Hi Puffin,
always test your transformer wiring first before connecting the PSU components.
Then test the transformer +PSU before connecting any downstream components.
Then test the amplifier for both DC output offset and oscillation before connecting speakers.
Do all of these tests initially with the light bulb tester in the primary feed to the transformer. Once each stage has successfully started up then test direct to mains.
always test your transformer wiring first before connecting the PSU components.
Then test the transformer +PSU before connecting any downstream components.
Then test the amplifier for both DC output offset and oscillation before connecting speakers.
Do all of these tests initially with the light bulb tester in the primary feed to the transformer. Once each stage has successfully started up then test direct to mains.
Nuuk. The problem is that there is a gremlin in the PS. The PS provides for +v, 0v and -v from a +/- secondary using a 7815 and a 7915. I got it to give me 30v rail to rail and 15v + & 15- (after initially having the problems mentioned previously.
Now for some reason it is only giving me -7v and +15. Anyway it's enough to let me get it working. So Audio1st, not ready to do a comparison yet, and I need to bould another one and sort out the PS.
AndrewT. Can you explain the light bulb test and where this should be connected. Is it on the Pos from mains, in between pos and tranny pos ?
Now for some reason it is only giving me -7v and +15. Anyway it's enough to let me get it working. So Audio1st, not ready to do a comparison yet, and I need to bould another one and sort out the PS.
AndrewT. Can you explain the light bulb test and where this should be connected. Is it on the Pos from mains, in between pos and tranny pos ?
Puffin, I presume that you mean you are using the +/-15v rails for a pre amp or buffer! If you are using the LM7915/7915 for the GC, they are not up to the job.
It would really help (you mainly) if you could give us all the details of your set up because you may damage components if you don't know exactly what you are doing! 😉
PS Have a look here for details of the light bulb trick.
It would really help (you mainly) if you could give us all the details of your set up because you may damage components if you don't know exactly what you are doing! 😉
PS Have a look here for details of the light bulb trick.
Hi Puffin,Puffin said:
if you can't understand Live, Neutral and Earth, are you safe to be left alone with building mains powered equipment?
Maybe you should get trained in safe electrical maintenance procedures.
AndrewT. It is always heartwarming to see such a neighbourly and concerned attitude. Thank you for your concern and sharing your expertise.
Hi Puffin,
I am genuinely concerned, not trying to score cheap points.
Do you really think we can leave you to experiment with mains powered projects when you appear to not know the difference between Live and Neutral?
I am genuinely concerned, not trying to score cheap points.
Do you really think we can leave you to experiment with mains powered projects when you appear to not know the difference between Live and Neutral?
AndrewT. I do know the difference between live and neutral. What is often alien to me are the practices and proceedures involved in learning how to do the things I want to with these chips and power supplies etc. I am very eager to learn, but often may appear stupid, because this is all a very steep learning curve. I have never studied electronics.
I feel very chuffed to have put together a 3886 chip that works. the power supply may be woefully inadequate, but as it managed to get some sound out of the mess I put together I thought I was doing o.k. Can 15v +/- damage an LM3886 ? I (in my naevity) thought that by erring on the side of caution with lower voltage, that this would avoid any catastrophes ?
What is the optimum +/- voltage ? 35-40v ?
Regards.
I feel very chuffed to have put together a 3886 chip that works. the power supply may be woefully inadequate, but as it managed to get some sound out of the mess I put together I thought I was doing o.k. Can 15v +/- damage an LM3886 ? I (in my naevity) thought that by erring on the side of caution with lower voltage, that this would avoid any catastrophes ?
What is the optimum +/- voltage ? 35-40v ?
Regards.
It depends on the impedance of the speakers that you are using.
I am still concerned about you using those voltage regulators! You say you want to learn but if you don't answer our questions, we are working in the dark! 😉
Nuuk. I can't really tell you any more. The PS provides +15, -15 and Ov. The speakers will be 8ohms. I am only experimenting at the moment with an old speaker.
A lower voltage supply won't damage anything as far as I am aware.
I think people are concerned because the regulators that you are using are only capable of something like 1A / 1.5A each (from memory).
However, if we were to assume that your speakers were an ideal 8 ohm load (pure resistance?), with a +/-15v supply you're probably looking at only getting about 8W RMS out of it (I think) before clipping, and this would be drawing about 1A. The regulators may get hot and would definitely require some sort of heatsinking. You also probably don't want them dropping more than, say, 10v (+/-25v supplies before regulation).
I imagine it would work though and - depending on the sensitivity of your speakers, the music and listening distance - may even be suitably loud.
