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tiefbassuebertr
diyAudio Member

Join Date: Jul 2005
Location: D-55629 Schwarzerden
Quote:
 Originally Posted by tiefbassuebertr german version from Elektor is read about http://www.magnetofon.de/supra/Supra_Elektor.pdf basic description of the topology you will find there: The most linear stage for large voltage swings - Lender's Circuit - diyAudio main disadvantage I mentioned in my last post. I want to modify the circuit in such way, that each input transistor runs with 3mA instead only 0,22 mA idle current. Secondly I want to use for the outputs power darlingtons (like BD675/BD676) an idle current between 50-100 mA. How I calculate the new values of the resistors R11/13/14 (pos. half) so as R10/18/19 (neg. half) from the first pdf link here ? Thank you very much for advices. Best thanks in advance.
the reason why still no response was posted in this matter is, that the thread is in the wrong folder.
Thank you for moving to the right folder.
I'm still interested in a solution.

Last edited by tiefbassuebertr; 21st December 2018 at 12:29 PM.

 21st December 2018, 02:27 PM #32 mkuehne diyAudio Member   Join Date: Mar 2010 Dear tiefbassuebertr, ...I don't see the point...? You believe, the higher current makes less noise or warmer sound? In principle then you'd have to lower the 68k resistors value first, they are the current source of the input pairs. In the same moment you make this about 15 times smaller, you also have a far lower impedance for the signal at this position, it would make sense to use a active current sources then, that feed more input stage current at a higher impedance. But this will add also its own noise. I think in the end you probably will gain absolute nothing, but you will have tested all the developers layouts, that were already sorted out before the circuit was published... By the way: if you increase the input current by this amount, it will be a simple chain calculation for the coupling/local feedback resistors. The output stage will increase current partly automatically, but you have to lower resistors not to get wrong voltage values... Yours Martin
tiefbassuebertr
diyAudio Member

Join Date: Jul 2005
Location: D-55629 Schwarzerden
Quote:
 Originally Posted by mkuehne Dear tiefbassuebertr, ...I don't see the point...? You believe, the higher current makes less noise or warmer sound? In principle then you'd have to lower the 68k resistors value first, they are the current source of the input pairs. In the same moment you make this about 15 times smaller, you also have a far lower impedance for the signal at this position, it would make sense to use a active current sources then, that feed more input stage current at a higher impedance. But this will add also its own noise. I think in the end you probably will gain absolute nothing, but you will have tested all the developers layouts, that were already sorted out before the circuit was published... By the way: if you increase the input current by this amount, it will be a simple chain calculation for the coupling/local feedback resistors. The output stage will increase current partly automatically, but you have to lower resistors not to get wrong voltage values... Yours Martin
Higher current makes better sound in all respects.
Typically available small signal transistors work at best with 10-12mA. I don't know why, but maybe cause ft is max - go to
https://www.infineon.com/dgdl/Infine...1541da0e3a1661
page 6 first diagram.
I don't know if this is to realize with this circuit.
If so, the SNR values get worse. But this in general doesn't matter, on phono preamp stages, because the record surface noise limits the value for signal to noise ratio anyway.

P.S.: this thread is wrong filed.
Where is actually the folder "RIAA Phono Stages" ?
Most threads to this topic are filed in the folders "Solid State", "Chip Amps" (RIAA with OP-AMPs), Tubes/Valves, "Analog Sources" and "Analog line level"

Last edited by tiefbassuebertr; 31st December 2018 at 03:25 PM.

 1st January 2019, 09:01 AM #34 mkuehne diyAudio Member   Join Date: Mar 2010 Hello tiefbassuebertr. I'd say ...what you I intend makes no sense as modification. That's a complete new development. Maybe heating up things has audible advantages, but the conception is that totally different then, many parameters will also worsen. You never get free gifts in physics. E.g. the supply will also heat up and need a change, better cooling and maybe lower voltages in general, the 68k replaced by current sources possibly works with just a JFET per branch, properly done I assume you'd use at least one transistor and a resistor each, would look awful in the old board layout. By the way the design has a well knowns problem with the highest frequencies, the response shows a gain decrease to factor 1 instead of minus infinite. Thus the square response shows a high overshoot in the slope. That would be the first thing I'd change, a 6dB post filter, decoupling buffer followed. The result is a different preamp...
scafas
diyAudio Member

Join Date: Dec 2007
Location: italia
pcb of sln elektor

i've some pcb for sale of thi project on my Eba..
diy pcb circuito stampato preamplificatore phono MM ELEKTOR SLN | eBay
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