Quad 606 into a 2 ohm load

[Colin151]

HI there,

Was just wondering if someone might know any info on this issue and be able to kindly give me some advice?

. I have a Quad 606 MK2 amplifier. I've seen info on the amp that says its stable "into any load". Its rated at 220 Watts into a 4 ohm load and of course was specifically designed for use with the 4 ohm Quad ESL63 speaker.

I need to find out if its going to be safe using it with a constant 2 ohm load, - this would be driving two pairs of Magneplanar 3 series bass panels in parallel. The load is completely resistive, so there is no change DC resistance over different frequencies, there would be no passive crossover components in between the amp and panels, I am using an active crossover instead.

If anyone has any ideas if the 606 is stable into 2 ohms it would be really appreciated if you could let me know. Alternatively a friend of mine suggested using a 1 ohm power resistor in series with the speakers to bring the load up to 3 ohms, and that should be much more likely to be safe.

I do alternatively have a NAD208 THX MOSEFT power amp which is probably the only serious power amp NAD made. But again I'm not sure it would be safe using it with a constant 2 ohm load. Its rated into 2 ohms for a short burst (if has a class G switching rail), but I'm not sure about constant. It has a very big PSU with 100,000 uF worth of capacitance though. They are know to be slightly unreliable which makes me wary!

If anyone has any kind advice it would be great to get some help,
Cheers,
Colin

[sreten]

Hi,

So why not put the panels in series and use the amplifier as originally intended ?

You want the extra watts of 2 ohm parallel ? very bad idea IMO for the Quad.
If series is loud enough without clipping, what is the problem being solved ?

rgds, sreten.



Very unusual impedance graph compared to dynamic speakers. Basically
a ~ 6ohm load, certainly not 4 ohm, the 606 was not designed for that.

[Colin151]

Yes I think you're right. Connecting the two pairs of Magnepan bass panels in series is the best and safest option, - each panel is a purely resistive 4 ohm load, so I'd get an 8 ohm load doing that. I heard before that connecting speakers in series can be problematic if the speakers are different in specs but these bass panels are all identical in specs so I think it should be fine.

My NAD 208 power amp can deliver a stable 250Watts into 8 ohms, and 600 Watts into 8 ohms for a short time (it has a Class G rail that can activate under transient bursts), so I think its better to used that the the less powerful Quad 606 (which delivers 140Watts into 8 ohms).

Yes I can see the impedance curve of the ESL63s is unusual compared to dynamic speakers and the overall impedance is well above 4 ohms.

[Colin151]

Looking at that data sheet for my NAD 208 THX amp it does say on the first page:

"The MOSFET output stage delivers power plus signal speed and control, driving any loudspeaker load,
even below I ohm."

Not sure again if this means a constant load though. This amp might be safer to use than the Quad 606 for a 2 ohm load (if the bass panels are wired in parallel). But then again if I series the bass panels to get an 8 ohm load the NAD 208 will still deliver plenty of power and it will definitely be safe.

Cheers,
Colin

[Mr Tube]

Maybe its a better idea to look for a second 606 and use one amp for each channel, make the input mono and one panel on each output.
Amps who can drive in to 2 Ohms needs big transformers and powersupply components, for driving in stereo 2x 400W in 2Ohm You need a 1200VA powertransformer.

[ingenieus]

I was playing around with a power amp design in LTspice recently. It is astonishing how quickly things go south when you drop the load resistance from 4 ohm to 2 ohm. To drive a 2 ohm load requires symmetrical input and voltage amplification stage to avoid asymmetric clipping (positive half of wave clips at far below the supply voltage). In addition to to the big transformer, lots of output transistors in parallel are needed to switch all that current. Here is what I came up with before I decided that it was not such a great idea. I already have a device with a big transformer that converts electricity into heat and sparks. It is called a welder!

[sreten]

Hi, still don't know why there are two bass panels per channel, and why, rgds, sreten.

[Colin151]

Hi Sreten,
Usually you would use one pair of Magnepans (I have the MGIIIa) full range (i.e. bass, midrange and tweeter all working). What I intend to do is have the midrange and tweeter running in this first pair like this, but split the bass signal between the bass panel in this main pair of speakers, and another pair of Magnepan MGIIIas so each bass panel is working at half the normal volume. This has advantages, - increasing headroom of course, and gives you the ability to angle the extra bass panels to avoid dipole cancellation giving deeper bass. And as the load is shared between the two pairs of bass panels its safe to EQ in a bass extension peak with a digital crossover if you wish. You won't get the famous "maggie slap" you can get with one set of bass panels only working.
I could also run this setup as a 4 way system, instead of a three way, and I might try that too at somepoint. I would need another amp most definitely for that obviously.

Of course the Magneplanar Tympanis have dual bass panels, - these have the same advantages. But in the Tympanis the each bass panel is 8 ohms instead of 4. This means in parallel the load is 4 ohms not 2 ohms like it is in my case!


Thanks for you other help guys. Yes I can see its not really a safe option to present a constant 2 ohm load to my amps. I will look for another power amp or connect in series.

All the best,
Colin

Originally Posted by sreten

Hi, still don't know why there are two bass panels per channel, and why, rgds, sreten.

[Mr Tube]

Finding amps who deliver power in 2 Ohms are not easy to find. The Accuphase P7000/7100 is an amp who can do the job:
2x 125W 8Ohm
2x 250W 4 Ohm
2x 500W 2Ohm
It have a transformer of 2000VA and 2x 12 power transistors paralleeld in the output stage, OK tis amp is expensive. Another amp is McIntosch with output transformer or a Tube amp but also expensive...
Maybe professional amps who are built to drive 2 Ohm loads but do this sound?

I think that bi-amping is the best option, then the Quad will be fine.
I have a 606 who drives speakers of 3,3Ohm and works fine. I did some mods to reduce the gain to 26dB.

The panels in series is not a good idea in my opinion

[sreten]

Hi,

You say you have a choice of two amps, why not use them both ?
They would both see 4 ohms.

rgds, sreten.