i have 2 X quad 306's could i bridge/parallel them and use them as mono blocks?

[izzzzzz6]

Hi forum fanatics
Would anyone know if it is easy to bridge a Quad 306? Is it as easy as inverting the signal to one of the channels and using both + speaker outs?
Would a parallel setup be better? I have just learned about this, it seems you join both inputs in parallel and then you can use both + & - outputs in parallel too, i never knew this before, i would be scared to damage something in the amplifier.
Can it really be this simple with all solid state amps?

James

[event horizon]

Yes, as you mentioned it's a case of inverting the input to one amplifier The output would then be taken from both + output terminals, the non inverted amp would effectively have the positive output (just to keep things in phase with everything else).

However there could be a bit of a problem Every Quad power amp i have ever come accross doesn't like a 4ohm load, & bridging the output even if using an 8ohm speaker the amplifier will "see" a 4ohm load as the output voltage will have doubled & so will the current.I'm sure it'd be possible to modify the protection so it'll drive a genuine 4ohm load, i did the same thing with a pair of 405s By the way, if your speakers happen to be 4ohm you might as well forget it as the amp will see a 2ohm load...

I would hate to see what happens if you parallel the amps. If there was ever any difference in output then current would flow from the amp producing the higher voltage into the lower one. The same applies to DC offset, any difference to the offset voltage will have the same effect - possible death of the output stage by violence (BANG!).

You could probably do it if you stick a low value resistor in series with the output of each amp & then connect the two leads left over together. The problem then is the damping factor will be stuffed & you'll be wasting power & introducing distortion.

[izzzzzz6]

Thanks for the great info, it puts me one more step closer to understanding electronics.
I may not do this with the quad 306 amps this time unless anyone can persuade me that it's a great idea. However i think i may try this in the future, would it be as simple as running one signal into the left channel as per normal and then taking that signal back out and plugging it in the right channel but out of phase? That doesn't make much sense to me as it would normally mean a dead short since the grounds for both channels are usually connected together. Is it a matter of connecting the + of the left channel of the amp to the + side of one mono input and the + of the right channel to the - side of that same mono input?
hmmmmm?

[405man]

If you look here, DADA Electronics - Downloads, at the 405 monoblock instructions, the first page shows how to parallel the amplifier increasing the power into low Z loads, I have built several copies of this design and used it successfully with 405, 306 and 606 amplifiers.

Stuart

[AndrewT]

note Quad's (series) guidance mentions 200W into 12 - 16ohms. This confirms that Quad are recommending a lowest load of 6ohms for the 405.
The parallel talks of 185W into 4ohm, again confirming ~8ohm as the optimum load for a 405.

The conclusion you can draw from Quad's guidance is that you can double the power into a half impedance load by paralleling
and
you can double the power into a doubled impedance load by series connecting (bridging).

[izzzzzz6]

Thanks for all this information, i don't really need more power at the moment but more so the ability to be able to drive a lower impedance load at about 30W/side. I'm wondering if paralleling two of these may make them a better match for the Quad ESL 57's (taking care not to turn up the volume too high). I also have a Leak Stereo 20 but from what i understand the Stereo 20 is best matched to the ESL's after modification and i'm not yet sure that i want to modify this amplifier as it's such a classic. Replacing old capacitors may be as far as i'm prepared to go with that one, i'm guessing that it would still be a good match for the esl's but perhaps not loud enough for my listening!?

[izzzzzz6]

Looking at the (Monoblock) plans to put the Quad 404 into Parallel mode it seems very simple and all the mods can be done externally, there are 2x .3ohm 4W Resistors on the output side one from each positive speaker terminal and then they join to become one + output.
In France i have managed to find 3W .22 Ohm resistors. Does anybody know the purpose of these resistors? Is it to help avoid the loads dropping too low (protection for the amp) Will the .22 Ohm resistors be enough and are 3W resistors large enough to use for this conversion with a Quad 306? I think i will order some 5k pots and some large resistors and try this on another amp as an experiment first, but it seems very simple. Does anybody recommend using any particular type of 5K pots or are the small circuit board type just fine? Thanks again.
James

[event horizon]

Originally Posted by izzzzzz6

Looking at the (Monoblock) plans to put the Quad 404 into Parallel mode it seems very simple and all the mods can be done externally, there are 2x .3ohm 4W Resistors on the output side one from each positive speaker terminal and then they join to become one + output.
In France i have managed to find 3W .22 Ohm resistors. Does anybody know the purpose of these resistors? Is it to help avoid the loads dropping too low (protection for the amp) Will the .22 Ohm resistors be enough and are 3W resistors large enough to use for this conversion with a Quad 306?

lol. Looks like i was right about sticking current sharing resistors on the outputs The resistors are there to make the amplifiers share the output current between them & so they don't attempt to push power into each others output stages as i mentioned previously.

You should be fine with the slightly lower value & power of the resistors. The amps are less powerful than the 405 & in consequence you won't need a 4W resistor, 3W will be fine. The slightly lower resistance value will also reduce power dissipation in the resistors to

Make sure you don't use a wirewound resistor! Use either carbon film or metal film resistors as these have lower inductance.

[AndrewT]

Originally Posted by event horizon

Make sure you don't use a wirewound resistor! Use either carbon film or metal film resistors as these have lower inductance.

but all three examples have a helical wound element.

[event horizon]

Originally Posted by AndrewT

but all three examples have a helical wound element.

Ok, ok

Look for something like this then

I hope that satisfies a little better Mr T.