Ross Compressor debug- IC pin value wacky?

Started by jlullo, January 29, 2007, 12:04:13 AM

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jlullo

Hey guys,
I finished my ross clone tonight (layout from tonepad).  I used all stock parts except for 2n5088 trannys (as suggested by fuzz central).  I wanted to check my values before i popped my IC into the socket and got these.  What's the deal with pin 5?  fuzz central lists that it's supposed to be 0.633v.  Also, how do my transistors and diodes look?

could someone please help me with this?

Q1
C- 7.24
B- 2.43
E- 2.03

Q2
C- 6.93
B- 2.89
E- 2.35

Q3
C- 9.15
B- 0
E- 0

Q4
C- 9.15
B- 0
E- 0

Q5
C- 9.28
B- 9.15
E- 8.84

IC
1- 0
2- 4.82
3- 4.83
4- 0
5- 8.40
6- 2.90
7- 9.30
8- 0

D1
a- 0
k- 9.29

D2
a- 0
k- 0

D3
a- 0
k- 0

markm

May be a good idea to check your resistor values as something is wrong with the voltages on the IC.
Look toward the P/S resistors and double check them.

MikeH

You probably already noticed, but the IC is oriented upside-down on the tonepad layot.  Meaning the notch faces the bottom of the board, as it is oriented on the page.  Outside of that I'd check for solder bridges and incorrect resistor values, it seems like you've got some stray DC somewhere.
"Sounds like a Fab Metal to me." -DougH

Ge_Whiz

Sorry, but did you say that these are the values obtained without the IC in the socket? If so, the IC socket values are probably meaningless.

jlullo

yes, those are the values without the IC in socket. should i retake them with them in the socket?  i thought it would be the same

jlullo

#5
Quote from: markm on January 29, 2007, 08:26:18 AM
May be a good idea to check your resistor values as something is wrong with the voltages on the IC.
Look toward the P/S resistors and double check them.

mark, what are the p/s resistors?

markm

Sorry.
The resistors in the power supply where the voltage divider is. 27K and 56K.

R.G.

Pin 5 is pulled to the negative supply by two diode drops inside the chip. The circuit outside the chip pulls pin 5 up through a 27K resistor and the sustain control to the emitter of the control voltage buffer transistor. With the chip out of the socket, pin 5 should be high, but less than the power supply.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

jlullo

#8
RG,
so does that mean that i'm cool?  do all of the values for the trannys and diodes seem right?

mark, i checked those out and they are the correct resistors w/ no solder bridges. 

jlullo

alright.  i just popped in the IC, and theses are my new values:

1- 0
2- 4.62
3- 4.64
4- 0
5- 0.61
6- 2.88
7- 8.98
8- 0

seems pretty close now, right?

jlullo

i just tried it out and it works perfectly!  i'm so excited.  i had such a hard time getting my first build to work, and no problems with this one.  Just one question, and i'm sure you all know what it is about-

i know that you're supposed to either set the trimpot in the middle and forget it, or turn both knobs all the way up and adjust it until you get the most noise.  I did the latter of the two, and didn't find a spot that had more noise then the other.  what should i be listening for exactly?

markm

I adjust mine by turning the comp pot up full and pluck a string on the guitar turning the trimmer back and forth listening for gating and setting it in the middle of the two points at which there is gating/distortion in the circuit.
Works for me.
A bit OT here but, I must fess up and say that I tried R.G.'s two 1K resistors in place of the 2K pot and it worked perfectly...Thanks R.G. for being right again!!  ;D

jlullo

mark, where do you set the level (while balancing the trimpot)?

markm

I just have it at unity....too loud and the Wife gets bitchy and then.....Mark don't get none!  :icon_lol:

jlullo

i think it got it.  there were two distinct points where it was gating, and i juust set it in the middle of the two points.  this thing sounds so good.  thank all of you for all of your help!

markm

Yeah that's where it oughta be.
Congratulations and enjoy....that's a terriffic circuit!