Phase reverse

[Lavane]

As a kid I remember an old timer in our model railroad club explaining that with his first stereo: "It was very important to phase the speakers, the guy who sold it to me insisted it had to be done, but there was no mention of it in the manual." He went on to explain "you used a simple AA battery and momentarily hooked it up to the speaker to polarize the magnet"
That is of course not exactly 100% accurate, but he did remember the basics.
You dont actually polarize the magnet with a AA battery. You check the polarity of the voice coil relative to the magnet.


One of those old guys who at one point knew everything but forgot critical bits over the years.

Now I polarize once, and then label the wires.
The phase switch on my HH Scott doesn't get touched.

I miss those old timers. I learned a lot from the old guys at repair shops when I was working at an electronic parts wholesaler in the 70's. I pulled orders and delivered to all the shops in a four county area. Yuba, Sutter, Butte and Colusa.
They were always more than happy to explain things.

 

[zackthedog]

I miss those old timers. I learned a lot from the old guys at repair shops when I was working at an electronic parts wholesaler in the 70's. I pulled orders and delivered to all the shops in a four county area. Yuba, Sutter, Butte and Colusa.
They were always more than happy to explain things.

Unfortunately, the only old-timer I ever spoke to was a guy at a repair shop in Bethesda, MD. I told him I was interested in building tube amplifiers and he told to forget it, it was much too hard. ;-(

 

[62caddy]

By routing the speakers thru it and flipping one channel on them.

I see. However the C22, MX110, MX112, 113, 114 & 115 don't have speaker connections. For the C24 & C26 that do, I'm 99% certain it's handled in the same manner. Affected channel is the right IIRC.

Someone with a schematic for the Fisher 800B (among others) should be able to answer how they did it.

 

[Pio1980]

ok looks like I misremembered, this actually sits upstream of the tone controls, between the source selector and the line stage. Either way it does work the same way. Added bonus though, the tape outputs on an S-7000 are buffered which is a relatively uncommon thing for this era. Extra different, the record output is also phase inverted if the switch is thrown that way.

View attachment 2339553

A-ha! Ingenious and well done!

 

[dcgillespie]

The top of the line Fisher preamps (202-T, 400CX, 400CX-2) and at least the Mac MX-110 series of preamps all had phase reverse circuits built into them that were independent of any power amp connections. In the Mac C11 however, the phase reverse switch operates by having the output of one channel from the power amplifier connect to terminals on the back of the preamp, with a second set of terminals then for the actual connection to the speaker for that channel. The Phase Switch then reverses the phase of the connected speaker when engaged.

Most integrated amplifiers accomplished phase reversal at the speaker level, although Fisher's top of the line EL34 based X-1000 integrated uses "electronic" means to accomplish that end like their preamplifiers that included that feature do.

Dave

 

[bimasta]

Phase was taken to be the sonic polar relationship between channels, absolute polarity is the relationship between the original sound polarity and the polarity of the sound produced at the speaker or earpiece.
Think of a tin can telephone model, a push pulse in at the speaking end produces a push pulse out at the receiving end, reproducing the exact same acoustic polarity. Sounds that have an asymmetrical polarity with more energy on the push pressure side of the wave pulse will sound unnatural and "wrong" to some listeners if it is reproduced as a "pull".

As an aside, the Edison vertical acoustic recording process always reproduced an inverted acoustic polarity, the Berliner acoustic disc recording process could do either, but I don't know if that was ever a factor back then. It would have mattered for the "liveliness" of the sound of the reproduction.

@Pio1980 Clearest explanation I ever heard. "Tin can telephone" – brilliant. Do people today even know of such a thing?