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Old 5th December 2012, 02:39 PM   #7761
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I like the way you stretched the capacitor wires Mr PP . Been there , done that . Polystyrene caps , that's dedication . When I repaired amplifiers I liked to put all the components neat . I would always use a scope to be sure it wasn't a choice . I note how carefully the diodes are joined . I remember a time when I did that .

For DVV and other would be sea dogs .

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Old 5th December 2012, 02:51 PM   #7762
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You know Mr PP . Change the op amp ( 5534, OPA 604 ) and some Motorola's , slight bias tweak . Compensation tweak . Who knows ?
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Old 5th December 2012, 03:11 PM   #7763
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Quote:
Originally Posted by nigel pearson View Post
I like the way you stretched the capacitor wires Mr PP . Been there , done that .
I followed the original PCB, that's all.
this "I just follow" thing reminded me of the time (circa '90 something again) when I was building this modulator for my ZX-Spectrum clone, only to be puzzled by the two paralleled output caps, one 1uF ad one 10nF or something. I went asking my "guru" how come I need to parallel 1/100 cap to a large tolerance electrolytic and he replied, much to my frustration "just follow the schematic, damn it".

Quote:
Originally Posted by nigel pearson View Post
Polystyrene caps , that's dedication . When I repaired amplifiers I liked to put all the components neat . I would always use a scope to be sure it wasn't a choice . I note how carefully the diodes are joined . I remember a time when I did that .
I clearly remember one old book mentioning styrene caps for the high-pass portion of the Baxendall tone control, I've known that since I was a kid. and all implementations I've seen (although based on mediocre active devices) obeyed that so I said to myself who am I to disagree. fast forward to cap listening LOL

anyway, just nostalgia, sorry for thread hijacking.
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Old 5th December 2012, 03:34 PM   #7764
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Not at all and I am sure others would agree Mr PP . I built my Sinclair calculator and would love to still have it , LED's you see . Sinclair should be respected for two things . His designs although a bit optimistic were often genuinely ahead of the typical shop bought designs . Number two if I get this right he had a company worth 150 000 000 back then . OK he got unlucky . It is unbelievable that he got so far on what were mostly kits . I seem to remember he was a writer in the early 1960's electronics magazines . Like myself making a living out of thin air then . I bet like me he enjoyed it . To market a class D amp in 1969 much as I distrust class D I still have to respect that . I am told they were better than they should have been . On paper they couldn't work all .
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Old 5th December 2012, 06:18 PM   #7765
dvv is offline dvv  Serbia
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Actually, in audio and appearently not only in audio, it makes good sense to parallel say a 220 uF electrolytic in the feedback loop with a metallized foil capacitor of say 470 up to 2.2 uF.

Preferably (but difficult to find) polycarbonate - if there is a faster capacitor on this Earth and on the free market, I don't know of it. Those boys do like 3,000+ V/uS, DAMN fast.

If making an AC coupled amp, I also bypass the input metallized foil Wima 10 uF cap with the same but 100 nF.
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Old 5th December 2012, 06:20 PM   #7766
dvv is offline dvv  Serbia
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Originally Posted by a.wayne View Post
DVV is salty .......
Whazzat supposed to mean, hombre?

And SMILE when you say that, stranger!
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Old 6th December 2012, 04:52 AM   #7767
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Quote:
Originally Posted by dvv View Post
Actually, in audio and appearently not only in audio, it makes good sense to parallel say a 220 uF electrolytic in the feedback loop with a metallized foil capacitor of say 470 up to 2.2 uF.

Preferably (but difficult to find) polycarbonate - if there is a faster capacitor on this Earth and on the free market, I don't know of it. Those boys do like 3,000+ V/uS, DAMN fast.

If making an AC coupled amp, I also bypass the input metallized foil Wima 10 uF cap with the same but 100 nF.
Is'nt there a ratio to be used when bypassing .. ?
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Old 6th December 2012, 06:46 AM   #7768
dvv is offline dvv  Serbia
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Originally Posted by a.wayne View Post
Is'nt there a ratio to be used when bypassing .. ?
If there is, I am not aware of it.

I do mine by ear, but then, I can afford to do so because I usually build mine for a friend, and only now for myself.

But if there is, I'd love to hear more about it. I love leraning new stuff.
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Old 6th December 2012, 09:57 AM   #7769
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An extract of the PDF below
[ One commonly used improvement is to load the input differential stage with a current mirror. This doubles the available drive current and therefore appears to double the slew rate. There are however other effects, it also doubles the gain, and to maintain the original stability margin we need to either double the compensation capacitor, which returns us to the original slew rate and so has no apparent benefit, or we could double the 100R degeneration resistors, then the gain is unchanged, the slew rate limit is doubled, and input stage distortion at lower levels is reduced. The impressive slew rate specification however is in practice unatainable in the example above, it could only be achieved with Vdiff = 2V, so with a 1V peak input signal that could never happen with any signal whether sine, square or whatever. ]

Slew Rate

I would love to see a very simple high slew rate amplifier ( 1000W would be OK ) . My mind says it needs nothing complicated . DC offset adjustment perhaps if running plenty of input stage current ?

The only thing I will say against bypassing is sometimes a high grade capacitor will be even better . People liked to go down in 10's . One friend does it is 1.618 ratio as best he can ( Phi ) .

I hope Andrew T is reading this . I said how curious Pi cubed is ( circa 31 ) . If needing a quick and fairly accurate value for Phi . 6/5 ( Phi . Phi ) = Pi . To be certain 1/Phi = ( Phi - 1 ) . Phi . Phi = 1+ Phi . Thus to a very good approximation 1.2 ( 1+ Phi ) = Pi .To the Egyptians I suspect it looked exact . I would also suggest no engineering problem on this planet would need it to be better ?
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Old 6th December 2012, 10:01 AM   #7770
AndrewT is offline AndrewT  Scotland
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Quote:
in audio and appearently not only in audio, it makes good sense to parallel say a 220 uF electrolytic in the feedback loop with a metallized foil capacitor of say 470 up to 2.2 uF.
Quote:
only to be puzzled by the two paralleled output caps, one 1uF ad one 10nF or something. I went asking my "guru" how come I need to parallel 1/100 cap to a large tolerance electrolytic and he replied, much to my frustration "just follow the schematic, damn it".
Quote:
bypass the input metallized foil Wima 10 uF cap with the same but 100 nF.
I read a paper that concluded that the minimum capacitance RATIO when paralleling an electrolytic with a film capacitor was 16:1
I did not understand all the maths but it did seem to make sense.
That was in the days before I saw what others are finding with ringing when doing such with low ESR capacitors.

If there is some truth in that conclusion, then 100:1 may well be a good ratio to use that gets one well away from the "ringing" condition
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