I find this is be far the most informative and interesting audio channel on youtube, Paul is a true master of audio engineering, and he explains with great clarity. Thanks Paul and more power to you.
I remember a Harmon Kardon amp from the '90s that had a selector for 4 or 8 ohms. That switch selected different secondaries on the power supply transformer and offered greater current with less voltage at the 4 ohm setting. That amp had no problem driving 4 ohm 12" Hsu Research subs with hundreds of watts with the selector on 8 ohms. Maybe it sounded better full range with a 4 ohm speaker set to 4 ohms. Never tried. Is anyone else jealous of Paul for the view from his office? Kudos for building great products and a company that provides jobs for others.
I have adjustable impedance on one of my favorite amplifiers from centrance and it works rather well. I have found it affects some headphones more than others. Some it makes for a more clean and lean sound and some it adds more body and bass without sacrificing detail and the class a power output. Not a regular 2 channel amp but thought I would chime in. Thanks paul!
in headphones there are more (and wider) variaties in impedance than with modern loudspeakers (mostly 4 or 8 Ohms) so yes, with headphones that make real sense and a hell of a difference!
@@MrsZambezi That's interesting but no real impedance matching. Lowering impedance is decreasing voltage and increasing current while maintaining the same power. It works, the way you describe, but you will lose a lot of power. And you are right that doing this wouldn't affect headphones. On the other hand, real impedance matching at the output rail will because in most amplifiers, the headphones are directly connected to the loudspeaker output, where the impedance of the headphones (32 Ohms and higher) will limit the current.
Many inexpensive solid-state receivers have impedance switches, not for selecting transformer taps, but to change the way the power supply operates. It is Usually an indication of compromised circuit design. One of my vintage pieces is an HH Scott Stereomaster 260, that brand's first solid-state integrated amplifier, which was introduced in late 1964. That unit has switch settings for 8-16 ohm or 4 ohm speakers. I'm not Exactly sure what it does, but I Believe it affects the level of negative feedback.
Simply lowers the rail voltage, so that the dissipation in the output devices does not exceed the safety limit. Amps generally try to operate as voltage sources, doubling the power with impedance halved.
@@spacemissing You're right, it's an adjustable voltage divider between the common tap of the output transformer and the cathode of the 12AX7 input in the feedback loop. It affects gain, hence the output impedance/damping factor.
@@paulb4661 I made an error in the model number, which I have corrected by editing above. My amplifier is not a 240; it is a 260 --- which is Solid State --- no 12AX7s in it.
There are some low-end receivers that have a switch for 8 ohm or 4 ohm speakers. Paul may not be familiar with these because they are budget designed and not stable with low impedance speakers. The switch changes the "A" and "B" speaker outputs from parallel to series if you switch to 6/4 ohm position. The great thing about PS Audio amps is that they deliver enough current to safely and efficiently drive a 4 ohm load, thus, no need for a switch.
Even some of the higher-end Yamahas still have this switch. On my particular yamaha, I'm wondering what impedance switch to use with my 6 ohm speakers. The speakers have 6 ohm nominal impedance but the amplifier has a setting that is either 8 ohm minimum impedance or 4 ohm minimum impedance. Half the people I talk to say leave it on 8, the other half of people I talked to said it's best to set it on 4. This has been so unbelievably frustrating because I've been trying to get a definitive answer for 4 days now.
Some solid state amps had a "speaker impedance switch" but all they did was detune the power supply in the lower impedance setting so an amp that was thermally unstable at 4 ohms under full B+/- would be a bit less pissed off at the reduced rails.
Paul, tube amplifiers obey electrical impedance matching theory, in general, solid state amps do not. There are two reasons why the manufacturer's impedance recommendation should be adherred to: (1) has the amplifier designer verified amplifier STABILITY under ALL possible load & ambient conditions? (2) has the designer verified SAFE output transistor & power supply capacitor operation under all possible load & ambient conditions? An unstable or unsafe amplifier could destroy itself and/or the speakers. If the above conditions are met, lower than recommended loads are fine as long as expected output power is reduced proportionally & the amplifier is well ventilated.
A lot A/V receivers have the switch to go from 8 to 4 ohms. The issue with the switch is it's a "limiter" of "filter" that cuts off the high and low ends so it will still work and not overload amp inside.
