Yamaha G100 212 II
Yes folks, one of the best kept secrets in the wide world of guitar amps is the late-70’s to early-80’s Yamaha G100 model (and similar) amps. They appeared in three series of models – series I, II & III – our pick would be series II which are very robust and obviously built to last the distance. Yamaha’s cosmetic approach is very conservative, but also quite distinctive.
check out the chassis – Yamaha G100 II
Yamaha obviously marketed these amps to compete primarily with the Roland JC120 series amps, and also the Fender ‘Twin Reverb‘. You can pick the Fender ‘Twin’ influence in the G100’s tonality, but in our opinion the G100 has a somewhat warmer tone and very powerful and flexible EQ. There are two channels, as you might expect in such an amp, each with volume treble/middle/bass controls and some ‘pull-on’ options. Common to both channels is (spring) reverb and a 3-knob parametric EQ.
Yamaha’s power amp module can be removed for repairs
This is a channel-switching amp. Channel A is warm and clean. Channel B has additional gain on board for some overdrive. Like any solid-state amp from this era, clean sounds are the main strength of the Yamaha. However, you could employ this amp effectively for most playing styles, excepting hard-rock, grunge and metal, etc. The power amp is modular and plugs into the power supply board. The module is fastened to the chassis via the large heatsink and is easily removed for repairs. The power amp design is quite an old-school 1970’s design, ie quite LO-FI, with a single-ended power supply which necessitates the use of a large output coupling capacitor to the speakers to block the DC voltage present at output (ie an electrolytic capacitor). Perhaps these are contributing factors to the Yamaha’s warmer sound ??
the G100 chassis is very serviceable
This example G100 was recently acquired by our regular customer, Ian Astill. We inspected the chassis and boards, as well as testing for electrical safety. The amp came up trumps apart from some very scratchy pots. Getting access to the pots for cleaning is not especially difficult. We removed the board behind the front panel and gave the offending pots a blast with FaderLube. These pots are the commonly used PCB mounting split-shaft/splined-shaft which facilitate a push-on style of control knob. Unfortunately, the shafts are often damaged and bent. Even worse sometimes the previous repairer has glued on some knobs, making removal without destroying the pot quite a challenge ! The bent shafts can be carefully straightened so there is no excuse for this approach.
parametric EQ on a guitar amp
Some say the original Yamaha speakers play an important part in this combo’s tonal response. If you are looking at acquiring one of these amps, this is probably something you should check out first. The parametric EQ is not easy to use – it takes time and effort and some experimentation to get a result. But the controls can be set for 12 o’clock and instead rely on the very functional channel (passive) EQ instead.
A well known user of these amps back in the day was American jazz guitarist Mike Stern. Americans Pat Metheny and Robben Ford are also said to have used these amps. I can recall seeing some Aussies using these amps back in the day including Rick Springfield. There is a rumour that these amps were designed by Paul Rivera, but the power amp design looks exactly like a standard Yamaha design, so who knows ?? The standard of assembly is very high, it’s little wonder these amps have survived so well, requiring very little in the way of service and repairs – mainly just damaged pots. IR.
ivanrichards 
December 26, 2017 at 6:37 pm |
i got a series 1 for free back in 2010! had been sitting in a crawlspace for years i got it home and twisted all the knobs a bunch to work the dust out and it has been fine ever since. factory distortion channel sucks so i ran a boss ds1 in front of it played an es335 and a squire 51 and had good results! other guys in the band i played with poo pooed it cuz they were tube amp snobs but i could smoke their hundred watt combo amps mine has both original 12s in the cab clean tone is awesome and it does great with pedals they are getting scarce nowadays too good time to sell cuz i don’t gig anymore
March 1, 2018 at 4:30 am |
Thanks for this article. It helped make my mind up to pick up a really nice 1 owner since new G100 B212 today.
I like Yamaha gear in general and the ability to input Stereo with 2 independent channels drew my attention to this amp along with how good it looked – I think she looks the goods. Very stylish looking piece of gear to my eyes.
I have a Atomic Ampifire pedal that outputs Stereo and I’ve been looking for an amp solution for some time (vs Headphones). Buying 2 amps and cabs wasnt going to work. I was also considering getting studio monitors as a solution, only downside being they wouldn’t be any use in a jam / gigging situation unless they were huge.
I brought all my gear I use at home into the store – Cash Converters – plugged in and it sounded amazing. A beautiful clean tone which once I mixed in the Atomic Amplifire (I use an Engl Fireball sim for my heavy tone) stayed very true to what I hear in my headphones. This wasn’t the case at all with other amp / cabs combinations I’ve used in the past.
So now I’ve got a beautiful clean sounding amp (that gets super loud) that takes very nicely to pedals and accepts stereo input.
All for 300 bucks. Happy days.
April 17, 2018 at 11:26 pm |
Very underrated amps. A high school friend had one around 1981, and I used my trusty DOD OD250 through the front end for grit. With the parametric EQ dialed in a certain way, it sounded like Michael Schenker’s cocked wah solo sound with the overdrive pedal. I found one to call my own a few years back for next to nothing. The reverb sound really nice on these as well. Kind of a cross between a Fender Twin and a JC120. Another sleeper are the old Lab series amps. Built like a tank, sound good, and cheap.
