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#1
Posted to rec.audio.tech
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Sony SCD-CA7ES Muting Circuit Modification
Ok guys, don't go flaming before I explain what I am doing here.
I want to replace the line muting transistors with relays, preferably without having to build a timer circuit to control them. And I MIGHT want to experiment with other opamps, resistor types in the audio path, and checking the stability of the PS and cleaning it up if needed. (That will come later) My question is if I can trigger a 5v reed type relay from the points at Q203 and Q501 that I have circled in red on the following image. And would this type of modification require 2 or 4 SPST relays to replace Q101, Q102 and Q201,Q202 The schematic image can be found he http://img521.imageshack.us/img521/4843/7esmodsqb4.png Any assistance with this would be greatly appreciated. J |
#2
Posted to rec.audio.tech
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Sony SCD-CA7ES Muting Circuit Modification
"i45one" wrote ...
Ok guys, don't go flaming before I explain what I am doing here. I want to replace the line muting transistors with relays, preferably without having to build a timer circuit to control them. And I MIGHT want to experiment with other opamps, resistor types in the audio path, and checking the stability of the PS and cleaning it up if needed. (That will come later) My question is if I can trigger a 5v reed type relay from the points at Q203 and Q501 that I have circled in red on the following image. And would this type of modification require 2 or 4 SPST relays to replace Q101, Q102 and Q201,Q202 The schematic image can be found he http://img521.imageshack.us/img521/4843/7esmodsqb4.png Any assistance with this would be greatly appreciated. Seems odd that there appears to be a stereo muting function (Q103 driving Q101 & Q201) AND separate muting functions for L and R channels. If you wanted to retain the full functionality, you would need 4 separate relays (or maybe use a DP relay for Q101 & Q201?) Without seeing the missing parts of the schematic, maybe Q103-Q101-Q201 is the power-on mute, and the other two are some kind of operational mutes? It should be easy enough to look up the gain and collector current ratings of the driver transistors and compare to the coil specs on your proposed relays. Don't forget to put diodes across the coils to snub any kickback EMF. |
#3
Posted to rec.audio.tech
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Sony SCD-CA7ES Muting Circuit Modification
Thanks for the input RC
Without seeing the missing parts of the schematic, maybe Q103-Q101-Q201 is the power-on mute, and the other two are some kind of operational mutes? Agreed... I don't have the unit yet, I will have it on Friday. I will be able to actually pinpoint what controls what and under what conditions. I got a good deal on this thing and got it mainly for a tinker box. It should be easy enough to look up the gain and collector current ratings of the driver transistors and compare to the coil specs on your proposed relays. Don't forget to put diodes across the coils to snub any kickback EMF. Both of the driver transistors have a IC rating of -100mA and min hfe of 50. As for the relays, I will have to find some that are suitable. I think you are correct in recommending DP relays on the main output. If you are interested at all in seeing the rest of the schematic, let me know and I can post it. Thanks again, J |
#4
Posted to rec.audio.tech
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Sony SCD-CA7ES Muting Circuit Modification
On the relays, I found some SPDT relays with 200 ohm coils which I
think would be a draw of 25ma @ 5v. I'm no technician, but an avid hobbiest so correct me if I am incorrect in my assumptions. Thats why I do these things, to learn :-) |
#5
Posted to rec.audio.tech
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Sony SCD-CA7ES Muting Circuit Modification
"i45one" wrote ...
On the relays, I found some SPDT relays with 200 ohm coils which I think would be a draw of 25ma @ 5v. I'm no technician, but an avid hobbiest so correct me if I am incorrect in my assumptions. Thats why I do these things, to learn :-) Georg Ohm would agree with your calculation. Is there a voltage rating on the relay coils? Are they 5V relays? |
#6
Posted to rec.audio.tech
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Sony SCD-CA7ES Muting Circuit Modification
On May 10, 11:57 pm, "Richard Crowley" wrote:
"i45one" wrote ... On the relays, I found some SPDT relays with 200 ohm coils which I think would be a draw of 25ma @ 5v. I'm no technician, but an avid hobbiest so correct me if I am incorrect in my assumptions. Thats why I do these things, to learn :-) Georg Ohm would agree with your calculation. Is there a voltage rating on the relay coils? Are they 5V relays? Yes, the coils are rated at 5V. I found some other relays rated at 6V with the same coil impedance. And to correct myself, I was speaking of DPST relays. There is one thing that has me a bit perplexed. One of the trigger transistors shows a switched voltage of -11.3. I am surely going to have to do some actual measurements of the circuit to see what transistors are controlling what and when. I also need to see what voltage states are produced during muted and unmuted operation. I will have the unit on Monday, so I will know for sure why there are multiple muting circuits. |
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