Blew up JFET's on Preamp

Destroyer OS. · 03:23 AM

Here is my power supply.

http://img.villagephotos.com/p/2003-4/144711/DOS317.gif

I have the system ground running to AC ground, and I am wondering if this caused the problem.

The pre-amp is just four JFETs and five resistors. The shunt to system ground (AC ground in my case in this instance) from the input is 510kohm.

15 - C
http://www.borbelyaudio.com/adobe/ae699bor.pdf

My neutrals on the RCA's are all connected.

I just want it to work! I do not have any heatsinks on the LM137's either if that matters... There is such low current....

The JFET's connected to the -24v blew up when I plugged it in. I just discovered another accident which was there was no load connected when I first turned it on either. There was not connection being made via the RCA's.

Destroyer OS. · 10th November 2009, 03:40 AM

Somewhere in the process my volume Pot got completely burned out as well.

CBS240 · 10th November 2009, 04:03 AM

Are you sure the gate of the lower fet (CCS) is connected properly? Without the gate connected, the CCS fet, as a depletion device, would be fully on, which would cause the top fet, the follower, to be fully on as well.

Destroyer OS. · 10th November 2009, 04:06 AM

Oh and my 3875 Chips in my amp are toast.

If my DAC is toast I will never probably have a stereo again for a long time....

Destroyer OS. · 10th November 2009, 04:09 AM

They are 170BL's... If you look at them from the front the right pin is +24v center is signal, and left is drain (out). Then on the other one it goes drain from other into the pin on right, then middle and left are jumpered via resistor, and -24v is connected to the resistor side away from the FET.

PSz. · 10th November 2009, 04:19 AM

Did you use coupling caps?

psz.

Destroyer OS. · 10th November 2009, 04:25 AM

Where at? The input or the output?

Neither. My DAC has them and the amplifier seemed fine without.

Destroyer OS. · 10th November 2009, 05:25 PM

Anyone Know why the JFET's blew? I assume that has everything to do with all of my other equipment but...

Michael Chua · 11th November 2009, 03:12 AM

Quote:

They are 170BL's... If you look at them from the front the right pin is +24v center is signal, and left is drain (out).

Looks like you got the pins reversed.

Regards
Mike

10th November 2009, 03:07 AM	#1
Destroyer OS. diyAudio Member Join Date: Nov 2005	Blew up JFET's on Preamp Here is my power supply. http://img.villagephotos.com/p/2003-4/144711/DOS317.gif I have the system ground running to AC ground, and I am wondering if this caused the problem. The pre-amp is just four JFETs and five resistors. The shunt to system ground (AC ground in my case in this instance) from the input is 510kohm. 15 - C http://www.borbelyaudio.com/adobe/ae699bor.pdf My neutrals on the RCA's are all connected. I just want it to work! I do not have any heatsinks on the LM137's either if that matters... There is such low current.... The JFET's connected to the -24v blew up when I plugged it in. I just discovered another accident which was there was no load connected when I first turned it on either. There was not connection being made via the RCA's. Last edited by Destroyer OS.; 10th November 2009 at 03:23 AM.

10th November 2009, 04:03 AM	#3
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	Are you sure the gate of the lower fet (CCS) is connected properly? Without the gate connected, the CCS fet, as a depletion device, would be fully on, which would cause the top fet, the follower, to be fully on as well. __________________ All the trouble I've ever been in started out as fun......

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10th November 2009, 03:40 AM	#2
Destroyer OS. diyAudio Member Join Date: Nov 2005	Somewhere in the process my volume Pot got completely burned out as well.

10th November 2009, 04:06 AM	#4
Destroyer OS. diyAudio Member Join Date: Nov 2005	Oh and my 3875 Chips in my amp are toast. If my DAC is toast I will never probably have a stereo again for a long time....

10th November 2009, 04:09 AM	#5
Destroyer OS. diyAudio Member Join Date: Nov 2005	They are 170BL's... If you look at them from the front the right pin is +24v center is signal, and left is drain (out). Then on the other one it goes drain from other into the pin on right, then middle and left are jumpered via resistor, and -24v is connected to the resistor side away from the FET.

10th November 2009, 04:19 AM	#6
PSz. diyAudio Member Join Date: Jul 2003 Location: California	Did you use coupling caps? psz.

10th November 2009, 04:25 AM	#7
Destroyer OS. diyAudio Member Join Date: Nov 2005	Where at? The input or the output? Neither. My DAC has them and the amplifier seemed fine without.

10th November 2009, 05:25 PM	#8
Destroyer OS. diyAudio Member Join Date: Nov 2005	Anyone Know why the JFET's blew? I assume that has everything to do with all of my other equipment but...