Ross Distortion

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Ross Distortion

Postby snmavronis » 06 Jul 2010, 01:13

I have an old tan Ross Distortion model R50 that I bought in 1982. It was my first ever pedal! The serial number is 0114591 and it was made in Taiwan. I still have the original box, store receipt, and warranty registration card. The bad thing is it no longer works. I probably fried something long ago using an adjustable 9V adapter using the wrong polarity. I'm going to try and repair it. Maybe just the RC4558N op amp or diodes are damaged. If I can't repair it maybe I'll reverse engineer clone it into a 1590B sized box like how the old Ross "script" versions looked. Funny side note about the Ross Distortion script version is that the PCB looks 100% identical in layout at least to the MXR Distortion+. I wonder what the connection is between Ross and MXR. There are no date codes on the pots. They are only labeled with their values: 181F - 500KC (Distort) and 181F - 50KB (Level). Here are some pictures of my broken vintage pedal maybe some can use for reference:

ImageImageImageImageImage
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Re: Ross Distortion

Postby gus » 06 Jul 2010, 01:27

I had a black Ross distortion IIRC it was a distortion plus circuit using 1/2 of the 4558 instead of a 741.

Power it with a battery remember to use a 1/4 plug in the input to complete the ground circuit and measure the pins of the IC the unused 4558 1/2 should have out to - in. The + in should go to 1/2 the supply voltage.
pins 1,2,3 should measure about 1/2 power supply voltage with no input signal , 4 to ground and 8 to +9VDC. Check the PCB for a burnt/broken trace, bad solder they look OK in the picture but pictures on the web don't always show trace breaks or bad solder.

EDIT it looks like 5 goes to ground and 6 connects to 7 so 5,6,7,should all measure close to 0VDC the 5,6,7 pin 1/2 of the the 4558 looks like the unused one

I would fix it and leave it stock
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Re: Ross Distortion

Postby Mattjames » 06 Jul 2010, 02:49

I had the same pedal... same prob... had to replace the reverse protection diode the lower red one (1N4148 I think)...
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Re: Ross Distortion

Postby snmavronis » 06 Jul 2010, 03:08

Mattjames wrote:I had the same pedal... same prob... had to replace the reverse protection diode the lower red one (1N4148 I think)...


Oh I hope that's the problem. I have some of those value diodes left over from my last project. Thanks.
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Re: Ross Distortion

Postby Mattjames » 06 Jul 2010, 03:13

I hope so to... here's some info that might help...
http://www.home-wrecker.com/ross.html

and I also would just repair it and leave it stock...
...
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Re: Ross Distortion

Postby snmavronis » 06 Jul 2010, 03:20

I'd like to leave it stock too. I noticed on that page you linked the photo shows larger CTS pots from 1978 and only 2 diodes. I guess after then compared to my picture they used 3 diodes and different 16mm pots or at least from Taiwan they did. I'll try to swap out that "red" diode (1N4148) tomorrow and see what happens. Another thing is I thought the Taiwan made R50 pedals were black instead of tan like this one?
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Re: Ross Distortion

Postby snmavronis » 06 Jul 2010, 18:05

So far I tried replacing the bottom "red" diode with a new 1N4148. But that didn't fix it yet. I still only get bypass clean tone and when I toggle the footswitch no distortion just silence.
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Re: Ross Distortion

Postby JOHNO » 06 Jul 2010, 23:49

Are you getting voltage to the IC?
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Re: Ross Distortion

Postby snmavronis » 07 Jul 2010, 01:36

I got 9V to the IC across pins 4 and 8 only when jumpering the 2 postive red wire leads of the DC jack to bypass it. It seems that the spring loaded metal inside the DC jack is not touching the metal going to the positive wire leads if you know what I mean causing an open circuit. When a DC plug is inserted it is supposed to open that connection to disengage the battery, but the way it is now there is no battery connection unless I short the DC jack positive leads together. I tested it that way and got distortion! At least the problem is minor and I'll replace the little DC jack to fix it. Thanks...
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Re: Ross Distortion

