Upgrading 4558's

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nacho459

Well-known member
Joined
Jul 20, 2004
Messages
339
Location
Pasadena CA
Once again I really don't understand much about solid state circuits and ICs and the such. So what do these little 8 pin thingies do? I imagine they are like tubes in that they can do a variety of things, and that you can swap different ICs to get a different sound, like swapping a 12AX7 for a 12AT7. I figure the 4558 is part of an amplifier. I googled 4558 and couldn't find much except people selling them.

The reason I ask, besides understanding, is that each module on my console has about several 4558dx, I don't have a schematic, but just by glancing at the PCB it looks like there are 3 on the EQ, one with the aux sends, and one by the bus assignments. I figure there is something out there that I can swap these out for to give me a sweeter sounding console. Some Burr Brown's or maybe even something discrete. I just remember someone once telling me to get rid of those 4558s.

Thanks
 
4558 are dual opamps a little better than a 741. However they don't seem to be equal between companys.

Part of some guitar effects sound can be due to the ic used. Some ICs when overdriven sound more musical than others.

The ts808 stuff is kind of based on the opamp used in the stock circuit. A JRC(NJR)4558 does sound nice in that circuit stock gain as well as a TI4558 at stock gain at higher gain you might want a different opamp.

At low gain settings most opamps sound about the same in the ts808 circuit.
FWIW IMO part of the 808 magic is somewere else in the circuit, I have modded many (ICs and other parts and adjustments to the circuit)and have had two real ts808s that sounded very good for testing for a short time. There does seem to be somthing to the 808 story, I think it might be something like the old vox whas, that had a low grade crappy core for the inductor that helps the sound ifthe storys are true.


Why the 808 stuff in this ost? If the 4558s are JRC or TI you might want to try the circuit at high gain settings to see if maybe they might add something nice to the sound. If they don't the good old 5532 would be the first sub I would try.
 
The 4558 is a standard dual opamp. It's a fairly old design and not really good for audio. Unless you want to build a Tube Screamer pedal, that is. There are several manufacturers, so google for RC 4558, NJM 4558 or BA 4558.

There are direct upgrades from JRC, i.e. the NJM 4560 and the NJM 4580. Those are widely used in more contemporary equipment such as Mackie, Samson, and Behringer. The NJM 4580 is virtually everywhere these days. You'll find it on zillions of soundcards, mixers, etc. Those chips will be a serious upgrade, but few people get excited about them. Depending on the circuit, NE5532 may be a better upgrade or TL072 or MC33078 or some snazzy Burr Brown part. There are zillions of other (dual) opamps out there that you can try. Just search the metas; there's lots of info on opamp upgrades.
 
OK, Yeah, that's what I figured, my console is an old TOA which was kinda the 80s version of Mackie. I definitely want to upgrade to Burr Browns or something quality. I'll look up some Dual Op Amps. If anyone knows any killer ones, chime in.

Thanks again.
 
[quote author="Rossi"]...i.e. the NJM 4560 and the NJM 4580...[/quote]
NJM2068 is a better opamp than either of these in my experience. 2068 has better speed and lower noise. 4580 has a little more drive, but the idle current is higher.

Depending on the circuit, NE5532 may be a better upgrade
Sure, no doubt, but you need to make sure that your power supply is up to the task of supplying current for a big swap over.

or TL072 or MC33078 or some snazzy Burr Brown part.
Oh, be careful about using FET input OAs in place where there were BJT amps.
 
I have been under the impression that the JRC4558D or JRC4558DD (as well as the TI RC4558P) was "the opamp of choice" for TS9 modders. I have a whole bunch that I have been collecting out of old Japanese radios from the 80's that I scrapped out. Its a good place to find them if thats what you are looking for - go to a goodwill and spend $1 and you will probably score some.

I think they are dual JFET opamps, but I have never seen the data sheet - this is all from TS9 modders sites.

Swapping them and the output resistors make the TS9 live up to the 808 specs - but keep in mind that its diodes that cause the clipping in the TS pedals. If you wanna go crazy, you can change some caps too that high pass some of the bass frequencies from the diodes (once again, this is just what I have heard through the vine) or the diodes themselves. I think the best thing to do before replacing the opamp is to grab some alligator clips and play with the caps and diodes.

if thats what you are doing with the 4558's that is.
 
4558 is bipolar input, actually, not FET. It's descended from the 741 single and the 1458 dual.

It was all right in its day but it's not a very good opamp by current standards. It's used nowadays only in guitar stuff and maybe some really cheap consumer gear.
 
> I have been under the impression that the JRC4558D or JRC4558DD (as well as the TI RC4558P) was "the opamp of choice" for TS9 modders.

