![]() ![]() ![]() Does this give me a clue as to the appropriate bias current? Otherwise, how do I know what my bias current is, to determine whether the resistors are at their optimum voltage? If schematics are needed for this, they're not available - so can this value be estimaed based on an educated guess?Ģ. (The other two shown off to the side measure 0.00!). 22ohm resistors as between 3.3mV and 3.5mV. Without having adjusted anything, I measure the four. But I don't quite have enough info to do this yet:ġ. Thanks for lifting off another veil of darkness. PICTURE OF ONE TYPE OF 2-LEG (SINGLE) EMITTER RESISTOR: PICTURE OF THE INSIDE OF MY Rotel 820A AMP: The other thing I'd still like to know is if and when I find the emitter resistors, where exactly do I attach the probes to determine the bias value, and what sort of readings might I be looking for? It looks very much like a pic I saw of a sealed, multiturn trim pot, so I'm guessing this is not a dual emitter resistor (plus it isn't very near all the output devices). There are two large capacitors and this device can barely be seen located behind the right cap. The only other part that looks significant has 3 legs and large black plastic top (the left corner rounded), marked with a "+ -", (PBL403). The markings of the beige resistors are: 2WJ, 8NA, 8NO and all are rated. ![]() Can you or anyone else take a look at this pic (below) of the inside of my Rotel, and spot the emitter resistors? If single emitter resistors have 2 legs, then I figure they'd have to be those large beige resistors, situated near the output transistors (there are 4 of them in a row, and 2 more off to the side). If emitter resistors aren't mounted to the heatsink, then I guess they would have to be the output transistors that I described. which of the legs of which ER), and if I should take the reading on my DMM voltmeter at DC setting? Thanks! So I'm not sure where should the probes go (ie. I presume its 3 ER's per channel (2 large, 1 small). There are 3 legs per resistor, which makes 18 legs in all. So if I understand correctly, the DC Offset measurement I took at the speaker output with my auto-range DMM voltmeter will not change with an adjusment of the BIAS trim pot, that the pots only change the values at the Emitter Resistors (ER).Īttached to the large heat sink, there appear to be two pairs of large emitter resistors (inside pair marked: DE 1047 8L2, outside pair marked: BE 817 8M4) and one pair of tiny emitter resistors (DF ? 8K). There are only two adjustment pots on the PCB, and they're both for BIAS. It doesn't seem much of a risk, since the amp hardly puts out any heat however long its on (even covering the air vents with thick padding, the heatsink still doesn't get very warm). I'm not really concerned with maintaining the original manufacturer's specs (which I don't have anyway), because my goal here is to adjust the bias trim pot so I can run the amp a little hotter, and hopefully improve the sound. My question is, can I go by this speaker output measurement to assist me in knowing how far to go with adjusting the amp's bias trim pot, or do I really need to be measuring the legs of an emitter resistor etc? And if I can use the speaker output measurement, which would presumably change as I adjust the bias trim pot, what voltage should I be looking to acheive, or what voltage should I stop at, to avoid blowing my amp (which I believe has no thermal protection for reasons of sound quality)?ītw, I don't have schematics and not interested in acquiring them wouldn't know how to read them anyway. I did measure the DC at the speaker outputs with a voltmeter they read about 58mV for one channel, about 64mV for the other. So I'd like to know if there's a real simple way to do it, as I don't have an electronics background. The amp does not heat up even after hours, so it seems like there's enough leeway to increase the bias. I'm thinking of adjusting the bias on my Rotel (class a/b) amp to try to improve the sound.
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