Two \bridges from One transformer question /
Hi
I am just in the process of building the L12-2 amplifier as replacement for a damaged dual mono white noise amplifier. (2 x 120 watt plus)
Sadly the Antrim 220VA ? transformer was blown on one amp due to house move).
I had intended to replace the remaining good one with a 300VA or EVEN higher with 38v ac per rail but I want to design/build it and fire it up with the existing 220VA just for now.
At some time in the past I seem to remember someone ? suggesting you could use two bridges from the one trafo to reduce load on the bridges.?
(I do still have the 2 x 35a bridges.)
Cannot QUITE remember if it was Pos from one and Neg on the other or just simply two identical wired bridges each firing seperate amp board or each providing a single rail.?
I would like to know the benefits of either IF THEIR ARE ANY ? as it suits the
casing space wise to have one large trafo.
Though I can possibly go back to pure dual mono at a push by trying to obtain another matching 220va trafo..
Each of the dual monos had a full set of snubber caps as well as
100nf bypass caps on each of the 4 x 1000Mf filter caps.
Also have a 17w resistor and 220nf across the input rails.
Ideally I need to make the decision sooner rather than later.
Suggestions and advice as usual will be appreciated.
Hi
I am just in the process of building the L12-2 amplifier as replacement for a damaged dual mono white noise amplifier. (2 x 120 watt plus)
Sadly the Antrim 220VA ? transformer was blown on one amp due to house move).
I had intended to replace the remaining good one with a 300VA or EVEN higher with 38v ac per rail but I want to design/build it and fire it up with the existing 220VA just for now.
At some time in the past I seem to remember someone ? suggesting you could use two bridges from the one trafo to reduce load on the bridges.?
(I do still have the 2 x 35a bridges.)
Cannot QUITE remember if it was Pos from one and Neg on the other or just simply two identical wired bridges each firing seperate amp board or each providing a single rail.?
I would like to know the benefits of either IF THEIR ARE ANY ? as it suits the
casing space wise to have one large trafo.
Though I can possibly go back to pure dual mono at a push by trying to obtain another matching 220va trafo..
Each of the dual monos had a full set of snubber caps as well as
100nf bypass caps on each of the 4 x 1000Mf filter caps.
Also have a 17w resistor and 220nf across the input rails.
Ideally I need to make the decision sooner rather than later.
Suggestions and advice as usual will be appreciated.
Does the transformer have dual secondaries? If only a centre tap then you are forced to use a single bridge.
If you can use two bridges then your ground is the point where you connect the +ve of the bottom bridge to the -ve of the top bridge.
If you can use two bridges then your ground is the point where you connect the +ve of the bottom bridge to the -ve of the top bridge.
Bridge rectifiers are seldom, if ever, wired in parallel. Choose one bridge for each application whether its a single bridge rectifying both +/- rails or 2, one rectifying +ve rail and the other, the -ve rail.
Here's some of the reasoning behind using dual bridge rectification and problems:
http://www.diyaudio.com/forums/pass-labs/93712-dual-bridge-rectifiers-psu-why.html
Google is your friend since there are many sites and threads here discussing and offering power supply designs. Searching topics also helps to define and understand what you are looking for so you can easily find more and better information by yourself.
Here's some basic designs found on the web. Note that in the first image, the 0 rails are isolated for some reason but they can be also be joined as a common ground, provided the transformer secondary winding is dual, where phase is correctly maintained.
Here's some of the reasoning behind using dual bridge rectification and problems:
http://www.diyaudio.com/forums/pass-labs/93712-dual-bridge-rectifiers-psu-why.html
Google is your friend since there are many sites and threads here discussing and offering power supply designs. Searching topics also helps to define and understand what you are looking for so you can easily find more and better information by yourself.
Here's some basic designs found on the web. Note that in the first image, the 0 rails are isolated for some reason but they can be also be joined as a common ground, provided the transformer secondary winding is dual, where phase is correctly maintained.
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Thanks for that (especially the wiring procedure) and also Ian for which I found the link to the TNT item from many years back.Interesting that he actual quotes a design that sounds better.
Also saw many usual testosterone fueled interesting arguments and counter arguments.Including a reason for saturation of trafo causing more noise, hmmm , a good reason for explaining why less is louder?
It has made me think that I will design the layout allowing for later changes and just use the one bridge for now due to single secondaries on existing trafo.
I will physically locate the second unused bridge with heatsinking alongside it for later use or experimenting at a later time. Then consider which type of higher rated trafo I go
for.
Once again many thanks , I, getting there inch by ehm several centimetres.
SLOW PROGRESS BUT
hello again,
after long delay various reasons I eventually purchased the 500VA traffo with 2 x 35v ac output hopefully giving me the most options.
http://www.rapidonline.com/pdf/82719.pdf
I thought this would be straightforward and checked their advice re wiring and was informed to parallel secondary red and yellow as well as black and orange and safely tie that away.