They are. Effects pedals abuse the chips; the exact way they respond to abuse is the "sound". And "minor" chip redesigns (that do not affect the "normal" performance) can make significant difference when you go outside the normal range.

> I think they are dual JFET opamps

No. 4558 is, as Gus says, an improved (and dual) 741. BJTs forever! Not only that, but mostly NPN. The PNPs in that process are cripples, used only to turn things around so an NPN can do the heavy lifting.

This isn't bad. The 101/741 family was a huge milestone in analog chips. Wonderful chip for many chores, even today. The 741 can be criticized for not being fast enough for clean high-level audio. (It wasn't even made for that.) The 4558, aside from being dual, pushed the speed of the 741 core, to the point that it was considered good enough for a lot of audio work. JRC is still selling tons of super-741 chips, using improved processes to give excellent audio performance.

The 101/741 design (most BJT opamps) has fundamental speed problems for general-use opamp-ing. The radically different BiFET opamps such as TL072 break the speed/stability problem better, and became the go-to devices throughout audio.

Aside from basic design, there is another audio issue. Most chip makers think low power consumption is a priority. In a lot of electronics, it is. Even in an 8-in board, the difference between TL072 and 5534 power demand will make a big difference in power supply size and cost. But the class AB output stages must NOT be allowed to run with too little idle current. If they are starved, the chips meet all published specs and give nice low power consumption, but garble the fine detail in good audio. The chip foundry awareness of this problem may have something to do with why certain brands and vintages of multi-sourced chips are favored by audio geeks. And since most opamps have MANY non-audio uses, most foundries are not focused on "our" needs. One reason we like NJR is that they have a large audio market, and are small enough to cater to it.
 
Milkmansound

It is more than the chip and resistors on the output buffer. Like I said I have modded a number of TSs and own 7 TS and ts type effects, all setup different (chips, caps, gain)(I let my friends try them not knowing what the mods are so they can pick the mod they want) not one of them is the same as a real TS808,one is as close as I can get so far. I believe I know why.

FWIW I was working on building and modding effects in 95 before the diy effect stuff web got big and worked on my first TS from tracing the circuit myself I found Jack's site DMZ at the time, R.G.'s site and the Lepers abode after that.

I can get close to the sound of an 808 that has the "808 sound" I have been told by friends that they all don't sound alike. There is one part that has no brand markings and gives just the right grit to smooth with signal level in the magic 808s. Any sub part of the same type or other type of build I try just does not have it. I am begining to think it was a run of a somewhat defective part that justs sounds good.

A 808 need a realy good player (I know a few) with a good amp and guitar to hear what it does. I have not been able to copy it and I doubt others have, but how can anyone tell unless they have a real 808 to check it against. Its not a big difference and it only realy shows with a good player and good equipment IMO.
 
[quote author="nacho459"]

The reason I ask, besides understanding, is that each module on my console has about several 4558dx, I don't have a schematic, but just by glancing at the PCB it looks like there are 3 on the EQ, one with the aux sends, and one by the bus assignments. I figure there is something out there that I can swap these out for to give me a sweeter sounding console. Some Burr Brown's or maybe even something discrete. I just remember someone once telling me to get rid of those 4558s.

Thanks[/quote]


Hi Nacho,

You might consider that replacing all your desk's opamps with Burr Browns or similar will probably cost more than simply buying a better desk with similar features. You will almost certainly have instability problems if you change the opamps to higher bandwidth ones, which you will have to troubleshoot. You may also need to build a bigger PSU to power the new amps.

Depending on what you use the desk for (monitoring or recording) you might just want to mod a few channels to sound better.
I considered doing this to my 16ch Mitec studio server because its got so many great features that I couldnt find in a newer desk, but the cost of the opamps and sockets alone was going to equal half of what i paid for the desk, let alone the time it would take to change every amp and fix all the problems that would occur.

At a time when you can find great old A class Soundcraft or Yamaha desks around for as little as $1k, it didnt seem to be worth the trouble to me.

YMMV of course ;-)

M
 
[quote author="mattmoogus"]You might consider that replacing all your desk's opamps with Burr Browns or similar will probably cost more than simply buying a better desk with similar features. You will almost certainly have instability problems if you change the opamps to higher bandwidth ones, which you will have to troubleshoot. You may also need to build a bigger PSU to power the new amps.[/quote]

I think I would only have to change one or two of the opamps on each channel, as I rarely use the EQ and am not worried with the aux sends. Also I have been thinking of rebuilding the power supply or at least getting it checked out cause I'm always worried that something is gonna blow up in there. I don't know why other then it's about 20 years old and whenever I shut it down it takes about 5 min for the console to "warm up".

