Can I Safely Run These Simultaneously???

smitty_p said:
Running into a higher impedance is fine for solid state amps, but it can cause problems in tube amps if the mismatch is too high. The problem is the output transformer on the amp. If you run the amp into too high of an impedance, it can create flyback voltages in the output transformer that can shorten its life. Usually, a 1:2 mismatch (i.e., 8 ohm output into a 16 ohm speaker) is fine. But, too much beyond that can be hard on the output transformer.
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I try to keep it within less than a 2ohm difference honestly. For example : i have a DSL50 head running into a 16 ohm and an 8ohm cab with the head set to 4ohms. The rough computed speaker impedance is about 5.4 ohms which would be fine, correct?
 
smitty_p said:
Running into a higher impedance is fine for solid state amps, but it can cause problems in tube amps if the mismatch is too high. The problem is the output transformer on the amp. If you run the amp into too high of an impedance, it can create flyback voltages in the output transformer that can shorten its life. Usually, a 1:2 mismatch (i.e., 8 ohm output into a 16 ohm speaker) is fine. But, too much beyond that can be hard on the output transformer.
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I've ran the 8 ohm cab from the 16 ohm output on the Origin head a few times, hooking up in the dark...
 
Clockworkmike said:
I try to keep it within less than a 2ohm difference honestly. For example : i have a DSL50 head running into a 16 ohm and an 8ohm cab with the head set to 4ohms. The rough computed speaker impedance is about 5.4 ohms which would be fine, correct?
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Personally, I wouldn't worry about a 4 ohm output into a 5.4 ohm speaker load.

But, I'm wild and crazy, like that!

The little secret is that during use the actual impedance seen by the amp constantly changes. The measured DC resistance of a speaker of 8 ohms, 16 ohms, etc., only applies at rest when not in use. However, speakers are reactive. During actual use the real impedance may rise and fall quite a bit.
 
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smitty_p said:
Running into a higher impedance is fine for solid state amps, but it can cause problems in tube amps if the mismatch is too high. The problem is the output transformer on the amp. If you run the amp into too high of an impedance, it can create flyback voltages in the output transformer that can shorten its life. Usually, a 1:2 mismatch (i.e., 8 ohm output into a 16 ohm speaker) is fine. But, too much beyond that can be hard on the output transformer.
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This has hit the nail on the head. Depending on the OT design, some amps handle mismatching better than others (generally, Fender amps handle it better than Marshalls). If mismatching, ALWAYS mismatch up (nominal speaker impedance higher than amps output impedance), & a 100% mismatch is the absolute limit. We can install flyback protection diodes on the OT, but really, it's best to just use the correct impedance cabinet.

Your Origin amp's output section is running in class AB1 Robert. Cheers
 
ivan H said:
This has hit the nail on the head. Depending on the OT design, some amps handle mismatching better than others (generally, Fender amps handle it better than Marshalls). If mismatching, ALWAYS mismatch up (nominal speaker impedance higher than amps output impedance), & a 100% mismatch is the absolute limit. We can install flyback protection diodes on the OT, but really, it's best to just use the correct impedance cabinet.

Your Origin amp's output section is running in class AB1 Robert. Cheers
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Right on! I learned the hard way on a Mode Four Marshall about gross mismatching. Blew one up 15 mins after i bought it new, returned it and got another free under warranty, then blew that one up 4 months later.

Found my issue out later on which was both my fault for not knowing any better and the stores kinda for not knowing either or telling me. The Mode Four had 2 series of cabs ( MF240A and MF240B with Vintage 30s, then the MF400A and MF400B with K100s). The MF240s were 16ohm single input cabs and the MF400s were 8ohm single input. The head has only 2 inputs but changes its output pending on the cab.

In input one with one cab, you need a 16 ohm load (MF240) and the amps power output was reduced to 235w. In input 2 with one cab it had to be a 8ohm load (MF400) and the power was increased to 350w output. But if you used two cabs to get a full 350w fullstack, it had to be a 16ohm load at each input, thus two MF400s wouldnt work, only two of the MF240s. They sold me the wrong two cabs which is why i was blowing the amp lol.
 
Robert Herndon said:
Stereo jacks measure 8 ohms each. Mono's measure 4 ohms each.
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Right and stereo means one half of cab so 2 soeakers. They are either 4 ohms each or 16. Chances are very high they are 16 but I would open the back and measure impedance of one speaker. They cannot be 8 ohm speakers. All the previous posts still apply unless by some weird chance they are 4 ohms
 
Jethro Rocker said:
Right and stereo means one half of cab so 2 soeakers. They are either 4 ohms each or 16. Chances are very high they are 16 but I would open the back and measure impedance of one speaker. They cannot be 8 ohm speakers. All the previous posts still apply unless by some weird chance they are 4 ohms
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I have an honest question: what good are stereo inputs really? Is it a choice of reducing half of the cabinet for output sake or is it more an option to run two amps into the same cabinet? Or both?
 
Clockworkmike said:
I have an honest question: what good are stereo inputs really? Is it a choice of reducing half of the cabinet for output sake or is it more an option to run two amps into the same cabinet? Or both?
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I would assume to run in stereo but with no separation seems pointless to me. I use mjne to reduce output a bit. Runnjng 2 amps woild be fun too.
 
Clockworkmike said:
I have an honest question: what good are stereo inputs really? Is it a choice of reducing half of the cabinet for output sake or is it more an option to run two amps into the same cabinet? Or both?
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Eric Johnson runs two Fender heads into a single stereo cabinet for his clean tone. Each half of the cabinet is mic’ed individually and sent to the mix as a stereo signal.

Incidentally, his dirty rhythm is a Two-Rock run in mono and his lead is a Marshall, also in mono.

He used to use a Dumble, but he’s been using the Two-Rock, instead. That’s what he used when I saw him.

So, yes. A stereo cab can be driven by two separate heads.
 
The problem is the odd number of pairs. The math doesn’t work. I have this combination of cabs ohm values...an 8Ohm 2x12, and a 4x12 that’s wired like his(4Ohm mono/2x8ohm stereo)...my 2x12 is switchable like his too...2x16ohm stereo.
That’s why I don’t bother trying to fit the square peg...
I pair my 8ohm 2x12 with an 8Ohm 4x12 instead, like this...
1603764457442.jpeg
The resulting load can be either 4 or 16 Ohms if I use my series/parallel box.

The choice of 16Ohm drivers in a 2x12 cab is a bit limiting in this scenario.
 
smitty_p said:
Eric Johnson runs two Fender heads into a single stereo cabinet for his clean tone. Each half of the cabinet is mic’ed individually and sent to the mix as a stereo signal.

Incidentally, his dirty rhythm is a Two-Rock run in mono and his lead is a Marshall, also in mono.

He used to use a Dumble, but he’s been using the Two-Rock, instead. That’s what he used when I saw him.

So, yes. A stereo cab can be driven by two separate heads.
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Very cool! And its awesome you saw Eric Johnson: man is a wizard. Thanks for clarifying this a bit too!
 
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