The speakers in my Vox AC30 (or any 2x12)

mark123

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I picked up a nice Vox AC30C2X the other day. Been playing it and it seems most of the sound comes out the back. There seems to be a dead spot at the front center as if the speakers are pointed outward at 30°. The sound gets louder as you move your head right or left. Does this imply that the speakers are wired out of phase?

I’m pretty sure they are wired in series with the OEM cable. I am going to have to crack it open and check things out.
 

mark123

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I couldn’t wait so I opened it up before getting ready for work. I just popped the wires off, ran the jumper from + of one to - of the other and checked the resistance. 12.8, perfect. Then I connected the wires from the OT. The dead spot in front of the amp went away.

Now I’m going to neurotically check the wiring of the speakers every day until the world ends because I’ll worry that I’ve done something wrong.
 

mark123

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It must have been incorrectly wired but I’m surprised that it still sounded great. I figured out of phase speakers would totally trash the tone but it just seemed to displace it from the front of the amp.

I’ll be farting around with it more in the next couple of days.
 

mark123

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I’ll photograph it when I open it up again to check bias and all that goodness.

It’s got a complement of fresh tubes. I’m no huge fan of JJs but these have the good ECC803s (long plate) in all the preamp positions. This is my first EL84 amp so I’ve not got anything to compare them with.
 

fitz288

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I’ll photograph it when I open it up again to check bias and all that goodness.

It’s got a complement of fresh tubes. I’m no huge fan of JJs but these have the good ECC803s (long plate) in all the preamp positions. This is my first EL84 amp so I’ve not got anything to compare them with.
I've got 803's in my O20H.
Huge improvement over the stock 83's.
Tried other tubes, and the 803's went right back in.
 

mark123

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I've got 803's in my O20H.
Huge improvement over the stock 83's.
Tried other tubes, and the 803's went right back in.
Long plate in V1 and matched triodes in the PI is the secret to toan! This is the hill that I’ll die on.
 

paul-e-mann

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I picked up a nice Vox AC30C2X the other day. Been playing it and it seems most of the sound comes out the back. There seems to be a dead spot at the front center as if the speakers are pointed outward at 30°. The sound gets louder as you move your head right or left. Does this imply that the speakers are wired out of phase?

I’m pretty sure they are wired in series with the OEM cable. I am going to have to crack it open and check things out.
These are nice amps and sound great, nice vintage tone, and the power scaling works nice. The only downfall is the loop, with a boost pedal in the loop I couldnt get a volume boost out of it for solos it only added more gain so I returned it and got an SV20H.

For your speaker phase issue, you can put a 9v battery on the speakers and if the cones move out your in phase, if they move in its out of phase.
 

mark123

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For your speaker phase issue, you can put a 9v battery on the speakers and if the cones move out your in phase, if they move in its out of phase.
I think you have a conceptual error here. It doesn’t matter if a speaker goes in or out with a DC source. The issue is when there are two (or more) speakers and one goes in and the other goes out.
 

paul-e-mann

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I think you have a conceptual error here. It doesn’t matter if a speaker goes in or out with a DC source. The issue is when there are two (or more) speakers and one goes in and the other goes out.
I've never done it, only read about it. Google will explain better if you want to try it, I was only mentioning there was a way to check. :yesway:
 

PelliX

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Long plate in V1 and matched triodes in the PI is the secret to toan! This is the hill that I’ll die on.

Yep, works a treat. Still, JJ EL84s in the output section deadens those amps for me a bit. If you can get Sovteks or Shuguangs (my fav), they really 'sing' more than the JJ's. Just my $0.02.
 

mark123

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Yep, works a treat. Still, JJ EL84s in the output section deadens those amps for me a bit. If you can get Sovteks or Shuguangs (my fav), they really 'sing' more than the JJ's. Just my $0.02.
Definitely going to get some Mullards or Sovteks for the EL84s. 👍
 

mark123

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I’ll photograph it when I open it up again to check bias and all that goodness.
Wait, these are cathode biased, aren’t they? I need a schematic.

I probably won’t fart around with the cathode resistor. I’ll just check it for problems and leave it alone.
 
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PelliX

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Wait, these are cathode biased, aren’t they? I need a schematic.

I probably won’t fart around with the cathode resistor. I’ll just check it for problems and leave it alone.

Yup, AC30's (valve based, of course) are all cathode biased. I say valve based, because there are and were semi and completely solid state models. Not applicable in your case, of course.
 

mark123

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Oh, no! What is happening. This amp is making me question whether I'm actually a Marshall guy or not. :eek:
 

PelliX

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Oh, no! What is happening. This amp is making me question whether I'm actually a Marshall guy or not. :eek:

More is more. You wouldn't turn down a brunette just because you often favor blonde, right? ;) Run them in parallel for a ... ok, let's stop there.
 

Chris-in-LA

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Oh, no! What is happening. This amp is making me question whether I'm actually a Marshall guy or not. :eek:
I just cranked my AC30TB today for the first time in years. It sounds a lot like my JTM45 clones. Sounds great especially through a cab with a V30 and Celestion gold, louder and brighter than with the stock Greenbacks. No harm in enjoying a Vox, they’re a classic for a reason.
 

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