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Old 19th September 2006, 09:57 PM   #1
pinco is offline pinco  Croatia
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Default Leach bipolar capacitors

I need 220/16V quality bipolar capacitor, I need them for Leach amplifier, 4.5. and I cant finde them in Croatia, and Farnell and RS, have only poor quality Nitai... Leach seed it is better to use bipolar, but you can put two regular i serial, I am worry of bas response if I use two 330uF i serial, it is only 165uF, and people complaining of week bas on regular value......., best capacitor I can find is Rubycon ZA, and I think it is bether to use two quality polarized capacitors then poor quality bipolar.....
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Old 19th September 2006, 10:15 PM   #2
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Default Re: Leach bipolar capacitors

Quote:
Originally posted by pinco
I need 220/16V quality bipolar capacitor, I am worry of bas response if I use two 330uF i serial, it is only 165uF, and people complaining of week bas on regular value.......

Why don't you use two 470 uF in series, that way you have ~ 235 uF , not far from your target value of 220 uF...
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Old 19th September 2006, 10:18 PM   #3
maudio is offline maudio  Netherlands
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I replaced this C with a short and added a simple dc-servo around a 411 opamp to my Leach. Works like a dream and no electrolytic C's in the signal path anymore.
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Old 20th September 2006, 03:18 AM   #4
AJT is offline AJT  Philippines
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i have used two 1000ufd/16 caps in series back to back without any problem.
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Old 20th September 2006, 12:02 PM   #5
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Don't forget that the bipolar is bypassed with a film cap - which would tend to hide any deficiencies of the electrolytic. Use a good quality cap there, the biggest you can fit.
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Old 20th September 2006, 01:02 PM   #6
djk is offline djk
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"people complaining of week bas on regular value......."

The absolute value really doesn't matter. Even with your values the pole will be less than 1hz.

I always run an input filter at a point where the speakers need to be cut-off. Then I change the pole in the feedback loop to a higher frequency than the pole formed by the power supply and the speakers. This makes everything sound better, protects the speakers, especially during clipping. Flat response to DC is not needed nor desirable.
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Old 20th September 2006, 01:22 PM   #7
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the bipolar cap is for C6 according to me if you are using 2 polarised cap the midpoint should be connected with a high value resistor ( 1 M ohm ) to a point with a dc voltage to keep capacitor polarised, common point between D13 & D14 if midpoint between cap is positive.

unfortunatly it will add ac current in D14 but should be low very low

This is my idea but should wait second advice........
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Old 20th September 2006, 02:00 PM   #8
ilimzn is offline ilimzn  Croatia
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Pinco, you have asked me this in another forum.
My advice: up to some 1.2-1.4V all electrolytics behave as bipolars - this is from a document from Nippon Chemicon, so as it were, from the horses mouth
In your configuration, this cap should only see millivolts, unless the output blows up (at which point it won't matter eather way). My advice would be to use a regular polarised cap, the best you can find, AND the highest value you can fit. Orient it so that the offset voltage corresponds to the polarity, If you are not sure of the offset polarity, you can orient it as you like, then measure the actual polarity, and correct orientation as needed. Also, use two diodes in series (1N4148 or similar) across the cap in anti-parallel (from - to +).
Unless you are using a special cap (like low ESR for switchers or specialised audio cap), use a voltage rating of 25 to 63V. The best way to decide is to check the manufacturer data to see which voltage rating at a given capacitance you need (so a few 100 uF) has the lowest ESR. There is a sweet-point and it is usually between those two voltages but it also depends on the actual capacitance (more actually on the order of magnitude of the capacitance). The reason for using a high value, much higher than would be needed to get clear of the lower end of the audio band, is that you want as little AC component of the voltage on this cap as possible, witin the audio band - when the AC component increases, capacitor distortion sets in. Exagerating the capacitance is a FAR cheaper and effective solution than using a boutique or special cap here!!! That being said, increasing the size of the cap might increase the magnitude of the turn-on 'thump', so unless you are using some sort of protection against this, it is something you need to consider, and if needed adjust by experiment.
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Old 20th September 2006, 03:07 PM   #9
pinco is offline pinco  Croatia
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Quote:
Originally posted by ilimzn
Pinco, you have asked me this in another forum.
My advice: up to some 1.2-1.4V all electrolytics behave as bipolars - this is from a document from Nippon Chemicon, so as it were, from the horses mouth
In your configuration, this cap should only see millivolts, unless the output blows up (at which point it won't matter eather way). My advice would be to use a regular polarised cap, the best you can find, AND the highest value you can fit. Orient it so that the offset voltage corresponds to the polarity, If you are not sure of the offset polarity, you can orient it as you like, then measure the actual polarity, and correct orientation as needed. Also, use two diodes in series (1N4148 or similar) across the cap in anti-parallel (from - to +).
Unless you are using a special cap (like low ESR for switchers or specialised audio cap), use a voltage rating of 25 to 63V. The best way to decide is to check the manufacturer data to see which voltage rating at a given capacitance you need (so a few 100 uF) has the lowest ESR. There is a sweet-point and it is usually between those two voltages but it also depends on the actual capacitance (more actually on the order of magnitude of the capacitance). The reason for using a high value, much higher than would be needed to get clear of the lower end of the audio band, is that you want as little AC component of the voltage on this cap as possible, witin the audio band - when the AC component increases, capacitor distortion sets in. Exagerating the capacitance is a FAR cheaper and effective solution than using a boutique or special cap here!!! That being said, increasing the size of the cap might increase the magnitude of the turn-on 'thump', so unless you are using some sort of protection against this, it is something you need to consider, and if needed adjust by experiment.
Thanks everybody on answers....

I have question for Ilimzn, on Croatian, sory....

Nije mi jasno, Sad san gleda, kod Rubicon ZL koji je visestruko jeftiniji od ZA, najmanja je impedanca mireno pri 100khz, kod 470uF je na 35V i iznosi 0,023 ohma, dok je kod ZA na 16V 0,025, jel si mislija na to??, zašto uzet veći kapacitet kondenzatora??, kazu da je zvuk mutniji ako se uzme veca vrijednost, mislin kazu, ja se nerazumin tolko....., nisan dobro svatija šta oćeš reć pa te pitan na domaćem,
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Old 20th September 2006, 11:07 PM   #10
djk is offline djk
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"the bipolar cap is for C6 according to me if you are using 2 polarised cap the midpoint should be connected with a high value resistor ( 1 M ohm ) to a point with a dc voltage to keep capacitor polarised, common point between D13 & D14 if midpoint between cap is positive."

This is good advise if the DC source is a battery.

Since the feedback point is the inverting input to the amplifier, any noise and/or hum will be amplified. In practice this sounds worse (unless using a battery), try it and see.

"That being said, increasing the size of the cap might increase the magnitude of the turn-on 'thump', so unless you are using some sort of protection against this, it is something you need to consider, and if needed adjust by experiment. "

Music is not symetrical. Having the pole in the feedback loop being very low will cause poor settling time on musical transients, particularly when the amp is driven hard. This is made worse by feedback, and the fact that the power supplies cannot be perfectly regulated. There is an article at the ESP website discussing this. Clamp diodes help, but do not do any more than limit the off-set.

One solution is the double integrator (servo) used by Crown in their VZ5000 amplifier. The schematic is on-line in their Legacy amplifier schematic library.
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