Yamaha G100-II / G50-II impedance matching

[Gary_Allen]

I’ve done a lot of reading on here, however this is my first post.

Over the past two years I’ve compiled a small collection of Yamaha G series amplifiers. I started with a one hundred- 410 (series I). Being the proud owner of a Paul Rivera era Fender Concert, I was naturally drawn to the G100-II & G50-II amps. I found a G100-112 II and it quickly became my go-to amp. I now own several versions of the series II amps and after doing my own research I am still a little unclear about the impedance requirements. On the rear panel they all have two speaker outs and state the following:

1 or 2: 4~8 OHMS/ SPEAKER
1 + 2: 8~16 OHMS/ SPEAKER
(I’ve attached a picture showing this on my G50-112 II. All version of the series II amps look the same as this example.)

the single speaker combo amps come stock with an 8 ohms speaker/load

the dual speaker combo amps come with two 8 ohm speakers wired in parallel for a 4 ohm load

I assumed that the minimum load for all of these amps is 4 ohms, but how it’s written on the back panel has me confused.

my plan is to use the g100-112 II with the stock 8 ohm speaker and a 1x12 extension cab with a 8 ohm EVM-12L. I think the speaker outs are wired in parallel, so the amp would see a total of 4 ohms.

I hoping to get clarification on the following:

1. even though this comes with an 8 ohm speaker, is it made to handle 4 ohms?

2. if so, will I be using both the internal speaker along with an 8 ohm extension cab without risking any harm to the amp?

sorry for the long winded post. Any info is greatly appreciated. Thank you

[bluenote61]

1. even though this comes with an 8 ohm speaker, is it made to handle 4 ohms?

2. if so, will I be using both the internal speaker along with an 8 ohm extension cab without risking any harm to the amp?

sorry for the long winded post. Any info is greatly appreciated. Thank you

Welcome here.
To answer your questions, guitar amps with a transistor power amp can usually accept a speaker impedance between 4 - 16 ohms.
Same will be the case for the Yamaha amps.
Also, the max. rated output power is depending on the connected total impedance. E.g. an amp with 50W rated on 8 ohms could deliver approx. 70W on 4 ohms (if the amp's power supply could bear that) and will supply approx. 30W on 16 ohms.
In the picture of your post I can read "Max. RMS output 50W". It's my interpretation that the 50W output power are corresponding to 4 ohms connected speaker impedance.

[va3ux]

I’ve done a lot of reading on here, however this is my first post.

Over the past two years I’ve compiled a small collection of Yamaha G series amplifiers. I started with a one hundred- 410 (series I). Being the proud owner of a Paul Rivera era Fender Concert, I was naturally drawn to the G100-II & G50-II amps. I found a G100-112 II and it quickly became my go-to amp. I now own several versions of the series II amps and after doing my own research I am still a little unclear about the impedance requirements. On the rear panel they all have two speaker outs and state the following:

1 or 2: 4~8 OHMS/ SPEAKER
1 + 2: 8~16 OHMS/ SPEAKER
(I’ve attached a picture showing this on my G50-112 II. All version of the series II amps look the same as this example.)

the single speaker combo amps come stock with an 8 ohms speaker/load

the dual speaker combo amps come with two 8 ohm speakers wired in parallel for a 4 ohm load

I assumed that the minimum load for all of these amps is 4 ohms, but how it’s written on the back panel has me confused.

my plan is to use the g100-112 II with the stock 8 ohm speaker and a 1x12 extension cab with a 8 ohm EVM-12L. I think the speaker outs are wired in parallel, so the amp would see a total of 4 ohms.

I hoping to get clarification on the following:

1. even though this comes with an 8 ohm speaker, is it made to handle 4 ohms?

2. if so, will I be using both the internal speaker along with an 8 ohm extension cab without risking any harm to the amp?

sorry for the long winded post. Any info is greatly appreciated. Thank you

1. Yes, it will handle a minimum of 4 ohms for all combinations of speakers. The external speaker jack is in parallel with the internal speaker jack.

2. The 8 ohm internal speaker plus an 8 ohm speaker connected to the External speaker jack would produce a final parallel load impedance of 4 ohms to the power amplifier. This satisfies the requirements printed on the chassis. A 16 ohm external speaker along with the 8 ohm internal speaker would produce a final load impedance of 5.3 ohms, which again satisfies the printed requirement of 4 - 8 ohm load.

3. If for some reason you replaced the internal 8 ohm speaker with a 4 ohm speaker, then you should not be connecting any other speaker to the External speaker jack. The internal 4 ohm speaker plus an 8 ohm external speaker would produce a final load impedance of 2.7 ohms, which is below the 4 ohm minimum. The 4 ohm internal speaker plus a 16 ohm External speaker would produce a final load impedance of 3.2 ohms, which is below the 4 ohm minimum.

[Gary-Allen]

1. Yes, it will handle a minimum of 4 ohms for all combinations of speakers. The external speaker jack is in parallel with the internal speaker jack.

2. The 8 ohm internal speaker plus an 8 ohm speaker connected to the External speaker jack would produce a final parallel load impedance of 4 ohms to the power amplifier. This satisfies the requirements printed on the chassis. A 16 ohm external speaker along with the 8 ohm internal speaker would produce a final load impedance of 5.3 ohms, which again satisfies the printed requirement of 4 - 8 ohm load.

3. If for some reason you replaced the internal 8 ohm speaker with a 4 ohm speaker, then you should not be connecting any other speaker to the External speaker jack. The internal 4 ohm speaker plus an 8 ohm external speaker would produce a final load impedance of 2.7 ohms, which is below the 4 ohm minimum. The 4 ohm internal speaker plus a 16 ohm External speaker would produce a final load impedance of 3.2 ohms, which is below the 4 ohm minimum.

thanks for the response. that certainly clears things up.

I assumed 4 ohm minimum was good to go for all of the series II amps, because it was my belief that they all were the same with the exception of the two speaker combos having a dedicated 3-band EQ for each channel. After reading the user manual I became a little unsure.

So… the G100-212II and G100-210II come stock with two 8 ohm speaker wired in parallel for a 4 ohm load and user manual states it’s 100 watts at 4 ohms. However, what through me through a loop was that the G100-112II and G100-115II come stock with a single 8 ohm speaker and the user manual stated it’s 100 watts at 8 ohms. Same goes for the G50-112II it states 50 watts at 8 ohms.

I know close to nothing when it comes to the tech side of things, so I was worried that if it truly is 100 watts at 8 ohms then running it at 4 ohms would increase the total wattage beyond 100 watts and potentially over work the amp and damage it in some way. But all of the amp models mentioned have the exact same impedance requirements on the back panel as pictured in my original post. So naturally I began to over think it and was in fear of harming my beloved G100-112II by running it at 4 ohms.