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Old 11th March 2007, 05:27 PM   #1
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Default Help on improved analogue stage

Hello,

as mentioned in a previous post I am looking to upgrade my CD Player.

One of the areas of intervention is the I/V and buffer / filter stage depicted in the schematics attached.

What is sure so far is that R4-R6 and R9 will be upgraded with Riken resistors, C6 subsituted by a Black Gate N type, IC1 will be substituted by 2 OPA627BP on a Browndog adaptor, IC2 the same or OPA2134 (need to check both).

The follwong components being left and:
1) I have problem sourcing capacitors in so small values
2) I am not sure on the type of resistor I should use in the feedback networks of the ICs.

1) I wanted to source som RelCap TEs but I have problems getting those, so I am think about alternatives. The only ones I found so far are
- 4,7nF Wima FKP2
- All other values and 4,7nF I can only find Silver-Micas or Styroflex.
- Currently some non defined yellow caps are in, look like small MKTs
Which ones can be recommended in which position?

2) I have some spare Rikens left but I am not sure whether they would suit the application.
I have a hard time finding Caddock MK132 or Vishay Dale CMF55 in 620Ohms.
Can I leave the original metallic ones in place or do you recommend the Rikens or or or...

Your help is very much appreciated.


Patrick
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File Type: jpg xrayv8_analogue_schem.jpg (25.6 KB, 163 views)
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Old 17th March 2007, 09:16 AM   #2
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Location: Westland
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Patrick,
in my Bitstreamed player from Meridian I have the same output concept. The same topology is used for very high grade (digital) meters, the aim being the offer of a completely symetric & balanced load to both outputs, with an extreme PSRR. However, the setting is very prone to 3rd harmonics and needs carefull adjustment!
But, do we need this complexity in audio?

A schema has been placed on the DIYaudio that uses a Nelson Pass balanced concept that only at the output links the two outputs (C43) for some filtering. The advantage: no feedback, no complex phase shifts. No slew rate limitations as the current pump does it's work...
This looks a good alternative to your setting, is simpler too to build.

Comment on the value of the summing resistor: Given the fact that it is running into 1.500 ohms it has been designed for a +/- 2 mA current source. I am not sure if this is the same as you have (because you have a 620 feedback resistor).
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File Type: jpg nelson pass voor i-v.jpg (42.5 KB, 100 views)
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