Why is there mono switches on integrated amplifiers

It's also useful to adjusting the azimuth alignment of a tape deck. Switch your amplifier into mono mode and then adjust the azimuth for the brightest sound (most treble).

And there are many videos online that were transferred from analog videotape using a mono VCR or camcorder, and rather than using a Y-adapter to feed the audio into both channels, whoever did the transfer only connected one of the audio channels -- so unless your amp has a mono button (or you have a Mac which can do it in the system settings), you'll be hearing audio only coming out of one speaker.

 

Yes! The azimuth should be set in mono mode to align with the tape. The azimuth on any recorded tape can be a little off... or way off, so this prep before transcribing is highly recommended. This should be standard practice. Most audiophiles no longer listen to tape, so the mono switch has one less purpose. I couldn't live without a mono switch.

 

Correct, but it's not that hard to find a separate mono switch box, or a phono preamp with a mono switch if you know where to look...

 

If you are talking about a receiver (which is integrated plus tuner), the mono switch may have a more useful purpose - to lock the tuner in mono reception mode. Since FM stereo uses a difference signal modulated on a higher frequency carrier, it can have much more noise on the fringe of reception, and sometimes it is better to just turn it off.

 

On a receiver or integrated stereo system, that is often the only thing the mono/stereo switch or button does -- it has no effect on any of the other inputs.

 

I am demoing a Luxman 509x right now, and hooked it up for the first time last night (with Rega P10 > Apheta 3 > Gold Note PH-10 and B&W CM9 speakers). On first run, the stereo playback of my 1st UK copy of "Wish You Were Here"—with the Line Straight setting which bypasses any tone control—was staggering. Huge soundstage, crazy dynamics—jaw dropping stuff. When I then played my all-but-pristine OG mono copy of "A Love Supreme" with the Mono setting, I didn't get the same results. I felt like the staging and imaging were compromised—like the instruments were on top of each other without enough space in the presentation and without the clarity of imaging. The overall authority just wasn't the same. I felt that the mono presentation wasn't even as good as my mediocre Integra home theatre amp I had just disconnected.

Anyone have any experience with mono playback on a Luxman or have any thoughts on why I might have had this experience?

 

I've put a simple DPDT center off switch in my cheapo Pyle integrated amp used with my near-field speakers. One of the one positions summed to mono and the other on position about "half mono" (about a 5kΩ resistor between inputs) to make a narrower sound field. I use it all the time with too-wide stereo recordings, it makes them much easier to listen to.

 

Hi.

If memory serves me right, )and that’s anyone’s guise), I remember a mono switch in my mid 80s Pioneer Receiver. It’s at main use was to improve the sound of a drifting or fading FM signal. The Mono button was used to acquire the stereo signal. One would the switch to stereo. If the signal was strong according to the gauge inside the tuning bar than one left the setting on stereo. But if not, one returned the button to Mono which would hold onto the signal.

 

I will never again buy an integrated amp (or pre-amp, if going w/ separates) that does not have a mono switch. I find it indispensable. ..I have many songs that were recorded in the early days of stereo where the stereo effect was exaggerated - such as, all the vocal coming from one speaker, and all the guitar from the other. ..Even quite a few early Beetles did this. These songs are much more enjoyable w/ the mono switch engaged. I may be creating some phasing issues, but the music is still more enjoyable for me.

Another reason I insist on a mono switch is that while I usually listen from a sofa that is centered b/w the speakers some 12' away, I am sometimes forced to listed to music sitting in one of the seats beside one of the speakers. For example, when it's very late in the PM or early in the am. ..I engage mono, then use my balance control to fully mute the farther speaker. This allows me to listed at very low levels so as to not bother people sleeping and still hear ALL the music. ..As an aside, this is also why I insist on having a balance control.

Accuphase
Luxman
McIntosh
Anthem

AFAIK, These are the only mfgs of present day gear offering Integrated amps w/ a Mono Switch.

I happen to have a McIntosh MA6600.

 

I had a mono switch added to my Croft Micro 25 preamp prior to purchase. It replaced the Mute switch.

The circuit design is such, however, that swinging the balance over to the left or right mutes the sound. Not sure why this is the case but it hasn’t ruined my life.

