I have seen that some stereo amplifiers from the 60s have a central channel, such as the Fisher X101D, or the Scott LK79, among others.
I know it is a connection between the 2 secondaries of the output transformers to run a third speaker called the center channel, I have seen the circuits and understand it, but I would need someone to technically explain how it works.
Thank you so much
Gusmore
I know it is a connection between the 2 secondaries of the output transformers to run a third speaker called the center channel, I have seen the circuits and understand it, but I would need someone to technically explain how it works.
Thank you so much
Gusmore
Its connected across both output transformers ,if the "X" and "Y" are a connection for a single speaker then it would reproduce in mono both outputs.
That is IF a single speaker is connected to the "centre " channel which is not the same as a woofer used for low bass in a centre channel of an modern entertainment system which is channeled electronically.
Or a multi channel 3.1/5.1 etc.
That is IF a single speaker is connected to the "centre " channel which is not the same as a woofer used for low bass in a centre channel of an modern entertainment system which is channeled electronically.
Or a multi channel 3.1/5.1 etc.
Going to the supermarket this morning (GMT ) 6A3sUMMER will get back .
Yes I have seen the Fisher X101D circuit its the early days (old school ) version of modern digitally controlled multi output systems, as such its pretty simple .
Connected directly across BOTH output transformer secondary winding's outputs without any sophisticated circuits it therefore has an output of the combined two channels .
If ONE speaker is connected to "X" + "Y" then its a mono output of the combined signals.
Yes I have seen the Fisher X101D circuit its the early days (old school ) version of modern digitally controlled multi output systems, as such its pretty simple .
Connected directly across BOTH output transformer secondary winding's outputs without any sophisticated circuits it therefore has an output of the combined two channels .
If ONE speaker is connected to "X" + "Y" then its a mono output of the combined signals.
Is all of this done with just the output transformers, but without any additional resistors, capacitors, or inductors?
In that case, it sounds like a single speaker + terminal would be connected to 8 Ohm tap of L, and speaker - terminal would be connected to 8 Ohm tap of R.
That is not a center channel, it is the Difference between L and R; not the sum of L and R.
In the early 70s, there was the Hafler matrix method of 4 channel sound. There were special vinyl recordings using the Hafler matrix mix. The L and R channel speakers were connected normally. Then, a second pair of speakers were connected in this way: + L rear, - L rear, a series resistor, - R rear, and + R rear. The + L rear was connected to the + L of the amp, and the + R rear was connected to the + R of the amp.
I had some of those vinyl recordings, and the matrix method was quite effective.
If instead, one speaker 8 Ohm terminal is connected to the amplifier 8 Ohm terminal of Left, and also to the amplifier 8 Ohm terminal of Right, and the common of the speaker is connected to common, then that shorts the L and R together.
That is not stereo, it is 'forced' Mono. That is not a center channel, it is effectively the only channel (L+R), even though it comes through 3 speakers, L, R, and Center.
In that case, it sounds like a single speaker + terminal would be connected to 8 Ohm tap of L, and speaker - terminal would be connected to 8 Ohm tap of R.
That is not a center channel, it is the Difference between L and R; not the sum of L and R.
In the early 70s, there was the Hafler matrix method of 4 channel sound. There were special vinyl recordings using the Hafler matrix mix. The L and R channel speakers were connected normally. Then, a second pair of speakers were connected in this way: + L rear, - L rear, a series resistor, - R rear, and + R rear. The + L rear was connected to the + L of the amp, and the + R rear was connected to the + R of the amp.
I had some of those vinyl recordings, and the matrix method was quite effective.
If instead, one speaker 8 Ohm terminal is connected to the amplifier 8 Ohm terminal of Left, and also to the amplifier 8 Ohm terminal of Right, and the common of the speaker is connected to common, then that shorts the L and R together.
That is not stereo, it is 'forced' Mono. That is not a center channel, it is effectively the only channel (L+R), even though it comes through 3 speakers, L, R, and Center.
Thats why I said----- "centre channel " in inverted commas and by the way the circuit diagram by Fisher says ---Centre channel .
If an output of a stereo audio signal (both channels) is connected to ONE Speaker tell me why without a shred of other components being connected -IE- direct connection you wont hear both channels reproduced on it--remember no other components attached just directly connected a voice coil reproduces the music signal it receives it does not have the sophistication to remove any part of the input.
If an output of a stereo audio signal (both channels) is connected to ONE Speaker tell me why without a shred of other components being connected -IE- direct connection you wont hear both channels reproduced on it--remember no other components attached just directly connected a voice coil reproduces the music signal it receives it does not have the sophistication to remove any part of the input.
Attachments
Gusmore,
Thanks for the schematic.
