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roadworn

Rules for cap bypassing? Forte ii crossover

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probably a biginner question and Iam...Iam building a crossover for my Forte ii's  that require a 7.5 cap for the tweeter section. I will be using Audyn plus caps for this build and the closest I can get would be a .68 and 6.8 giving me 7.48uf.

Iam thinking of adding a an additional two Audiocap PPT Thetas 0.01uF to get me to the 7.50 that is specd for the ALK style crossover. In addition I believe the Thetas will add a bit more clairity.

I read on another fourm that adding more than  0.01 % for bypassing can cause phase issues.  Any thoughts about this?  From what I understand Part of the ALK design is to help get rid of phasing issues with these horns and I certainly dont want to spoil that process.

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Given the 2% tolerance of your chosen caps, the 0.02 uf seems superfluous.

Disclaimer: I am not an engineer or expert in crossover design. Others here with more expertise may also chime in.

@Deang

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Total capacitance is one thing, but adding miniscule-value "bypass" caps as a means of altering the sound quality throughout the passband is utter nonsense.  Do the math.  Taken individually (which is what will happen), the ultra-small-value caps will only pass appreciable signal well above the audio range of your ears!  No way in any known universe that will improve what you can actually hear...

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16 minutes ago, glens said:

Total capacitance is one thing, but adding miniscule-value "bypass" caps as a means of altering the sound quality throughout the passband is utter nonsense.  Do the math.  Taken individually (which is what will happen), the ultra-small-value caps will only pass appreciable signal well above the audio range of your ears!  No way in any known universe that will improve what you can actually hear...

To point then I would not expect any audible advantage to adding the Thetas but would accomplish the net goal of proper Capacitance ?  So at that point I may as well just add two more 0.01uF  Audyn plus's or any other .01uf cheep cap with no ill effect?

Edited by roadworn

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7 minutes ago, roadworn said:

To point then I would not expect any audible advantage to adding the Thetas but would accomplish the net goal of proper Capacitance ?  So at that point I may as well just add two more 0.01uF  Audyn plus's or any other .01uf cheep cap with no ill effect?

 

Correct.  Plus the difference between 7.48 and 7.50 uF is an insignificant 1/4%. 

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2 hours ago, glens said:

Total capacitance is one thing, but adding miniscule-value "bypass" caps as a means of altering the sound quality throughout the passband is utter nonsense.  Do the math.  Taken individually (which is what will happen), the ultra-small-value caps will only pass appreciable signal well above the audio range of your ears!  No way in any known universe that will improve what you can actually hear...

 

If there is an effect ("if") and the mechanism was that the total capacitance was increased by a very small amount, then I would readily agree with you. 

However ....

Please keep in mind that bypass capacitors are commonly used by the big audio manufacturers (especially in power supplies). For instance they were used by Nelson Pass, Adcom and others.

 

Is it audible? Well they thought the benefit was enough to warrant the change and higher parts count.

What is the mechanism? Unknown - as far as I can tell. 

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If you were to actually measure your 6.8 & .68 caps with +-2% tolerance you could end up with a range of 7.33 to 7.63. I would bet they will not be spot on though they will be close, So adding the .01 caps will most likely not “zero in” on the target 7.5 value. What I have done in the past is to measure all caps and then pair up the combos that makes the closest to 7.5 (in this case) giving you the least spread in values. In other words say we measure both 6.8's and one gives you 6.82 and the other is 6.89 and then the .68's give you ..67 & .69. One would pair the .67 + 6..89 and .69 + 6.82. Hope that makes sense.

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1 hour ago, PrestonTom said:

Please keep in mind that bypass capacitors are commonly used by the big audio manufacturers (especially in power supplies). For instance they were used by Nelson Pass, Adcom and others.

 

Two significant factors there as compared to using them in a loudspeaker crossover, which I'd gathered was the current topic.