This parallel seems at odds with previous advice here.Especially in ensuring lowest noise etc.
i checked the outputs across each pair orange to yellow and red to black at 39 volt a/c no load .Same for them paired.
Prior to connecting to the bridge KBPC3504 a/c inputs I checked the diodes with dmm.......Also checked the spare bridge previously unused.
Everything seems ok.
Wiring up each pair to bridge produces only 29v DC plus and minus on either bridge I tried.
Not what I expected, .
Note Ive Wired up two 1000uf Elna caps correctly.
(also note 20000uf each rail when Im satisfied its configured correct)
So I contacted them again.
I was advised THEY had misunderstood my intention and I needed to opt for a dual bridge configuration.
Im told not to connect anything to the star earth. (orange/ black)
Most important was to tie the orange/black together floating and use the red and yellow for obtaining my + & - 49v DC .
I am less than confident in the advice and obviously concerned how to correctly wire this up for best results and get the 49V approx output.
note....Output is for the kit amp on thread .
http://www.diyaudio.com/forums/solid-state/196089-l12-2-cfp-output-amp-120w-2-8r-21.html.
Beginning to think I will need idiot proof instructions if help is out there.
To be honest I was quite satisfied with the sonic performance of the single old single bridge and 200VA traffo before it exhausted itself trying to drive both amps.
Though If needed I am prepared to go for the almost two pure monoblock layout and purchase another 20000u but it will be a tighter squeeze in the box.
Thanks in anticipation.
hello again,
after long delay various reasons I eventually purchased the 500VA traffo with 2 x 35v ac output hopefully giving me the most options.
http://www.rapidonline.com/pdf/82719.pdf
I thought this would be straightforward and checked their advice re wiring and was informed to parallel secondary red and yellow as well as black and orange and safely tie that away.
This parallel seems at odds with previous advice here.Especially in ensuring lowest noise etc.
i checked the outputs across each pair orange to yellow and red to black at 39 volt a/c no load .Same for them paired.
Prior to connecting to the bridge KBPC3504 a/c inputs I checked the diodes with dmm.......Also checked the spare bridge previously unused.
Everything seems ok.
Wiring up each pair to bridge produces only 29v DC plus and minus on either bridge I tried.
Not what I expected, .
Note Ive Wired up two 1000uf Elna caps correctly.
(also note 20000uf each rail when Im satisfied its configured correct)
So I contacted them again.
I was advised THEY had misunderstood my intention and I needed to opt for a dual bridge configuration.
Im told not to connect anything to the star earth. (orange/ black)
Most important was to tie the orange/black together floating and use the red and yellow for obtaining my + & - 49v DC .
I am less than confident in the advice and obviously concerned how to correctly wire this up for best results and get the 49V approx output.
note....Output is for the kit amp on thread .
http://www.diyaudio.com/forums/solid-state/196089-l12-2-cfp-output-amp-120w-2-8r-21.html.
Beginning to think I will need idiot proof instructions if help is out there.
To be honest I was quite satisfied with the sonic performance of the single old single bridge and 200VA traffo before it exhausted itself trying to drive both amps.
Though If needed I am prepared to go for the almost two pure monoblock layout and purchase another 20000u but it will be a tighter squeeze in the box.
Thanks in anticipation.
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I didn't see that advice anywhere.
You are right, it is at odds with what we said.
Orange and yellow one rectifier, red and black to the other. If you tie yellow and black together you cannot use two bridges, it becomes a centre-tapped transformer.
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update and not much progress
Well I finally got back to the project.
Light bulb was installed as per a previous instruction/ reminder.
I have now rewired the output from transformer in line with tnt pic 3. ie two bridges using One for Pos and one for neg. Each getting the 39vac
Then Spare pins from pos on first bridge wired to neg on second bridge and taken to ground.(star earth). No caps wired in at this point.
So measurements accross each ac input 39v ac.🙂
Measurement at correct v+ and at V- each (Bridge one + Bridge 2 -)
are + 69.9 volts and -69v DC .😡
References to ground/star earth. Not what I expected again.
At no point does the lamp brighten.
I then reversed one of the a/c input pairings to get simlair measurements.
I am now beginning to suspect both bridges are faulty despite measurement/check.? or is it simpler than that ?
I am off to get two more bridges from a different source.
Well I finally got back to the project.
Light bulb was installed as per a previous instruction/ reminder.
I have now rewired the output from transformer in line with tnt pic 3. ie two bridges using One for Pos and one for neg. Each getting the 39vac
Then Spare pins from pos on first bridge wired to neg on second bridge and taken to ground.(star earth). No caps wired in at this point.
So measurements accross each ac input 39v ac.🙂
Measurement at correct v+ and at V- each (Bridge one + Bridge 2 -)
are + 69.9 volts and -69v DC .😡
References to ground/star earth. Not what I expected again.
