A simple question. Why would nonpolarized caps (back to back itty bitty electrolytics in one can) be used for the feedback resistor, instead of a regular electrolytic? Is there supposed to be some "magic" in that?
What effect would I hear, (unfair, not knowing me, you can't assume I could hear at all
) if I were to use larger electrolytics, like 47uF or 100uF? I did play with one channel for awhile using no cap at all, but rather jumpered to ground. Thanks from a relative newbie.
What effect would I hear, (unfair, not knowing me, you can't assume I could hear at all
) if I were to use larger electrolytics, like 47uF or 100uF? I did play with one channel for awhile using no cap at all, but rather jumpered to ground. Thanks from a relative newbie.That cap in the feedback is part of a high pass filter. If it operates as such, filtering the signal, then D. Self alleges it increases the distortion of the amplifier.Sparky OR said:
His simple test, for minimal distortion, was to measure the AC voltage across the cap. The closer to near zero the better.
The caps' main purpose is as a DC block to reduce the amplifier gain @ DC to ~ 0dB (1times). The audio signal should be filtered before it enters the amplifier. Now we are talking about two high pass filters. If either move the filter F-3dB frequency into the audio band then they are audible. So the question becomes: how far below the audio band do these filters go and then your question on discernibility no longer applies to the filtering effect but on whether the caps affect the audio quality of the signal. There is much argument on these interlinked effects of the DC blocking abilities of the two DC blocking caps. Omitting them is not an option for an AC coupled amplifier. The designer can design a DC coupled amplifier, but that is a very different exercise from AC coupled design.
Here is the thing...
if you use commercial source - they all have capacitors at the output so you don't need capacitor at the input of the amplifier.
And what about the cap on the feedback to ground? Remove it and measure the DC offset voltage at the output of the amp. If the voltage is in the range of +- 100mV I would not worry. All Pass Labs amps have offset voltage it the same range. In reality the offset voltage of Gainclone amps (LM3875, LM1875 and TDA2050) is somewhere between 10 to 40mV without the cap in the feedback. I must say that this feedback cap has big influence to the sound (almost the same as input cap); but it's your call.
if you use commercial source - they all have capacitors at the output so you don't need capacitor at the input of the amplifier.
And what about the cap on the feedback to ground? Remove it and measure the DC offset voltage at the output of the amp. If the voltage is in the range of +- 100mV I would not worry. All Pass Labs amps have offset voltage it the same range. In reality the offset voltage of Gainclone amps (LM3875, LM1875 and TDA2050) is somewhere between 10 to 40mV without the cap in the feedback. I must say that this feedback cap has big influence to the sound (almost the same as input cap); but it's your call.
well, that's what our friends said. I will try as you've suggested, ...this time I'll be very careful. My CD player is an old Sony CDP950, bought in 1988..has 2 rca outputs, the one connected with headphone has quite DC big offset, or maybe the output caps are dried out?
thanks my friend
TPS
thanks my friend
TPS
Look into AN-1192. DC servos are shown and described in there.ide2003 said:
Igla said:
Absolutely. The biggest trouble for speakers would come from a broken IC, which could bring DC at rail level to the output. But for that we all use DC protection cicruits that cut the output off in that case, don't we?
As I said before...it's your call.
Someone like minimal schematics and minimal impact to sound, the other one goes in direction of maximum parts you can stuff in an average enclosure. It's always a compromise between a purity of the sound with a potentialy danger and maximum parts you can imagine with average weiled sound.
If someone would stuff his amp with everything you can find on the net, then DIY makes no difference and at the end it would be cheaper to go to the store and buy a nice Technics amp. It would sure look nice with all those lights and VU meters and all those knobs and buttons.
Someone like minimal schematics and minimal impact to sound, the other one goes in direction of maximum parts you can stuff in an average enclosure. It's always a compromise between a purity of the sound with a potentialy danger and maximum parts you can imagine with average weiled sound.
If someone would stuff his amp with everything you can find on the net, then DIY makes no difference and at the end it would be cheaper to go to the store and buy a nice Technics amp. It would sure look nice with all those lights and VU meters and all those knobs and buttons.
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