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

[MoltenVoltage]

So 8 years after it crapped out on me, I finally got around to fixing my Mu-Tron Phasor II.  Someone here posted a new schematic recently which was a big help, but also was way off.  My unit was from 1979 as stated on the PCB, and the original schematic is dated 1976 (the one that is floating around that is so blurry its nearly impossible to read).  The one that was recently posted follows the 1976 version and has a number of different components and values compared to the 1979 version.

Anyway, I started trying to fix it 8 years ago before I knew much, but I had socketed the chips and saved the original RC4558 chips with orange dots painted on them.

I purchased some JRC4558 chips from SmallBear a while back and during another repair attempt had these in the sockets.  I swapped out the big power capacitors and it started working again, but it didn't have that same intensity that it used to - in fact when "Feedback" was turned all the way down there was no phasing, even though there used to be quite a bit even when Feedback was all the way down.  I found the original 1979 RC4558 op amps and put them back in and all of a sudden that magic intense sound that I love from this pedal re-appeared!

I now have proof that the new JRC4558 chips do NOT sound the same as the RC4558 chips made in 1979.  I have no idea why this is the case.

Perhaps one of the veterans here has an idea why.  If they are physically the same, perhaps Mu-Tron "matched" the RC4558's for each pedal, kind of like you do with JFET's on the Phase 90?  If not, I suspect that the manufacturing process or materials are fundamentally different than they were in 1979.

Anybody else's ideas would be welcome!

[Derringer]

not all 4558 chips made today are 100% equal though ... right ?

[trjones1]

The real test would be to take out your '79 4558s and put them in a distortion/OD circuit and see how they compare to the new JRCs. 

[analogmike]

no comment

[Mark Hammer]

Well, here is the internal architecture of the RC4558 and the NJM4558.  The RC version is the one with values listed.  The NJM diagram shows none.  I have no idea about the values of the internal components, nor whether, even if the values were identical, the fabrication process resulted in any functional differences, or whether currently available datasheets for Fairchild semiconductors accurately represent Raytheon chips from 30 years ago.

But, unless you can spot something that I didn't, I can't see any differences in their design.

[R.G.]

I now have proof that the new JRC4558 chips do NOT sound the same as the RC4558 chips made in 1979.  I have no idea why this is the case.

One possibility is that the RC4558 was not made by New Japan Radio Corporation. They made the "JRC" version, which was a copy of the RC version. I'd have to go look for my archeological databooks for who made the original "RC4558", and it's first second source, and it's second second source, and so on.

Perhaps one of the veterans here has an idea why.

I personally would go with the "made by different companies" explanation.

If not, I suspect that the manufacturing process or materials are fundamentally different than they were in 1979.

This is most assuredly true. In the analog effects world, we exist on the leftovers of the "real" electronics industry. They update their semiconductor fabs at intervals to do things like keep up with the rest of the industry (the alternative being going broke) and to keep product lines in operation when the fabs are worn out. Today's processes and materials are several orders of magnitude cleaner, more replicable, and predictable. Semconductor fabs are very, very specialized $1B tools.

It is possible that you found a situation where the exact result of those opamps reacted well with something in your circuit. Input resistance is one thing I'd guess might happen - I don't know this is a fact, I'm just bringing it up as an illustration of what might happen. The input impedance of an ideal opamp is infinite. No real opamps go there, although CMOS opamp inputs get remarkably close. The original opamp structures with single (especially PNP) non-darlington input diffamps had a lot of variation in the input impedance. As long as it was good enough, people just didn't talk about it, and EEs who could figure out how to use what they had to do some special effect got big raises. The well-thought-of NE5532, for instance, has a noninverting input impedance of about 100K. That's well down into the "mess with your input bias and filtering" range. I'd guess that one works well in your circuit, one doesn't, for reasons which are abundantly not clear. Generalizing from this to "there are magic JRC4558s" as is the common (advertising driven) wisdom is not necessarily logically valid.

not all 4558 chips made today are 100% equal though ... right ?

Yep. Especially if they're not made by JRC. I'm overworking the "JRC4558" issue because it's hyped to death, and I believe unjustifiably so.

no comment

I'll take that to mean "I told you so...", right?

Maybe. We pretty much all know by now my definition of magic - magic is any technology you don't understand. And in this case, we just have a situation where one opamp sounds different from another. OK. Been there. There are situations where people can hear slight differences, if the testing is very, very careful. There are many situations where listeners can be led into giving the "right" answer, and this is in fact easier to do than doing a fair (in the sense of carefully unbiased) test.

It is very, very difficult to not "hear" what you expect and want to hear.

Well, here is the internal architecture of the RC4558 and the NJM4558.  The RC version is the one with values listed.  The NJM diagram shows none.  I have no idea about the values of the internal components, nor whether, even if the values were identical, the fabrication process resulted in any functional differences, or whether currently available datasheets for Fairchild semiconductors accurately represent Raytheon chips from 30 years ago.

