Yet another "Can my amp handle this?" thread

[Unclejunebug]

I've been researching different speaker designs on this site for awhile now and I'm finally at the point where I've made my choice, my shopping cart is full, but I'd like to get some opinions about my current amp before I bite the bullet.

I've decided to go with the Swope MTM's for main surrounds because I like the look, size of the cabinets, and as my first DIY project they don't seem too over the top in terms of difficulty. I'm not well versed in how mixing speaker impedance will effect an amp though. I currently have a Yamaha RX-V363 that is powering a Polk center and two Polk surrounds, all which are 8ohm speakers. The Swopes are designed to be 4ohms so if I do go with this design I'll be combining two 4ohm speakers with three 8ohmers.

According to my receiver's manual at 8ohms it is rated for 100W/ch. There is a menu option to select a 6ohm load but I haven't seen any power rating for the USA model when running at 6ohm.

So am I trying to do something that's out of the realm of possibility for this amp? Will adding two 4ohm speakers to the mix cause too much of a load on my amp?

[BOBinGA]

You should be just fine. The product FAQs say that the protection circuit could active if using speak with less than 4 ohms impedance:

"Other problems which might cause premature shut off can include using speakers with impedance of less than 4 ohms."

This implies that 4 ohms is OK. Plus surround channels are rarely called on to produce most of the sound and therefore draw less current.

-Bob

[Unclejunebug]

Great, I appreciate the response BOBinGA. I figured I would be ok, but haven't ever mixed speaker impedance ratings before.

So follow up question then for my own knowledge. As I understand it receiver speaker terminals are generally in parallel. If I set my receiver to 8ohms and connect five speakers, each with an 8ohm rating the total load impedance becomes 8ohms/5 speakers or 1.6ohms. Is there some internal impedance matching that's going on to raise the load up to 8ohms?

If there is the load would be increased by a factor of 5 to equal 8ohms. So using the Swopes I would have two speakers with a 4ohm rating and three with a 8ohm rating. Since a 4ohm speaker is two 8ohm speakers in parallel, if I'm thinking about this correctly the math becomes 8ohms/7 speakers or 1.14ohms.

So if there is impedance matching going on and with my receiver set to an 8ohm load the total load impedance would still use the same factor of 5 but the total load would equal 5.7ohms.

Am I completely wrong here or am I on track? If I am correct it seems it would be better for me to set my receiver to the 6ohm setting to make the total load only 0.3ohms less than the minimum rating rather than 2.3ohms or would that make any difference at all? The 6ohm setting would result in less of an excess current draw, correct?

[BOBinGA]

The speakers are NOT in parallel. Each speaker is driven by a separate amplifier, so one is not directly influenced by the others. The reason the manufacturer asks you to keep the impedance of each speaker at 6 ohms is so that the output transistors on each amplifier are not asked to produce too much current. Lower impedance = higher output current into the speaker. Current = heat, so too much current will burn up the transistors. That's why they install a protection curcuit to shut down the amp before transistors burn up.

To a lesser degree, the amplifier is also limited by the power tranformer. The more current you ask it to supply, the lower voltage it supplies and this reduces the power output. The more speakers you have connected, the more current you ask the power transformer for. This is where the "parallel" part comes into play. All five amplifiers are connected in parallel to the power transformer and the more you add, the more current the transformer has to supply. Most HT receivers do not have big enough tranformers to supply enough current for five 4 ohm speakers, but the output transistors will fail long before the transformer will.

I am not familiar with your receiver, but if it has a 6 ohm setting (I've never seen an amp with this), it is likely just inserting a 1 or 2 ohm resistor in series with the speakers to increase their impedance to about 8 ohms. This will have a sonic effect by raising the Q of the speaker and causing the mid bass output to increase slightly.

I looked at the impedance of Paul's Swopes (excellent choice BTW) and the minimum impedance just barely reaches 4 ohms. Most manufaturers would call this a 6 ohm speaker, so again, you should be safe. But since you have three 8 ohm speakers and two "6 ohm" speakers, I would just set the receiver to 8 ohms. Then if the amp shuts down when you play it very loud (loud = high current), then set it to 6 ohms. Otherwise, just keep it set for 8 ohms.

Sorry for the long explanation, but I hope this clarifies a few things for you.

