ross compressor

[blanik]

hi all, i'm boxing all the effects i've been doing for a while (russion big muff, pulsar, orange squeezer, ross comp, LPB 1, second rat... more boards coming...  )

so far they all work on the first run (no credit here. i'm using tonepads PCBs...) now it's turn to box my ross comp and behold !..  it doesn't work...  when i started it the first time i heard a loud POP in my amp... then, nothing.. after toying a couple of seconds i got some faint sound when the 2 pots were maxed... but you can tell it's not normal... not distorted or anything, just very low volume (and being a comp, i couldn't tell if the compression was working as it's supposed)

here's some values i got...

IC
1: not connected
2: 4.27 V
3: 4.27 V
4: 0 V (grounded
5: 0.68 V
6: 2.81 V
7: 8.95 V (battery value)
8: not connected

D3: 536     (662 reversed reading)
D2: 538     (661 reversed reading)
D1: meter freaking out?? (normal beep when i'm connected i the right direction but no value (or too high?))

Q1: E: 1.36 V
       B: 1.89 V
       C: 7.59 V

Q2: E: 2.18 V
       B: 2.81 V
       C: 6.76 V

Q3: E: 000 mV (looks like grounded on my meter)
       B: 00.2 mV
       C: 8.57 V

Q4: E: 000 mV (looks like grounded on my meter)
       B: 00.2 mV
       C: 8.57 V

Q5: E: 8.04 V
       B: 8.94 V
       C: 8.94 V

i'm reading 4.81M between input and ground...

any clues? 


r.

[Thomas P.]

I think there's a problem with Q5: its base should be at the same potential as the collectors of Q3 and Q4. From your readings it looks like it's somehow connected to the supply voltage.
Check for solder bridges between collector and base of Q5.

Regards,
tomboy

[blanik]

i checked but can't fing any solder jump... 

is it possible that if Q5 busted on power up, that it would short internally?
(i used 2N3904 for all 5... can i replace a single one of those with 5088? don't have more 3904..)

R.

[bancika]

yeah, you can. I'm messing with my build and tried all combination with 2N3904, 2n5099, 2n5089, 2n2222A and they all sound similar (crappy). The point is, mine has some problem

[Thomas P.]

I just looked at the layout and to me it appears that there is no way you could get different readings on either the collectors of Q3/Q4 and the base of Q5 since they are connected to the same trace. Even though Q5 would be damaged the reading of the collectors of Q3/Q4 should be the same!
This yields to the question: did you measure correctly (sorry if it sounds offensive - I mean it very objective!) - the voltage of that particular trace should be the voltage you need to know.

Of course you can replace Q5 with a 2N5088 but as I pictured before I don't think this will solve it. Maybe you could remeasure and tell where exactly you've measured.
For now I would advice you to check the partsvalues in this area - I will measure mine and compare it.

Regards,
tomboy

[blanik]

sorry, you were right, seems like i made mistakes reading some values... (marked with **)

Q1: E: 1.36 V
       B: 1.89 V
       C: 7.59 V

Q2: E: 2.18 V
       B: 2.81 V
       C: 6.76 V

Q3: E: 000 mV (looks like grounded on my meter)
       B: 00.2 mV
       C: 4.98 V **

Q4: E: 000 mV (looks like grounded on my meter)
       B: 000 mV grounded **
       C: 4.98 V **

Q5: E: 4.98 V **
       B: 8.86 V
       C: 0.00 V grounded **

the IC readings were ok

R.

[Thomas P.]

are you sure about Q5? because the base should be 4.98V (according to Q3 and 4). Also collector and emitter need to be switched.

regards

[blanik]

the problem might be around that area... the diode D1 gave me weird values and it's connected straight between ground and Q5...

what are the values of your D1?

R.

[blanik]

grrrr, i removed D1 and Q5 to check them alone.... D1 was correct 530 on the meter... Q5 hFE was 172 on the NPN side of the tester... i put back a new 914 for D1 and i tried a 5088 for Q5... nothing changed still have the same very faint sound (about 1/5 of the bypassed signal...) when pots opened wide...


