Vintage Distortion Plus using U741cp?

[Monsta-Tone]

Please forgive me if this has been beaten to death already. I did a search but did not find much.

I have an M-104 version of the MXR Distortion Plus.
It has a
JR27AD
LM
741CN

I noticed on ebay that most of the guys selling vintage ones talk about the U741cp chip.

Is there a huge difference? Is the U741cp not made anymore? I couldn't find it at Mouser.

Also....has anyone done these mods to their M-104: http://www.premierguitar.com/Magazine/I ... _Mods.aspx

Sorry for all of the newbie questions. I know a lot about amps and almost nothing about pedals yet!

[Monsta-Tone]

I meant for the title to say.....Modern vs. Vintage Distortion Plus using U741cp?

[Electron Tornado]

For the op amp, search for the datasheets for each and see if you see any differences in the specs. The diodes and capacitors used will have much more effect on the sound of a specific pedal than the op amp. This kind of discussion comes up from time to time, but no one has ever provided any hard data to support claims of this or that op amp is "better" in a particular stompbox.

Brian put a lot of mods in that article. The great thing about the Distortion + (or DOD OD250) is that they are very simple circuits. I would encourage you to breadboard the stock circuit, and try all of those mods one at a time, keeping detailed notes, and you'll find somethings you like.

I built a pedal based on the Dist + and I did a similar mod to C3. I only used hard clipping (D1/D2), though I have several diode combinations in one pedal. I used a 100k pot for the output, however. I don't think this was in the article, but also try changing the value for C4. Between the Dist + and OD250, one uses 1uf and the other uses 10uf. I used 4.7uf.

Another thing to try with the clipping diodes - some people may or may not like the sound when using both sets at the same time, although you may (try it and decide for yourself). You can add a switch to remove the diodes D1/D2, so you can use only the other set alone, or no diodes at all. I would also try various diode combinations and see what you like. You can make them selectable with a switch. If you don't want to use both sets of diodes at the same time, use a DPDT switch to switch them between the two positions in the circuit.

Again its simplicity makes it a great circuit to modify, and the result can be a very versatile pedal. When you finally build it, post what you came up with.

[Monsta-Tone]

Right on! Thank you!
I figured that the chip thing was just snake oil, but you never know!


Just out of curiosity, what did the 100k pot do for the Output?
I am guessing that it would provide a little more volume since there is more resistance between the signal to ground.

Like I said, you could fill a sandwich bag with my pedal knowledge!

[Browser]

CP is better than CN in a micro amp for what it's worth.

[Monsta-Tone]

Is there an audible difference?

[roseblood11]

CP is better than CN in a micro amp for what it's worth.

Prove it!!! And explain the difference between the two versions, please.

[Electron Tornado]

Right on! Thank you!
I figured that the chip thing was just snake oil, but you never know!

Just out of curiosity, what did the 100k pot do for the Output?
I am guessing that it would provide a little more volume since there is more resistance between the signal to ground.

I thought the 100k pot gave a bit better control of the output level. It's what I typically use for that as well.

For more info on your op amp question, take a look at this:

If you want to try a test on your own, get a 741 and a TL071 and try the circuit with each. Unfortunately, you're not testing blind, so you reeeeeally have to be honest with yourself about what you hear (or don't hear but think you do because you wish you did ).

CP is better than CN in a micro amp for what it's worth.

Prove it!!! And explain the difference between the two versions, please.

Do you have a link to a datasheet(s) so we can see the specs for both? Can you tell us what criteria make one "better"?

[Browser]

Prove it!!!

I have the original and the its reversed clone if you live around Eau Claire WI I'll let you have them for a week otherwise only my attestation.

[Browser]

Prove it!!!

I have the original and the its reversed clone if you live around Eau Claire WI I'll let you have them for a week otherwise only my attestation.

EDIT: Could be a tolerance thing although 20% never made me pay notice before so who knows.

[Electron Tornado]

I have the original and the its reversed clone if you live around Eau Claire WI I'll let you have them for a week otherwise only my attestation.

