Another Ross Comp Debug...yay!!!

[ppatchmods]

Ross Comp from the vero:
http://www.aronnelson.com/gallery/main.php/v/Toneys-Album/Rossv4.jpg.html

I get no output without bridging some of the traces with my finger but all i get is output and volume when i do that. no sustain/compression. i omitted the attack/decay switch and took r1 from C to B of q5 and took out r3 altogether. i also used mpsa18's for trannies. i also used 2 1k's instead of a trim(i know there is a debate over this but i thought i would try it). other than that everything is stock.

q5  
E=8.39
B=7.77
C=8.92

q4
E=0
B=0
C=8.92

q3
E=0
B=0
C=7.77

q2
E=2.29
B=2.45
C=6.57

q1
E=2.14
B=1.44
C=6.72

IC
1=0
2=3.83
3=3.83
4=0
5=0
6=8.92
7=2.45
8=0

circuit protection diode checks out
other 2 diodes are 0v @ both ends

Thanks in advance for any help! I've been debugging/starring at this thing all week. i think i even dreamed about it once...it was a glorious dream. i compressed it into a few minutes and it sustained all night...sorry maybe i should move that to the circuit humor thread....or maybe not

[jkokura]

Looks like somethings wrong around Q3 and Q4, perhaps they're in backwards?

Have you got an audio Probe?

Jacob

[ppatchmods]

they are in right. i'll try to probe around them this afternoon. i compared the readings to others and they seemed to be close.

[Govmnt_Lacky]

Looks like somethings wrong around Q3 and Q4,

I agree with Jacob. Those trannys look suspicious (no pun intended!)

Never seen a proper working transistor with voltage JUST on the Collector.

[ppatchmods]

the readings do seem to be off compared to fuzz central...

here is the comparative:
http://fuzzcentral.ssguitar.com/ross.php

[MikeH]

q5 voltages look sketchy to me

[jkokura]

No offence, they might be fine and the problem is elsewhere, but when you get those kind of readings my first gut instinct is to see if they're in backwards. I'm not sure of the Vero layout you're using, nor do I know if it's verified. I have seen that transistors made to the same specs by two different companies can have different pinouts. Double check the pinouts of the transistors you're using, and if they're socketed, try just turning them around.

I think it's fairly safe advice for me to say, "don't rely on the image layout to tell you how to orient your transistors, rely on the pinout of the data sheet."

Jacob

[Toney]

 Hi, the layout has been verified many times over and shows "E" for emitter expecting standard 2n5088 EBC pin out.

As always, soldering, parts ID and with Vero missing trace cuts are the most likely culprits, closely followed by my favorite -mucking up something obvious in the pots/jacks when I am tired and not concentrating at the and of a build  
Do you have a loupe or magnifying glass?
I'd start with a really careful inspection of you soldering and then move on to a track by track continuity test with the multimeter to eliminate any bridges , they can be mighty sneaky!
Next, break the layout into segments around each active and with a pen tick off and verify each component.
You'll get it up and running

[ppatchmods]

ill get a magnifying glass after it. the trannies are in correctly. i built 2 of these lastweek with the same parts. i had to troubleshoot both of them but got them going after a day or so. this one is a bit different. i'm not using the attack/decay mod on this one. i'll keep checking it over. thanks guys

[ppatchmods]

i'm getting 0v readings on both ends of r19 & c16 going to lev 3, and also the neg side of c17 going to lev 1. that means i have nothing going to my volume pot? c17 is connected to ground so i understand that, but i'm concerned with r19 & c16. i replaced c14 to see if that was the problem but it gives me the same readings. anybody have a working comp they can take some readings on for me? thanks

[JDoyle]

All of the voltages look off in one way or another - except Q4, that looks pretty good.  

Q5 feeds the current into the OTA and needs to be on for anything to come out - because the OTA needs current into Pin 5 (the Iabc port) in order to even turn the circuit on.

With Q5's base below it's emitter it isn't on. Check to make sure it isn't backwards because the emitter is about a diode drop above the base - that screams misorientation.

Q4 looks good, if 8.92 is your raw battery voltage BUT Q3's collector should be the EXACT same as Q4's, in your case there is more than a volt difference, that is a lot for a point on the circuit that should be directly attached. Find out why this is so.

Vbias should be about one third of V+: 27k/27k+56k = .32 which allows Q2 to be ideally biased with maximum headroom for a phase splitter. With a V+ of 9V Vbias should be about 3 volts and therefore the emitters of Q1 and Q2 should be about 2.4V

Q1's base is below it's emitter - again by about a diode drop. Check orientation.

