From: jeff@hawk.svl.cdc.com (Jeff Needham)
Subject: Re: Spica upgrading
Originator: tjk@csd4.csd.uwm.edu
Organization: University of Wisconsin - Milwaukee
Date: Fri, 21 Aug 1992 13:07:03 GMT

skao@tcs.com (Simon Kao) writes:


>crossover that could be upgraded and improve the sound. I decided not to
>part with the bucks, so I still would like to know what modifications can
>be made (if any) to the electronics of the Spica, and, do they work, and, if
>they do, how is the sound changed?

Two approaches work in this regard.  First components, then topology.

The jacks on the back and the wiring within is quite thin and also could stand
some improvement.  What I did I would recommend, but I will try and recommend
a more sane approach from my experience.

First, ALL the capacitors were replaced with MIT Multicap 10% expect where
the larger values were concerned.  First off MIT currently does not make
a 47uF capictor and if they did, it would cost slightly less then a typical
Tim de Paravicini piece of equipment.  As it was, I still spent close to
$250 on a more economical mix of MIT/WonderCap/Solens.

Advice:  Use Wondercaps everywhere and use low value 1% matched MITs across
	 them.  This should control the costs. Someone read in a trade
	 magazine that what helps a great deal is 1% matching and this 
	 only adds .50 a cap in my case which is insignificant.  Use heavier
	 internal wiring and double up on the woofer leads if you like.  
	 Wire is quite cheap (even CARDAS chassis) by Multicap standards!

	 Replace the posts, either with a set that fit into the small cup,
	 or by drilling a set of holes.  I choose to use Edison music posts.

	 For Sub-ed systems, the Xover box can be illiminated by wiring
	 caps directly between inputs (where the sub is fed) and outputs
	 (where the TCs are fed).  All you need is an extra set of jacks on
	 the back of the Sub.  In the SpicaSub case, the aluminum is quite
	 soft and very easy to drill.  This means only 1 set of cables to
	 the Sub and one set out towards the amplifier versus 1 set to Sub,
	 1 Set to Xover, 1 set from Xover to Amp.  Values are typically .050
	 to .080 and these are not common.  Using existing Multicaps in series
	 worked.  The leads were so long on MITs, that no wire was needed. 



Topology (biwire)

	Separating the low-pass and high-pass networks often results in more
	detail and better image focus.  These are TC strengths and combined
	with the work above should be quite rewarding.

	The cost is mostly wire, and a set of posts.  You want to hand wire
	the components together and remove the PCB completely.  Hand
	wiring and embedding the entire network in epoxy is worthwhile.


Although you may feel that the change has no basis in fact (at least I have
no hard facts),  the sound will change; count on it.  I and a few others who
are not that pro-Spica (I trust their ears more than I do my bias) feel it 
was very quite positive.

Finding information on the bi-wire circuit will be a challenge.  I know of
people who have bi-wired TCs, but we don't know how to do it.  Anyone with
any hints?  Otherwise, I have to track down the person who did the work.

Tweaking is almost as much fun as listening ;-)  Others have told me that
I might as well build a pair from scratch.  I can't saw or nail straight!



jeff




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