Speakers and amps an impedance

muncybob · 3:19PM

I'm test driving an integrated amp. I know the amp can be run at either 8 ohms or 4 ohms. I've been enjoying it at the default 8 ohm configuration. I think I'm finally hearing what others have been saying about the Polk L600s in that a sub isn't really needed and the clarity/mids are great.

But as usual I wonder what changes I could expect if I change it to the 4 ohm taps to match the nominal impedance of the L600. I hesitate to change this myself as the unit is a loaner and it;s not exactly EZ PZ to do.

billbillw · 3:29PM

I guess that depends on the amp. What are we dealing with here? Class A/B, Class D, Tube amp? I know with the Class A/B amps that use a switch, things generally sound better if you leave it a 8 ohm and just use common sense with the volume knob. The switch usually enables some current limiting.
Class D amps often prefer lower impedence and make really stable power at 4ohms.
I don't have any tube amp experience, so someone else will have to chime in if that is what you are looking at.
How is the change made on this particular amp?

heiney9 · 4:08PM

You don't mention, but sounds like you are running a tube integrated?

Tubes are a different animal than solid state. They are only as good as the output transformers.

It also sounds like it's doing a pretty good job if you are hearing the extended bass you didn't with what you were running before. I can say as an owner of L600's in a medium sized room, I don't need subs for music.
Trust me..............I don't

H9

heiney9 · 4:10PM

What amp, what do the connections look like that it's not easy to change taps? You won't hurt anything just make sure the unit has been powered off for more than a few minutes.

H9

muncybob · 4:12PM

Correct on the tubes call. Trying out the Rogue Audio Cronus Magnum III....not the dark edition.

The wires are so small and in a bit of a cramped area and with the tremors I get in my hands it would not be easy for me.

heiney9 · 4:14PM

billbillw wrote: »

I guess that depends on the amp. What are we dealing with here? Class A/B, Class D, Tube amp? I know with the Class A/B amps that use a switch, things generally sound better if you leave it a 8 ohm and just use common sense with the volume knob. The switch usually enables some current limiting.
Class D amps often prefer lower impedence and make really stable power at 4ohms.
I don't have any tube amp experience, so someone else will have to chime in if that is what you are looking at.
How is the change made on this particular amp?

I does ALL depend on the amp and he hasn't told us yet. Current limiting by a switch (on SS) is not a particularity good amp.
The biggest knock on class D was always they couldn't handle less than 8 ohms.....that has changed in the past few years as designs have matured.

H9

heiney9 · 4:16PM

muncybob wrote: »

Correct on the tubes call. Trying out the Rogue Audio Cronus Magnum III....not the dark edition.

The wires are so small and in a bit of a cramped area and with the tremors I get in my hands it would not be easy for me.

That's a well built beefy amp. Usually the 4 and 8 ohm taps are speaker terminals and swap speaker cables. I didn't realize there was a small internal switch.

billbillw · 5:20PM

heiney9 wrote: »

The biggest knock on class D was always they couldn't handle less than 8 ohms.....that has changed in the past few years as designs have matured.

H9

It's been more than a few years. My old Wyred 4 Sound ST500 made 250wpc into 8ohms and 550wpc into 4ohms without a sweat. That was a design from ~2008 or so.
Back to Bob's issue. I was reading a review of the Cronus Magnum III at Enjoy the Music, and it does sound like it is bit of work to change from 8ohm to 4ohm output. Its not a switch, but you have to move wires around inside the chassis.
"The amplifier is factory set to match 8 Ohm speakers. But you can adjust the speaker load resistance to either 4 or 8 Ohm's depending upon your speakers. But this involves a bit of work. You need to:
1. With a Phillips screwdriver remove the 14 screws holding the top cover. At this time you would have removed the four KT120 output tubes. Insure the amplifier has been turned off for about 30 minutes and the amplifier power cord is connected a ground.
2. With a 0.5" wrench remove the outermost nut from the red positive binding post. Leave the black wire with heat shrink on the post.
3. Remove the 8 Ohm tap (Green wire marked 8) from the binding post. Careful to leave the black wire with heat shrink on the post.
4. Remove the polyurethane tubing from the yellow 4 Ohm wire and lug.
5. Place the polyurethane tubing on the 8 Ohm wire and lug.
6. Place the 4 Ohm wire onto the binding post, and then replace the outer nut. "
That sounds like a patience tester, but it would probably sound better if configured correctly.

heiney9 · 5:32PM

That is involved. Must be a reason they don't just use the speaker taps like many other designs. Probably for better sound and performance.

I could be mis- remembering class D amps of the past. I was never interested in them because I didn't care for the sound profile. Watts has never been a good indicator of sound/performance unless your only goal is high SPL. I'm speaking in general and not knocking any one's gear just because it's high wattage.

The past 20 years I haven't had more than 30 wpc in a SS amp. My current amp is 25 wpc and I still haven't reached its limits.

H9

billbillw · 5:52PM

I've had a few speakers that really needed the watts and current in my large room. I actually need more for the PSB Stratus Gold in my living room now. I'm being patient with plans to get some of the newer Class D monos that can push 500 or so watts into 4.
The NAD I'm using has an auto current limiting circuit, so it doesn't really put out any more watts or current into 4ohms than it does into 8ohms and it is something like 150w into either load.

Speakers and amps an impedance

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