Exploding output fets SPL Dynamics D8s

[Perry Babin]

That was to try to stop the dumping of the rail caps but didn't work.

Do you have any P-channel jfets?

 

[Maxikill97]

I don't have a specific J-fet, but I do have plenty of P-channel fets, would this work too?

P-channel fets I have:
IRF9640
IRF9540
IRF5210
FQP22P10
FQA36P15

 

[Perry Babin]

I don't know any way to make them work with as few parts as I might with a p-channel JFET.

Can you easily get something like the J174? Don't order yet.

 

[Maxikill97]

I can order a J176.
Is this OK?

Annoying that there always comes 9eu shipping costs, with a component from €0.23. So I need to wait until I need to order some bigger components.

 

[Perry Babin]

Its on resistance is much higher than the 174.

What about the P1086?
https://www.mouser.com/datasheet/2/676/jfet-p1086-p1087-interfet.r00-1649106.pdf

 

[Maxikill97]

I can't get the P1086.
Mouser is pretty expensive from here, and the websites that have some more substitutes as well.

Is a J175 good maybe?
If it also may be a N-channel that gives more options.

 

[Perry Babin]

I didn't mean to order from Mouser. I was simply posting the datasheet.

I don't know about the J175. I'm not 100% sure about the J174.

The N-channel would require more parts.

 

[Maxikill97]

Hmmmmm. Seems like P-channel Jfet is not a popular stocked item here.
RS-online has some options, but I can't order from them.

I can get a J174, but this costs me about 12USD for a single piece.
Do you think it is possible with a J175 and J176? If not, I can order the J174

 

[Perry Babin]

How expensive are the 175/176?

I'm assuming that the greatest part of the cost is shipping.

You may need to order more than one in case they are damaged in testing.

I will tell you up front that this may not work and the cost may be a complete waste of money.

I'm assuming that you have the other components that would be needed, a 10v (or close) Zener and a resistor or two (probably between 10k and 100k).

 

[Maxikill97]

In that case, I will just order some J174. If this has the biggest chance of succes.

J175 and J176 are 0.30usd each with 9usd shipping (i can order a lot more parts with that)
J174 is 3usd each with around 9usd shipping. No other parts can be ordered since they are very expensive and a small shop.

I have both other components (resistors and 10v zeners) in house.
When the item is arrived I will reply in this thread again.

 

[Perry Babin]

If you haven't ordered yet, you can order (to try) the 175 and 176 for future reference.

 

[Maxikill97]

Ok, I will order them.
When they are in house, I will reply again in this topic.

 

[Maxikill97]

So, got the parts in house.
I have:
J174 Jfet
9.1v, 10v, 11v zener diodes

 

[Perry Babin]

Do you have a jumper on Q10 on the driver board?

 

[Maxikill97]

The jumper from post #57 can be soldered on, yes.

 

[Perry Babin]

I don't remember what the setup is and I'm not going to read the entire thread.

As of now, will the amp power up and produce audio?

Are you using full rail voltage or low voltage for the rails?

 

[Maxikill97]

Ahhh, ok, let me give a liiitle explaination.

Output fets explode with normal rail voltage.
I made a 15v rail voltage. Amp works properly.
Output fet switching does not wait until full rail voltage is reached, it's switches immediately after power up.
We tried to delay it, but it was not possible.
We needed a J174 and 10v zener diodes to delay the switching until full rail voltage is reached.
I ordered the J174 Jfets and they came in house today.

 

[Perry Babin]

With the 15v rails. does it drain the rail caps immediately when the amp switches off?

 

[Maxikill97]

Correct. Rail caps empty after switching off

 

[Perry Babin]

Connect the source leg of the jfet to the emitter of Q52. Connect the drain to the collector of Q52.

Do not make a connection to the gate of the jfet.

Does that prevent the amp from oscillating and prevent it from draining the rail caps when the amp is powered off?