Dueland Silver By Pass Caps

[Ittaku]

On 13/03/2020 at 11:14 AM, mbz said:

Years ago, I bypassed (0.01uf) the tweeter cap (4.7uf) on some vintage altecs. I immediately noted that the "sound hurt my ears". That went on for about 1 week of daily listening, so something is going on. I was just after an explaination hopefully based on some math, both appear beyond you.

By the way, there is science to explain that ringing can occur when you have two caps in parallel that are more than 10x their value apart. This could easily explain the unpleasant sound you were hearing. When bypassing, my rule is to bypass with only 1/10th of the value of the smallest capacitor to avoid this phenomenon. In fact for really large values (such as in a midrange crossover) where I'm unable to use the finest caps, I always make sure to use at least two caps - one at 90% of the capacitance required, and then one at no less than 10% of the capacitance required of the highest quality I can put in there. In your case, if you still wanted to use the 0.01uF, you could have used 3 main caps of regular quality of a 4uF, 0.56uF, 0.1uF, and then bypassed it with your high quality .01uF cap. There's a good chance the bulk of the quality improvement would have just been by using multiple caps of the regular quality anyway since that would have decreased the series inductance and resistance.

[mbz]

On 01/05/2020 at 1:40 PM, Ittaku said:

By the way, there is science to explain that ringing can occur when you have two caps in parallel that are more than 10x their value apart.

Not trying to put you on the spot but are you able to share a link so I can follow up. I will accept the answer that it was something that you read some time ago...

[Ittaku]

2 minutes ago, mbz said:

Not trying to put you on the spot but are you able to share a link so I can follow up. I will accept the answer that it was something that you read some time ago...

Unfortunately that knowledge goes back to when I first started building speakers >25 years ago, so I have no idea where I read it nor where to direct you to, but I'll start googling and perhaps we'll both find it at the same time.

[MattyW]

31 minutes ago, Ittaku said:

Unfortunately that knowledge goes back to when I first started building speakers >25 years ago, so I have no idea where I read it nor where to direct you to, but I'll start googling and perhaps we'll both find it at the same time.

I've read the 1/10th rule in a few places too. You're not imagining it or anything.  Too lazy to Google to find again. 

Edited May 2, 2020 by MattyW

[Ittaku]

Here's one of the first resources I could find about self resonance and how two capacitors can interact and make things worse.

https://resources.pcb.cadence.com/blog/2019-capacitor-self-resonant-frequency-and-signal-integrity

Whilst not mentioned on that page specifically, the effect is minimised by never allowing caps to be more than 10x the difference in capacitance.

 

In this example below, they are 100x difference.

 

[Ittaku]

Another paper I found showing the same thing:

 

 

From here:

https://www.cypress.com/documentation/application-notes/an1032-using-decoupling-capacitors

 

The frequency where the impedance shoots up dramatically is way outside the audible spectrum, but these values are 1000s of times smaller than those used in audio. Note how insanely high the impedance gets in this second example.

[davewantsmoore]

On 12/03/2020 at 7:24 PM, mbz said:

First up, I hope we are only talking about bypassing caps that are in series with the drivers. No bypassing of caps that connect across the driver.

You hear this repeatedly....  yet there is no reason to think it would be true.   A parallel cap should be just as relevant.

 

[muon*]

Aren't those examples of decoupling power supplies? And the base cap being an electrolytic?

 

Got anything specific to what we are talking about? By-passing a larger film capacitor with a smaller film capacitor in signal coupling?

[Ittaku]

46 minutes ago, muon* said:

Aren't those examples of decoupling power supplies? And the base cap being an electrolytic?

 

Got anything specific to what we are talking about? By-passing a larger film capacitor with a smaller film capacitor in signal coupling?

This has nothing to do with whether the cap is electrolytic or metallised or film. It's a simple mathematical relationship to do with the intrinsic resistance and inductance that all capacitors have to some degree. The best capacitors are said to be "non-inductive" but it's still not zero inductance, it's just exceptionally low, and there still is always going to be a resistance associated with the device. The real circuit for any two capacitors in parallel therefore is, as the paper above shows, as follows:

 

Hopefully the best film capacitors will have such low inductance and resistance that the resonant values causing an impedance peak will be far beyond the audible range, but it will still  happen. Without intrinsic measurements of each of the sub-properties, you cannot know what they actually are in practice, and precious few cap designs come with these specifications.

