Friend of mine has this Channel Master integrated amp, which works fine other than the fact that the outputs are wired anti-phase. You can clearly see this from the schematic.
You will notice that the opt xfmr primaries are wired opposite, based on the color codes. There does not seem to be any way to correct this, using the controls on the amplifier. So far, the only correction seems to be swapping around the speaker leads on one channel. Interestingly, they chose to gnd the 4R taps, rather than the traditional C taps.
There is a selector switch, that offers CH1, CH2, MONO, STEREO or REVERSE - but none of these correct the phasing. It seems clear that this anti-phase wiring was intentional - but why?
Full Sam's document is here: https://nerp.net/~legendre/audio/Channel_Master_6601.pdf
You will notice that the opt xfmr primaries are wired opposite, based on the color codes. There does not seem to be any way to correct this, using the controls on the amplifier. So far, the only correction seems to be swapping around the speaker leads on one channel. Interestingly, they chose to gnd the 4R taps, rather than the traditional C taps.
There is a selector switch, that offers CH1, CH2, MONO, STEREO or REVERSE - but none of these correct the phasing. It seems clear that this anti-phase wiring was intentional - but why?
Full Sam's document is here: https://nerp.net/~legendre/audio/Channel_Master_6601.pdf
Are you making this determination from the amplifier wiring itself or from the schematic shown? Sam's diagrams have been wrong before and I suspect this is the case here. You should also notice the center channel take-off and feedback from the secondary on channel 1 is different then 2. Quite confusing by a poor drawing.
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Let's put it this way: Testing by ear, and then verifying by scope, proved that the two channels are anti-phase with respect to the chassis markings. And this is what one would expect, if the schematic is correct - which it apparently is.
At first I thought the 'reverse' switch position would swap relative phase, but it actually swaps channels L to R. If you notice, they also elected to ground the 4R tap, rather than the C / Common.. which is a bit odd itself, but not all that crazy.
Again, it's like the design is intentionally anti-phase, which makes no sense.
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+1 to SAMS' errors.... but this is indeed intentional. The NFB loop comes off the other end of the secondary. This is so the Center Speaker gets a difference signal.
You can do a massive re-wiring (eliminating the center speaker provisions). Or just do as you say: flip one speaker.
You can do a massive re-wiring (eliminating the center speaker provisions). Or just do as you say: flip one speaker.
So you say this is due to the presence of the "center" speaker feature? Thing is, several different designs from this era implement a pseudo-center channel speaker, and I've never seen one that requires wiring the L&R channels anti-phase. That is just plain weird.
Under what conditions would the L&R speakers +ever+ be wired in-phase, per the chassis markings? While your info is helpful, I can't imagine any such config.
Yes, it is odd, as there is an anti-phase output without reversing the primary - just use the 0 terminal from one side, 16 on the other (4 Ohm - grounded - SHOULD be a center-tap). Perhaps their transformers didn't have the exact ratio and this odd wiring change gave them equal levels for the center channel.
Perhaps, but center channel or not, the output terminals of the amp are effectively mislabeled. And even in the day, how many people actually +used+ a center channel speaker? I'd wager 90% of users would just hook up a pair of matched LS and call it good (or call it bad, as the system is anti-phase and sounds like total crud).
It would be interesting to see what the owner's manual says about this. There must have been some rationale..
While we're on the topic, what was the point of the Center Channel simulation, anyway? Was this hangover from the era when it was common to own un-paired Hi-Fi speakers, and as such there was poor to little center-fill?
As the mono/hi-fi era transitioned to stereo in the later 1950s, it was typical for a listener to add a second speaker that might not be identical to the single speaker they used with the mono system. This might explain the perceived need for a center channel, pseudo or not.
What do you know?
As the mono/hi-fi era transitioned to stereo in the later 1950s, it was typical for a listener to add a second speaker that might not be identical to the single speaker they used with the mono system. This might explain the perceived need for a center channel, pseudo or not.
What do you know?
Nothing is odd in grounding 4 Ohm; what is the voltage between 0 and 4? And what is between 4 and 8? Remember, they are summing outputs for the center channel!
If you were addressing my comment, I don't think I said it was +odd+, but rather interesting as in unexpected. The only place I'm used to seeing this is in designs with cross-coupled opt tube cathodes, such as AR were so fond of using (D76 for a typical example).
I don't recall ever seeing the 4R tap grounded in any classic designs, whether or not they implement the center channel.
BTW - I did a little reading on the center chan issue. Apparently it is a hangover from the early stereo days, but not necessarily to address mis-matched speakers. The early stereo systems regular used a center channel (some recordings even done in 3-chan) with certain experimental systems using up to five front channels. So there was a customer perception - valid or not - that there could be a "hole in the middle" and such, the center was there if needed. This was partly due to the fact that the speakers might be placed some distance apart, and the coherence of older speakers was often sub-par and they could not always be counted on for good center-fill imaging.
Or so I take it.
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Today this connection to the center channel speaker is called a "bridged" amplifier. Connection of the 4 Ohm tap to signal ground provides a balanced output signal and a balanced feedback signal for free. Audio Research, for example, would connect output valve cathodes to this balanced feedback. (Small actual effect, but free.) Still useful with high slope valves like EL84, etc.
All good fortune,
Chris
All good fortune,
Chris
An in-phase sum fills the front center.
An OUT-phase sum goes to a *rear* speaker to enhance ambiance supposedly hidden in the recordings of the day.
Both tricks do something. A weak out-phase sum behind you is subtle but audible and sometimes more "enveloping".
An OUT-phase sum goes to a *rear* speaker to enhance ambiance supposedly hidden in the recordings of the day.
Both tricks do something. A weak out-phase sum behind you is subtle but audible and sometimes more "enveloping".
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