Simplistic NJFET RIAA

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Salas

Salas

diyAudio Chief Moderator
Joined 2002
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ikoflexer said:


I hear you sir. Any pointers to particular makes of polyprop caps with low ESR? I have quite a bunch of them of different makes, and not one has low ESR but I do have already have some electrolytic ones with low ESR.

I forgot to mention something else different in the buffered regulator. The power mosfets are COLD. They run at much lower quiescent current. The simulation does not show especially much current going through the darlington, yet it gets warmest of them all. I am not inclined to change it again for a highest current through the mosfets, it if works already so well.
Click to expand...

Do you have a Solen 0.1-0.22uF to parallel your low ESR electrolytic, so to do even better? Canadian distributor of SCR I believe?

The current is governed by the CCS. Must be 212mA with Vbe/3R3. Can you measure it at the input?
 
iko

iko

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Joined 2008
hoktuna said:
My local supplyer do not stock 550`s nor 560`s.
I have bc549b and bc559b,will they do the job in the shunt?
I´m almost done with the wireing,just have to fix the ac inlet and switch and maybe a fuse.:)
Click to expand...

I can only speak of my experience with the BC550B instead of the BC550C. It worked for me just fine. The higher gain of the C is desirable, but I cannot say how much it affects performance. The scope trace looked very good.

The 549 seems to have a bit lower maximum allowed voltage, 30V, instead of 50V for the BC550. But in this circuit, I don't think you'll get more than 25V across the transistor anyway.
 
iko

iko

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Joined 2008
salas said:


Do you have a Solen 0.1-0.22uF to parallel your low ESR electrolytic, so to do even better? Canadian distributor of SCR I believe?

The current is governed by the CCS. Must be 212mA with Vbe/3R3. Can you measure it at the input?
Click to expand...

Don't have a solen, but I'll see what I can get. I'll measure the current probably tomorrow, as I have to get ready for some guests.

Later.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
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hoktuna said:
My local supplyer do not stock 550`s nor 560`s.
I have bc549b and bc559b,will they do the job in the shunt?
I´m almost done with the wireing,just have to fix the ac inlet and switch and maybe a fuse.:)
Click to expand...

No, if you do the 36V version as I think you do. In that, the driver npn is going to see 33.5V across. Don't you have access to some 45 or 60V npn low noise high hfe part?
 
RCruz

RCruz

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Joined 2006
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Hi Salas

Yesterday I noticed the 560r (554r real) resistor I was using to load the shunt during testing, was really hot so I decided to measure the current flowing.

By my calculations: (I=V/R) ;R load = 554 ohms; Vout = 28.2 Volts, the current should be 50.9 mA.

In reality I am reading 78.2mA

I decided to change the loading resistor to a 1kr (988r real) and now the current reading is 43.3 mA

Am I missing something ?

Is there a problem with my DMM ?

Regards

Ricardo
 
Salas

Salas

diyAudio Chief Moderator
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Did you measure with your DMM set for current in series with the dummy load? There it is just I=V/R. We use 500R so to have about 50mA, which is comparable with 2 phono channels of your version, so to judge the reliability with given sink on the shunt Mosfet, stability over time, and correct voltage output. Maybe the dummy resistor isn't so big for the heat it develops so its resistance plays way off?. Or the DMM does tricks?. I usually use 3 times the Wattage of actual dissipation on resistors. So I would use a 5W dummy in your case. If it has 28.2V across, and it is 500R and holding, there is no way than running anything different than 56.4mA through it. But being able to measure correctly as expected or not what the dummy consumes, is irrelevant to the PSU. As long as the dummy sinks some current and nothing oscillates, when the voltage is stable at nominal, all is working well.
 
A

AndrewT

R.I.P.
Joined 2004
RCruz said:
I measured with the DMM set for mA,
Click to expand...
that's your mistake.

add a 1r0 or 10r 1% resistor in series with your load. Now measure the voltage drop across the test resistor.
What current is flowing?

Measure the voltage across your hot load resistors.
What resistance are they when hot? Store that change in resistance knowledge for next time it's needed.
 
RCruz

RCruz

Member
Joined 2006
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Thank you for your comments Gentlemen !

Ok.. I know resistance is variable with temp rise but the differences I read are too uge. With a 560r and 28v I read 78mA... that should mean the resistor droped to 360r...:hot:

So I decided to make the same setup with my old analog MM and.... bingo... I get 50mA.

The issue is in the DMM (I bought it for 9€ in a supermarket that sells china stuff :cannotbe: )

I am glad this happened before I started using the DMM for more serious matters.

Now back to business:
About the resistors in the Riaa... can i use 1/2w for R1 and R3 ?

Ricardo
 
Salas

Salas

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Joined 2002
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Off course you can use 1/2W. Those cheap DMMs are normally OK for Voltage measurements and Ohmic measurements. In series I have heard they are not that reliable, but I think that the situation has gone way across the acceptability line with the particular one you mention.
 
RCruz

RCruz

Member
Joined 2006
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Yes it is really bad... I need a new reliable one... Already spoke with my Wife about it ;)

I just bought all the resistors and the zener so I can start building.
I must put some resistors upright because they are so big 1w and 2w carbons.
Would you point me the resistors that need to be high quality (those that might affect sound quality the most) ?

Ricardo
 
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