jrockhead said:
Whoa, if you have 1 big star ground that you are bringing everything to (both audio grounds and power grounds) then you are certainly misunderstanding what the DIY book says and it is the cause of your hum.
leadbelly said:
Yeah, you are not kidding. But unfortunately I re-read the power supply chapters in both of his books and it has the signal grounds and the power supply grounds connected to the same point, star ground.
He even states that you the builder in MOST cases don't need a ground lift or anything like that IF all is implemented properly. Properly???Still working on it......
But to clarify what I mean by a small 60 Hz. hum, with a shorted input to the pre-amp and the pre-amp output connected to the main amps, and the volume pot at full signal input I have a 5 millivolt peak to peak hum at the speaker outputs. So small I can't hear it but I can only see it on my scope. Worst case scenario in regards to noise and hum. No change with an open input so I guess the layout is pretty good.
I'm striving for perfection here or as close as possible. I rebuilt the switching inputs with relays and added metal shielding to the pre-amp and relay boards, removed about half of the signal shielded cable so the signal path is as short as possible.
I then re-routed and removed signal ground returns, moved the mains power switch to the rear panel, basically did everything I could think of to lower noise and hum and I got it down to 5 millivolts from 15 millivolts p-p.
So the last little bit will only come in small increments and that is why I asked about the speaker returns. I THOUGHT I had the optimum connections and I was out of ideas. I tried isolating the signal grounds via a 4.7 ohm resistor and a .01 cap and the hum got worse. But if I had a ground loop with the speaker returns that might booger things up and fool me.Have to go back and try some new ideas that you guys gave me.
Best Regards, Marcus
I still don't know for sure if I should use 2 or one bridge('s), so if anyone could shed more light on this...?
Lucky enough I found two inductors in the garage, steel laminate, with the number
201 175Z1108 on it and the number 30 too, a bit further and smaller written.
Its dimensions are (steel laminate core only) 55mm wide, 66mm high 23mm thick
With the windings, the thickness is about 44mm
height of the winding 30mm and 41mm wide.
thickness of the wire is 1.7mm, incl. the varnish , that calculates to 2.27mm²
So I think this is 14 gauge wire (1.63mm / 2.08mm²)
With a basic DMM I measure no resistance at all, even if I put both in series, still 0.0 Ohm...
How can I estimate the inductance of this inductor?
Should I put one inductor in the 0V IF I'm using the center tap method? Which I'm still not sure if it would be the better way.
(This PSU would be used for a 5 channel system for DVD, high pass at 80Hz)
I did a simulation and it's difficult to get a low ripple.
CLC of 15mF - 2.2mH - 5.6mH looks reasonable, but not satisfying 🙁
(I used a current loading of 6A on this 160VA sim, almost the maximum of the toroïd.)
I have those cap's already and inductors too if those described above should turn out to be about that size? 🙄
Discovered this:
0.5V ripple on a 40V rail is not that big of course; 1.25%
0.5V ripple on a 12V rail is a lot worse; 4.17%
What ripple % is acceptable??
I have received the bridge's: KBPC3506 😎 (35A 600V)
Thanks!
Lucky enough I found two inductors in the garage, steel laminate, with the number
201 175Z1108 on it and the number 30 too, a bit further and smaller written.
Its dimensions are (steel laminate core only) 55mm wide, 66mm high 23mm thick
With the windings, the thickness is about 44mm
height of the winding 30mm and 41mm wide.
thickness of the wire is 1.7mm, incl. the varnish , that calculates to 2.27mm²
So I think this is 14 gauge wire (1.63mm / 2.08mm²)
With a basic DMM I measure no resistance at all, even if I put both in series, still 0.0 Ohm...
How can I estimate the inductance of this inductor?
Should I put one inductor in the 0V IF I'm using the center tap method? Which I'm still not sure if it would be the better way.
