tube screamer - couldnt make it work

[okuzster]

i built this, didn't worked.

while input is connected, i matched the output to the input and followed the line till i stop getting signal, and it stops at 1uf np cap (red dots on scheme and layout).

i am quiet much a newbie but i am thinking the problem starts there. do you agree, do i need new caps? or what can be the problem?

thanks

[graemestrat]

A first guess would be to check if your IC is in the right way around?  Then check your dc power and the bias supply 4.5v.

[duck_arse]

voltages, okuzster, voltages! each IC pin, each transistor pin, and the Vb voltage for kicks. also, photos of what you've built. please.

what sort of "NP" cap did you use?

[GibsonGM]

This is a good format for listing out those voltages the Duck is asking for:  http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Most likely the problem is not big, just a simple mistake somewhere.  Those voltages will help to find it!   Don't short your IC pins together as you probe them with your meter...

[nonoxxx]

The sound stop before or after the coupling cap? And are you sur you are using the good transistor type?

[Kingmafw]

Hi okuzster,

Share us some pictures of your build (front and back), please.
I'm sure members of DIYstompboxes can help you.

[okuzster]

sorry for late response, i was a bit busy with some other stuff. thanks all for replies. here are photos:





voltages are;
battery is 9.7v
for ic leg 1; 7.4v
leg 2; 0.8v
leg 3; 0.7v
leg 4; 1.4v
leg 5; -
leg 6; 0.4v
leg 7; 5.4v
leg 8; 6.2v

for both transistors, collectors 7.2v, base and emitters are 1.4v

Vb is 2.4v

1uf np caps are kind of film caps i think, i am not sure.

the sound stops after the cap. i am not sure if transistors are good, i am using whatever i can find from local stores.

[antonis]

Both transistor Collectors & Leg 8 of IC should stand at exactlly your battery voltage..

Both transistor Bases should stand about 600mV higher that Emitters..

Vb should be half of battery voltage..

V at leg 3 & leg 5 should be Vb..
(exact value depends on your multimeter impedance..)

V at leg 4 should be 0 Volts..

Obviously there are more than one wrong part placement/value.. 

I should start tracing from Vb, disconnecting one by one all bias resistors..

[bloxstompboxes]

I believe the problem is that he has mirrored the mask when etching. If you look at the tonepad part layout against his picture of his board component side, they are mirror imaged.

[duck_arse]

I believe the problem is that he has mirrored the mask when etching. If you look at the tonepad part layout against his picture of his board component side, they are mirror imaged.

good catch.

funny how builders handle this when it happens, and it happens a fair bit. in your case, okuzster, you've managed to swap the IC and the transistors [correctly] and electro cap direction, which most people would miss. the top tantalum cap would need to be reversed as well.

how to fixxe? either pull the IC out and bend its leads over so it is upside down, then plug it in and see, or pull the socket out of the board, and solder the IC to the copper side, without socket. your IC might be fritzed as is.

and this:

leg 4; 1.4v
leg 5; -
leg 6; 0.4v

we don't allow " - " in our voltage measures. if it is 0.00, write that down. if it really does read "-", tell us that.

[okuzster]

i swapped the transistors' legs but forgot the IC, right. gonna try putting the IC updside down then. or maybe building new pcb, mirrored this time as it should be.

with "-" i try to meant 0.00. it didnt get any value. i ll write it right next time.

[deadastronaut]

my son in law did the exact same thing ...your not alone. 

[okuzster]

i put ic upside down and it worked, thanks all. drive pot was feeling like always at max but that probably only a soldering problem or something, will look at that tomorrow. it was my first working stomp box, it meant a lot.

[Marcos - Munky]

It's a common mistake, I did it a lot when I've started

Btw, nice pcb tracks.

[thermionix]

drive pot was feeling like always at max

Check for a short (solder bridge or copper scrap) on the board around where the drive pot wires connect.