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Old 22nd January 2011, 02:05 AM   #1
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Location: Malaysia, Selangor
Default modification to my old radio

I have an old radio (well... maybe 10 years or so) which the CD player is faulty, and tape feature(which most of us didn't use nowadays).
It doesn't have any line-in for me to input any other audio hardware which i can make use of the radio (as a speaker).
I kind of like it, so I decided to modify it make it useful.


My idea was to rectify the CD input into a line-in port, which most modern music players have. I will interested to hear others idea and opinion.

I have the manual of schematic circuit drawing of that particular radio player called PHC-ZW770L.
But I myself couldn't fully have the idea where should I edit it, as I only have little knowledge about audio. These are the following problem i'm facing:
- As commonly known, a stereo adapter have 3 wiring, which is ground, Left & Right. I'm thinking of connect these 3 wiring of another line in cable to take over CD's wiring.
In the circuit board, i only found/know it have a L&R-channel input, but i didn't found any words match of grounding purposes. ( the part consists of wiring such as "R.CH", "L.CH", "CD.5V(CD-H)", "CD.GND", "P.GND", "P.VDD(6.2V)"

- Is it possible to just disconnect the wiring for CD's and Tape' to save electricity(as in didn't use at all), or we need to edit a little bit to do so ? (like changing resistors as so on).
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Old 22nd January 2011, 03:42 AM   #2
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Colour by numbers :
R.CH.......Right channel
"L.CH"......Left
"CD.5V(CD-H)....CD High -Logic status
"CD.GND" Ground
"P.GND" Power Ground and "P.VDD(6.2V)".....Power supply...whether or not "D" stand for Digital ,surely by cutting those connections ,the CD section won't receive any power . I guess the input selection is made via an electronic switch ,which may send itself an 'high' logic level to CD-H pin .
The same function is accomplished via mechanical switches in an usual (self-activating at tape function push ) tape section,which usually feed the motors ,either .

A tester to check voltages and logic levels may be useful .
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Old 22nd January 2011, 06:09 AM   #3
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Quote:
Originally Posted by picowallspeaker View Post
Colour by numbers :
R.CH.......Right channel
"L.CH"......Left
"CD.5V(CD-H)....CD High -Logic status
"CD.GND" Ground
"P.GND" Power Ground and "P.VDD(6.2V)".....Power supply...whether or not "D" stand for Digital ,surely by cutting those connections ,the CD section won't receive any power . I guess the input selection is made via an electronic switch ,which may send itself an 'high' logic level to CD-H pin .
The same function is accomplished via mechanical switches in an usual (self-activating at tape function push ) tape section,which usually feed the motors ,either .

A tester to check voltages and logic levels may be useful .
Hm...... don't quite understand fully, but I will ask for clarify, such as :
- CD High ? Logic status ? (understand it somehow related to logic gate, but could you give a example that what it may be, and how it works)
- CD.GND and PWR GND, what is the different ? (to which connection).
- I checked wikipedia, and VDD stands for +terminal
- What I meant is thatt if i cut off the power for CD player, will it make the systems unbalance ? (such as radio itself take too much of power or so on)

So, in your opinion, i'm make a additional stereo input line(TRS system), which has 3 terminal:
Tip Terminal - Left Terminal - L.CH
Ring Terminal - Right Terminal - R.CH
Sleeve Terminal - Ground Terminal - CD.GND ??(not sure)

Should that be the connection ? or the sleeve terminal connect to P.GND/CD-H ?
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Old 22nd January 2011, 06:24 AM   #4
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Quote:
Originally Posted by picowallspeaker View Post
Colour by numbers :
R.CH.......Right channel
"L.CH"......Left
"CD.5V(CD-H)....CD High -Logic status
"CD.GND" Ground
"P.GND" Power Ground and "P.VDD(6.2V)".....Power supply...whether or not "D" stand for Digital ,surely by cutting those connections ,the CD section won't receive any power . I guess the input selection is made via an electronic switch ,which may send itself an 'high' logic level to CD-H pin .
The same function is accomplished via mechanical switches in an usual (self-activating at tape function push ) tape section,which usually feed the motors ,either .

