caouldn't tell because the AM radio was too much of a distraction.) If anything, the TV introduces more distortion than the amp. Keep the TV output low and let the amp provide the needed gain. Stick with the supply you have. |
#3
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TV speaker amplifier
A) Allong with the TV sound, it blends in the strongest AM station in town. The amplifer module I bought just has 5 unshielded wires coming out of it, and for the input, I used 20 inches of lamp cord connnected to a 1/8" phone plug, which plugged into the earphone jack of the tv. I guess the fix most likely to work is to replace the lamp cord with co-axial shielded cable. Right? Excellent first step... and the Kemo data sheet for this amp specifically says that the input cable must be screened. If you've got AM incursion, you should also try to "choke" the wires coming into, and out of the amplifier. You can get small "clamp-on" ferrite RFI blockers - they're similar to the tubular ferrite cores that you find on many USB and video cables, but they come in two parts in a plastic shell so you can clamp them onto an existing cable. Use one on the input cable, one on the power cable, and one on each speaker cable... this should keep the AM signal out of the amp. B) It's probalby much too loud. I have to turn the tv volume down from a maximum of 50 to about 15. Then let it get amplifed again by the amp. I'm figuring the TV output has less distorition, and that using it at low volume which then gets amped by this thing introduces distortion. (Though I caouldn't tell because the AM radio was too much of a distraction.) The remedy for this seems to be to change wall warts. Right now I'm using a 12VDC, 500mA adapter, which I chose mostly because it was the first I saw in my box that had the end, the tip, cut off already. The spec says it can use 4.5 to 12VDC Reducing the voltage will probably reduce the *maximum* volume (before it distorts) but probably not reduce the volume at any specific TV volume setting (that is, it won't reduce the amplifier's gain). Yeah... I just looked at Kemo's web page and it says that this amp has an input sensitivity of " 80 mV". That's not much voltage at all. Your TV set is almost certainly "overdriving" the input with too much voltage, and could be forcing it into distortion quite easily. Kemo's data sheet shows the use of a 10k potentiometer (presumably an "audio taper" type) as a volume control. I'd suggest that you get one (Radio Shack or similar) and wire one up as the data sheet shows... this will let you adjust the gain. See http://www.kemo-electronic.de/datasheets/m031n.pdf I paid no attention to polarity, since it's a monaural output, but when I put in a shielded input, I could make sure that the shield is conected to what the instructions say is the ground, if it matters??? Yes. Do as they say. Unlike their drawing, I don't have the pot wired into the input, because the TV is 9 feet away from the bathtub. Rather it's in the wires that go to the speakers, from a 1930's record player, mounted above the tub (for the last 30 years.) . You should have a pot (or a simple two-resistor fixed attenuator) in the input circuit, so that you don't overdrive the amplifier and force it into distortion. You don't need to remove the pot you have placed in the speaker wiring... just add a 10k pot as the data sheet says you should do, use this to "turn down" the amp's sensitivity to the point where it's acceptable, and leave this pot at that setting. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
#4
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TV speaker amplifier
"micky" wrote in message news Well, last night, I finished the first draft of the amplifier for my bathroom tv speaker. Thanks for the advice earlier It works well** except for two problems. A) Allong with the TV sound, it blends in the strongest AM station in town. The amplifer module I bought just has 5 unshielded wires coming out of it, and for the input, I used 20 inches of lamp cord connnected to a 1/8" phone plug, which plugged into the earphone jack of the tv. I guess the fix most likely to work is to replace the lamp cord with co-axial shielded cable. Right? Or I could just wrap some kind of shielding around the wire that is there. Like heavy duty aluminum foil taped in place. Good idea. Easier becaue I wouldn't have to hunt for some shielded cable, or solder a phone little plug to the end. . B) It's probalby much too loud. I have to turn the tv volume down from a maximum of 50 to about 15. Then let it get amplifed again by the amp. I'm