 

Moving the function sw. from fm stereo to fm knocks out all multiplex noise on my receiver.
Never use my mono sw. It's so oxidized it doesn't work anyway.
The original Magic touch of Floyd Cramer was only released in mono.
In 1965 it was re released in stereo due to public demand. Electronically Reprocessed.
I'm listening to it right now and it sounds pretty good. Doesn't sound reprocessed. Much better
than the mono version. It has left/right and center info with no reverb or echo.
I guess it depends on the engineer who did the re mastering as to how it sounds.
It actually sounds better than many of my true stereo records.

 

I have a mono switch on my Phono amp. Listened last night to "Steaming with The Miles Davis Quintet" and "Relaxin With The Miles Davis Quintet", both MONO. Sound was excellent!

 

I think I understand the above, but is a mono switch at all beneficial for a mono recording on a modern stereo LP, which I assume is cut with a stereo lathe to have both channels playing the same thing? Or is it just for older, one-channel mono recordings?

 

Different switch.

 

To put it succinctly, a record may have music in mono, but the surface noise, click, pops, etc are always in "stereo." The mono switch helps make them less obtrusive.

 

Same switch.

Here for example, is a Sansui G-3000 FM Stereo receiver schematic:



You will see in the lower left, S02a, front panel mono switch, connects to pin #12 of the Stereo MPX decoder chip - to disable FM stereo decoding.
That is a dual-position switch. The second set of contacts, S02b, makes the mono button also bridge the left and right channels of the preamp together.

 

OK then . . . different switch on most amps/receivers.

 

Yeah the NAD's had them, I think some of the old Marantz's had them too.

 

After reading this a few times, and watching some Youtube videos, I think I'm getting closer to a basic understanding of this.

First of all, is it correct to say that the mono groove is lateral but the stereo cart/stylus nevertheless is still trying to play the "sides" of the groove (L-R below) in addition to appropriately playing the lateral groove (Mono below)? (The mono cart effectively is saying screw the L-R sides, I'm just playing the lateral groove.)

If so, how does a mono switch fix the problem? I take it it somehow shuts down the L-R, but what is the mechanism or process it employs to eliminate the unnecessary and pesky L-R?

Don't be afraid to put it into layman's terms or use an analogy the uneducated like me can understand.

 

Basically, when switch is set mono,
The two channels are mixed together
And the stereo channel eliminated
Thus, your phono stage sees one channel
The mono one and noise from the vertical channel is removed.
Try playing mono record with switch on
And using one channel only.

 

Unless you mean there effectively are three “channels” at issue in a mono recording - two vertical (what would be L-R if the record were a stereo LP) that have noise but no music and one mono (the lateral groove where the mono music resides), I still don’t (and likely never will) understand this.

 

I'll take a crack at this; if I confuse you more, I apologize. I'm going to start with walking through how the groove is laid out; it's a bit roundabout, but it comes back at the end.

Imagine yourself sitting in front of your turntable, looking squarely at the front of the cartridge as a record is playing. The groove the stylus is in would be coming directly toward you as it comes under the cart.

On a mono record, the groove is (ideally) of uniform depth and width, and the single signal is encoded in side to side motion; a mono cart only picks up side to side motion, not up and down. Let's arbitrarily say a movement of the stylus to your left - toward the label - results in a positive voltage on a mono cart, and a movement to the right - toward the rim - results in a negative voltage. [Google 'Absolute Phase' for the rabbit hole I'm glossing over with the voltage polarity - have fun with that.] Any up and down is ignored, so a lot of groove noise, rumble, etc., gets filtered out by the cart. This is a big benefit of playing a mono record with a mono cart - noise reduction.

