Coupling Cap question for active system?

PT914 · « **on:** 17 Mar 2005, 07:58 pm »

Hi fellow fiddlers, just can't stop looking for improvements. Hope I am in fact improving my system, seeing that sound memory is so very short.

I am presently thinking of changing C1, I think everyone is callinng this the coupling cap, on a lower power Aksa 55. I made it a 21W. It is powering the tweeter in an active system, crossover at 1545 Hz.

Here's the question, can I use a 0.1 uF or even a .033 uF cap for C1 seeing that these caps -3 dB point is 33.9 Hz and 103 Hz respectively? These lower value caps are way less expensive and much smaller. Has anyone tried these lower value caps? I was thinking of Vcaps.

Thanks,
Philip

PSP · « **Reply #1 on:** 18 Mar 2005, 02:15 pm »

Hi Philip,
Yes, you can do that. This is a simple Passive Line-level XO, see
http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

I've from time to time inserted a series cap between the GK-1 and the AKSA amp to roll off the lows as I worked on integrating my sub, but I've never implemented a "real" line level XO.

So, if you know the input impedance of your amp (43K, I believe for the 55W AKSA) you can try it out and let us know how it sounds. All XOs apply some phase shift to the signal, so keep that in mind as you design the XO and listen.

Good luck,
Peter

jeffreybehr · « **Reply #2 on:** 18 Mar 2005, 04:02 pm »

914, don't let PSP confuse you. The only thing you need to know about filter's phase shift is that it'd be nice to keep it far out of your pass band. I'd put your new filter point 2 or 3 octaves lower than the bottom of your pass band. I guess you're using the crossover in the speaker?

Now you can buy a higher-quality cap because it's lots smaller. Consider the V-Cap TFTFs, here. http://www.v-cap.com/

PSP · « **Reply #3 on:** 18 Mar 2005, 05:57 pm »

Confusing??? Geez, I'm sorry if sending Philip to a website that provides some development related to his question was "confusing". I'm from the "teach someone to fish" school, and hope that if someone has a question, they will ask. I've observed that most of the folks here are pretty smart (and civilized, too), so I think it works well to explain just a little, and--based on the reply--continue the discussion at an appropriate level of detail and depth.

My reference to the phase shift was intended to be "don't forget that there's a phase shift" with the hope that--if he needed more info--he would ask for it, or go read about it somewhere. Philip may have known this very well, he may have been clueless, I don't know... but my reply respectfully allowed him to set the level of the discussion.

I often visit AC during 3 minute breaks during work... so I can't usually take the time required to ensure, beyond any doubt, that my stuff is totally clear to everyone that could possibly read it. I do my best within those constraints and hope people who have questions will ask.

All the best,
Peter

AKSA · « **Reply #4 on:** 18 Mar 2005, 09:25 pm »

And I for one am always grateful for Peter's posts; he is measured, courteous, always helpful and considerate, and sincere. Thanks Peter!

Jeffrey, tut tut, you were a tad heavy handed here...... Phase shift is indeed inevitable, but you are right; as long as the corner frequency is a couple of octaves below the crossover of the tweeter as dictated by the passive crossover, all is well. Thus, if crossover is 1500Hz, then setting up the input cap to the amp for a corner at around 350Hz would be fine. This corresponds to 10nF nearest preferred value, hardly a big figure....

A word on teflons. I've tried them on the charge suckout role in the AKSA, and the top end and midrange is wonderful. But no bass - EXACTLY what you need here, Philip. Strongly recommended.

Cheers,

Hugh

kyrill · « **Reply #5 on:** 18 Mar 2005, 10:41 pm »

Quote from: AKSA

. . . , but you are right; as long as the corner frequency is a couple of octaves below the crossover of the tweeter as dictated by the passive crossover, all is well. Thus, if crossover is 1500Hz, then setting up the input cap to the amp for a corner at around 350Hz would be fine. ...

Hi Hugh

What if the capacitor is placed between the AKSA (say 30 watts) and (in my case ribbon tweeter) the tweeter in an active filter setup? crossover being 2000 hz?

Same reasoning only higher power cap?

AKSA · « **Reply #6 on:** 19 Mar 2005, 03:27 am »

Hi Kyrill,

Yes, absolutely! However, your impedances are very different; the Zin of the AKSA amps is 43K; that of a tweeter is typically 8R and sometimes 4R. Let's say two octaves below 2KHz, this is 500Hz, so we need 8R capacitive reactance at this frequency. This corresponds to 39uF for 8R, and double this for 4R.

