Rotel 1572/1575 Power Spec?

[WelshOne]

Can anyone tell me please what the power output is of these amplifiers after 4ohm?

I understand they are 250w into 8ohm, 500w into 4 ohm...............?

My speakers dip down to 3.6ohm, and im curious as to whether my 1575 is sufficient for them.....it certainly sounds good?

The speakers are 803D, HTM2D, 805S. Im considering getting two 1572's to compliment my 803D's, i.e. one amp per speaker, and then the remaining channels on the 1575 to biamp the centre.

Not sure if this will be money well spent, hence the question regarding sub 4ohm impedances, and if crossing the speakers at 60hz yeilds enough of a power release to make any audible difference?

Thanks

David

[MickeyVee]

I have Martin Logan Clarity's and impedance drops down to 1.1 ohms at 20Khz.
I've had great success driving them with the 1067 & 1560 AVR's and recently added a 1572 to drive them. The benefit was a little more overall dynamics and micro-dynamics. The class D amps definitely drive them better than the older class AB amps.

Also, I guess t really depends on where in the spectrum your speakers dip down.

I believe that you will be happy with the 157x series of amps. If you get a chance to audition before you buy, they're definitely worth considering.

[WelshOne]

Thanks MickyVee.

I actually have the 1575, and im really happy with it.

Ive just had an Audionet IV amp to try, and in biamp config it sounds very fast, but its also quite hard, too edgy for my liking. The 1575 sounds softer, more musical, less stressful.

The funny thing is, I had a similar sound from the 803D's when I biamped them with the 1575, I percieved it to be faster and tighter, but it became quite aggressive in its overall presentation?

And to top it off, im now getting distortion from the right speaker when biamping with the 1575, its as if the speaker or the amp doesnt like it? Switc back to stereo or a different amp and it disappears?

I wonder if this has something to do with the way the amp modules are configured, i.e. the way they share power off each other?

Either way, im not too sure if biamping is giving me the sound I thought it would, its just too aggressive/forward for me?

Any comments on my ramble really appreciated!

[Kevin D]

You removed the jumper wires/bars from the back of the speakers when you bi-amped right?

Kevin D.

[WelshOne]

Yep.

i.e:

Left Pre Out (1570) - Y Phono Splitter - Two pairs of phonos - One Phono into main left amp input channel - 2nd phono into rear left input channel. Same set up again from Right Pre Out.

Left Speaker - Bi wire speaker cable - positive wires to both positive speaker terminals - 1st positive wire to main left amp channel input - 2nd positive wire to rear left channel input.

Same again for negative wire/amp channel.

Then when switching on the pre/pro, there is quite a loud pop from the speakers, and you can see the bass drivers suck in/out briefly. Music appears fine for a few seconds, then the right speakers HF becomes distorted.

I swapped the speaker wires around and it made no difference, the right speaker did it again?

I was and still am very confused?

Any thoughts?

[Glen B]

A loud pop/thump and woofer cone suck-in could be an indication of substantial DC offset or a malfunction of the output relay circuit. Significant DC offset will also result in substantial, audible harmonic distortion. Try swapping the preout connections and see if the distortion appears in the left speaker.

[WelshOne]

A loud pop/thump and woofer cone suck-in could be an indication of substantial DC offset or a malfunction of the output relay circuit. Significant DC offset will also result in substantial, audible harmonic distortion.

That sounds about right? I had a similar, but quieter distortion when I tried biamping the HTM2D centre!

What, if anything could I do about that, or is it down to the design of the amp?

Thanks!

[Glen B]

You need to identify whether you indeed have DC coming from the source component, preamp/processor, or amp. Turn on the amp with nothing connected to the inputs. If there is no pop/woofer cone suck-in, that rules out the amp. Move on from there, connecting channels one at a time.

[WelshOne]

You need to identify whether you indeed have DC coming from the source component, preamp/processor, or amp. Turn on the amp with nothing connected to the inputs. If there is no pop/woofer cone suck-in, that rules out the amp. Move on from there, connecting channels one at a time.

Thanks :T

[srb]

Some power amplifiers just don't like to have their inputs connected in parallel with another power amplifier's inputs, as is done with a passive Y-cable. In your case, I would suspect you would be fine if the preamplifier had a pair of buffered/isolated pre-outs for each channel.

In a different scenario, I have an Airport Express' stereo line out into a Y-cable to send a summed mono signal to a single amplified speaker. It sounds terribly distorted. It works fine that way with the previous Airport Express wireless B/G model, but something was changed in the analog output circuitry in the newer wireless N model, which gives me distortion.

Steve

[mjb]

Yes, you're halving the input impedance with two similar amps in parallel, and some sources may struggle to provide the current, hence the distortion. Try using a tape loop, or an aux output or something, for the second amp rather than a Y cable.

[srb]

Yes, you're halving the input impedance with two similar amps in parallel, and some sources may struggle to provide the current, hence the distortion. Try using a tape loop, or an aux output or something, for the second amp rather than a Y cable.

A tape loop is usually a fixed line output not affected by the volume control, so I guess it would have to be an output in front of the volume control like a second pre-out or a sub-out (without a lowpass filter).

I've tried passive bi-amping several times, but have always had better results using a larger, more powerful single stereo amplifier (or two monobolcks) in lieu of passively bi-amping with comparatively smaller stereo amplifiers.

Steve

[mjb]

A tape loop is usually a fixed line output not affected by the volume control, so I guess it would have to be an output in front of the volume control like a second pre-out or a sub-out (without a lowpass filter).

sorry, it needs to be variable for obvious reasons - a second pre-out if available would be ideal.

I've tried passive bi-amping several times, but have always had better results using a larger, more powerful single stereo amplifier (or two monobolcks) in lieu of passively bi-amping with comparatively smaller stereo amplifiers.

This is my experience too. I think all you're actually doing with passive bi-amping is increasing the head room. You'll notice a better improvement using a more powerful amp versus two lesser ones bi-amped.

[Glen B]

Some power amplifiers just don't like to have their inputs connected in parallel with another power amplifier's inputs, as is done with a passive Y-cable. In your case, I would suspect you would be fine if the preamplifier had a pair of buffered/isolated pre-outs for each channel.

Schematics for some older model Rotel surround receivers and processors show each preout being driven by its own 16dB gain stage. I would hope that later models are similarly configured.

Yes, you're halving the input impedance with two similar amps in parallel, and some sources may struggle to provide the current, hence the distortion.

The OP is experiencing distortion in one channel. The inability to drive multiple outputs should manifest itself in both channels. It also does not explain excessive woofer cone movement upon turn-on.