Anybody use a Dynaco QD-1 Quadaptor? [Archive] - Audio & Video Forums


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11-30-2004, 07:40 PM
I have a Dynaco QD-1 Quadaptor I built as kit costing $18 in the early 70's. This is a passive system that adds two more rear channels to two stereo channels. It is hooked up to the two stereo speaker outputs of the amp and has four outputs for four speakers. The circuit consists of a rear speaker rheostat and two resistors and switch to allow two channel operation or four channel operation. So I was into surround sound in 1970!!

It seams to add depth to some music with good stereo separation.

Anybody still use a Dynaco Quadaptor besides me?


Resident Loser
12-01-2004, 06:13 AM
...use the circuit, it did have some nice qualities...source dependent...

Known in some circles as the "Hafler hookup" it simply took the out-of-phase info available to one degree or another on all it's not exactly "quad" (although what actually comprised "quad" was never really answered and the industry itself caused four-channel's demise)...more of an "ambience recovery" scheme. I came across the circuit in the early/mid 70s in an article in either High Fidelity or Stereo Review and used it for a while( a DIY breadboard affair) until I finally went for full separates...In late 1970-whenever I called HK, the manufacturers of my brand new Citation 19 amp and inquired as to pros and cons of continued use...since the circuit has you wiring the two speaker "hot" leads to feed the "rears", they felt it might result in problems, so I dropped it...I forget what the tech issues were, so I'm still not comfortable with trying it again, although from time to time it pops up in my head...since it actually did work.

jimHJJ(...certainly an interesting idea...)

12-01-2004, 10:11 AM
At least I can say that I did try the device. I did not like the way it performed. Those two power resistors are hooked in series to your front two speakers robbing you of power on a two channel amp or receiver. There are other variations of the Dynaquad circuit floating around. Two of those variations that I have deployed use a l0 ohm l0 watt resistor that is wired to the common ground of the two rear speakers and then grounded to the receiver. The second variation is to use a loudspeaker in place of the resistor mentioned. This will create a center channel fill in to the Dynaquad matrix. Both the center channel speaker and resistor will give you rear channel separation.
I have had excellent results from certain two channel recordings both on vinyl and cds' whether or not they were enhanced for quad, dolby surround or not. I found the study of this circuit to also be very interesting particulaly when you draw the latter circuits I described on paper. There is more than meets the eye on the function of Dynaquad and it is facinating.

12-05-2004, 09:46 AM
ive used dynaquad and wouldnt be without it. for one thing, i dont have to go six channels to hear surround with my SACDs. regular stereo sources are all enhanced with the ambience recovery (which is what you really want in surround) and LIVE recordings sound just that, LIVE with the audience sitting with you at the rear and sometimes all around.

and no BASS MANAGEMENT to dick around with. nor do i use a center. that requires a speaker of nearly exactly the same tonality of your left and right fronts.

this avoids all the hype of things like the columbia SQ fiasco was pushing. sq and qs discs sound quite fine this way as do the aforementioned stereo. once the rear channels are adjusted for near inaudibility on regular stereo, anything that might occur in the rear does so quite nicely. tomita and the moody blues put things in the rear that come back in good evidence with the passive dynaquad.

it is unlikely that you will harm your amplifier using this circuit. i used it with an old sony and old sherwood receiver, and all my separates ever since, up to and including the 200wpc adcom i use now.

nobody notices the rears until i turn them off. the soundfield collapses to the front and THEN they notice.

highly recommended.