I was wrong in the post above, after a second look it's pretty obvious that the ne5532 chips are dual channel... doh!
Checked the voltages on the ne5532 chips - one of them stays cool (U102) and gives the full 15V on pin 4 and pin 8. The other only has -3 and -1 volts on pin 4 and 8 (U105) and gets quite warm while the amp is switched on. I'm assuming that this is the broken one.
Can I assume that this is simply a voltage drop due to a toasted ne5532 chip? Or is it likely to indicate a busted 15v regulator? Can this be fixed?
If the regulator can't be fixed, perhaps I can patch the supply from the U102 regulator onto the new U105 chip instead?
I found some 16mm pots that look similar on rapid electronics. The balance knob in the diagram is a 20K one so I am getting a 47K one as this is the most similar I can find. I will also get some sockets, thanks for that suggestion reddish. (Is this the right sort of thing: http://www.rapidonline.com/Cables-C...ow-profile-DIL-IC-sockets/63772/kw/dil+socket ?)
I'm learning loads about amplifiers here, this is great. I might consider trying to build my own amplifier once I've fixed this one. (Of course I should be revising for my second year physics exams instead
)
Sam
Checked the voltages on the ne5532 chips - one of them stays cool (U102) and gives the full 15V on pin 4 and pin 8. The other only has -3 and -1 volts on pin 4 and 8 (U105) and gets quite warm while the amp is switched on. I'm assuming that this is the broken one.
Can I assume that this is simply a voltage drop due to a toasted ne5532 chip? Or is it likely to indicate a busted 15v regulator? Can this be fixed?
If the regulator can't be fixed, perhaps I can patch the supply from the U102 regulator onto the new U105 chip instead?
I found some 16mm pots that look similar on rapid electronics. The balance knob in the diagram is a 20K one so I am getting a 47K one as this is the most similar I can find. I will also get some sockets, thanks for that suggestion reddish. (Is this the right sort of thing: http://www.rapidonline.com/Cables-C...ow-profile-DIL-IC-sockets/63772/kw/dil+socket ?)
I'm learning loads about amplifiers here, this is great. I might consider trying to build my own amplifier once I've fixed this one. (Of course I should be revising for my second year physics exams instead
)Sam
Yep, the warm one with hardly any voltage will be the duff one. It is probably shorted internally and that is why the power pins are low - the regulators have short circuit protection and will have limited the current, causing a voltage drop.
Pull the busted NE5532 out and then check the voltages from the regulators with no chip there. If the regs are fried, well they're only cheap too. They are 78L15 for the +15V and 79L15 for the -15. 20p for the 78L15 and 28p for the 79L15 🙂
The damage could have been a lot worse. We all make mistakes!
If you are really keen for learning about how amplifiers work, Rod Elliot has a great set of articles at his page.
Pull the busted NE5532 out and then check the voltages from the regulators with no chip there. If the regs are fried, well they're only cheap too. They are 78L15 for the +15V and 79L15 for the -15. 20p for the 78L15 and 28p for the 79L15 🙂
The damage could have been a lot worse. We all make mistakes!
If you are really keen for learning about how amplifiers work, Rod Elliot has a great set of articles at his page.
Thanks Jaycee, I couldn't find any suitable pots so I'll just leave the balance broken. I never use it anyway.
Got a couple of ne5532s, a pair of sockets and 78/79l15 chips on order just in case.
Let's hope we can get sound out of this thing soon 🙄
Thanks again for the help!
Sam
Got a couple of ne5532s, a pair of sockets and 78/79l15 chips on order just in case.
Let's hope we can get sound out of this thing soon 🙄
Thanks again for the help!
Sam
It should be possible - if you had damaged the power amps any further, I would have said it's scrap due to cost... but the preamp in the Cambridge is very simple and the opamps etc are dirt cheap.
It works!
I couldn't find a pot for the balance control so I just glued the plastic knob onto the chassis for aesthetics. Apart from that, the amp works perfectly. It sounds great!
Thanks so much Jaycee for your help, couldn't have even got close to fixing it without your patient guidance.
Sam
I couldn't find a pot for the balance control so I just glued the plastic knob onto the chassis for aesthetics. Apart from that, the amp works perfectly. It sounds great!
Thanks so much Jaycee for your help, couldn't have even got close to fixing it without your patient guidance.
Sam
Yeah I only needed to replace the op amp - I put a socket in so I can replace it again in future as well if I have to.
The amp sounds just fine, I trimmed the bias pot to 13mv and it seems to be working ok.
I'm pretty happy with it overall, £5 spent on repairs isn't bad for this amp.
Thanks again
Sam
The amp sounds just fine, I trimmed the bias pot to 13mv and it seems to be working ok.
I'm pretty happy with it overall, £5 spent on repairs isn't bad for this amp.
Thanks again
Sam
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