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wishkahdaddy
08-17-2011, 05:40 PM
Just curious who has experience with running a 4 ohm amp with an 8 ohm speaker? I've been reading in a few different forums where this was a common practice for Mr. Dumble. Just curious what others have experienced-good or bad.
Thanks

Steve Hotra
08-17-2011, 05:44 PM
Good question! I would like to know that as well.

chillerthanmost
08-17-2011, 06:17 PM
slightly earlier break up with a small volume drop

gillman royce
08-17-2011, 06:28 PM
It's safe to do as long as the ohmage is above the specific designation. In other words, 4,8 & 16 are ok; 2 ohm - no no

GCDEF
08-18-2011, 07:47 AM
It's safe to do as long as the ohmage is above the specific designation. In other words, 4,8 & 16 are ok; 2 ohm - no no

Not necessarily. Some amps tolerate a mismatch, others don't. Read the manual to see if it's safe.

Bluzeboy
08-18-2011, 07:50 AM
Not necessarily. Some amps tolerate a mismatch, others don't. Read the manual to see if it's safe.


Yep... even if they tolerate the mis-match.. probably no more than 1 each way.. i.e. 4 ohm into either 2 or 8 ... assuming this is a tube amp.

plexistack
08-18-2011, 08:52 AM
My amp tech says it's a no-no, but it keeps him in business.
If you really want to pay for a new OT, go for it.

riffmeister
08-18-2011, 08:59 AM
I know of at least one world class touring pro that does it........Fender amp with a 4 Ohm tranny into an 8 Ohm speaker.

Personally, I have done mis-matches in both directions (e.g., 8 Ohm tranny into a 4 or 16 Ohm load) without incident. But it's a good idea to keep everything matched if possible.

crzyfngers
08-18-2011, 09:01 AM
i've run a 4ohm speaker in my 8ohm amp.(boogie mk1). i like the sound of that.

JubileeMan 2555
08-18-2011, 09:18 AM
Been doing just that in my homebuilt vibroverb for over a couple of years. 4ohm bassman tranny into a 8ohm JBL.

People like to freak out about missmatching, but its not an exact science. Speakers don't produce a constant 8ohms of resistance, and from what I can tell, different tube manufacturers even claim different required reflected loads. This is why most say one missmatch isn't a problem...because ITS NOT.

leodiditright
08-18-2011, 09:30 AM
Is your guitar tech paranoiac?

My amp tech says it's a no-no, but it keeps him in business.
If you really want to pay for a new OT, go for it.

leodiditright
08-18-2011, 09:31 AM
Yep! doin' it all the time with my '72 Bandmaster Reverb into an 8ohm cab.

slightly earlier break up with a small volume drop

Bluzeboy
08-18-2011, 09:34 AM
Yep! doin' it all the time with my '72 Bandmaster Reverb into an 8ohm cab.

Wait a minute.. I thought the 72 Bandmaster was 8 ohm.

leodiditright
08-18-2011, 09:50 AM
It could... but I think it's 4 ohm. Maybe a real authority vintage amp specialist will chime in...

Wait a minute.. I thought the 72 Bandmaster was 8 ohm.

crzyfngers
08-18-2011, 09:53 AM
It could... but I think it's 4 ohm. Maybe a real authority vintage amp specialist will chime in...

not a specialist but i had a blonde one. it was 8ohm.

leodiditright
08-18-2011, 09:55 AM
How did you find out? because on the back panel of my silverface, there is no indication.

not a specialist but i had a blonde one. it was 8ohm.

crzyfngers
08-18-2011, 09:58 AM
How did you find out? because on the back panel of my silverface, there is no indication.

amp tech.

Bluzeboy
08-18-2011, 09:59 AM
not a specialist but i had a blonde one. it was 8ohm.

