I bought an arbitrary function generator, it will do a sine wave. I need this to set my adcom 5800 bias correctly. Can someone tell me exactly how to do this on this machine, according to adcom specs, I have it set on 1khz but I don’t understand the (Ampl) on the bottom what to set it at. Also when they say input, what is that referring to?
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I don't wnat to sound rude but first up you should have read the user manual that comes with sig gen then taken a look at the front of the sig gen and thought about it before having a play (with nothing connected). It is plain that there are several functions.
The first is of course the signal generator.
One of the other functions, presumably accessed by the left/right arrows under the blue knob, is a counter (it counts the number of cycles of a separate signal fed into the input socket in a certain time period).
The LCD screen will tell which function is active and presumably also tell you the count when in that mode. In sig gen mode I presume the screen will tell you the signal amplitude, which is probably adjusted by the blue knob.
The first is of course the signal generator.
One of the other functions, presumably accessed by the left/right arrows under the blue knob, is a counter (it counts the number of cycles of a separate signal fed into the input socket in a certain time period).
The LCD screen will tell which function is active and presumably also tell you the count when in that mode. In sig gen mode I presume the screen will tell you the signal amplitude, which is probably adjusted by the blue knob.
Hi Joe,
Strange, they want you to get it hot for 5-6 minutes by making it produce power into a load, then let it cool down for 15 minutes, then do the adjustment. WAIT FOR IT TO COOL DOWN 10 MINUTES MORE, THEN CHECK FOR "DRIFT". I'm sorry but what an idiotic way to go about it... I wouldnt suppose whatever ambient temperature makes any difference... What if the bias is so out that it blows up during the 80 Watts power burn heating phase?
If it was me, I'd just adjust it to the 800 cold and leave it on all day, watching attentively what the drift does as it warms up. If you see the 800 value climbing, just back down the adjust until you get a stable value over time. Save the trouble of function generator, resistive load connections.
Strange, they want you to get it hot for 5-6 minutes by making it produce power into a load, then let it cool down for 15 minutes, then do the adjustment. WAIT FOR IT TO COOL DOWN 10 MINUTES MORE, THEN CHECK FOR "DRIFT". I'm sorry but what an idiotic way to go about it... I wouldnt suppose whatever ambient temperature makes any difference... What if the bias is so out that it blows up during the 80 Watts power burn heating phase?
If it was me, I'd just adjust it to the 800 cold and leave it on all day, watching attentively what the drift does as it warms up. If you see the 800 value climbing, just back down the adjust until you get a stable value over time. Save the trouble of function generator, resistive load connections.
It must be preheating. And they know how well the box is preserving the temperature - hence the waiting time. I would follow the instructions to the point.
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I think it’s just doing the old 1/3 power preconditioning, which checks to see if it can handle full power dissipation before proceeding to set the bias for real. I’d set it low initially, say 1/10 of what’s specified, before the preconditioning test. Some random setting may indeed be too high for that.
A good many (ie most made today) will either thermal and shut off or just blow up operated at 1/3 power sine wave for longer than a few seconds. The old Adcoms aren’t supposed to.
A good many (ie most made today) will either thermal and shut off or just blow up operated at 1/3 power sine wave for longer than a few seconds. The old Adcoms aren’t supposed to.
Amplitude is another word for peak voltage of the waveform. IIRC these cheap signal generators (no user manual typically) are calibrated for a 50 ohm load, so with a high impedance load they produce twice the voltage shown on the display - anyway try using it set to 1V, apply to aux input of the amp and use the volume control of the amp to adjust the output power. Start with volume control set to minimum to avoid nasty surprises.
Or just skip that part, I don't think its going to make any difference!
[ 83W is about 26Vrms into 8 ohms. ]
I guess that as those cheap sig gen's have so little spent on the hardware or interface design, you can't expect any time spent on documentation - For instance despite being DDS, switching frequency isn't done phase-coherent...
As others have said... all you are doing here is driving the amp hard to heat it up. Music will do, turn it up really loud and go out and shut the door for half an hour 😉
You set the amplitude on the generator to give a representative line level signal. So you could turn the volume on the amp to say 70% of full and then alter the amplitude on the generator to achieve your rated output. No mention of covers on or covers off the amp. Do you have two suitable 100w+ 8 ohms resistors?
+1 to that 🙂
I also think the method of inserting an ammeter etc is a recipe for disaster... is there no other way to derive the current such as the time honoured volt drop over a resistor method. These are the kind of scenarios we see so often on here, a perfectly good working amp that suffers some unexpected mishap.
If you type "adcom user manual" into bing, they will give you a link to the user manual on their website which you download as a pdf file. If you do not have a pdf viewer download one from irs.gov .
I have the adcom 565 manual, and it does not have a picture of the front panel. It states there are unbalenced RCA jack inputs, and balanced XLR-3 inputs. Your signal generator has a BNC coax output. That is unbalanced. You need to buy or make a BNC coax male to RCA plug male connector. If you do not know what a RCA jack looks like, look one up on a distributor website like newark, digikey, or mouser. Or download the user manual from another brand of amplifier whose manual writers are not such idiots.
Furthermore I would not trust a signal generator that came without a manual, to produce a 1 Vrms output. I would check with a VOM or scope. The only DVM that will read correctly AC scale on 1 khz is an "RMS" one, and those are useless for seeing oscillations over 7 khz, which adcoms are prone to. I use an analog VOM, a Simpson 266. You can also use a scope. Vrms =~0.7* Vpp. Use 2 clipleads to access the input signal inside chassis on the back of the RCA connector. Unfortunately the major distributors newark digikey mouser do not sell packs of 60 v rated alligator clip leads anymore. I buy them from parts-express.com . Or you can buy a pamona grabber to dual banana plugs cable. Unfortunately many meters these days have jacks that spit out banana plugs. Example the klein sold at home depot. Klein probes are suitable only for touching screws inside 460 vac electrical panels.
The proper way to measure output transistor idle bias current, is use the pamona grabbers to measure DC voltage on both ends of an emitter resistor for one of the output transistors. I=V/R where R is the emitter resistance value. Short the input while you are making this test. I would follow the adcom heat soak procedure exactly except the idiotic ammeter insertion instruction. A current on one output transistor for an amplifier with 10 output transistor pairs, will be 1/10 the current of the 10 transistors added together through the power supply link you did not remove. If your amplifier has 20 output transistor pairs on each channel, then that is 40 ma per individual output transistor pair. That is pretty extreme, and 80 ma if there were 10 pairs is rediculous. Most amplifiers want 20 ma per TO3 output transistor pair.
BTW I acquire 8 ohm 500 watt resistors by buying two 4 ohm >250 watt resistors at a distributor or surplus house, and soldering them together. I use 16 ga or thicker wire for this many watts. Takes an 80 w or bigger iron to solder 16 ga. I make a bracket out of sheet metal to penetrate the ends and hold the resistors up off the concrete step I lay them on when measuring high wattage amplifiers. Surplus houses like apexelectronics.com and surplussales.com have been cheaper for high wattage resistors than mainline distributors.
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No I don’t have 100w resistors, I have lots of resistors due to fixing car amplifiers and doing diy stuff Mr pass posts. But no never had a need for a 100w resistor. I think I’ll just run the amp with the 4ohm speakers it’s hooked to for a couple hours with my multi meters hooked up and watch the ma, I’d say after that much run time, it should be nice and warm