Paralleling two power amps for extra power

[timhum]

I have bought a 12 channel power amp an ArtSound AMP1250 to make a pair of Gale 401 speakers active.

The Gales have a pair of LF drivers, a mid and a tweeter each. I plan to use all 12 of the 50 Watt amps to power the various drivers through an active crossover of course.

It would be good to power each LF driver with a pair of 50 watt amps and indeed there is a facility in the amp to bridge a pair but the bridged amp requires a minimum load of 8 Ohms. The drivers have a minimum impedance of half of that. I could connect the drivers in series and use the bridging option but it occurred to me that I could connect two power amps in parallel and use them to drive each LF driver. More current delivery and low impedance tolerance would be the advantages.

Is this a possibility? If so, is there anything to look out for to make sure each amp's output does not interfere with its partner? I am only investigating this in order to use all the amplification at my disposal, each power amp has its own gain pot and that is how I will balance the overall sound once set up.

I will put some sort of soft start up or speaker protection into the system to avoid a fat mains switch on thump trashing the tweeters but the possibility of pairing up LF power amps is attractive if it works!

All offers of advice will be gladly received.

 

[Mooly]

I would not recommend paralleling two amplifiers (even though nominally identical) unless they are designed expressly to allow that.

The slightest imbalance in gain will cause one amp to 'source' and one to 'sink' massive currents, possibly destructively.

The slightest imbalance in frequency response between the two amps would do the same as above.

Any DC offset, even a few millivolts, would do the same.

On power up, the amps almost certainly have slightly differing time constants and that would cause momentary and massive overload of one or both of the amps output stage.

There could be stability issues.

 

[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

 

[abraxalito]

Use output transformers - these effectively allow you to put the two channels in series and present the optimum load impedance. I'm doing that with my tiny TDA8932 classD modules without any issues.

 

[MIKEVO]

Tim, I would get your actives up and running just using 6 of the channels and keeping it simple.
Leave the other 6 channels dormant.

This way, you will still benefit by giving the power supply an easier time by having extra current in reserve, so dynamics should be better.

If you are unhappy with the sound, you could look into other options later.

 

[timhum]

Thank you for all your advice. For me, with limited electronics experience, all the advice is most helpful and practical.
I shall avoid connecting the amps in parallel and instead go with a version of MIKEVO's advice. I can use a separate amp for each of the two bass drivers in each speaker. It will be very adequate in a domestic environment! The 8 Ohm minimum bridging amp load impedance implies that each amp module is happy with 4 Ohms each and that should suit the drivers.
With this arrangement I only waste two amp modules but as MIKEVO says, the power supply will have some extra reserve which can't be a bad thing. I do not expect to stress the speakers or the amp in my average sized listening room!

 

[timhum]

"
With this arrangement I only waste two amp modules but as MIKEVO says"

Maths was never my strongpoint. I "waste" 4 amp modules of course, not two.

 

[sreten]

Hi,

Paralleling amplifiers is a doddle, despite the dire warnings given so far.

You must add series output resistors, to all parallel outputs, say 0.22R.

With 12 channels, six each side, use 4 channels bridged /
parallel for bass and the other two for mid and treble.

rgds, sreten.

 

[irext]

Unless each amp has it's own individual power supply I can't see how paralleling two amps will provide any benefit. Since the amp you are describing would appear to have a common power supply for all channels then the two paralleled outputs would be swinging to the same supply rails. In other words, the same voltage across the load at any given moment. Or am I missing something. I'm happy to be proven wrong.

 

[timhum]

Unless each amp has it's own individual power supply I can't see how paralleling two amps will provide any benefit. Since the amp you are describing would appear to have a common power supply for all channels then the two paralleled outputs would be swinging to the same supply rails. In other words, the same voltage across the load at any given moment. Or am I missing something. I'm happy to be proven wrong.

Same voltage certainly but twice the current delivery into a 4 Ohm load than a single amp would supply. Paralleling two amps together is different to bridging so more current rather than voltage is the desired outcome.

Bridging two amplifiers together effectively doubles the voltage at the loudspeaker but that only works if the loudspeaker load is double what each amp is capable of safely dealing with, i.e. the amplifier modules in this kit are specified into 4 Ohms and in bridged mode the minimum impedance required is 8 Ohms.
That is how I understand it.Googling around and following the leads on here, I see it is possible to do but taking note of the warnings, I shall be playing it cautiously at least until I fancy possibly trashing a fairly pricey amplifier in the quest for a few more dBAs.

 

[irext]

Given the same power supply and same load how can it be twice the current with the amps in parallel? Imagine you have a given load and a given voltage and you switch the load across that voltage source. Ohms law dictates what current will flow. Put another switch in parallel with the first switch, no change in current. No extra power. I do realize that there is a certain loss in the output semiconductor and putting two in parallel will halve that loss but you won't gain a doubling of current.

 

[jan.didden]

Agreed. The signal across the speaker will not change so there will not be more sound power.
The only advantage would be with very low load impedances where a single amp would run out of current, but that doesn't seem to be the case here.

Jan

 

[timhum]

Thank you irext and Jan.didden,
I understand more now. The Gale 401 speakers I am activating were known as amplifier killers when they were in production, now many years ago of course. The speakers' impedance which included the crossover and drivers went below 4 Ohms and trashed many a decent amp back then. It was with that in mind that I considered the extra current to be a worthwhile goal. I quoted 4 Ohms for brevity. At the levels I shall be operating, the benefits would be academic.

The presence of enough amp modules to parallel up was tempting but this forum and its helpful members have saved me from finding out the above the hard way!

Thanks again,
Tim

 

[irext]

Totaly agree. In this instance though the power supply to all 6 of the amplifiers is common so each channel is accessing the same power source so really the only benefit would be less stress on each output stage. You would need to have low value resistors in series with each output to ensure current sharing (as mentioned previously). They would act like emitter resistors in a complimentary output stage which has output transistors in parallel.

Agreed. The signal across the speaker will not change so there will not be more sound power.
The only advantage would be with very low load impedances where a single amp would run out of current, but that doesn't seem to be the case here.

Jan