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Old 11th August 2003, 03:45 AM   #1
Tomek is offline Tomek  United States
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Default Question about output capacitor.

Hello, I have been currently working on SE solid state amp., which has 4700 uF output capacitor. The highest quality capacitor which I have is Panasonic AA computer grade one. This capacitor will be bypassed by 1 uF film cap. Is it a good idea to use Panasonic cap in the signal path?
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Old 11th August 2003, 04:12 AM   #2
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Default Re: Question about output capacitor.

Quote:
Originally posted by Tomek
Hello, I have been currently working on SE solid state amp., which has 4700 uF output capacitor. The highest quality capacitor which I have is Panasonic AA computer grade one. This capacitor will be bypassed by 1 uF film cap. Is it a good idea to use Panasonic cap in the signal path?
As long as you can keep a DC bias voltage on the cap it'll work. Ideally if the DC bias voltage is at least as high as the amp's peak voltage swing.

se
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Old 11th August 2003, 04:25 AM   #3
Tomek is offline Tomek  United States
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Thanks for the response. Capacitors which I have are screw mount GAA series rated at 100 VDC. Project is a amp. designed by Pavel Macura ( http://www.sound.westhost.com/project83.htm). The only change is to my psu, I will use lower voltage - 25 volts.
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Old 11th August 2003, 05:23 AM   #4
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Quote:
Originally posted by Tomek
Thanks for the response. Capacitors which I have are screw mount GAA series rated at 100 VDC. Project is a amp. designed by Pavel Macura ( http://www.sound.westhost.com/project83.htm). The only change is to my psu, I will use lower voltage - 25 volts.
That'll work. Though I'd recommend experimenting with some other caps when you get a chance.

se
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Old 11th August 2003, 10:10 AM   #5
Jay is offline Jay  Indonesia
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I have built several amps using output capacitors (The Pavel-Macura was I think the best sounding one). Usually they are low wattage amps so I thought maybe I could have a higly dynamic amp by using an over-rated output caps so I used not only massive capacitance but also higher voltage capacity. They are rated 150V to 450V (very big), Hitachi and Nichichon. My first impression was that the bass quality was undeniable, but I'm not very surprised because that was what I had expected from the system.

Later on, I tried to question the use of such an output capacitor. You must have known that many said that an output cap as well as output transformer in tube amps will degradate the signal. But you must have also known that it is easy just to say what other people have said. Bottom line, I changed the cap into normal quality cap. It was easy to recognize the change, but not at all an improvement! (Since then I used the caps in other projects without question)

Same capacitance, highly different voltage, different class of brand, different mounting. So should I have believed that the main reason was the voltage capacity? I thought, probably, that the mounting also played a role (you cannot mount the big caps on PCB!) This conclusion was affected by my other experiences combatting oscilation in the output stage. I have always omitted zobel network in amplifier output to increase dynamic, and only use it if I had to. The use of off-the-board output caps had helped a lot.

Later I will build another one using smaller darlington, 2SD1793, higher fT and not TIP


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Old 11th August 2003, 10:42 AM   #6
Jay is offline Jay  Indonesia
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Oh boy! The darlington is the current source! No wonder a TIP could sound so good


** Just Another Thought From A Different Kind Of Angle.
** If it is about electronics theories, I know you guys are better than me.
** If it is about ears, I know I'm one of the best.
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Old 11th August 2003, 06:03 PM   #7
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Quote:
Originally posted by Jay
Later on, I tried to question the use of such an output capacitor. You must have known that many said that an output cap as well as output transformer in tube amps will degradate the signal. But you must have also known that it is easy just to say what other people have said. Bottom line, I changed the cap into normal quality cap. It was easy to recognize the change, but not at all an improvement! (Since then I used the caps in other projects without question)
By the way, it's worth noting that you don't have to take everything from the main output cap.

For example, if you've got a bi-wirable pair of speakers and the high-pass section has a series cap ahead of any shunt resistors or inductors, in most cases you can feed it straight from the amp's output and eliminate the main output cap from that part of the circuit.

se
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Old 14th August 2003, 05:01 PM   #8
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Hi everybody,

regarding project83, you may try to enlarge output capacitor to 10000 uF just to obtain optimal bass response and to minimalize distortion of bass frequencies (I have tried it). In every case connect the 1uF - 10uF foil cap in parallel with the electrolyte.

Cheers, Pavel Macura
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Old 14th August 2003, 05:03 PM   #9
PMA is offline PMA  Europe
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Hi Jay,

TIP is really only a current source for the MOSFET (IRFP350) connected in common drain mode.

Pavel
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Old 16th August 2003, 02:34 PM   #10
Tomek is offline Tomek  United States
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Hello, thank you all for the response. I might be able to obtain ELNA Tonorex caps, but for time being I will be forced to use Panasonic ones. I have four of them, so I will use them in setup suggested by Mr. Macura for lower bass response.
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