I bought my Vox about 20 years ago and it sounded great, plenty of volume. But after a while it sounded like it was getting quieter. Wasn't noticeable but then it got to the point where I was cranking the volume 3/4's. So it sat in my room for about 15 years, rarely played.
Fast forward to 2020 lockdown and I thought I'd have a good look at it now I've got a signal generator and scope, oh, and unlimited time!
So, 1kHz 100mV in Normal input, I get 22V at the PI coupling caps but only 3V at the speaker. Thought, that not right. Put the scope on the caps and the PI is in phase, the signal is the same on both sides, not 180deg reverse. Changed the caps same issue, I've replaced all the resistors in the signal path.
Any ideas?
Aaron
1964 AC30 VOLUME ISSUE
Moderators: pompeiisneaks, Colossal
1964 AC30 VOLUME ISSUE
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Re: 1964 AC30 VOLUME ISSUE
That's normal. A speaker is a current driven device. It needs lots of current but not much voltage.
Most likely just a scope triggering issue. To see the phase difference you need to trigger the scope on one vert channel only.Put the scope on the caps and the PI is in phase, the signal is the same on both sides, not 180deg reverse. Changed the caps same issue, I've replaced all the resistors in the signal path.
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Re: 1964 AC30 VOLUME ISSUE
Or he could have one of the channels inverted?sluckey wrote: ↑Sat May 23, 2020 1:15 pmThat's normal. A speaker is a current driven device. It needs lots of current but not much voltage.
Most likely just a scope triggering issue. To see the phase difference you need to trigger the scope on one vert channel only.Put the scope on the caps and the PI is in phase, the signal is the same on both sides, not 180deg reverse. Changed the caps same issue, I've replaced all the resistors in the signal path.
~Phil
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Re: 1964 AC30 VOLUME ISSUE
So,update. User error it was inverted. It’s a push pull switch and a lead must have got caught and pulled it out. The Marshall I worked on earlier scoped fine.
Sad news though, thanks to Beasley helping me to diagnose it, output transformer had gone bad.
Aaron
Sad news though, thanks to Beasley helping me to diagnose it, output transformer had gone bad.
Aaron
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Re: 1964 AC30 VOLUME ISSUE
Well a nice Hammond replacement up grade cost a tad less then 100 Dollars and should take you less then 1 hour to cut the only one out and slap in the new one!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Re: 1964 AC30 VOLUME ISSUE
I bought a Hammond for my AC 30 build and cannot be happier!!
Markus
Markus
.........Now where did I put it?
Re: 1964 AC30 VOLUME ISSUE
Hi Steve and Marcus,
Just so happened that I installed a Hammond replacement yesterday. And its back! I'd forgotten how loud it was.
It wasn't as direct a replacement as they claim, in mine the original lays on the side and the mounting bolts are in the middle. And the cover plate bolts that attach to the side didn't line up either. Will get the original rewound one day.
Thanks,
Aaron
Just so happened that I installed a Hammond replacement yesterday. And its back! I'd forgotten how loud it was.
It wasn't as direct a replacement as they claim, in mine the original lays on the side and the mounting bolts are in the middle. And the cover plate bolts that attach to the side didn't line up either. Will get the original rewound one day.
Thanks,
Aaron
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Re: 1964 AC30 VOLUME ISSUE
Hi Aaron
Sound wise- What are your thoughts??
Loud yes- but to my ears pretty musical sounding OT?
Markus
Sound wise- What are your thoughts??
Loud yes- but to my ears pretty musical sounding OT?
Markus
.........Now where did I put it?
Re: 1964 AC30 VOLUME ISSUE
Im a big fan of the Hammond Transformers. They're nice and big and have a lot of weight in them. I use them in most of my builds.
My VOX is the Treble model, so cuts through great and has that VOX chime. Nothing like the new ones, to me anyway
Thanks,
Aaron