Voltage rating should be at least double the rail voltage, viz 63V for your 'little' AKSA.

Cheers,

Hugh

PT914 · « **Reply #7 on:** 22 Mar 2005, 06:52 am »

Thanks everyone. Was gone for the weekend, will try something around 10 nF. Only delay will be burning in caps, something like 200 to 400 hrs.

Has anyone burned in caps before installing them? Since these caps aren't polarized, can I just send a signal through the caps to brake them in or do I need a voltage applied across the caps plus the signal?

Thanks,
Philip

aurelius · « **Reply #8 on:** 23 Mar 2005, 02:32 am »

Hey Philip,

I believe (from DIYaudio.com) that you have built an Orion system?

I am also in the process of building an Orion using 8 x AKSA 55N+s...

I would be very interested as to how the VCap swap-out goes for you.

One other question/comment... I wonder at the potential benefit of RTX, OSCON, Blackgate, Auricap, VCap, Riken Ohm, etc in my GK-1 & AKSAs when the active crossover is full of garden variety polypropylene & metal film...

My internal logic is certainly willing to entertain the notion that tweeks in the AKSAs will have an audible benefit, because they are downstream from the active crossover. I can also believe that any additive analog signal processing (low order distortion, etc) provided by the tube stage in the GK-1 will also impact (for better or worse) what I hear. What becomes more difficult to accept is the notion that any benefit obtained by (for example) swapping out C1 in the GK-1 with a Rel Cap RTX will not be entirely masked by the active crossover.

Any thoughts/comments?

Regards

Mark C.

PT914 · « **Reply #9 on:** 23 Mar 2005, 06:30 am »

Hi Mark,

I recently got the Orion system working(Aksa 25, Aksa 40, and Aksa 100) and am trying to get a baseline, but I keep changing things so it's kind of hard to say what caused what. Hopefully, while I get the v-caps and brake them in, I won't change anything and get a baseline.

I'm still working on improving the activecross but I think I crossed a major hurdle. The power supply is subpar. I built a power supply to 18v and used FRED diode.. wow!...really quite background and clearer highs. I also built a second crossover so I could take the sub output that Hugh built into the GK-1 and fed that signal just to the base. Thanks Hugh. The base notes are more well defined, example...the kick drum's base sound starts perfectly with the treble part of the attack. Anyway I'm satisfied with the base part, for now. Oh, I didn't use polypropylene caps in the crossover. I used PPS.

A change in C1 in the amplifier even if it is down stream of the active crossover is very audible. I just changed the cap at C1 on the Aksa 25 to a TFT and put the BG that came with the Nirvana Plus to the C1 spot on the GK-1 since it was already broken in. Crystal clear highs, 80% from amp C1 and 20% from GK-1. I can't image a v-cap could improve on this but I'll let you know about the v-caps.

Really enjoying the system.

Latter,
Philip

MikeC · « **Reply #10 on:** 23 Mar 2005, 07:17 am »

Me too - Building an Orion system, that is.

I am also interested in further specific tweaks for the amps in such a system. I am still a long way from being finished, but this is what I have so far:

Crossover using mostly PPS caps (direct signal) and some polyprops (mostly shunt caps) and Dale resistors. I also have built a regulated 15V PS with Schottky diodes as rectifiers.

Bass amp is a 100W N+ with additional 50% reservoir capacitance and larger rectifier diodes.

Treble amp is a 25W N+ with Relcap teflon for the charge suckout and Schottky diodes for the rectifier. I could also consider Gingers latest tweak here, but I should finish the amp first.

Mids will be handled by a standard 55W N+ (still running my Ariels) with Schottky diodes for the rectifier.

I also have a separate crossover to output low bass (<40Hz) to a pair of subs, but I will only settle on final crossover frequency once the system is complete.

I will let everyone know when its finished, just don't hold your breath.

Mike

PT914 · « **Reply #11 on:** 24 Mar 2005, 01:16 am »

Mike,

Looks like your system will sound great from the start.
Have fun building.

Philip

aurelius · « **Reply #12 on:** 15 Jun 2005, 11:15 am »

Did anyone ever drop a Vcap in at C1 on an AKSA 55?

