All 4558's are not created equal! - Mu-Tron Phasor II proves it

[MoltenVoltage]

Thanks for the pictures.  I added a picture of the backside to the one I posted.  Looks like mine has two different chips, but most of them seem to be from 1976 if that is the date code.  Very different layout.

I'll bet you're right about the date code as all mine begin with 79 and 80.

As far as the dots go, They aren't consistently where the orientation dot is, so that probably isn't the reason.  As far as speeding up assembly, there is only one type of chip in the pedal, so nothing to get confused about there.

I suppose we could just ask the inventor at
http://www.mu-tron.org/
whether they matched op amps...

I sent him an email.  I'll let you know if/when he replies.

[analogguru]

As far as the dots go, They aren't consistently where the orientation dot is, so that probably isn't the reason. 
.....
I suppose we could just ask the inventor at
http://www.mu-tron.org/
whether they matched op amps...

I sent him an email.  I'll let you know if/when he replies.

I don´t think that they were "MATCHED", maybe they were "selected" - for low input current.
Put some TL072 instead of the 4558 and look/listen what happens.

analogguru

[JDoyle]

I don't know much about this, but a test I think would be beneficial would be to go back to the original orange dot opamps and then switch JUST the 4558s that make up the LFO and LDR drive circuit.

If that degrades the sound from the original then I would suggest that the opamps were selected for output swing ability (how close they can get to the power rails). The old TI datasheet notes a 'typ' ability of getting to within 1V of the rails, BUT in the worst case, the opamp would only be able to swing within 3V of the rail. That is a huge difference.

If switching them out of the LFO/LDR drive circuit causes no change at all then it is the signal path where the change of opamps affects the sound of the circuit - but in that case I am completely stumped because they aren't being asked to do much all that taxing for an opamp...

[R.G.]

Another interesting thing to do would be to put a scope on the LFO. Since one symptom is that the phasing disappears, maybe the "bad" opamps won't start in that LFO circuit. Or maybe it oscillates above LFO frequencies.

... Hmmm maybe the decoupling caps on the power supply are old and dried up and the "bad" opamps oscillate because of this..

maybe

[Rectangular]

@ R.G.

" The test is to listen to a random selection of a, b, and c, including most especially times when each of the posibilities is followed by each of the others and including itself. That is, the sequence b, c, c, a, b, a, a, b is a legal one. The person taking the test records two things for each listening test - whether they hear a difference, and which one they think it is (could also be best, moderate, worst, etc.). If the differences are real, the person will do much better than random chance at recognizing which is which. If they can't, they're guessing, or worse. "

I actually did a bunch of blind A/B tests with my polyphase pedals, and I could always tell which one was which. I'm sure that if someone skilled enough went in and put a slew of trimpots in all the right places, you could "tweak" the circuit to respond more/less like the original. but as it stands, the original Howard David design was built for those crusty old 1970s 4558s that EH loved so much  (because they were so dirt cheap).

[R.G.]

@ Rectangular

I actually did a bunch of blind A/B tests with my polyphase pedals, and I could always tell which one was which.

I'm sure that's true for comparing different pedals, especially old EH pedals. There is essentially no chance that more than one polyphase would have the same set of tolerances

If you meant comparing RC4558s to JRC4558s in the same pedal, I think that would be a harder comparison.

Just out of curiousity, did you set up the tests the way I recommended?

[Voltron]

Any conclusions about this?

From what I read

- In some aplications, replacement of the same opamp model wouldn't get it operating 100% as it originally did.
- Different manufacturers of the same opamp would not meet same exact specs.
- There's a high possibility that even the same opamp from same manufacturer had changed in specs thru the years passed, in order to upgrade their product.

So, that prolly means that theres no easy fix to restore an old broken circuit, at least when the faulty opamp needs SOME CRITICAL SPECS to be to be 100% as in the original. So the answer would be to find which specs are critical on the aplication and try to find a replacement that meets the same specs.

