use amps biwire termals for a 2nd speaker set

davidguest

Standard Member
Joined
May 28, 2007
Messages
99
Reaction score
0
Points
49
will this work or will everything go up in smoke:

I have a Cambridge audio a4 amp - only designed to support one pair of speakers but is designed to support bi-wiring so actualyl has 2 sets of speaker connects.

I am currently using it with a pair of 8 ohm JBL control 1 speakers.

my question is this: I have a spare set of JBL control 1s - can I attach them to the other speaker terminals so that the amp is actually driving 4 identical speakers, then spread them around a little for pseudo surround. ( the amp is being used with a TV & PC for movies & games not really for hi-fi.
I cant think of any reason why not - the impedance will probably drop but the amp should be designed to cope with a single pair of 4 ohm speaker & I don't drive it hard.

I can't find any schematics for how those 4 speaker terminals are connected inside of the Cambridge audio amp but that should be guessable ?

All this gear is out of warranty though so asking first seems the way to go.

generalising the question - would this work for an set of 4 speakers with an amp that has 4 terminals intended for bi-wiring ?
 
You could make your own proper pseudo surround sound system if you like. You'll get surround effects from the rear speakers without spending a penny or blowing anything up.

Basically, wire them in series across the two output channels on your amplifier.

If you're not sure how to do this:- Twist together the + wire from one speaker with the - wire from the other speaker. Don't connect these wires to your amplifier. Now, put the remaining + wire into the red 'L' terminal on your amplifier and put the remaining - wire into the red 'R' terminal.

You'll be surprised just how effective it is.
 
ok - I understand that - but wiring in series will double the resistance ( the impedance), if I recall my A-level physics correctly ?

presumably I can alternatively manually wire them in parallel for a 4 ohm resistance.

I used to be well up on this stuff for setting up 2x12, 4x12 8x12 guitar amp+speaker combos As I recall, parallel is louder but drop the impedance too much & you can damage the amp. Series is safer but quieter, I have more power than I need to fill the room with sound though, so that should not be an issue

But I am curious to know which of these is achieved by using all 4 speaker posts on the CA amp, those 4 speaker posts must already either be in-series or in-parallel pairs, under the lid, or is some of the amplification circuitry duplicated for bi-wire output. they are not labelled treble/bass i.e. either single pair sounds the same so there is no crossover in the amp ??

I suppose I could take the amp cover off & peek but I don't know how visible the internal wiring will be

PS I am not positioning the 2nd pair as rear speakers, so I don't want any out-of phase effects. Imagine a 40 inch flat screen TV on a stand then add speakers positioned behind the TV at each corner , forming a "square" which is wider & taller larger than the TV. We have shelves set into an alcove behind the TV which is where I am placing the speakers. Currently I have only the high pair; a 2nd low pair , close to rear wall should add more bass for movies. The TV speakers stay on, giving clear, well positioned dialogue. The hi-fi speakers add extra depth, width, bass...their volume is controlled separately by the Cambridge audio amp
 
Last edited:
The speaker posts are just in parallel, nothing exciting than that.

I wouldn't parallel your secondary speakers if you're trying my idea because you will then be presenting a pretty nasty load to your amplifier (less than 3Ω).

If you're just connecting all four up (as two stereo pairs), then you'll be OK.
 
The speaker posts are just in parallel, nothing exciting than that.

& that's all there is to making an amplifier "bi-wire" capable ?
seems an awful con !

I think I get it now any way, thanks - if I get plenty of volume via your "in series solution" that seems safer.
 
Best not get a discussion of 'is bi-wiring a con' going. It will run for pages and has been done to death ;)

Personally, yes - I think it's a load of rubbish. Others will disagree...
 
Best not get a discussion of 'is bi-wiring a con' going. It will run for pages and has been done to death ;)

Personally, yes - I think it's a load of rubbish. Others will disagree...

agreed, but I'd never quite twigged that when you follow the instructions saying - "remove the connecting strip between the two sets of terminals on you rspeakers and run 2 wires to the amp", then you are just exchanging a connecting strip at one end of the wire for a hidden connecting strip at the other end, inside the amp ( between its speaker posts) ! IF true that that's real snake -oil speaker wire salesmanship!

I honestly thought there was "something" more than that going inside of the amp - maybe I will take the lid off & look-see.
 
I promise you there is nothing between the two sets of terminals on the back of your amplifier other than a dead short!

If you have a speaker A/B switch, then there will be a switch or relay, but they are just paralleled together.

Flip this on it's head for a minute... What do you expect could possibly be there inside your two channel amplifier apart from two channels of amplification?
 
I promise you there is nothing between the two sets of terminals on the back of your amplifier other than a dead short!

If you have a speaker A/B switch, then there will be a switch or relay, but they are just paralleled together.

