Ross 1978 USA Tan Distortion Project

[Steve Mavronis]

I think I'm going to start making a custom PCB layout for the Ross 1978 USA Tan Distortion based on this schematic I quickly re-drew on top one of my other wiring diagrams. Is anyone here familiar with the USA made tan Ross Distortion (the R50 wide box) see this circuit schematic (inside the I, O, G, V circle pad markers) as accurate?



I haven't finished building my 1977 MXR Compressor clone yet but I am thinking of making myself the Ross Distortion maybe after. I do own a real tan Ross Distortion but it says made in Korea. I want to see if the USA version sounds much different and it will be a fun classic pedal project to make anyway. Then I'll have three pedals based on the 741, 3080, and 4558 chips to add to my collection! When I'm finished I'll post a link to share the PCB layout in PDF format at 300dpi for those interested in using it.

[zombiwoof]

I think I'm going to start making a custom PCB layout for the Ross 1978 USA Tan Distortion based on this schematic I quickly re-drew on top one of my other wiring diagrams. Is anyone here familiar with the USA made tan Ross Distortion (the R50 wide box) see this circuit schematic (inside the I, O, G, V circle pad markers) as accurate?



I haven't finished building my 1977 MXR Compressor clone yet but I am thinking of making myself the Ross Distortion maybe after. I do own a real tan Ross Distortion but it says made in Korea. I want to see if the USA version sounds much different and it will be a fun classic pedal project to make anyway. Then I'll have three pedals based on the 741, 3080, and 4558 chips to add to my collection! When I'm finished I'll post a link to share the PCB layout in PDF format at 300dpi for those interested in using it.

I have a tan U.S.-made Ross Distortion, what I've read is that it's based on the MXR Distortion+ (supposedly "upgraded" as Ross also did with the Ross Comp, which is an "upgraded" version of the DynaComp).  I'm not sure if the brown one is superior to the black Korean version, but I got the brown one for the "cool" factor.  I do think it sounds slightly nicer than my original Distortion+, but both are good-sounding pedals

I would add that if you are making a MXR DynaComp clone, it would be nice to add an attack control to it, which neither the MXR or the similar Ross Comps had.  The preset attack is one of the limiting factors in the use of those comps.  If you wanted to keep it looking vintage, you could put in an external trimmer for the attack, but it would be more useful on the outside of the box.

Al

[Steve Mavronis]

I would add that if you are making a MXR DynaComp clone, it would be nice to add an attack control to it, which neither the MXR or the similar Ross Comps had.  The preset attack is one of the limiting factors in the use of those comps.  If you wanted to keep it looking vintage, you could put in an external trimmer for the attack, but it would be more useful on the outside of the box.

Thanks for replying Al. They did have an attack control, but on the inside as a trimpot mounted to the PCB. I did the same with my clone PCB layout just to be semi-authentic as possible to the original concept. I wouldn't mind an external attack knob on the top, but I was thinking you probably set it once to your desired trim level and forget it. Maybe I'll modify that for a future revision. But I might drill a hole into the bottom lid directly over the attack trimpot so you can use a phillips screwdriver to adjust it if needed without taking it apart. I've never used a compressor before so I'd like to ask is it really adjusted alot? Here's my original layout pattern illustration for my '77 Dyna Comp clone and you can see the attack trimpot next to the 3080 IC socket. All resistors are vertical:



Except for the high part density of the Dyna Comp (for this small sized board) as compared to the 250 Overdrive and MXR Distortion+, I know Ross Compressor is too a rather simple project but I want to get a few early classic pedal clones under my belt before I attempt a new original circuit effect.

[zombiwoof]

I would add that if you are making a MXR DynaComp clone, it would be nice to add an attack control to it, which neither the MXR or the similar Ross Comps had.  The preset attack is one of the limiting factors in the use of those comps.  If you wanted to keep it looking vintage, you could put in an external trimmer for the attack, but it would be more useful on the outside of the box.

