Relative importance of the quality of DC-blocking cap?

Lost81 · « **on:** 14 Oct 2004, 05:54 pm »

Hi guys,

In my efforts to continue to tailor 2 of my AKSA 100W Nirvana monoblocks for bass duty, I have stumbled upon this (forgot who wrote it):

1.0uF Auricap for DC blocking. Hugh and I reckon the original .47uF does limit LF a tad.

How important is the quality of the capacitor here?

The reason why I am asking is because percyaudio.com has a minimum order of $25. Two 1.0uF 200V Auricaps @ $9.50 each is still under the minimum order.

Now, the 1.0uF 425V TRT DynamiCap is $17.95 each. Two of them will meet the minimum order requirements.

Or should I stick with the 1.0uF Auricaps for the bass monoblocks and replace the stock .47uF caps in the treble monoblocks with 0.47uF Auricaps ($7.95 each) to meet the minimum order instead?

Or shall I just go to 1.0uF Auricaps for all 4 monoblocks?
(There is some formular for calculating the frequency a certain value of capacitor lets through, yes? No point letting the treble / midrange monoblocks process frequencies that will be filtered out by the passive crossover in the speakers anyways...)

I'm going for the best bang for the buck here.
(1.0uF Teflon and Film capacitors are out of the question here as they are in the hundreds of dollars).

FWIW, the specs for my speakers are:
3-way sealed, with bandpass bass
Freq Response: 55Hz - 20kHz +/- 1.5dB
LF Response -6dB: 32Hz
Norminal Impedence: 6 Ohms
Sensitivity SPL 1M/2.83V: 90dB
Recommended Amplifier power: 30 - 250 Watt/Channel
Max SPL (per pair): 112dB
Crossover Frequencies: 110Hz & 3kHz
Effective Volume: 42 litres
Drive Units:
LF 200mm Polypropylene

HF 170mm Aerogel
25mm FF cooled silk dome

Thanks!

-Lost81

jeffreybehr · « **Reply #1 on:** 14 Oct 2004, 07:54 pm »

Coupling capacitors do indeed sound different, each and every one. Whether you or I can hear all those differences is another question. If you are a skilled and discerning listener...a golden-eared audiophile...instead of a tin-eared audiofool as I am most of the time, you probably can hear most of the differences among various capacitors.

I see 3 issues here--
1. The quality of the cap in your all-but-bass (AKA '8-octaves') amps;
2. The crossover frequency and hence cap value for your 8-octaves amps; and
3. The hi-pass crossover frequency of your bass amps.

1. Auricaps have a reputation for VERY-high overall quality, as do TRT DynamiCaps. I bought the latter for my c-j premier 11As, only because I felt they would sound a little better based on reading about them, not testing them in my amps. See these (http://www.altavistaaudio.com/caps.html) comments by Mike Elliot, founder and designer of Counterpoint and head of Alta Vista Audio. I expect you'll get lots of opinions on capacitor quality from fellow AC-ites. I used North Creek Zens and Harmonies (http://www.northcreekmusic.com/Zen.html) in my speaker crossovers recently. They sound LOTS better than the previous combination of SCRs, Rels, some 'styrenes, etc.

2. You might benefit from installing a higher-frequency (than stock) hi-pass filter in your 8-octaves amps, but I'd be inclined to leave its frequency as is. The formula for calculating filter frequency is F = 159155/RC, where F equals the filter (= -3dB) frequency in Hertz, C = the capacitance in microFarads, and R equals the resistance in Ohms. The R value you'll get from the load resistor (to ground) that follows the coupling cap. Do you have a schematic diagram for your amp(s)?

3. The minimum filter point for good bass quality and quantity at least was generally at least 2 octaves below the lowest audible frequency, or around 5 Hz. If I were doing it, I'd go another 2 octaves down and choose something in the 1- to 2-Hz range. Calculate what cap values you'd need for 1 Hz and 2 Hz and see what cap values are available in that range.

Good luck. I'll be interested in your results.

Lost81 · « **Reply #2 on:** 15 Oct 2004, 08:10 am »

Wow,

Thanks for the valuable load of information, jeffrey!

In the amplifiers, the load resistor is 47K ohms.
Currently, with 0.47uF, F (-3dB) = 7.2048 Hz.

With 1.0uF, F (-3dB) = 3.38627 Hz

I also looked at my pre-amplifier's DC-blocking output cap, it is 1.0uF.

If I increase the DC-blocking output cap in the pre-amp to 1.5 uF, F (-3dB) = 2.25751 Hz.

My guess is, unless I increase the capacitance in the pre-amplifier to 1.5uF, it will make no sense to increase the capacitance of the DC-blocking cap in the inputs of the bass amplifiers beyond 1.0uF. (I.e. Can't put in what was already taken out earlier).

Do you know if the common-rule-of-thumb for electrolytic capacitors (i.e. higher voltage for the same capacitance value = lower ESR) applies to film caps?

I only need 200V rating.
They are offered in 200V, 450V, 600V, 1500V, 3000V.
Wondering if getting a higher voltage rating will result in any perceivable sonic improvement.