At no point does the lamp brighten.
I then reversed one of the a/c input pairings to get simlair measurements.
I am now beginning to suspect both bridges are faulty despite measurement/check.? or is it simpler than that ?
I am off to get two more bridges from a different source.
Something is not right.
Two by 35Vac should gives ~ ±50Vdc
Disconnect the transformer from all it's output wires. Retain the Bulb Tester.
Measure the powered secondaries alone.
Yep Andrew
all wiring to bridge(s)disconnected
As stated each pair red/black or yellow/ orange = 39.1 v a/c
black to orange= 0.495 v a/c ? not steady
red to orange = 37.2 vac
yellow to black = 37.2 vac
finally red yellow = 0.452 vac again not steady
Replacement single bridge shows exactly as before
ie either pair of a/c to the bridge produces a measurement
of 36v DC from poss to neg and reversing leads on Dmm produced reversed dc measurment of -36v.dc.
Its still an enigma to me.
all wiring to bridge(s)disconnected
As stated each pair red/black or yellow/ orange = 39.1 v a/c
black to orange= 0.495 v a/c ? not steady
red to orange = 37.2 vac
yellow to black = 37.2 vac
finally red yellow = 0.452 vac again not steady
Replacement single bridge shows exactly as before
ie either pair of a/c to the bridge produces a measurement
of 36v DC from poss to neg and reversing leads on Dmm produced reversed dc measurment of -36v.dc.
Its still an enigma to me.
Identify that red and orange are the same winding.
Identify that yellow and black are the same winding.
If so, then that will fully explain why black to orange and red to yellow give nonsense results. They should be isolated from each other.
That's what an isolating transformer does. It is designed to achieve isolation.
What is the Primary voltage when the outputs are measured, no point in half the results.
Why are red/black and yellow/orange giving sensible readings?
Why are they different from the other two sets of readings?
Identify that yellow and black are the same winding.
If so, then that will fully explain why black to orange and red to yellow give nonsense results. They should be isolated from each other.
That's what an isolating transformer does. It is designed to achieve isolation.
What is the Primary voltage when the outputs are measured, no point in half the results.
Why are red/black and yellow/orange giving sensible readings?
Why are they different from the other two sets of readings?
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That's normal.
That is not normal, especially the 37.2V ones. All those readings should be zero.
35Vac plus 6% regulation comes to 37.1Vac for open circuit.
If the Primary voltage were 242Vac instead of 230Vac, then the secondary would be 39.1Vac.
If the Primary voltage were 242Vac instead of 230Vac, then the secondary would be 39.1Vac.
Andrew
Red and Black are the first winding of the secondaries
Yellow and orange are the second pairings.
Red and Yellow are the DOT start of each sec winding.
This is clearly marked on the traffo
Clearly identified on their drawings
Vigortronix Toroidal Transformer 500VA 0-35V 0-35V | Rapid Online
Measured voltage tonight is 238 vac and each secondary pair is 38.35Vac
To me this is a sensible pair of vac readings.
Its after this when I go to the bridge that I am failing to understand
Again that is what I half expected.
So , based on what I reported thenDo you think that the trfaffo is faulty internally?
I suspect I will have to go back to Vigortronics (Rapid)
my experience, when playing music, the average power draw at ear splitting volumes will just be a fraction of the FTC rating of the amp so no need to worry that much...
having said this, you can get by with heat sinks salvaged from discarded ATX pc psu's....
even if running class A, 45 amps of current seems hugely unrealistic, about 10% of that more lkely....😉
There is something weird if you have nothing connected to the secondary at all and you get those readings.
With nothing connected to the secondary and POWER OFF, measure ohms between yellow and black, it should be infinite, i.e. open circuit.
Another set of testing on this weird situation.
This mornings a/c input 239 each sec is now 38.9Vac
resistance accross prim blue/brown 3.1 ohm
resistance accross sec red/black pair is 0.4 ohm *
yellow/orange same 0.4 *
Any other combinations of color checks are + infinity with Precision Gold DMM set to 2000M
Connected up both bridges again (In case I am dreaming) seperate pairs.
measured accross bridges 35.8V DC
Mentally running out of ideas./ options.
Think I might be back on medicine soon?
redoing all tests again
Rechecked the diodes...done.
Hi
This mornings a/c input 239 each sec is now 38.9Vac
resistance accross prim blue/brown 3.1 ohm
resistance accross sec red/black pair is 0.4 ohm *
yellow/orange same 0.4 *
Any other combinations of color checks are + infinity with Precision Gold DMM set to 2000M
Connected up both bridges again (In case I am dreaming) seperate pairs.
measured accross bridges 35.8V DC
Mentally running out of ideas./ options.
Think I might be back on medicine soon?
redoing all tests again
Rechecked the diodes...done.
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