Or, you could re-work the whole circuit aplication for working with new, current production stock parts. Aiming to the same operating performance of the original device.

You know, at this point I'm thinking museums exist for a reason. Maybe we should try to leave the past on the past and keep walking. It's really cool to learn old stuff and how the world used to spin. But you can't put your arms around a memory, think what happened to Christopher Reeves character at the end of Somewhere in Time.

http://www.youtube.com/watch?v=9uicvPZSKIM

[slashandburn]

You know, at this point I'm thinking museums exist for a reason.

You noticed then, that this was a 3 year old thread, then.   Thats a relief, now nobody will need to come across as a total dick for pointing that out!

Im interested too. I dunno. Maybe they're all as individual as we are.

Iain 

[R.G.]

Any conclusions about this?

I'm pretty certain that there never will be, for reasons I'll get to.

From what I read
- In some aplications, replacement of the same opamp model wouldn't get it operating 100% as it originally did.

That is correct. The question is then WHY. It can't be magic - there has to be a real, physics-and-electrons reason for differences.  I have some suspicions based on long observation of engineers pulling their hair out and biting off their fingernails waiting on the latest run of silicon chips.

First, let's start with why feedback amplifiers in general and operational amplifiers in particular exist. They are there so that the wild variations of devices and tolerances of active devices can be "hidden" under a cover of excess gain spent to cover up and reduce the external visibility of the variations.  Specifically, the idea of an opamp is that the internals of the opamp do not matter at all as long as the opamp is not forced to operate outside the linear input and output ranges, or made to follow signals faster than it physically can. Feedback as a concept has been so successful that the music and audio industries, let alone most of the rest of the things controlled by electronics would not exist without it.

But that doesn't say anything about either (1) operation on the edges of input or output linearity or (2) trying to make it follow signals faster than it can. Sadly, a whole lot of the musical effects business is based on making the funny side effects of operation on the edge BE the effect. So we're almost certain that there will be some funny stuff. The problem is that the "funny stuff", the edges of proper, expected operation, is not the same from opamp type number to type number, nor on wafer to wafer, and certainly not over decades and many different competing manufacturers. The reliance on the funny edge effects, or even the occasional operation at those edges, mean that an opamp with nominally better performance in the sense of faster, more linear, less "funny stuff" won't sound the same, just like a person's walking gait may be different with different shoes. Is it the same? Probably not. Is it worse or better? That's very hard to tell, because "better" may mean "has more of the side effects I liked about the old, mildly crippled one".

- Different manufacturers of the same opamp would not meet same exact specs.

No, I don't think that's it. In one sense, all opamps (or other chips) exist only as mildly imperfect single examples of the datasheet specifications. A datasheet specifies certain things; minimums, maximums, and typical values. For instance, almost all of them specify absolute maximum supply voltage. Does that mean every example of that type of chip will die if you go one millivolt over the specified maximum? Of course not. Some of them will go far over it without damage. What the manufacturer means there is "if the chips of this type that you buy won't work at least up to here, you can get them replaced under warranty. If you go over, don't call me and cry about it. I warned you."

Things like gain, frequency response and output voltage range are often specified as a minimum, or worse yet as a "typical". Obviously, if it's at least the minimum, it's good to sell it as that chip. If all you have is "typical" **the chips you get may have any value at all for that spec and you have no recourse at all**.

What I'm getting at here is that it is likely that different manufacturers' versions of the same opamp part number probably WOULD pass the same spec - but they would SURpass it by varying amounts. Good, conservative engineering makes a virtue of taking all that into account to be sure that any part meeting the data sheet will work. Wild-eyed gonzo engineering assumes that most of the chips will be the specs a little. Suicidal engineering presumes that we can test for the few special chips that are far better in some ways. Uninformed design simply uses chips and if they seem to work, OK, ship it.

And more importantly, THE SPEC SHEETS DON'T SPECIFY THE THINGS THAT WOULD LED YOU TELL WHICH CHIPS SOUND BETTER OR WORSE IN AN APPLICATION.