figuring the TV output has less distorition, and that using it at low volume which then gets amped by this thing introduces distortion. (Though I caouldn't tell because the AM radio was too much of a distraction.) The remedy for this seems to be to change wall warts. Right now I'm using a 12VDC, 500mA adapter, which I chose mostly because it was the first I saw in my box that had the end, the tip, cut off already. The spec says it can use 4.5 to 12VDC **I'm using a Kemo M031N monaural amplifier module that sells for about 8 dollars at MCM Electrronics. Rated at 3.5 watts. I'm glad I didnt' get the 8? wattt version that was about 13 dollars. It's "box" is open on one side but filled with some sort of hard filling. It has 5 unshielded wires coming out of one side. Two for the input. And two for the speaker plus two for the power, which share one negative wire. Which makes 5 total. I paid no attention to polarity, since it's a monaural output, but when I put in a shielded input, I could make sure that the shield is conected to what the instructions say is the ground, if it matters??? Unlike their drawing, I don't have the pot wired into the input, because the TV is 9 feet away from the bathtub. Rather it's in the wires that go to the speakers, from a 1930's record player, mounted above the tub (for the last 30 years.) . Thanks. Oh dear ... Arfa |
#5
Posted to sci.electronics.repair
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TV speaker amplifier
Arfa Daily wrote:
"micky" wrote in message news Well, last night, I finished the first draft of the amplifier for my bathroom tv speaker. Thanks for the advice earlier It works well** except for two problems. A) Allong with the TV sound, it blends in the strongest AM station in town. The amplifer module I bought just has 5 unshielded wires coming out of it, and for the input, I used 20 inches of lamp cord connnected to a 1/8" phone plug, which plugged into the earphone jack of the tv. I guess the fix most likely to work is to replace the lamp cord with co-axial shielded cable. Right? Or I could just wrap some kind of shielding around the wire that is there. Like heavy duty aluminum foil taped in place. Good idea. Easier becaue I wouldn't have to hunt for some shielded cable, or solder a phone little plug to the end. . B) It's probalby much too loud. I have to turn the tv volume down from a maximum of 50 to about 15. Then let it get amplifed again by the amp. I'm figuring the TV output has less distorition, and that using it at low volume which then gets amped by this thing introduces distortion. (Though I caouldn't tell because the AM radio was too much of a distraction.) The remedy for this seems to be to change wall warts. Right now I'm using a 12VDC, 500mA adapter, which I chose mostly because it was the first I saw in my box that had the end, the tip, cut off already. The spec says it can use 4.5 to 12VDC **I'm using a Kemo M031N monaural amplifier module that sells for about 8 dollars at MCM Electrronics. Rated at 3.5 watts. I'm glad I didnt' get the 8? wattt version that was about 13 dollars. It's "box" is open on one side but filled with some sort of hard filling. It has 5 unshielded wires coming out of one side. Two for the input. And two for the speaker plus two for the power, which share one negative wire. Which makes 5 total. I paid no attention to polarity, since it's a monaural output, but when I put in a shielded input, I could make sure that the shield is conected to what the instructions say is the ground, if it matters??? Unlike their drawing, I don't have the pot wired into the input, because the TV is 9 feet away from the bathtub. Rather it's in the wires that go to the speakers, from a 1930's record player, mounted above the tub (for the last 30 years.) . Thanks. Oh dear ... Arfa That's gotta be one of the funniest post I've seen in some time now.. Jamie |
#7
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TV speaker amplifier
In article ,
micky wrote: Ah, let me ask about these lines from the instructions: With too high ohmic voltage sources it may occur self-oscillation of the amplifier (constant sound). In that case it is convenient to place directly at the module and parallel to the cables of the current supply (+ and -) Parallel to the cables? Not across the cables? I know this is translated from German, but still. "Parallel to" is more standard terminology in electronics.. "across" is colloquial English. They really mean the same thing in this case... connect the capacitor's + and - terminals to the + and - power terminals on the amplifier right where you connect the wires from the wall wart. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