There are extra taps on the output transformer secondaries.
One is L - (not common) - = it is out of phase versus the 4, 8 , and 16 Ohm taps.
One is R - (not common) - = it is out of phase versus the 4, 8 , and 16 Ohm taps.
The common of those secondaries is one tap up. the commons are connected to amplifier circuit commons, like B-, bottom of output tube self bias -, etc.
1. One purpose of the extra taps was to run a Headset:
The tap plus 330 Ohm resistors from each tap runs the L and R Headset.
The headset signals are out of phase with the regular L and R speakers.
2. The other purpose of the extra taps was to be able to run an extra speaker to create an
expanding effect acoustically.
You have already stated: The [same] extra taps also connect to the "center" speaker.
This is not a "center" channel. Just because you place the "center" speaker between the L and R speakers, does not make it the sum of L + R.
Consider a stereo recording, with the lady singer exactly between the 2 recording microphones.
Her voice will be the same signal phase and amplitude coming out of the L and R speakers. (that makes a Pseudo acoustic effect, which makes you hear her as if she was in the middle between the L and R speakers, even though there is no speaker there.
A true "center" speaker coming from a 3rd channel amplifier that was L+R, would put out her voice.
But the L - tap and R - tap have exactly the same voltage and phase of her voice signal.
The difference is Zero, and No sound comes out of the "center" speaker.
The only sound coming out of your "center" speaker is the signals that are Not in the center of the stereo recording, only the performers on the Left side of the recording, plus only the performers on the Right side of the recording.
I hope that complex discussion explains it.
Thanks for the schematic.
There are extra taps on the output transformer secondaries.
One is L - (not common) - = it is out of phase versus the 4, 8 , and 16 Ohm taps.
One is R - (not common) - = it is out of phase versus the 4, 8 , and 16 Ohm taps.
The common of those secondaries is one tap up. the commons are connected to amplifier circuit commons, like B-, bottom of output tube self bias -, etc.
1. One purpose of the extra taps was to run a Headset:
The tap plus 330 Ohm resistors from each tap runs the L and R Headset.
The headset signals are out of phase with the regular L and R speakers.
2. The other purpose of the extra taps was to be able to run an extra speaker to create an
expanding effect acoustically.
You have already stated: The [same] extra taps also connect to the "center" speaker.
This is not a "center" channel. Just because you place the "center" speaker between the L and R speakers, does not make it the sum of L + R.
Consider a stereo recording, with the lady singer exactly between the 2 recording microphones.
Her voice will be the same signal phase and amplitude coming out of the L and R speakers. (that makes a Pseudo acoustic effect, which makes you hear her as if she was in the middle between the L and R speakers, even though there is no speaker there.
A true "center" speaker coming from a 3rd channel amplifier that was L+R, would put out her voice.
But the L - tap and R - tap have exactly the same voltage and phase of her voice signal.
The difference is Zero, and No sound comes out of the "center" speaker.
The only sound coming out of your "center" speaker is the signals that are Not in the center of the stereo recording, only the performers on the Left side of the recording, plus only the performers on the Right side of the recording.
I hope that complex discussion explains it.
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Of course they should be --in phase but that is down to the quality of both channels being in phase to start with .
Are you going to take it up with Fisher as to their labeling --not my labeling of the "centre channel" ?
Are you going to take it up with Fisher as to their labeling --not my labeling of the "centre channel" ?
Notice that the center channel speaker differential connection is between the 16 ohm tap of one channel, and
the 0 ohm tap (C) of the other channel. This gives a mono signal, since the two nodes are "out of phase".
That is, ( 1/2 plus V - 1/2 minus V ) = plus V ........which is mono.
The headphones, being ground referenced, are connected from each 0 ohm (C) tap to ground.
the 0 ohm tap (C) of the other channel. This gives a mono signal, since the two nodes are "out of phase".
That is, ( 1/2 plus V - 1/2 minus V ) = plus V ........which is mono.
The headphones, being ground referenced, are connected from each 0 ohm (C) tap to ground.
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rayma and duncan,
Good eye on the schematic.
My eyes are 75 years old, and the schematic was not the clearest.
I did not catch the "center" speaker connection to R channel 16 Ohm tap.
However, we need to look at the schematic a little closer too:
The Headphone output resistors connect to the Extra L tap and Extra R tap. They do not connect to the 0 (C) tap (well, the Common of the headphones do).
And C taps are at amplifier ground.
As I said already, the headphone signals are out of phase with the main loudspeakers phase.
(depending on the manufacturers phase versus their connectors; and depending how you connect the loudspeakers to the C and x Ohm tap.).
No, I will not go to Fisher and tell them about what I have observed from this study.
