debuging an isp decimator g string kit,That2181c questions

[nonoxxx]

Hello

I had buid an isp decimator kit and I encounter some problem when trying to set the trim pot, in fact the result while moving the trimpot is either too lound and fuzzy or too low and noisy.

What are the corrects voltage for the THAT 2181C chipset?

I have :

That 2181C :
1: 3.66
2: 4.8
3: 4.2
4: 4.8
5: 1.45
6: 4.20
7: 8.4
8: 4.20

also i would like to know if it's normal that the THAT  ic I got in the kit dont' have the notch that indicate the first pin.

Thanks

[antonis]

Mass production notces are costly.. 

(It should have a dot pointer..)

[nonoxxx]

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 .

[antonis]

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

Plz define "authentic"... 

[nonoxxx]

not a fake

[antonis]

If you "google" THAT 2181C you'll get plenty of pics and datasheets with the vast majority in Chinese symbols/ideograms..
(but all of them have a notch..)

So, may your IC (without notch) be considered as the "king of fakes"..?? 

[nonoxxx]

so it is a fake fake

[Hatredman]

so it is a fake fake

What about some pics of your faked fake?


--
Scarlett Johansson uses a Burst Box with her Telecaster.

[nonoxxx]

thanks, I will take some pics today,
I retried it and in fact a can achieve an unity gain but there is a king of light hiss added when engaging the noise gate , (this hiss is not present when the noise gate is off ) and when  increasing the threshold the hiss disappear but come back when playing (gate opened)...

[nonoxxx]

I tried to audio probe the circuit , but I must admit that I don't know what to expect of this circuit .

Does someone can give me some clue of what I should check ?

Is it normal that I get no audible sound from the output of the THAT2181c, the sound seems like disappear and reappear after the opamp U1A (with the noise )

[PRR]

> no audible sound from the output of the THAT2181c

That is normal. (The output is a current at zero voltage swing, converted back to a voltage by the following opamp.)

[nonoxxx]

Thank you PRR..

So I am not out of the woods ... ( I tried to translate a french expression lol)
I take a look at the THAT corp website but the documentation is too complicated for my electronic level .

Do you know some source that explain how this kind of circuit work ?

And concerning the zero voltage swing conversion, if I understand correctly the noise  is not present at the input of the THAT chipset so it can come only from the conversion of this voltage swing  or from   the the pin 5,2 or 4 but I noticed nothing when I made the audioprobe

[antonis]

Maybe this helps...
(it's a basic block of variable Q filter using 2181 as VCA..)




Or your query is about how a Voltage Controled Amplifier works..??
(an inside anatomy of the IC..)

[nonoxxx]

My query was about how a Voltage Controled Amplifier work ? lol
...

At this time , I try to use all my neurons, to understand the data sheet  and how these stuffs works lol

[nonoxxx]

I find the problem,

I suspected the MPS2222A so I desolder it and I  put a socket and try with a 2n3904 , now it works
, just the potentiometer range is different  ( the max threshold is at the half of the pot range  )  but the gate is doing a great job ,  I will email the seller to get another MPS2222A. (strangely it didn't work with a 2n5088)

Thanks a lot for all your replies.

[Kennt82]

"max threshold is at the half of the pot range"   That's my experience using a PN2222A.   I guess I should try a MPS2222A (with a few spares).  What are the differences I should be paying attention to on the spec sheets?

[nonoxxx]

sorry it was not a MPS2222A but a pn2222A in the kit. so the same as yours

[nonoxxx]

but despite the different range with the 2n3904 the threshold work fine, it's more dificult tu set but it work

[nonoxxx]

"max threshold is at the half of the pot range"   That's my experience using a PN2222A.   I guess I should try a MPS2222A (with a few spares).  What are the differences I should be paying attention to on the spec sheets?

Perhaps by increasing the value of the 22 k connected to the threshold pot (R8 on the PCB of my kit).

[Kennt82]

For clarity, mine is a build of Sabro's using this Galego schematic.  It has a 68k coming from the Threshold lug #2
http://2.bp.blogspot.com/-l2NRTEh3J54/T-8ppoN5mNI/AAAAAAAABm0/L-RQt6ykI84/s1600/ispscheme.jpg

You're using this kit, which has a different value there, as you said.  http://www.efekty-diy.pl/decimator.html (schem. in pdf)
But things are better for you now and threshold is usable over half ?