[quote author="plexirob"]so the best way making a perfect clone, would be to first to buy the orignal unit, and then measure every component one by one. Check voltage/frequence in different stages in the unit etc?[/quote]
Well, having an original unit always helps make a better clone, but I was actually talking about just looking at the schematic and quickly estimating the bias currents. You don't need an actual unit in front of you to do that. You know that the voltage at any given point, be it DC or the AC audio signal, cannot be higher than the voltage from the power supply (usually +24 or +/- 15V or some variation). You know that a resistor limits the amount of current which can pass through and also has a certain amount of voltage drop across it. You also can keep in mind that it is rare for any single transistor to draw more than 10mA (or more like 3 -7mA) current from the power supply... except for the output transistors which may be driving a large line level signal through a hefty output transformer. Combine this with all the losses from the accompanying passive components are you get the total current draw, which you already seem to know. Using ohms law and keeping these key factors in mind, you can quickly calculate or estimate what kind of operating conditions the components are seeing based on the schematic diagram.
I am confused when you say 'measure the frequency'. Perhaps you are too? Understand that there are two types of voltages in audio circuit. 1) DC (direct current), which is 0 Hz, and comes from the power supply (the transistors "shape" this flat line into a larger copy of the squiggly line which is your audio). 2) AC (alternating current), usually measured in RMS. This could be the AC power coming from the wall which is either 50 or 60 Hz, or this could be the audio signal and associated noise which encompasses an entire spectrum of frequencies from about 15Hz and upwards. Unless you're feeding single frequency test tones through the unit you will not able to measure the frequency. Music is complex waveforms, tons of frequencies at once. The AC from the wall and the AC that is your audio signal are both measured in RMS (root mean square). A +4dBm line level signal is only 1.23VAC, and it is very rare to find audio levels as high or higher than +26dBm, which would be about 15.5VAC.
At least i know what I'm gonna be busy with, learning electronics.
Very busy! Reading all the great stuff on this message board could take a year... and then there are so many great books and articles out there. DIY is addictive!
Maybe you could help with another problem I'm on a power supply transformer hunt. The distrubutor only specifies the tranformer like this:
2x24 V 80VA
What I need to know if it can produce 500mA, is there a formula that I need to know?
2x24 means it has two secondry windings, each providing 24 VAC. This can also be written as 24-0-24, because that's what you'd have if wired them in series and called the ceter terminal ground (aka 0V).
There are many ways to wire a mains transformer.
The 80VA means 80 Volt-Amps. This tells you it can provide 80V at 1 amp, and determines the size of the transformer. So at 24V that transformer would be capable of providing roughly 3.3Amps. Obviously 80VA is much more than you need for your 1/2Amp @ 24VDC and you should get something smaller.
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Anyway, I'm not very knowlegable compared to many folks on this message board and the things I've justed dicussed are only the tip of the iceberg. I'm going to shutup before I give out misinformation. If you want to learn audio electronics you should click on the .:Meta-Meta:. link at the top of this website and start reading. The "Electronics 101" and "useful information for newbie DIYers" are good places to start. You'll also find that almost any project-specific question has already been asked 5 times, and if it's not in the Metas you can search for it.
