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Old 1st November 2011, 09:21 PM   #3001
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Fine, i will take the time to listen to them. On the other hand, electronics can be improved too. The Buffalo Bill Linestage makes my Forsell CD player sound so good that i have a hard time to keep up with my phono rig. I really think that most CD players have problems with the analog stage.
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Old 1st November 2011, 09:36 PM   #3002
MiiB is online now MiiB  Denmark
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haha .. you have a forsell toastmaster.. I'am impressed... true the analogue section is the thing, IV conversion sen-cen could be the key.
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Old 1st November 2011, 09:42 PM   #3003
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Yes, sophisticated simplicity and a good PSU. I have the Forsell since 1993. 18 years now.
Many players have come and gone but non sounded as organic, big, transparent and dynamic. And that with an 18Bit Crytal chip set. Forsell selected that one for my private use to begin with. Communicate THAT on the Blowtorch thread, that even players made in series with the same parts sound different and you get slaughtered.
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Old 1st November 2011, 10:01 PM   #3004
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by Joachim Gerhard View Post
Here is it, Ricardo. The input can be setup in two ways. Transconductance and alternative Transimpedance. The Transconductance circuit has gain independent from the cartridge impedance, but we loose the advantage of less distortion with less gain when the cartridge impedance goes up. A good compromise can be found by juggling the RIAA components. It should not have more gain then necessary for best overload margin and least amount of distortion. Transimpedance RIAA needs different thinking then normal passive or active RIAA.
Thank you Joachim

I will start collecting parts now. Please bear in mind I am a builder (experinced one) with a good and trained ear, but lacking the ultimate knowledge to modify any schematic unless I fully understand it´s principles.

I will grow along while building this so, in order to avoid making this thread too boring to some, I will contact you by PM if I need any assistance.

IMO PSU makes a really big difference when the amplifying circuits are very simple. I believe it will be so in this case also and I have a special PSU in mind already.
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Last edited by RCruz; 1st November 2011 at 10:17 PM.
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Old 1st November 2011, 10:22 PM   #3005
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Quote:
Originally Posted by RCruz View Post

I will grow along while building this so, in order to avoid making this thread too boring to some, I will contact you by PM if I need any assistance.
how about dedicating an own thread to your build? There could never be enough phonopre-threads around!

Rüdiger
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Old 1st November 2011, 10:24 PM   #3006
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No, this circuit is not fuzzy with PSU. It has excellent PSU rejection ( double current mirror,
telescopic cascode ). Still PSU is important and yes, if the circuit has poor PSU rejection the more so. I prefer if you ask me your questions here on the thread. For the profit of others.
I appreciate that you trust me and build my circuit. It is not that hard. When you use the Transimpedance input, make sure that the Fets are well matched to avoid DC into the cart.
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Old 1st November 2011, 10:25 PM   #3007
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Rüdiger, i thought about that. I separated my Nobrainer with little success though.
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Old 1st November 2011, 10:43 PM   #3008
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by Joachim Gerhard View Post
No, this circuit is not fuzzy with PSU. It has excellent PSU rejection ( double current mirror,
telescopic cascode ). Still PSU is important and yes, if the circuit has poor PSU rejection the more so. I prefer if you ask me your questions here on the thread. For the profit of others.
I appreciate that you trust me and build my circuit. It is not that hard. When you use the Transimpedance input, make sure that the Fets are well matched to avoid DC into the cart.
Ok... I will post here all my findings. I see this one does not use an output opamp (I like opamps but IMO discrete designs without global NFB sound much better)

First question... C7R16 should determine most important 500.5Hz (318uS) zero pole.

I get C7R16 = 0.1 x 32400 = 324uS What is the reasoning behind that ?

Second question... what is the probability of cart damage if one of the input fets fail when using a Transimpedance circuit ? (Or if one of the PSU rails stops working)
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Old 2nd November 2011, 01:06 AM   #3009
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I posted the correct formula in post 2987. The components interact somewhat. When one side fails maximum 16mA can flow when you use two 2SK170BL with Idss = 8mA. With your 20 Ohm cartridge that is U = 20 x 0.016 = 0.32 V. So we have 0.32V x 0.016A = 5.12mW.
I think that is too little to fry your cart. When you do not trust the Transimpedance input build the Transconductance input. There only the gate current flows and that is miniscule.
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Old 2nd November 2011, 09:02 AM   #3010
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Perfect

Why did you choose J310 ?

Can it be replaced by k170 ?
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