Decimator Gstring Debug / Help!

[jmasciswannabe]

I've built it but the signal is either too fuzzy or too loud depending on where I turn the trim. Even when it is loud you can hear the fuzz creep in as the guitar signal fades out. I've jotted down my voltages, if anyone has a working one and could post, I'd be incredibly grateful. Or if anyone has suggestions on where to audio probe to find the problem, that would be great, too. Like where I hsould be hearigjn clean signal after pin 1 on the bottom left opamp.

Here's the schem. Unfortunately, there hasn't been a revised one for the Gstring with matching components (duals dropped for quads.)

http://2.bp.blogspot.com/-l2NRTEh3J54/T-8ppoN5mNI/AAAAAAAABm0/L-RQt6ykI84/s1600/ispscheme.jpg

Here's the layout:
https://dl.dropbox.com/u/3565959/ISP%20G-String%20Public.pdf

I've used tl074 instead of the lf347.

Here are my voltages: 9.54 at input

Bottom left opamp:
8.85
8.85
0
0
4.0
4.4
4.4
8.85

Bottom right quad:
4.4
4.4
4.0
8085
4.4
4.4
4.3
4.5
4.4
4.4
0
4.3
4.3
3.8

top right quad:
3.6
3.6
3.5
8.85
4.6
4.6
6.4
5.6
2.6
2.6
0
4.4
4.4
4.4

Top left dual:
4.4
4.4
4.4
0
3.4
4
2.2
8.85

THAT IC:
4.4
3.7
4.4
0
1.54
4.11
8.85
4.4

[damas]

Are you connect your trimpot like this?

[jmasciswannabe]

yeah, I initially tried a trimpot and then flipped it and then used a standard pot but all the same thing. terribly fuzzy 75% of rotation, starts cleaning up and getting louder, goes past unity volume and is about good, but still can hear some fuzziness, especially when the signal starts to die out.

Maybe there is something wrong after the trim, as I gather it controls voltage to a few of the chips. That's why I am hoping someone will post there WORKING voltages up.

[jmasciswannabe]

Well, I figured I'd build another one. And it's good to go. Still trying to debug the first one I build, though. I am going to post working voltages on the mega thread page for folks trying to debug in the future.

[damas]

Good job
sorry did not give you more help

[lars-musik]

Hello Friends,

I seem to have run in a similar problem. I cannot find any obvious problems and have checked the pcb and soldering joints carefully with a binoclular microscope. No bad joints, no interlacing traces. Besides some resistors I had to manufacture in series I used all components named in Galegos layout and the corresponding offboard wiring (this one http://imageshack.us/a/img402/9002/offboardwiring.jpg).

The thing just doesn't work. Somehow a distorted sound comes through when the noise reduction potentiometer is completely closed and the trim pot is about half open. When turning them further sometimes a scratchy sound appears and then vanishes swiftly.
I figured that in order to eliminate other potential sources of faults (namely some noisy beginner's fuzzes i put in the loop in the first test setup)  it would be best to test it like this: guitar -> guitar in and git out -> dec-in  and dec –out-> amp. That should work, shouldn't it?

@ jmasciswannabe: have you debugged your first attempt? Where/how did you start.
@all: Has anybody yet recorded voltage read-outs from a working board? Where would you start? I find it difficult to debug that one due to the Dec-In/Out loop that overloads my small brain in terms of signal flow.

Any suggestions welcome. Although I guess I'll etch another board soon and just start all over. Good thing i socketed the ICs.

Lars


EDIT: I just saw that this is my first post in this forum. I am following you since quite a while and I really like what I'm reading here. Thanks to all of you contributing this fine circuits and layouts. And of course all of you who helped others and will help me in the future!

[lars-musik]

Problem solved. After intense audioprobing I found the initially socketed the 1N5819 guilty. Removed socket, removed problem, removing noise now.

[Versus]

Hi guys!
1) I`m sorry for my bad English, I`m Russian, I`m learn:)
2) Thank`s you for watching!
I finished build my G-String (Slade`s circuit), but I have problems. When I set "Threeshold" on 70%, Decimator is don`t work, the signal is disappears.
I decided to test PCB.

5,1k resistor is work but  signal is lost!
Can you say me what i must verify for normal work my g-string?

[Govmnt_Lacky]

@Versus

Looks like some pretty close traces in that area. Did you look at the solder side of your board to make sure there are no solder bridges?

[Versus]

No soldier bridge! All carefully!

[Govmnt_Lacky]

No soldier bridge! All carefully!