To move up to the next level of console I realized it's gonna cost me between $20-40K to get where I want to be. So I think I'm stuck with what I got and am going to try to rebuild and mod the console over time.
 
OK, I'm looking around and I can get the NJM2068 at Mouser for $.35 each... pretty cheep.

What do you guys think about the OPA 2134? If I get 100+ I can get em for about $1.57 each not very cheep, but I'm guessing sound better then the NJM2068. I just don't want to blow up my PSU.

Do any of you guys live in the LA area and wouldn't mind looking over my console so I don't blow it up?
 
Yes on what Paul said. The first line you read in the abstract of a data sheet is "runs on 0.00000007" microamps. I certainly don't care about this, but other people do. Battery operated or solar powered stuff comes to mind

I am scanning the "Engineer's Mini-Notebook-Op Amp IC Circuits right now. It is a good beginners (and sometimes experienced geek's) referance that is out of print from Radio Shack. I will not scan all the kid's projects in the back, but will put up the main info.
cj
 
BG Micro has the NJM2068 for .33, good site sometimes to find certain things for cheaper then the usual people.
 
[quote author="nacho459"]What do you guys think about the OPA 2134? If I get 100+ I can get em for about $1.57 each not very cheep, but I'm guessing sound better then the NJM2068.[/quote]
Nacho,
You might not get 2134 to work as a drop in. It is a FET input OA. I have had success in using it in place of this very opamp, but there were other things that needed to be changed to really get better performance.

If you have the schem for your board, look and see if there are caps in the feedback that are larger than 22pF, if so, you probably need to take a look at the other ckt values and determine if any are limiting the bandwidth.

If you don't have the schem, GET IT! I would put quality machine pin sockets on one channel (or two) swap OAs and then LISTEN to it before I made any big money or time commitment. Make incremental changes. Post the schem and ask questions here if you need more guidance.

Sometimes, improving just the PS can make a diff in the whole board, btw.

HTH!!
Charlie
 
[quote author="SonsOfThunder"]If you have the schem for your board, look and see if there are caps in the feedback that are larger than 22pF, if so, you probably need to take a look at the other ckt values and determine if any are limiting the bandwidth.

If you don't have the schem, GET IT! [/quote]

I would love to get the schematic, but I can't find it. I have emailed TOA and asked for the module and PSU schematics but they told me they couldn't find it. I think I am gonna need to pay someone to reverse engineer one of the modules. I don't really have the time or expertise to do it myself. I know if I had the schematic we could really take off and do all sorts of mods and really trick this console out. If anyone wants to reverse engineer this thing into a schematic contact me and I'll send you an input and master module.

edit: OH CRAP! I just checked back at the TOA page and they now have a support page with all the discontinued products, I'm downloading a RX-7 manual, I may be in luck!

edit: No dice, they just have the "user's" manual which just tells you how to use the console. I emailed TOA again, maybe now someone will be able to help me. :?
 
OK, I got the schematics from someone at TOA!

Here's the input module,
http://www.459audio.com/RX7input.jpg

and here's the power supply.
http://www.459audio.com/RX7PSU.jpg

It appears that IC M2 and M3 are only used in the EQ circuit, M5 is the output buffer for the direct outs and bus 1-4, M6 is the output buffer for the insert send and the aux sends, and I'm not too sure what M4 is doing except doing something with the HPF and EQ. :?
It also looks like most of the feedback loops are 150-470pF.

Any input anyone can give please chime in. I have been wanting to swap out the M1 op amp in the mic pre for something more high end, but I mainly use outboard pre's so it's the mixing side I'd like to upgrade first.

I asked about this console before http://www.groupdiy.com/index.php?topic=3184 and for some reason I kept thinking it had 4458's. Sometimes I think I'm dyslexic.

So I'm thinking of going with the NE5532, or maybe I'll buy a few of the NJM2068, and some NE5532. and just do some AB tests. What's the difference between all the NE5532's? Mouser 5532s

Thanks to anyone with ideas.
 
Nachoman,

It looks like we've forgotten about you, but that is not the case. I am going to print out the schem and go over it this weekend and make some recommendations then.

Peace!
Charlie
 
Thanks soooo much, I'm hoping the PSU will have the strength to provide the current for the more hefty op amps. It has a fairly larger transformer so hopefully I'm in luck.

Thanks a lot to all of you who share your time and knowledge to those of us who are just starting to understand electronics. We would be still shopping at Guitar Center if it weren't for you!

Here's to you! :grin: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness:
 

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