You could set them up with an A/B box and do a You Tube video of them.

Another test is to remove the op amps from both pedals, install sockets, test both chips in each pedal and see if you hear a difference. It would be great to video that, since you can edit it to play the tests back to back.

[roseblood11]

The tolerances and maybe the type of the caps (although that´s probably another mojo nonsense) might play a much bigger role here than the opamp does.
I compared some 741´s and they all sounded the same. The talk about the "early versions" is just bullshit. There are some small differences regarding the noise level. old czech metal can versions named maa741 worked best in my builds.
http://www.diax.pl/pic/7346.jpg
The chip doesn´t add much to the sound in a Dist+/Dod 250, as most of the clipping comes from the diodes.
Opamps have a bigger influence in circuits without clipping diodes, have a look at the Black Cat OD-1, for example.

[Cannibal]

The tolerances and maybe the type of the caps (although that´s probably another mojo nonsense) might play a much bigger role here than the opamp does.
I compared some 741´s and they all sounded the same. The talk about the "early versions" is just bullshit. There are some small differences regarding the noise level. old czech metal can versions named maa741 worked best in my builds.
http://www.diax.pl/pic/7346.jpg
The chip doesn´t add much to the sound in a Dist+/Dod 250, as most of the clipping comes from the diodes.
Opamps have a bigger influence in circuits without clipping diodes, have a look at the Black Cat OD-1, for example.

I agree with you, roseblood. I've build a zendrive and i tried switching an opa2134, an opa2604 and a tl062 and noticed no difference between the first two, and found it slightly brighter with the TL062 (could be because of the FET input?). However, when i disconnected the clippers i notice minor differences between the burr-browns, and the TL sounded very different from the other two. However i don't think i would have noticed any difference betwenn a regular tl062 and mojo "early version" one, simply because they are the same opamp!

[Electron Tornado]

Here's a web site where they guy has sound samples of various ships in a Tubescreamer. He's got some cable comparisons on there as well. http://www.andrewmartinmusic.net/fr_home.cfm

There's no chip mojo in Tubescreamers either. Another person took a look at the waveforms using a sound editor and found some differences, but they were so subtle that they would be inaudible.

When this topic comes up I always ask for some hard data or which spec(s) on the datasheet makes the difference. So far, no one has produced anything. Nevertheless, I still encourage Browser to do a comparison and put it on You Tube.

[roseblood11]

btw: is the Youtube Compressor available as a pedal?

[Browser]

I referred to a micro amp driving a clean tube amp and the Dist + is entirely different. That's why I said for what its worth. Everything SS sounds basically the same when it's clipped with only two exceptions I'm aware of and the 741 isn't one.

[waldo041]

For this demonstration I used an original stock 1980 MXR Distortion+ circuit and pulled the 1n270 diodes out and placed a socket in for the opamp. I had the volume pot full on and the Distortion pot at 50%, all opamps were scoped with this setup. I only swapped the opamps. I chose this setup to show that there are differences in the opamp.

TL071


LM741CN - company A


LM741CN - company b


UA741CP - Original 80's Chip


741CP - Original 74 Script Chip - Note: I have 3 of these and tested all of them, they all were the same.


Looks like the U741CP and 741CP clip faster then LM741's and the diodes are only rounding the already clipped signal, no?

~waldo

[fakcior]

Not exactly. In Distortion+ diodes are hardclipping, so they clip signal boosted by opamp. And if they clip earlier than opamp (I presume they are) then difference between opamps minimized.

Cheers and Happy New Year!

[waldo041]

Not exactly. In Distortion+ diodes are hardclipping, so they clip signal boosted by opamp. And if they clip earlier than opamp (I presume they are) then difference between opamps minimized.

Cheers and Happy New Year!

This would suggest that the opamp is irrelevant and imparts nothing, to include harmonic content, upon the signal in which it is boosting, is that true?

~waldo

[fakcior]

Use of the diodes make different opamps sound more similar, but it doesn't mean they sound the same.