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noobman92 26th November 2010 07:55 PM

reuse cassette player equalizer
 
hey guys
i am new to this forum, and new to DIY audio stuff overall. Though i have soldered together a few audio projects (headphone amplifiers, audio transmitters).

i need to build a 3 band equalizer circuit for my headphones (Sennheiser HD212Pro), with ipod nano 5th gen as the sound source. i found a working vintage philips stereo radio recorder (Philips 15DR669) which i opened up.i found the equalizer mounted on a separate plate with 3 bands + one Volume Control (i guess potentiometers).the equalizer circuit was connected to the motherboard (with all the amplifiers) using six cables (black red yellow, then again black red yellow). The equalizer circuit contains two transistors (one is BC148, it has HC148B visible, the other one has digits erased), i can post the amplifier ICs on the motherboard if needed. how can i use this circuit as a headphone amplifier? what are the six cables for? is it like input then output? but then how does this circuit get its voltage? please note, i tried collecting data on equalizers but failed at the point where i needed to know how thay are connected in these cassette players. can i use this as a headphone equalizer? or maybe use it in conjunction with a diy amplifier? i need crystal clear sound, and precise, visible control over the sound that reaches my heapdhones. thanks in advance
please be paitent, if any data is needed, i can post it.

picowallspeaker 26th November 2010 09:22 PM

If the identification of the path of each one of the six cables is the problem,
I may help you :)
2 are left and right channels entering the circuit
2 are left and right channels that go out
1 is the Ground (also supply - negative )
1 is the positive of the supply (+)

Just check the voltage of the supply (could be in between 10 to 30 V ...)

noobman92 28th November 2010 12:49 PM

thanks for the quick reply picowallspeaker
can i also use this equalizer board with a diy headphone amplifier? i am thinking of building a CMoy for my Sennheiser HD212Pro headphones.would these things work well together?
also, i put the board back on the Philips stereo recorder i took it out from, and i notice a constant hum in the background. in the radio mode, auxiliary mode, and the tape mode too. is there a problem with the player? or is it that these old players were built that way?

picowallspeaker 28th November 2010 02:25 PM

Hum may depend on many things . It may be lack of shielding or ground loops ,but also faulty capacitors in the power supply (if the apparatus is very old ,it is likely to be that ). Even ,when you put back where it was ,you omitted to solder the wire that connects the ground to the chassis which acts like a shield.
General warning also ...is better that you do the experiments with low cost DIY things as there won't be great losses if something fails :little chip-based amplifiers and cheap speakers (like early PC gear)may be good . No good to try devices with earphones on as they may destroy your ears :cannotbe:
Well ,I'm not expert , but it is better to know what's behind and after each stage of a circuit ,and get the knowledge to some basic stuff like DC or AC coupling of the stages , impedance and ratings ( max voltage and current of the components in the circuit )and also layout etc. etc.etc.
So , for a precise answer to your question ,you should post the circuit on the forum and see if it may work .


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