2015 VOX Ac30c2 service manual

[Dave H]

The only difference between the one I posted above and the TSC one is that TSC includes the .022uF coupling cap inside the Tone Stack and the one I copypasted has it outside the picture, coming from the earlier stage.
But that does not affect EQ at all.

So the circuits are different but their EQ is similar?

[J M Fahey]

Those tone stacks don't look right?
No bass caps,

???? ... the Bass cap is C2 .

and the Fender mid cap is shown as 10nF, rather than the regular BF 47nF (22nF on some models).

But this is not a BF tone stack !!!!!!!
Itīs a VOX/Gibson GA70/Fender Pro 6G5-6G7 one !!!!

Download TSC http://www.duncanamps.com/tsc/ to view and play with the more usual arrangements.

I suggest you do and check the VOX tone stack there compared to the one above ... you will be surprised

The only difference between the one I posted above and the TSC one is that TSC includes the .022uF coupling cap inside the Tone Stack and the one I copypasted has it outside the picture, coming from the earlier stage.
But that does not affect EQ at all.

Tom Phillips

Quote Originally Posted by pdf64 View Post
Those tone stacks don't look right?...

I agree. What's the source of those figures Juan?

Well, those come straight from the mouth of the horse: the Manufacturers themselves:

What I posted:


from VOX showroom (who are suppossed to know about VOX?) http://www.voxshowroom.com/uk/amp/ac30_tb_hood.html

Fender Pro 6G5 or 6G7 tone stack

As you see, that "mystery" tone stack is in fact way more known than most remember.

Important detail: many consider this very clever Tone Stack "a mistake" , plain "wrong", "an error which was mysteriously copypasted without analysis or correction" and similar demeaning designations; the fact is this is VERY CLEVER and you can check what I say by ... ummmm ..... playing with TSC.
Just move the Bass slider 0 to 10 and marvel.

Fact is this is a THREE pot, Bass/Mid/Treble control , where the Bass pot is also the Mid control.
Of course, since one pot (Bass) does the work of two, you can not set them separately, they are linked.

Let me show both pots (look at the schematics above):

* Bass pot: wiper-to-top section.
Its function is to more or less short the Bass Capacitor (.01 or .02uF) .
Fully shorted: minimum (0) Bass
Fully open: as much Bass as possible (10)

* Mid pot: wiper-to-ground
Fully shorted: 10k resistr shorted: no mids (notice Mid notch gets MUCH deeper, as much as 14 dB or so)
Fully open: Mid notch gets less dip, so "maximum Mids"

Please confirm this by playing with TSC Bass pot settings and see how it strongly adjusts Mids too.

But ... but .... isnīt having both controls linked a problem?

Not really.

With control on 5, you have a good balanced amount of Bass and Mids.

On 10: maximum Bass and 0 Mids (wiper shorts it), which gives the impression of even more Bass

On 0: zero Bass (Bass cap fully shorted). ... in principle this would sound unbearably thin BUT ... now "invisible in plain sight" 10k mid setting resistor is free to do its job.

VERY VERY clever and in no way a "lucky mistake" as VOX Showroom calls it.

[pdf64]

So C2 has a solid state rectifier.. can recall many problems trying to get a decently made tube rectifier as well as possible problems with the filter capacitor load.

With tube rectifiers and the post '60's guises of Vox, my perception is that the failings may seem to be due to incompetent 'designers' rather than the device.
Unfortunately the tube rectifier is used as a scapegoat.

[Tom Phillips]

Those tone stacks don't look right?...

I agree. What's the source of those figures Juan?

