A mod for a '65 Vox AC-10

[miserlou]

Hi folks, I just recently acquired a '65 Vox AC-10 Ten Twin, it's a really special amp and sounds awesome. I've got a question that I thought someone in the forum might be able to help me with.

I love the sound of the Vox amps I've owned but I've always wished for a mid range control. I know this may be sacrilege to some, but depending on the style of music I'm playing, it would be nice to have a mid control. Is it possible to do a mod that could be reversible on my AC-10 that would allow me to turn down the mids? Maybe have a hidden pot somewhere on the inside?

Thanks for having this forum active, I look forward to hearing from some of you. I've attached a schematic, I'm not sure if it's the correct one for my AC-10.

Miserlou

[tubenit]

When you ask a question like this, please post a schematic of the exact amp you are referring to. 


Respectfully, Tubenit

[tubenit]

I am wondering if these schematics would be helpful and perhaps easier to read?


After looking at these schematics, I would be inclined to consider an EQ pedal. This would allow you to boost the mids .......... and/or use the pedal as a mild boost pedal.  And it wouldn't be intrusive and would allow you to leave the amp stock.   Just a thought to ponder?   


With respect, Tubenit

[HotBluePlates]

I agree with Tubenit that using a graphic or parametric EQ pedal is the way to go for your needs.

[jordan86]

I will “third” that idea. So simple. And the amp stays intact. Everyone wins. An EQ pedal is such powerful tone shaping tool. There are even some new digital ones with presets you can work through. Scoop mids or more chimney cleans. Or push 800-1000hz for lead boost. Cuts lows to punch through a dense mix. So handy.

There may likely be a ‘that pedal show’ episode or two on the power of an eq pedal. If so, it’d be worth a watch.

[pdf64]

The best mod for that amp would be to fit a mains fuse.
Perhaps Vox overlooked that other countries don’t already have a mains fuse incorporated into the plug.
Or they didn’t expect to export any 

[Jalmeida]

Hi folks, I just recently acquired a '65 Vox AC-10 Ten Twin, it's a really special amp and sounds awesome. I've got a question that I thought someone in the forum might be able to help me with.

I love the sound of the Vox amps I've owned but I've always wished for a mid range control. I know this may be sacrilege to some, but depending on the style of music I'm playing, it would be nice to have a mid control. Is it possible to do a mod that could be reversible on my AC-10 that would allow me to turn down the mids? Maybe have a hidden pot somewhere on the inside?

Thanks for having this forum active, I look forward to hearing from some of you. I've attached a schematic, I'm not sure if it's the correct one for my AC-10.

Miserlou

I have no suggestion on the mid control. One mod that is often done on these and really opens up the amp is simply replace the 220K input resistors with 68K.

[HotBluePlates]

... One mod that is often done on these and really opens up the amp is simply replace the 220K input resistors with 68K.

There is a little more to it than that, because the inputs are not wired like a Fender.

     This causes "the other channel's 220kΩ" to be in-parallel with the 1MΩ, so the signal is cut by half and the loading of the pickup is greater.

     If we only replace the 220kΩ with 68kΩ, the half-signal issue remains and the loading issue gets worse.  So then we would look to make the input jack wiring more Fender-like.

I'll have to look to see what the previous owner had done to my 1965 AC10 Twin:

[Jalmeida]

... One mod that is often done on these and really opens up the amp is simply replace the 220K input resistors with 68K.

There is a little more to it than that, because the inputs are not wired like a Fender.

     This causes "the other channel's 220kΩ" to be in-parallel with the 1MΩ, so the signal is cut by half and the loading of the pickup is greater.

     If we only replace the 220kΩ with 68kΩ, the half-signal issue remains and the loading issue gets worse.  So then we would look to make the input jack wiring more Fender-like.

I'll have to look to see what the previous owner had done to my 1965 AC10 Twin:

You replace both input resistors on the either channels, not one resistor. The AC15 uses the same input wiring, but with 68k resistors.

[kagliostro]

Some years ago I noticed that VOX input wiring is different from Fender and Marshall, I asked and Sluckey analised it for me

If I remember correctly on Sluckey's Scap Book there is a page (or two) dedicated to that analisys

https://sluckeyamps.com/misc/Amp_Scrapbook.pdf

Franco

[sluckey]

You replace both input resistors on the either channels, not one resistor. The AC15 uses the same input wiring, but with 68k resistors.

The AC-10 input jacks are wired differently from the AC-15 input jacks.

The AC-10 jacks are both identical in operation. Plug into a jack and the signal goes through a 220K to the grid but there is a 180K shunt resistance (220K||1M). So, there is a voltage divider consisting of 220K and 180K. Therefore, slightly less than half the signal actually reaches the grid. This is the same for either jack.

The AC-15 jacks are wired like the typical Fender Hi/Lo jacks. The Hi jack delivers 100% of the signal to the grid, but the Lo jack only delivers 50% of the signal to the grid. This is because of the 2:1 voltage divider consisting of the 68K and 68K.

[HotBluePlates]

You replace both input resistors on the either channels, not one resistor. The AC15 uses the same input wiring, but with 68k resistors.

What Sluckey said.

This is reflected in the AC10 schematic vs the AC15 schematic.  Notice the 1MΩ resistor is in a different place, and more importantly has a different connection relative to the switched contacts of the jacks.

[Jalmeida]

I stand corrected.

However it is still a common mod that does change the sound. And when I played with it I liked the 68k better. So take that for what it’s worth.