Next step:

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[Versus]

which scheme is used in Slade`s layout? Can you post me?

[Versus]

Hi guys! I set up my g-string and now he is work but when I wring max gain on my distortion (Wampler Triple Wreck) - noise skipped. Is it normal ?

[Harold]

I have some troubles with this build too, with my audio probe I can trace the signal going to the THAT2181, but mutes between the 20k and pin 1 of the THAT. There used to be a big iSP topic somewhere, but I can't seem to find it?

http://www.diystompboxes.com/smfforum/index.php?topic=88902.0 leads to "The topic or board you are looking for appears to be either missing or off limits to you."

Any first thoughts before I measure all voltages on the THAT?

[mremic01]

Are you sure you're using the C version of the THAT2181C? There are a few other versions that have been reported not to work in the Decimator

[Harold]

Jep: C version.

[mremic01]

Hi guys! I set up my g-string and now he is work but when I wring max gain on my distortion (Wampler Triple Wreck) - noise skipped. Is it normal ?

I'm not sure what you mean by 'wring max gain'. It would also help to know where the Decimator is in your signal chain. I used mine first, before any distortion. That way it cuts any noise before it gets amplified. Some guys run the noise gates last to deal with noise introduced by having lots of effects. I found that that didn't work as well. It was much better at stopping noise earlier in the pedal chain. But if there's buzz or hum in your signal, it will let that through with your playing. It won't start gating until the signal its getting from your guitar is over a certain loudness, as set by the threshold.

From your earlier post where you were having your signal cut out when the threshold was at 70%. That's normal. When you set the threshold high, it needs an even louder signal going into it before it stops gating and lets your signal through. I have two actual Decimators, not DIY builds, and they both work best at about 9 o'clock to 10:30, well under 50% of the pot's rotation. Any more than that, and it barely let's my signal through. If you're running it after other pedals that boost your signal, you might need to set it higher. 

I just finished up a build using Slade's layout and it's working just like my stock units. It's not the G String, but I'll see if I can post some voltages when I get home from work tomorrow or Tuesday. Does anyone know what the trimpot does? I didn't even need to touch it and it sounded fine.

[J0K3RX]

No offence but, In my most humble opinion, running the Decimator first in your signal chain is kinda like wiping your butt before you take a crap! 

Connect the Decimator INPUT to the loop "send" and Decimator OUTPUT to the loop "return". Place all high gain/distortion pedals in front of the amp/preamp and Decimator INPUT. You can put your Delays,  Reverbs, chorus pedals etc after the Decimator and before the loop return to avoid cutting off reverb, delay repeats or whatever... 

[mremic01]

No offence but, In my most humble opinion, running the Decimator first in your signal chain is kinda like wiping your butt before you take a crap! 

Connect the Decimator INPUT to the loop "send" and Decimator OUTPUT to the loop "return". Place all high gain/distortion pedals in front of the amp/preamp and Decimator INPUT. You can put your Delays,  Reverbs, chorus pedals etc after the Decimator and before the loop return to avoid cutting off reverb, delay repeats or whatever... 

Then you just have your noise coming from somewhere else. I've never had noisy cables/pedals/preamps. It's always started at the guitar. If you've got hum or buzz coming in from somewhere, the trick is to have the gate kill it before something else amplifies it. After it's amplified, you've got to turn the threshold up to match and then your note decays suffer. The one I just built is doubled up with an Engineer's Thumb. They work perfectly together. The Decimator stops the noise before the compressor can bring it up. It's like taking a whole lotta Metamucil and never needing to wipe, cause the poo was already nice and clean going through. I've heard of some guys using two Decimators though. One in front and one in the loop. The first one gates any noise before it gets amplified, the second one takes care of noise that's gotten in further down the signal chain. I haven't used a G String yet, but I've never needed anything more than the initial gate at the front of my board.

[Harold]

The recommended position of a noise gate in your effects chain is all the way at the back. Gernerally people want to kill noise from a drive/distortion/fuzz. Non-G-Stringed Decimators won't perform well at that position because with a switchable drive, your dynamic range is way too big for a tight noise gate.

That's what's so brilliant about the G-String: it "listens" to your guitar signal before compressing/expanding/etc and mutes a loop according to the input volume.


... if you can get your G-String to work

Does anyone know what the trimpot does? I didn't even need to touch it and it sounded fine.

You can/must use the trimpot to set unity volume. I don't add a bypass to mine, so I have to check unity volume with a separate bypass looper.