Nuuk said:
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.
An externally hosted image should be here but it was not working when we last tested it.
Nuuk said:
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.
Nuuk said:
This is as Andrew advised. This will have to be later though.
Nuuk said: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.
Hey guys, let's all just calm down. It's too early in the morning for me
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.
markiemrboo said:
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.
BWRX said:Hey guys, let's all just calm down. It's too early in the morning for me
Heh.
I think I could even see why separate bridge rectifiers would work as you suggested, but it does indeed somehow still seem to be interacting in a very similar manner as before.
Yeah. This was my backup plan, but really I wanted to have it all off the same transformer as I said. I also did really want one regulated power amp supply per channel, but it would have to be unregulated or one for both channels. This isn't so much of a problem mind, I wouldn't be able to fit it all in the case if I had a separate transformer for the preamp and three regulated supplies.
I am hesitant to finish it off by using a seperate transformer for the power amp and pre amps, as I am currently the only person able to test things (I think). I don't really want to leave it without a conclusion, you know?
Sadly I don't have any negative regulators, and have no electronics shops near by. Postage for small orders kills me
Ok, some measurements from Andrew's questions.
With both supplies connected, the AC to AC of bridge's seem OK and "normal" at ~27v (25v transformer).
The DC output terminals of the bridges also seem OK at ~36v. I remeasured the power amp caps, and I got the same ~36v (this is probably expected).
I measured the preamp caps, and the positive side of that supply (remembering the problem is apparently with the negative rail) was at ~36v, rose pretty quickly to ~44v and then slowed down, but was (I think) still rising.
This seems strangely similar in behaviour to how the negative rail regulated output starts at -28v and drops to ~-18v then slows down dropping. The negative rail, at the output of the caps / input to the regulator is OK / "normal" at ~36v.
With the preamp regulator unplugged both lots of the caps (on the preamp side) are normal at the expected ~36v. The output of the negative rail after the regulator, as mentioned, starts at -28v and drops to ~-18v.
With both supplies connected, the AC to AC of bridge's seem OK and "normal" at ~27v (25v transformer).
The DC output terminals of the bridges also seem OK at ~36v. I remeasured the power amp caps, and I got the same ~36v (this is probably expected).
I measured the preamp caps, and the positive side of that supply (remembering the problem is apparently with the negative rail) was at ~36v, rose pretty quickly to ~44v and then slowed down, but was (I think) still rising.
This seems strangely similar in behaviour to how the negative rail regulated output starts at -28v and drops to ~-18v then slows down dropping. The negative rail, at the output of the caps / input to the regulator is OK / "normal" at ~36v.
With the preamp regulator unplugged both lots of the caps (on the preamp side) are normal at the expected ~36v. The output of the negative rail after the regulator, as mentioned, starts at -28v and drops to ~-18v.
which caps measure 36Vdc? the smoothing on the rectifier should measure 36Vdc, the power amp caps after the regs should measure +28Vdc and -28Vdcmarkiemrboo said:
can the connection between the two halves of the reg PCB be separated to create two completely independant 28Vdc supplies?markiemrboo said:
Does the swing to 44v coincide with the swing to 18v?
Is the regulator breaking down on excess voltage? 36Vdc rising to 44Vdc might be over maximum spec.
A bias building up on a capacitor?
A capacitor breaking down? you are losing 2V.
Note also that the 15V regulators are seeing a voltage drop 36Vdc -15Vdc =21Vdc with just 25mA they are getting warm and by the time they pass 50mA they are hot. I wonder if the changing voltage is a clue to an excess temperature effect?
Confirm again,
If you connect both 15V reg with the 28V regs disconnected, the +-15V supplies are OK and with a lower value dummy load (watch that dissipation).
Then with the the 15V regs disconnected, the +-28V supplies work correctly?
The 15Vdc regs can avoid some of the dissipation by adding a series R between the rectifier and the smoothing caps.
AndrewT said:
This is correct.
I have three entirely separate, but identical PCB's. Two for the power amp left and right channels with 2.2k / 100R, giving 28v and one (the preamp supply) with 1k / 100R, giving ~14v.
