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Old 16th April 2012, 11:51 AM   #7521
AndrewT is offline AndrewT  Scotland
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if you require 28Vdc from the Salas Style Regulator, you may find that 25Vac is too low. 30Vac is certainly enough for worst case conditions.
But that CCS mosFET may require an enormous heatsink to survive worst case conditions with 30Vac fed from highest mains voltage. Notice I said "survive". That is not the same as work and regulate properly.

I describe "survive" as: the circuit returns to normal operation and works to full undamaged specification after the worst case event is completed.
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Old 18th April 2012, 07:21 AM   #7522
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Hi
would 50V parts for C4(100u/63V) and C2(100u/63V) do the job? I'm going to power shunt regulator 1.0.5 with 28VDC.
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Old 18th April 2012, 08:42 AM   #7523
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That was 38VDC not 28VDC. Sorry for the typo.
Attached Files
File Type: pdf Salas-RIAA-V1102F0.pdf (191.1 KB, 108 views)

Last edited by Milos P.; 18th April 2012 at 09:07 AM. Reason: pdf
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Old 18th April 2012, 11:36 AM   #7524
Salas is offline Salas  Greece
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Yes, no problem.
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Old 18th April 2012, 01:35 PM   #7525
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Thanks.
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Old 19th April 2012, 11:26 PM   #7526
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Hi,
All options for the preamp seem to be designed for some 300-500 mV of output.
Is it possible to design the basic circuit for 5mV input sensitivity (MM) with 50 dB gain, so output will be some 1,5 V to match my digital sources??
I realize that overload issues might be of importance.
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Old 20th April 2012, 01:44 AM   #7527
Salas is offline Salas  Greece
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If you will play an LP record you will realize that with the recommended Simplistic NJFET Riaa gains the sound levels of a an average CD recording are near if just a bit louder for the same volume pot position due to the way the dynamics on a record are cut. Hitting over 0dB often. I did those tests early in the design stage. High output levels if needed for other reason, like a low overall gain system, would need to resort to a loop feedback design with opamp second stage to keep THD low, or to add a X3 stage to this one's output.
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Old 20th April 2012, 08:17 AM   #7528
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What Pieter means is that he will use a passive Line - here a TVC or autoformer and dealing with the same signal voltages like a CDP delivers. So we need a 20dB more gain.

@Salas
If I understand you correct you mean when designing the phono stage with that +20dB, allover 66 ~ 72dB, you shozld do this like you described?
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Old 20th April 2012, 08:31 AM   #7529
Salas is offline Salas  Greece
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He should add a basic (OpAmp?) line gain stage after the Riaa to pot passively drive a 0dbV+ amp then. If he will drive with 5mV 50dB using this phono circuit only, it will overload with THD noticeably.

But he makes transformers, why not wind +6dB & +12dB taps? Sowter has autoformer pots with +6dB extra taps for instance. That way he can avoid an active line boost. 5mV on the 37dB MM circuit + 12dB =1415mV. Although he may end up using up to the +6dB. Records are louder many times.

*No, that thing does not have to do with overall design of this one, was talking of other possible circuits.
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Old 20th April 2012, 10:01 AM   #7530
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Quote:
Originally Posted by Salas View Post
He should add a basic (OpAmp?) line gain stage after the Riaa to pot passively drive a 0dbV+ amp then. If he will drive with 5mV 50dB using this phono circuit only, it will overload with THD noticeably.

But he makes transformers, why not wind +6dB & +12dB taps? Sowter has autoformer pots with +6dB extra taps for instance. That way he can avoid an active line boost. 5mV on the 37dB MM circuit + 12dB =1415mV. Although he may end up using up to the +6dB. Records are louder many times.

*No, that thing does not have to do with overall design of this one, was talking of other possible circuits.
Salas,
Thanks for your input.
I understand that the 5mV / 50dB will, as I already expected, lead to maybe intolerable THD.
Yes I could make +6dB or even +12dB taps (realize however that this requires double or four times the number of windings, requiring a totally different design for my autoformer, compromising other important parameters at the same time!) but these things do not come for free. Step up ratios alter impedance relationships between source and load squared in a negative way, that's why I don't like that in inductive volume controls where a main advantage is that load impedances are transformed "down" at attenuated volume settings in order to get better driving ability for the next stage - very good "passive" preamps in other words; a 12dB step up would make the source impedance close to 1k (I don't believe the specified output impedance of the source follower output - it will be closer to 60 ohms instead of 30 ohms as the transconductance of that stage will not reach the max 22 mS of a 2SK170).
There should be more elegant ways to squeeze up the gain and preserve low output impedance, but preferably not with an op amp ; a discrete op amp topology like the output of the Pearl Two is a better option maybe, but that one runs on bipolar power supplies
Or maybe an additional 2SK170 stage cascaded to the first output stage, before the output follower; could something like this being designed direct coupled with the available power supply? With reference to the circuit of post 417, could the output stage (2SK170 with 6k8 drain resistor - source follower) be replaced by two cascaded 2SK170 stages - source follower to reach the overall 50 dB gain? Higher power supply voltage required to do this?

Last edited by pieter t; 20th April 2012 at 10:29 AM.
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