AV system plus seperate amp - same speakers

[David A]

Can I do this if so how?

I've got a Yamaha DSPAX763 as an AV amp, it feeds a sub, rear speakers, B&W centre and B&W 603s as the front pair.

I'd like to have an valve amp (no real reason, just because) and have this feed the 603s when listening to music. I.e. AV amp for AV, valve for music, same front speakers.

So essentially the speakers would be connected to two amps...somehow...

Any thoughts?

Dave

[David A]

Think I've answered my own question, I need one of : http://www.homehifi.co.uk/products/TC-7220.html

Unless anyone knows of anything better?

[pstruck]

Looks like a good gadget.

I have the same dilemma and currently have the output from my AV amp connected to one of the set of speaker binding posts and the output from my stereo amp to the other. I'm sure there's a (or several) very good reason why I shouldn't do this. I never have both amps on at the same time, so thought this might be ok. It all sounds ok. Hopefully I'm not bu66ering something up by doing this.

I guess alternatively is to run pre-outs from the AV amp into my stereo amp for the front pair and just have the speakers connected to the stereo amp.

[David A]

pstruck said:

I guess alternatively is to run pre-outs from the AV amp into my stereo amp for the front pair and just have the speakers connected to the stereo amp.

I thought of this, but there would likely be mucking about with different volume levels once the valve amp was changed.

[DavidY]

pstruck said:

I guess alternatively is to run pre-outs from the AV amp into my stereo amp for the front pair and just have the speakers connected to the stereo amp.

This is the way to go especially if your stereo amp has a unity gain input, otherwise calibrate the AV system with the stereo amp volume set at 12 o'clock. A couple reasons for doing this:-

1) You are using the better amplifier to drive the stereo speakers - AV amps are ok but usually have limited reserves on their power supply
2) You are not switching speaker cables - This unless done properly, runs the risks of shorts, damaging the output stage in the amplifier. It also is likely to have a significant changeover thump (sound out of the speakers) when switching between amplifier sources, potentially damaging the speakers (or at least making you cringe each time it happens)

[DavidY]

Another point unless you speakers are very sensitive then a valve amp may struggle to drive them properly anyway.

Edit - OK looking at the specs of the B&W 603 S3 they are 90dB sensitivity, which means that on the face of it a valve amp should be ok, however they have a nominal impedance of 8 ohms but this dips to 3 ohms at certain frequencies, which means they are relatively current hungry and as such will prefer an amplifier that is capable of doubling its output into a 4ohm load (ie say 100W into 8ohms and 200W into 4ohms). Most valve amps will not be able to do this. That said a valve amp may sound ok, there is only one way to find out and that is to try one.

Edited by DavidY on Saturday 16th July 17:09

[Driller]

DavidY said:

Another point unless you speakers are very sensitive then a valve amp may struggle to drive them properly anyway.

Edited by DavidY on Saturday 16th July 17:09

Are you sure about that?

[DavidY]

Yes, because Valve amps are typically low power, so if your speakers are 83dB sensitivity 1 Watt driving them will produce 83dB at 1 metre, if they are 92dB then 1 Watt will produce 92dB at one metre. Decibels are not a linear scale but a logarithmic one. Valves are typically used with high sensitive speakers, and almighty transistor mono blocks are used with low sensitive speakers.

See here http://www.diyaudio.com/wiki/Loudness_and_Speaker_...

[Driller]

Interesting stuff. The reason I questioned your post was because I was considering guitar valve amps, alot of which are 50w or 100w going into a 4x12 cab.

Recently there have been quite a few low powered guitar valve amps arriving on the market (5w or so or even 1w) and when these are connected to a 4x12 cab they still make one hell of a racket. Of course this is not the same as it's comparing valve with valve.

So I checked out the sensitivity of the average Celestian speaker for the first time ever-turns out it's almost 100dB

[DavidY]

That would explain it!!!

Having an amplifier with sufficient power reserves makes the dynamic swings in the music/soundtrack better, as the amplifier can handle the on-demand requirements of the source material. This usually results in amplifiers with very beefy power supplies, something that a lot of AV amps lack, in this situation they are relying on the active subwoofer performing this duty.

I don't have a sub-woofer but I can still make earth moving bass, as 1) my speakers go low and 2) I have a serious power amplifier (which at 53kg requires two people to move it!)

[Driller]

What amp an speakers are you running out of interest David?

[DavidY]

I run a 4.0 system. I used to run it 2 x Meridian 559 (each bridged into monoblocks) for the fronts and 1 x Meridian 558 5 channel amp (bridged) for the rears. That was about 1000W per channel up front and 650 per channel for the rears!! The dynamics were just awesome and I never ran out of headroom, but it was 130kg of amplifiers!

The 2 x 559 were definitely best for music but since my system is now about 95% AV and 5% music, I 'downgraded' to using just the Meridian 558 on 4 channels, each channel driving 200W into 8ohms. These are real current driving designs, with the 559 capable of driving 150 Amps into 1 ohm loads!

My Front Speakers are Shahinian Obelisks and the Rears are Shahinian Arcs. The Obelisks are difficult to drive as they have a sub 2ohm dip in their impedance curve, so they work best with big transistor amplifiers (Meridian, Pass Labs, Plinius, Krell, etc)

Amplifier http://www.meridian-audio.info/public/558%5b80%5d....

Speakers http://www.shahinianacoustics.com/ - the speakers are fused, never blew them with all those power reserves, but the drums when driven by the 2 x 559 would make your chest move!

[Driller]

Thanks for that. Those amps sound...chunky! (ETA this is not pejorative, they sound awesome!)

Had overlooked Shahinian so had a look at the website. On the Obelisks:

"Let's remember that any sound in the universe has a polyradial trajectory away from its point of source; not direct, axial. Does it not seem reasonable to attempt duplicating reality?"

One of those things that you never consider but that seems obvious after you read it for the first time.

Edited by Driller on Sunday 17th July 10:44

[David A]

David A said:

Think I've answered my own question, I need one of : http://www.homehifi.co.uk/products/TC-7220.html

Unless anyone knows of anything better?

An update, got one of these (actually the first one was faulty its been sent back for a refund). The working one seems to work pretty well and is nice that each channel seems to be completely isolated.

Dave