Simplistic NJFET RIAA - Page 215

RCruz · 9th August 2009, 07:56 PM

I am strugling with heatsinks....

Would this one be suitable for the shunt ? H S MARSTON - 05DN-00500-A-200 - HEAT SINK, 4.5°C/W http://pt.farnell.com/jsp/search/pro...jsp?sku=414189

Or two of those (one per mosfet) AAVID THERMALLOY - 6398BG - HEAT SINK, TO-220/218, 4.4°C/W

http://pt.farnell.com/jsp/search/pro...sp?sku=1213473

Ricardo

Salas · 9th August 2009, 08:58 PM

I prefer the second one per Mosfet, and R1=10R.

RCruz · 9th August 2009, 09:12 PM

Thank you...

I believe I will have to review the shunt pcb layout... because of the fins in the heatsinks.

Ricardo

PS
I have R1 = 14r 1w

Salas · 9th August 2009, 09:17 PM

If its a big problem, use the first option, with 14R is surely enough.

RCruz · 10th August 2009, 12:45 PM

I did a new layout so I can fit the individual heatsinks....

I calculated a led string dropout of 6,39v, using 14r I have ICCS with load = 174 mA

Using R1 = 10, I get 259mA... is this viable ?

Ricardo

Audiofanatic · 10th August 2009, 12:47 PM

Hi Jaap,

I can not PM you, your e-mail button is disabled.
Please contact me regarding your PCB's for the SALAS RIAA.

Thanks in advance.

Best regards,

Audiofanatic

Salas · 10th August 2009, 01:37 PM

Quote:

Originally posted by RCruz
I did a new layout so I can fit the individual heatsinks....

I calculated a led string dropout of 6,39v, using 14r I have ICCS with load = 174 mA

Using R1 = 10, I get 259mA... is this viable ?

Ricardo

Depends on the Vgs of the exact part, but with such Leds I would surely use the 14R so not to overshoot 200mA.

RCruz · 11th August 2009, 12:06 AM

The green leds I used presented an average of 2,1v drop.

I now found some smaller yellow leds with 1,9 drop. Using 3 leds I get 5.7v... if my calculator is correct, admiting Vgs 3.4v, i can use R1=10r and get away with 190mA ICSS (230-40)... am I right ?

Ricardo

Salas · 11th August 2009, 02:40 AM

Yes if Vgs will be like that. You just measure the drop across the resistor in the end, and if its non usefully excessive, you make it higher R. I prefer the yellows slightly for best noise also. Its that the greens are easier to predict for those they don't match them.

RCruz · 11th August 2009, 01:54 PM

I will match the leds before use so I will know vdrop in advance.

Using your formulae: ICCS=(Vdrop-VGS)/R1 I can find R1.

After building the shunt I will measure R1 drop and using ohm´law I will verify the current.

Looking very good already.

Ricardo

9th August 2009, 07:56 PM	#2141
RCruz diyAudio Member Join Date: Sep 2006 Location: Cascais Blog Entries: 1	I am strugling with heatsinks.... Would this one be suitable for the shunt ? H S MARSTON - 05DN-00500-A-200 - HEAT SINK, 4.5°C/W http://pt.farnell.com/jsp/search/pro...jsp?sku=414189 Or two of those (one per mosfet) AAVID THERMALLOY - 6398BG - HEAT SINK, TO-220/218, 4.4°C/W http://pt.farnell.com/jsp/search/pro...sp?sku=1213473 Ricardo __________________ RC

9th August 2009, 09:12 PM	#2143
RCruz diyAudio Member Join Date: Sep 2006 Location: Cascais Blog Entries: 1	Thank you... I believe I will have to review the shunt pcb layout... because of the fins in the heatsinks. Ricardo PS I have R1 = 14r 1w __________________ RC

10th August 2009, 12:45 PM	#2145
RCruz diyAudio Member Join Date: Sep 2006 Location: Cascais Blog Entries: 1	I did a new layout so I can fit the individual heatsinks.... I calculated a led string dropout of 6,39v, using 14r I have ICCS with load = 174 mA Using R1 = 10, I get 259mA... is this viable ? Ricardo __________________ RC

10th August 2009, 12:47 PM	#2146
Audiofanatic diyAudio Member Join Date: Oct 2002 Location: The Netherlands, Utrecht	PCB Hi Jaap, I can not PM you, your e-mail button is disabled. Please contact me regarding your PCB's for the SALAS RIAA. Thanks in advance. Best regards, Audiofanatic __________________ Be nice to animals.

11th August 2009, 12:06 AM	#2148
RCruz diyAudio Member Join Date: Sep 2006 Location: Cascais Blog Entries: 1	The green leds I used presented an average of 2,1v drop. I now found some smaller yellow leds with 1,9 drop. Using 3 leds I get 5.7v... if my calculator is correct, admiting Vgs 3.4v, i can use R1=10r and get away with 190mA ICSS (230-40)... am I right ? Ricardo __________________ RC


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9th August 2009, 08:58 PM	#2142
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	I prefer the second one per Mosfet, and R1=10R.

9th August 2009, 09:17 PM	#2144
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	If its a big problem, use the first option, with 14R is surely enough.

11th August 2009, 02:40 AM	#2149
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Yes if Vgs will be like that. You just measure the drop across the resistor in the end, and if its non usefully excessive, you make it higher R. I prefer the yellows slightly for best noise also. Its that the greens are easier to predict for those they don't match them.

11th August 2009, 01:54 PM	#2150
RCruz diyAudio Member Join Date: Sep 2006 Location: Cascais Blog Entries: 1	I will match the leds before use so I will know vdrop in advance. Using your formulae: ICCS=(Vdrop-VGS)/R1 I can find R1. After building the shunt I will measure R1 drop and using ohm´law I will verify the current. Looking very good already. Ricardo __________________ RC

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