- There's a high possibility that even the same opamp from same manufacturer had changed in specs thru the years passed, in order to upgrade their product.

Yes and no. It is almost certain that the same opamp from the same manufacturer has changed as their processes changed over the years. It is very certain that the specs did not change, so the products now probably won't exceed the written specs by the same amount or in the same funny ways. They'll pass the same specs - but the specs are not what you are interested for effects design.

So, that prolly means that theres no easy fix to restore an old broken circuit, at least when the faulty opamp needs SOME CRITICAL SPECS to be to be 100% as in the original. So the answer would be to find which specs are critical on the aplication and try to find a replacement that meets the same specs.

Aye, there's the rub. It's almost certain that the spec does not tell you something that you need. It's not that there is some critical spec it needs to pass. It's that the critical thing for the sound was never specified at all. It is extremely unlikely that an effects builder could ever figure out what the critical disregard for the specifications was, or what the critical NON-specified things was for an opamp, and then go test other opamps to find out if they're funny or wrong in the same way as the old one. "The answer" as you state it is correct - but nearly impossible, even with a barn full of specialized equipment.

Or, you could re-work the whole circuit aplication for working with new, current production stock parts. Aiming to the same operating performance of the original device.

That's one good way. Or you could plop in what modern production parts you can actually get, and pick the ones that are closer - or even better. "Good" and "better" change with musical styles over time. I've listened to some music I thought highly of back in the 1970s recently - and I find the distortions to be screechingly horrible. Funny - I thought they were good back then. 

[Gus]

Looking at this if this is the correct for the phasor in this thread
http://www.aronnelson.com/gallery/main.php/v/RLBJR65/Mu-Tron+Phasor+II+pg2.GIF.html?g2_imageViewsIndex=1

IC 6 and IC 5 will make a difference due to different offset voltages and currents.  It can be as  simple as the drive waveform shape and current to the LED changing with different opamps

[Voltron]

Looking at this if this is the correct for the phasor in this thread
http://www.aronnelson.com/gallery/main.php/v/RLBJR65/Mu-Tron+Phasor+II+pg2.GIF.html?g2_imageViewsIndex=1

IC 6 and IC 5 will make a difference due to different offset voltages and currents.  It can be as  simple as the drive waveform shape and current to the LED changing with different opamps

Look, obviously I don't know much about electronics. I don't really understand why so much fuss about a circuit like this one, all I can see is too many opamps interacting too much each other. For me it's obvious that kind of circuit needs an expert spending a long time tweaking.

And sorry for the necro, fairly long post got me hooked didn't check the date.

[Voltron]

THE SPEC SHEETS DON'T SPECIFY THE THINGS THAT WOULD LED YOU TELL WHICH CHIPS SOUND BETTER OR WORSE IN AN APPLICATION.

Aye, there's the rub. It's almost certain that the spec does not tell you something that you need. It's not that there is some critical spec it needs to pass. It's that the critical thing for the sound was never specified at all. It is extremely unlikely that an effects builder could ever figure out what the critical disregard for the specifications was, or what the critical NON-specified things was for an opamp, and then go test other opamps to find out if they're funny or wrong in the same way as the old one. "The answer" as you state it is correct - but nearly impossible, even with a barn full of specialized equipment.

Damn, great. So what we need is a science branch which specializes in research and measure non linearities and behavior of certain electronic devices when they are misused or absurdity?... hmmm, I thought that was quantics about.

I've listened to some music I thought highly of back in the 1970s recently - and I find the distortions to be screechingly horrible. Funny - I thought they were good back then. 

I think that's kinda normal for aging males. They become too sensitive to high freqs and then start to dim that range or hearing. ALso could be some kind of health condition related to cardiovascular or diabetes issues. Anyways, thanks for the reply.

[R.G.]

Damn, great. So what we need is a science branch which specializes in research and measure non linearities and behavior of certain electronic devices when they are misused or absurdity?... hmmm, I thought that was quantics about.

