QuestionQUESTION: I had asked about repairing a amp and informed you that the part # WAS AFZ34N. Sorry. The part # IS RFZ34N which you probably recognized as soon as you read it. Once again I apologize for the inconvenience.
ANSWER: RFZ34N seems to be a small power FET transistor. It probably has many equivalent devices that can be substituted if you know the parameters of the amplifier circuit.
What is the question? I got previous question from you about the amplifier going up in smoke. Does this question relate to that one? Please explain.
---------- FOLLOW-UP ----------
QUESTION: Yes, this the same amp. The FET was source of smoke. Checked power connections at time of disconnect BUT it happened so fast that I am not 100% certain that power was connected properly and connection was in a difficult place to see. I would assume that the FETs are insulated from the heat sinks ( thus the white grease (D.E. I assume) and paper). Is it possible the FET grounded through the heat sink or more likely they could fry from improper power connection. Because of power requirements I am looking at installing a isolated 24V (4 battery) supply and would like to know if there is a instructional site where one can go to to learn how to build a high amp 15V choke for the 3 amps,1-1000w and 2-1200w.Thank-you for your time, help and KNOWLEDGE As far as ratings go ***** out of *****
ANSWER: Yes, there is a potential short between the case of the FET and the heat sink. It can be due to a faulty washer or bare wire that is too close to the metal parts of the chassis. But, I lean towards improper battery connections. Most amps, mostly the less expensive ones who have less knowledgeable users, have diodes in the power line to make it harmless if the supply voltages are reversed. In the more expensive units they do not do that because the diodes rob some voltage in the forward conducting mode.
What do you need the choke for? For crossover networks there are lots of online helps available. For battery supplies you generally do not need a choke for ripple reduction. But, for whatever you are thinking about you need to know what dc resistance you can tolerate (resistance of the wire used in the winding) and the inductance in Henry units or mH. Then you can go about googling for design ideas and formulae. The design requires you to know what form factor you are going to use as well; iron core, toriod, air core, ets. Application will dictate what type you need. If passing audio levels of significant power you must consider saturation levels, hysterisis distortion and such if using iron core or other metal cores. Air core is best but requires very big coils with lots of wire and therefore lots of resistance unless you use very big wires - which makes the coil very large. Does that make sense?
One last thought; if you are thinking to power the amps off one set of batteries, you would not be advised to isolate them with chokes. Why? That increases the impedance looking back from the amplifier and effects the low frequency power response to some degree. But, let me know more specifically what you are wanting to do and we can go another round on it.
Cheers.
PS: Sorry about the ratings. I shut it off because I just got tired of reading them and it was taking up too much time - both for me and for the system and for the readers......
---------- FOLLOW-UP ----------
QUESTION: With the 3 amps (1-1000/2-1200) I should have a max draw of 110 amps.If I am correct these units should ideally run at 14.5V (10.5-16V). This unit is eating batteries and alternators quicker than a tour buss full of dieters at a buffet. I am running a 120A alt. with 1 (12V)deep cycle tractor-trailer bat. and its not enough so I was thinking that I could mount a 24V/160 amp. alt. and 4 batteries. Then all I would have to do is cut the feed back to 14.5-15V from 24V for my supply. Thinking is that this should maintain optimum voltage and be able to maintain required amp. draw. Connecting 12V from this would give me the capacity but in a short while not the voltage, same old problem. As for FETs..Thank-you very much..replacing them in short order. The head unit-- since its so far away that's a storm for another day. All I can say is that it sure is nice to talk to someone who has a open knowledgeable mind. Still 5/5
AnswerYes, you need lots of current to power up so much audio output power. But, I think your calculations are off. If the max draw were 110 amperes that will produce only about 1300 watts total (12v times 110 amps; or 13.5v times 110 amps for 1485 watts).
But, you are talking about 1000 plus 2 times 1200 = 3400 watts of audio. To get this you need to pull 3400/13.5 = more like 250 amperes.
I think you need more than twice the current you are estimating! That is not impossible, it just requires a bigger power plant from your vehicle. You can see that a 120 amp alternator is inadequate if you are driving the amps hard. For soft background music where the amps are idling at low power it would be alright. But, for cranking levels you will need lots more power whether it is coming from a bigger alternator plant or additional batteries doesn't matter - you just need a bigger supply.
Batteries stay pretty much to full voltage until they are near discharge when they fall off rapidly. Most amplifiers work pretty well and do not show any sign of distortion or strain until voltage drops below 11v or 10.5v. They are called 12v batteries because that is where the voltage settles under normal conditions. The 13.5 voltage is what it takes to charge them up.
However, the amplifier's audio power output may vary a little as the batteries discharge but it really isn't audible because the human hearing does not distinguish a change in loudness until at least 2db change in the power. The change in output from 12v to 11v is less than 2 db.
So, I think your problem is not enough current to drive those big amps.......
Cheers.