But, unless you can spot something that I didn't, I can't see any differences in their design.

Yeah, yeah! Raytheon. Then Fairchild!
The problem with looking at opamp schematics is that everything matters as long as feedback doesn't cover it up - which is the whole point of opamps, having feedback cover everything up. Reading some of Bob Widlar's history in designing opamps is fun and instructive. The funny, second and third order effects that happen in opamps can depend on things like chip layout and thermal balancing as much as schematic.

I'm reminded of Robert Heinlein's quip "Can one horse run faster than another? Of course! But which one? Differences matter."

[analogguru]

I have no idea .... whether currently available datasheets for Fairchild semiconductors accurately represent Raytheon chips from 30 years ago.

No they don´t - have a look at the TI-datasheet:
http://www.ti99.com/exelvision/website/telechargement/rc4558.pdf

But, unless you can spot something that I didn't, I can't see any differences in their design.

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.

analogguru

[Derringer]

[maarten]

To me it sounds like you have proof that the 4558 chips IN YOUR POSSESSION do not sound identical; you have no proof (yet?) that the new chips sound different from the old ones....In any productionbatch there will be some variability, which mostly will overlap with the variations in any other batch. Individual products from different batches might therefore be more identical soundwise than the extremes from one single batch....

Maarten

[Rectangular]

I've actually encountered this before, too. I've tried to replicate my old Electro Harmonix Polyphase about a dozen times...  but no matter what, even with the exact same circuit, the 4558s in the 5 all-pass filters just don't sound the same as the original ones. Ive swapped them out with difference batches, models, manufactureres over and other again, even with 4558s i salvaged from old radio and VCR gear.

In particular, this 100% affects how the "feedback" controls sound and respond.  I can't get it to feedback anything like the original one.  I'm wondering if this is something unique to phasors or circuits using cascading all-pass circuits. maybe with 1 4558, the difference is negligible,  but with 5, a synergy is created ?


I agree that the hype around 4558s is ridiculous, because most of the hype is around TS-909s or 808s or whatever; distortion circuits. I think that with phasors, theres a more complicated relationship happening.

[12Bass]

Just wondering why people are still using 4558s these days when there are much better op amps out there.....

[frequencycentral]

Just wondering why people are still using 4558s these days when there are much better op amps out there.....

  Go stand in the corner and think about what you said!  

[R.G.]

I agree that the hype around 4558s is ridiculous, because most of the hype is around TS-909s or 808s or whatever; distortion circuits. I think that with phasors, theres a more complicated relationship happening.

Phasers use cancellation of signals with certain phase shifts as the fundamental basis of their operation. Cancellation is a demanding thing - you're taking the difference of two things and watching carefully whether it's zero or not.

I'm always yelling about "get the numbers". Human ears are incredibly fallible, as our brains modify and fill in whatever bits they want to, and do this below the conscious level. If there is a huge difference in sound, it should result in a huge difference in cancellations, and that should be measurable. If someone wanted to "prove" that different 4558s make different phaser sounds - and I have no data that says this should not be the case! - then it will show up as a difference in the sharpness of the null for a given frequency.

This kind of follows the line of reasoning below:
1. There is no magic, only stuff you don't understand. If/when you understand it, it ceases being magic.
2. Different opamps affecting phasers will be amenable to measurement if the effect is real and not human suggestibility. There are two ways to find this out. One is the EE/numbers way, the other is the psychological wan. The psychological way means setting up a test where the person does not know whether he's listening to a) the RC4558, b) the JRC4558, or c) some other opamp, and neither does the person doing the switching between setups. 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.

The EE/numbers approach says to extract some subset of the circuit and try it both ways, looking for the time and frequency response and writing down the results. If the effect is real, either the time or frequency response will be different. (If you disagree with this assertion, tell me what the ear hears that's not either time or frequency response...  .)

I would set up the phaser in question with LFO sweep disconnected, input a sine wave and diddle the sine wave until I got as deep a null on the output as possible. I'd then change opamps and re-null, noting whether it nulled at a different frequency and/or different ultimate depth.

The complicated thing in all this is not the phaser or opamps. It's the human brain listening to it. The human brain and mental state is the most complex object in the known universe.

[Morocotopo]

I made a Polyphase clone some time ago. I put in it some off the shelf 4558´s, and the thing didn´t work. Not "worked less" or "worse", it didn´t phase at all (my brain can play tricks on me, but I swear it didn´t phase!!). I got some BA4558´s and bingo, it worked! I don´t know if just like an original, ´cause I never heard one of those.

What does this add to the topic at hand? I Don´t know. You figure it out...

EDIT: Spelling!!! 

[MoltenVoltage]

Like I said in the original post, objectively speaking, there was no audible phasing with the Feedback control all the way off using the SmallBear JRC4558 chips, but there was a good amount of phasing when the Feedback was all the way up.

