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SurfGuitar101 Forums » Gear »

Permalink making a Vox surf

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I think I'm not the only fan of Vox amps around here, so this may be useful to someone. I've figured out a way to dramatically surf-ify the reverb in the current line up of Vox AC amps (at least the AC15C and AC30C.

So, first, I replaced the stock reverb pan, a short, three spring, cavernous washy 8EB3C1B with a long, two spring, medium decay pan 4EB2C1B. This makes a substantial difference to the quality of the reverb, but there still isn't enough quantity.

Next, I tried increasing the reverb gain by putting a guitar boost pedal between the pan and the reverb return. As luck would have it, this gave the amp drip so long as I kept the gain under 10dB. Any more becomes a squeal fest.

With this information, I asked a buddy who's an electrical engineer to review the schematic and look for possible gain inside the circuit. Yesterday he gave me the recipe - change C37 from 330pF to 100pF and change R52 from 100k to 330k. Why these values? Well, I'm not an EE so I have no idea!

Also, as an added bonus, the Surfy Drip works with the Vox reverb circuit! The taper isn't as good as with Fender style circuits, but it works.

Video of the final result here: DEMO VIDEO

Also, check the video description for links to the in process testing videos.

here are C37 and R52 on the circuit board:
image

here is how the surfy drip is connected to the reverb circuit. I put the jack for the pedal through one of the plastic grilles so no drilling of metal or wood.
image

here you can see the RCA splitter where the surfy drip jack attaches at the reverb return. Also, note the full length reverb pan (4EB2C1B) fits just fine inside the head.
image

Last edited: Jul 31, 2020 23:24:46

Awesome!! I’ve just started reading about tube circuits and I look forward to understanding those peaky resistors and caps someday. Finding those components seems fairly straightforward (to someone who knows how to read those things!) but knowing what to put there is magical knowledge. I’d love to know exactly how they work, which I’m sure I will eventually. Robrob’s site is my starting point, and his recommended reading is next. PCBs scare me, although I know they can be easy to service.

Nice work! Such a different tone than Fenders! To me it sounds less “sharp” and more “buttery.” Thanks for sharing this!! It actually sounds very similar (the reverb not the tone) to a ‘64 reverb tank I’ve got.

Hey, Mel, I am a Vox fan as well having had two handwired AC30's and currently an all-tube AC10 which I am in love with for recording and jamming. It has "the" tone that I prefer for what I am doing and it has just the right amount of real tube distortion with the proper settings. I did replace the original el cheapo Chinese tubes with Mullards which did make a noticeable positive difference sound-wise. The onboard reverb sounds fine as is, my trusty old Fender reverb tank is not needed.

If I was recording strictly uber-clean trad surf, I'd use a Fender but for the more popular edgier stuff, I am blown away by this little beast. And when cranked, it might be the loudest relatively inexpensive 10W guitar amp on the market.

image

Jack
aka WoodyJ
The Mariners (1964-present) http://themarinerssurf.wordpress.com/
HulaHounds (1996-2013)
The Surge! (2004, 2011-2012)
X-Rays (1997-2004)
Various non-surf bands that actually made money (1977-1990)

Last edited: Aug 01, 2020 10:20:40

The Vox sound, IMO, is great for Surf. One of my most used amps is a Winfield Cyclone, which is quite similar to an early AC-15, with an EF-86 in the front end. Actually, Mel, I believe you were in the room the first time I ever played that amp, at one of our Gretsch events in Marana, AZ. My initial comment was; “who says small bottles can’t Surf?” Just add reverb, and they are good to go. In the case of my amp, there is no onboard reverb, so I rely either upon my pedals, or my tank.

I doubt that I’ll ever own a Showman, at this point, but perhaps I’ll someday have an AC-30.