[oc disorder]

Just thought this might add some clarification re the C2 version from ultimate guitar.

http://www.ultimate-guitar.com/reviews/guitar_amplifiers/vox/ac30c2

"The AC30C2 amp became available in early 2010. Most stores had this amp during the months of February and March. This is a 30 watt class A all tube amp. It is comprised of three 12AX7 tubes and four EL84 tubes. Different for this model is that the faulty value rectifier was replaced with a solid state version. Purists will not like this, but I can say that the sound is solid and I can do without the headaches of having a value rectifier cease working. This model has the classic Vox AC30 sound and chime. The speakers have been improved with Celestion Greenbacks (25 watts a side). This is a two channel amp and is plenty loud. It has that beautiful UK sound. It has a nice spring reverb and the classic Vox tremolo."

So C2 has a solid state rectifier.. can recall many problems trying to get a decently made tube rectifier as well as possible problems with the filter capacitor load.

As I understand it purists prefer the character of the tube rectifier with all it's failings ...

Would have thought this would have a far greater effect than any minor variations in tone caps.

[pdf64]

Those tone stacks don't look right?
No bass caps, and the Fender mid cap is shown as 10nF, rather than the regular BF 47nF (22nF on some models).
Download TSC http://www.duncanamps.com/tsc/ to view and play with the more usual arrangements.

[vioman19]

Thank you JMF that helps ALOT !!

[J M Fahey]

VOX has used the same klunky (but hey, it's *their* version of clunky and an important part of their signature sound) tone control everywhere, since forever and in a thousand amps, specially AC30 , so I very very much doubt they changed values specifically on your model.
So it should be the same as this:

I have seen a 56pF cap in the place of the 47pF one, a very small change, if any (considering caps were 20% tolerance).

As of possible mods: you can't really decrease the 47/56pF one, parasitic cable capacitance must already be close to that value.
Increasing it will make the amp have more high mids and be less chimey, it will cease to be a VOX without actually becoming a Fender or Marshall.

If you decrease the .022 ones you rise bass turnover frequency and probably amp will become more middy and less bassy.
If you increase it the opposite will happen, the amp will be somewhat more hollow sounding, more scooped.

[vioman19]

The problem is that I don't know the cap values that are on the stock PCB

[vioman19]

Thank you all for your comments. I did all the mods to date including going with a more vintage feel of the speakers and tubes. The amp sounds amazing as it stands right now. I am in no way knocking the Stock VOX but I am a professional player and I want to take my sound that extra step including going with the woden clone output transformer and the classic JMI spec caps. Here is a forum that Lyle Caldwell posted on the mods that he performed to get the JMI spec in the new ac30 c2.
Vox AC30C2 Mods with Variable Voltage - MyLesPaul.com

[J M Fahey]

It's not the values of the caps it is the caps themselves that they used. I want to mod the crapp caps they used and use mojo caps to get a more vintage feel out of the amp

Sorry to hear that because it won't happen.

Least important part in sound is capacitor brand and age.

Speakers are 1000000 times more important, difference can easily be heard and measured.

If anything, try to get a couple **old** speakers , same as those used in original VOX amps (which will cost you a few hundred $$$) or some old VOX , which will cost you a few thousand ... but is the real thing.

[Enzo]

Well, if you know the values, and all you want to do is change the brands of caps in the amp, seems like the new schematic wouldn't be necessary.

[DrGonz78]

Thanks JMF. But that manual is the one that is older and don't match the new amps. It's not the values of the caps it is the caps themselves that they used. I want to mod the crapp caps they used and use mojo caps to get a more vintage feel out of the amp.

The schematic probably won't include a parts list. If it does include a parts list, it probably won't include the part manufacturer. Just saying that all you need to know is the value of the caps involved, which includes voltage rating and capacitance. Just be aware that changing those caps won't make a huge difference or possibly even any difference at all. If it makes you happy that is all that matters and if you can hear it then that is what is important.

[Dave H]

For your eyes only ..... and maybe 2000 Million others

Does that mean 2000 Million people can see all the crap I post on here? Just as well I'm not using my real name then. Oh wait!

[vioman19]

Thanks JMF. But that manual is the one that is older and don't match the new amps. It's not the values of the caps it is the caps themselves that they used. I want to mod the crapp caps they used and use mojo caps to get a more vintage feel out of the amp.