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Old 7th June 2012, 07:13 PM   #31
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Based on the circuit in post 15 and a rough sim, I get R17=86k, R23=14.4k (12k+2.4k).

C1 is too small to feed an EQ so that should be 0.47u otherwise it may sound a bit bass shy; 1.5dB down @ 20Hz.

I like the coupling cap in the grid of the 2nd stage, then it can be 0.1u or smaller if the grid resistor is bigger than 470k. However that can make getting the EQ caps hard in 1% values. I like silver mica so not too hard to get 1% or better in high voltage types.

Also not sure if a 0.22u on the output is big enough. I'd use 0.47u to 1u. Depends what it's driving of course.

cheers,

Stephen
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Old 8th June 2012, 01:49 AM   #32
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Based on the circuit on post #15, Zout of 6922 cascode = Ra // (mu+2)xRp = 22K // (33+2)x3K = 18,189 ~ 18K. As C7, C9 and R23 were calculated based on R1 at 100K, R17=100K - 18K = 82K.
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Old 8th June 2012, 04:34 PM   #33
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The calcs most people make a simplistic at best as they very rarely cover most of the variables even the most obvious ones.

Part of the calcs most people miss is the varying load of the EQ esp at low frequencies that will affect the low end and most people forget about the coupling cap effects esp at low frequencies plus the grid load effects of the 2nd stage.

Lipshitz while a great starting point misses out all these real world variables. Also look at the assumptions Lipshitz makes for the output Z of the driver and the load ratio of the load. Valve circuits almost never meet these assumptions.

Hence the reason I use a sim. Sim the cct, buy the 1% parts, stick them in and presto, done. Unless some gross errors have been made, that should be the end of it.

cheers,

Stephen
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Old 20th June 2012, 08:13 AM   #34
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Default Cathode Follower

Hello again

I intend to add a cathode follower stage at output as shown in the attached schematic. Can you please kindly advise me if it's ok and if C14 can be removed and what the value of R should be?

Many thanks and regards
Andersen
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File Type: jpg 6922 phono stage pre-amp CF1.jpg (84.6 KB, 135 views)
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Old 7th September 2012, 05:27 AM   #35
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Default Final Result

Finally, I completed my phono pre-amp with the attached schematics and the actual RIAA curve. Great result, right?

Thanks, all for your help.
Attached Images
File Type: jpg 6922 phono stage CF pre-amp.jpg (73.3 KB, 93 views)
File Type: jpg RIAA Curve.jpg (146.9 KB, 85 views)

Last edited by Andersen; 7th September 2012 at 05:30 AM.
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Old 28th April 2013, 05:25 PM   #36
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Hello

Great RIAA curve but the attached schematic looks a little bit strange. C9 has a lager value than C7; I have never seen that before. Typing error ???
/GoranSk
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