As I remember (which could very well be faulty). The 61 was 8 ohm 62 - 64 was 4 ohm (like the Bassman) then back to 8 ohm for the Silverface guys.. but.. that's just what I THINK I remember :-)

Jimsz
08-18-2011, 10:03 AM
When I purchased my Mack amp, I asked Don about speaker impedance mismatch as the amp had two 8ohm outputs. He replied:

"So, you can plug each speaker into its own jack. Or, you can use any configuration you like into one jack: both in parallel for 4 ohms or both in series for 16 ohms. You CANNOT harm the amp regardless of what impedance you plug into one or both jacks. Allow me to explain.

The jacks in our amps are wired to the 8 ohm tap on the output transformer. However because of the relatively low power output of our amps (under 50 watts) and the high quality of the output transformers (Hammond) and the tubes (JJ), they are perfectly happy to have any impedance speaker cabinet plugged in. At the voltages and power levels that we run, the output tubes and the output transformer never come close to being damaged.

Because we get this question so often, we actually tested all or our amps by applying an input signal to the front of the amp (at a level higher than any guitar pickup could produce), turned the volume to '10' and left the amp running for over an hour... with nothing plugged into the speaker jack and then with a dead short across the speaker jack! Theses tests simulated the absolute worst case scenarios.

We took measurements throughout the test periods and confirmed that at no time did the output tubes or output transformers see voltages and currents anywhere near their maximum limits - they were just fine. So, if you ordered any of our amps, you would get two jacks that can each be hooked up to any cab or speaker impedance. "

Bluzeboy
08-18-2011, 10:09 AM
You know.. now that I think about it for a second.. maybe it was the speakers that were 8 ohm.. but really.. I don't remember.. Someone will chime in I'm sure.

rmconner80
08-18-2011, 10:09 AM
Assuming a pair of 6L6s and the typical 4K primary plate-plate impedance:

4 ohm OT with an 8 ohm speaker = 8K plate-plate impedance
8 ohm OT with a 4 ohm speaker = 2K plate-plate impedance

I don't like the sound / feel of it, and I don't think it's a good idea for the OT or the tubes. It's kind of like bumping along at 25 miles an hour in 5th gear at 1800 RPM... or driving 60 mph in 3rd gear at 5500 RPM. What's the point when you can match them the way they were intended to run?

In most amps nothing breaks though.

leodiditright
08-18-2011, 10:15 AM
According to the info on the ampware website, yes the 2x12 original Bandmaster cab was 8 ohm so the amp's head should be 8 ohm too...

If it's really the case, I'm getting no mismatch running it into my one 15" 8 ohm cab.

You know.. now that I think about it for a second.. maybe it was the speakers that were 8 ohm.. but really.. I don't remember.. Someone will chime in I'm sure.

wishkahdaddy
08-18-2011, 11:07 AM
You can match them the way they were inteded to run in every scenerio??? Please inform me then on how I can match a 4 ohm amp to an EVM12L that only comes in 8 ohms or 16 ohms and I run a 1x12 cab. Please don't tell me to get a 2x12 cab or to go with a different speaker... That's my situation and why I started this thread.
Thanks

Assuming a pair of 6L6s and the typical 4K primary plate-plate impedance:

4 ohm OT with an 8 ohm speaker = 8K plate-plate impedance
8 ohm OT with a 4 ohm speaker = 2K plate-plate impedance

I don't like the sound / feel of it, and I don't think it's a good idea for the OT or the tubes. It's kind of like bumping along at 25 miles an hour in 5th gear at 1800 RPM... or driving 60 mph in 3rd gear at 5500 RPM. What's the point when you can match them the way they were intended to run?

In most amps nothing breaks though.

Bluzeboy
08-18-2011, 12:16 PM
That's my situation and why I started this thread.

