B1 Buffer Preamp

[Harolda]

Hello

i just finished a prototype for a cross over circuit using B1 buffers. I build every thing on Perf board. I checked the circuit over and over but there seems to be a shortcut between the +9V and -9V rails (that is also what i can measure with my multimeter). What could be the problem?

The only components that can cause a shortcut between the +9V and -9V rails are the 2sk170. Are the broken? But i made 6 PCB with every PCB 4 buffers (symmetrical signal) and on every PCB i have the shortcut

My 2SK170 are connected like this

1) first 2sk170:
- Gate to input
- Source to drain of second 2sk170
- Drain to +9V
2) second 2sk170
- Gate and Source to -9V
- Drain to source of first 2sk170 --> connects to PLLXO network.

Any ideas?

[bigaudioscotto]

You May want to email Nelson Pass.
I am sure he has an answer.
nelson@passlabs.com

[juma]

Originally Posted by Harolda

....

Any ideas?

High resolution pictures of both sides of perfboards would help.

[Harolda]

i will post somue pictures, first i have to disassemble everything

[Nelson Pass]

Check the pinout of the Jfets.

Looking at the flat side with the pins coming out the bottom,
Left to Right: Drain, Gate, Source

[Harolda]

Hello Nelson,

yep i checked that (also with the 2sk170 datasheet) and i don't see any mistakes. But it takes some time to dissasemble. I will post a picture of one buffer circuit after that.

This is how it looks like, but you can't see the details in this picture:

B1-PLLXO (HP or LP)-B1-attenuator-B1.

regards,


Harold

[Harolda]

I found the faulty buffer stage. When i hooked up the battery power supply to one buffer after another, i found the shortcut on one buffer. I will have a look at that tomorrow and check the solder points.

regards

[bigaudioscotto]

Best of luck.
you will love it when you get it going.

[Harolda]

I found two problems:

1) I found a short cut in one of the 2sk170 legs and corrected it
2) In the first buffer of the HP i found a resistor of 1K iso 1M to ground, stupid mistake. I had to take out the board because one of the jfets was burned. I now use the 1st buffer of the LP to also drive the HP filter.

Now i have sound coming from the system on a very low volume for the Hp and no sound from the LP. Before I build in the buffers, i checked the PLLXO with visual analyser for the correct filter frequency and everything worked fine.

Some more research into the circuit to find out what could be the cause of this issue

regards

[Harolda]

Yeas yeas it finally works. Beautiful. it will be late tonight.