Actually, that's what all of pedal building is about.   

Well, OK, not so much the measurement, but the research of and exploitation of, for certain.

[induction]

I've listened to some music I thought highly of back in the 1970s recently - and I find the distortions to be screechingly horrible. Funny - I thought they were good back then. 

I think that's kinda normal for aging males. They become too sensitive to high freqs and then start to dim that range or hearing. ALso could be some kind of health condition related to cardiovascular or diabetes issues. Anyways, thanks for the reply.

Maybe I'm misunderstanding your statement, but the usual forms of hearing loss, both age-related and noise-induced, preferentially reduce sensitivity to high frequencies, rather than increase it. I think that a more likely explanation is that people's tastes just change over time and with exposure to new sounds.

[R.G.]

I've listened to some music I thought highly of back in the 1970s recently - and I find the distortions to be screechingly horrible. Funny - I thought they were good back then. 

I think that's kinda normal for aging males. They become too sensitive to high freqs and then start to dim that range or hearing. ALso could be some kind of health condition related to cardiovascular or diabetes issues. Anyways, thanks for the reply.

Maybe I'm misunderstanding your statement, but the usual forms of hearing loss, both age-related and noise-induced, preferentially reduce sensitivity to high frequencies, rather than increase it. I think that a more likely explanation is that people's tastes just change over time and with exposure to new sounds.

... and that's what I meant. I'm an engineer, and I know about age related hearing loss and noise-induced hearing loss. I was worried about noise related hearing loss in my late teens and have been an earplug user all my adult life. And you are also correct in that both age and noise related hearing loss tend to wipe off the highs first. I'm aware of my hearing status - and it's quite good for someone of my age.   

What I meant, in detail, was that the fuzz sounds that were popular and that I enjoyed back then are more unpleasant by comparison to the sounds we get out of today's much-improved distortions. Not much surprise there - they often came from circuits that we would today dismiss as not sounding very good.

You're correct - I meant that the preferences for distortion now, some 40+ years later, has changed, and I think for the better.

[Electron Tornado]

You noticed then, that this was a 3 year old thread, then.

And as yet, still no data ...

[R.G.]

And as yet, still no data ...

Actually, there's a LOT of data here. Just not the simple, easy "here, one's better (or not) than another" kind of thing.

The data here requires you to think. I don't know about you, but I'm always exhausted after I have to think. 

[Electron Tornado]

Actually, there's a LOT of data here. Just not the simple, easy "here, one's better (or not) than another" kind of thing.

I didn't mean a "which one is better" kind of conclusion. I was hoping to see some kind of comparison showing "here is how the two (old and new) are different", or how they behave in the circuit. In larger sense (and maybe I've missed the discussion over the years), I've also never heard or read an explanation for the second diode in the NJM4558 vs the RC4558.

The data here requires you to think. I don't know about you, but I'm always exhausted after I have to think. 

Yeah, it sometimes makes me tired, too. But, ya know, it's a good kind of tired....

[Voltron]

"here is how the two (old and new) are different"...  I've also never heard or read an explanation for the second diode in the NJM4558 vs the RC4558.

You missed this, at first page thread:

The secret is very simple:
D1 was not included in the older chips.  I assume, it was introduced later to inprove the "normal" audio performance (slew-rate, bandwith, high-frequency response).
But this should be without any audible effect in a Mu-Tron Phasor II.

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or how they behave in the circuit. In larger sense

If you mean the mutron circuit, oh well, the circuit designer was emailed but seems like not interested in talking?. From what I read, every circuit would need extensive testing and measure but most people wouldnt have the resources and equipment to do that (as testing on a dozen vintage mutrons at the same time, etc). I think thats why is so important to have these forums with owners reporting their experiences. But yea, also keep in mind for how long have people been talking about how the fuzz face circuit works... and prolly will keep talking about it for some more.

[aron]

OK but JRC is not the same as RC. At least that's what I thought.