Now that we know the real question.. What amp are you using?

brucesinger
08-18-2011, 02:09 PM
I believe you can do it to some extent with the Boogies. The Mark series combo amps had and 8 ohm jack and two 4 ohm jacks on the back. The 8 ohm jack went to the speaker in the combo. The 4 ohm jack went to an extension cab with an 8 ohm speaker in it. I remember asking the question with my little combo/ext cab stack, and was told it was perfectly acceptable.

strat a various
08-18-2011, 02:31 PM
Do we know which amp is in question here? Marshall amps can be sensitive to an impedance mismatch ... Fenders are generally pretty tolerant.
I believe 4 ohm tranny to 8 ohm spkr = possible flyback voltage that could damage the tranny.
8 ohm amp to 4 ohm spkr works the tubes a little harder, but is probably safer in Fender amps at least.
Twin Reverb runs into 2 ohms when an ext. spkr is also plugged in ... it's designed that way.
on the other hand, I ran a drip-edge Bassman for hundreds of loud gigs with an 8 ohm box, no issues.

tlpruitt
08-18-2011, 02:59 PM
Stock Bandmaster Reverb has a 4 ohm output impedence.

leodiditright
08-18-2011, 09:44 PM
Stock Bandmaster Reverb has a 4 ohm output impedence.

That's what I thought. But why the matched 2x12 cab that was sold with it has an 8ohm impedence?

VintageKnob
08-19-2011, 12:00 AM
Fenders (vintage I guess) seem to handle this just fine. I had a '72 SF Twin that I'd plug a showman cab into and play the hell out of it. I never thought about it back then, it had the "ext. cab" input, so I used it.

My buddy's set up for years was a blackface bassman (8ohm) into a 16 ohm Marshall cab - really rocked.

YMMV

- D

tlpruitt
08-19-2011, 08:24 AM
That's what I thought. But why the matched 2x12 cab that was sold with it has an 8ohm impedence?

The 'cabinet' may be correct/original but if the cabinet measures 8 ohms then the speakers in the cabinet are not correct/original .

Bandmaster Reverbs were made from '68-'80 and Fender 2x12 cabinets from that era were always 4 ohms (with two 8 ohm speakers wired in parallel giving a 4 ohm load).

If your 2x12 cabinet measures 8 ohms then that means it has either two 16 ohm speakers wired in parallel or two 4 ohm speakers wired in series. Either way those speakers are not original for the 2x12 cab that came with a Bandmaster Reverb amp.

Schroedinger
08-19-2011, 09:00 AM
You can match them the way they were inteded to run in every scenerio??? Please inform me then on how I can match a 4 ohm amp to an EVM12L that only comes in 8 ohms or 16 ohms and I run a 1x12 cab. Please don't tell me to get a 2x12 cab or to go with a different speaker... That's my situation and why I started this thread.
Thanks

There are really two questions that you are asking.

First, is it safe for the amp and the speaker? The answer is- it depends. The speaker would probably be fine. Whether the amp would be fine depends on what type of output tubes it's running, and how the output transformer is built. A lot of the newer boutique-type amps that you see discussed here have pretty burly output transformers, and would be fine. But I don't know that I'd do this with a cheaper amp, or a vintage amp, or a newer vintage-spec amp. A big part of their characteristic sound is the somewhat-wimpy output transformers used back then.

Intuitively, it would seem that over-loading (using an 8 ohm speaker on a 4 ohm tap) would be safer. In fact, it's the opposite with tube amps. It's safer to under-load (use a 2 ohm speaker on a 4 ohm tap) because they usually can't swing enough current to burn up the transformers.

Second question, will it sound good to you? The answer is- maybe. It will absolutely sound different than using the same speaker on an 8 ohm tap. The main thing that will be affected is the damping; in your case, it will probably sound a little tighter and more congested than normal, and not as loud.

So in summary- I think you can try it to see if you like the sound. Tube amps are generally pretty tolerant of stuff like this, as long as you're careful. I would start at reasonable volume, and as you turn it louder feel the output transformer with your hand every five minutes or so. If it gets hot, then stop immediately.

