Bi amp question

crashb4

Guys,
First, Happy new year to all. I have a question that I would like your expert opinions on. I am currently running a Rotel RMB1075 5 channel amp into my 1st gen SDA SRS. The amp is rated at 200W at 4 ohms x 5 channels. Would there be any benefit or pitfall to bi amping to these speakers? I.e. R.f. To low frequencie and r.r. To high. Only looking for more headroom
Thanks for any input.

Schurkey

1st Gen SDA SRS are "4-ohm" speakers. If your amp shares the power supply among the various channels, I'd expect no difference unless the heat sinks get overly-warm in the channels that are actually driving the SRS.

If the amp uses separate power supplies for each channel, you might gain some current (amperage) output by bi-amping as you've described.You don't gain any voltage unless the amp is severely current limited at less than a 4-ohm load; enough so that voltage sags when the current demand increases.

Edit: I looked at the owner's manual for the RMB-1075
http://rotel.com/product/rmb-1075 then click on "Resources" then click on "Owner's Manual".
They list "120 watts" into an 8-ohm load, but don't specifically state that all channels are driven.
They don't list a power spec at all for 4-ohm loads. Where are you getting the 200-watt figure?

crashb4

I don't rely on manufacturer's specifications for amp power ratings. They are not nearly as accurate as real world tests and often do not tell the whole story. Here are the results of actual tests on this amp.

http://www.soundandvision.com/content/rotel-rmb-1075-5-channel-power-amplifier-measurments#Ll3s2zUo1FztoEsb.97

"With all five channels driven into 8ohms, the Rotel clipped (1% THD+noise) at 131 watts per channel at both 20Hz and 1kHz. Into 4ohms, clipping occurred at 204Wpc at 20Hz and 212Wpc at 1kHz. With two channels driven, the RMB-1075 clipped at 161Wpc into 8ohms and 264Wpc into 4ohms. All results presented here are for the left channel, to the nearest watt, at a line voltage of 120V.—TJN"


Far more telling than the Rotel spec sheet.

Thanks for your reply.

pitdogg2

That amp will never have the current needed to do those speakers justice no matter how you Hook it up.

I smell the magic smoke about to leave the building.

crashb4

The amp actually drives the speakers effortlessly. 60% volume can nearly drive you from the room. The unit remains luke warm to the touch and provides quite a punch. That being said, the goal is a Krell KSA-200S. With a new house purchase, that will have to wait. In the meantime, the Rotel is quite pleasing.

F1nut

The amp is rated at 200W at 4 ohms x 5 channels

Definitely not.

What those Sound and Vision specs are showing is the power supply is shared as evidenced by the drop in output when more than 2 channels are driven. Therefore, pitdogg2's comment has merit.

I would suggest not using more than 2 channels.

crashb4

This amp is strictly two channel currently. It will be returned to its natural habitat (HT duty) when I secure a true two channel amp. I understand the limitations of a shared power supply and work within its capabilities. I guess that I answered my own question with the quoted test results. I do appreciate the input by all.

gp4jesus

I pretty much concur w/the consensus.

Schurkey wrote: »

If the amp uses separate power supplies for each channel...

It does not. The 1075 is, essentially, a very robust, much higher SQ AVR power amp section w/ a single secondary transformer winding driving a rectifier (RB) & cap bank (CB). It's first gen ancestor, the 985 (Mk 1), rated @ 100 WPC/8 ohms, offers a single secondary transformer winding driving 3 RB & 3 CB to drive 5 channels. The CC gets its own RB & CB*. The left front & surround share a RB & larger CB** as do the right front & surround. Parasound's HCA-855 & 1205 specs claim separate secondary windings, CB, & CB for each channel. I have yet to look under the hood to verify same.
* 20Kuf ** 30Kuf

Schurkey wrote: »

1st Gen SDA SRS are "4-ohm" speakers. If your amp shares the power supply among the various channels, I'd expect no difference unless the heat sinks get overly-warm in the channels that are actually driving the SRS.

If bi-amping w/an AVR, a frequent debate on this forum, results in cooler chassis temps that can't be bad.

Schurkey wrote: »

you might gain some [add'l] current output by bi-amping*...

If you have the wire, bananas, & that commodity which eludes me, time, try it*. If your amp runs cooler w/no SQ penalty you've gained something however small.

Happy 2017, Tony