As for the treble / midrange pair of monoblocks, I will probably leave the stock values of the DC-blocking capacitors as they are (i.e. 0.47uF). I may, however upgrade them to Auricaps or TRT DynamiCaps.

Cheers,
-Lost81

jeffreybehr · « **Reply #3 on:** 15 Oct 2004, 07:47 pm »

"In the amplifiers, the load resistor is 47K ohms. Currently, with 0.47uF, F (-3dB) = 7.2048 Hz. With 1.0uF, F (-3dB) = 3.38627 Hz. I also looked at my preamplifier's DC-blocking output cap, it is 1.0uF. If I increase the DC-blocking output cap in the pre-amp to 1.5 uF, F (-3dB) = 2.25751 Hz. My guess is, unless I increase the capacitance in the preamplifier to 1.5uF, it will make no sense to increase the capacitance of the DC-blocking cap in the inputs of the bass amplifiers beyond 1.0uF. (I.e. Can't put in what was already taken out earlier)."

You're correct about changing both caps; I certainly didn't think of it. For the best bass, I'd be inclined to change the bass amp's input cap to 2 - 3 uFs and the preamp's output cap to around 4. Circuit designers at least used to have a concept of staggering filter poles in equipment with successive filters (such as vacuumtubed [fono] preamps which could easily have 5 filter caps in them), but I don't know anyone who knows whether that staggering has the filter points increasing or decreasing in series. Maybe another 'Gonist can help us. If the better-sounding 'stagger' has the filter points going up, then put the 4 in the preamp and the 3 in the poweramp.

"Do you know if the common-rule-of-thumb for electrolytic capacitors (i.e. higher voltage for the same capacitance value = lower ESR) applies to film caps? I only need 200V rating. They are offered in 200V, 450V, 600V, 1500V, 3000V. Wondering if getting a higher voltage rating will result in any perceivable sonic improvement."

Don't know about changing ESR, but I do understand that GENERALLY, and all other things being equal, thicker film (= higher voltage rating) equals better sound. If you have a choice and the increase in price isn't prohibitive, go with a higher-voltage rating.

"As for the MR/treble pair of monoblocks, I will probably leave the stock values of the DC-blocking capacitors as they are (i.e. 0.47uF). I may, however upgrade them to Auricaps or TRT DynamiCaps."

Excellent idea. You might try paralleling caps in a way that you could try a 'base' cap that would give you a filter point somewhere in the low- to mid-bass (say, 20 - 50Hz) and add another to get it to the original point. That way you could determine by listening which sounds better. IOW, install a, say, 0.1 - 0.15uf cap ( = 34 - 23 Hz) initially, listen for a few days, and then add a 0.33 or 0.47 to the first cap to see how the system sounds then.

Playing with capacitors can be addictive; be careful.

kyrill · « **Reply #4 on:** 16 Oct 2004, 10:02 am »

There is something puzzling me

if the interconect between pre amp and amp make the two units "one" unit, beit with 2 pcb's why do we need two capacitors in series at both ends of the interlink and thereby halve its value?
or the output cap of the pramp can be removed or the the input cap of the power amp. (not both of course)
as no cap sounds better than any cap

The idea that a cap can break down so 2 is safer than one is valid for any cap wherever its place in the design. We should double any component that may break down in some future that might endanger the system?

So, There is something puzzling me
If these caps are condoms for protection as the master so clearly put it, why should I wear two?

PS Jeffrey, Nice to see yr photoo, just like in the AVS forums
Hope you will start a trend

PS

jeffreybehr · « **Reply #5 on:** 16 Oct 2004, 05:47 pm »

Kyrill, thx for the comment on the pic.

Manufacturers build equipment that must work in every audio system anyone can put together, and it must be reliable. Probably it would be safe to operate an output-couplerless preamp with these particular poweramps since they have input couplers. But perhaps the preamp would output a DC surge on warmup that would damage another poweramp.

I'd certainly test this in the preamp--see if there's a turn-on surge, what the steady-state DC offset is if any, etc. The output cap could be simply jumpered for some of this.

WerTicus · « **Reply #6 on:** 16 Oct 2004, 06:01 pm »

remove the cap completely it will sound even better.

kyrill · « **Reply #7 on:** 16 Oct 2004, 06:27 pm »

Quote from: jeffreybehr

But perhaps the preamp would output a DC surge on warmup that would damage another poweramp.

I'd certainly test this in the preamp--see if there's a turn-on surge, what the steady-state DC offset is if any, etc. The output cap could be simply jumpered for some of this.

In the GK-1, C21 (the output cap) is the last component in the chain. Turn surge cannot go thru that cap, can it?
And C1 is the very first cap in the signal path of the AKSA.
Even if DC would come from the preamp on its turn-on (because C21 is removed) it will be blocked by C1.

Jens · « **Reply #8 on:** 16 Oct 2004, 07:05 pm »

Quote from: kyrill

Quote from: jeffreybehr
But perhaps the preamp would output a DC surge on warmup that would damage another poweramp.

I'd certainly test this in the preamp--see if there's a turn-on surge, what the steady-state DC offset is if any, etc. The output cap could be simply jumpered for some of this.

