Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Msn I had a frrling something was wrong...I tried powering it with 2 transformers today and the opamp is messedup now. I can measure the output from the unity gain buffer fine and it works properly but the second output is ruined..I get spikes or similar.
I have been meaning to ask, how do I reduce voltage some without using a huge resistor....I have these voltage regulator componeents that are smps regulators in a package(buck regulators), they only require an inductor, few caps, and shotky diode outside of them...The ones I have are rated to supply 3 amps.
It is woerd because my oscope measured 34V DC, and my CHEAP meter measured 42! Maybe the cheap meter loaded the trasformer?
Since my regulator is SMPS and it is attenuating voltage I should have little to no loss right? Btw, I was wrong about my other transformer beeing bad...I properly measured it today. Also, I forgot, the transformer is a 12.6-0-12.6 and NOT 12-0-12...So it is about 50VA I guess. So for 20Wrms, and 50VA I should be fine right?
Question, my SMPS regulator is variable, so what voltage should I dial it to with a measured rectified DC voltage of 34V from my supply? That was measured unloaded btw..I am going to use a trimpot to vary the out voltage...
Well I figured out that it was something else wrong not my opamp....I repplaced all transistors and it works...but cannot get over 7.5v without clipping or distortion in a 4 ohm load. Maybe its the BC friver transistor's current limit?
The transistors are simply emitter-followers. Their output swing is almost as much as their input swing.
7.5V p-p? Then the peak output is (7.5V/2=) 3.75V and the peak output current is (3.75V/4 ohms=) 938mA.
At 2A the minimum current gain of a TIP41 or TIP42 is 20 so the base current is (2A/20=) 100mA that the BC547 and BC557 can handle at their maximum.
Maybe you got their emitter and collector pins connected backwards? They are 1= Collector, 2= Base and 3= Emitter while American little transistors are 1= Emitter, 2= base and 3= Collector.
I mean't 7.5V RMS...Ieven got it to 8VRMS but that was pushing it because the waveform started to distort(sinewave input).
Now I know what people mean by crossover distortion...It sound fine at lower volumes but when it get's up there in power you can tell the distortion some....I need to build that biasing network...I have tried it before but it attenuated and made the output sound horrible, is there a particular diode I should use or is anything okay?
8V RMS is 11.3V peak. Then the peak current in the 4 ohm speaker is (11.3V/4 ohms=) 2.83A. If your TIP41 and TIP42 output transistors have low but passable current gain then the poor little BC transistors are overloaded with 157mA.
Please use driver transistors that can handle the high current.
Crossover distortion is reduced at high output levels. It is bad at only a few volts of output.
You would need 4 diodes to cancel the base-emitter forward bias voltages of the 4 transistors but a single transistor and two resistors can do it and even be adjustable. The diodes or single transistor can be mounted on the heatsink of the driver or output transistors to cancel "thermal runaway" (current causes heat which causes more current which causes more heat over and over until destruction. But the diodes or single transistor turn on more when they get hot which brings down the current and heat.
I am awaiting the 2n4401/3 transistors right now so for now I will be easy on the amp.
Can you explain how to do it with a single transistor and two resistors?
I figured that the higher the volume the more the crossover distortion would be...So maybe It is a limitation distortion, probly of the BC transistors running into their limit?
Crossover distortion causes 2.8V p-p or less to be missing from the output so the level where 2.8V p-p is most of the signal has the worst crossover distortion.
That is a fairly low level. Increasing the volume reduces crossover distortion.
I joined together a couple of amplifiers to show you how to make your amplifier:
that makes sense. My distortion was comming from my source I figured out. Thanks for the schematic I want to try it..
I was wondering, what is that noise that alot of home music stereos make...it sounds like a transformer or somthing.....It's a sound you can hear through the speakers when no signal is playing because it is light but always seems to be there....it seems to have to do with the input jack or something because when I play with my 3.5mm input jack and the wire from it leading to the board it seems to be responsible. If I connect a male to male cord into the input jack the noise is much less and is uneffected by volume(higher volume= louder noise) like the noise is when no wire is plugged in. It is like a transformer sounding tone when a wire is plugged in. Can I kill all "idle noise"..well I am sure the noise is always there actually but its so small that it's only heard when no signal is running or at pauses.
On my amp, the top peaks of the waveform get distorted(fuzzy) but only at a certain position on the volume potentiometer. I can turn the pot up all the way and get a clean sine output on my scope....but at other random positions before the max turn of the pot I ge tat weird distortion. Is it because I'm running my opamp at a relatively high supply voltage or something? It's bugging me...I just switched the driver transistors out for the better 2n4401/3 and I have them in correctly EBC. I can take a pic of my scope to show you what the output looks like..
Okay I just swapped out the opamp and realize it was the opamp...I had a good opamp in first, the BBopa2134..and swapped it for a cheaper tl082..But I got not fuzzyness at the peak..Does this mean I sort of damaged the first op amp?
If the amplifier produces low frequency hum or buzzing when the source is not playing then the input wiring is picking up "mains hum" interference that is from all the electrical wiring all around. That is why all audio equipment is connected together with shielded audio cable. The shield blocks mains hum.
Also, you said you made the amplifier on a proto board. If it is a simple breadboard with hundreds of contacts and hundreds of connecting wires then of course the rows of contacts and wires will pickup mains hum. You need a compact pcb, maybe in a metal box connected to 0V.
The high stray capacitance all over a proto board also causes a wide bandwidth opamp to oscillate (produce fuzziness at the top of the waveform).
Also, many opamps including the TL082 oscillate when their output drives the capacitance of a shielded audio cable. Add a 100 ohm resistor in series with the live wire of the cable.
It honestly isn't bad...not really even noticeable unless veeery close to the speaker I was just curious mostly due to other cheap stereos I have from the store that do it.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