Personally... I would ditch the regulators and go with a basic cap filtered split supply 🙂 +/- 35vdc is usually recommended for an 8 ohm load, and +/- 28vdc for a 4 ohm load I think. This would require a 25vac and 18vac (or 22vac) transformer, respectively.
I think people are concerned because the regulators that you are using are only capable of something like 1A / 1.5A each (from memory).
However, if we were to assume that your speakers were an ideal 8 ohm load (pure resistance?), with a +/-15v supply you're probably looking at only getting about 8W RMS out of it (I think) before clipping, and this would be drawing about 1A. The regulators may get hot and would definitely require some sort of heatsinking. You also probably don't want them dropping more than, say, 10v (+/-25v supplies before regulation).
I imagine it would work though and - depending on the sensitivity of your speakers, the music and listening distance - may even be suitably loud.
Personally... I would ditch the regulators and go with a basic cap filtered split supply 🙂 +/- 35vdc is usually recommended for an 8 ohm load, and +/- 28vdc for a 4 ohm load I think. This would require a 25vac and 18vac (or 22vac) transformer, respectively.
Nuuk. I have re-read your recent posts. I thought I had answered all your points. If I haven't then it's because I may not have understood what was being asked of me.
The transformer gives 12volts ac. This is fed to a board. Copy of Circuit diagram attached.
http://i73.photobucket.com/albums/i239/saxonsex/ps.jpg
As I said before this is only for experimental purposes and I will sort out a proper supply in due course. Apart from the supplies made for the Chipamp kit, (which are now installed) it was all I had which provided +v, 0v, -v.
The transformer gives 12volts ac. This is fed to a board. Copy of Circuit diagram attached.
http://i73.photobucket.com/albums/i239/saxonsex/ps.jpg
As I said before this is only for experimental purposes and I will sort out a proper supply in due course. Apart from the supplies made for the Chipamp kit, (which are now installed) it was all I had which provided +v, 0v, -v.
Thank you. So you are using the regulators in the supply to the LM3886.
A 12v transformer will provide about 16.92 volts after the rectifier. I'm not being pedantic here! Those regs require around 2 volts more than they output (ie 17v) to work properly. That is possibly the problem that you were talking about with your PSU!
A 12v transformer will provide about 16.92 volts after the rectifier. I'm not being pedantic here! Those regs require around 2 volts more than they output (ie 17v) to work properly. That is possibly the problem that you were talking about with your PSU!
Nuuk. O.K I now understand !. I have a 30+30 tranny. The 7815/7915 should take a max of 35v input voltage. Should I try using this tranny ?
The tidier version
http://i73.photobucket.com/albums/i239/saxonsex/newBd.jpg
The tidier version
http://i73.photobucket.com/albums/i239/saxonsex/newBd.jpg
Hi Puffin,
the PCB you posted is designed to use a 4 diode bridge rectifier fed from a centre tapped transformer.
It is presently working with half wave rectifiers for each polarity.
The ripple will be enormous this way , with the result that the regulators will be in drop out mode much of the time.
Judging by the relative sizes of the components this looks like a low current PCB for powering a few opamps, not for a power amp.
Remove the PCB and build a simple PSU.
Buy a centre tapped or dual secondary transformer. 22Vac+22Vac 100VA to 160VA for single channel or 200VA to 300VA for two channels for driving stereo into 8ohm speakers. 25Vac+25Vac would also drive 8ohms but would be too high for the now common 4 to 8ohm speakers that have become very popular over here.
Use a 4diode bridge rectifier and a pair of smoothing capacitors.
These can all be hardwired together, you don't need a PCB nor do you need any regulators.
You may find it worthwhile, if building a two channel amplifier, to use dual bridge rectifiers fed from a dual secondary transformer. This seems to be the better way to avoid hum in a 2channel amp.
the PCB you posted is designed to use a 4 diode bridge rectifier fed from a centre tapped transformer.
It is presently working with half wave rectifiers for each polarity.
The ripple will be enormous this way , with the result that the regulators will be in drop out mode much of the time.
Judging by the relative sizes of the components this looks like a low current PCB for powering a few opamps, not for a power amp.
Remove the PCB and build a simple PSU.
Buy a centre tapped or dual secondary transformer. 22Vac+22Vac 100VA to 160VA for single channel or 200VA to 300VA for two channels for driving stereo into 8ohm speakers. 25Vac+25Vac would also drive 8ohms but would be too high for the now common 4 to 8ohm speakers that have become very popular over here.
Use a 4diode bridge rectifier and a pair of smoothing capacitors.
These can all be hardwired together, you don't need a PCB nor do you need any regulators.
You may find it worthwhile, if building a two channel amplifier, to use dual bridge rectifiers fed from a dual secondary transformer. This seems to be the better way to avoid hum in a 2channel amp.
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