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Old 5th May 2013, 10:07 PM   #5911
pchw is offline pchw  United States
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Thanks, Salas, off to heating up the soldering iron now :-)
It is going to be fun to explore !!
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Old 6th May 2013, 02:06 PM   #5912
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Default Reflektor Advanced

Hi, Reflektor lovers.

The output voltage of Reflektor is set by LED, diode and/or resistor. However, for these parts raise impedance of circuit, C2 is required. If you choose an appropriate capacitor, you will get excellent performance.

On the other hand, it is the fact that C2 limits the performance.
To solve these problems I experimented on a method with Vgs (th) of the MOSFET.

The result is big improvement. Hearing this sound, I am noticed that the sound of previous Reflektor is colored and modulated.

But this method includes some problems.
1) MOSFETs that has low impedance are not many.
Luckily STP55NF06L that I have in hand shows good performance.

2) Fine voltage adjustment is not possible.
I know that many people need +3.3V but I can't find appropriate MOSEFT yet.

Some tweak.
J2 and J3 are effective to decrease impedance of the M3. Without these JFETs it runs well.
R7 and R9 must be needed. Without these resistors parasitic oscillation is caused.

I hope that somebody will try and improve this idea.
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Old 6th May 2013, 02:27 PM   #5913
Salas is offline Salas  Greece
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Using a biased Mosfet as Vref is one thing, but if you find a dedicated low noise/impedance-low voltage Vref (3 legged chip) maybe you can go active ref simpler and more effectively?
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Old 6th May 2013, 02:59 PM   #5914
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Hello Kazuo Ozawa san
Congratulations for you persistent work.I too would like to build few reflektors with voltage output of 3.3V(digital) and 5V(analog) to power on my dual mono pcm1794 dac but it seems that I have to be more patient
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Old 6th May 2013, 05:23 PM   #5915
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I did a research and found 2.048V and 4V shunt voltage references on my supplyer`s site
this could be one of them Voltage Reference - Shunt Voltage Reference - LM4040A20 - TI.com
pro/cons with passive stuff?
my dac 3.3V supports max 4V and the 5V does 6.5V , don`t know the maximum for the amanero without the 5v reg.
are there any chances for the dacs to damage at 3.4-3.5V and 5.4-5.5V?

Last edited by schultzsch; 6th May 2013 at 05:26 PM.
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Old 7th May 2013, 01:08 PM   #5916
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Quote:
Originally Posted by Salas View Post
Using a biased Mosfet as Vref is one thing, but if you find a dedicated low noise/impedance-low voltage Vref (3 legged chip) maybe you can go active ref simpler and more effectively?
Mr. Salas always points out good point.

I guess it is ideal that impedance of collector of Q4 is sufficiently low and phase shift changes slowly within AF area.
For this reason, the large electrolytic capacitor may be not good.

I intended to try the same idea that you mentioned.
However the behavior of Vref chip is not ideal in many case because the internal amp is relatively comprexe. It is the reason why I did not adopt Vref chip.

In that respect, the MOSFET is very simple and near to ideal IMO.
However, I have not really evaluated Vref chip. I do not deny that it may be good enough.

Thanx
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Old 7th May 2013, 01:22 PM   #5917
Salas is offline Salas  Greece
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Basic concept adopted passive Vref and AC filtering (capacitor) for simplicity reasons, still exploring active reference options can bring benefits and optimization headaches but its worthy in many cases. If your voltage setting was higher some LM329 single or string with 0.8 Ohm dynamic impedance and 7uV noise would be interesting as I had mentioned in the past. Maybe just good info for other users. Is there no need for basic noise filtering with a film cap in the Mosfet ref doing some good? Because Mosfet is not considered low noise in general, but then again maybe impedance VS freq is main matter in your application. Anyway, good mod work as always, congratulations.
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Old 7th May 2013, 01:29 PM   #5918
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Quote:
Originally Posted by schultzsch View Post
I did a research and found 2.048V and 4V shunt voltage references on my supplyer`s site
this could be one of them Voltage Reference - Shunt Voltage Reference - LM4040A20 - TI.com
pro/cons with passive stuff?
my dac 3.3V supports max 4V and the 5V does 6.5V , don`t know the maximum for the amanero without the 5v reg.
are there any chances for the dacs to damage at 3.4-3.5V and 5.4-5.5V?
Hello, schultzsch
Oh you have already searched!
However, as I mentioned above, I think that vref chip is inappropriate for this purpose.
Thanks a lot for your contribution.
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Old 7th May 2013, 01:45 PM   #5919
Salas is offline Salas  Greece
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P.S. STP55 non L version may give you bit more Vref if needed.
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Old 7th May 2013, 01:51 PM   #5920
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Quote:
Originally Posted by Salas View Post
Basic concept adopted passive Vref and AC filtering (capacitor) for simplicity reasons, still exploring active reference options can bring benefits and optimization headaches but its worthy in many cases. If your voltage setting was higher some LM329 single or string with 0.8 Ohm dynamic impedance and 7uV noise would be interesting as I had mentioned in the past. Maybe just good info for other users. Is there no need for basic noise filtering with a film cap in the Mosfet ref doing some good? Because Mosfet is not considered low noise in general, but then again maybe impedance VS freq is main matter in your application. Anyway, good mod work as always, congratulations.
Interesting ! I am attracted and will study further.
Mr. Salas, thanks for useful information.
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