With the old RC4558 chips, it worked like I remembered, with a pleasant rich phasing with the Feedback control all the way off, and a very intense over the top phasing with it cranked all the way up.

My best guess is that both types of chips are capable of the more intense sounds, but the folks at Mu-Tron dialed in the circuit based on the 1979 RC4558 chips which have different characteristics, whether that's input impedance, gain, whatever.  I suspect this might be the case because a lot of compenent values differed from the 1976 schematic, and sometimes by quite a bit, although the resistors and capacitors that linked the 6 stages were the same.

If that's not the case, maybe Mu-Tron matched the 6 different op amps to make a set for a particular Phasor II.  Someone hand painted little orange dots on each one - I don't know whether that was Mu-Tron or the manufacturer, but it was pretty sloppy, so I am guessing Mu-Tron.  Perhaps it was color-coding performed after testing, or perhaps it was just to make the orientation marking more visible.

I haven't built a TS-808, but will have to now so I can test whether the vintage chips sound more intense than the new JRC4558 chips.  Unlike with the Phasor II, the results will be somewhat subjective.

[foxfire]

Just wondering why people are still using 4558s these days when there are much better op amps out there.....

  Go stand in the corner and think about what you said!  

holy crap you are funny! i'm still chuckling...

[foxfire]

this may be a it off track but i got myself one of these a while back and was so underwhelmed that i all but resoldered every joint, replaced the electrolytic and broke a trim pot trying to adjust it...anyway it's better now but still underwhelming enough that i bought another one to compare it to. side by side the first one sounds better to me. it's got a slightly smoother sweep and the control over the rate is smoother which probably has to do with the replacing the caps. i had the idea tat these were the "holy grail" and were gonna give me that super lush phase i was looking for. my old morley pro phaser is way more intense. now my setup is geared towards making my guitar which is tuned down to C sound like a bass as much as it sounds like a guitar so i don't know if that's where my problem is or if i was just expecting too much from this pedal?

[Paul Marossy]

Human ears are incredibly fallible, as our brains modify and fill in whatever bits they want to, and do this below the conscious level.

I totally agree, way too fallible.

[PRR]

I bet the new ones have better Gain-Bandwidth than the ones made in the 1970s.

The only spec is "Typ 3MHz". Back when i didn't understand "Typ", I wondered why many of these would hardly do 2MHz GBW. "Typ" covers a lot of slop.

One thing JRC has been very good at is taking the classic 101/741 topology (4558 is in this flock) and improving performance. Higher speed, stronger output. This is nearly "natural" as Silicon technology improves. Perhaps unavoidable as the old fab wears out, and you must cut a new mask for your less-old fab. Also as you use the improved resolution of your less-old fab to get more chips per wafer, better costs.

Lookit how OLD this part is. When it was new, an IC CPU would not run 1MHz; today a 3,000MHz CPU is routine. Transistor count has gone up by factor of 10, while die size has not gone up so much. When Intel spends the $1B for a new fab for the ever-swifter Sexium, they find lesser products for the old fab, until they stop those. It goes to auction and a lesser semi house buys it, until they too move up to faster/smaller devices. It may linger in the Legacy Products cellar of a large semi-house. But there is a large market for older fabs, including JRC.

I can't make a case for GBW really affecting a chain of unity-gain amps.

However, being a chain, small differences (in GBW or cleanliness) multiply.

> when "Feedback" was turned all the way down there was no phasing

This circuit "SHOULD" phase with any opamp.

However pure phasing, withOUT mix or feedback, is nearly inaudible. Maybe it IS notorious due to some quirk of the original-recipe 4558?

[R.G.]

However pure phasing, withOUT mix or feedback, is nearly inaudible. Maybe it IS notorious due to some quirk of the original-recipe 4558?

I'd sure like someone to set up the test, feed it a test signal and take scope pictures.

So much pure - um - mysticism gets spread around about magic parts. The single unifying thread seems to be that "you can't get them like that any more, and these few I have left are very expensive".

There is something inside humans that *wants* there to be magic, and we fall for it every time some tease gives us a little peek at the Promised Land.

Oddly enough, very few of the people who contend that certain hard-to-get parts are unexplainably, non-measurably magic are willing to subject the magic to cold-sober testing. It sure seems like if something has a Wow-factor that's big, it ought to be measurable. The hifi tweako world has gone so far as to suggest that if you have to test instead of just hearing the magic, you're defective. Talk about the emperor's clothes!

I should explain - I do believe that a kind magic does exist, magic of the sort where if you study long and hard, you can understand and do things which appear to be improbable or impossible to the lay person. By my definitions, we here are all practicing magicians; of different skill levels, perhaps, but magicians nonetheless. But we owe it to ourselves and our little community not to let our junior members get sidetracked in understanding the magic.