And even if I owned that amplifier, I would not connect the "Center" speaker.
But . . . it was a good curiosity, and perhaps gave a sweet sounding and interesting acoustic sound for the times.
And no, the extra L tap, and 16 Ohm R tap are not always out of phase.
That is because some signals on a stereo recording already have out of phase signals of L and R, before they even get sent to the amplifier.
Out of phase once, and then going through another out of phase process = in phase.
Over the years I have seen hours of XY displays of stereo recordings, at home and also at several different venues. And on different recordings, music of many kinds, different signal sources, CD, vinyl, FM stereo, tape recorder, etc.
When looking at these XY displays on different stereo recordings, you can see everything from a straight line at 45 Degrees upward slope, to a complete circle filled in with many different paths and directions, causing it to look a lot like a flower.
What you get is anything from near mono, to all kinds of in phases, out of phases, and different amplitudes.
Good eye on the schematic.
My eyes are 75 years old, and the schematic was not the clearest.
I did not catch the "center" speaker connection to R channel 16 Ohm tap.
However, we need to look at the schematic a little closer too:
The Headphone output resistors connect to the Extra L tap and Extra R tap. They do not connect to the 0 (C) tap (well, the Common of the headphones do).
And C taps are at amplifier ground.
As I said already, the headphone signals are out of phase with the main loudspeakers phase.
(depending on the manufacturers phase versus their connectors; and depending how you connect the loudspeakers to the C and x Ohm tap.).
No, I will not go to Fisher and tell them about what I have observed from this study.
And even if I owned that amplifier, I would not connect the "Center" speaker.
But . . . it was a good curiosity, and perhaps gave a sweet sounding and interesting acoustic sound for the times.
And no, the extra L tap, and 16 Ohm R tap are not always out of phase.
That is because some signals on a stereo recording already have out of phase signals of L and R, before they even get sent to the amplifier.
Out of phase once, and then going through another out of phase process = in phase.
Over the years I have seen hours of XY displays of stereo recordings, at home and also at several different venues. And on different recordings, music of many kinds, different signal sources, CD, vinyl, FM stereo, tape recorder, etc.
When looking at these XY displays on different stereo recordings, you can see everything from a straight line at 45 Degrees upward slope, to a complete circle filled in with many different paths and directions, causing it to look a lot like a flower.
What you get is anything from near mono, to all kinds of in phases, out of phases, and different amplitudes.
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"Not the clearest " , I have had both eye lenses replaced with plastic due to cataracts ---world of difference ,no glasses required .
I do know it costs $1000,s in the USA but I got it done on the NHS ,its well worth getting done great clarity.
I do know it costs $1000,s in the USA but I got it done on the NHS ,its well worth getting done great clarity.
Thanks for all the answers.
I have read, in audio and electronic magazines of the 60s, the advertisements of stereo amplifiers with a central channel, and I was curious about this.
I had also warned that the connections are not symmetrical.
Look at the circuit that I publish in attachments about a stereo amplifier with a central channel from the 60s, made in my country.
Connections are similar, but not the same as the Fisher X101D.
I await comments.
Best Regards
I have read, in audio and electronic magazines of the 60s, the advertisements of stereo amplifiers with a central channel, and I was curious about this.
I had also warned that the connections are not symmetrical.
Look at the circuit that I publish in attachments about a stereo amplifier with a central channel from the 60s, made in my country.
Connections are similar, but not the same as the Fisher X101D.
I await comments.
Best Regards
Attachments
I think to explain it simply there's a reverse tap on the top output transformer so this generates -R to one terminal of the speaker and L to the other. Thus the speaker generates L+R. Its rather clever. You could hang a subwoofer here. By playing with the taps more you could even widen the stereo image.
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Thanks for the answer,
I don't think the speaker connection generates L + R, for me it is more complex.
I think it is not that simple, it is easy when the manufacturer indicates what the connection is like, and another thing is if you do not know, and you have to do it yourself.
For example in a system with output transformers where their respective secondaries have 3 taps, 4 ohms, 8 ohms, and common (common to ground).
1) if one connects R tap 8 ohms, and L tap 8 ohms the sound is rare, and cut off, the voices are not heard or are heard poorly.
2) if one connects R tap 4 ohms and L tap 8 ohms, the sound is much better, the voices are heard, predominantly treble, mid-range, and bass attenuation.
3) If one connects R tap 8 ohms and L tap 4 ohms the sound is much better too, but different, and inverse to 2)
It is good to read carefully what 6A3sUMMER explained, perhaps he can comment something more about it.-
Best Regards
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Except that Rayma was correct. I have worked on some of these amplifiers and his explanation is the correct one, it is mono (sum) out of the center speaker.
