Question with using receiver as pre/pro for 1075

[myki]

I just got a Rotel RMB-1075 and a Marantz SR4500 as a temporary pre/pro. I will need to save up for the RSP-1066 or 1068 first.

I've hooked all my speakers to the 1075 so the receiver only acts as a pre/pro. I've noticed that even with no speakers attached to the receiver, it gets pretty warm. A lot warmer than the receiver WITH speakers connected. And definitely a lot warmer than the 1075.

Will I damage my receiver's built-in amp this way? I'm thinking that maybe the receiver's amps are driving harder since it sees a load with infinite ohms (no speakers, no flow).

So I'm thinking, maybe I should connect my surrounds to the Marantz just so that it doesn't complain of driving air!

Any suggestions or insights?

Maybe I could get a skilled electronics guy to open up the receiver and temporarily disable the amps. That might reduce heat, reduce wear-and-tear, reduce electric consumption, and maybe even improve the quality of the pre-pro.

[Aussie Geoff]

Hi,

Interesting. One thought for you is that many amps use a class A/B curcuit where they run in a class A mode for low power (can be 1-20W per channel) and move to class B at a higher power level. A thing called a BIAS current is set internally to control the level between the Class A and Class B. Now Class A is on on all the time and therefore generates heat all the time... So your Reciever could be (with no load) running all channels as class A and therefore generating (say) 5 x 10W heat doing nothing!... It should be designed for this - so as long as the ventelation is good and you can still touch the amplifier without feeling burnt I'd not worry.

Geoff

[Andrew Pratt]

I ran my rotel receiver as a pre amp with out and load on it for months with out any issue at all. The receivers don't have nearly as much heat sink material as the 1075 power amps do so they'll naturally run hotter

[jlee]

I posted this on another thread, but got no response... I had an RMB-1095 and when upgrading to CAM-200 monoblocks, I had CAM-200's for the fronts, RB-1080 for the rear, and was using the 1095 ONLY for the center channel while waiting for my 3rd CAM-200. It blew the center channel... hooked it up to the right front... worked fine for a few days... then it blew... hooked it up to the right surround... worked fine for 1.5 weeks... then it blew.... hooked it up to the left front and it worked... but thankfully at this point, my CAM-200 arrived and I traded in my damaged (but to be fixed under warranty) 1095 to the dealer... what could cause something like this? Did the folks at Rotel assume the 1095 would always be hooked up with at least 2 channels and somehow that 1 channel was being overloaded or something?

[Aussie Geoff]

Jlee,

I've never heard of this issue before...

One possibility is that you were blowing the internal channel fuses of the RMB-1095 (which can also happen to the RB-1080 with some speaker / wire combinations... Given that you were switching the same speaker and wire to each channel...

Quite a few peoiple run the RMB-1095 in stereo etc as a fallback so I don't see why it should blow one channel.

Anyway - with it gone now - it probably doesn't matter...

Geoff

[jlee]

>I've never heard of this issue before...
One possibility is that you were blowing the internal channel fuses of the RMB-1095 (which can also happen to the RB-1080 with some speaker / wire combinations... Given that you were switching the same speaker and wire to each channel...

Thanks for being the only guy to take the time to respond!

>Quite a few peoiple run the RMB-1095 in stereo etc as a fallback so I don't see why it should blow one channel.

Right, but in this case this was ONE channel only (not stereo). I've ran the 1095 with just 2 channels before with no problem.. this only happened when a single interconnect and single speaker cable was attached to it. Weird huh?

>Anyway - with it gone now - it probably doesn't matter

Yeah, just curious though... cuz I too have never seen something like that.

[myki]

Hi,

Interesting. One thought for you is that many amps use a class A/B curcuit where they run in a class A mode for low power (can be 1-20W per channel)
Geoff

Hi Geoff,

Your post made me researched on what kind of "Class" the Marantz receivers are. And you're right! Here is what I got:

Marantz SR4500 AV Receiver ¯SÂI¤Î³W®æ¡G
¡E 125W X 7 (6 ¼Ú©i EIAJ)
¡E §¡µ¥¿W¥ß 7 Án¹D©ñ¤j¾¹
¡E ¨âÁn¹D®É*«¼½®É±Ä¥Î 12W Smart Class A ¤u§@
¡E ¨ã³Æ SACD ¡® DVD AUDIO *«¼½*n¨D¤§ ¶W°ª ¼eÀW©ñ¤j
¡E ±Ä¥Î Cirrus Logic CS49400 32 BIT DSP ¹Bºâ´¹¤ù
¡E ±Ä¥Î Cirrus Logic CS42428 , 24BIT / 192KHz ¼Æ½X / ¼ÒÀÀ Âà´«¾¹

I don't know what language it is but there's a line which says 12W Class A. So your hypothesis was correct. So that means I'm wasting 12W x 7 = 84W of electricity. I guess that's okay.

These companies should put a switch to disable the amp sections since a lot of receivers are being used as a pre/pro already.

[myki]

I ran my rotel receiver as a pre amp with out and load on it for months with out any issue at all. The receivers don't have nearly as much heat sink material as the 1075 power amps do so they'll naturally run hotter

Thanks Andrew. At least now I can use with confidence.

Geoff's post made it clear to me why my Marantz SR4500 ran hotter without speakers.

WITH SPEAKERS:
- Receiver mostly runs in Class B mode and most energy are used to drive the speakers

WITHOUT SPEAKERS:
- Receiver runs in Class A mode, consuming 12W per channel, and this 12W can't go anywhere so is converted to heat

Now I'm wondering if it will be advisable to just use the Marantz (which I exchanged for the SR5500 last night) to drive the surrounds. That will make the RMB-1075 drive the 3 front speakers with more power.

What do you guys think?

[Aussie Geoff]

Myki,

Personally (as a 1075 owner) I'd use it for everything. I noticed a big increase in rear channel realism and detail when I added the 1075 for the rears to my old Denon receiver - sounds seemed to now be 3 dimensional - with distant sounds sounding distant - 80W is not too much to waste for that...

However the best way (IMO) is to try it an see - pick something with a good surround track (I like Daredevil or the opening tracks of Gladiator for this) and compare - I'll bet you stay with the 1075 with confidence after that...

Re your thoughts on the 1075 being better with less channels used - its power ratings in tests are almost the same 1 channel driven as 5 channels driven (unlike 99% of receivers etc) - I don't think you'll save much. The only area where I'd expect a gain would be in low impedance loads (e.g. 4 ohms or less) where the 1075 can run out of current with all channels driven so can't double the power (200W instead of 240W) - but this is very theoretical as no one in real life drives all channels ot the max at once!

Geoff

[myki]

Geoff,

Ok. I'll try that. I'll listen to both setups you've suggested using Daredevil and Gladiator and I'll report my findings. I'll most probably do it over the weekend.

If I do connect all my speakers to the RMB-1075, then I can just get a pair of speakers for the bedroom and connect it to the multi-room speaker outs of the Marantz.

I'm on the lookout for interconnect cables as well but the choices here in my area are very limited. Right now, the only one that fits my $30 per IC budget is XLO TwinAx, IXOS XHA203, or QED Qunex 1. I can't believe how many choices you have their in the US. Will it be okay if I scrimp on cables? Or should I just save for $60 cables?