On a stereo record, you have two signals in a right angle 'V' forming the groove, and a stereo cart has coils at the same right angle, so it's possible to have a motion in one of those planes without requiring motion in the other. The left signal, encoded on the left (label side) of the groove as you look at it, moves the stylus from your left hip to your right shoulder, and the right channel, on the right (rim side) of the groove, moves the stylus from your right hip to your left shoulder. The curious thing about the way the signals are laid down is that the right channel phase is inverted in the groove. If we say that a left channel motion toward your left hip results in a positive voltage in that channel (and motion toward your right shoulder results in a negative), then a right channel motion toward your right hip results in a negative voltage, rather than the positive voltage you would expect if you were to simply mirror the left channel (and a positive voltage comes from a motion toward your left shoulder). Your cart takes care of un-inverting this - the coils for the right channel are also wired 'upside down' from the way you'd expect if you mirrored the left, so the result coming out of the pins on the back of the cart is correct - no trickery needs to be implemented for this phase correction in your amp.

Now, imagine you have an identical signal in both left and right channels (a mono recording) you're using to drive a stereo cutter head (which would be set up the same way as your cart). The positive voltages in the left channel correspond to a movement toward your left hip; the positive voltages in the right channel correspond to a movement toward your left shoulder. The up and down cancel each other out, and you're left with only a motion to the left on that positive voltage. You're using a stereo head to cut a mono record.

So, that's the difference between mono and stereo for carts and grooves; how does the switch come in? [Buckle up; this gets out there but does eventually come back.]

There's a different form of encoding stereo signals called 'Mid-Side'; it essentially corresponds to what you get if you somehow read a stereo groove with a stereo cart twisted 45 degrees out of azimuth off to one side. The 'Mid' corresponds to the lateral motion of the groove, and represents the signal common to both channels - sounds that appear in the middle of the stereo image (kick drum, bass, lead vocals on many rock discs, or violas and woodwinds on many orchestral recordings). We understand this one already - it's the mono signal, and it's the same thing you'd get if you played a stereo disc with a mono cart.

The 'Side' is the up and down motion in the groove, and corresponds to signal that appears uniquely in one channel or the other - anything panned to one side. This sounds strange - how do we get both left and right out of the single 'Side' channel? - but the key is to remember that if the 'Mid' is 0 degrees, the 'Side' is 90 degrees - not the 45 degrees either way we're used to with left/right separation. Also, as with L/R stereo, a particular instrument doesn't have to be all in one channel or the other. In fact, almost everything on a stereo record has a 'Mid' component in a Mid-Side encoding, regardless of whether it has any 'Side' component.

To convert between the two types of stereo signals, we can set up this system of equations:
L+R=M (left plus right equals mid - our mono signal common to both left and right channels)
L-R=S (left minus right equals side - anything equal in both left and right channels would get cancelled out by this; something in just the left channel would be a positive signal in the 'Side' channel, and something in just the right would be a negative signal)
1/2M+1/2S=L (mid plus side equals left - the 1/2's are there to cancel out the doubling of signal strength that would occur otherwise)
1/2M-1/2S=R (mid minus side equals right)

Dropping in some numbers to each formula in order, with five examples:
L+R=M: 1+1=2 (positive mono signal to both left and right) OR 1+.5=1.5 (a signal twice as strong in the left channel as in the right) OR 1+0=1 (a signal only in the left channel) OR 1-.5=.5 (a signal 'outside' the speakers to the left that shows up as an inverted signal in the right channel to achieve this - yes, this is possible) OR 1-1=0 (a scratch in the groove that moves the stylus straight down and sounds as a 'pop' in the extreme left of the soundstage - note this cancels in the mid channel, as would a piece of debris that moves the stylus directly up!)
L-R=S: 1-1=0 (note our mono signal cancels in the side channel) OR 1-.5=.5 OR 1-0=1 OR 1+.5=1.5 OR 1+1=2
1/2M+1/2S=L: 1+0=1 OR .75+.25=1 OR .5+.5=1 OR .25+.75=1 OR 0+1=1
1/2M-1/2S=R: 1-0=1 OR .75-.25=.5 OR .5-.5=0 OR .25-.75=-.5 OR 0-1=-1

Circling back to the question of how the switch works (I told you we'd get back here)... the mono switch is basically acting to electrically perform that first equation - it adds the signal from the left channel and the right channel to give us the mono 'Mid' channel. Going back to the first section about how the groove works, any signal (or noise) that results in a lateral motion of the stylus shows up as the same polarity voltage in both channels, and so gets summed; any signal (or noise) that results in an up and down motion of the stylus shows up as a positive voltage in one channel and a negative voltage in the other, and so gets cancelled. A signal in the left or right channel only will be present in the mono 'Mid' channel, but not as strongly as a signal of the same strength in each of the left and right channels, which is why playing a stereo record with a mono stylus results in the kick, bass, and lead vocals (or the violas, shudder) being twice as loud as the instruments out to the side.