In the GK-1, C21 (the output cap) is the last component in the chain. Turn surge cannot go thru that cap, can it?
And C1 is the very first cap in the signal path of the AKSA.
Even if DC would come from the preamp on its turn-on (because C21 is removed) it will be blocked by C1.

Hi Hugh,

What's your view on this issue?

Cheers,

Jens

AKSA · « **Reply #9 on:** 16 Oct 2004, 09:06 pm »

Ah, yes Jens, blocking caps,

I have previously given my view on removing these caps.

Technically either C21 on the GK1 or C1 on the power amplifier is superfluous. However, you remove one at your risk.

An amplifier without a blocking cap is a disaster waiting to happen. A preamplifier without a blocking cap is a catastrophe waiting to happen. The sonic damage of both these caps in series over just one, say C21, is so slight as to be almost imperceptible. This is one situation where the subjectives and an obsessive nature will easily throw caution to the winds. Remember, this is electronics! It relishes any opportunity to go wrong, and actively looks for it!

Human memory is flawed. With one component unprotected it will only be a matter of time before the two are separated and a third is inserted into the chain, very likely (and Murphy was an optimist) with some slight DC on the output. Any offset on this third component will be faithfully relayed to the speaker driver through an unprotected amp. Bingo!! Your speaker is HIV positive, and your amplifier may have full blown, unwelcome symptoms...........

Cheers,

Hugh

Lost81 · « **Reply #10 on:** 16 Oct 2004, 10:05 pm »

Quote from: AKSA

Ah, yes, blocking caps...

Human memory is flawed. With one component unprotected it will only be a matter of time before the two are separated and a third is inserted into the chain, very likely (and Murphy was an optimist) with some slight DC on the output. Any offset on this third component will be faithfully relayed to the speaker driver through an unprotected amp....

Exactly my thoughts

-Lost81

AKSA · « **Reply #11 on:** 16 Oct 2004, 11:38 pm »

Thank you Benny, appreciate the almost Shakespearian acceptance of the ineffable in your response........

Jeffrey, I must say your patrician visage adds grace and gravitas to our deliberations, and your whimsical smile is entirely in keeping with the ironic sub-plot which often features here!

Thank you for your comments, most welcome!

Are you really a famous photographer? What cameras do you use?

Chars,

Hugh

kyrill · « **Reply #12 on:** 16 Oct 2004, 11:43 pm »

Quote from: AKSA

Ah, yes, blocking caps,
..

An amplifier without a blocking cap is a disaster waiting to happen. A preamplifier without a blocking cap is a catastrophe waiting to happen......

Hi Hugh

I remember, but you played it safe and as you do now again.
And If I read NOW well, difficult to do late at night, Hugh is very right.
A third component will fail the logic.S O my rant is not necessary and I deleted it
Thanks for yr advice Benny. . . .
: ) K.

Lost81 · « **Reply #13 on:** 17 Oct 2004, 12:17 am »

Hi kyrill,

If I have not misread Hugh's post, one of the points he raised is if / when another component gets inserted between the TLP / GK-1 and the AKSAs.
If the component leaks DC, then bad things may happen.

Or, components get swapped around, and a TLP / GK-1 without DC-output protection gets paired with another amplifier.

Or, conversely, in the same scenario, an AKSA without DC-input protection gets paired with another pre-amplifier.

-Lost81

jeffreybehr · « **Reply #14 on:** 17 Oct 2004, 04:47 am »

Quote from: AKSA

Thank you Benny, appreciate the almost Shakespearian acceptance of the ineffable in your response........

Jeffrey, I must say your patrician visage adds grace and gravitas to our deliberations, and your whimsical smile is entirely in keeping with the ironic sub-plot which often features here!

Thank you for your comments, most welcome!

Are you really a famous photographer? What cameras do you use?

Chars,

Hugh

Well, TYVM, Hugh, for your nice comments. I do try to be helpful AND thoughtful.

I AM a fotografer (even tho I can't spell it), but famous I'm not. My pics can be seen at http://community.webshots.com/scripts/controlPanel.fcgi . I shoot a Canon EOS 1Ds and an assortment of all-Canon primes but for a Zeiss/Contax 28/F2.

BTW, I agree completely with your conservative approach to DC-blocking caps--the benefits of stopping DC on the way out AND in.

Do YOU have a philosophy on filter-point staggering of caps in series?

If price were no object, what coupling caps would you choose for YOUR system's amps and preamps? Excluding the hyper-expensive teflon-film caps?

WerTicus · « **Reply #15 on:** 17 Oct 2004, 07:02 am »

what about paper in oil caps?

kyrill · « **Reply #16 on:** 17 Oct 2004, 08:45 am »

Quote from: jeffreybehr

Well, TYVM, Hugh, for your nice comments. I do try to be helpful AND thoughtful.

I AM a fotografer (even tho I can't spell it), but famous I'm not. My pics can be seen at http://community.webshots.com/scripts/controlPanel.fcgi . ..

Hi Jeff
The above adress is very general and needs searching for your indeed beautiful landscapes and the Porsche mod....
why not this address?

http://community.webshots.com/user/jeffreybehr