Postby JOHNO » 07 Jul 2010, 02:23

I'm glad you found the problem. Those crappy little dc jacks can be a problem at times. I use that kind of jacks in my builds and have had the same problem.
Just swapping part's in and out for no good reason is not a good way of debugging a circuit. You have to check for voltage first. And if there is none then find out why, like you have done. If there is voltage in the correct place's then get out your trusty audio probe and start at the input and work you way through the circuit following the audio path until you can find the cause of the problem. Building stomp boxes is one thing but debugging them when they don't work is another.
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Re: Ross Distortion

Postby snmavronis » 07 Jul 2010, 03:11

You are right. I was premature to change the one diode based on a suggestion without testing voltages and continuity first. Although I did think that I might have damaged it using the wrong polarity adjustable adapter months ago with the cover off when I saw it glow red and yanked out the plug. This is a learning experience and some mistakes come along with it, teaching you to know better the next time.
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Re: Ross Distortion

Postby JOHNO » 08 Jul 2010, 11:46

snmavronis wrote:I noticed on that page you linked the photo shows larger CTS pots from 1978 and only 2 diodes. I guess after then compared to my picture they used 3 diodes and different 16mm pots

Looking at the schematics at the home wrecker site I noticed the black version has three diodes for asymetrical clipping but, there is no reverse polarity diode drawn on the schematic. In the tan version there are two diodes for symetrical clipping but, no reverse polarity diode drawn on the schematic. But I can't find any gut shot's from a black version to confirm that it had three diodes for clipping. In the pic's I can find one version had two diode and the other had three diodes but one of those diodes was for polarity protection. Maybe there is an error in the schematic? Anyone have any further information?
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Re: Ross Distortion

Postby snmavronis » 08 Jul 2010, 13:23

Maybe the 3 diodes on mine is for asymetrical clipping vs an extra for polarity protection or maybe it's an interim version during the transition from USA to Taiwan. If no information surfaces to confirm things I'll try to start tracing this one out next week. Hopefully there is enough information in the photos I posted for others interested to do it too. This makes me curious.
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Re: Ross Distortion

Postby Mattjames » 08 Jul 2010, 15:08

Well back after puter crash.
The ross i had was bought new in 83 it was tan had 2 silicon for clipping and one for protection... it stopped working so i unplugged the wallwart threw in a battery to debug it and noticed the bat got hot which led me to that diode it was shorting to ground... after changing it out all was fine.. but i could never find a schem that matched the one i had....
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Re: Ross Distortion

Postby JOHNO » 09 Jul 2010, 07:43

snmavronis wrote:Maybe the 3 diodes on mine is for asymetrical clipping vs an extra for polarity protection

No the third one on yours is for polarity protection. I can see in the photo's it goes from +9v to ground.
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Re: Ross Distortion

Postby snmavronis » 13 Jul 2010, 14:37

I'm back from vacation and my dad brought me over some 1/8" DC power jacks so I can replace the broken one. The only difference is the original is a plastic enclosed type and the ones he gave me are open metal frame type. They almost look like miniature 12B stereo jacks. I can't find a web picture to show you how they look.

As far as my use of the pedal I have no problem replacing a different style DC jack as long as it works again. Personally I wouldn't even care if it was retrofitted with a Boss style 2.1mm jack. Out of curiousity is using a 'minor' non-original repair part like this going to ruin its collectable resale value? I wouldn't be pretending I didn't replace the DC jack and polarity diode. Everything else is original though. I'm not sure if I want to keep it or not since I like overdrive sounds better from other pedals.
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Re: Ross Distortion

Postby snmavronis » 13 Jul 2010, 23:50

Well I just replaced the defective DC jack and now it works. Sounds pretty nice too. I haven't heard the thing in decades!
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Re: Ross Distortion

Postby JOHNO » 14 Jul 2010, 14:07

snmavronis wrote:I'll try to start tracing this one out next week.

How's the trace going?
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Re: Ross Distortion

Postby rhandy gaye » 14 Jul 2010, 14:32

here's a trace i made.

not perfect, but close.

cheers, rhandy.
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Re: Ross Distortion

Postby Lonkero » 14 Jul 2010, 15:04

Isn't this Ross distortion dod 250 variant? Not so good apparently since people do not clone it so much as other variants.
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