Simplistic NJFET RIAA - Page 99

RCruz · 8th February 2009, 04:02 PM

Here you have a pdf showing how many jfets for each current.

Is 8.5 a good value or should I look for 6.5 mA ? (I still have some jfets to measure).

Ricardo

Salas · 8th February 2009, 04:42 PM

8.5mA is very good for the Rsource resistors I recommended.

Salas · 8th February 2009, 04:45 PM

Quote:

Originally posted by ikoflexer

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.

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?

hoktuna · 8th February 2009, 05:46 PM

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.

iko · 8th February 2009, 06:00 PM

Quote:

Originally posted by hoktuna
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.

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 · 8th February 2009, 06:05 PM

Quote:

Originally posted by salas

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?

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 · 8th February 2009, 07:01 PM

Quote:

Originally posted by hoktuna
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.

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 · 9th February 2009, 12:52 PM

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 · 9th February 2009, 02:41 PM

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.

RCruz · 9th February 2009, 03:17 PM

I measured with the DMM set for mA, in series with the load resistor.Maybe my DMM is not correctly set.
Tonight I will try and measure with an analog MM.

The shunt delivers 28.2v steady with any of the loads (and even without any load).

Ricardo

9th February 2009, 12:52 PM	#988
RCruz diyAudio Member Join Date: Sep 2006 Location: Saxon Blog Entries: 1	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 __________________ RC

9th February 2009, 03:17 PM	#990
RCruz diyAudio Member Join Date: Sep 2006 Location: Saxon Blog Entries: 1	I measured with the DMM set for mA, in series with the load resistor.Maybe my DMM is not correctly set. Tonight I will try and measure with an analog MM. The shunt delivers 28.2v steady with any of the loads (and even without any load). Ricardo __________________ RC

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8th February 2009, 04:42 PM	#982
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	8.5mA is very good for the Rsource resistors I recommended.

8th February 2009, 05:46 PM	#984
hoktuna diyAudio Member Join Date: Sep 2004 Location: Eskilstuna	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.

9th February 2009, 02:41 PM	#989
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	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.