Ohm question

leftyguitarman · 10-31-2009, 04:35 PM

My buddy has one of these: Marshall AVT50 Guitar Combo Amplifier (50 watt, 1x12 inch) from zZounds.com

He blew the speaker a while back and can't find a 4 ohm replacement speaker. Could he use an 8 ohm speaker or a 16 ohm speaker, or does it have to be a 4 ohm speaker?

Paragon · 10-31-2009, 04:46 PM

https://taweber.powweb.com/weber/

Boshizzle · 10-31-2009, 04:48 PM

The answer to your question depends on who you ask. Personally, I don't ever use a speaker unless it matches the output requirements of my amp. That being said, some people claim that SS amps aren't as picky about speaker impedance as tube amps.

Does it have an ohm selector switch on the back? If not, you could get an impedance matcher. But, it might cost less just to get a 4 ohm speaker.

rickym · 10-31-2009, 05:02 PM

12" Bugera 4 ohm 50 watter.
Bugera 12" 4ohm 50watt Replacement Speaker - eBay (item 370278964229 end time Nov-21-09 15:40:20 PST)

Eminence Texas Heat.
http://cgi.ebay.com/Eminence-Texas-H...item5188e8eb6e

Atomic · 10-31-2009, 05:04 PM

with impedance you can always go up but never down. SS amps are not as picky with output impedance matching as tube amps are, but it is best to match when possible. putting an 8 ohm load on a 4 ohm output will most likely not be an issue.

axepilot · 10-31-2009, 06:58 PM

Quote:

Originally Posted by Atomic

with impedance you can always go up but never down.

That is true for SS amps. Go below the minimum rated impedance of a SS amp and you will blow the final amps.

With a tube amp, the output transformer is the critical component. While it's always best to match the speaker load, most modern tube amps can live with a 2:1 mismatch either way...................I wouldn't push it any farther or you'll be tickling the dragon.

jrnic · 11-01-2009, 11:32 PM

I am currently using an 8 ohm Speaker in my Marshall combo that originally had a 4 ohm speaker. No problems whatever. Like it was said above, you can go up in ohms but not down.

Big John · 11-02-2009, 12:34 PM

5 seconds with Google and I found the manual...

Quote:

i. Combo Version (AVT50)
This socket allows you to connect your AVT50 into an external loudspeaker system, provided it has an impedance of 8 or 16 ohms. By using any one of our comprehensive range of extension cabinets, you will be able to unleash the massive amount of tonal options that extra loudspeakers will provide.

...blah, blah, blah...

WARNING:
Always provide the AVT50H with a load equal to, or greater than, 4 Ohms. Using the two loudspeaker outputs, with cabinets rated at 8 Ohms each, the full 50W of the specially designed AVT power amplifier will be unleashed.

In other words, the factory speaker in the 1x12 combo is an 8 ohm speaker, and always has been. If it was a 4 ohm speaker and you got a wild hair one day to plug in an extension cab, the total load would be below 4 ohms which, according to the warning in the manual, is not good.

axepilot · 11-03-2009, 08:00 PM

Quote:

Originally Posted by jrnic

I am currently using an 8 ohm Speaker in my Marshall combo that originally had a 4 ohm speaker. No problems whatever. Like it was said above, you can go up in ohms but not down.

It all depends on whether the amp is tube or SS:

Tube - Matching impedance is best, but mismatching a lower speaker load is the safer bet. Mismatching with too high a speaker load risks flyback in the OT - and it will kill the OT. Most modern tube amps can safely handle a 2:1 mismatch either way, but matching is the safe bet. With older tube amps, match the impedance - time is not on their side and some of them have delicate OT's.

SS - can be operated into a straight open because they have no OT. Running a speaker load lower than minimum rated impedance will fry the final amps.