(This PSU would be used for a 5 channel system for DVD, high pass at 80Hz)
I did a simulation and it's difficult to get a low ripple.
CLC of 15mF - 2.2mH - 5.6mH looks reasonable, but not satisfying 🙁
(I used a current loading of 6A on this 160VA sim, almost the maximum of the toroïd.)
I have those cap's already and inductors too if those described above should turn out to be about that size? 🙄
Discovered this:
0.5V ripple on a 40V rail is not that big of course; 1.25%
0.5V ripple on a 12V rail is a lot worse; 4.17%
What ripple % is acceptable??
I have received the bridge's: KBPC3506 😎 (35A 600V)
Thanks!
What is the 160VA toroid voltage?
6A continuous output sounds too high.
A 160VA 12V+12V (6.6A+6.6Aac) transformer after derating for capacitor filter input becomes a 3.3A+3.3Adc PSU.
6A continuous output sounds too high.
A 160VA 12V+12V (6.6A+6.6Aac) transformer after derating for capacitor filter input becomes a 3.3A+3.3Adc PSU.
The Idea of chokes is to stop various forms of PSU noise getting into the amplifier.
In a regular TR / bridge / cap supply when the diodes switch off, VHF ringing is induced in the secondary coils of the transformer. This ringing is one of major sources of bad sounding solid state equipment.
A snubber circuit ( 0.1 - 1.0uF & 60ohms ) across the secondary will stop this ringing - this makes a massive impact on sound quality.
Without the snubber cct, 2 inductors will not be fully effective because the VHF noise in the secondaries will sneak in up the earth lead.
Even with the snubbers you will still get a better result with 2 bridges & 4 inductors because there are still other sources of noise that is best kept out of the amp e.g. mains born noise.
With four chokes and no snubbers the noise levels will be better than with two chokes but if you want the best value and least work fix then the snubbers alone are clear winners.
My inclination would be to use all these measures.
You may think all this is over-the-top . . . . . . and I think you would be right I guess you just have to decide if you want good or excellent results . . . . 😉
In my experience I have always found that measures to reduce noise are well worth the effort.
Good Luck
In a regular TR / bridge / cap supply when the diodes switch off, VHF ringing is induced in the secondary coils of the transformer. This ringing is one of major sources of bad sounding solid state equipment.
A snubber circuit ( 0.1 - 1.0uF & 60ohms ) across the secondary will stop this ringing - this makes a massive impact on sound quality.
Without the snubber cct, 2 inductors will not be fully effective because the VHF noise in the secondaries will sneak in up the earth lead.
Even with the snubbers you will still get a better result with 2 bridges & 4 inductors because there are still other sources of noise that is best kept out of the amp e.g. mains born noise.
With four chokes and no snubbers the noise levels will be better than with two chokes but if you want the best value and least work fix then the snubbers alone are clear winners.
My inclination would be to use all these measures.
You may think all this is over-the-top . . . . . . and I think you would be right I guess you just have to decide if you want good or excellent results . . . . 😉
In my experience I have always found that measures to reduce noise are well worth the effort.
Good Luck
Your amp will be very silent if u use two bridge rectifiers(explained in one thread by top brass, can't find it)
Gajanan Phadte
Gajanan Phadte
Thank you for the replies.
I think it would be better if I came up with some drawings now, it's difficult to put everything in text only.
What program should I use that is simple enough for beginners? 🙂
That 'top brass' article is something I'd like to read, switching to google now.😀
I think it would be better if I came up with some drawings now, it's difficult to put everything in text only.
What program should I use that is simple enough for beginners? 🙂
That 'top brass' article is something I'd like to read, switching to google now.😀
O... forgot to say, it is 12V and 6.66A per secondary. (±13.5V unloaded)
So my maximum power simulation at 6A is wrong then... Good to know!
Is that because the output of the amp is divided over the two secondary windings, each a half sine?
This load would be a class A situation, but I like to simulate for the worst to be save.