Even though you don't want to hear it, the best solution is to get a correctly rated speaker or use a pair to get the correct rating.

tlpruitt
08-19-2011, 09:28 AM
You can match them the way they were inteded to run in every scenerio??? Please inform me then on how I can match a 4 ohm amp to an EVM12L that only comes in 8 ohms or 16 ohms and I run a 1x12 cab. Please don't tell me to get a 2x12 cab or to go with a different speaker... That's my situation and why I started this thread.
Thanks

One solution is the Weber Z-matcher. Allows you to match just about any amp output impedence with any speaker impedence.

There are really two questions that you are asking.

First, is it safe for the amp and the speaker? The answer is- it depends. The speaker would probably be fine. Whether the amp would be fine depends on what type of output tubes it's running, and how the output transformer is built. A lot of the newer boutique-type amps that you see discussed here have pretty burly output transformers, and would be fine. But I don't know that I'd do this with a cheaper amp, or a vintage amp, or a newer vintage-spec amp. A big part of their characteristic sound is the somewhat-wimpy output transformers used back then.

Intuitively, it would seem that over-loading (using an 8 ohm speaker on a 4 ohm tap) would be safer. In fact, it's the opposite with tube amps. It's safer to under-load (use a 2 ohm speaker on a 4 ohm tap) because they usually can't swing enough current to burn up the transformers.

Second question, will it sound good to you? The answer is- maybe. It will absolutely sound different than using the same speaker on an 8 ohm tap. The main thing that will be affected is the damping; in your case, it will probably sound a little tighter and more congested than normal, and not as loud.

So in summary- I think you can try it to see if you like the sound. Tube amps are generally pretty tolerant of stuff like this, as long as you're careful. I would start at reasonable volume, and as you turn it louder feel the output transformer with your hand every five minutes or so. If it gets hot, then stop immediately.

Even though you don't want to hear it, the best solution is to get a correctly rated speaker or use a pair to get the correct rating.

+1 on what Aaron said.

leodiditright
08-19-2011, 09:53 AM
The 'cabinet' may be correct/original but if the cabinet measures 8 ohms then the speakers in the cabinet are not correct/original .

Bandmaster Reverbs were made from '68-'80 and Fender 2x12 cabinets from that era were always 4 ohms (with two 8 ohm speakers wired in parallel giving a 4 ohm load).

If your 2x12 cabinet measures 8 ohms then that means it has either two 16 ohm speakers wired in parallel or two 4 ohm speakers wired in series. Either way those speakers are not original for the 2x12 cab that came with a Bandmaster Reverb amp.

My cab is not a 2x12, it's a one 15" Eminence Legend, and this speaker is 8ohm, so I'm running my 4 ohm '72 Bandmaster Reverb into this 8 ohm cab, and all the amp techs in my area are saying that it's safe, they say that the opposite will be unsafe (running a 4 ohm amp into a 2 ohm cab)

So I guess it's like with doctors, they all have their own theories and practices and the poor patients are left in the clouds...

jtm622
08-19-2011, 10:06 AM
The Mesa amp manual definitely says that it is a "safe mismatch" to run their 8-ohm output into a 16-ohm speaker cabinet...

evets618
08-19-2011, 10:23 AM
Just a guess, but Eminence Legends are inexpensive and fairly common. I would imagine it's rather easy to re-cone one to four ohms.

tlpruitt
08-19-2011, 11:27 AM
My cab is not a 2x12, it's a one 15" Eminence Legend, and this speaker is 8ohm, so I'm running my 4 ohm '72 Bandmaster Reverb into this 8 ohm cab, and all the amp techs in my area are saying that it's safe, they say that the opposite will be unsafe (running a 4 ohm amp into a 2 ohm cab)

So I guess it's like with doctors, they all have their own theories and practices and the poor patients are left in the clouds...

Not sure why you quoted me. My response, that you quoted above, was in response to your statement about a Bandmaster Reverb being sold with a 2x12 cabinet that measured 8 ohms:

But why the matched 2x12 cab that was sold with it has an 8ohm impedence?

