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FDP Forum / Fender Amps: Vintage (before 1985) / Twin Reverb II (Rivera-era) speaker impedance question

Stratopastor

Stockton-on-Tees

now even awesomer
Aug 21st, 2018 02:41 AM   Edit   Profile  

hi... I've been asked a question about the TRII by an owner in the Netherlands.... the manual says an extension speaker should be 8 ohms but there's an original-looking sticker by the relevant socket, obscuring the 8 ohm legend, and saying 4 ohms. The schematic shows four speaker sockets when in reality there are only two; two labelled 4 ohms, two labelled 8 ohms, plus a note 'alternate output impedance value - see backplate for value'.

So; they made some amps for 4 ohms and some for 8, yes? why?

Meanwhile, I guess this chap should ignore the manual and follow the sticker on the back panel...

Thanks for any wisdom!

scroll down for TRII manual and schematic

socal
Contributing Member

California

Aug 22nd, 2018 03:15 AM   Edit   Profile  

Hi SP, I'm no amp tech, but here's what I think for starters & I'm sure the tech pros on here will post soon.

I think it depends if your guy has a combo or a head unit. Both the combo & the head unit have only two speaker jacks on the back panel (One for the internal speaker on a combo & an external speaker jack. Two speaker jacks for external speaker cabinets on the head unit.)

The two speaker jacks on a combo are labeled for a minimum 4 ohms. The two speaker jacks on a head unit are labeled for a minimum 8 ohms. This info is from the amp pics on the Reverb website.

I believe the schematic is showing 4 speaker jacks (two labeled minimum 4 ohms & two labeled minimum 8 ohms) to accommodate both the combos and the head units on one schematic.

So I believe the combo is correctly labeled minimum 4 ohms because the factory internal speakers are 2×12 8 ohm speakers wired in parallel. And an external speaker cabinet should also send a minimum 4 ohms to the combo amp whether the speakers are wired in parallel or in series. (Also, taking into account, if the external speaker cabinet has one, two or four+ speakers.)

For the head unit, the external speaker cabinet should send a minimum 8 ohms to the head unit amp (either external speaker jack) whether in parallel or in series and whether the speaker cabinet contains one, two or four+ speakers. (I believe the #1 left speaker jack should always be connected first before the #2 right speaker jack is connected. I may be wrong on that.)

I believe this info is correct, but the expert amp techs should be chiming in with their info.

Stratopastor

Stockton-on-Tees

now even awesomer
Aug 22nd, 2018 03:31 AM   Edit   Profile  

hey Socal, thanks for this. It is a combo, what you say makes sense, and looking at photos on Reverb is a clever idea which I will keep in mind!

socal
Contributing Member

California

Aug 22nd, 2018 03:37 AM   Edit   Profile  

Also, SP, if your guy has a combo, it could be that Fender used a head unit back panel instead of a combo back panel & just stickered over the minimum 8 ohm label. How is the #1 right speaker jack labeled? If it is a combo I think both speaker jacks are for 4 ohms.

socal
Contributing Member

California

Aug 22nd, 2018 03:40 AM   Edit   Profile  

Just wanted to help out what I could, SP. You do so much for PRIIs. Thx & regards, bro.

Stratopastor

Stockton-on-Tees

now even awesomer
Aug 23rd, 2018 01:04 PM   Edit   Profile  

That's nice of you mate, cheers.

The sticker labels both jacks as 4 ohm. Also, there's something on the parts list called '4 ohm plate'.

FDP Forum / Fender Amps: Vintage (before 1985) / Twin Reverb II (Rivera-era) speaker impedance question




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