Flip this on it's head for a minute... What do you expect could possibly be there inside your two channel amplifier apart from two channels of amplification?
duh - well now that you put it that way, clearly I never thought it through...

so when I use an amp like my new marantz PM6004 that supports 3 combinations: speakers A, B, or A+B; its been engineered to work well with the lower impedance of running A+B, in parallel ?

Same with the Technics I used to own that would also run 2 x speaker sets at once. maybe those amps use relays or test impedance somehow before committing to drive the double sets

but I now assume that an amp that's designed to work with only 1 pair of speakers is not made so robustly, impedance wise
 
Nah, they just parallel them... Most amplifiers have protection circuits in them - if you overload them, they will shut down.
 
Nah, they just parallel them... Most amplifiers have protection circuits in them - if you overload them, they will shut down.

interesting... why did you previously say
"I wouldn't parallel your secondary speakers if you're trying my idea because you will then be presenting a pretty nasty load to your amplifier (less than 3Ω)."

surely you get 4ohm load if you parallel 2 x 8ohm speakers - or is that 8ohm a nominal value which will actually vary from make to make.

why would an amp with 2 speaker set supports not also suffer from " a pretty nasty load"....

I suppose my other option is to swap out the cambridge audio A4 for something cheap + used+ similar dimensions & similar sound quality but which has speaker select controls ( & a remote would be nice) - like maybe an old Technics ? Might even almost break even if I buy & sell carefully on ebay.

some of the vintage Arcam, & Rotel range also support 2 speaker sets but they are more expensive. I recently sold off 2 technics though as they were beginning to show their age - e.g. crackles in volume pot in once case & I could not budge the case screws in order to get in there with switch cleaner. I've never had issues with CA amps but I am wary about buying 25 year old gear which could die on me at any time.The cheapest new amp solution seems to be the Pioneer A10 or A20
 
I was talking about my pseudo surround idea.

You already have an 8ohm speaker connected to each channel.

If you then paralleled the two rear speakers together, they then become a 4ohm load. Connecting this new 4ohm load across the two terminals would then be presenting a sub 3ohm load to your amplifier.
 
I was talking about my pseudo surround idea.

You already have an 8ohm speaker connected to each channel.

If you then paralleled the two rear speakers together, they then become a 4ohm load. Connecting this new 4ohm load across the two terminals would then be presenting a sub 3ohm load to your amplifier.

gotha - thanks.

I vaguely recall that back in the day , when dolby 1st launched "surround" - with a single mono rear channel- there was a "poor man's" solution which relied on phasing - basic dolby surround used a differences method to encode & then extract the rear channel signal, so you could fudge it with out-of-phase speakers instead of buying a proper dolby decoder. Just out of curiosity do you recall how that set up was done. I don't want to actually do it , just want to recall how the trick worked
 
That's exactly what I suggested in my first post.
OK - I re-read it more carefuly this time.

back to the A4 - I have just found the warning below,

Cambridge Audio amplifiers | PsyMusic UK

Just a little heads up about these nice little amplifiers, specifically the A3, A4, A5, A300 series etc. (They're all 60-70W amplifiers, and loads of people have them)

I've had several in to repair recently, and become accustomed to their simple design. (Which is probably why people think they sound good.) Unfortunately they suffer smoky death from a few problems that are easily avoided.

1) The amp is not designed for 4 ohm loads. That means no wiring up of 4 (8 ohm) speakers - you will kill it.

2) The transformer inside is under-rated in terms of power capability. While this is generally not a problem, avoid playing at high volume for extended periods. Like at parties. You *will* smoke it. You'll know if you've smoked it if you turn it on and you get no power light at the front, and there's a nice enamel burning smell. A replacement is only £15 but you have to take the *whole* thing to pieces to remove it. (High volume for an hour [or two, touch wood] should be fine though.)

3) There is only simple short circuit protection. Don't wire up or fiddle with the speakers or wires with the power on. It's a lottery whether the protection will fail. If you're lucky it'll be fine. If you're not, bye bye output transistors at £5 a pop and there's two of them for each channel. Plus a few burnt resistors and possible exploded capacitor. Not good.
 
These are very low cost amps, so you can't expect too much from them.

If the Power Supply was adequate, then you might (MIGHT) be able to run 4 ohms if you put a ventilation fan over the heat sinks. However, as the previous post indicated, the Power Supply does not seem to be adequate. In this case, I think you are dead in the water.

My advice, buy a new amps. But with what you have, it seems you are limited to one pair of speakers, which is probably why they only put one pair of speaker terminals on the amp.

Steve/bluewizard
 

The latest video from AVForums

TV Buying Guide - Which TV Is Best For You?
Subscribe to our YouTube channel
Back
Top Bottom