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Old 22nd March 2011, 11:43 AM   #911
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Yes, the verbal description of the circuit does not help that much, since it is kinda complex too....
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Old 22nd March 2011, 01:27 PM   #912
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Here's the preamp chassis. Schematic to come

Andy
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Old 22nd March 2011, 02:01 PM   #913
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Here's the schematic. Still grappling with scanner software so may not be optimum - we'll see. Please point out any errors

Andy
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Old 22nd March 2011, 02:14 PM   #914
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Andy, it looks splendid.

I particularly like the stacked array of Vitreous enamel resistors.

Is that the LCR motor cap in the blue plastic enclosure? If so, may I humbly recommend a go on their newly-acquired AMPOHM audio MKPs? These are HUGELY better than the motor-type, in my trials.

The motor series pay no heed to mechanical resonances, and the sound really varies according to whether they were wound tightly (e.g.: before important football match) or slack (Friday afternoon).

AMPOHM WOUND PRODUCTS|FP-CA-30-AU|AUDIO CAPACITOR, 30UF, 630V | Farnell United Kingdom
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Old 22nd March 2011, 02:24 PM   #915
massimo is offline massimo  Italy
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Nice preamp Andy, but isn't the o/p cap value (0.1u) a bit too low?
Those Russian teflons are available up to 0.47uF/200 V, a couple of those are on my desk right now
Huge and heavy, 180 grs each.
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Old 22nd March 2011, 02:39 PM   #916
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Quote:
Originally Posted by massimo View Post
Nice preamp Andy, but isn't the o/p cap value (0.1u) a bit too low?
With the 1 Meg resistor corner frequency is 1,6 Hz; is that low enough?
Maybe with an input resistance of the power amp paralleled it will go up a bit.
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Old 22nd March 2011, 03:20 PM   #917
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Quote:
Originally Posted by Rod Coleman View Post
Andy, it looks splendid.

I particularly like the stacked array of Vitreous enamel resistors.

Is that the LCR motor cap in the blue plastic enclosure? If so, may I humbly recommend a go on their newly-acquired AMPOHM audio MKPs? These are HUGELY better than the motor-type, in my trials.

The motor series pay no heed to mechanical resonances, and the sound really varies according to whether they were wound tightly (e.g.: before important football match) or slack (Friday afternoon).

AMPOHM WOUND PRODUCTS|FP-CA-30-AU|AUDIO CAPACITOR, 30UF, 630V | Farnell United Kingdom

X2, or the Mundorf Tube-Caps.
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Old 22nd March 2011, 03:32 PM   #918
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Quote:
Originally Posted by andyjevans View Post
Here's the schematic. Still grappling with scanner software so may not be optimum - we'll see. Please point out any errors

Andy
About PSU: under AZ1 are two diodes? values & type?

For 10uF MKP I prefer Auricap.
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Old 22nd March 2011, 04:33 PM   #919
massimo is offline massimo  Italy
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Quote:
Originally Posted by pieter t View Post
With the 1 Meg resistor corner frequency is 1,6 Hz; is that low enough?
Maybe with an input resistance of the power amp paralleled it will go up a bit.
When your 1M R is in parallel to a 100K load its value becomes 90.91K and when in parallel with 50K equals to 47.62K
I would consider those values only when you calculate the corner freq. (17.5 and 35.5 Hz)
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Old 22nd March 2011, 04:54 PM   #920
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Quote:
Originally Posted by massimo View Post
When your 1M R is in parallel to a 100K load its value becomes 90.91K and when in parallel with 50K equals to 47.62K
I would consider those values only when you calculate the corner freq. (17.5 and 35.5 Hz)
Of course you are right.
I guess Andy is aware of this.
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