10-31-2009, 04:35 PM	#1 (permalink)
leftyguitarman Senior Member Join Date: Apr 2009 Location: Anthem, Arizona Posts: 1,283 Thanks: 2 Thanked 5 Times in 3 Posts	Ohm question My buddy has one of these: Marshall AVT50 Guitar Combo Amplifier (50 watt, 1x12 inch) from zZounds.com He blew the speaker a while back and can't find a 4 ohm replacement speaker. Could he use an 8 ohm speaker or a 16 ohm speaker, or does it have to be a 4 ohm speaker? __________________

10-31-2009, 04:46 PM	#2 (permalink)
Paragon Senior Member Join Date: Apr 2008 Location: SE Michigan Posts: 801 Thanks: 3 Thanked 0 Times in 0 Posts	Re: Ohm question https://taweber.powweb.com/weber/ __________________ Memphis "The Paul" • Mightymites Partscaster • Lace Sensor Gold Vox AD60VTX • VC12 Vox VT30 • Crybaby Classic Danelectro Nifty Fifty 4Sale?

10-31-2009, 04:48 PM	#3 (permalink)
Boshizzle Senior Member Join Date: Nov 2008 Location: In The Extreme Middle Posts: 521 Thanks: 0 Thanked 10 Times in 1 Post	Re: Ohm question The answer to your question depends on who you ask. Personally, I don't ever use a speaker unless it matches the output requirements of my amp. That being said, some people claim that SS amps aren't as picky about speaker impedance as tube amps. Does it have an ohm selector switch on the back? If not, you could get an impedance matcher. But, it might cost less just to get a 4 ohm speaker. __________________ 2008 1959 Reissue Les Paul / 2008 1960 Les Paul Historic VOS FOR SALE / 1974 Gibson Les Paul Special '55 Reissue / 1964 Gibson Country Western Acoustic / 2008 Fender Custom Shop '56 Strat / 2005 Epiphone '57 LP Goldtop - Skynyrd 30th / Agile PS-1000 / 1977 Ovation Legend / 1975 Fender Acoustic / Stelling Red Fox Banjo / Peavey Heritage VTX / Blackstar HT-5 Mini Stack / Epiphone Valve Sr. / Fender '65 Reissue Deluxe Reverb FOR SALE

10-31-2009, 05:02 PM	#4 (permalink)
rickym Senior Member Join Date: Jan 2008 Location: Monrovia, CA USA Posts: 853 Thanks: 7 Thanked 0 Times in 0 Posts	Re: Ohm question 12" Bugera 4 ohm 50 watter. Bugera 12" 4ohm 50watt Replacement Speaker - eBay (item 370278964229 end time Nov-21-09 15:40:20 PST) Eminence Texas Heat. http://cgi.ebay.com/Eminence-Texas-H...item5188e8eb6e __________________ *ShamRockers-1Up/Press Play On Tape-The Eric Clapton Social Group-The VOX club*

10-31-2009, 05:04 PM	#5 (permalink)
Atomic Senior Member Join Date: Aug 2009 Location: N'orlins :D Posts: 1,294 Thanks: 38 Thanked 19 Times in 7 Posts	Re: Ohm question with impedance you can always go up but never down. SS amps are not as picky with output impedance matching as tube amps are, but it is best to match when possible. putting an 8 ohm load on a 4 ohm output will most likely not be an issue. __________________ -Joe Multi-For Sale Thread! Urgent! click here! Join My Forum!!!! My band Atomic Pilot on: YouTube atomicpilot.com Myspace Twitter My Music Thread VM Worn Cherry Refin MIM Tele Refin

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11-01-2009, 11:32 PM	#7 (permalink)
jrnic Senior Member Join Date: Oct 2007 Location: Long Island, NY Posts: 384 Thanks: 0 Thanked 2 Times in 1 Post	Re: Ohm question I am currently using an 8 ohm Speaker in my Marshall combo that originally had a 4 ohm speaker. No problems whatever. Like it was said above, you can go up in ohms but not down.

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