How to boost treble sound - biamping?

I have a pair of Castle Howard S2 (large floorstanders) driven by a Quad 44/405. There is a noticeable lack of treble definition and sparkle. There is nothing wrong with the amp (I have checked by trying a different pair of speakers!} and there is ample volume to the Howards, they just sound a over-mellow. The 44 preamp has a sort of tone control but it's too subtle to make much difference..
Would biamping with another 405 help?
And if I were to biamp, how to do it? The 44 preamp has been modified and has RCA outputs, but only one set. I think the original DIN sockets are still connected.

 

Passive biamping will do nothing whatsoever, as each amplifier still carries the whole signal, and the loudspeaker's passive crossover still operates as before.

Active biamping, i.e. with an electronic crossover between the preamp and power amps can make a very positive difference provided the crossover is fully adjustable for level and crossover frequencies. You will need to remeove the loudspeaker's passive crossover and bring out connections to the individual drive units. Then, you will have to adjust the level of the crossover outputs to account for the different sensitivity of the drivers.

Whilst this can be done by ear, it's a lot more accurate to do it using a measuring microphone and software such as REW, which is free, and very competent.

Unless mistaken, the Castle Howards are a three-way system, so to get the best out of them you need to tri-amp, not just bi-amp. It's what I did with my B&W 801s, converted those to active operation using three power amps and an electronic crossover.

If your 'speakers are too mellow and the Quad's tone controls insufficient, then it sounds to me that the tweeters may not be performing as they should. It's possible that the tweeters have ferrofluid in them, which after all these years may have gone gummy and reducing the output. I don't know the tweeters which Castle used, so don't know if they used ferrofluid, but many did, so taking a tweeter apart and cleaning out the magnetic gap and replacing the ferrofluid may be all it needs.

Castle loudspeakers were always considered accurate and low coloration rather than exciting, and well worth getting working properly.

S.

 

I have time and time again discovered that the interconnecting cables have a tremendous affect on the sound of the frequencies. try Decwares interconnects they will make all the difference. Steve Deckert has a philosophy that if the first watt does not sound right there is no point to continue! Speaker cables also have a affect as well,so experiment.

 

I have time and again discovered that the interconnecting cables have no effect whatsoever.
Try any old bits of coax, they will all be the same.
Speaker cables have no effect either as long as they're thick enough so their resistance (note:- not impedance) is no more than 10% (better still 5%) of the loudspeaker's impedance.

S.

 

As Serge said it's most likely to be faulty tweeters due to old ferrofluid gumming up the voice coils. Also check that the tweeters are actually functioning at all as tweeters are easily blown by driving the speakers loud with an amp that's not powerful enough. Yes, not powerful enough! This is the single most common fault with speakers.
If the OP has only recently bought the speakers as a secondhand purchase then this could be worth checking.

 

Pull the crossovers out and rebuild them with better quality parts. Get the crossover schematic from the manufacturer if you can as Inductor blues might not be written unlike the caps and resistors.
Replace iron cored inductors with air- Cored eg from Jantzen or Dayton audio or US Coils. Replace ALL non polar electrolytic caps with good polypropylene caps and put a bypass cap on the tweeter cap eg use Sonicap on the tweeter with a Miflex copper foil (0.01uf) bypass cap. As a minimum try Jantzen Superior Z (the red ones) WITH a Cornell Dubilier C940 0.01uf bypass or better still a Mundorf Gold Silver Oil 0.01uf bypass.
For large Inductors on the bass circuit look at US Coils Super Q Inductors. But if this gets too big you may need to build a new point to point wired crossover on a piece of 3mm MDF.
Replace resistors with wire wound types the green Dayton or Jantzen resistors are good don’t use the white ceramic resistors that normally show up on factory crossovers
There’s s great capacitor Test review on Humble Homemade HiFi site
For more like this follow the videos from GR-Research on YouTube about speaker upgrades)
Also line the inside of the cabinets with some damping material - see the GR-Research NoRez product or similar add cross bracing if there isn’t any already.
I order my crossover parts from soundimports.eu and Audiophonics.Fr if you want you can also replace the internal wiring with OFC copper with Teflon or Polyethylene insulation