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Old 18th January 2008, 04:57 AM   #1101
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Default My mistake

Reviewing the pics again, I see your film caps are right on the pins, good job!
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Old 18th January 2008, 07:45 AM   #1102
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Quote:
I am happy to see people trying novel deas on powering these circuits. Even a small increrase in resolution would be welcome.
Thatís the fun part off DIY audio!! Push the limits.

For the plainness; the pictures were taken during the test. The circuit is like the one I posted.
In the version I built in in my pre-amp, the reference (IC2, IC4) is a LM336-2.5 with 100uF and 100nF in parallel, the transistor (T1, T2) is a BC517 darlington and R2 and R4 are 130 Ohm. I use the regulated filament supply of the tube amplifier to power the circuit.

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Old 18th January 2008, 11:41 AM   #1103
mikelm is offline mikelm  England
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I just put a 100uF cap across the two diodes use for CCS Vref and it did indeed bring another level of refinement to the sound

my experience has taught me not to put a small bypass cap across a larger one unless the small cap has a snubber resistor in series - I have seen in spice* & heard with my ears what confusion it creates so once I get a new supply of caps I will try 1uF & 0.2 ohms across all my 100uF caps.

mike

*estimated lead inductances need to be included
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Old 18th January 2008, 01:23 PM   #1104
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Mike,

Take a LM285-1.2 reference (at the cost of only 1 Euro each) to replace the two diodes and you will gain about the same amount in performance as you did with the capacitors! (And leave the capacitor in place.)

Itís funny, but more and more I become convinced that driving the LEDís is as critical as normal amplifier circuitry. So treat the LEDís with the same care as the rest of your circuitry. And itís explicable, because every little change in the amount of light the LED emits is directly translated in a change of resistance of the LDR. And thatís why we will end up with something really sophisticated.

Peter
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Old 18th January 2008, 02:06 PM   #1105
mikelm is offline mikelm  England
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Peter,

do you think that

NATIONAL SEMICONDUCTOR LM285BYZ-1.2

is better than

ON SEMICONDUCTOR TLV431ALPG ?

I have the choice
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Old 18th January 2008, 02:42 PM   #1106
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Mike,

I donít know what will give best results sonically. With a TLV431 the current source becomes a feedback design because the voltage at the ref input is held constant. I have measured the output of this CCS in 1 kOhm with a 5 Ĺ digit DVM and it is rock steady. Even the last digit. So 1mA in 1 kOhm gives a reading of 1.00000 V. When you take a LM285BYZ-1.2 the last two digits will show some fluctuations because Vbe changes are not compensated. But what is best sonically, I donít know. I am using now a LM336-2.5 and darlington and that outperforms my test setup which was based on a TL431 with a BC550C. But signal wiring is much shorter now so I am not sure where the benefit comes from.

Peter
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Old 18th January 2008, 02:47 PM   #1107
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Dear Pietjers,

If possible can you please kindly post your latest schematics? I am getting very confused as to what is being used in your latest design that gives the best results.

Yours

Arthur
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Old 18th January 2008, 05:54 PM   #1108
EUVL is offline EUVL  Europe
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Without having tested the circuits, I would personally go for TL431 rather than 336 or 285. It makes much better current control.

If you really want a open loop design for whatever reasons, then just use 2x or 3x red LED driven by a J511 as your voltage reference. Not rock stable, but then very low noise, and no global feedback (if that is the sex appeal).


Patrick
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Old 18th January 2008, 05:57 PM   #1109
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Peter, is there a error in the orientation of the LDR's used for signal out on your schematic?
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Old 18th January 2008, 08:45 PM   #1110
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Arthur,
There is no such thing as a latest design. But there are several voltage reference options to suit the attenuation range and input Ė output impedance you need. The rest of the circuit remains the same. See post #1001 (and later) for details.

Patrick,
We donít know yet what gives the best results sonically. It doesnít make sense to make extended theories because the only way to find out is to try things and let you ears judge.

Badge,
There is no error in the circuit diagram as far as I know.

Peter
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