I'm not sure I follow here? Any chance you could you explain? I have a feeling I might be wanting to look at the scope to answer this question?
Not entirely sure. I could be being blind, but I am only seeing a 35v as a maximum "differential voltage" between "in and out". Given that "out" is currently 13.6v I think this would mean it is still in spec just about, but I am not sure.
I don't know what you mean here? Where should I be looking for this and how would I check?
Losing 2v where? You mean 27 x 1.414 = 38v and I am only seeing 36v? I thought this was a rough estimate calculation, but if it's not is this not 'diode' losses from the bridge, or does this calculation take this in to account?
Yep. I've not left it on long enough for the heatsinks to get even warm.
Not sure what you mean here either, sorry
Yeah, the +-15v (or 13.6v) supply seems just fine with the 28v supply disconnected. I've had it connected to the preamp (without other supplies connected) and the preamp works OK from it. It is only when there is another regulated supply connected that things start going haywire.
I've only got one +-28v supply connected at the minute, but that seems to be outputting the correct voltages regardless of whether the preamp supply is connected or not.
This is handy to know, thanks.
Hi,
are you powering up through a mains light bulb?
I don't want this blowing up in your face while trying to measure a series of voltages.
The caps issue.
Measure the voltage across every electrolytic with power on to find any that have an odd voltage on them.
You are looking for one that is too low or too high or reverse polarity.
are you powering up through a mains light bulb?
I don't want this blowing up in your face while trying to measure a series of voltages.
The caps issue.
Measure the voltage across every electrolytic with power on to find any that have an odd voltage on them.
You are looking for one that is too low or too high or reverse polarity.
AndrewT said:
I'm not. I know I should be.
I appreciate the [very real!!!!] concern.
Ah, now this would be why you really want me to do the light bulb thing? In this case it is next to impossible for me to do safely. No offence, but I don't think I am going to risk doing that
Unless you meant removing all of the caps and testing them one by one...
All I can say here is that unless some cap casings are marked wrong, all cap polarities are correct, and also none exploded, at least, while they were running 24/7 for about a month before hand!
Hi mark/everyone else.
I had some time to simulate the circuit that I proposed to be correct and it is in fact not correct either. The schematic in this post will not produce one properly regulated negative rail voltage (whichever desired regulated voltage is closer to ground potential between the two negative rail regulators). The larger voltage will regulate properly as will the two positive rail regulators. The circuit still suffers from the same issue as the previous one. The positive regulators work by sending a constant current (set by the resistor between the output and reference terminals) through a resistor that is tied to the circuit's reference voltage; which is normally ground. Unfortunately, using positive regulators to derive negative rail voltages means that the reference voltage is also the rail voltage. This poses problems as mentioned earlier (when trying to use 4 positive regulators to make a dual voltage split rail supply) and I can't see any easy way around it other than to give each regulator it's own separate secondary.
I had some time to simulate the circuit that I proposed to be correct and it is in fact not correct either. The schematic in this post will not produce one properly regulated negative rail voltage (whichever desired regulated voltage is closer to ground potential between the two negative rail regulators). The larger voltage will regulate properly as will the two positive rail regulators. The circuit still suffers from the same issue as the previous one. The positive regulators work by sending a constant current (set by the resistor between the output and reference terminals) through a resistor that is tied to the circuit's reference voltage; which is normally ground. Unfortunately, using positive regulators to derive negative rail voltages means that the reference voltage is also the rail voltage. This poses problems as mentioned earlier (when trying to use 4 positive regulators to make a dual voltage split rail supply) and I can't see any easy way around it other than to give each regulator it's own separate secondary.
BWRX said:
Hi BWRX,
Thanks for taking the time to think this over and come to a conclusion
I can confirm that separate transformers works, and so it's definatley not a fault with my boards or wiring, as that is how I am now running it and it is giving the correct voltages.
The only problem I have now is level balance in the preamp because of a crappy pot. I reckon I am going to go the stepped attenuator route. Still sounding good though! I am convinced it's better than the Cambridge Audio I had previously. It may just be my imagination, but I am happy is what counts eh
Cheers
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