Time to debug the nayna out of this ISP Decimator.

[stonerbox]

I built the Decimator and it got very low output. I have to dime my preamp to even hear barely anything with a fully maxed out Pharaoh Fuzz in the front of the Decimator.. yep it's that low!  I have gone over the cuts three times, components placement two times and everything seems perfectly fine, seems..

The first time I plugged it in I had put the two LF347N in backwards and probably fried them (sent +9v to -V pin). The burned LF347N are now swapped and I also tried replacing the LF353p for a new one. I have not tried swapping the transistors or the THAT IC, could any of these got burnt too?

I audio probed it and signal goes down substantially at R3>THAT input pin (1).

Subbed:
Many of the 20k with 18+1.3k resistors.
The 1M trimpot with a 1M potentiometer .
1n5819 with a BA159.

1n5819
http://www.alldatasheet.com/datasheet-pdf/pdf/2818/MOTOROLA/1N5819.html
BA159
http://www.alldatasheet.com/datasheet-pdf/pdf/33912/WTE/BA159.html

Here is the layout: http://www.sabrotone.com/?attachment_id=1380

THAT2181C  (U8 on layout http://www.alldatasheet.com/datasheet-pdf/pdf/123669/ETC1/THAT2181C.html)
1 7.1
2 6.5
3 7.9
4 6.5
5 5
6 7.9
7 9.4
8 7.9

LF353p (U5 on layout http://www.alldatasheet.com/datasheet-pdf/pdf/27193/TI/LF353P.html)
1 7.9
2 7.9
3 1.4
4 0
5 7.9
6 7.9
7 7.9
8 9.4

LF347N (U7 on layout http://www.alldatasheet.com/datasheet-pdf/pdf/8576/NSC/LF347N.html)
1 7.5
2 4.5
3 4.2
4 9.4
5 2.2
6 2.2
7 2.2
8 2.7
9 5.8
10 3.9
11 0
12 6.5
13 7.2
14 7.2

LF347N  (U9 on layout http://www.alldatasheet.com/datasheet-pdf/pdf/8576/NSC/LF347N.html)
1 1.5
2 1.2
3 1.2
4 9.4
5 1.2
6 1.4
7 1.5
8 1.5
9 1.5
10 1.1
11 0
12 6.2
13 1.2
14 8.5

2n5551
e 7.8
b 1.47
c 3.7

Pn2222a
e 4.9
b 0.5
c 0 (?!)

[PRR]

Always give a schematic!

http://1.bp.blogspot.com/-6MIbm-Xv_iA/T_niVO0XcxI/AAAAAAAABuc/0hEt6sjJ5UU/s1600/decscheme.jpg

This really should be trimmable to a LOT of gain.

> signal goes down substantially at R3>THAT input pin (1)

Input is a virtual earth, so it output. You expect "no" audio voltage at these points. Nothing proved.

Output of U5.1 should be good audio level.

> THAT2181C
> 2 6.5
> 3 7.9
> 4 6.5

DC voltage on pins 2+4 *must* be nearly equal to DC voltage on pin 3. (60mV difference switches the '2181 from off to live.)

In true THAT style, the circuit is large and subtle. I'm not going to suss it out tonight. An "obvious" dynamic check is the DC voltage on C4, the signal rectifier filter cap. This should go more-positive with signal. Then U7.4 pin 14 should go even more positive with signal.

Disconnect one end of R31. Disconnect the pot-wiper end of R36 and tack it to '2181 pin 3 or Vr. That should give unity gain all the time.

> Pn2222a
> e 4.9
> b 0.5
> c 0 (?!)

This is clearly odd. Base should be 0.6V up from ground, 0.5V is plausible. Emitter is clearly grounded, so why 5 Volts? I think Collector should float to some positive voltage.

I suspect you have E and C confused. Confused on your notes or confused on your build?

[nickbungus]

Sorry, I don't mean to hijack the thread Stonerbox, I was just wondering if you or any others have come across a PCB layout? 

In my opinion (and skillset), this size circuit is too big for Vero but the YouTube videos of this pedal look awesome.

[stonerbox]

After checking for issuse over and over again I found out that I had put the Pn2222a in the place of the 2n5551a and vice versa.  Still no sound though..

Always give a schematic!

http://1.bp.blogspot.com/-6MIbm-Xv_iA/T_niVO0XcxI/AAAAAAAABuc/0hEt6sjJ5UU/s1600/decscheme.jpg

This really should be trimmable to a LOT of gain.

> signal goes down substantially at R3>THAT input pin (1)

Input is a virtual earth, so it output. You expect "no" audio voltage at these points. Nothing proved.

Output of U5.1 should be good audio level.

