The "Bedrock" Vox AC15TBR Prototype Amplifier - 1995






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After purchasing the Vox brand from Rose-Morris in 1993, Korg transferred production of the
AC-30 from the Vox facility in Wellingborough, Northamptonshire, England to Marshall Amplification in Milton Keynes, England. Marshall started producing the Vox AC30TB(X) for Korg in 1994. Barring the addition of a standby switch, the AC30TB(X) returned to the original and authentic JMI AC-30 circuit design. The AC30TB(X) also marked the return of the legendary Celestion Alnico Blue speaker.

Sales for the Vox AC30TB(X) exceeded all expectations. Korg hoped to build on this success in 1996 by introducing a modern version of the iconic Vox AC-15. Unlike its dual channel JMI forebear, the new AC-15 imagined by Korg would have a single channel control section. The complex "Vib/Trem" circuit from the original AC-15 would be replaced with tremolo and spring reverb. The new amp would also augment the original passive "Tone Cut" control with the active "Top Boost" tone circuit from the AC-30.

Korg approached Marshall Amplification in both 1994 and 1995 with their AC-15 concept. Korg hoped that Marshall would be willing to produce both the AC-30 and this new AC-15. While Marshall was willing to continue to produce the AC-30, they declined both offers to manufacture the AC-15.

From England to New England...
When Marshall Amplification expressed no interest, Korg turned their search stateside for another amp manufacturer to build the AC-15. Bedrock Amplification of Framingham MA seemed to be the perfect fit for this project.

Bedrock was one of the earliest "boutique" builders of guitar amps. They achieved national recognition in 1988 when Joe Perry and Brad Whitford from Aerosmith endorsed 100 watt Bedrock stacks.

In a letter sent to Korg USA dated September 22, 1995, Bedrock Amplification president Jay Abend detailed the progress Bedrock was making in developing the new AC-15. He indicated that CAD drawings for the printed circuit boards and a prototype chassis were right on schedule for a product launch in early 1996. Faceplate and rear panel artwork were also under design. The cabinet proportions had been finalized and the delivery of ten prototype birch cabinets was pending. Bedrock provided a sketch of the cabinet size and proportions, please see that sketch below and at left.

Bedrock designed a eight tube circuit for the new AC-15. It included five 12AX7 tubes in the preamp, two EL84 output tubes and one 5Y3 rectifier.

The letter continued with a lengthy discussion about the design of the output transformers and their effect on tone. It was also mentioned that sample 12" speakers were ordered from Eminence for evaluation (see photo at left). The letter also discusses 10" speakers from both Eminence and Celestion, suggesting a 2x10" version of the amp was also under development.

Jay Abend also indicated the details of the manufacturing contract with Korg were being finalized and that Bedrock was willing to fine tune the design of the new AC-15 as needed. Several working prototypes were delivered to Korg in the fall of 1995.

The Bedrock produced Vox AC15TBR made its debut at the January 1996 Winter NAMM show in Anaheim California. It was prominently featured on the trade show floor and in the full color flyer from Vox shown below. All seemed on course for Bedrock to start production of the new AC-15.

... and back to England
Jim Marshall was unaware that Korg had been working with Bedrock to develop a reissue AC-15. After Marshall noticed the Bedrock AC-15 prototypes at the 1996 Winter NAMM trade show, he reversed his prior decision regarding the AC-15. Korg received a fax from Marshall several weeks after the trade show stating that Marshall now wanted to build both the AC-30TB and the AC15TBR. This created quite a quandary for Korg.

Bedrock had obviously invested a lot of time and money developing the AC-15. However, Bedrock was a small company with limited manufacturing capacity. Marshall was better equipped to deliver large numbers of amps to Vox in a timely manner. Further complicating matters, Marshall amps were distributed in the US by Korg. I suspect that Korg did not wish to risk their relationship with Marshall by proceeding with Bedrock. In the end, Marshall was awarded the production contract.

The dimensions of the Marshall/Vox AC15TBR cabinet were identical to the Bedrock AC-15 prototype. However, the circuit for the UK made AC15TBR was a completely new design from Marshall lead engineer Steve Grindrod. An interesting detail: the Vox AC15TBR by Marshall eliminated the "Tone Cut" control.

Marshall produced the Vox AC15TBR from mid 1996 to 2004. Bedrock Amplification went out of business in 1997.





Please click on the following link for an "under the hood" look at the Bedrock Vox AC-15.


"Bedrock" AC15TBR Specifications
Year
1995
Production Numbers
A few prototypes
RMS Power Rating
15 watts RMS
Channels
One with two inputs
Controls
Volume, Treble, Bass, Cut, Reverb, Tremolo Speed, Tremolo Depth
Tube Complement
Five 12AX7, two EL84, one 5Y3
Dimensions
23¼" wide, 16¾" tall, 10" deep


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Photos and editorial content courtesy Gary Hahlbeck, North Coast Music


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