The current production Vox AC15C1 by Korg is one of the most popular tube amplifiers being used among P&W guitarists today. At $599 USD for a new 1×12 combo it is undoubtedly one of the best bang-for-the-buck amplifiers readily available through major music retailers. Though these Chinese made PCB amplifiers have many strengths, they also have a few common weaknesses that are widely recognized among those who own them. Notably, poor bass response, grainy mids, and ice pick highs. In my experience working with AC15C1 and AC15CC owners to help them improve their tone I happened across a non-invasive formula that takes these little amps from good to great. Every one of these AC15 owners has thanked me for helping them bring out the mojo in their amp. I recommend trying these upgrades in the order listed. If you find a point where you are completely satisfied with the results, stop. Continue to the next step if you decide you want to take it to the next level. We usually don’t use our articles to sell product. However, a couple of the items recommended in the article are items we offer. We encourage you to purchase these products from whomever you please and support local businesses whenever possible.
1. Don’t clip the bright cap yet! ($0)
Most guys don’t realize that the Chinese Alnico Blue or Greenback is the reason for the shrill top end on these amplifiers. Clipping the bright cap removes the chime that made the original AC15 famous.
2. Install a Bad Cat Celestion Speaker ($189) *minus whatever you sell the original speaker for.
There are many speaker options that will yield a sonic improvement in these amps, and the Bad Cat Celestion is a proven example. So much so, my customers and friends have deemed it “The AC15 Saver”. This custom designed speaker is the secret weapon for balancing the tone on these amps. Developed for Bad Cat by Celestion to combine the percussive low end of a G12H30 with the creamy cone response of vintage Bulldog alnico, this 65w/ 100 db speaker gives the AC15C1 and CC solid bass, pulls the mids together, and puts a smooth layer of cream on the top end. Once this speaker is installed you may be glad you didn’t touch that bright cap. If it’s still too bright for your taste after this speaker upgrade, then you may want to give the bright cap mod a try. It’s an easily reversible mod if done correctly.
3. Replace the Speaker Cable & Plug ($15)
Believe it or not that short little cable can make a slight difference. If you decide to order your Bad Cat speaker from the “Buy Now” option above or our website http://tonesmiths.com/collections/amp-lounge/products/12-celestion-speaker we will solder on a premium speaker cable with a heavy duty 1/4″ pancake plug or 1/4″ female jack for absolutely free upon request. This is the same cable, plug, and jack used by Bad Cat. This addition will ensure strong solder joints, proper phase connections, and save you time on the install too.
4. Install a New Set of Tubes ($60-$75)
There are many brands to choose from when your looking to retube your amp. JJ, Electro-Harmonix, and Groove Tubes are the most popular since they’re easily available at most music store chains. But there’s a brand heralded by hi-fi enthusiasts that will absolutely change your life. These tubes are produced by legendary tube designer Peter M. Watson’s company PM Components. The crazy thing is they’re only a couple dollars more than JJ. I recommend their 12AX7HG for the V1 position, 12AX7A for reverb (not needed for the CC), a 12AX7LM for the phase inverter, and a matched pair of their amazing EL84s. All I can say is prepare to be awed at the increase in output and fidelity these premium tubes provide. They’re so good I dedicated an entire Tonesmiths Report to them The Best 12AX7 on the Market. PM Tubes are only available through a couple US sources. My friend Israel at http://www.tubeboutique.com is the fastest and most reasonable. He offers matched tube sets for every version of the AC15, has great prices, and ships fast.
Here’s a YouTube demo of an: AC15C1 with PM Tubes
5. Upgrade the Output Transformer and Choke ($260 parts/ $200 labor)
This is the most costly and labor intensive upgrade. At this point you will be into your amplifier a total of $850 if you purchased it new at $599. Upgrading the OT and choke to a Mercury Magnetics drop-in replacement will push your investment into the $1,300 range if you have to pay a professional to install them. You could buy a used boutique amp or an AC15HW for that! I would only recommend this upgrade if you are 100% convinced that you need more bass and touch sensitivity after the upgrades and you are planning to keep this amp for a very long time. *Note: With the exception of the transformer upgrade these mods have also been performed on the AC15HW with great results.