The output transformers have their 4R taps grounded, like Audio Research amps have always done.
(ARC uses this feature for balanced feedback.) This gives +Vout on the 16R tap, and -Vout on the 0R tap.
Each of these outputs is at half of the total output amplitude, and they are "out of phase" with each other.
The 4R tap is electrically a center tap of the secondary, halfway in voltage from the 0R tap to the 16R tap.
With this topology, we should avoid calling the 0R tap "common", because it is not grounded.
Instead the (common ground) headphones return to the 4R tap, which is grounded.
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If you want a real wide image on a 2 channel stereo, just connect one of the speakers out of phase (and only one of the speakers, L only OR R only). That will cause almost all the sound to appear outside and beyond the 2 loudspeakers (Left sound to the left of the left speaker, and Right sound to the right of the right speaker).
The image will appear wide, because there is very little sound in the middle, and you also will cancel almost all of the bass. The results depend on the various recordings you play back.
But seriously, do not listen this way, unless it is just out of curiosity.
I have a friend that has gone to many audio shows, and he always finds some vendor who has had either the L or the R speaker connected out of phase (and they do not even know it).
It is a little like the mistake they made on the Hubble space telescope . . .
Check your setup.
Is your system lacking bass? does the sound emanate beyond the speaker spacing?
Is there hardly any sound in the middle . . . check the phase on both your speakers.
But if you are really seriously wanting to have a center channel, spend a little money.
Purchase an extra amplifier (for the center channel). Then use a resistor from the Left channel output tap, a resistor from the Right channel output tap, and connect the output of those two resistors to the input of the 3rd channel amp, and connect the Common tap of the stereo amp to the common input of the 3rd channel amp.
Now you have a True Center Channel.
The image will appear wide, because there is very little sound in the middle, and you also will cancel almost all of the bass. The results depend on the various recordings you play back.
But seriously, do not listen this way, unless it is just out of curiosity.
I have a friend that has gone to many audio shows, and he always finds some vendor who has had either the L or the R speaker connected out of phase (and they do not even know it).
It is a little like the mistake they made on the Hubble space telescope . . .
Check your setup.
Is your system lacking bass? does the sound emanate beyond the speaker spacing?
Is there hardly any sound in the middle . . . check the phase on both your speakers.
But if you are really seriously wanting to have a center channel, spend a little money.
Purchase an extra amplifier (for the center channel). Then use a resistor from the Left channel output tap, a resistor from the Right channel output tap, and connect the output of those two resistors to the input of the 3rd channel amp, and connect the Common tap of the stereo amp to the common input of the 3rd channel amp.
Now you have a True Center Channel.
RE: Post # 7 schematic:
The impedance of the various output taps:
With both the L and R 4 Ohm taps grounded, that means that the C taps are (- phase) 4 Ohms away from ground.
And that means that the 16 Ohm taps are ( + phase) 4 Ohms away from ground.
We have one end of a "center" speaker connected to the L channel - phase 'common' tap which is 4 Ohms away from ground; and the other end ofthe "center" speaker connected to the R channel + phase tap that is 4 Ohms away from ground.
Now we are loading the various Ohm taps with a L and R speaker, and at the same time with a center speaker.
That means they outputs are nominally overloaded.
Probably should connect L and R speakers this way:
16 Ohm L and R speakers to 8 Ohm taps.
8 Ohm L and R speakers to 4 Ohm taps.
And 4 Ohm L and R speakers to 4 Ohm taps (Oh, but the center speaker is already loading the taps).
And the center channel speaker should be either 8 or 16 Ohm.
As I said in my earlier post, if you want optimal center channel performance, use another amplifier for the 3rd channel.
The impedance of the various output taps:
With both the L and R 4 Ohm taps grounded, that means that the C taps are (- phase) 4 Ohms away from ground.
And that means that the 16 Ohm taps are ( + phase) 4 Ohms away from ground.
We have one end of a "center" speaker connected to the L channel - phase 'common' tap which is 4 Ohms away from ground; and the other end ofthe "center" speaker connected to the R channel + phase tap that is 4 Ohms away from ground.
Now we are loading the various Ohm taps with a L and R speaker, and at the same time with a center speaker.
That means they outputs are nominally overloaded.
Probably should connect L and R speakers this way:
16 Ohm L and R speakers to 8 Ohm taps.
8 Ohm L and R speakers to 4 Ohm taps.
And 4 Ohm L and R speakers to 4 Ohm taps (Oh, but the center speaker is already loading the taps).
And the center channel speaker should be either 8 or 16 Ohm.
As I said in my earlier post, if you want optimal center channel performance, use another amplifier for the 3rd channel.
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