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SET amp with Quad 2905

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Posted on April 5, 2014 at 09:02:44
M3hak@hotmail.co.uk
Audiophile

Posts: 2
Location: London
Joined: April 5, 2014
Hi,
I am thinking of using an Allnic A6000 50 watts Class A amp with Quad 2905..
I read on a Quad forum that SET amps are not good with Quads due to impedance matching issues.
I know the Allnic is 8 ohms. My current Conrad Johnson is 4 Ohms.
I don't pretend to even know what impedance is (or necessarily how to spell it !) but any advice on this would be gratefully received ,
Cheers,
Howard.

 

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RE: SET amp with Quad 2905, posted on April 5, 2014 at 10:33:23
banpuku
Audiophile

Posts: 1008
Joined: January 19, 2006
Howard,

I have Quad ESL-63s (predecessor to the 2905) and have used a 20watt class A solid state amp with them. The sound was good, but not great.

I recently purchased a lafayette KT-550 vintage amp. 25 watts class A tube. They drive the 63s wonderfully. Best bass I have ever had in my home. I don't listen super loud, but loud enough so the orchestral crescendos and Zeppelin are enjoyable.

I suspect the 50 watts class A will be a great match. Class A in both solid state and tube is the way to go, in my opinion.

My lafayette has 4, 8 and 16 ohm taps. The 4 ohm tap was better with the 63s, as the bass improved. The 8 ohm was next best.

FYI: the impedance of the quads is all over the map, depending upon frequency.

Pat

 

RE: SET amp with Quad 2905, posted on April 5, 2014 at 10:34:11
banpuku
Audiophile

Posts: 1008
Joined: January 19, 2006
I forgot to add, the Lafayette KT-550 is not SET, as it is Push Pull pentode.

 

RE: SET amp with Quad 2905, posted on April 5, 2014 at 12:01:32
M3hak@hotmail.co.uk
Audiophile

Posts: 2
Location: London
Joined: April 5, 2014
Thanks Pat - that's a help ! I previously used a Radford STA 25 with the Quad 2905 s and I also found that the sound was better with the 4 ohm setting.
Appreciate the reply !!

 

I drove Quad 989s with 50-Watt Antique Sound Lab Explorer 805 SETs..., posted on April 5, 2014 at 19:58:00
jeffreybehr
Audiophile

Posts: 5699
Location: Phoenix, Arizona
Joined: December 10, 2004
Contributor
  Since:
December 13, 2004
 photo Quadand805DT_1000h_zps283fa089.jpg
...and loved the sound. Don't remember which output tap I used.

 

RE: SET amp with Quad 2905, posted on April 6, 2014 at 19:39:29
RGA
Reviewer

Posts: 15177
Location: Hong Kong
Joined: August 8, 2001
The basic thing about impedance is that it relates to how difficult (or demanding) a loudspeaker will be for the amplifier.

Think of a speaker as a series of water pipes. At 8 ohms think of it having an 8 inch diameter pipe - the amplifier pushes water through this 8 inch pipe and a given pressure. The guy (preferably with a playboy model) is taking a shower at the other end and is happy and all things are good.

For some reason they need to use a 4inch pipe

But when the impedance drops to 4 ohms (4 inch diameter pipe) the amplifier has to work much harder to push water through the smaller pipe to get the same amount of water to come out. Indeed, the amplifier has to work twice as hard to achieve the same output of water. If the pipe is reduced to 2ohms (2 inch diameter pipe) the amplifier has to work twice as hard again.

Now the playboy model is a bit playful and likes to turn the nozzle (oh behave) and this causes the shower to continuously change diameters (ahem) and so it goes from 2 inches to 4 inches to 8 inches and back and forth continuously (is it hot in here?). Those fluctuations make it difficult for the amplifier because it may be asked to to push water through a two inch pipe in the bass but only required to push water through a 10 inch pipe in the midrange and 5 inch pipe in the treble. And it may be doing them all simultaneously.

As you can see it would be much easier if the amp only had one size pipe to push water through at the same level. Thus a flat impedance loudspeaker tend to be the easiest speakers to drive for an amplifier.

I'm going to go have a shower now - good luck on your amp search.

 

RE: SET amp with Quad 2905, posted on April 7, 2014 at 03:39:12
Frihed89
Audiophile

Posts: 15703
Location: Copenhagen
Joined: March 21, 2005
The concern is that they are a "reactive" load, where impedance is positively related to frequency. The 57s were very reactive. I don't know about your model, as i have never seen an electrical load and phase diagram. Their impedance varies widely, but that doesn't mean they are reactive unless the impedance rises with frequency across the frequency spectrum. Nowadays, the solution to reactive speakers is to run a SS current amp (with a JFet or Mofset output stage), which is a sledge hammer approach, a favorite of Americans.

In general, lacking more information, best to call upon the experience of 2905 users. The 57s ran well on many fairly modestly powered tube amps.

 

Maybe this will help., posted on April 7, 2014 at 23:45:00
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
Naz runs 845 SET amps on Martin Logans which are the same principle as the quads..My CLXs are dual panel full range but I also use the Descent subs which are powered with servo amps.
Here is a link with the discussion.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: SET amp with Quad 2905, posted on April 8, 2014 at 06:34:32
Gordon Rankin
Manufacturer

Posts: 2928
Joined: June 9, 2000
Gang,

Really only the Quad 57 was capable of being driven by SET's. After the 57's Quad paid more attention to the linear response of the speakers. This meant complex network equalization and driver changes, both of which resulted in a hard, low sensitivity speaker.

You would be best served by a PP amp with some feedback in it.

Thanks,
Gordon
J. Gordon Rankin

 

RE: SET amp with Quad 2905, posted on April 9, 2014 at 01:41:26
morricab
Distributor or Rep

Posts: 9160
Location: switzerland
Joined: April 1, 2005
Gotta respectfully disagree with you on this one Gordon. I doubt that an 8 watt SET will cut it but I drove my Acoustats for years with 30 watts of SET power (KR Audio VA350i) and it was heavenly. It drove other tough STATs as well (Audiostatic and STAX). It would also have no problems whatsoever with the Quad 2905s.

 

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