McIntosh put an auto-transformer (single winding) on their early solid state amps and for several good reasons. Early power transistors in the 1960s were not reliable. So they designed the output stage to be stable into 2 ohms then used the auto transformer to match the speaker nominal impedance. Another benefit was speaker protection. The driven 2 ohm tap had very low DC resistance. So if an output transistor shorted, the transformer winding would shunt the DC current to ground until the fuse blew. This was highly reliable whereas even today fuses alone and protection relays are not as fool proof.
Most modern run of the mill Japanese stereo and AV receivers still have this switch. Most component amps seem to make it a point to design to be at least 4ohm or lower. It would be interesting to know what these switches due in the lower end solid state amps.
I read somewhere (when reading about my Yamaha RX-V4A) that the software switch at least actually changes the max rail voltage on the power supply for the output stage sees or something along that line, so in fact it just changes the limit such that lower impedance speakers act less stressful on the amp circuit. In the case of my DIY 5.1 cinema the speakers I am designing end up being around minimum of 4.54ohms @ 300hz, i think I've ended up not even changing the setting and left it set on 8ohm in the receiver, or might set it to 6ohm at least to relieve the stress a bit.
@@tobiasautoandaudio7337 If my Yamaha integrated amplifier has two options: 1. 8 ohm minimum impedance. 2. 4 ohm minimum impedance but my speakers have a 6 ohm nominal impedance rating, which option should I choose?
My Yamaha separates from the late 80s M line has buttons on the front of the amp to go from 2 ohm, 4 ohm, 8 ohm. This amp puts out 260 wpc at 8 ohm , I rarely touch them
Some tube amp manufacturers use switches, e.g. Decware. Not sure what the respective advantages and disadvantages are, guessing one costs more than the other, but surely space restrictions may the primary reason.
So Paul what kind of a load do you have on those three outlets and that power strip? Hopefully, each outlet is on its own circuit, because if it's not the insurance company will probably use this video as evidence to not pay a claim on any electrical fire. Just sayin
I would not call it automatic, a solid state amp is in essence a voltage source, so it needs no impedance matching. You would also not call a drive train with only one gear ratio an automatic transmission.
If it's a modern solid state amplifier it should be just fine. The thing is to never go below it's rated output impedance ... i.e. don't connect 4 ohm speakers to an 8 ohm amplifier. Going higher just makes the amplifier's job easier.
@@bikdav In multi-channel amplifiers it's done to protect the power supply. Lower impedance speakers draw more current... so they adjust the outputs to safe levels.
I worked in consumer electronic manufacturing for about 40 years. We typically had a "mess" going on in our shop because of constantly changing equipment around. Our prototypes were nicknamed "tucker" because of all the open and looses wires. We would try different amps, pre-amps, speakers, etc, and it looked messy.
Paul, receivers - av or stereo (such as YAMAHA and ONKYO) - have this. NOT one expert has given us a valid reason why. All I got was snooty and uniformed responses from audiophiles.
This is likely related to the current limits of the power supply. A 4 ohm load will draw twice as much current as an 8 ohm one. So to protect the power supply they will reduce the output on each channel.
@Douglas_Blake_579's answer is the correct Technical answer AND the Manufacturering answer is to meet Safety regulations. Manufacturers need these switches in or to 'detune' their AVRs which would then PASS safety tests whereby the amplifier is run very hard for very long and the Heat disapation abilities of the AVR were able to keep up and therefore giving the Manufacturer a PASSING grade which then gave them their Safety Certification (so for example the "UL" safety certification). So IMO, if any AVR / Amplifier is in need of this switch (which the manufacturer toutes as a FEATURE), I look elsewhere! Please note that there are a few rare (and I mean very rare) occasions where it was NOT done for passing safety standards and instead to help maximize output for owners of 4 ohm speakers vs 8 ohm speakers, but so very rare was this the case for solid state amplifiers (for Tube amplifiers as Paul mention sure).
@@johndaddabbo9383 "Safety Standards" also includes not burning down your house when you overheat the power supply feeding a 7.2.4 setup, all running at 4 ohms. 11 channels, 50 watts each, 4 ohm loads == 40 amps DC load.