> THAT2181C
> 2 6.5
> 3 7.9
> 4 6.5

DC voltage on pins 2+4 *must* be nearly equal to DC voltage on pin 3. (60mV difference switches the '2181 from off to live.)

In true THAT style, the circuit is large and subtle. I'm not going to suss it out tonight. An "obvious" dynamic check is the DC voltage on C4, the signal rectifier filter cap. This should go more-positive with signal. Then U7.4 pin 14 should go even more positive with signal.

Disconnect one end of R31. Disconnect the pot-wiper end of R36 and tack it to '2181 pin 3 or Vr. That should give unity gain all the time.

> Pn2222a
> e 4.9
> b 0.5
> c 0 (?!)

This is clearly odd. Base should be 0.6V up from ground, 0.5V is plausible. Emitter is clearly grounded, so why 5 Volts? I think Collector should float to some positive voltage.

I suspect you have E and C confused. Confused on your notes or confused on your build?

Shoot, forgot the schematic! Thanks for digging it up man.
I followed your instructions, disconnecting R31 and rewiring R36 (wiper side) to pin 3 of THAT but unfortunately there was no improvement in the volume issue.

Here are some updated readings with the resistors connected the way PPR recommended:

THAT2181C 
(U8 on layout)

1 7.5
2 8.2
3 8.3
4 8.2
5 5.5
6 8.3
7 9.4
8 7.6

LF353p
(U5 on layout)


1 2.9
2 5.5
3 2.6
4 0
5 8.2
6 7.5
7 8.5
8 9.4

LF347N
(U7 on layout)

1 4.4
2 3.2
3 2.9
4 9.4
5 1.4
6 1.7
7 1.7
8 2.5
9 4
10 3.9
11
12 4
13 4.3
14 4.3

LF347N
(U9 on layout)

1 1.5
2 1.5
3 1.1
4 9.4
5 1.1
6 5.8
7 1.5
8 1.5
9 5.8
10 4.2
11
12 3.8
13 1.2
14 8.2


2n5551 (Q4 on layout)
e 1.1
b 1.3
c 4.5

Pn2222a (Q1 on layout)
e 0
b 0.7
c 5.5

[stonerbox]

Resurrecting the dead! Blasphemy!

I returned to this circuit and I found something strange.

On the Sabrotone layout the V+ is connected to THAT2181C's third pin and the datasheet says that pin 3 is SYM. Pin 7 however says V+ and is connected to U5's pin 6 (non-inverted input).

That is definitely not right BUT people have used this layout and got it to work before so I'm confused. What are your thoughts?

Edit: nothing to see here, move along. I f-cked up.

http://i.imgur.com/17dJ6sw.png

[stonerbox]

-Fresh start-

Ok guys I spent all day (yesterday) rebuilding this thing from scratch and now I got signal but no gating.
It's clean on the lower output settings but if I almost crank the 1M pot it turns into a super loud oscillating fuzz, beyond that it just cuts out. I guess that is just what happens if you max this thing out or is something wrong here?

Anyway, I'm building this thing as a Christmas gift for an old friend that had a really tough time lately. His father passed away this summer and he and his longtime girlfriend just separated, talk about rough times.  It would mean the world to me if you could assist me in debugging this thing and get it to work. Harold, are you still here? Voltage readings from a functional Decimator would be greatly appreciated.

Sabaton Layout http://www.sabrotone.com/?attachment_id=1380
Original Schematic (differs in some of the resistor and cap values) http://2.bp.blogspot.com/-l2NRTEh3J54/T-8ppoN5mNI/AAAAAAAABm0/L-RQt6ykI84/s1600/ispscheme.jpg

Here are the voltages of a working (?) decimator clone by Mremic01 but sadly without the THAT voltages.
http://www.diystompboxes.com/smfforum/index.php?topic=99848.msg956273#msg956273



THAT2181C
(U8 on layout)

1 4.5
2 4.5
3 4.5
4 4.5
5 1.9
6 4.5
7 9.2
8 4.5

LF353p
(U5 on layout)

1 4.5
2 4.5
3 1
4 0
5 4.5
6 4.5
7 4.5
8 9.2

LF347N
(U7 on layout)

1 8.5
2 5.5
3 5.5
4 9.2
5 2.9
6 2.9
7 2.9
8 1.5
9 6
10 2.6
11 0
12 0.1
13 8.2
14 8.2

LF347N
(U9 on layout)

1 2.6
2 4.2
3 4.2
4 9.1
5 4.5
6 4.5
7 4.5
8 4.5
9 4.5
10 4.5
11 0
12 3.8
13 4.5
14 4.5


2n5551 (Q4 on layout)

From top to down on the layout
E 2.9
B 3.1
C 8.4

Pn2222a (Q1 on layout)
From top to down on the layout
e 0
b 0.5
c 1.8

[Kipper4]

The that chip voltages are in that thread too just above your reference.
And yours look a bit low compared

[stonerbox]

The that chip voltages are in that thread too just above your reference.
And yours look a bit low compared

Don't know how I managed to miss that post. Thanks Klipper!