Those inductors would be to reduce the voltage ripple even further, not really to get the VHF out but of course, that's a nice bonus.
First I would like to know if someone can throw a guess at the description of the two inductors described above please? that would be great to know because I'm not planning to buy a lot anymore, trying to do it with stuff I have from years ago and buying only the necessary stuff.
Thanks.
(Maybe I should start another thread for those inductor question, since not everyone that might know the answer, is also reading this thread → completely different title.)
So my maximum power simulation at 6A is wrong then... Good to know!
Is that because the output of the amp is divided over the two secondary windings, each a half sine?
This load would be a class A situation, but I like to simulate for the worst to be save.
Those inductors would be to reduce the voltage ripple even further, not really to get the VHF out but of course, that's a nice bonus.
First I would like to know if someone can throw a guess at the description of the two inductors described above please? that would be great to know because I'm not planning to buy a lot anymore, trying to do it with stuff I have from years ago and buying only the necessary stuff.
Thanks.
(Maybe I should start another thread for those inductor question, since not everyone that might know the answer, is also reading this thread → completely different title.)
Hi Bart,
a normal capacitor input filter is a difficult load for a transformer.
After passing through the rectifier the smoothing caps receive short lived high current pulses when charging up.
These high current pulses create a lot more heat in the transformer than a continuous AC current that the manufacturer rates the transformer at. (Power loss=heat generated=I^2*R).
Most manufacturers advise derating their transformers to 70% of the AC rating.
Using this, your 160VA becomes 112VA.
Now look at the voltage on the smoothing caps. It's roughly SQRT(2)* Vac your 12Vac becomes 17Vdc.
Apply 112VA and 17Vdc and the maximum continuous DC current is 112/[17+17]=3.3Adc.
Note these two conversions result in the continuous DC current ~=half the rated AC current. Using this output current the transformer will run hot, roughly the rated temperature that the manufacturer uses. Most builders would like to run the transformer cooler and for ClassA they aim for the continuous current to be around half the maximum. Your 160VA is now supplying 1.67Adc continuous and running cool.
Class AB is generally not troubled with this due the the inherent ability of a transformer to tolerate short term overloads. Instead you see/measure a BIG sag in voltage as the load current temporarily rises.
a normal capacitor input filter is a difficult load for a transformer.
After passing through the rectifier the smoothing caps receive short lived high current pulses when charging up.
These high current pulses create a lot more heat in the transformer than a continuous AC current that the manufacturer rates the transformer at. (Power loss=heat generated=I^2*R).
Most manufacturers advise derating their transformers to 70% of the AC rating.
Using this, your 160VA becomes 112VA.
Now look at the voltage on the smoothing caps. It's roughly SQRT(2)* Vac your 12Vac becomes 17Vdc.
Apply 112VA and 17Vdc and the maximum continuous DC current is 112/[17+17]=3.3Adc.
Note these two conversions result in the continuous DC current ~=half the rated AC current. Using this output current the transformer will run hot, roughly the rated temperature that the manufacturer uses. Most builders would like to run the transformer cooler and for ClassA they aim for the continuous current to be around half the maximum. Your 160VA is now supplying 1.67Adc continuous and running cool.
Class AB is generally not troubled with this due the the inherent ability of a transformer to tolerate short term overloads. Instead you see/measure a BIG sag in voltage as the load current temporarily rises.
Thank you for the clear explanation, Andrew.
The simulation showed a big ripple indeed and this has to be reduced with more capacity, so it's solving one problem and creating another on the way. 🙁
Is it true that a single bridge PSU sags less then dual bridge PSU's?
I heard that this was important for bass amplifiers.
In the simulation the ripple is also less with a single bridge (if I did it right ) Total capacity the same, meaning using the 4 capacitors in dual bridge and then simulating with the same 4 on the single bridge and double the voltage, same current.
I need some software now, any suggestions?