@@Douglas_Blake_579 You're too funny. Simply set the switch as you advise -OR- use 8 ohm speakers (either way) and then CRANK the volume and you will STILL fry the AVR/Amp/Receiver. So a moot point buddy. "Burn down your house" too funny 😆.
@@johndaddabbo9383 Oh boy... another bruised ego. People are best advised to follow the manufacturer's recommendations ... that is if they still want the warranty and don't want to damage their equipment or reduce it's lifetime. The objection is to this "I know better than the engineers" thing that so many people have going on these days. 40 years in the trade and I've rarely seen any case where that is actually true.
There are some modern solid state amps (AV receiver, at least) that do have "impedance" switches which only switch to lower voltage power transformer secondaries for 4 ohm operation. Sort of cheating to get away with smaller power transformers, I suspect. The amp sections run cooler too, as the VI product is less across the power transistors. Like I say, sort of cheating.
I find this is be far the most informative and interesting audio channel on youtube, Paul is a true master of audio engineering, and he explains with great clarity. Thanks Paul and more power to you.
I remember a Harmon Kardon amp from the '90s that had a selector for 4 or 8 ohms. That switch selected different secondaries on the power supply transformer and offered greater current with less voltage at the 4 ohm setting. That amp had no problem driving 4 ohm 12" Hsu Research subs with hundreds of watts with the selector on 8 ohms. Maybe it sounded better full range with a 4 ohm speaker set to 4 ohms. Never tried. Is anyone else jealous of Paul for the view from his office? Kudos for building great products and a company that provides jobs for others.
I have adjustable impedance on one of my favorite amplifiers from centrance and it works rather well. I have found it affects some headphones more than others. Some it makes for a more clean and lean sound and some it adds more body and bass without sacrificing detail and the class a power output. Not a regular 2 channel amp but thought I would chime in. Thanks paul!
in headphones there are more (and wider) variaties in impedance than with modern loudspeakers (mostly 4 or 8 Ohms) so yes, with headphones that make real sense and a hell of a difference!
@@hugoromeyn4582 The impedance switch on SS amplifiers just reduces the rail voltages on low impedance speakers. It has no effect on headphones.
@@MrsZambezi That's interesting but no real impedance matching. Lowering impedance is decreasing voltage and increasing current while maintaining the same power. It works, the way you describe, but you will lose a lot of power. And you are right that doing this wouldn't affect headphones. On the other hand, real impedance matching at the output rail will because in most amplifiers, the headphones are directly connected to the loudspeaker output, where the impedance of the headphones (32 Ohms and higher) will limit the current.
@@hugoromeyn4582 No, that's what the switches do.
Many inexpensive solid-state receivers have impedance switches,
not for selecting transformer taps, but to change the way the power supply operates.
It is Usually an indication of compromised circuit design.
One of my vintage pieces is an HH Scott Stereomaster 260, that brand's first solid-state integrated amplifier,
which was introduced in late 1964. That unit has switch settings for 8-16 ohm or 4 ohm speakers.
I'm not Exactly sure what it does, but I Believe it affects the level of negative feedback.
Simply lowers the rail voltage, so that the dissipation in the output devices does not exceed the safety limit. Amps generally try to operate as voltage sources, doubling the power with impedance halved.
@@paulb4661 Maybe in most cases, but not in the SM260,
where the switch is plainly in the speaker circuit, not in the power supply.
@@spacemissing You're right, it's an adjustable voltage divider between the common tap of the output transformer and the cathode of the 12AX7 input in the feedback loop. It affects gain, hence the output impedance/damping factor.
@@paulb4661 I made an error in the model number, which I have corrected by editing above.
My amplifier is not a 240; it is a 260 --- which is Solid State --- no 12AX7s in it.
There are some low-end receivers that have a switch for 8 ohm or 4 ohm speakers. Paul may not be familiar with these because they are budget designed and not stable with low impedance speakers. The switch changes the "A" and "B" speaker outputs from parallel to series if you switch to 6/4 ohm position. The great thing about PS Audio amps is that they deliver enough current to safely and efficiently drive a 4 ohm load, thus, no need for a switch.
