Op amps in Yamaha G100

[bigc]

So last night I openned up one of my Yamaha G100 amps to give it a dousing of DeOxit and I noticed that the op amps on the preamp board are JRC 4558D chips.  I'm not real familiar with electronics but I did a little googling and it looks like those are very sought after in old pedals and such.  Is this why I dig the sound of my amp so much?  Are there any compatible op amps that would be improvements over these?

Thanks.

[va3ux]

The JRC 4558D chips were used in the old Ibanez Tube Screamers and were considered to be the 'secret' to the tone of those pedals. The chips are still made today but under the company name New Japan Radio. Hype - or not - but there's a belief that older 4558 made by the original JRC company sound different (ie. 'better' - in a Tube Screamer) than the newer 4558 chips made by NJR.  You'll find these chips in a lot of SS amps, such as your Yamaha, plus Peavey, Polytone and many others.
You probably can change the sound of your G100 by substituting different pin-compatible chips. There are higher fidelity chips available. But personally, I wouldn't mess with the already-good sound of a G100.

[J M Fahey]

Your Yamaha really sounds good, so, don´t mess with it unnecessarily.

[morris888]

There are many opamps like these like the NE5532, TL072, TL082. These opamps would be a "good replacement" if you only consider electronics. But if you are looking to replace a JRC4558 you should try with different opamps until you get the sound that you want.

[GLUGSTER]

Sounds like elective brain surgery.

[gpw]

  Just a dumb question, but could anybody tell me how to improve/smooth the distortion tone (That knob) in my G100...  Sorry, I'm a tube amp builder, and have limited knowledge of SS, but am willing to learn...   Mentioning op amps made me think of distortion pedals,diode clipping,and how those can be adjusted/biased... Thinking the same might apply to my OLD Yam..which still sounds pretty sweet...? Used for Clean oldies venue, but when we tried the distortion , it was kinda' grainy ,ratty sounding, harsh really ...

[J M Fahey]

Hi GPW. Can somehow scan or trace and post the schematic ? Thanks.

[teemuk]

I'm quite sure that a selection of schematics to Yamaha's G-series amps can be found from ampix.org. I remember that the collection had at least the G-50, and two alternative G-100 schematics (for the different versions of that amp).

[J M Fahey]

Hi BigC. I do like very much those Yamahas, specially for their excellent clean sound . I´ve been looking at the schematics (thanks Teemu for the links, thanks Enzo for posting them). They´re very good, if somewhate dated (obviously, they come originally from the late 70´s), they were state of the art for that date.
Specially interesting is the use of Fets emulating tubes, unfortunately only on the input circuit. The distortion is not bad,it´s comparable to an MXR Dist+ or similar, but definitely not "tubey".
There´s not much you can do, I think that your best bet would be to build some good pedal and stick it in your setup.
Changing OpAmps would do very little, if anything, to change the sound.
The power amp is *very* interesting, *very* HiFi, surely ripped, from some of their Hi Fi line, bur not "rocker" at all.
Your best bet would be a good pedal or pedalboard and use it only as a faithful amplifier (or use the combo very loud, allowing the output stage distortion to smooth the somewhat fizzy preamp dist.) ... but your neighbours will hate you.
Bye.