Need help - CD Player output voltage attenuate?

FileFixer

Well-Known Member
My CD player technics SL-PS770D have 2V output voltage as many CD players on market. I must to connect WiFi transmitter on the CD analog output but as CD player have 2V on its output then I have overboosted output from WiFi receiver. On all my other audio equipment I dont have this problem and all work perfect.
Fore that reason I do some research to resolve this problem but I'm not so sure if that's the right way.

This is schematics from my CD Player...

SL-_PS770_D_AD_output.jpg


I want to change resistors R829 and R830 with different resistors values and attenuate output voltage on 200mV or 250mV. I use online calculator to calculate how much -dB is need to attenuate this signal to adequate voltages and calculator show me this results...

Input_sensitivity_gain.jpg


Input_sensitivity_gain1.jpg


I`m also found different calculator what measure how much we need resistance to make voltage divider and it calculate that, if I keep output impedance on 47kOhm, I need to change resistors R829 and R830 to 205 kOhm for -19.78dB/205mV output or use 162 kOhm resistors for -17.95dB/253mV...
This is that calculations...

205k.jpg


162k.jpg


I need some help to confirm me is all of that can to be correct or not?

Thanks to all...
 
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You might try some line level attenuators just plug them into the output rca jacks. I use them on a CD player connected to a tube preamp. Same kind of problem, The CD output was a bit hot. https://www.parts-express.com/harrison-labs-12-db-rca-line-level-audio-attenuator-pair--266-244 I used these. They also have 3 and 6db versions. It looks like your looking for a bit more though. You could also add a resistor between two rca jacks in series with whats already in the CD player to get where you want it to be. Basically building your own line level attenuator. That way you could tune it before swapping resistors in and out in the CD player.
 
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10 times voltage is 20 dB so that calculations looks correct but, intuitively, 205K ohms seems too high to me. Try it and measure the output. You can't hurt anything.
Rick
 
My CD player technics SL-PS770D have 2V output voltage as many CD players on market. I must to connect WiFi transmitter on the CD analog output but as CD player have 2V on its output then I have overboosted output from WiFi receiver. On all my other audio equipment I dont have this problem and all work perfect.
Fore that reason I do some research to resolve this problem but I'm not so sure if that's the right way.

This is schematics from my CD Player...

SL-_PS770_D_AD_output.jpg


I want to change resistors R629 and R630 with different resistors values and attenuate output voltage on 200mV or 250mV. I use online calculator to calculate how much -dB is need to attenuate this signal to adequate voltages and calculator show me this results...

Input_sensitivity_gain.jpg


Input_sensitivity_gain1.jpg


I`m also found different calculator what measure how much we need resistance to make voltage divider and it calculate that, if I keep output impedance on 47kOhm, I need to change resistors R629 and R630 to 205 kOhm for -19.78dB/205mV output or use 162 kOhm resistors for -17.95dB/253mV...
This is that calculations...

205k.jpg


162k.jpg
You could modify Z2 to keep the output of your CD player near the actual value, keeping Z1+Z2 around 50KOhm

I need some help to confirm me is all of that can to be correct or not?

Thanks to all...
I think 250mV output could be fine, that's 162KOhms for the resistors. You could modify Z2 to keep the output of your CD player near the actual value, keeping Z1+Z2 around 50KOhm, instead of increasing Z1 so much to keep Z2 at 47K. I think something near 15 or 22K could work. I don't know if C819 should be modified if you do this.

What's the input sensitivity and input impedance of your WiFi receiver? Use those exact values to do your math in the voltage divider calculator and you'll be fine. Vout must be the sensitivity of the receiver, ZL must be the input impedance of the receiver. Z2 is already 47K but I'd try 15K.

Or, as said, try to attenuate the signal after the output.
 