A tester to check voltages and logic levels may be useful .
I had to say thanks first of all for your reply, it gives me a lot of information.
There is something i'm not very clear about what you said :
- CD High ? Logic Status ? (well... i know it is related to logic gate, but can you explain by giving some example what it works for)
- CD.GND / P.GND, what is it connected ?
- VDD stands for +terminal
- If the CD player power was cut out, will the radio player itself would get damaged some imbalance power ?

I wanted to replace the CD input to external input (input line), was thinking to mount a 3.5mm trs female connector, so what would be correct combination ?
Quote:
Tip terminal - L.CH
Ring Terminal - R.CH
Sleeve Terminal - CD.GND (very uncertain)
No change to "P.GND", "P.VDD", "CD.5V(CD-H)",
Would this be the correct connection ?
There is also control panel for CD player, would it affect my input sounds ? (such as the left&Right channel is not detected, so no sounds release from CD mode (which the input replace by external source)
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Old 22nd January 2011, 07:10 AM   #5
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MMhhhh..From my point of view , better install and use classic RCA cinch ,they're 'heavy duty' compared to the 3,5 mm stereo jacks .
Cutting the Vdd and Gnd (also)lines would fully disconnect the CD section ...at the very end you could physically cut the part
Usually the signal (L and R) exits the CD section with two (1---4 uF ) capacitors, so you'll have to check if the following stage is AC or DC coupled...but at 99 % also the source you'll use will be DC coupled with its own output capacitor
Digital ground and main ground (and positive ) are usually kept separate ,to prevent noises go trough the supply lines . Don't know if CD -H brings also the 5 V for the ICs..Would be useful to know ( you may use it to activate a relay which switches a device ...).
Would be also very keen of you if you take a look at the inside of the amp , and tell which model or kind is the (integrated) amp I like to keep in touch ( read : read the datasheets ) with the beast that controls my mind
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Old 22nd January 2011, 02:26 PM   #6
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LOL.... Beast within ? X.x and sorry for accidentally double-posted (wrong clicked)

Well.... naturally RCA is better in terms of heavy duty, but most of the time, my input is from computer or mp players, so i make it TRS is going to make my life easier. But i was thinking, maybe i should make it RCA then convert it to TRS, so its better ? (or is it possible to make 2 parallel input line of RCA and TRS ? which make it quite universal)

As mention in he 2nd paragraph in your post, the GND means for P.GND ? (well... sometimes i'm quite confused with those different term, so better to spell the complete name )

In the 3rd paragraph, you mention about the L&R Channel, but i don't quite get it, but is it ok to just directly connect the input from computer or other source directly to the "L.CH","R.CH" ? (which is Tip&Ring Terminal in the term of TRS connector)

In the 4th paragraph, about the digital ground and main ground, could you specific what is the abbreviation used ?(like P.GND ?)
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Old 22nd January 2011, 02:33 PM   #7
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Well.... I like to fulfill your wish for look at the Amp, but too bad i'm not good at these thingy (this thingy is kinda old system, very complicated, unlike computer internal connection, seems mixed up)
But I can take a photo of it and let you see which is it, then we can know the features and constructions.
I also have a schematic diagram of the radio, but is it legal to post it here for you ? or any forums rules against that ?
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Old 22nd January 2011, 02:34 PM   #8
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Location: Malaysia, Selangor
ohhh yeah, one more thing. I saw alot of place in the diagram have "B+", what does it stands for in electronic or audio world ?
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Old 24th January 2011, 02:57 AM   #9
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I found this manual online, i guess it will helps alot

http://www.promelec.ru/UPLOAD/xml/scheme/PHC-ZW770L.pdf




The part I mention is KH306, on page 4(bottom right corner), should be the vital piece for my project
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Old 25th January 2011, 06:46 AM   #10
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Could not resist to say : now it's time to dismantle the speaker !!
Funny thing ...I had a boombox very similar but older without cdp...same kind of amplifiers ,same VC equalizer ,but REAL switch(...a switch ! )and also Aux-CD input . Funnier thing is that the speakers were so good that now they are employed in my main speakers (helped by two woofers each).

So...good luck ! Now you have everything you need to do the changes
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