Yes it does. It's also strange that Q1's e reads 2.9v

[slacker]

Something's wrong round pins 12 - 14 of U7, depending on the setting of the threshold pot you should get somewhere between about 2 and 6 volts on on pin 12 with the same voltage on pins 13 and 14. Possibly pin 12 is shorted to pin 11.

Might be other errors, that one just stuck out.

[stonerbox]

Something's wrong round pins 12 - 14 of U7, depending on the setting of the threshold pot you should get somewhere between about 2 and 6 volts on on pin 12 with the same voltage on pins 13 and 14. Possibly pin 12 is shorted to pin 11.

Might be other errors, that one just stuck out.

You are absolutely correct sir! The voltages goes from 9.3v down to 0.1v after R21.

[stonerbox]

Found the culprit, kind of anyways. as soon as I disconnect R35 (a 270k -> ground) the voltages goes back up but is only adjustable in between 7.6 to 7.9v. To say the obvious, there must be coming voltage from another place.
_______________________________________
Update: I disconnected R22, R35 and no change what so ever.. Between pin 12 and R21 I still get 7.6 to 7.9v no matter what. I check for solder bridges and that the cuts in this area are correct.

Is the voltage coming from inside the LF347?
_______________________________________

One last update before I crash.

I resoldered everything connected to pin 12 and now the voltage is almost right, 0.9v-7.9v. Still no gating going on..

New voltages:

LF347N
(U7 on layout)

1 7.9
2 7.5
3 7.2
4 9.2
5 7.2
6 7.2
7 7.2
8 4.5
9 6.5
10 6.2
11 0
12 5.8
13 7.2
14 7.2

LF347N
(U9 on layout)

1 7.9
2 5.8
3 7.9
4 9.2
5 5.3
6 4.5
7 8.2
8 1
9 0
10 5.2
11 0
12 3.9
13 4.5
14 4.5

[slacker]

Just spotted another problem, pins 8, 9 and 10 of U9 should all be about 4.5 volts, with pin 9 at 0 no signal is getting to the control circuitry so that would explain why you're getting no gating. Check the trace cut on the row between pin 9 of U9 and pin 4 of U5, that's would be my first guess at where the problem is.

[stonerbox]

Just spotted another problem, pins 8, 9 and 10 of U9 should all be about 4.5 volts, with pin 9 at 0 no signal is getting to the control circuitry so that would explain why you're getting no gating. Check the trace cut on the row between pin 9 of U9 and pin 4 of U5, that's would be my first guess at where the problem is.

I'll do that, thank you for being a trooper and helping me in this!

I'm starting to wonder if the permanent marker pen I used color the cuts somehow works as a lead? - Awkward explanation but hey, I'm @#$%ing Swedish! 


Update:
Fixed a link underneath the U9 that was wired in "backwards" and now the voltages look almost perfect. However there are still some issues present.

LF353p
(U5 on layout)

1 4.5
2 4.5
3 1.2 (?)
4 0
5 4.5
6 4.5
7 4.5
8 9.2

LF347N
(U7 on layout)

1 3.4
2 3.1
3 2.9
4 9.2
5 2.8
6 2.8
7 2.8
8 4.6
9 3.5
10 3.5
11 0
12 0.8
13 2.8
14 2.8

LF347N
(U9 on layout)

1 3.4
2 4.3
3 4.3
4 9.2
5 4.6
6 4.6
7 4.6
8 4.6
9 4.6
10 4.6
11 0
12 3.8
13 4.6
14 4.6

[PRR]

> LF353p
> (U5 on layout)
> 3 1.2 (?)
>
> LF347N
> (U9 on layout)
> 14 4.6

If I read the schematic right, these are the SAME point ("Vr"). Why are they not the same voltage?

> still some issues present.

What does that mean?

[stonerbox]

> LF353p
> (U5 on layout)
> 3 1.2 (?)
>
> LF347N
> (U9 on layout)
> 14 4.6

If I read the schematic right, these are the SAME point ("Vr"). Why are they not the same voltage?

> still some issues present.

What does that mean?

Not according to the Sabro layout.
Sabrotone Layout http://www.sabrotone.com/wp-content/uploads/2011/09/Decimator.gif
Original Schematic http://2.bp.blogspot.com/-l2NRTEh3J54/T-8ppoN5mNI/AAAAAAAABm0/L-RQt6ykI84/s1600/ispscheme.jpg

What I meant was that a lot of voltages have been improved this past week but the gate is obviously not functional yet. Things have gone from bad to better but there are still some issues present in this build.