So the short version is that the switch allows the 'V'-shaped coils to virtually act together as a single lateral coil, like a mono cart, reducing some noise, eliminating some noise altogether, and helping to bring the mono signal to the fore.

Sorry that took so much room; I tried to pare this down as much as possible, but I wanted to get all the way down to the basics in hopes it would easier to follow all the way through.

 

Thanks, but I don't think I'll be quitting my day job to work in audio any time soon.

When you say "the short version is that the switch allows the 'V'-shaped coils to virtually act together as a single lateral coil, like a mono cart . . .", that suggests to me that a stereo cut of a mono recording wouldn't benefit from a mono switch and certainly not a mono cart (as they already "act together"). This dovetails with a question I posed at a related thread - namely, whether a modern (post-1970) LP of a mono recordings could benefit from a mono switch or a mono cart if it is cut with a stereo lathe. I further assume virtually all of them (post-1970 records, that is) are, with certain audiophile exceptions.

Here's a 1975 record of all mono recordings (left) next to a record from 20 years before (right), also entirely mono recordings. I assume, however, the one on the left has stereo groove as you describe while the one on the right has a mono groove. Why would RCA cut the record on the left in the same manner as the one on the right, given that virtually everyone back in 1975 had a stereo set up? Would anyone? Specialty labels? How can one tell?

 

From what I can gather, the major US labels phased out mono in 1968; presumably, the mono cutter heads went out at about the same time, though I haven't seen anything to specifically confirm or refute that point. It does appear that any mono recording cut by a major after that time would have been cut with a stereo head receiving the mono signal on both channels. Presumably this would be the case for your '70's Benny Goodman compilation - I believe they were an RCA label, and RCA certainly would have been using stereo heads exclusively in the mid '70's. There may have been some smaller or specialty labels running mono cutters later, and it's possible that a disc from outside North America, Western Europe, or Japan might be true mono much later, but that would be something to look at on a case-by-case basis.

There are a couple of possible benefits to using a mono cart; the one that would also apply to using the switch would be noise reduction, since any groove debris causing vertical motion wouldn't be picked up. However, with clean records in good shape on a modern low-rumble player, this may not have much of an effect - it's more beneficial on older, noisier records, particularly if the cutter introduced some rumble on its own. So you're right in thinking there's not a lot of benefit on post-'68 monos, unless they're dirty or worn.

The cart choice itself may also have a benefit not specific to mono vs. stereo - stylus size. Since the original spec for the Columbia Microgroove Long Playing Record was a 1 mil conical stylus, some of the older monos may have heavy wear at the points in the groove such a stylus would contact; using a smaller stylus or an advanced profile can sometimes get to an unworn part of the groove and recover a better signal as a result. (There is also occasionally the opposite effect - I have at least one side of a '50's Columbia mono disc [E. Power Biggs' Mozart Organ Tour] that was either cut using a worn cutting stylus or was from the end of its stamper's run, so the groove is quite shallow, and trying to use a microline bottoms out the stylus tip and sounds terrible. Conical works much better for that side.)

 

Excellent analysis. Exactly what I was looking for.

To your following point:

There may have been some smaller or specialty labels running mono cutters later, and it's possible that a disc from outside North America, Western Europe, or Japan might be true mono much later, but that would be something to look at on a case-by-case basis.

I would not necessarily assume post-1970 records made by companies such as Swaggie (example, which I recently purchased, below) to be mono records cut with a stereo lathe. They seem to specialize in old mono recordings and would have no reason to make other than true mono LPs.



Record sets that include both stereo and mono recordings, like the following, would have to be cut entirely for stereo.



I guess there isn't a way to figure out whether records such as Swaggie LPs are true mono unless they say so (e.g., one cannot figure it out by looking at the groove with a jeweler's loop).