Just a quick power supply capacitance question

[Nuuk]

For the preamp I replaced the 2.2k with a 1k. This gives (when working on its own) +-13.6v.

This may not be relevant but I would expect nearer to 15 volts with 91R/1K!

[markiemrboo]

Originally posted by Nuuk


This may not be relevant but I would expect nearer to 15 volts with 91R/1K!

No, well spotted.

I should have looked carefully at the diagram myself. I couldn't find 91R resistors, so I am using 100R's. That is, 100R + 2.2k and 100R + 1k.

Sorry for the confusion!


EDIT: For the power amp I am using 'commercial' metal cased bridge rectifiers, not MUR860's, and multiple 2200uF caps, not a single 4700uF. For the pre amp I am using 1N4007 DIY rectifiers (a possible source of error, so picture attached) and multiple 680uF caps.

Diodes on all regulators I have used 1N4007's.

[Nuuk]

I should have looked carefully at the diagram myself. I couldn't find 91R resistors, so I am using 100R's.

That's exactly why we are hustling you for what you have done, rather than the circuit diagram that we have used and know is correct.

[Nuuk]

For the pre amp I am using 1N4007 DIY rectifiers (a possible source of error, so picture attached) and multiple 680uF caps.

I don't think you have a problem with that IN4007 bridge but just check the voltage across those 680 uF caps.

[AndrewT]

Hi,
that 10k dummy load you first tried is not as bad as first feared.
The 100r draws 12mA through the reg + another 1.5mA/2.8mA through the dummy load.

[markiemrboo]

Originally posted by Nuuk


That's exactly why we are hustling you for what you have done, rather than the circuit diagram that we have used and know is correct.

I'm trying my very hardest to stay calm and patient, and till you said this I was getting along just fine. This is where things start to stress me out, because AFAIK "correct" by your terms means you have built it, but only with supplies which are set (by said resistors) to give the same voltages post-regulation.

I am still confident that if someone else were to actually try what I am trying, with one supply set to give different voltages than the other, you would no longer be saying you know it is "correct" and you would see for yourself what I am seeing.

For a single supply, yes, I totally agree. It works absolutely fine. It is correct. Until I tried with one supply giving different voltages, yes, both supplies were measuring correctly and I was none-the-wiser, even though they were apparently indeed "wrong", as BWRX has explained.

I am indulging in this debugging process because I know full well I am capable of error (being "only human" after all), very very likely even more suspectible to error being a newbie, you are also after all the experts, and [I like to think] I have an open mind. From what I gather you have accepted, after BWRX's explanation, that the first diagram was in error.

I can understand why it is hard to accept that I am still seeing the same behaviour, even after implementing his initial solution. You obviously have respect for BWRX. I can tell that he certainly has far more electronics knowledge than I, and so I can understand fully why this would point to an error made by me, rather than by him. It is far more likely I made the error. At the same time, I know BWRX is, as I am, also capable of error, and that an explanation of the problem doesn't necessary mean the initial solution is correct. I've often thought I had a solution to a coding problem, and it didn't work as I expected.

As I have said before, I don't care if I am "wrong". I even hope I am wrong about all this. I hope it's a wiring error, or some other error on my part. I hope it's possible to do.

Originally posted by Nuuk


I don't think you have a problem with that IN4007 bridge but just check the voltage across those 680 uF caps.

This is as Andrew advised. This will have to be later though.

[markiemrboo]

Originally posted by AndrewT
Hi,
that 10k dummy load you first tried is not as bad as first feared.
The 100r draws 12mA through the reg + another 1.5mA/2.8mA through the dummy load.

Ah, ok. Good to know. This would probably explain why, without the dummy load and individually I was seeing the correct output voltages then?

I will still measure voltages of caps and rectifiers as soon as I can.

[Nuuk]

OK Markie, you seem to have a problem with me trying to help, so I'll bow out now and hope that Andrew can help you sort out this problem.

Good luck!

[markiemrboo]

Originally posted by Nuuk
OK Markie, you seem to have a problem with me trying to help, so I'll bow out now and hope that Andrew can help you sort out this problem.

Good luck!

Not so much a problem with you trying to help, and I hope the post didn't offend you.

It is more a problem (possibly just to do with my personality / mentality or something and nothing to do with you at all) of insisting that I am wrong without any thought at all that BWRX's solution is actually at fault, and we don't know why yet. The stress effect I am currently experiencing from such an apparently harmless post may have been amplified by previous "****-taking" / winding up. If I have reacted inappropriately I hope the mods will sort it out. I'm not too good with stress.

Anyway, as I said, I can certainly see why it points to me being wrong, Andrew also thinks this should work, and I'm not giving up in the debugging process and trying to find out where I might be wrong

I will certainly quite happily try any suggestions you might think of, but if I have scared you away then thanks for the luck. I might also add that without you hassling we wouldn't have known I was using 100R resistors, and this helped Andrew. It is certainly good that you nitpick and you going would be a loss to the thread.

Should the thread come to a conclusion and you no longer follow it, I will shoot you a quick PM so you can read it and, if it wasn't just an error on my part, update your site.

[BWRX]

Hey guys, let's all just calm down. It's too early in the morning for me

Originally posted by markiemrboo
At the same time, I know BWRX is, as I am, also capable of error, and that an explanation of the problem doesn't necessary mean the initial solution is correct.

I most certainly am capable of error, and the "correct" schematic I posted may in fact contain error. It was correct as far as I could see, which isn't much at times.

From what mark has explained thus far I do not think he has miswired anything. Clearly the regulators for the negative rail are interacting because they share the same secondary even though they are isolated by separate bridge rectifiers.

I didn't get a chance to think about this last night and probably won't again until the weekend. Luckily others are willing to help out as well!

Until then, using a different transformer with dual secondaries for the preamp regulators will definitely, without a doubt work and is a better solution. Another option would be to use positive regulators for the power amp rails and then use a positive and negative regulator for the preamp rails. That will also work.