Maestro FSH-1 (Filter Sample/Hold) mods

[Mark Hammer]

The next step is probably to verify the pins of the 245 FET.  FETs drive me crazy with the different pinouts they have.  Get the datasheet for the brand you are using.

[funkiness]

The next step is probably to verify the pins of the 245 FET.  FETs drive me crazy with the different pinouts they have.  Get the datasheet for the brand you are using.

I've just done that  :wink:  and pinout is correct.

Some more info about strange voltages on Q2:
+8,1V for Drain pin
+7,36V for Source pin
+7,36V for Gate pin

Little question... yesterday when I was testing I have reversed Q2...  Do you think it can damage it ?

And what can I check now ?

Thanks for your precious help, french forums aren't so helpful !

[funkiness]

Up !
I still hope a brillant idea will hit me.  :?

[Mark Hammer]

Je songe à une idée aussi! :cry:

Looking at it, R26 the trimpot should be able to adjust the filter frequency by feeding current into the Iabc pin (pin 5).  See if changing that trimpot results in signal at the output of IC1.

[funkiness]

Great idea, thanks ! I will try that.

[funkiness]

Mark, here are the tests results.

By changing R26 I still don't have any audio signal at the output, but I notice a strange thing !

With R26 turned fully clockwise:
+0,6 V for IC1 pin5
-7 V for IC2 pin5  :?

With R26 turned fully counter clockwise:
-1,3 V for IC1 pin5
-7 V for IC2 pin5  :?

That lead me to believe that the problem was IC2 chip.
I was right. After swaping IC1 chip with IC2 chip, I got the -7 V for IC1...
So I will buy some new 3080 to test again.

But a question Mark, do you think that with only IC1 working I should already have some sound on the ouput ? (because i actually don't have any sound  :cry:  ).

[funkiness]

Up !

[funkiness]

Well, after 5 months of sleep, i come back.
I will build the filter part on a breadboard to understand a bit more.

[chemosis]

is there any other mods for the filter side. i love the filter side but was wondering if i could possibly change the overall frequency sweep to a lower register to make it a lower low pass filter.