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Old 3rd August 2001, 12:45 AM   #1
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Hi,

I'm currently finishing my a dual-mono setup of the JLH 1996 design.

I have this remote idea about tantalium bipolar capacitors that they better approach the 'perfect' capacitor than 'normal' bipolar capacitors and thus block DC but are more transparent to higher frequencies.

Any opions, measurements, comments??

Jos
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Old 3rd August 2001, 12:59 PM   #2
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Default Tantalum capacitors

First, I don't think I know any bipolar tantalum capacitors. I don't think there are any, and believe me I have a made a thorough research on bipolar caps recently for a project I am working on.

Second, tantalum capacitors were reported as bad sounding on the capacitors article, by Jung and Marsh, published in Audio magazine years ago. Tantalums also have a problem that they have to be biased by some voltage applied directly to work properly. I have seen tantalum caps catching fire very easily, and they were just bypassing, not the main ones.

To solve chemical capacitors distortion problem, as that also happens with electrolytic types, the advise was to use two caps, back to back, with the joint point being polarized to V+ or V- (depending on that joint polarity) through a resistor. Arranged in such a way and bypassed by a film cap, these caps would they spec almost as a polyester cap.



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Old 3rd August 2001, 07:00 PM   #3
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My experience is that tantalum and ceramic caps
are the worst. And they actually measure bad.
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Old 3rd August 2001, 07:20 PM   #4
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Tantaliun caps are great for computers but death for audio. From my experance with them the charge and dischage rates change with DC bias. If they are used for power supply bypass this isn't much of a problem but never use them in the signal path.
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Old 4th August 2001, 03:39 PM   #5
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Default Beg to differ

I've found Tantalums to offer some of the best sound for coupling in audio. They have measurably lower distortion than electrolytics, and to my ears sound better than anything I've tried, including OS-Con's etc. They're used by a number of high-end manufacturers in expensive amplifier designs.

As suggested above, many circuits suffer from incorrect biasing of capacitors, something that should be a done for all polarised capacitors, but is essential for tantalums, if only because they will fail catastrophically if this is not observed. The spec. for most tants is 0.2V reverse voltage MAX!. You need to ensure that when signals are passing through the cap this is not exceeded or even approached.

A pull down on one lead, and suitable DC biasing, preferebly via a potential divider will allow them to perform at their best.

Andy.

P.S. I agree about ceramics they measure bad and are very microphonic.


[Edited by ALW on 08-04-2001 at 10:41 AM]
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Old 10th August 2001, 01:51 AM   #6
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Wink re: comments

first off all,
thanks for the various comments.

Let me make one thing clear: I've messed up major by naming tantalium capacitors 'bipolar'.

The Dutch short for a capacitor with an explicit + and - lead is ELCO (from ELektrolitische COndensator) but I do not know an appropriate English term.

I basically made a wrong translation.

Basic intention was to query about 'normal' tantalium capacitors with + and - leads.

Over the years I've blown up several: incorrect connection, slightly higher voltages etc, but their advantage in DC-regulating circuits still crept up.
So when finishing the JLH design (and power-supply), finding some capacitors needed for DC-coupling the use of tantaliums crossed my mind.

All in all, the response has been very welcome.
My JLH amp is now done without any tantaliums and it's nearly finished....


Jos
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Old 14th August 2001, 02:43 PM   #7
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Andy,

Could you please elaborate on how to put a bias voltage on tantalum caps.

Somewhere in this forum, I also read that series connected electrolytic caps require an appropriate pole bias voltage at the junction, in order to perform well. Could someone throw more light on this?
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Old 16th August 2001, 10:00 PM   #8
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Default Using Tantalums

Samuel,

Here's an example circuit, consisting of a complimentary feedback pair with current source, running from a single 24V supply. Ignore the specific semiconductor types, as I had limited ones available in the SPICE software.

The input and output coupling capacitors are tantalums
(C8, C9). The input has a pull down of 100K (R20) to keep the input at 0V DC, the +ve terminal has a divider (R21,R22). The divider provides bias for the tantalum (12V), and the complimentary feedback pair.

At the output, the amplifer is nominally biased to sit at half rail (12V) for max swing, hence this provides bias for the tantalum. The -ve side of the tantalum has a pull-down (R16) to keep it at 0V D.C.

This circuit measures and sounds great, I hope it helps you understand the principle!

Andy.

Click the image to open in full size.
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Old 18th August 2001, 12:28 PM   #9
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Andy,

Thanks very much for the schematic. Can the same principle be used when higher value electrolytic capacitors are used back-to-back in the gain/feedback arm of most conventional amplifiers. For example, a 470uF electrolytic and a film 470nF cap are used in Anthony Holton's N-channel amplifier. I used two 1000uF ELNA electros in series in place of the 470uF. Can I use the same principle to bias the junction of this series connected pair?

BTW, how do you upload schematics on to this site? I use Electronics Workbench V.5 for simulations. Would this be of any use in this regard?

Thanks in advance.
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Old 22nd August 2001, 04:04 PM   #10
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Default Caps

Hi,

Here is another attempt to look at caps characteristics for different types.

http://members.aol.com/sbench102/caps.html

FWIW,

Greg
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