#8
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TV speaker amplifier
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#9
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TV speaker amplifier
micky formulerede spørgsmålet:
On Sat, 2 Mar 2013 09:58:40 -0800, (Dave Platt) wrote: In article , micky wrote: Ah, let me ask about these lines from the instructions: With too high ohmic voltage sources it may occur self-oscillation of the amplifier (constant sound). In that case it is convenient to place directly at the module and parallel to the cables of the current supply (+ and -) Parallel to the cables? Not across the cables? I know this is translated from German, but still. "Parallel to" is more standard terminology in electronics.. "across" is colloquial English. Thanks. I would have thought the word was perpendicular, not parallel. If you think of "Parallel to the end of the cable" it makes sense. Leif -- Husk kørelys bagpå, hvis din bilfabrikant har taget den idiotiske beslutning at undlade det. |
#10
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TV speaker amplifier
On Mon, 04 Mar 2013 11:39:37 +0100, Leif Neland
wrote: micky formulerede spørgsmålet: On Sat, 2 Mar 2013 09:58:40 -0800, (Dave Platt) wrote: In article , micky wrote: Ah, let me ask about these lines from the instructions: With too high ohmic voltage sources it may occur self-oscillation of the amplifier (constant sound). In that case it is convenient to place directly at the module and parallel to the cables of the current supply (+ and -) Parallel to the cables? Not across the cables? I know this is translated from German, but still. "Parallel to" is more standard terminology in electronics.. "across" is colloquial English. Thanks. I would have thought the word was perpendicular, not parallel. If you think of "Parallel to the end of the cable" it makes sense. Leif Hmmmm. Thanks. |
#11
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TV speaker amplifier
On Tue, 05 Mar 2013 07:24:40 -0500, micky
wrote: On Mon, 04 Mar 2013 11:39:37 +0100, Leif Neland wrote: micky formulerede spørgsmålet: On Sat, 2 Mar 2013 09:58:40 -0800, (Dave Platt) wrote: In article , micky wrote: Ah, let me ask about these lines from the instructions: With too high ohmic voltage sources it may occur self-oscillation of the amplifier (constant sound). In that case it is convenient to place directly at the module and parallel to the cables of the current supply (+ and -) Parallel to the cables? Not across the cables? I know this is translated from German, but still. "Parallel to" is more standard terminology in electronics.. "across" is colloquial English. Thanks. I would have thought the word was perpendicular, not parallel. If you think of "Parallel to the end of the cable" it makes sense. Leif Hmmmm. Thanks. Parallel as opposed to "in series with". In other words, across. |
#12
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TV speaker amplifier
Den 05/03/2013, skrev Pat:
On Tue, 05 Mar 2013 07:24:40 -0500, micky wrote: On Mon, 04 Mar 2013 11:39:37 +0100, Leif Neland wrote: micky formulerede spørgsmålet: On Sat, 2 Mar 2013 09:58:40 -0800, (Dave Platt) wrote: In article , micky wrote: Ah, let me ask about these lines from the instructions: With too high ohmic voltage sources it may occur self-oscillation of the amplifier (constant sound). In that case it is convenient to place directly at the module and parallel to the cables of the current supply (+ and -) Parallel to the cables? Not across the cables? I know this is translated from German, but still. "Parallel to" is more standard terminology in electronics.. "across" is colloquial English. Thanks. I would have thought the word was perpendicular, not parallel. If you think of "Parallel to the end of the cable" it makes sense. Leif Hmmmm. Thanks. Parallel as opposed to "in series with". In other words, across. Which makes the interesting question: Is a bulb/speaker/motor/whatever connected in parallel or in series with its connecting cord? :-) Leif -- Husk kørelys bagpå, hvis din bilfabrikant har taget den idiotiske beslutning at undlade det. |
#13
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TV speaker amplifier
Which makes the interesting question: Is a bulb/speaker/motor/whatever
connected in parallel or in series with its connecting cord? :-) In parallel. Think of stripping the power cord of small sections of insulation and attaching additional loads. |
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