AA network modification - Battery biased crossover network

[Guest " "]

super....below is a nice schematic redrawn by GotHover

[cfelliot]

I have been following this thread with interest and have a question.

Isn't it critical that all the capacitors in the bridge, be matched in terms of DCR?

Otherwise, there exists the possibility of a potential difference between the input and output to the bridge with resultant current flow outside the bridge?

I would think an easy test would be to put a voltmeter between input and output looking for 0 volts!

PS Wouldn't shunting each cap with a 1% 1meg resistor guarantee this?

[Guest " "]

cfelliot I would like to understand your question and recommendations a little better....so do not take my response in a negative way. My implementation of the battery charge/bais uses 4 capacitors in a bridge form. All caps have some leakage, 10ua or less is considered an in spec capacitor. So in a worse case senerio, dc leakage would never leave the bridge because there's no ground reference outside of the bridge. Both the + and the - poles of the battery are used exclusively within the bridge and each bridge has it's own independent power source. Any test from any point within the bridge to ground results in zero. Capacitor resistance is measured in ESR. So if we shoot for a goal of matching them, what would actually be happening. Series set Cap#1's ESR+Cap#2's ESR would be ESR_value_A, Series set Cap#3's ESR+Cap#4's ESR would be ESR_value_B. The two sets in parallel results in ESR value C (A+B/2=C). The crossover network would see an ESR value of "C" in spite of the acknowledgment that no one capacitor in the bridge would have an ESR value exactly equal to "C". So, in my mind, the bridge averages out the ESR's making the need to match them not important. Most implementations of battery biasing uses two caps instead of 4, and in most implementations the battery is connected to ground. In a two capacitor approach, you have the problem of cumulative ESR in addition to having the DC source tied to the ground reference. My approach avoids both issues. If I thought that adding resistors in shunt would even add a theoretical benefit, I would certainly do so, since there costs is so low. So, please, continue your questions, perhaps, I'm missing something very fundamental.

[cfelliot]

speakerfritz,

No worries, just a discussion! Excuse my use of DCR and not ESR. I've been looking at speaker specs too long. []

I understand what you are doing in terms of AC and it's a great idea, but my question is around DC characteristics. I'm not talking about capacitor value matching, rather ESR matching. I have no idea how this varies from cap to cap.

[djk]

I'm not sure this is the best way to do it.

In use there is a very low impedance from X to Y (X to ground of less than 0.1Ω, and Y to ground of less than 1Ω).

[Guest " "]

Cfelliot

I did some checking. Putting a resistor in series with a cap compared to putting a resistor in parallel with a cap, does not change the ESR. So adding shunt resistors would not effect ESR. I have seen shunt resistors used when needing to charge large capacitors which are wired in series. But in this, case, the capacitors are very small. Maybe I'll understand better if you plug in some numbers. One version with no shunt resistors. another version with shunt resistors.

[cfelliot]

ESR is the wrong term.ESR is AC! Not sure what the cap spec for DC resistance is which should be defined by the V over the leakage current. Let me call it DCR. It's tens of meg ohms for sure, but it still forms a voltage divider.

The idea of the shunts (parallel) is to normalize this resistance in each leg. Assume A has a DCR of 20Meg and B is 30Meg:

30/(20+30) = .66 * V = 6V

Shunting both capacitors with 1Meg resistors makes A= 909K and B=952K

952/(909+952) = .512 * V = 4.6V (Much closer to 1/2 V)

If leakage currents are pretty constant from cap to cap then this is a big never mind.

[Guest " "]

Interesting point....the circut provides an AC service, but internally and internally only, it has a DC component. Since the parts costs is so low, and there is a theoretical benefit, I'll go ahead and add them. I think that the differential ground reference that the series resistors provide will probably have some charging benefit. Thanks for hanging in there and explaining.

[nola]

Hello folks:

I found this old thread by accident when searching for the differences between an AA vs AL-3 crossover network (which I never found a "proper" answer to).

This idea sounds interesting to me. However, is it something that only 5 people on the planet do? Does it fall into the same category of other apparently weird stuff that makes perfect sence, like powering up our gear using a car battery at 6 or 12 V DC to avoid any AC hum and other AC issues (which I think makes so much sence that it seems mind boggling that almost no-one does it)?

[djk]

From a 20 year old review on some Infinity loudspeakers:

"According to Infinity, premium-quality parts and high-quality internal
cabling are used in the crossover network. Each driver has its own
isolated, glass-epoxy crossover circuit board. A unique aspect of the
Epsilon's design is the use of two 9V batteries per loudspeaker to bias
the joining point of a series/parallel set of capacitors in the tweeter
network; this is said to noticeably improve the top end. The battery
bias is applied through a high (5 megohm) resistor, limiting the demand
on the batteries. As a result, the batteries' active life expectancy is
equivalent to their shelf life—about two years."

Harmon owns Infinity, and they started using this technique in some of their top-of-the-line JBL models (4348, DD66000, etc.)

Vandersteen Model 5A uses battery bias.