Hi, i salvaged this old transformer from an old Bang and Olufsen amp. I want to use it for a gainclone project, but i am wondering if the VA value is big enough. How is it possible to determine this value? There i no information on the transformer itself. I do have the diagram of the amp it was salvaged from, but i cant figure out if it can tell me anything.
Thanks
Thanks
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If you are not able to look it up, or measure it, then as a last resort you can weigh the transformer.
I put the catalog data for (these Triad transformers) into a spreadsheet and performed linear regression.
Not surprisingly, there is a very good straight line relationship (R^2 = 0.998!) between weight and VA rating. I think Bob Cordell's book on amplifier design mentions this linear relationship, for toroidal transformers. However these Triad transformers in the attached plot are laminated, non-toroidal types.
I put the catalog data for (these Triad transformers) into a spreadsheet and performed linear regression.
Not surprisingly, there is a very good straight line relationship (R^2 = 0.998!) between weight and VA rating. I think Bob Cordell's book on amplifier design mentions this linear relationship, for toroidal transformers. However these Triad transformers in the attached plot are laminated, non-toroidal types.
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Ok thanks, the transformer weighs 1721 grams, so i could possibly assume that the VA value is about 120 right?
may be a bit more than 120VA, but surely less than 200VA
somewhere in between
nice C-core
should be ok for a modest chipamp
if voltage fits
somewhere in between
nice C-core
should be ok for a modest chipamp
if voltage fits
I am considering using it with some of the kits around, audiospector or chipamp.com. Do you know if there is any guides on how to use a center tapped transformer with these kits. Is it even possible?
Thanks
Thanks
amp kits should be ok with that
but their power supply kits seem to be designed with double bridge for dual secondaries trafo
but you may take a look at Dantimax LM4780 kit
open schematic file, and you will see how it uses a CT trafo
Dantimax (elektronik) - Preamps_-_poweramps
other power supply kits may be converted to using one bridge
Well, thats very convenient. I live in Denmark and i have already sent Dantimax a mail asking them if their kits are compatible with CT transformers. Thats not necessary anymore 🙂.
In that diagram one of the secondaries is listed as 37V AC. That is FAR too high for most chipamps, definitely for the LM4780/LM3886.
Sorry but 37VAC means around 52V , well within a LM3886 ratings.
Of course, having a single secondary, it means a single supply amp, with output coupling capacitor.
It will give you around 30W into 8 ohms and 55W into 4 .
Not bad at all.
Check the Power vs Voltage (figure 37) on the datasheet.
http://www.ti.com/lit/ds/symlink/lm3886.pdf
Of course, having a single secondary, it means a single supply amp, with output coupling capacitor.
It will give you around 30W into 8 ohms and 55W into 4 .
Not bad at all.
Check the Power vs Voltage (figure 37) on the datasheet.
http://www.ti.com/lit/ds/symlink/lm3886.pdf
You mention one of the secondaries, the one at 37 VAC (Could be the gray-gray or perhaps Blue-Blue). The other secondary, the CT secondary (Blue-Black-Blue) i measured to be at 18 VAC(Blue-Black). Is it even possible to use a single secondary for a stereo amp. I though it would have to be at least a CT secondary? If not, was is preferable. The single secondary at 37 VAC or the CT secondary at 18.5 VAC? Thanks
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its a C-core with two seperate coils😉
funny thing is, toroids may not have been available yet, so B&O have used these small sized trafos that would fit into the well known flat B&O designs
that it is a C-core is just a sideeffect, but to your benefit now
a C-core have a small airgap, and is said to better resist DC/noise coming through mains voltage
ought to be perfect for a small chip amp
funny thing is, toroids may not have been available yet, so B&O have used these small sized trafos that would fit into the well known flat B&O designs
that it is a C-core is just a sideeffect, but to your benefit now
a C-core have a small airgap, and is said to better resist DC/noise coming through mains voltage
ought to be perfect for a small chip amp
Sorry for my lack of knowlegde on this subject, but just to clear up. If i want to use this transformer with a stereo amp (Dantimax) kit, I will have to use the blue-black-blue secondary at 18.5 VAC? The grey-grey is not useable for anything right?
You have to specify @ which current.
Probably it's the opposite : the Grey-grey carries the current necessary for the
amplifier ( and I would restore the original, if possible)
and the 18.5-0-18.5 is for small current such preamplifier etc.
Probably it's the opposite : the Grey-grey carries the current necessary for the
amplifier ( and I would restore the original, if possible)
and the 18.5-0-18.5 is for small current such preamplifier etc.
But is it possible to run a two channel stereo amp, with just one secondary?
PS. Just measured the grey-grey. It is 37 VAC as assumed. The blue blue is around 39-40 VAC. Blue Black 18.5-19.5 VAC.
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Nowadays most of SS amplifiers run with dual tensions (provided by a CT trafo)
which allows more CMRR and other things, like the elimination of the output capacitor. If your transformer is done that way, it meets the specifications of that project, which is quite common. I have lots of ( no, I have thrown them away !) 30-40 V transformers from amplifiers like that. That voltage is what the output devices of the time supported; also the current is limited.
As JM Fahey in #10 said, expect some 20-30 W from each channel with such
transformer.
which allows more CMRR and other things, like the elimination of the output capacitor. If your transformer is done that way, it meets the specifications of that project, which is quite common. I have lots of ( no, I have thrown them away !) 30-40 V transformers from amplifiers like that. That voltage is what the output devices of the time supported; also the current is limited.
As JM Fahey in #10 said, expect some 20-30 W from each channel with such
transformer.
you need thickest wire secondary and hopefully it delivers acceptable voltage
16-22 VAC suits LM3886 gainclone nicely.
Trying to sum up again.
I will be using the blue-black-blue CT secondary at 19 VAC for the stereo project, and just leave the grey-grey for no use.
I will be using the blue-black-blue CT secondary at 19 VAC for the stereo project, and just leave the grey-grey for no use.
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