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Old 1st September 2005, 04:27 AM   #11
CBS240 is offline CBS240  United States
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Ah yes, I guess because the signal is going through the electrolitic and electrolitics are noisy. Since were talking about Hf noise the film cap is very small in value relative to the electrolitic. I believe I understand. It looks like this principle applies to the PS filter caps also. Hmm, I guess this is related to wires generateng Rf noise acting as antaneas without any shielding. Since the capacitor is in series with a resistor(feedback resistor), it obviously makes a LP filter. I have a "bench amp" I am playing with using a DC blocking electrolitic like this. Since this is my circuit, the way I see it, improvement is always good even if sometimes it requires major changes. I guess this is why it has so far remained a "bench amp". It works quite well but chalk up one more improvement yet to make.....
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Old 1st September 2005, 08:41 AM   #12
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Default It is wonderfull what a single capacitor can do positive or even negative to

An amplifier, and this turns our hobbie, profession for others, so interesting.

One single wrong capacitor value, or in a wrong place, can destroy the audio quality, reading we see the enormous consequences when we forget something.

I think this is fascinating and keeping me "on" for so long time (45 years)...everyday something brand new to learn.

This forum is wonderfull, and there are people that made it better, Eva is one of those that put a lot of brigth in our forum, the know how is clear as she can see every detail alike some microscope.

Goooood!

regards,

Carlos
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Old 1st September 2005, 09:51 AM   #13
Eva is offline Eva  Spain
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Paralleling capacitors of different kind and whose values differ more than an order of magnitude is something that is seldom seen outside audio circuits. That's because a resonant system is always created by doing so, and Q may be high, but audio people just don't care about that, they don't even measure the result, they act following strange pseudo-scientific criteria.

It's said that it's good to paralell different kinds of capacitors so everybody does it without thinking. Actually, it's a good way to create high Q resonant systems. Damn, I've even created a several Mhz resonator by just paralelling two 10uF 10V ceramic capacitors (with very low impedance at HF) with some PCB leakage inductance inbetween. It was in an SMPS and I was absolutely puzzled when I saw the ringing. I had to solder them together to solve it.
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Old 1st September 2005, 10:08 AM   #14
tlf9999 is offline tlf9999  United States
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Quote:
Originally posted by Eva
audio people just don't care about that, they don't even measure the result, they act following strange pseudo-scientific criteria.

. Because in audio, science and facts don't matter. Fictions rule instead.
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Old 1st September 2005, 11:57 PM   #15
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And, if anyone's interested, here's the PSRR of the same design I exampled earlier - but with just resistive tail resistors on the input stage instead of 2BJT CC sources!

Once again adjust down by 29dB for the amplifier gain. That's 71dB total and over 30 times inferior to the CC source! Also,
102 dB < 0.001% in THD terms while 71 dB is 0.03%. How much of your THD would you like coming from the PS commutation hash?

Cheers,
Greg
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Old 2nd September 2005, 12:05 AM   #16
tlf9999 is offline tlf9999  United States
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Quote:
Originally posted by amplifierguru
Also,
102 dB < 0.001% in THD terms while 71 dB is 0.03%. How much of your THD would you like coming from the PS commutation hash?

Cheers,
Greg

How many of us can hear thd down to 0.03%?
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Old 2nd September 2005, 12:22 AM   #17
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Well, how about I couch it differently.

Consider a tune with heavy mid bass and some very delicate top detail. The mid bass is causing significant supply modulation and generating n harmonics on the supply which are injected though the PSRR to produce an elevated noise floor consisting of a haze of generated harmonics blurring the detail and depth/size of soundstage. Softens any harshness by burying it - but something's obviously missing with a 71 dB noise floor.

Your preferred sound?

Cheers,
Greg
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Old 2nd September 2005, 01:11 AM   #18
CBS240 is offline CBS240  United States
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I think this would not make a difference if you are listening to Pantera but if you like classical music it might be noticable. What do you think?
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Old 2nd September 2005, 01:13 AM   #19
tlf9999 is offline tlf9999  United States
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Quote:
Originally posted by amplifierguru
The mid bass is causing significant supply modulation and generating n harmonics on the supply which are injected though the PSRR to produce an elevated noise floor consisting of a haze of generated harmonics blurring the detail and depth/size of soundstage.

I am not sure Guru. Think about a line stage linked through the junction capacitance with the prior current mirror load factor that when under driven causes massive unsolicited inter-phase and time-dependent modulation that reverse travels up through just the minority carriers and the vertical SCR structure in a typically fused semiconductor tri-layers back into the feedback node where it finally meets with the stronger-than-necessary bass that a typical drumer will NOT produce as you and I can attest through our ears and our less-than-ideal hearing which is further impacted by a intermittent power supply that modulated the alternator through the power grid.

Do you think it will have any negative impact on how the electrons tranverse in an oxygen-free copper and aluminum oxidized wire?
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Old 2nd September 2005, 01:40 AM   #20
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Very funny.

But the problem is very real with any Class AB amplifier (see thumbnail). Is this what you want to listen to?


Hash on typical 28,000uF 70V supply when driving 8 ohms at 1KHz sine wave at 5W rms only. Not my listening preference.
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