Hello, i recently built a small preamp kit, and after bulding it, and firing it up, it seemed to have a tremendous amount of distortion. The distortion is plainly audible, and after checking the connections, i noticed that the ground isn't wired correctly.. Could this be the source of the problem?? Or is there something more? What would be the best way to track down this problem?? Tia
Dave
Dave
some preamp work
well today i sat down and set up the grounds properly (i think??) But unfortunately there is still massive distortion🙁 What's the next step in trying to fix this problem?? tia
Dave
well today i sat down and set up the grounds properly (i think??) But unfortunately there is still massive distortion🙁 What's the next step in trying to fix this problem?? tia
Dave
Do you have any test equipment? A signal generator, volt meter and oscilloscope are very handy to have at this point.
Later BZ
Later BZ
equipment
I don't think i have any of that stuff, but there's a possibility of a voltmeter.. What are the options at this point?? tia
Dave
I don't think i have any of that stuff, but there's a possibility of a voltmeter.. What are the options at this point?? tia
Dave
Well Dave, I or anyone else for that matter need to know more about the circuit. Just what preamp is this, a circuit diagram would help a lot. A disciption of what the distortion sounds like would help too.
You need some way to make a few measurements to find out what is going on with the circuit. With out that anything I or anyone else says would just be a wild guess.
Later BZ
You need some way to make a few measurements to find out what is going on with the circuit. With out that anything I or anyone else says would just be a wild guess.
Later BZ
distortion description
Here is the what the distortion sounds like- when you first power up the preamp, everything is quiet, and then if you start the music, it plays fairly cleanly for a few seconds. After that, the sound becomes very garbled and disgusting sounding. Hope this helps! Tia
Dave
Here is the what the distortion sounds like- when you first power up the preamp, everything is quiet, and then if you start the music, it plays fairly cleanly for a few seconds. After that, the sound becomes very garbled and disgusting sounding. Hope this helps! Tia
Dave
dead capacitors?
Hi, if there is a dead capacitor, how would it be tracked? There aren't too many of these, so even if it required some kind of testing for each of them (there are 12) it wouldn't be bad 🙂 Thanks!
Dave
Hi, if there is a dead capacitor, how would it be tracked? There aren't too many of these, so even if it required some kind of testing for each of them (there are 12) it wouldn't be bad 🙂 Thanks!
Dave
Check collector voltages wrt earth.
C of Q2 should be around 8V; C of Q1 should be around 4V.
Then measure the voltages across the emitter resistors and calculate the current flowing by Ohms Law.
Do this at no signal immediately on switch on, and follow the voltage carefully for the first ten minutes. If it changes after a short time, it's likely to be a cap. First one to look at would be C1, then C3, then C2. Often it's easier to just swap them out and see if it makes a difference. Remember, you are finding a fault quickly, not agonizing over methodology.
Cheers,
Hugh
C of Q2 should be around 8V; C of Q1 should be around 4V.
Then measure the voltages across the emitter resistors and calculate the current flowing by Ohms Law.
Do this at no signal immediately on switch on, and follow the voltage carefully for the first ten minutes. If it changes after a short time, it's likely to be a cap. First one to look at would be C1, then C3, then C2. Often it's easier to just swap them out and see if it makes a difference. Remember, you are finding a fault quickly, not agonizing over methodology.
Cheers,
Hugh
Those are all relatively small caps=cheap caps. Id simply swap them as AKSA wrote. Its the fastest way to eliminate the dead cap option.
Magura🙂
Magura🙂
replacing capacitors
Which capacitors should be replaced, the electrolytic ones, or the ceramic disc ones? A friend of mine also mentioned to me that these are very heat sensitive, and since i have a high wattage soldering iron they could have just been melted🙁 What is a good wattage iron to work with for soldering these? Also, if this preamp does turn out nice, which capacitors could be upgraded to nicer ones later on?? tia
Dave
Which capacitors should be replaced, the electrolytic ones, or the ceramic disc ones? A friend of mine also mentioned to me that these are very heat sensitive, and since i have a high wattage soldering iron they could have just been melted🙁 What is a good wattage iron to work with for soldering these? Also, if this preamp does turn out nice, which capacitors could be upgraded to nicer ones later on?? tia
Dave
How high wattage is your iron? 15 to 30 watts should be plenty for what your doing. Transistors can easly be damaged by too much heat as well as film caps.
Have you taken those voltage readings yet?
Later BZ
Have you taken those voltage readings yet?
Later BZ
voltages
Hdtvman,
Are you testing the actual voltage at the transistors themselves, or the capacitors after them? If so, which capacitors do you mean? How exactly would you do this- put the positive lead and negative lead from the multimeter on each end of the capacitor? Also, there are different voltage settings on the multimeter. Since the power supply for this project is 12v dc, would i use one of the dc settings? There are a few choices: 60v, 12v, 3v, 0.6v.. thanks!
Hdtvman,
Are you testing the actual voltage at the transistors themselves, or the capacitors after them? If so, which capacitors do you mean? How exactly would you do this- put the positive lead and negative lead from the multimeter on each end of the capacitor? Also, there are different voltage settings on the multimeter. Since the power supply for this project is 12v dc, would i use one of the dc settings? There are a few choices: 60v, 12v, 3v, 0.6v.. thanks!
Am I being stupid ...
but how are Q1/Q3 biased ????
EDIT
I think I see now
Are you feeding it with too big a signal ?
Dave
but how are Q1/Q3 biased ????
EDIT
I think I see now
Are you feeding it with too big a signal ?
Dave
signal
The input of the preamp is being fed by a Rotel Rcd-02 cd player, which is a 2 volt signal. The funny thing about the schematic for this is that there is no volume control in this, so i'm beginning to wonder if i'm using this circuit for the wrong purpose. The manual itself calls it a "stereo preamplifier" , and here is what it says for uses: "This pre-amp can be used to boost speaker sound on conventional cassette or record players where unamplified speakers are too weak to deliver audible sound. Some of its features include Stereo and Auto Gain Control. Output can be directly connected to a set of earphones." Any thoughts??
Thanks!
Dave
In other words, is this meant for driving a power amplifier??
The input of the preamp is being fed by a Rotel Rcd-02 cd player, which is a 2 volt signal. The funny thing about the schematic for this is that there is no volume control in this, so i'm beginning to wonder if i'm using this circuit for the wrong purpose. The manual itself calls it a "stereo preamplifier" , and here is what it says for uses: "This pre-amp can be used to boost speaker sound on conventional cassette or record players where unamplified speakers are too weak to deliver audible sound. Some of its features include Stereo and Auto Gain Control. Output can be directly connected to a set of earphones." Any thoughts??
Thanks!
Dave
In other words, is this meant for driving a power amplifier??
thanks- Status
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