Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jerzey2222 on January 11, 2016, 08:34:49 am
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Hello
I was wondering if someone could help me mod the speaker inputs on my amp. It's a Mesa boogie mark iii. It has 3 inputs. 8ohm - 4ohm - 4ohm. I have a pair of 8ohm cabs. I would like to utilize all the input jacks because through trial I noticed the amp sounds better in the 8ohm jack instead of the two 4ohm.
I would like to put the one (8ohm) cab in the 8ohm jack of the amp and mod to two 4ohm inputs in series so if I used a y cable on the two 4ohm jacks it would equal 8ohms. So basically I would like to utilize all 3 jacks. Mesa's manual encourages modding the inputs for proper impedance match.
I believe the inputs are wired in parallel. Can someone help me? I'm new to cliff jacks.
Hers a pic of the 3 inputs.
(https://farm6.staticflickr.com/5747/23482973225_e5de063e98_o.jpg)
(https://farm1.staticflickr.com/572/22855801273_6246ce5537_o.jpg)
(https://farm1.staticflickr.com/688/23114949109_2813be9212_o.jpg)
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Those speaker jacks on your amp are OUTPUTS, not inputs. What you are asking is not possible. You have two 8Ω cabs. When connected in parallel the total speaker impedance is 4Ω. The proper way to connect those two 8Ω cabs to that amp is to plug one cab into a 4Ω jack and plug the other cab into the other 4Ω jack.
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Hi there , welcome to the forum !
Check out this link (http://el34world.com/charts/Charts.htm) it explain how speaker wiring works, it will help with the speaker jacks as well by understanding how it works.
Maybe you don't need a mod for the speaker jacks, If you have a 2x 8Ohms cabs, both in parallel will do 4Ohms. If you have 2x 4Ohms cabs, in series they will do 8Ohms. Or lets say speakers, will work the same way.
Do as Sluckey says, he knows stuff man !
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Thanks for the reply. I know about the two 4 ohm jacks. That's actually what mesa says to do in the manual. By experimenting, when I put an 8ohm cab in the 8 ohm output the tone sounds superb. It gives off more highs and volume as it should because the impedance is a perfect match. Now when I do both cabs in the suggested 4ohm outputs both cabs sound softer and loose a touch of high end. I'm not sure but I assume it because of the way the amp is built and the way the outputs are tapped to the trannie. So believe it or not I even plugged one cab in the 8ohm and the other in the 4ohm and that sounded better than the suggested two 4 ohms. BUT, sure enough the cab that was connected to the 8ohm had the clarity and the cab in the 4 ohm was soft. I want to find a way to get both cabs to sound like when one is in the 8ohm jack. I think there is a significant difference. If there is absolutely no way to make it work I'm thinking about selling the speakers for two 16 ohm so I could parallel them and utilize the 8ohm jack. Is there anything that can be done? How could i use the 8ohm jack with two 8ohm speakers? (Cabs)
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Have you tried a simple "Y" cable to connect your two 8Ω cabs to the 8Ω jack on the amp? I know this is a mismatch but wanted to know if this gets the sound you want.
It may be possible to rewire your speaker cabs, but we need more info. How many speakers in each cab? What is the impedance of each individual speaker?
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I haven't tried a y cable to the 8ohm jack yet. As far as my setup it is quite simple. I was saying I had two 8ohm cabs to make it easy to understand but what I have is one cab with two 8ohm speakers. But each speaker has its own jack input. So I have to use 2 speaker cables. 1 for each speaker
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OK. You can only wire those two speakers for 16Ω (series) or 4Ω (parallel). Temporarily rewire the speakers inside the cab for 16Ω and plug into the 8Ω jack on the amp. Then temporarily rewire those two speakers inside the cab for 4Ω and plug into the 8Ω jack on the amp. Does either of those configurations get what you want?
Be aware that either of these configurations is a mismatch to your amp. The sound may be different, but neither will give you the full power of the amp. I don't recommend running the amp dimed with this mismatch. I definitely would not wire the cab for 16Ω and plug into the 4Ω jack on the amp.
I don't know what else to say about this amp and this cab. Is it possible that there's a difference between the two speakers?
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I was afraid of this always being a mismatch. The speakers are actually an exact match on the ohm meter. And which ever one is plugged in the 8ohm jack sounds the best. I swapped them both on the 8ohm jack and it's definitely not a speaker issue. I wish I knew why the 8ohm jack sounds better?
Is there now way to mod the amp to combine the two 4ohm jacks to equal 8ohm with a y cable? In the manual Mesa says it's possible to mod to make two 8 ohm jacks for two 16 ohm cabs. How is this done??
Perhaps there's a way to convert the 8ohm jack to a 16ohm by combining all the jacks? Then I could tie the cab in series for a total of 16ohms. I might call Mesa about a solution but if someone could assist please do. It's gona be a pain to trade or sell the two speakers for two 16ohmers.
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I wish I knew why the 8ohm jack sounds better?
That's better to you. May not sound better to someone else. A lot of people like the sound of a 16Ω speaker better than an 8Ω speaker. So, I do believe that different speaker impedances must have a different sound, but it's something I cannot hear with my poor hearing.
Is there now way to mod the amp to combine the two 4ohm jacks to equal 8ohm with a y cable?
No.
Perhaps there's a way to convert the 8ohm jack to a 16ohm by combining all the jacks?
No again. There's no magical way to wire those jacks to produce another impedance. The 8Ω and 4Ω impedances are solely determined by the windings of the output transformer (OT) and those impedances are the only choices you have unless you are willing to replace that expensive OT.
In the manual Mesa says it's possible to mod to make two 8 ohm jacks for two 16 ohm cabs. How is this done??
That's easy. Just move the jumper from the green wire to the yellow wire. Look at the attached pic to see what I mean. If you do this, it would be a good idea to relabel the center jack so you know it's now 8Ω. Then plug one 16Ω cab into an 8Ω jack and plug the other 16Ω cab into the other relabeled 8Ω jack.
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would *mis-phased* speakers cause the lack-luster sound when wired as 4ohm? My Son swears he hears a difference, me, not so much, anyway, fwiw
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would *mis-phased* speakers cause the lack-luster sound when wired as 4ohm? My Son swears he hears a difference, me, not so much, anyway, fwiw
Heck yes. 2 speakers wired out of phase with each other will cancel a lot of the output from them.
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You haven't said if the speakers are the same exact brand and model.
And you haven't said if the cabs are the same exact brand and model.
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Both speakers are 8ohm celestion V30's. In one cab
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I guess I have 2 speakers for sale or trade. :dontknow: I need two 16ohm V30's! :help:
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I guess I have 2 speakers for sale or trade.
As an experiment test the phasing of them; 2 gator clips, a 9v battery. hook a gator to spkr +, another to spkr -, clip say the spkr - to the battery -, then just touch the other gator to the battery + While watching the spkr. Did it *push out, or pull in*?. repeat with the other speaker. Your goal is to make them both go the same direction, which means you might have to swap speaker leads to make that happen.
anyway, fun little experiment :icon_biggrin:
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Have you tried to wire the speakers in parallel for 4Ω load, and use the 4Ω jack? that does match yes?!
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Your cab currently has three choices, wire the cab in series for 16 ohm total impedance or wire the cab in parallel for 4 ohm total impedance, or each speaker jack plate cords going to separate 8 ohm speaker output jacks on the amp.