Even some of the higher-end Yamahas still have this switch. On my particular yamaha, I'm wondering what impedance switch to use with my 6 ohm speakers. The speakers have 6 ohm nominal impedance but the amplifier has a setting that is either 8 ohm minimum impedance or 4 ohm minimum impedance. Half the people I talk to say leave it on 8, the other half of people I talked to said it's best to set it on 4. This has been so unbelievably frustrating because I've been trying to get a definitive answer for 4 days now.
I remember the PS Audio having an outboard power supply..lol. Wicked. Love this educational channel.
Some solid state amps had a "speaker impedance switch" but all they did was detune the power supply in the lower impedance setting so an amp that was thermally unstable at 4 ohms under full B+/- would be a bit less pissed off at the reduced rails.
Paul, tube amplifiers obey electrical impedance matching theory, in general, solid state amps do not. There are two reasons why the manufacturer's impedance recommendation should be adherred to: (1) has the amplifier designer verified amplifier STABILITY under ALL possible load & ambient conditions? (2) has the designer verified SAFE output transistor & power supply capacitor operation under all possible load & ambient conditions? An unstable or unsafe amplifier could destroy itself and/or the speakers. If the above conditions are met, lower than recommended loads are fine as long as expected output power is reduced proportionally & the amplifier is well ventilated.
A lot A/V receivers have the switch to go from 8 to 4 ohms. The issue with the switch is it's a "limiter" of "filter" that cuts off the high and low ends so it will still work and not overload amp inside.
McIntosh put an auto-transformer (single winding) on their early solid state amps and for several good reasons. Early power transistors in the 1960s were not reliable. So they designed the output stage to be stable into 2 ohms then used the auto transformer to match the speaker nominal impedance. Another benefit was speaker protection. The driven 2 ohm tap had very low DC resistance. So if an output transistor shorted, the transformer winding would shunt the DC current to ground until the fuse blew. This was highly reliable whereas even today fuses alone and protection relays are not as fool proof.
Most modern run of the mill Japanese stereo and AV receivers still have this switch. Most component amps seem to make it a point to design to be at least 4ohm or lower.
It would be interesting to know what these switches due in the lower end solid state amps.
I read somewhere (when reading about my Yamaha RX-V4A) that the software switch at least actually changes the max rail voltage on the power supply for the output stage sees or something along that line, so in fact it just changes the limit such that lower impedance speakers act less stressful on the amp circuit. In the case of my DIY 5.1 cinema the speakers I am designing end up being around minimum of 4.54ohms @ 300hz, i think I've ended up not even changing the setting and left it set on 8ohm in the receiver, or might set it to 6ohm at least to relieve the stress a bit.
@@tobiasautoandaudio7337 If my Yamaha integrated amplifier has two options: 1. 8 ohm minimum impedance. 2. 4 ohm minimum impedance but my speakers have a 6 ohm nominal impedance rating, which option should I choose?
My Yamaha SS amplifier has an impedance switch for the speaker output (RS701, AS301, etc)
I have a fairly modern (last year) Yamaha amp that is switchable between 4 ohm and 8 ohm.
My Yamaha separates from the late 80s M line has buttons on the front of the amp to go from 2 ohm, 4 ohm, 8 ohm. This amp puts out 260 wpc at 8 ohm , I rarely touch them
Some tube amp manufacturers use switches, e.g. Decware. Not sure what the respective advantages and disadvantages are, guessing one costs more than the other, but surely space restrictions may the primary reason.
I use crown power amps no need to select what impedance I am running just have to make sure all my speakers are 8 impedance and lower 😊
So Paul what kind of a load do you have on those three outlets and that power strip?
Hopefully, each outlet is on its own circuit, because if it's not the insurance company will probably use this video as evidence to not pay a claim on any electrical fire.
Just sayin
More like a voltage selector
I find the switch limits current on 6ohm mode so i just leave it in 8 ohm mode and my yamaha seems to have more top end jam.
Some guitar amps have different speaker outputs for different ohm ratings . Be nice if it was done automatically .
So Paul,
What is that new product sitting there teasing us?😄
NAD amps have had such switches
I would not call it automatic, a solid state amp is in essence a voltage source, so it needs no impedance matching. You would also not call a drive train with only one gear ratio an automatic transmission.
