debuging an isp decimator g string kit,That2181c questions

[nonoxxx]

On mine before th transistor swap the gate was adding noise ,t it's fine now with the 2n3904 , but the pot is usable only on the half of his range, like it's doing all the job but with a limited sweep.


On your layout the voltage diveder is slightly different for 9 v it give 0.3 v more at the output, but you get the same issue ?

[nonoxxx]

We should wait for a reply of some of this forum's electronic gurus 

[nonoxxx]

Personnaly I think if you are using really hot pickups , (active) and very hot pedal like EPboosters , the threshold pot will cut the  signal later .

Here is the reply of the guy of the website
"
I used MPS2222A, 2N2222, PN2222 etc with no problems.
I am using that gate in my pedalboard and it completely mute the signal at 2-3'o clock.
But the wide range is good when you using only two wires and conect the gate after some loud stompbox not guitar.
You can adjust range by adding serial resistors/trimmers  to the threshold pot (it's just voltage divider connected between vcc and gnd)

"

[Kennt82]

"really hot pickups , (active)" &  "completely mute the signal at 2-3'o clock."   

Same for me. Even with that, it's still usable.

[nonoxxx]

I think it's normal ,It 's better to cut a little sooner, than ... never      lol , do you have tried a real g string?


Personnaly I tested it with not too hot pickups (Dimarzio titan), the output is really lower than your EMG's and a ts808 clone and for me it cut all the signal between 12 and 1 'o clock.

[anotherjim]

The use of Q4 makes no sense to me. Despite a bias setup that looks over complicated, surely its performance is entirely dependant on any particular transistors current gain?
High Hfe like 2N5088 might work better if C & E are swapped for much lower gain.

I have a suspicion (only that) that that C7 should be at R19/R20 and not on that THAT
Then Q4 would act as a power on delay due to the charge time of C7, which is the only reason I can see for it existing.
Anyone got a better insight?

[anotherjim]

Having read the THAT datasheet. Pin 5 to the negative supply should be via a resistor that sets the device current (no signal) to 2.4mA. It has everything to do with keeping the devices internal circuits happy but nothing to do with VCA operation.
Examples have 5.1k with +/-15v supply. +9/0v will need less resistance.
Working examples of the design you have are probably entirely due to a lucky Hfe for that transistor passing the right amount of current.

[antonis]

The use of Q4 makes no sense to me. Despite a bias setup that looks over complicated, surely its performance is entirely dependant on any particular transistors current gain?
High Hfe like 2N5088 might work better if C & E are swapped for much lower gain.

I have a suspicion (only that) that that C7 should be at R19/R20 and not on that THAT
Then Q4 would act as a power on delay due to the charge time of C7, which is the only reason I can see for it existing.
Anyone got a better insight?

Jim, maybe it's used as "current source"..
(I can't see on which specific leg is connected so I can't say if there indeed is a need for this..)

On a second thought, it should have some kind of Collector "load"..

[anotherjim]

Yeh, I think it's meant to be a current sink, but I suspect its been copied from another circuit that works differently.
It's connecting the chip negative supply. THAT corp suggest a fixed resistor for it.

[nonoxxx]

Do you  know some ressources that explain how this kind of chipset works ?

[anotherjim]

Most of what there is can be found here....
http://www.thatcorp.com/2181-series_Trimmable_Blackmer_IC_Voltage-Controlled_Amplifiers.shtml#spec

[Kennt82]

In 2011, there was an almost 40 page thread here trying to figure this out. It produced
many schematics and layouts that had a few things off and was closed, presumably to not
lead anyone astray.  I could only find a few pages on Wayback and this early posting by
Galego, who drew the schematic mine is based on says this:

(page 15)
https://web.archive.org/web/20111112041345/http://www.diystompboxes.com/smfforum/index.php
?topic=88902.280

"Why did you use a 2N2222? You're supposed to use a MPS2222, looking at the datasheets,
the MPS seems to have half the gain of the 2N2222, I don't know if it could be the reason
why yours isn't working properly, but I'd start there."

The follow up pages won't appear. For most of our uses, those 2222's seem interchangeable,
but maybe in this case it matters?

[rankot]

Have anyone successfully built this? Which schematic / PCB did you use?

[Kennt82]

Nonoxxx got his working.  As I wrote on the last page, I used the Sabro layout, along with his gstring add on. There may me some slight differences, especially on the loop connection. 

It works wonderfully. I can use a setup with a hot pickup and maxed out heavy distortion pedal slamming into a high gain metal amp resulting in a mess of feedback/hum/hiss where the noise is as loud as my playing. This will quiet it up completely.

The issue was the threshold pot being useless past noon. My first quick fix was using a an A10k Log pot. That helped a bit, but after adding 5k trimpots to lugs 1# and #3 (that's the most useful one), I can really adjust it and make full use of the threshold control.

[pinkjimiphoton]

Thanks Antonis,
I asked that to be sure that the ic is authentic, before to go more in depth .

Here is the link for the schematic and instructions https://guitar-electronics.eu/pl/p/file/42fd5a13487d279cf2d36d6798969890/Decimator-G-String.pdf

It's in polish but google trad work fine .

i built this from the kit above, began boxing it tonite. couldn't figure it out at first cuz the nomenclature was a little weird.
you plug your guitar in to guitar in
you plug guitar out into all your fx
you take the signal at the end of the chain before echoes/reverbs and that goes to the gate in<dec in>
you take the gate out <dec out> to your echoes/reverbs/amp
i appear to have mixed up some wiring that i gotta sort out tomorr...err... today but its definitely working and doing its thing.

karol's kit seems to be alright. nice parts in it, bit of a trick to fit in a 1590b but looking forward to trying it. i'm not crazy about my ns2 i'm using now.

but anyways, yeah, at least the decimator g string variant is built and working and the link above has a legit kit.