The simulation showed a big ripple indeed and this has to be reduced with more capacity, so it's solving one problem and creating another on the way. 🙁
Is it true that a single bridge PSU sags less then dual bridge PSU's?
I heard that this was important for bass amplifiers.
In the simulation the ripple is also less with a single bridge (if I did it right
) Total capacity the same, meaning using the 4 capacitors in dual bridge and then simulating with the same 4 on the single bridge and double the voltage, same current.I need some software now, any suggestions?
Hey Guys
I am in the process of building 2 aleph monoblocks with a 2kva 35-0-35 (3 leads out of the torroid) in each. If I understand from an earlier post that if the transformer has only the above configuration and not 2 separate 35v taps then I would be unable to use dual bridges?
Is there a possibility of using 2 and how would they be configured?
Your time and help is greatly appreciated.
Cheers
Greg
I am in the process of building 2 aleph monoblocks with a 2kva 35-0-35 (3 leads out of the torroid) in each. If I understand from an earlier post that if the transformer has only the above configuration and not 2 separate 35v taps then I would be unable to use dual bridges?
Is there a possibility of using 2 and how would they be configured?
Your time and help is greatly appreciated.
Cheers
Greg
Hey,
Well firstly I would like to know if it is possible otherwise there is no choice to make. Secondly Nelson Pass is using 2 in his newer designs and I thought that I would like to stay up to date with technology and PSU developments. I must admit it is rather confusing.
Thanks for your time
Greg
Well firstly I would like to know if it is possible otherwise there is no choice to make. Secondly Nelson Pass is using 2 in his newer designs and I thought that I would like to stay up to date with technology and PSU developments. I must admit it is rather confusing.
Thanks for your time
Greg
a dual secondary can use either a dual bridge rectifier or a single bridge rectifier.
A centre tapped transformer can only use a single bridge rectifier arrangement.
But this does not prevent using paralleled bridges to feed separate PSUs.
There is no advantage in using dual rectifiers for quality of output DC.
But, there may be an advantage when powering two or more amplifiers from the same PSU. Some claim it removes the hum problem.
A centre tapped transformer can only use a single bridge rectifier arrangement.
But this does not prevent using paralleled bridges to feed separate PSUs.
There is no advantage in using dual rectifiers for quality of output DC.
But, there may be an advantage when powering two or more amplifiers from the same PSU. Some claim it removes the hum problem.
no.
AndrewT said:
There is an advantage to using dual rectifiers. It is in the flux distribution of the transformer. Don't know why it would make a difference in the hum level for two or more amps, though.
http://www.diyaudio.com/forums/showthread.php?postid=1067745#post1067745
see link in my edited post.
Also, see:
http://www.diyaudio.com/forums/showthread.php?postid=143874#post143874
Also, see:
http://www.diyaudio.com/forums/showthread.php?postid=143874#post143874
hi everyone,
I built chip amp w/ center tapped transformer. It has no hum at all. I have a separate power supply board and the amp board connected with 3 wires/ channel i.e. +,-,gnd. is this the good way of wiring it as per mikelm / megajocke said? or how should I adjust it?
and if it is a dual secondaries setup, there will be 4 wires/ channel to the amp board is this the proper way?
or should I combine ps board and the amp board? any benifit? 😕
one last question, if I go for 4 single secondary transformers, would there be any benifits compared with one transformers with 4 secondaries.
Thank you. 🙂
I built chip amp w/ center tapped transformer. It has no hum at all. I have a separate power supply board and the amp board connected with 3 wires/ channel i.e. +,-,gnd. is this the good way of wiring it as per mikelm / megajocke said? or how should I adjust it?
and if it is a dual secondaries setup, there will be 4 wires/ channel to the amp board is this the proper way?
or should I combine ps board and the amp board? any benifit? 😕
one last question, if I go for 4 single secondary transformers, would there be any benifits compared with one transformers with 4 secondaries.
Thank you. 🙂
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