[ak645]

Does anyone know how to make one?

 I want it to go between VTL 5.5 preamp (output impedance 185 ohms) and Mccormack DNA-1 amp (input impedance 100 kohms) to keep low bass out of ACI Sapphire-3 speakers.Figure a first order roll off starting around 40-50 hz.

 Thanks!
 Andy

[JohnR]

This might help:

http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

[ak645]

Thanks John,cool site!

 So I figure a .033 uf cap would give me a 50-60 hz crossover point.I notice they show a resistor between signal and ground.Is this really needed? There's already a 100 kohm resistor on the amps input.

 Now for the fun part,picking out caps.Enough freakin' math already! I could go with Multicap RTX,that would match the coupling caps on the preamp.The problem with that is they're only seven bucks each,and most places have a twenty five dollar minimum.Or I could go with a pair of TRT Dynamicaps which is what the amp has.About twenty five samoleans per pair,so they meet the min order.Or I've heard great things about the RelCap teflon and tin (TFT) caps,about fifty clams the pair.Expensive,but maybe worth it? Any opinions welcome.

 Thanks!
 Andy

[tom1356]

You should consider the Mundorf silver PIO caps.
As close to no cap as it gets.
Good luck and let us know how you make out.

[mgalusha]

Andy,

You shouldn't need an extra resistor since you know the input impedance of the DNA-1.

I keep an Excel spreadsheet handy for this exact calculation. I use a re-arranged version of the same formula. In cell C5 I have the following:

Code: [Select]

=0.159/(C3*C4) * 1000000

I enter the desired corner frequency in C3 and the input impedance in C4 and presto, C5 shows the needed cap.

As for caps I use some old polystyrene caps. The REL RTX you mention are polystyrene and would probably work very well. I have tried Auricaps and Jensen Copper foil in oil in this application and I much prefer the polystyrene. Oddly enough the cheap Xicon metalized polypropylene actually work pretty well. Hugh Dean mentioned once that the Auricaps don't always work well in situations without DC bias. Perhaps that was why they didn't sound like I expected. I haven't tried the TFT but they are supposed to be very nice. If you try them, please post your impressions.

mike g

[ak645]

Thanks Guys! I ordered a matched pair of the Relcap TFT's .033 uf.Should give me a 3db down around 50 hz.I'll check back in a couple weeks,let you know how it goes.

 Cheers,
 Andy

[ak645]

Well,I've now had the high pass caps installed for around three weeks now.They've done some good things objectively.Bass has more definition,Better overall detail and imaging.However the down side is big.PRAT is lost,system seems slow.Just doesn't sound like music anymore.

 I've tried adjusting speaker position and subwoofer volume,crossover,and phase with VERY limited success.Sadly I must conclude that this experiment has been a dismal failure.

 Ah well,I'm only out about sixty clams,so no big deal.Might start looking around for some new speakers,possibly some Selah line arrays.

 Cheers!
 Andy

[mgalusha]

Andy,

Sorry to hear the experiment didn't work out well. I use a similar configuration and have found as you did that the caps can make all the difference in this setup. Some of the expensive caps really didn't work well in this configuration such as the Auricaps and Jensen. The only one's I've been able to tolerate are some NOS polystyrene and some of the Xicon metalized polypropylene.

On thing that has occured in my system is a very long break in time for these caps, perhaps due to the very small signal going through them. I cobbled together a "Cap-rack" (as shown here) to assist with break in. A week on the rack at 20 volts makes a big difference. Works wonders on Black Gates as well.

Mike G.

[doug s.]

andy, for only ~thirty clams more, ya may wanna try these - supposedly wery transparent, according to some folk who have tried 'em...  and, they may offer a free trial...

http://www.audioc.com/accessories/Hipass.htm

doug s.