I never posted anything in this thread about the safety of impedence mismatches. I have a Bandmaster Reverb and several Bassman heads and I have run them all into 8 ohm cabs at various times. As many have stated above it is not the optimal speaker load to get all that the amps are putting out (headroom, bandwidth, etc.) but the amps survived.

wishkahdaddy
08-19-2011, 11:54 AM
Well after reading the posts here, asking a few people who I really trust, and reading a lot of info on the net, I came to the conclusion that I'm safe to run a 4 ohm amp into an 8 ohm speaker. One very high end amp builder said that you will not "blow the amp" by doing this at all. In fact, some people seem to like this set-up better with their own rig and do it on purpose. It seems that this was common practice for Dumble and he even sent combo amps that were set up this way (4 ohm amp into a single 8 ohm speaker). From 3 very reliable sources I discovered that your OD channel will probably get a bit more "dirty" earlier as well as losing clean headroom.

Thanks for your posts and thoughts on this subject. I feel I discovered the answer that I needed.

On a side note, since the name "Dumble" was mentioned, I suppose I opened up a can of worms...If it gets ugly I'll simply delete the post. This thread is not about Dumble. It's about mismatched loads so please remember that as I'm sure this topic is important and can help others also. Please, please, please, stick to the topic. Thank you

boogiejem
08-19-2011, 01:31 PM
I used to run my Mesa MKIV combo with the 8 Ohm speaker into the 4 Ohm output all the time. It reduced the output a bit but I preferred what it did to the tone of the amp - overdriven and clean it smoothed/warmed things out and took some of the harsh edge off.

GCDEF
08-19-2011, 01:47 PM
Just remember what works for one amp doesn't work for all. Generalizations like this can be wrong and costly. Check the owner's manual rather than going by somebody else's experience with another brand amp that has nothing to do with yours.

Rockledge
08-19-2011, 01:49 PM
If I remember my electrical training right, you cannot run a less impedence tube amp into a higher impedence than its rating, but you can with solid state.

I think that when you run a solid state amp at its lowest tolerable impedence rating you get the hottest sound with the most tone. Running 4 ohms into 8 isn't very efficient and you will lose a lot of punch and probably some low end beef as well.

I use to really like the old Crate amps that you could run at 2 ohms. Man those things sounded hot when you ran them that low.


But you have to be VERY careful. I thought I could get away with running my 6 ohm vintage Kustom head into 4 ohms and found out the hard way I was mistaken.
Running into less ohms in solid state gives you SEDs (smoke emmitting diodes).
Running into more ohms in valve gives you smoke emmitting diodes.

ChorusCrackpot
08-19-2011, 01:50 PM
I run an 8 ohm to 16 ohm speaker mismatch. It sounds good, and is safe. But I'm starting to miss the impact I'd feel from running 8 ohms into 8 ohms.

Marshamps
08-19-2011, 01:51 PM
More load is never an issue. Less load is the no no. No load is bad news!!!! Thats for tube amps only!!!!
Transistor outputs never use other than amp asks for.

GCDEF
08-19-2011, 02:10 PM
More load is never an issue. Less load is the no no. No load is bad news!!!! Thats for tube amps only!!!!
Transistor outputs never use other than amp asks for.

That's not correct. More load is actually worse for a lot of tube amps than less load. Transistor amps only ask for a minimum. Sounds like you have it backwards.

I hate these threads. There's always so much wrong information in them.

leodiditright
08-19-2011, 11:11 PM
That's not correct. More load is actually worse for a lot of tube amps than less load. Transistor amps only ask for a minimum. Sounds like you have it backwards.

I hate these threads. There's always so much wrong information in them.