May 2, 2019 at 1:53 pm |
I am selling one of these at the moment, i need to shave down some of my kit. If any one knows any one that is interested feel free to contact me: phipp@hotmail.co.uk
August 6, 2019 at 3:53 pm |
I agree with Dave above. These are killer clean pedal platform amps and the spring reverb is almost as good as a tube driven onboard fender unit. Its a long accutronics tank and stops just short of full-on surf drip. Funny, but I got mine with the dreaded glued-on knobs! LOL. Why do people do this? Anyway, got em all off and since they were all missing the silver inserts I replaced them with chinese silver push-on marshall amp knobs and it looks stock. The only problem is, onstage they are so reflective I cant see where the indicator line is! So I might have to find something else that I can actually read. I’ve gigged with JC120’S for many years and this is a great, cheaper alternative with a better boost/overdrive channel and MUCH better spring reverb. Whats not to love?
October 2, 2019 at 8:20 pm |
Do you know what size the potentiometer is for the push pull pot? Thanks!
August 6, 2019 at 4:00 pm |
Oh, all I did to my Yamaha G100-II was replace the two large 2200uf filter caps with nice,new Sprague replacements. These are HARD to find in a 35mm width so I payed way too much to get these, but my amp is worth it! 😉
October 2, 2019 at 8:06 pm |
Hi! Do you know what resistance the push pull pots have in this amp!?? Thanks!
October 3, 2019 at 6:10 am |
Matthew, fortunately for you there are schematics online for these old amps, you should be able to find the answer there!
February 22, 2020 at 6:50 pm |
https://www.youtube.com/watch?v=fyBMvjxII-8 Paul Rivera about yamaha
February 23, 2020 at 12:23 am |
Well, just bought a 1×12” G50II. It looks brand new [40 years old!] and retains all the tone of the G100II in a less back-breaking format.Put me down as a fan!
July 10, 2020 at 11:13 pm |
These amps do sound pretty good stock, but they definitely need modifications to the tone stack to really open them up. This was no fault in the design, because Yamaha was shooting for the “late 70’s sound”, which was very mid-scooped with emphasis on the lows and highs. You can see it on a graph when you input the values into a tone stack calculator (it’s a Fender blackface-style tone stack in these). With a few simple mods you can turn these into tone machines where the fat switch is actually usable and you can turn your Bass knob past 3 without it turning your sound into mud.
July 13, 2020 at 1:14 pm |
I kind of like the Fender tone stack! 😉 But I’m all ears for fat switch mods! I wish they made the fat switch footswitchable, but it is kind of muddy stock…
September 6, 2020 at 11:34 pm
Yes, the fat switch is pretty muddy stock because the bass is already over-emphasized IMHO.
If you have the service schematic, here are the mods (this will have to be done to each tonestack section for each channel):
1) Change the 10K “slope resistor” to 20K
2) Replace the 1uf Bipolar capacitor going to the Bass potentiometer with a 0.47uf film cap.
3) Replace the two back-to-back 1uf Tantalum capacitors going to the Midrange potentiometer with one 0.47uf film cap
4) Replace the 1K Midrange potentiometer with a 2K potentimeter
These mods restore a lot of the midrange and volume loss that occurs in the stock tonestack. You will notice after the mods that the amp sounds more “open” and it sounds very good with the fat switch pulled. After the mods, the fat switch works more as a boost, like it should. At that point, you use the fat switch on for single coils, and off for humbuckers.
Let me know if you need the schematic. I would be happy to email it to you with the changes noted.
July 20, 2020 at 10:50 pm |
These amps were indeed designed by Paul Rivera. He recently posted a great YouTube video talking about the design process. I’m lucky enough to own one of these and will never sell it. The speaker was blown out when I got it, so I replaced the stock Yamaha for an Eminence. It’s one of the best sounding amps I’ve ever played.
Here’s a link to the video of Paul Rivera talking about the Yamaha G100:
October 28, 2020 at 11:37 am |
I know it was forever ago, but yes, Paul Rivera was on the design team for these amps.
January 20, 2021 at 8:21 am |
Could you please explain the specs of the footswitch or the schematic of it? Is it sending a switching signal or is it just an on/off switch? Just aquired a pristine G100 212 II, but the switch is missing. Thanks for the reply!
January 20, 2021 at 5:36 pm |
Hi, Its just a stereo ‘latching’ footswitch. I use two Boss fs5l’s and a Y cable.
February 9, 2021 at 5:57 pm |
I bought a mark II g100 112 pretty recently and to be honest, it is amazing. I didn’t know what people meant when they said that some amps made good pedal platforms until I picked this up but now I totally understand. This article says that it isn’t suited to hard rock or metal but let me tell you that it very much is, every pedal sounds so good through this amp especially high gain distortion and fuzz. One thing I’m still a little unsure of is how to effectively use the parametric EQ, I have used it to emulate a cocked wah sound, but this is not always desirable. How are other people using it?
February 10, 2021 at 9:08 am |
Thats a great question! It is kind of tricky to use the parametric. I used to leave everything at noon on the EQ [the straight up notches are ‘off’.] But now I’m tightening up the bass by cutting it a little and adding a little very high presence.
August 5, 2022 at 2:18 pm |
Paul Rivera did help design these amps, there’s a video on YouTube of him discussing these amps and his involvement.
August 13, 2022 at 2:26 pm |
I have one of these and can say this article is accurate..the tone is warm but powerful.
I have the version with just one massive speaker (seen the same with two smaller speakers)
The reverb feed had shorted so I disconnected that. Shame!
By the way, this amp is heavy. And seriously robust
January 24, 2024 at 7:55 pm |
I own the G100 210. I bought it in the early 80s and will not sell it. This amp is WAY underrated, I played hundreds of gigs with it and it covers everything from rock, to jazz, to funk, to blues. Very much like a Fender Twin without the maintenance 🙂 . Good luck, if you see the Yamaha G100 210 for a reasonable price….buy it, you will not regret it.