-Bob

[Unclejunebug]

Yes, that does clarify a few things indeed. Thanks for the explanation! Sometimes a long explanation is the best explanation.

I feel more at ease now about my choice then and I"ll leave my receiver set to 8ohms and see how it goes. I plan on eventually replacing the Polk center and surrounds with Swopes as well so maybe when I get to that point, and if my receiver starts to crap out on me, I'll just be forced to buy a new toy .

[AdelaaR]

I have a similar receiver, the RX-V771.
I read somewhere that the "6omh" setting on these Yamaha's does nothing but lower the maximum power output so to protect against overheating.
They apparently only have that option to pass certain tests to be able to market it as "6ohm compatible".
According to what I've read it's best to keep the setting at it's original "8ohm" to have full power and dynamics and as long as your speakers are sensitive enough and you don't drive them way too loud it shouldn't present a problem.

[Unclejunebug]

I have a similar receiver, the RX-V771.
I read somewhere that the "6omh" setting on these Yamaha's does nothing but lower the maximum power output so to protect against overheating.
They apparently only have that option to pass certain tests to be able to market it as "6ohm compatible".
According to what I've read it's best to keep the setting at it's original "8ohm" to have full power and dynamics and as long as your speakers are sensitive enough and you don't drive them way too loud it shouldn't present a problem.

Good to know, I'll stick with the 8ohm setting then.

Can I ask what sort of setup you're driving with that receiver and what the load ends up being?

[gregnash]

This is good information as I am in a similar situation as the OP.
I have a pair of Polk RT25s that are about 15yrs old and they were with my Sony STR-DG500 and had been running well. Unfortunately, it seems that during our vacation the Sony decided to crap out as I am only getting sound from one side (left) no matter what I do.

I went and picked up a Yamaha RX-V471 on clearance at my local BB for $257 out the door (display model) and it seems like a great little amp. I had originally joined this forum a few years ago to build myself a set of towers and a sub to match the RTs but never got around to it, then moved, changed jobs, etc.

Anyways, I am back and looking at building the Swope to add to the RTs. The plan is to start with the sub (dont currently have one and would love one and have approximately 450sqft for the livingroom/diningroom area to fill. I figure that I can work with the sub and if it turns out ugly or the building portion is just not my thing then really I can hide the sub in a corner and utilize it.

[AdelaaR]

Good to know, I'll stick with the 8ohm setting then.

Can I ask what sort of setup you're driving with that receiver and what the load ends up being?

I have no idea about the loads, but I drive 2 full Statements and their center channel in combination with 4 F4's as surrounds ... I use the 8ohm setting without any problems ... I just make sure the amp has enough space on top for ventilation and I never drive them beyond -0dB and do most of my listening between -20dB and -10dB.

[gregnash]

I have no idea about the loads, but I drive 2 full Statements and their center channel in combination with 4 F4's as surrounds ... I use the 8ohm setting without any problems ... I just make sure the amp has enough space on top for ventilation and I never drive them beyond -0dB and do most of my listening between -20dB and -10dB.

Do you have a subwoofer attached to the setup?
I know a really dumb question, but looking at the sub for the Swope set, using the BASH 300w amp, I dont see a "single" LFE in that would be used with the monaural sub cable from the receiver. Am I missing something here or am I just completely blind? :rofl:

[Unclejunebug]

I have no idea about the loads, but I drive 2 full Statements and their center channel in combination with 4 F4's as surrounds ... I use the 8ohm setting without any problems ... I just make sure the amp has enough space on top for ventilation and I never drive them beyond -0dB and do most of my listening between -20dB and -10dB.

That sounds about where I expect to be. Currently my listening range is between -20db and -30db and I've never come close to -0db. With the Swopes I expect the need to increase my range a bit due to the lower ohm rating so I think I'll be ok with this receiver. Thanks for the help everyone, I appreciate it!

Now I just need to start building

[Unclejunebug]

Am I missing something here or am I just completely blind? :rofl:

If this is the amp there's a LFE Line Level input in the bottom right corner. Maybe you should get those eyes checked .

[fbov]

http://www.audioholics.com/education/amplifier-technology/impedance-selector-switch-1

Required reading when discussing amps and speaker load ratings. Common sense prevails, if you just use it.