On the IC pins 6 and 7 are the only two active pins (1 and 8 should never measure a voltage as they are unused) which look right. Pin 7 is at a proper Vbias and pin 6 seems to be at V+. Pins 2 and 3, the inputs, are biased higher than what should be the bias voltage so something is screwy there.

But the biggest problem overall is that Pin 5 is at 0 Volts. This means the OTA is off. Pin 5 is a diode input to a current mirror. The current into pin 5 is mirrored by another transistor and forms the bias current of the whole OTA. So for the OTA to be on, pin 5 MUST measure at least 0.6V

My observations: Don't discount a backwards transistor or diode (check those too). There is something wrong with the way you omitted the attack decay switch - the collectors of Q3 and Q4 should be EXACTLY the same. Something is also wrong with your biasing to the OTA and the Q1, Q2 and Q5 transistors - but could just be because they are in backwards.

Good Luck!

Regards,

Jay Doyle

[ppatchmods]

jay, thanks for the reply! i have checked the pinouts some many times that i will forever have them memorized.    i agree with q3/q4 readings being off. just yesterday i started getting a .6v reading on pin 5 of the 3080 so that is pretty good. i will look into the way i omitted the switch and maybe just add the switch instead. also, i'll take a close look around those above mentioned trannies. more than likely i have something bridged that i can't see with my naked eye. thanks again and i'll post my findings.

[ppatchmods]

a couple of corrections: pin5 of the 3080 is measuring .06v not .6 so something is going on there. the problem definitely looks like an improper bias of the 3080 or the B of q5. because q5's B is off, it is throwing the C's of q4 &q3 off which are both measuring at 7.75-7.77.  also, i got the order of the pins wrong on the 3080, so 5-6-7-8 are reversed.

could the bias of the 3080 be throwing everything else off? i built 2 others a week ago, and used the exact same parts with no issues...aside from some minor soldering mishaps. i'll keep poking around. thanks

[ppatchmods]

can the biasing of the 3080 be causing such a low reading on pin 5 of the 3080? i used 2 1k resistors instead of the trim.

[ppatchmods]

was messing with this at lunch and realized that the C & B of q5 directly affect the voltage of pin 5 of the 3080. this was probably pointed out in one of the comments by Jay, but it clicked for me when working on it.  i'm pretty sure omitting the attack switch is the problem. i'm gonna add it tonight and see what i get. i'll let you know. thanks

[ppatchmods]

ok...tried putting a 3904 in q5 and i get the same readings. i also tried to adjust the bias and i get no change on pin5 of the 3080. i tried the do the attack mod and the readings on q5's E & C are even lower. any help would be appreciated. i've been staring at this thing too long. 

[Toney]

 Hi,
Sorry i have been away for the past few days - I meant to shoot this over to you.

http://www.aronnelson.com/gallery/main.php/v/Toneys-Album/Ross+Compressor+-+No+mods.PNG.html

Make sure your mod to the mod (back to standard) goes like so.
Just remove R3 and the switch and then flip R1 so it is connecting between the base and collector of Q5.
Have a good look at Q5... its collector is directly connected to 9v, it's base to R1 (150k best to check it when you flip it over) and the collectors of Q3 and Q4. It's emitter to pin 3 of the sustain pot (500RA check this too). How about C4 (Is it 10uF? Positioned correctly?)
From there check  R21 (27K check!) and on to pin 5 of the CA3080 (which you have double checked is orientated correctly.
Quadruple check it for bridges - do a continuity test between tracks 1-6 with the trannies out.
Good luck 

[ppatchmods]

toney, thanks. this is how i had it wired so i must have a solder bridge somewhere. i've gone over this board about 20 times it seems like. i'll check what you suggested.

also, i think i've been calling the base, the collector on the trannies. i hope i haven't confused anyone...but myself. thanks

[ppatchmods]

question: is the voltage to pin5 affected only by r21 (27k) or does the sustain pot have a big affect on it?

also, would the sustain pot have an affect on q5 or does q5 affect the sustain pot?

i'm pretty sure that q5 is my problem. i replaced it with a 3904 and got the same readings.

[MikeH]

i'm pretty sure that q5 is my problem. i replaced it with a 3904 and got the same readings.

If thats the case I'd look a little more for a) solder bridges (they are SO easy to get with vero)  and b) an incorrect component/component connected to the wrong track.