Quad 11 in parallel?

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10-Jul-2017 07:50 PM

hummph

hummph

Posts: 25

I have read somewhere that it is possible to parallel the outputs of two Quad 11 amplifiers. If so would it be necessary to balance the inputs in the same way as mono-blocking the 303?

This is just for an experiment to see if there's any difference in the sound.(Don't want to run four amps for to long in this heat!) I'm using Esl 57"s.

Thanks

Ken

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11-Jul-2017 08:42 AM

Joost Plugge

Joost Plugge

Posts: 912

You can do that in the same way as described for a Quad 303. But wait for the comment of EJP, he is more experienced than me with tube amplifiers.

Joost Plugge

DaDa Engineering

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12-Jul-2017 05:47 AM

EJP

EJP

Posts: 1357

I can't agree with your source.

Valve amplifiers have large source impedances in the valves, and require large load impedances in the primary of the output transformer. By paralleling two Quad IIs, you would be halving the output impedances at the secondaries, which will reflect into the primaries as half the load impedance for the valves, which will increase distortion markedly and possibly take the valves out of their designed operating conditions. It will also cause the amplifiers to drive each other's finite output impedances, which could cause all kinds of bad things to happen.

There is also no benefit in doubling the available current to the ESL-57s.
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12-Jul-2017 12:38 PM

hummph

hummph

Posts: 25

Thankyou for your replies.

I have been searching for the the source of the paralleling information and I have found that it's from the Quad user manual.(I think a late issue with the red and black cover). This is the description:

"The reliability and consistent performance of the Quad 11 power amplifier has led to its use in professional, industrial and scientific applications. The unconditional stability allows any number of units to be connected in parallel without interaction. The flexibility of multiple unit operation is of value where increased power is required, and where it is necessary to retain the excellent characteristics of a single Quad 11 power amplifier"

Interesting- especially where they state "any number of units"!

Thanks

Ken

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13-Jul-2017 02:07 AM

EJP

EJP

Posts: 1357

Well that is amazing. Well done Peter Walker.

Still no benefit.
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14-Jul-2017 10:12 AM

hummph

hummph

Posts: 25

Yes indeed!

Possibly beneficial into normal speakers?

Back in the mid/late 1950's Wharfedale hosted live v recorded concerts and used Quad 11 amplifiers. In the book, "A Pair of Wharfedales"' there is a wiring diagram with four Quad 11's connected in parallel to four Wharfedale speakers also in parallel. An 80 Watt neon  indicator unit is connected via a transformer.The inputs are split four ways with no balancing/trimming.

Incredible to think that 60-80 watts and four speakers had enough volume to fill the Royal Festival Hall.

Might be of interest to someone!

Regards

Ken

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16-Jul-2017 09:45 AM

EJP

EJP

Posts: 1357

Possibly beneficial if you have low-sensitivity 2-ohm speakers, or you're playing Festival Hall with 8 ESL-57 in parallel.
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