SDA2 A with NAD question

Hansen2112

I recently picked up a set of sda2 A's and am running them with a NAD 7240PE that is supposed to be high current even though only 40 Wpc. Apparently this receiver has lots of Headroom and should be okay I think, sounds good to me right now.

Question is regarding the impedance setting on amp, can be set for 4(normal) or 8 ohm. I understand these speakers can dip down to 4 Ohms at times but shouldn't I leave the setting on 8 to maximize current? If I put to 4 ohm setting does that not then limit current which the speakers require?

On a side note I have an opportunity to buy a BK ST-202 power amp from a neighbor, would this be a better option to run with the Polks?

Thanks for any help

pitdogg2

They start at 4 ohm and can drop to 3 ohm or lower. Leave the setting at 8ohm. The switch is just a current limiting device and could starve the speakers. You will need a more robust higher current and wattage amp. You cold get along well with the current amp as long as you do not want to get your rock n roll on...

Hansen2112

Nice, that's kind of what I thought. However the manual for this receiver kind of suggest that current increases in the 4 ohm setting. Either way they sound pretty good now

Gardenstater

After reading the NAD manual, I would definitely leave it on the 4 Ohm (normal) setting. I'd also leave the soft clipping on if you play loud.

invalid

I've owned the 2a's since 1987, and they are definitely harder on amps than any other 4ohm speaker I have owned.

Hansen2112

From the manual

Not sure if it's marketing Mumbo Jumbo, I thought higher power and current at 8 ohm setting.

I've already got two different answers, one saying leave it at 4 the other saying definitely put it at 8. Now I'm really confused LOL

Gardenstater

Sorry only trying to help not confuse Read the manual just a bit further, especially the CAUTION:



Whether or not they are being deceptive I couldn't tell you, but it would be a little late to come up with hype to make a sale, in the owner's manual. That would probably be in advertising copy. It doesn't seem to encourage a sale to me though anyway.

Hansen2112

Yeah that makes sense, I agree. Think I'll just leave it at 4 for now until I can find a more suitable amp.
Anyone got any reviews of the BK ST 202, and how it would work within the SDAs?

Recently recapped I understand

Gardenstater

If you wanted to take a skeptics approach of proving to yourself, you could maybe play some whitenoise at a reasonably high volume level as measured with an sPL meter and measure the temperature of the amp after an hour with the switch in either position. See if it runs cooler in the 4 Ohm position. I'd probably do the 4 Ohm first and then shut down the experiment if the 8 Ohm goes much higher.

Clipdat

How loud do you usually listen?

Hansen2112

Not super loud, and my Listening Room is fairly small. Again the speakers sound great and I'm really digging the sda effect but just curious if I am getting the most out of them with this amp and its ohm setting.

Gardenstater

Is it possible to borrow your friend's neighbor's amp and give it a spin, on your system? The power is much higher obviously. Should be more capable if it is able to handle the low impedance without getting too hot and if it has the headroom to handle musical peaks without clipping. I didn't find the manual online.

Clipdat

Very open ended question. What does "the most out of them" mean? Every amp sounds different, regardless of it's wpc rating. You could go to a 100-150wpc amp and hate the sound compared to the NAD.

Clipdat

Oh and regarding the ohm setting I would just try it each way and see which sounds better. It won't hurt the amp or the speakers.

pitdogg2

In most instances that switch is a current limiting feature. Reading that still leads my to believe it is STILL a current limiting feature. It's throttling back the receiver so it doesn't run away with current i.e. heat. An amplifier with a good power supply will nearly double the wattage from 8 ohm to 4ohm and then again into 2ohms.
An amplifier or receiver that cannot do that will get very hot. Your instructions actually speak about that.

My .02

Try it both ways.
I agree with @invalid. I've had those speakers and they cooked more than one receiver due to the inability to be able to provide the current needed to drive the speakers.

If the B&k has been recapped it's a decent starter amp.

Gardenstater

My turn to be confused I guess and not being snarky. How do they produce "maximum power" into 2 to 6 ohms by limiting current? So this is just mumbo jumbo then I guess. Ohms law has to still apply. Maximum power meaning the most power without overheating amp? So much of what manufacturers claim regarding amps seems to be misleading so I wouldn't doubt it......

I think it'd be really interesting to see which switch position results in the lowest amp temperature when producing 90 dB sPL with whitenoise and at what volume knob position.

pitdogg2

Limiting current keeps the output transistors or other stuff from going nuclear. Have you found a 4 ohm output rating from the manufacturer? I didn't.

Gardenstater

Not continuous average power rating no. That is pretty common though in my experience from looking at specs of even highly respected amplifiers. They do give Dynamic Power ratings into 4 and 2 ohms of 200W and 250W, when the switch is set to 4 ohm setting. 6dB Dynamic headroom at 8 ohms is huge.

pitdogg2

Sorry Geo, Homie don't play that dynamic power stuff. It also states clipping at 50 wpc at 1kHz.

invalid

What does this impedance switch do on the NAD? Does it lower the rail voltage?

xschop

If you could run dual monoblocks, would you then have SDA-2A's with NADS?