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All good incite from the group . Thank you. ALexander you are probably dead right . I will measure them just for kicks when I get the caps and let you know what I find. This crossover voodoo is new to me. In normal theory like pwr supplies it seems correct that you would just make up the best combo for the correct Capacitance, but clearly when it comes to Sound being put through a cap all bets are off as many factors (and opinons) seem to make a difference in the final voicing of a crossover. For me and and this  ($$$) level of mucking about with crosovers I think I will just use the two caps and be done at 7.48uf  However, I enjoy the chase and find it cool to find out that abnormal thinking is what makes all us creative types ... well creative with our experiments. Iam and old roadie and most of my high end is gone and I have terrible ringing, most of this is lost on me I would bet, but I cant help myself haha. Thanks again to the group on these pages, you guys rock.

 

Edited by roadworn

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2 hours ago, glens said:

 

Two significant factors there as compared to using them in a loudspeaker crossover, which I'd gathered was the current topic.

Yes Glens, that is correct , sorry, I should have clairified. Iam talking in crossovers.

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I read somewhere when I was researching caps for my latest crossover build that it was better to use two caps similar in value instead of staggered values. For example, if you needed 20uf, it would be better to use two 10uf caps instead of one 19 and one 1uf. I have no idea if that is true and if it makes a difference. I just thought it was curious. I didn't follow that advice, by the way.

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10 hours ago, glens said:

 

Two significant factors there as compared to using them in a loudspeaker crossover, which I'd gathered was the current topic.

You missed my point, but I won't bother

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6 minutes ago, kevinmi said:

I read somewhere when I was researching caps for my latest crossover build that it was better to use two caps similar in value instead of staggered values. For example, if you needed 20uf, it would be better to use two 10uf caps instead of one 19 and one 1uf. I have no idea if that is true and if it makes a difference. I just thought it was curious. I didn't follow that advice, by the way.

 

I think the idea (whether it is an appreciable effect or not), was that the series resistance for the caps would be lower by running two in parallel. Usually caps with lower ESR are more costly. My guess, is that if you ran the numbers, the effect could be vanishingly small on the actual output of the speaker.

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Yes. JBL did it for years for that very reason. Parallel a small foil cap with an electrolytic to lower the ESR. Later, the prices of Mylars dropped, and they started using those.

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2 hours ago, PrestonTom said:

You missed my point, but I won't bother

 

I actually didn't, but it seems you've missed mine.  In electronic devices local bypass caps at the power feeds is a very real necessity (one factor) and where load impedances are high enough, small-value caps passing signal actually become relevant (second factor).  As to what those manufacturers you mentioned are actually doing where and when with bypasses, I plead ignorance as I've never looked over any of their schematics.

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2 hours ago, Deang said:

Yes. JBL did it for years for that very reason. Parallel a small foil cap with an electrolytic to lower the ESR. Later, the prices of Mylars dropped, and they started using those.

 

Or, maybe they realized that the low ESR of the small cap actually only had effect in unnecessary regions and they were wasting money trying to save it?

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2 hours ago, kevinmi said:

I read somewhere when I was researching caps for my latest crossover build that it was better to use two caps similar in value instead of staggered values.

 

That's always been my understanding and it makes complete sense to me. 

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26 minutes ago, glens said:

 

Or, maybe they realized that the low ESR of the small cap actually only had effect in unnecessary regions and they were wasting money trying to save it?

It’s possible. 
 

They now do DC biasing in their high end stuff. Along with Vandersteen and someone else I can’t remember. 

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The DC biasing that JBL does is interesting, although I have never heard or measured a "with and without" configuration.

Out of curiosity, do your customers ever request a build with DC biasing

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I’ve built three sets. Carl owns a pair. 
 

The funniest thing about this hobby is watching everyone call bullshit on each other 90% of the time. 
 

John Warren told me it makes sense with electrolytics, but not with films. I don’t argue with John. otoh, DJK swore by it, and I sure didn’t t like disagreeing with him either!
 

 

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