Any reports?

Thanks,

Mark

andyr · « **Reply #13 on:** 15 Jun 2005, 12:33 pm »

Quote from: aurelius

Did anyone ever drop a Vcap in at C1 on an AKSA 55?

Any reports?

Thanks,

Mark

Mark,

Hugh specifically commented that he had tried a teflon cap - in his case, RelCap TFT - at C1 and this is no good for a full-range AKSA as it removed base (V-caps are teflon). But, obviously it would be a great idea for the treble amp in a 3-way active system and possibly even the mid-range amp, provided you crossed over at, say, 500Hz or so.

Regards,

Andy

andyr · « **Reply #14 on:** 15 Jun 2005, 12:39 pm »

Quote from: aurelius

Hey Philip, ...

One other question/comment... I wonder at the potential benefit of RTX, OSCON, Blackgate, Auricap, VCap, Riken Ohm, etc in my GK-1 & AKSAs when the active crossover is full of garden variety polypropylene & metal film ...

Mark,

Why do you say that an active crossover will be "full of (common-or-)garden variety polypropylene & metal film"?

I used all RelCap RTXs in the filter circuits of my Rod Elliott 3-way active crossovers (with BGs in the power supply) and the same Beyschlag metal films that Hugh utilises in the AKSAs. Surely you can do the same with SL's crossover PCB?

Regards,

Andy

aurelius · « **Reply #15 on:** 15 Jun 2005, 12:59 pm »

Quote from: andyr

Mark,

Why do you say that an active crossover will be "full of (common-or-)garden variety polypropylene & metal film"?

I used all RelCap RTXs in the filter circuits of my Rod Elliott 3-way active crossovers (with BGs in the power supply) and the same Beyschlag metal films that Hugh utilises in the AKSAs. Surely you can do the same with SL's crossover PCB?

At roughly 36 signal caps in the SL Xover, I'm imagining what it feels like to have one kidney? I'm sure I could get a lazy couple of $K on the black market...

In truth , I'm not so worried about the polypropylene caps in the circuit now... I'm slowly gaining a better appreciation of the contribution of various compnents in my system. If I beef up the Xover power supply, all should be well...

And re: the Vcap question, both Philip & Peter suggested that they would try... I was just wondering about their experiences.

Take care.

Mark

PT914 · « **Reply #16 on:** 15 Jun 2005, 04:13 pm »

Mark,

My expericence with the Vcap has been good but difficult to evaluate. It takes 400 hours to break in and my musical memory is in minutes. Besides, in the 400 hours I changed other things. The best improvement to my system(Orion powered by Aksa 100, 55, and 25 through GK-1R) by ranking:
1. "Felicia" power conditioner to active crossover, Gk-1R, and cd.
2. Super Jung power supply to crossover
3. Ginger's mod to C4 to Aksa 25 and 55
4. Vcaps to Aksa 25 and 55
I'm still modifying the caps and bridge diode to the Super Jung regulator with Hugh's power boards.

Philip

aurelius · « **Reply #17 on:** 16 Jun 2005, 11:39 am »

Thanks Philip,

I appreciate the benefit of your experience...

I intend to build "Felicia" power conditioners for my active crossover and Gk-1R at some point in time.

The only reason I asked about the V-caps at this point in time was that I was on Chris Venhaus' site ordering some Eichmann binding posts and wondered whether I should grab some V-caps at the same time, but at US$31 a pop, I decided to buy a couple of nice bottles of red instead.

Regards,

Mark

Greg Erskine · « **Reply #18 on:** 16 Jun 2005, 09:12 pm »

Quote from: aurelius

....I'm imagining what it feels like to have one kidney?...

Cruel bastard, after a recent visit to hospital, I found out I have only one kidney.

So, if you need someone to listen to audio equipment then compare it to one kidney then I'm your man. How good would AKSA equipment sound if I had 2 kidneys?

Greg

aurelius · « **Reply #19 on:** 19 Jun 2005, 11:05 pm »

Are you taking the piss?... oops sorry; insensitive metaphore

Its good to know I have a reference should the temptation ever take me, although I must concede that the likelyhood of a second kidney contributing significantly to the perceived sonics is fairly remote... if however, one had no kidneys, I'm pretty sure a dialisys machine would help break up room modes.