It is currently Mon Mar 16, 2020 4:12 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 11 posts ] 
Author Message
Post subject: Prosonic combo - Using an extension cab (Ohms discussion)
Posted: Thu Mar 19, 2015 1:56 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Jul 16, 2007 4:18 pm
Posts: 46
All- I have read a number of FAQs, articles, manuals, etc. online regarding how to calculate ohms for speaker cabs. I still have an open question as it pertains to the Prosonic COMBO. The reason? Fender's documentation on how this amp's speakers and ohm switching actually works is sort of open to interpretation. I am ultimately trying to determine if I should be using an extension cabinet rated at 8 ohms or an extension cabinet rated at 16 ohms IN CONJUNCTION WITH the combo's factory speakers. Here's what I think I know:

1. There are two factory 8 ohm speakers. I am *assuming* they are wired in parallel, presenting a load of 4 ohms out of the box with NO external cabinet connected (just the two factory speakers). Correct or incorrect?
2. The rear of the amplifier is labeled something akin to "8 ohms minimum, total" between the Mains jack and the external speaker connection jack. This label is one of the things that has me questioning myself.
3. The amplifier's manual states that using the extension speaker jack on the combo amp automatically switches the amplifier impedance to 8 ohms. Great... but what does this mean for the main factory speakers when used in conjunction (simultaneously) with an external cabinet?

I *think* I need to use an external 16 ohm cabinet in conjunction with the main speakers, but to anyone who is positively sure how this should work, I'm all ears! There are so many forum posts on the 'net about ohms, but I can't find the silver bullet one regarding the Prosonic combo. Hopefully this becomes the go-to one. Thank you!


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Prosonic combo - Using an extension cab (Ohms discussion
Posted: Thu Mar 19, 2015 3:43 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
I'm betting your amp's internal speakers at 8Ω each are wired in series.

Instead of assuming, why don't you measure the existing load with an ohmmeter?

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: Prosonic combo - Using an extension cab (Ohms discussion
Posted: Thu Mar 19, 2015 4:27 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
divebomb wrote:
...3. The amplifier's manual states that using the extension speaker jack on the combo amp automatically switches the amplifier impedance to 8 ohms...


This is a clue that would lead me to believe that Retroverbial is correct, the internal speakers are 16 ohms total, and the amp is using the 16 ohm tap.

The speaker jacks are likely in parallel (as they are on the head version, which has an impedance selector switch), and plugging in an external cab of 16 ohms would put the external cab in parallel with the internal speakers, making an 8 ohm total speaker load.

As stated, check the internal speakers to see if they are in series, and check the resistance with an ohmmeter. Unplug the internal speakers to measure their resistance at the plug, and you should get something close to their impedance. If you read something like 12 to 14 ohms of resistance (somewhere around that), then the internal speakers would be 16 ohms impedance.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Prosonic combo - Using an extension cab (Ohms discussion
Posted: Thu Mar 19, 2015 4:35 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Jul 16, 2007 4:18 pm
Posts: 46
Thanks gents. I do not own an ohmmeter. I think you're correct about the series wiring. The below snippet is from a Prosonic schematic I found online. I am no electrical engineer, but I think this is illustrating series wiring.

Image


Top
Profile
Post subject: Re: Prosonic combo - Using an extension cab (Ohms discussion
Posted: Thu Mar 19, 2015 4:52 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
That diagram does show speakers wired in series. It also shows the switching jack for the external speaker.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Prosonic combo - Using an extension cab (Ohms discussion
Posted: Thu Mar 19, 2015 4:56 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Jul 16, 2007 4:18 pm
Posts: 46
Cool. So... we surmise that using an external cabinet rated at 16 ohms (my Marshall 1960A is calling my name) should do the trick?


Top
Profile
Post subject: Re: Prosonic combo - Using an extension cab (Ohms discussion
Posted: Thu Mar 19, 2015 5:01 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Go for launch! Plug that bad boy in and let us know how it sounds.

BTW, you can also unplug the internal speakers and plug the cab into the amp's main jack to use the cab by itself for some sonic variety. :idea:

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Prosonic combo - Using an extension cab (Ohms discussion
Posted: Thu Mar 19, 2015 5:34 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Jul 16, 2007 4:18 pm
Posts: 46
Success! Or at least I can report that nothing crapped itself in the 15 minutes I played it. Thanks for your input guys. You know, I had run it through my 1936 cab (8 ohms) a while back and it sounded cruddy. This may explain it. Thankfully nothing failed on me seeing as I likely had the wrong impedance matchup at the time.

At any rate, the "correct" cab sounded quite nice using my '08 Les Paul Traditional, especially with the neck pickup. Buttery violin type tone.

Fender really could have done a better job back in the 90s explaining how this amp was/is wired up. Even a simple mention of series wiring would have been helpful.


Top
Profile
Post subject: Re: Prosonic combo - Using an extension cab (Ohms discussion
Posted: Thu Mar 19, 2015 6:43 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
divebomb wrote:
At any rate, the "correct" cab sounded quite nice using my '08 Les Paul Traditional, especially with the neck pickup. Buttery violin type tone.


Cool!

8)

For future "experimentation" with your amp, go to Home Depot, Lowe's, or any other big-box hardware store and pick up a digital multi-meter. A decent chicom-made DMM is only ten or twelve bucks and you'll also find it of indispensable use when working on the electronics of your guitar, checking patch cables for continuity, measuring wall-socket voltage, etc.

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: Prosonic combo - Using an extension cab (Ohms discussion
Posted: Thu Mar 19, 2015 9:25 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
It might not be the impedance mismatch that was the cause of the poor sound, but maybe just the particular speakers with this particular amp. An impedance mismatch that slight is likely not going to cause poor sound, maybe, but I doubt it. Using the internal 16 ohm speakers with an external 8 ohm cab will give you 5.33 ohms total, not a big mismatch at all.

To find out, unplug the internal speakers, plug the 8 ohm cab into the main speaker jack, and use a dummy plug in the external jack. This will give you an impedance match to test the 8 ohm cab.

A dummy plug is just a guitar or speaker plug with no wires connected to it.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Prosonic combo - Using an extension cab (Ohms discussion
Posted: Mon Oct 31, 2016 6:43 am
Offline
Hobbyist
Hobbyist

Joined: Mon Oct 31, 2016 6:39 am
Posts: 1
Hi guys, what about using an 8 Ohm device like the Marshal SE-100 (speaker emulator). Any advise?


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 11 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: