how could i have possibly screwed this up this bad? ;) ross distortion

[pinkjimiphoton]

so...used to have one of those tan ross distortions. always liked it, but had sold it or bartered for a satchel or something, i dunno, years ago.

so i figured..nothing to it, figured would give me something to do while shirking some other responsibility.

so i found this here schematic, which is supposed to be verified...



and figured, ok, let's work up a vero... so i did. this is it.



but...it don't work. i can kind of get it to work, but that's only an annoying oscillating howl...the distortion pot does nothing (and am i right that on the schematic the jumper should be towards the +, not ground?) at all,  and i'm getting weird voltages i'm not expecting.

pin  1 4.12
     2 4.17
     3 3.61
     4 0
     5 0
     6 8.0
     7 8.0
     8 8.28

i've tried a lot of different chips, some motorboat, some oscillate at bug pitch.

if i pull the dang chip, it passes audio. wtf?

i've looked this thing over, traced it thru point by point, as far as my simple brain can see, it matches the schematic..

is the schem wrong maybe? anyone else built one of these?

thanks!

[slacker]

Layout looks good to me. Pin 5 should go to point N on the schematic not ground but I don't think that's causing your problem.
Your voltages look correct for the pin 1,2,3 side of the opamp. I would check the trace cuts, especially the one at h4, if that was not completely cut it would stop the gain pot working and give the thing stupid amounts of gain, which might cause your oscillation problem.

[Gurner]

To me those two VCC/2 1M resistors (two R6s? ....wtf) look too large & may cause unstable type probs...I'd use something like 47ks - even better use that unused opamp as a voltage follower & feed in the junction of those two resistors into the unused opamp pin5 (remove the gnd that's  on pin 5 presently though!)  - the output of the opamp then becomes a nice low impedance vcc/2 (vref)

If the gain pot has no effect, then this is the area of exploration.

Try pulling the top leg of R4 out & instead temporarily put a 500k resistor from the lower leg of C3 to ground (which would yield a gain of about 2) or a 1M resistor (unity gain) ....this should at least give us a little more info to go on.

Pin 1 DC level should be almost identical to pin 3 ....it's not (that's possibly because there's a problem somewhere along the path R3->C3->R4 ->RV1->gnd.

[Gus]

Can you try a 47uf, 100uf etc for C7?

pins 5, 6 and 7 should be the same voltage

If the chip is in a socket remove the chip apply power to the circuit and measure pin 3 voltage again should be at 1/2 the 9VDC.  Now I don't know what the input Resistance of you meter is and it could be loading the 1 megs
SO
here is a simple trick measure pin 3 to ground and measure pin 3 to 9VDC even if the meter loads the 1meg the voltage divider being made of two one megs should show the same voltages even if it is not 1/2 the 9VDC supply.

You can try moving pin five from ground to N. I would add a 1k in series with pin 5

As noted by others both R6's could be made lower 100K would work fine with a 1meg you might want to make C6 10uf.

[pinkjimiphoton]

thanks brothers,
i too thought this schem looked a little dicey, but it matches all the others i've found.

at the suggestion of you guys, and the guys on the other forum, i've taken the liberty to make some changes...

i am gonna try and change c7, but if that doesn't work, am scrapping the whole project and re-doing it.

i've done another layout with the changes i'm making, and will post it when i'm done if it works out.

it MAY be a problem with the chips, too... some of these gave me similar problems on another cct recently, they could be cooked and i don't know about it.

onwards and upwards..

[Johan]

it MAY be a problem with the chips, too... some of these gave me similar problems on another cct recently, they could be cooked and i don't know about it.

..since it belongs to te D+/dod250 family, I'd try a 1458 instead of 4558. its a dual 741...if you can still find one.
J

[pinkjimiphoton]

tried 1458, 5532, tl072/82

all the same results.

[wavley]

it MAY be a problem with the chips, too... some of these gave me similar problems on another cct recently, they could be cooked and i don't know about it.

..since it belongs to te D+/dod250 family, I'd try a 1458 instead of 4558. its a dual 741...if you can still find one.
J

The original was a 4558, so the circuit should work with one.  I miss mine, this has been on my list to build for a while.

Did you forget one of your cuts? Looks like 4d, 4h, 8e, f, g, and h

Good luck Jimi!!

[pinkjimiphoton]

alright.... as it turned out, there were multiple problems... the unused side of the chip was oscillating, and that was making everything nuts.

i tried tieing pin 5 to vref, no dice. ended up shorting pins 4,5,6 and 7 together.
now we had some output, bit still no distortion.

so i worked my way back from the pot, and tested everything. turned out to be bad solder on the 1m resistor between 1 and 2. fixed it. gain pot was achieved.

tried a 50k gain pot...sounded pretty good, but went with the original.

i swapped out c4,c6 and c7, added one more cap (to help nuke the maggots chewing in your ears way up high noise) and a transient protection resistor. also added reverse polarity diode.

this thing is freekin SWEET. i tried every opamp i had, and some sounded killer, some not so much. my favorite was the 1458, but in the end, it was lacking a little body in the mids...so i tried stacking a tl072 on top of it, in parallel.

i LOVE IT. sounds just like the distortion i remember from my youth..stacking the opamps gave it a slightly different charachter, but i like it...stupid pedal trick to come soon.

the best part? i fit it all on the original board with a couple minor modifications. (yes, i socketed the chip, always do)

so...verified...here ya go, Ross Da Boss...the minor reworking of the Ross Distortion (the tan one)

[Gus]

Here is something I posted before

Use two duals
one for distortion and 1/2 power supply ref
2nd for the input buffer and output gain stage

[pinkjimiphoton]

nice!! i gotta look at that closer when i'm awake...thanks gus!

i took this thing out for a spin tonite.. it definitely needs a power supply. them two chips suck a battery dry quick, and you get JAGGED SHARDS OF FUZZ. it's kinda cool, it sounds "broken"... a lot titer on a wart, i'm gonna try it on 12 v and see if i like it better. still gotta tweek a little...still haven't found a proper "little" amp to monitor with... they always sound different before they get used live.