*sight*

R. 

[Thomas P.]

did you check resistor values?

another thing: when I measured my (working) unit yesterday I couldn't get a constant value on the collectors of Q3/Q4 (and base Q5). It starts at 8.5V and goes down to 7.1V and then it somehow changes a bit. did you experience something like that?

and maybe it's time to tell which revision your layout is after you built it - because when I looked at it yesterday it looked different (colorwise) from some time ago.

Regards,
tomboy

P.S.: you did check if you wired the pots backwards, did you?

[bancika]

check Q3, Q4 and Q5.
I fixed mine yesterday and here are my voltages:
Q3, Q4
E: 0
B: 0.65
C: 9.5
Q5
E: 9
B: 9.5
C: 9.6
Hope it helps

[Thomas P.]

my Q5 is as following:

E: 8.51V
B: 7.87V
C: 9.05V (aka V+)

In comparison with bancikas measures it seems your voltage drop at the base is too low. Now if you look at the schematic you have this 150k resistor from V+ to the collectors Q3/Q4 and the bas Q5.
From the measurements the resistance from this point to ground appears to be (much) larger (say >1M) than 150K because almost all voltage is dropping across it. If you would have had an 1.5M instead of a 150k the voltage would be ~4V.
So my advice for now is check this particular resistor to be 150k!

Regards,
tomboy

[bancika]

It's OK, I made MH variable recovery mod with alters 150K resistor. In the middle position which gives 160K I get
E: 8.56
B: 7.9
C: 9.2
which is very close to yours

[blanik]

hi, i started to check the resistors color codes with a flashlight and noticed that R 150k coming out of IC 6 is actually 150 ohm... could tah be it?

R
could i have busted the IC internally but still get the correct values?

[Thomas P.]

do you mean the one going to Vb?
This could be a problem (of course, you should always check for correct population of the board before posting - no offens)

Regards,
tomboy

[blanik]

don't worry, i checked twice but on the cheap resistors i used it's hard to differenciate between purple, brown or gold... there was just a slight difference in color between the 3rd rings of both...


i had checked pot wiring too...

*update*

i changed the 150 ohm for a 147k (didn't have 150 so i wired 100k and 47k) WORKS NOW!!! 

first time i try the ross comp... i noticed a very slight loss of bass freq (subtle) when it's on and i hit the 6th strigng compared to bypassed signal... and to have same volume on or off the volume needs to be turn up about 75-80% of it's full travel.

are those details normal for the ross comp?

R.
thanks for all the help!

[Thomas P.]

actually I had the problem of too much bass - but I think I built the dynacomp and got rid of some small cap.

For the controlls: I use mine with Volume at ~80% and Sustain at ~60% - ~90%

Glad that it worked for you!!!

Regards,
tomboy

[blanik]

it seems the main (only) difference between the dynacomp and the ross is some tweaking in the EQ... people say the Ross is "clearer" more "transparent" wich all mean it's got more highs (or less lows) lol

does anyone have mods or tweakings to put back a little bass in the ross?

R.

[kvb]

double the size of the output cap to .1uf for more bass output.

I believe the input cap should stay at .47uf to avoid flabby overdiving of the chip, but I did not try it myself. So . . .

[blanik]

heuuu dumb question... wich one is the output cap? 
could it be the 0.05uF before the 10k that goes to the wiper of the level pot? (just a guess here...)

R.

PS on some earlier tread about trimpot adjustment for Ross or Dynacomp, RG said: "In most cases, you can either set the pot to middle and forget it or replace it with two equal value resistors and forget it."

well i can confirm that to be true, in mine the sound (and backgorund noise) is only influenced when the trimpot is completly turn one way or the other, the whole middle range (about 80% of the total trimpot travel) doesn't make the slightest difference in sound or noise level.... next time it's gonna be two 1k resistors...