Why do modern PP OPTs have 16 Ohm taps? - diyAudio
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Old 5th February 2013, 03:30 AM   #1
MGH is offline MGH  United States
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Default Why do modern PP OPTs have 16 Ohm taps?

It seems like almost all standard PP OPTs from different manufacturer have 16 ohm taps, even though there are hardly any modern speakers that are nominally rated at 16 ohm. Is there any other reason for this?
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Old 5th February 2013, 03:40 AM   #2
Pano is offline Pano  United States
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Nostalgia?
Most of the commercial tube amps I see now have 8 and 4 ohm taps.
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Old 5th February 2013, 04:32 AM   #3
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Old 5th February 2013, 05:54 AM   #4
tinitus is offline tinitus  Europe
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because hard core fullrange speaker enthusiasts have 16ohm speakers ?

but maybe 4 - 6 - 8ohm would be more useable in real life
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Old 5th February 2013, 05:59 AM   #5
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Old 5th February 2013, 08:14 AM   #6
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by MGH View Post
It seems like almost all standard PP OPTs from different manufacturer have 16 ohm taps, even though there are hardly any modern speakers that are nominally rated at 16 ohm. Is there any other reason for this?
Adding extra 16 Ohm winding is not "that" expensive, if you think about relationship between impedance and winding turn. This is true for cheap design.

OPT manufacturer is not amplifier manufacturer and not speaker manufacturer. You want flexibility/usability with your OPT so you want to provide variable taps.

16 Ohm tap doesn't mean that your speaker must be 16 Ohm to be optimally connected. If your amp works best with low impedance, may be you can hook up low impedance speaker to high impedance tap (of high impedance primary), to get the correct impedance ratio.

In case of expensive OPT (silver winding for example), may be you don't want to waste taps. Because flexibility is very costly. Amplifier designer will prefer an exact primary impedance (that will give optimum amplifier performance) at average high end speaker impedance (secondary impedance), i.e. 5 Ohm.
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Old 5th February 2013, 10:15 AM   #7
DF96 is offline DF96  England
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It may arise from interleaving of windings. A push-pull output transformer must necessarily have an even number of sections in its secondary. Two is not enough; eight may be too many. Four sections gives a set of impedances in the ratios 1:4:9:16, depending on how you wire them in series/parallel.
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Old 5th February 2013, 10:36 AM   #8
tinitus is offline tinitus  Europe
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if you have one 4k trafo with 4-8ohm out
could it happen that it will be listed as a 8K trafo, leaving the former 8ohm tap to now be be a 16ohm tap
or maybe the other way round

I know this have been debated to be far from optimal
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Old 5th February 2013, 11:02 AM   #9
palmas is online now palmas  Portugal
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16Ohm winding is made out of two 4Ohm winding in series, and the 8Ohm is a tap in one of them. So it is easy to have 4 and 16Ohm, and a little more difficult to have 8Ohm.
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Old 5th February 2013, 11:12 AM   #10
tinitus is offline tinitus  Europe
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my trafos have 0-6-8-12ohm
or at least supposed to
I wonder how that works ?

but 0-4-6-8 might be nicer
would that work, or be a problem ?
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