boozehound labs jfets

[oltern8]

i recently fried my jfets on my boozehound by connecting the power supply the wrong way round. I've purchased some matched replacements from ebay and have installed them. The audio is getting to my amp but its whisper quiet i can just about hear it at full volume on my amp. So the question is have i fried the jfets again.

 

[AndrewT]

did you check and measure your Ebay jFETS?

Post your results.

 

[jan.didden]

Also, you may have fried something else in addition to the JFETs.
Any BJT, diodes, zeners on that unit?
Electrolytics often also go with reversed polarity.

Jan

 

[Hikari1]

Replace the 4 electrolytic caps. I bet your problem will be solved.

 

[oltern8]

Hi

No I didn't check the jfets. They were purchased as match quads i have a multimeter with an adapter but am unsure how to use it to check them. There are no diodes or bjt and I removed the 4 electrolytic caps as I prefered the sound using my bozure psu1 power supply which uses panasonic fc caps.

is it possible to check the transistors with my multimeter and adapter? the adapter appears to be for pnp & npn type transistors.
The transistors were posted to me from the usa is it possible that they were damaged by an electrostatic charge in transit or when i installed them.

thanks for everyones help

oli

 

[Hikari1]

The phono stage should work without the electrolytic caps but the caps do provide some benefit as they provide a little decoupling for each gain stage, basically better isolating each stage, power-wise. Leave them out for now.

Now, assuming everything is hooked up correctly, it has to be the jets. They are the only active device in this simple preamp. And they are the only devices (other than the electrolytic caps) that could be damaged by reverse voltage.

Are you sure you have the power hooked up correctly? The board is labelled poorly, the pad closest to the "Power" text is actually ground. Looking at the attached pic the power pad closest to the top of the pic is positive. I bet this is what got you in trouble in the first place.

Test with your meter. Measure between the "+" pad on one of the caps and a power solder pad. When you find the power pad that reads "0" or close to it on your meter this is positive. The negative solder pad on your power in should also have "0" continuity or close to it with the "ground" pad on the other side of the board.

If power is hooked up backwards and you still had the electrolytic caps on the board they would be damaged and possibly save the jfets. If you dont have caps on the board and you hook up the power backwards the jfets may be damaged.

 

[oltern8]

Yeah i connected the negative instead of the earth...what a plonker. mystery solved.

thanks

oli

 

[Hikari1]

Yeah i connected the negative instead of the earth...what a plonker. mystery solved.

thanks

oli

You shouldnt have any negative power...just pos and ground. Is this because of the psu you are using? Try 16 aa batteries. This phono likes batteries and 24v. Or just use the positive and ground outputs of the psu.

Your jfets may be ok.

 

[oltern8]

thanks hikari.

looks like i've blown them a bit annoying but you live and learn. I will install some panasonic fc on the board for possible protection purposes when i get some more jfets.

thanks

oli