Thanks for replying Al. They did have an attack control, but on the inside as a trimpot mounted to the PCB. I did the same with my clone PCB layout just to be semi-authentic as possible to the original concept. I wouldn't mind an external attack knob on the top, but I was thinking you probably set it once to your desired trim level and forget it. Maybe I'll modify that for a future revision. But I might drill a hole into the bottom lid directly over the attack trimpot so you can use a phillips screwdriver to adjust it if needed without taking it apart. I've never used a compressor before so I'd like to ask is it really adjusted alot? Here's my original layout pattern illustration for my '77 Dyna Comp clone and you can see the attack trimpot next to the 3080 IC socket. All resistors are vertical:



Except for the high part density of the Dyna Comp (for this small sized board) as compared to the 250 Overdrive and MXR Distortion+, I know Ross Compressor is too a rather simple project but I want to get a few early classic pedal clones under my belt before I attempt a new original circuit effect.

Steve,
I've never heard that the original DynaComps had an attack trimpot on the board, I don't think that's right.  If it is, then many people didn't know about it, because the biggest complaint about them was that the attack was preset by a cap and resistor (which can be replaced by a trimpot to get variable attack).  Because of the preset slow attack, most players used them with the sensitivity set low, and the level/output up, because if you set the sensitivity higher you'd get severe "pumping", or a slow swelling up of the volume when you hit a chord for instance.  This was very limiting, and is why Dunlop later brought out the Super Comp with the attack control on it.  But a trimpot would be a good compromise, as it wouldn't change the vintage look, but if you wanted to use different settings of compression you'd have to open it up (a hole in the case to access the trimpot might be a good idea, as you said).

Did you make your layout from an original Dynacomp pedal, or did you get the schematic from somewhere?.  If you got the schematic from another source, the trimmer may have been added.

Also, I was under the impression that the first script versions of the DC had the metal-can 3080 in them, not the DIP version.  Are you using the DIP version because of the cost and availability of the metal can version?.

I recently bought a Whirlwind Rochester Series Red Box, which is a script Dynacomp with true bypass and LED, it doesn't have an attack knob but when I looked at the board I do see what looks like a trimpot (covered up by a little round sticker), which may or may not be an attack trimmer, I'm going to find out.  It has the DIP version of the 3080 in it.

Al

[Steve Mavronis]

Yeah I didn't trust all the variations and 'improvement' mods done to most user made Dyna Comp schematics. All the gut shots from a 76 and 77 era Dyna Comp that I've seen have the trimpot. On the 76 model it's above the metal can 3080 and in the 77 it's above the IC 3080 chip. Maybe it's not the attack control you are speaking of (I thought it was) or maybe it's just some bias trim? If it's just some 3080 bias adjustment i'm glad I didn't design for a knob there! LOL. But in either case my goal is to recreate the 76/77 era Dyna Comp even if it doesn't have an attack adjustment, because it is considered a classic. I just looked at the Dunlop manual for the new re-issue vintage script 76 version and they don't mention adjusting attack so I guess it's just for a factory trim setting.

I used an actual 1977 Dyna Comp (the first with the IC chip 3080) MXR factory schematic that came from someone here selling them plus actual factory black boards (re-drew this picture for clarity) and this green PCB diagram too for the actual trace routes:

[Steve Mavronis]

I forgot to answer one of your other questions. My board will have the 8 pin DIP socket for a chip 3080 but I still could install a metal can 3080 into the DIP socket by bending the legs to a 4 on each side pattern looking like a spider. I did that with my 741 OD to install a 1979 RCA metal can op amp.

Hmm I like the looks of that MXR Super Comp. If it has board mounted jacks like their other newer modern pedals I'm not fond of that in case a cord is stepped on near the jack connection.

[skumberg]

Hi,
In my Tan U.S.A unit the C7 on your schem is a 1n914 voltage protection diode. Otherwise it seems alright. The 1uf are color coded so I don't know the values. But I think they are tantalum. From top to bottom Brown-Black-Green with a blue stripe on the side. The diodes measure 0.240 and 0.219 Volts in circuit.

[Steve Mavronis]

Thanks. My Tan 'made in Korea' unit has that extra diode too. Interesting since most Korean models were black. Is the level pot really linear log and not audio log? Also if I had chosen the narrow box Ross to model after it would be much easier since it's really an MXR Dist+ clone. Because the later Ross model uses a 4558 op amp instead of the 741 that means I can't modify from my 250 PCB layout because the IC pinouts are different.

I based the re-drawn schematic part values on this one:

[skumberg]

Is the level pot really linear log and not audio log?

I can't read the values of the pots only some production codes are visible. But when I tested it the volume increased smoothly which should indicate a log pot.