how to bridge a Quad 606?

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I have built units in the past to split and balance the input and parallel the output of the 606 based on what Quad did with the 405 details of which can be found here , about half way down the page. I used a pair of 606s to drive my ESL63 with spectacular results. I suspect that amplifier clipping is the main culprit in triggering the protection circuits in the 63s, with the bridged 606s the 63s went unbearably loud and I never activated the protection. I have since built dipole subs and am using 1 606 for the subs and one for the 63s ideally I would like to try 4 bridged 606s but that is for a later date.

Thank you Scotland...

Andrew I don't know much about amplifiers so could you explain what the load issues are with a bridged amp?

Stuart is this parallel set up the same as bridging? Did you set up your 606 amps exactly the same way as the discription in the 405 PDF?

Please dont worry I won't be doing the work! I will get an electronics technician to do it but I would like to accumulate the necessary info first.
One last question have any of you had any ecperience with removal of the protection circuitry in the 606? I have heard the improvement of this in the 405 and assume it would be the same in the 606. The intended application for this bridged 606 will be PA work so I want to make sure if removal of the protection circuitry is a good plan. Thanks for your responses.
with a bridged amplifier, each amp sees half the load impedance.
Start with an 8r0 resistive load and drive it to 40Vpk, with the output/load current = 5Apk, the equivalent of 100W into 8r0.
Now bridge a pair of amps and drive both of them to the same output voltage.
Each amp sees 4r0 and sends 10Apk into the load. The load feels 40Vpk coming from each side and effectively is driven to 400W (80Vpk).
each amp is driving 200W into 4r0. The bridging rule is double the power into double the impedance.
Now change the load from 8r0 resistive to 8ohm reactive.
The output stage and the preceeding drivers see the reactive load and try to drive the same currents and the same voltages into the load, but this time the increasing voltage does not always coincide with increasing current. For a 45degree phase angle the output stage sees an IV stress of approximately double the resistive case, causing raised junction temperatures and using more of the transient and continuous SOAR. If your load has 60degree phase angle loading over parts of the frequency range then the IV stress can approach 3times the resistive case (this is the part I design for since it seems to cover most worst case conditions).

The net result is that your 606 could be relatively safe driving either 4ohm or 8ohm speakers in normal mode, but when bridged the acceptable range of loads is 8ohm to 16ohm to remain in the same SOA range.

Now think about PA work.
What will the ambient temperature be where the amps are located?
Will you be in attendance as you would in the domestic situation?
Will the amps be working just as hard or might the voume be turned up a bit? or a lot?
Will the protection be effective for the more demanding PA duty?
What if you disable the protection?
See where I have taken you?

Need I say that the combination of bridging and PA and disabling protection is liable to be an amplifier killer.
Points taken...

Thanks for the detailed reply especially regarding the protection circuit. I guess what I will do is to make some adjustments to my expectations. I will use the amp to run a two way guitar speaker. One channel will drive an Eminence commonwealth 12 (designed to be driver by a SS amp) and the other will driver a high effiency mid range driver (in concert with the 12 in driver) if I match the two drivers in terms of efficiency and power handling then I should not have any troubles. I am interested to know what would need to be adjusted (in tha amplifier) to compensate for input? Guitat pickups and effects devices don't put out enough to driver the 606 to full power. Thanks.
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