# Scratchy sound on TC50s



## JackF999 (Jan 30, 2013)

Okay guys I need your help pleaseeeee.......

I have had a pair of Spica TC50s for 15 years..
( I know their not DIY but I know some here have extensive 
experience with crossovers and probably have had some
experience in troubleshooting old speakers )

One speaker has developed low volume, scratchy sound...
I researched and found a Spica site that states that the 
bipolar electrolytic caps should be replaced...
( They tend to fail open )

I switched wires from the other channel and the problem is still there...

Jon Bau, the creator, used Bennic bipolar 10% but manually
matched them per crossover.

I want to use PartsExpress metal film ( Jon says are good ) but
the 40uf is 2 1/2 inches x 2 inches, kinda big for the crossover board
and costs $10....
( Not a biggie but I would probably change all caps for metal film so ouch )

If I raise the volume using the other channel all the sound is present
( woofer and tweeter ) but subdued and scratchy..

So,,, what do you think, am I on the right track replacing the caps
to solve this problem ???

( Pretty SURE connections from the amp I make is good )

These are my beloved, treasured little gems.....

Please comment..........

Thanks sooooo much...........


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## fbov (Aug 28, 2008)

Without a circuit diagram of the XO, it's hard to say what a given component might do if it failed. Upgrading electrolytics to film caps is a good idea, but you could stick with electrolytics if space is an issue. They're a common tradeoff in modern designs, for large values and in non-critical parts of the circuit. 

I see no downside to replacing all with film caps, as well as any resistors that sho signs of browning. 

HAve fun,
Frank


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## JackF999 (Jan 30, 2013)

Frank, thanks for commenting...

I see on ebay people are selling Cap meters for cheap... opinions ?

I saw on Parts Express they sell a DATS unit that in addition to
measuring driver units, also measure caps, inductors and resistors.

The cap meters are about $40, but if I could buy a DATS for $100
that would give me additional usage for only $60 more.

What is the opinion of the quality for measuring caps ect... of the DATS unit ?

Has anyone used the oscilloscope/signal generator function on a DATS and
how well does it work?
( I could use it to see how good my ST70 output transformers are )

Thanks for responding.......


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## JackF999 (Jan 30, 2013)

I've read a little more on caps and found out I would
probably need to measure and duplicate the ESR for the
original caps for this speaker.

I would probably need to add some resistance to the new
caps since the ESR would not be the same as the old Bennic
caps.

Oh Boyyyyyy,, complications.

As Roseanne Roseannadanna ( fofanna.....) always said...

"If It's Not One Thing, It's Another"


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## fbov (Aug 28, 2008)

Odd, the line I recall is "Nevermind."

You're diving a little deeper than necessary here. The creator may have custom matched component values, but you don't know what value he was targetting, so my best advice is to target nominal and don't spend money on extreme tolerances. ESRs are very small; coil DCR we account for, ESR not so much. 

Cap/coil measurement capability is useful, but only if you have a target value, which you don't. As an additional capability for a digial meter, I'd spend a little extra for the capability, but not much. DATS is a wonderful tool for the DIY speaker designer, but understand it's prior incarnation was called "Woofer Tester 3." This device measures Theil/Small parameters for the driver under test, and generates an impedence vs. frequency sweep required for crossover design. It will also measure capacitance, resistance and inductance. 

Remember, you're trying to breath new life into an old friend, not restore to "like new" condition. I would start with standard poly film caps at nominal levels, and if you're worried, get a couple small-value caps, too. Capacitance adds in parallel, like resistors in series, so you can tweak a crossover by attaching parallel caps with aligator clips.

Have fun,
Frank


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