My speakers are 16 ohms and always wondered if my 8 ohm amplifier was the best match or should i find one rated to 16 ohms?
If it's a modern solid state amplifier it should be just fine.
The thing is to never go below it's rated output impedance ... i.e. don't connect 4 ohm speakers to an 8 ohm amplifier. Going higher just makes the amplifier's job easier.
@@Douglas_Blake_579 appreciated
@@gtric1466
You're welcome.
But where did you find 16 ohm speakers in this day and age?
@@Douglas_Blake_579 i think Zu makes 16 ohm speakers.
@@Ian-wh8ut
Interesting ... It's been literally years since I've seen 16 ohms. Thanks
How'd I would love to spend a day at that facility. I would not be able to leave.
My onkyo 7.1 reciever want information on lowest speaker impedance. Setting of min. 4 or min 6 ohm.
Mine has this. NOT one expert gave us a valid reason why.
@@bikdav your reciever use more power when low impedance speakers suck on the reciever.
@@bikdav
In multi-channel amplifiers it's done to protect the power supply. Lower impedance speakers draw more current... so they adjust the outputs to safe levels.
@@Douglas_Blake_579Exactly, which is why one should not use the switch for driving their 4 ohm rated speakers 😊
@@johndaddabbo9383
Gee lets see now ... loose a couple of DB output or kill the power supply? Hmmm... which will I choose?
Look at the unsafe wiring mess. is that a PS audio standard.
I worked in consumer electronic manufacturing for about 40 years. We typically had a "mess" going on in our shop because of constantly changing equipment around. Our prototypes were nicknamed "tucker" because of all the open and looses wires. We would try different amps, pre-amps, speakers, etc, and it looked messy.
Paul, receivers - av or stereo (such as YAMAHA and ONKYO) - have this. NOT one expert has given us a valid reason why. All I got was snooty and uniformed responses from audiophiles.
This is likely related to the current limits of the power supply. A 4 ohm load will draw twice as much current as an 8 ohm one. So to protect the power supply they will reduce the output on each channel.
@Douglas_Blake_579's answer is the correct Technical answer AND the Manufacturering answer is to meet Safety regulations. Manufacturers need these switches in or to 'detune' their AVRs which would then PASS safety tests whereby the amplifier is run very hard for very long and the Heat disapation abilities of the AVR were able to keep up and therefore giving the Manufacturer a PASSING grade which then gave them their Safety Certification (so for example the "UL" safety certification). So IMO, if any AVR / Amplifier is in need of this switch (which the manufacturer toutes as a FEATURE), I look elsewhere! Please note that there are a few rare (and I mean very rare) occasions where it was NOT done for passing safety standards and instead to help maximize output for owners of 4 ohm speakers vs 8 ohm speakers, but so very rare was this the case for solid state amplifiers (for Tube amplifiers as Paul mention sure).
@@johndaddabbo9383
"Safety Standards" also includes not burning down your house when you overheat the power supply feeding a 7.2.4 setup, all running at 4 ohms.
11 channels, 50 watts each, 4 ohm loads == 40 amps DC load.
@@Douglas_Blake_579 You're too funny. Simply set the switch as you advise -OR- use 8 ohm speakers (either way) and then CRANK the volume and you will STILL fry the AVR/Amp/Receiver. So a moot point buddy. "Burn down your house" too funny 😆.
@@johndaddabbo9383
Oh boy... another bruised ego.
People are best advised to follow the manufacturer's recommendations ... that is if they still want the warranty and don't want to damage their equipment or reduce it's lifetime.
The objection is to this "I know better than the engineers" thing that so many people have going on these days. 40 years in the trade and I've rarely seen any case where that is actually true.
Yamahas still have these switches though.
Hahaha Palos Verdes, I'm next door in torrance Beach
There are some modern solid state amps (AV receiver, at least) that do have "impedance" switches which only switch to lower voltage power transformer secondaries for 4 ohm operation. Sort of cheating to get away with smaller power transformers, I suspect. The amp sections run cooler too, as the VI product is less across the power transistors. Like I say, sort of cheating.
Then there is McIntosh with their Autoformer just to confuse things
theres nothing confusing about it
@@SantanKGhey1234 Not about it, but how it relates to Paul's video, with transformers being a valve/tube thing.