Yep, that's why we call the knowledgeable people amp doctors because they are as confuse as people's doctors: wrong diagnoses pretty often, innapropriate treatments and the like (sorry if I'm sounding a little harsh)
cars repairmen are a little like that sometimes too, but we as musicians can't be wrong, because as Miles Davis used to say or whoever said it: there are no wrong notes in music...:D

ChorusCrackpot
08-21-2011, 10:35 AM
How would it sound to run a 4 ohm amp output into a 16 ohm speaker?

mad dog
08-21-2011, 11:01 AM
Had some experience with this lately. Safety and sound are often two separate issues. Aaron Smith covered it pretty well. In my own experience, I'm not really comfortable with a mismatch, however you assess it.

Got a '60 brownface pro recently. Had a story. Someone had swapped in a '70s bandmaster 4 ohm OT, glued on the old OT faceplate or whatever you call the part with the codes. No change to the dusty old JBL 8 ohm D130, which had apparently gone in the amp sometime before. The amp sounded quite good, though the bass would fuzz out quick if you turned bass up much at higher volumes.

I got a Z matcher and tried it both ways. Much better sound with no mismatch. A little louder, not a huge difference there, but fuller, more natural sounding. Ended up putting a weber Cali ceramic with the aluminum dome at 4 ohms in the amp. The speaker feels like a better match with this amp.

That same JBL is now in a 1x15 cab. I've run it as an extension speaker in various setups, also as an only speaker with an Allen Encore. That particular speaker just doesn't sound right at 4 ohms. By contrast, a 2x12 cab with two Emi Legend GB 16 ohm ceramics is wired for 8 ohms. This sounds just as good as an extension cab at 4 ohms as it does at 8 ohms.

So it's not usually the safety angle that makes me decide as much as the sound. Never heard a mismatch that was better than a match. With some speakers, mismatching can really degrade the sound.
MD

el burro
08-28-2011, 03:51 PM
so, could i run 2 16ohm celestions parallel for 8ohm in my hotrod deville, which has to 8ohm speakers running 4ohms?

solitaire
08-28-2011, 05:54 PM
so, could i run 2 16ohm celestions parallel for 8ohm in my hotrod deville, which has to 8ohm speakers running 4ohms?
Yes you can, but it's not advisable.

candh
08-28-2011, 10:28 PM
I have a '64 blackface Bassman (4 ohm) that I run into a single 8 ohm cab.

Here's a different slant:

I run JJ 6V6 's in place of the 6L6's. I like the tone, impedance is matched and JJ's handle the voltage fine. It's a case by case workaround but it might be worth a try.

vibrostrat43
08-28-2011, 11:28 PM
It's safer to run a 1:2 transformer:load (ex: 4 ohm OT, 8 load) mismatch than a 2:1 (ex: 8 ohm OT, 4 ohm load) in general...OT's don't really like it either way, BUT it runs the tubes cooler with 1:2 mismatch. Still Stevie Ray Vaughan supposedly ran his amps with a 2:1 mismatch which gives the opposite sound of many of the mods that were done to his amps i.e. it runs the tubes hotter and gives a more raw and loose sound (most of the mods done to his amps were to increase headroom, but it should be noted that he had many amps so he may have had a few that were supposed to breakup easy and some that were supposed to stay clean).

One thing I've learned from some reading is that if you want to reduce the power in your amp that has a quad of tubes, but don't want to risk harming your transformer when pulling a pair of tubes, you can attach a load that's double the OT's rated load.

The tubes and OT transformer will behave exactly as before, but there will be some difference in tone because the transformer was wound for 4 of the tubes in your amp and not 2. Generally, you get a more compressed sound than stock.

You can also do the same thing with an amp that has 2 6L6's by replacing them with 6V6's and doubling the load...of course there are a couple of other considerations to make when doing this (plate voltages, screen voltage and screen resistor, and of course a rebias). The 6V6 isn't exactly a half power 6L6, but it's not far enough off to cause any more problems than say...an 8 ohm OT into a 6 ohm load. Tube life will be shortened some, and the OT may be a bit uncomfortable, but it's a good way to get earlier breakup.