My DOD 250 OD Clone w/RCA 741 Metal Can?

[Steve Mavronis]

Today I decided to see how my pedal works with a Metal Can 741 op amp vs. DIP in the IC socket. I don't really notice much of a sound difference but since it is a vintage RCA 741 should I keep it in or go back to the Motorola LM741CN op amp DIP version? I don't know if I'm kinda out of 'gray spec' or not using the Metal Can 741 although RCA 741's were used around 1979 in the gray DOD 250. Here are some pictures I just took. What do you think?

[Joe Hart]

I like it. I've always liked the metal can ones (and the all in line ones, too!) because they look different. Where did you get it?
-Joe Hart

[Steve Mavronis]

My dad found 2 of those RCA metal can 741's at his work and gave them to me a while ago but I never tried one until now. I may make myself a couple spare pedals for experimentation purposes to see if anything can be improved. I have a very slight trace path revision to the PCB layout involving an electrolytic cap relocation to the other side of the diode pair (so it connects on the traces like the original DOD) that I want to compare with to see if I hear any difference, and maybe try regular electrolytic caps vs. the tantalum ones. Dunno I'm still locked in development mode I guess!

[Bad Chizzle]

Hey, Steve

It looks outstanding! You do amazing work in those. Just want to keep looking at it.
The metal can 741 looks saweeeet! Hey, um... Can I buy one of your awesome boards from you so I can do a build? I'm Not set up for making them and it would be so cool to Put one together using one of your boards! I alway build on perf. It would be fun to do one on something made for the circuit. If you don't want to do it it's cool, just popped into my mind.

Chuk

[Toney]

Those orange caps - they are ceramics?

Also, can I make a suggestion? I have taken to putting a thing zip strap around the tab on the socket for negative battery lead as strain relief, making sure it is a touch shorter than the positive as they are just begging to be ripped out by the user when changing batteries.

  Looks good Steve.

[Steve Mavronis]

Those orange caps - they are ceramics?

Also, can I make a suggestion? I have taken to putting a thing zip strap around the tab on the socket for negative battery lead as strain relief, making sure it is a touch shorter than the positive as they are just begging to be ripped out by the user when changing batteries.

I'm not 100% sure but I think those caps are film type?

Thanks for your suggestion about strain relief. I did use a strain relief with the loops where the 4 wires attach to the PCB and I looped wires around the jacks, in the same direction so I can rotate them in the opposite direction if they needed to be removed or re-soldered. I see from my picture than I didn't loop the black battery wire around the input jack on the left, nor the red battery wire around the DC jack on the right. I think they were the first wires I put on when I was trying to figure out a neat wiring pattern to use. Maybe I thought there was enough slack with the length of the battery leads. But if I looped them around the jacks first that may act as psuedo strain relief since any pulling force would grip and distribute against the jack body.

P.S. I'm trying to get used to the idea of using a metal can 741. I couldn't really find any specs on that RCA package. Does anyone know if there is any internal circuit difference between that and the Motorola LM741CN chip that I was using? Maybe I should put it back, I don't know.

[Steve Mavronis]

Today I might try out another metal can version of the 741. This time it is a LM741 (instead of RCA's CA741) made by National Semiconductor with their older ≈ logo, during the time of Charlie Sporck (1967-1991). I have two of these in the metal can package, one designaled as LM741CH (with SH8912 code) and the other as LM741H (with SH31AB code). Can anyone decipher these codes to maybe date them?

Here is the National Semicondoctor spec datasheet on their LM741 series: http://www.national.com/ds/LM/LM741.pdf

I know the metal can versions handle higher temperatures better than the dip versions. That's probably not critical in stompbox applications. What I'm testing for is if any 741's have less noise or sound different, particularly with inverted chords dissonant sound quality. They have a more raspy sound and I was wondering if anything would help smooth them out some?

Also if anyone was wondering - to make the metal can package fit into a dip 8 pin socket, I spread the legs of course with pins 1-4 on one side and 5-8 on the other at angles to match the square socket hole positions flattening them without touching the rim. Then to tightly bend them down at the right width I used a domino! You can use anything that is the right width of the socket pin rows. then I snipped the legs to the same length, approximating how far the dip package legs insert into the socket holes.

P.S. Bad Chizzle, I'm sending you an email about your PCB inquiry. I saw you online and it reminded me.

[newfish]

Steve, your work is as impeccable as ever.

Always a joy to see such a neat build - well done!

[dune2k]

You could also try the MAA741, it was made somewhere in eastern Europe & also comes in TO-99.

[kupervaser]

Steve, I've been following your DOD 250 threads for a while now, man you take this thing reaallyy to far, it's like an obsession. Looking doog, I really enjoy reading all these posts.

[Steve Mavronis]

Thanks guys. This has been an obsession! I wouldn't even know about the DOD 250 if it weren't for my exposure to the music of Yngwie Malmsteen and his sweet solo tones (especially on the neck pickup) so it's all his fault, LOL.

But since I've been getting into cloning this stompbox I've been getting interested in the 250's cousins, the MXR Distortion+ and Ross R50 and 'script' Distortion. Cloning the 250 makes me learn and curious at the same time. I'm always looking for improvements, not by modifying the original design, but just on a quest to better duplicate the tone that the original had. That's why I post so much questioning things like part types, trace layout and part positioning, etc.

I should really get ahold of my dad's scope and graphically measure from different points in the circuit for better signal comparision instead of just subjective listening alone to compare.