Can someone explain to me the reason for this stereo amplifier to wire the output transformers out of phase from each other? The primaries are flipped from each other and the feedback windings are also flipped from each other but the speaker taps are wired in phase so the outputs are essentially out of phase from each other if you hook up your speakers correctly. I don't believe it's a drawing error since there's an amp on eBay that someone wrote a warning on the bottom plate about its reverse phase so it is wired correctly according to schematic. Very strange. This is also the second half of an integrated amp (full pdf schematic) section but can be used independently. But in the preamp section there's no phase switching on either channel. Head scratching.... 😕 
Any thoughts?
Any thoughts?
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Since the DC resistances of the primaries' halves (210/180 Ohm) are the same for both channels, I suspect the transformers are wired exactly the same too, just color-coded differently for some reason.
But for a production run it doesn't make sense. The factory workers still had to wire according to the schematic and how do they know which transformer is wired which phase or color coded correctly? In this one particular unit the owner even scribbled a note at the bottom plate to warn about the out of phase wiring.
It doesn't indeed.
Especially considering the fact that both OPTs have the same part number.
I'm just guessing 😀
I suspect it was a drawing mistake but it was corrected on build.
Maybe done to confuse Chinese copiers ?
Maybe done to confuse Chinese copiers ?
Actually this was quite commonly done so that a "center" channel speaker could be connected across from right to left. In most cases, the 4 Ohm (center tap) connection was grounded, giving a reverse polarity output without reversing the primary. However, in this unit, it appears that the speakers must be connected in reverse polarity. However, the instruction card and factory specification do not mention this - the instructions do mention the center channel connection, which requires phase inversion.
Oddly enough, the ASP-80 (made at the same time) used the aforementioned grounded 4 Ohm tap, keeping the other transformer connections the same for both channels. And its companion preamplifer, the ASP-8, has a phase reversal switch. (not mentioned - this would change center channel from sum to difference...)
On further reflection, the problem may be believing the Sams schematic - I don't have the Stromberg schematic for comparison, but will check it at the AWA museum next time I'm there.
Oddly enough, the ASP-80 (made at the same time) used the aforementioned grounded 4 Ohm tap, keeping the other transformer connections the same for both channels. And its companion preamplifer, the ASP-8, has a phase reversal switch. (not mentioned - this would change center channel from sum to difference...)
On further reflection, the problem may be believing the Sams schematic - I don't have the Stromberg schematic for comparison, but will check it at the AWA museum next time I'm there.
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Yes, makes sense when I read the instructions again - 8 Ohm center speaker is connected between 4-Ohm taps; 16 Ohm between 8-Ohm taps. On my page: Made In Rochester