Another Filter Sample + Hold problems thread...

[chicago_mike]

Ill start with voltages, since everything, solder connections and all look just fine..

IC 2 4558
PIN        Volts
1          +6.35
2            0
3            0
4           -0.25
5           +2.54
6           +3.30
7           +1.29
8           +6.99


IC 3  4558
PIN         Volts
1             +6.17
2             +2.86
3             0
4             0
5             +1.28
6            +5.96
7            +1.35
8            +6.99

IC 1   LM13700    (sorry my IC's are not in order, didnt want to retype for an hour..)
PIN         VOlts
1            +0.67
2            -0.21
3            -0.19
4            0
5            -2.91
6             0
7             0
8             0
9              0
10           0
11            0
12             -6.97

13   -0.02
14   0

15   0


16   -.066


Umm, why is this reply window freaking out?? I cant get shit in order..

[StephenGiles]

Compatability view perhaps would do the trick??

[chicago_mike]

Yeah. I forgot that I have that option in IE. yes.....yes I still use IE.

[chicago_mike]

OH....

Do i flip MPF102's or just the BF245's ?

[Ry]

Mike, check out both pages of this thread (voltages and pinouts for the FET are covered):

http://www.diystompboxes.com/smfforum/index.php?topic=69381.0

This should help, but let me know if you still have issues, I can crack mine open and help you debug.

Ry

[chicago_mike]

Hey RY

THanks...

One oddball thing. THe Tonepad pdf. the first one.  look at the layout and notice the little G on the fets... Im looking at the schematic and it looks like the placement of the G is wrong. Am I correct?

[chicago_mike]

I checked out the thread and a few others, but I can find anything on using the MPF102's. A couple peeps say they use them, but didnt say anything about needing to switch them or swap 2 legs or whatever.

I get that and I'm confident this sucker will work. I added a low pass / band pass switch to it and want to try that out.

[Ry]

I'm looking at the tonepad layout/schematic and seeing what you're talking about.  The Gate 'G' indication is in the wrong spot for the pinout of the BF245A (the flat side of the FET is facing the wrong direction).  The 'G' symbol is, however, in the correct spot for the circuit to work.  Now, looking at a data sheet for the mpf102 (link below), the pinout is reversed from the BF245A BUT because the layout is screwy, you need to actually put it in like the layout shows for the BF245A, and everything should line up.

http://www.qsl.net/n4xy/PDFs/Semiconductor_Data_Sheets/mpf102.pdf

Good catch!

Ry

[chicago_mike]

Christ almighty this shit is screwy!!! 

Happy Easter RY!

[Ry]

Hahaha, happy easter to you!

Now I can't wait to see what you come up with for the filter switching!   

[chicago_mike]

I have a short somewhere...

Im not using a charge pump im doing the 2 9volt thing. So ground is connected to the middle of the 2 batteries..like normal.

I get my +9 but I dont ready any -9.

If I pull the connection off, I get the -9. So somewhere I have a short. But where is the question, because right fron the -9 from the charge pump..Im not getting anything.

could the caps be bad?? the 2 220uf's that are in the -9 circuit?

[chicago_mike]

to clarify:

in the layout, where the pump would be outputting the -9, is where my negative lead is. And this is reading 0. Nada, nuttin, zip, zilch, mega-negatory....

take it out... -9 all day long.

So....the caps seem okay and so does the 470ohm resistor...why am I not seeing the -9? ARGH!!!

[chicago_mike]

Found the short....

Now..Its ticking..YAY!

still no audio passing thru. But its ticking now.

Shit, its a start!

[Ry]

Cool!  The FSH-1 is always tricky when it comes to the trimmers, patience is key!  It should filter in the filter mode, but the sample and hold takes some fiddling.

[chicago_mike]

Well right now its not doing anything except ticking...

Soooo... bad IC's?  another short? Doomafloogen? Break light fluid? Ruptured Resitor plate? 

[Ry]

Ticking is good, it's always been the first step when I build one.  Play with the pots a little, get an audio probe going when all else fails.  You're nearly there!

[chicago_mike]

okee dokee.

[chicago_mike]

AHHHHHHHHHHHHHHHHH

ALMOST!!!!!

I get ticking but no sample hold. I do get the filter..sort of when I switch to sample + hold.

The filter works more or less. As does my Low Pass Filter tap. But some times, if I touch the switch, I get a real loud low hum...above 60hz.

So Ill recheck my rechecked soldering.


I'm still thinking of a 10K Linear pot instead of a switch to blend between LPF and BPF outputs.

[chicago_mike]

Okay, so the ticking vs. the actual smaple and hold effect...

Is this just swapping the npn and adjusting the trimpots? I adjust the 10K and that seems to be a volume for the sample + hold. I hope thats kinda what it is..

The other guy, I dont seem to get anything noticeable....hmmmm

[chicago_mike]

Ima lso thinking of changing the 4558's to TL072's or some OPA 2604's I have.