[muon*]

So this is audible? I expect so.

 

I know I have run into timing issues in a bypass situation, they were different cheap film caps, can't recall what they both were but one was a Bennic.

 

Edit: caused an echo effect in the vocal range.

They were to make up a single value, I think they were a 1.5uf and a 1uf of different makes, both metallised film.

Edited May 2, 2020 by muon*

[mbz]

9 hours ago, davewantsmoore said:

You hear this repeatedly....  yet there is no reason to think it would be true.   A parallel cap should be just as relevant.

 

Caps connected in parallel with the driver are for shunting unwanted frequencies. Difficult to see how bypassing such caps would improve the audio going to the driver or are we again talking about providing a lower impedance path for RF. Many early crossovers used electrolytics in these "parallel" positions, they were adequate since they are not in the audio path. I'd spend the extra $ and use budget PP for longevity.

Some spend $$ on these caps and then bypass...

[davewantsmoore]

13 hours ago, mbz said:

Caps connected in parallel with the driver are for shunting unwanted frequencies. Difficult to see how bypassing such caps would improve the audio going to the driver

The current flowing through the parallel circuit, is directly relevant to the current flowing through the speaker

13 hours ago, mbz said:

or are we again talking about providing a lower impedance path for RF

I'm not, No.

13 hours ago, mbz said:

Many early crossovers used electrolytics in these "parallel" positions, they were adequate since they are not in the audio path.

I've done plenty of tests (note proper controls are important), which show an electro cap is inaudible vs other..... so I'm not trying to tell you to "bypass everything everywhere with unobtanium quality capacitors"

 

.... only pointing out that, circuit theory says quite clearly that all the people generalisaing that "shunt/parallel circuits aren't in the audio path".... are making an error of logic.

 

[mbz]

9 hours ago, davewantsmoore said:

he current flowing through the parallel circuit, is directly relevant to the current flowing through the speaker

Keep in mind this is an "AC circuit". Also the purpose of the parallel element is mostly (resistors can be in parallel) to provide a lower impedance path for "unwanted" frequencies.

[davewantsmoore]

1 hour ago, mbz said:

Keep in mind this is an "AC circuit"

Yes, my comment still stands.

[MattyW]

On 11/03/2020 at 10:34 PM, muon* said:

I haven't used these yet but know their reputation and have used, and use other Duelund capacitors, but will be adding these across the tweeter caps on a pair of Aurum Cantus Melody 103 speakers of a friend in a few weeks for him, while in there I'll be changing the internal wire to Duelund 20awg solid core copper in oil impregnated cotton.

I think the cap in them is a Mundorf Mcap Supreme, so the Duelund Silver bypass caps will go across those.

Hi Ian, how did the Aurum Cantus speaker upgrade go?

 

I really should have upgraded my F620's when I had them as they were certainly held back by stock caps. Nonetheless happy with the open baffles that have replaced them.

[muon*]

52 minutes ago, MattyW said:

Hi Ian, how did the Aurum Cantus speaker upgrade go?

 

I really should have upgraded my F620's when I had them as they were certainly held back by stock caps. Nonetheless happy with the open baffles that have replaced them.

Haven't done them yet, with what he wants I need to wait for the JDM Caps from Duelund to be released so we can replace the base cap which I think are Mundorf MPK, so decent but far from top tier. The bypasses will go across the Duelund JDM's on the tweeter side, I want to have a look at what the midwoofer inductor is like before that as we may replace them if they are Iron core as stock.

[MattyW]

13 minutes ago, muon* said:

Haven't done them yet, with what he wants I need to wait for the JDM Caps from Duelund to be released so we can replace the base cap which I think are Mundorf MPK, so decent but far from top tier. The bypasses will go across the Duelund JDM's on the tweeter side, I want to have a look at what the midwoofer inductor is like before that as we may replace them if they are Iron core as stock.

Cool, keep me in the loop on this.  Keen to hear how it sounds.  Especially the JDM caps.

[muon*]

I should say Mundorf MKP, like these, but won't know until I pop a mid-woofer out when I'm over there next.