The artist formerly known as: Synchro

When Surf Guitar is outlawed only outlaws will play Surf Guitar.
My Guitar WebSite
Dead Thread

Very cool mods....that Vox reverb definitely gets wet and surfy now.
Not many on board reverbs (even Fender) get that level of drip. What brand of 4EB2C1B pan did you use?
I have a DeLisle Nickelbox combo, which is loosely based on the vintage Vox AC4 circuit (EL84 w/EF-86 in the front end) but in a good sized cab ( 20W x 18.75H x 9.5D) w/ a 12" speaker and it sounds great for surf and instro. The onboard reverb is tube driven and sounds great but is much more in the Ampeg camp than Fender but I have no need to futz around with it as I have an outboard tank for drippy, surfy and pretty much anything else and can switch back and forth between the amp reverb and the tank.

Last edited: Aug 02, 2020 11:50:39

WoodyJ, that sounds like a great little combo! Good tubes make a surprising difference.

Syncho - yes, I remember that! I wish I'd paid more attention to the amp at the time. Do you find the EF86 microphonic at all? I've heard the EF86 sounds great but has a tendency to get microphonic, though that may be more of an AC-30 issue (the original AC30/4 had the EF86 channel, but it was replaced with a 12AX7 in the follow up AC30/6).

Surfadelphia - the pan I got is a MOD. Personally, I think Ampeg combo reverbs sound great, at least in the 60s Reverberockets, Geminis, and the B12XT. Of course, nothing beats a proper outboard tank for surf!

MelWaldorf wrote:

WoodyJ, that sounds like a great little combo! Good tubes make a surprising difference.

Syncho - yes, I remember that! I wish I'd paid more attention to the amp at the time. Do you find the EF86 microphonic at all? I've heard the EF86 sounds great but has a tendency to get microphonic, though that may be more of an AC-30 issue (the original AC30/4 had the EF86 channel, but it was replaced with a 12AX7 in the follow up AC30/6).

Surfadelphia - the pan I got is a MOD. Personally, I think Ampeg combo reverbs sound great, at least in the 60s Reverberockets, Geminis, and the B12XT. Of course, nothing beats a proper outboard tank for surf!

No real problems with the EF-86. I’ve heard all sorts of horror stories about microphonic EF-86, but I must have a dozen laying around, all of which I’ve tested and never found a bad one.

The thing is, the EF-86 responds differently from the typical 12AX7 front end. It has a very broad range between the absolutely clean range and the broken up range. It will sort of sing, like it’s approaching breakup, but it just keeps singing, unless you really push it. The sound is very Voxy.

The artist formerly known as: Synchro

When Surf Guitar is outlawed only outlaws will play Surf Guitar.
My Guitar WebSite
Dead Thread

While EF86's are surely not the most robust tubes, their tendency for going microphonic probably has more to do more with application. Most vintage amp circuits (like the AC4, etc) that utilized the EF86 were taken from old hi-fi circuit designs which were not taking into account surviving the rigors of being inside a cranked up guitar amp combo next to a raging, vibrating speaker. What some boutique amp makers have done who utilize the EF86 is redesigned/adapted those circuits to better handle the rigors inherent in a cranked guitar amp. At least that's what I've been told Smile .

Surfadelphia wrote:

While EF86's are surely not the most robust tubes, their tendency for going microphonic probably has more to do more with application. Most vintage amp circuits (like the AC4, etc) that utilized the EF86 were taken from old hi-fi circuit designs which were not taking into account surviving the rigors of being inside a cranked up guitar amp combo next to a raging, vibrating speaker. What some boutique amp makers have done who utilize the EF86 is redesigned/adapted those circuits to better handle the rigors inherent in a cranked guitar amp. At least that's what I've been told Smile .

My Cyclone is a head:cabinet arrangement, which may be an advantage, with regard to microphonics. However, I have played them in combo form, which works well, but there is a solid pine board between the speaker and the chassis. I’ve had this Cyclone for roughly 6 years, and it’s been pretty good to me.

The artist formerly known as: Synchro

When Surf Guitar is outlawed only outlaws will play Surf Guitar.
My Guitar WebSite
Dead Thread

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