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SLN Pre-Amp - Elektor Aug 1982

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#22
sound of this card

I built this preamp according to the letter to the wiring diagram, it works perfectly but the sound 'pissed brilliant high frequencies and poor at low frequencies.
how can I tweak the circuit to obtain a balanced sound?

pre-supa-001.jpg
 
#23
GlidingDutchman said:
I want to attempt building this phono pre-amp (see attached schem).

Any tips and ideas on how to possibly improve the circuit?

I am going to configue it for MC cartridges.
Click to expand...
Yes. I would say, the choice of input transistors in parallel mode isn't the best, because only 0,22mA/each transistor is adjust (15V/68K).
Unfortunately I am not able, to call you the ideal choice. Maybe jFETs are a better choice.
 
#27
tiefbassuebertr said:
Yes. I would say, the choice of input transistors in parallel mode isn't the best, because only 0,22mA/each transistor is adjust (15V/68K).
Unfortunately I am not able, to call you the ideal choice. Maybe jFETs are a better choice.
Click to expand...
german version from Elektor is read about
http://www.magnetofon.de/supra/Supra_Elektor.pdf
basic description of the topology you will find there:
http://www.diyaudio.com/forums/soli...age-large-voltage-swings-lenders-circuit.html
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.
 
#30
Gain?

AndrewT said:
+55db of gain from an LTP+VAS single stage amp sounds quite ambitious.
Click to expand...
Where is that value from? The relation of R15/R14 makes 55dB, but no sense. Usually I'd take the feedback-filter 1kHz impedance in relation to R14 - if I made no mistake, that's about 35dB@1kHz. Only the lowest bass gain is about 20dB higher...
And what is ambitious about 55dB sub-bass gain? There are BC550C/560C used, each with at HFE at least about 400 (a combined current gain of more than 90dB), both stages with voltage gain. Enough for low distortion by a certain amount of feedback even in the bass - but also low enough for absolute stability and slope fidelity... 🙂
 
#31
tiefbassuebertr said:
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.
Click to expand...
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.
 
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#32
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
 
#33
mkuehne said:
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
Click to expand...
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/Infin...n.pdf?fileId=db3a304314dca389011541da0e3a1661
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"
 
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#34
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...
 
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