HAve fun,
Frank

[Bear]

Some good advice.

To an extent, all amplifiers and receivers share power. For a truly well-designed dedicated amplifier, this is done at the plug. Downstream from the plug is a power transformer that 'converts' (transforms) the voltage from the wall into something usable by the internal circuitry. Good amplifiers and better receivers use a toroidal transformer, with the receivers having a dedicated one for the amplification that is separate from the other electronics. Downstream of the transformer are the amplification circuits themselves.

Too much current being required at the output/speaker side of the device can cause one or more of these sub-assemblies to overheat and/or to trip a protection circuit/limiter/fuse. Poorly designed or cheaply made products don't have robust protection or build quality and can cause damage. As others have said, let common sense prevail, and go gently if you have any question about whether it can handle the load. The good news is that if you find that it can't handle the power requirement at a volume you find pleasing, then it's time for a new receiver!! :T

Final thought not covered by the above: that wall plug thing. Big amps produce lots of power, but they consume it, too. A class AB amp might be up to 50% efficient, so it is pulling double from the wall what it is putting into your speakers. If the plug you've chosen to use is shared by a bunch of other appliances, then the load might cause issues with others on that leg of your power service, up-to and including tripping the circuit breaker. If you run into issues, don't forget to include looking at the house's power distribution, rather than just looking at the receiver itself.

[gregnash]

If this is the amp there's a LFE Line Level input in the bottom right corner. Maybe you should get those eyes checked .

LOL.. yup that is it, think I was looking at the Dayton 250w amp as well and now see that while it has the dual connections it does have one labeled as "MONO" so assuming that is the single cable connection. Like I said, figured I was missing something. :E

[Glen B]

I read somewhere that the "6omh" setting on these Yamaha's does nothing but lower the maximum power output so to protect against overheating.
They apparently only have that option to pass certain tests to be able to market it as "6ohm compatible".
According to what I've read it's best to keep the setting at it's original "8ohm" to have full power and dynamics and as long as your speakers are sensitive enough and you don't drive them way too loud it shouldn't present a problem.

Receiver 4-ohm and 6-ohm impedance switches lower the rail voltage, which has the effect of limiting the maximum current in the output stage devices.

[Glen B]

Good amplifiers and better receivers use a toroidal transformer,

Audio balderdash and manufacture-speak intended to increase sales. Toroidal transformers are smaller and lighter than their E-I cousins of equivalent capacity and radiate a lower magnetic field, but are not necessarily "better". Toroids allow more EMI/RFI noise to pass from primary to secondary, and are more susceptible to power line DC offset that E-I types. Both have their pros and cons. Some of the finest high end amplifiers employ E-I type transformers.

[Unclejunebug]

Wow, thanks everyone for helping out a noob :P. I just placed my order with PE (using the click through of course) and can't wait to get started!

I'm sure I"ll have plenty more questions along the way.

[Bear]

Audio balderdash and manufacture-speak intended to increase sales. Toroidal transformers are smaller and lighter than their E-I cousins of equivalent capacity and radiate a lower magnetic field, but are not necessarily "better". Toroids allow more EMI/RFI noise to pass from primary to secondary, and are more susceptible to power line DC offset that E-I types. Both have their pros and cons. Some of the finest high end amplifiers employ E-I type transformers.

If the market adopts something, then it becomes a point of parity, not a point of differentiation. You don't increase sales when you are at parity with your competitors (hence the use of the term "parity"). The reason why the market adopts something in a widespread fashion may then be relevant from a performance perspective, or not.

I won't get into a debate when someone comes at me from a perspective of "balderdash" who take me to task for a generalization who then immediately makes one of his own. Sorry, but there are general advantages to toroidal transformers that give them an advantage in most applications where the component budget allows for it. Is this insurmountable? No. Lots of Class D amplifiers don't use toroidal transformers that are considered "high end" by many people (begs all sorts of questions about what performance and/or price level is "high end" versus the ever dreaded and scorned "mid-fi"). That being said, there aren't terribly many "high end" receivers of which I am aware that do not use a toroidal transformer. Whether it is there for performance reasons or "marketing" reasons is irrelevant from a population definition perspective. The same goes in large part for discrete amplifiers, outside of some of the Class D stuff, mentioned above. Are there exceptions? Yes. Are they numerous? No.