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10 times voltage is 20 dB so that calculations looks correct but, intuitively, 205K ohms seems too high to me. Try it and measure the output. You can't hurt anything.
Rick

Good idea, thanks... I have test CD which include 1kHZ tone on 0dB.and this Test CD also have 1kH on -20dB.
 
Why are these two resistors?

If you think why I want just these resistors but not some other...?
Because that I cant to change any resistor on IC891 why these two resistors (10K) does not do anything on Op-amp with gain and output signal is 0dB gained with these two resistors.
All components between letter A and B contain stage for digital optical output and any changes on these stage aso can change characteristics on optical output.
Last what I can to change is these two resistors with 330Ohm and 47kOhm but I dont want to change output impedance on analog audio outputs wich is in this situation 47k.
So, only what I can to change is these two resistors, R829 and R830 if I want to lowering gain on output.
 
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I think 250mV output could be fine, that's 162KOhms for the resistors. You could modify Z2 to keep the output of your CD player near the actual value, keeping Z1+Z2 around 50KOhm, instead of increasing Z1 so much to keep Z2 at 47K. I think something near 15 or 22K could work. I don't know if C819 should be modified if you do this.

What's the input sensitivity and input impedance of your WiFi receiver? Use those exact values to do your math in the voltage divider calculator and you'll be fine. Vout must be the sensitivity of the receiver, ZL must be the input impedance of the receiver. Z2 is already 47K but I'd try 15K.

Or, as said, try to attenuate the signal after the output.

With Analog output from CD I go to Analog input on Receiver then signal going from receiver VCR output to WiFi transmitter an this signal from VCR output is passthrough. Receiver have 47k input impedance.
 
Yes, you are right... I`m thinking on Receiver input... Sorry... To much numbers for 3AM. :)

index.php
 
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Receiver have 47k input impedance. I want to keep output impedance that can be match with input impedance.


In the world of audio for analog signals it is not necessarily needed or a good idea to match source and load impedances. The general rule of thumb is for the source impedance to be at least 5 times smaller than the load impedance and in a lot of cases it is on the order of 10 times.

Note the manual indicates a 10K Ohm load or greater for an output impedance of 600 Ohms.
 
Just imagine you add a volume pot (a voltage divider) at your analog output. If you replace the 47k with a volume pot, the circuit keeps seeing a 47k resistor, but you take just a part of the signal to the next stage. That's what you do if you reduce the 47k and increase the 330ohm. It's like moving a potentiometer as long as you keep the total at around 47 or 50K. Or, replace the 47k with a 50 kohm trimpot and take the signal from the wiper ( connect the mid pin to the analog output) and adjust to your taste and check the sound quality (again, I'm not sure if you need to modify that capacitor in parallel with the 47k)
 
A lot of cd players have variable output with remote control.

Look for a used Denon DCD-1500.
 
had a look at the Denon DCD-1500 schematic,
https://www.hifiengine.com/manual_library/denon/dcd-1500.shtml

and the volume control is located at the input of the last OPamp (IC891 in your unit)

Take a look at the Denon schematic, check the Headphones volume control (since the analog audio out has a digital volume control), and you'll see how it's done, you can add a trimpot at the input of IC891 so you keep all the output impedances untouched.

If you post a wider pict of your schematic we can suggest some more ideas.
 
R829 and R830 has replaced today with 162 kOhm resistors and everything is all right now. Sound is much quieter than before, maybe little quieter then I want to be but WiFi transmitter work perfect and sound is not overboosted as before. I think that this resistors can be matched on 100 kOhm to be perfect. Now it have 745mV on output Peak to Peak, before that modification it have 2V peak to peak voltage on 1kHz signal.

This modification is very easy to do...

Output1.jpg


Output2.jpg
 
i built a box with basically this inside . also had more rca sockets and a switch . but thats another story . was built for 12v system .i now use at for go no go testing of phono in .
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I think to put two pots inside CD player but things is gone on other side. :) Maybe in near future I puting two multi trimmer and set resistance in quiet precicise values.
 
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