César Dîaz, a prominent advocate of tube amps and vintage guitars, worked as an amp tech and gear advisor for notable musicians such as Stevie Ray Vaughan, Eric Clapton, and Keith Richards. During his time working with Bob Dylan, Dîaz shared insights on guitarists’ gear and tone, providing a deep dive into how he helped shape Vaughan’s sound.
Stevie Ray Vaughan, who was relatively inexperienced when Dîaz first met him in 1979, benefited significantly from Dîaz’s expertise. With little guidance at the time, Vaughan had much to gain from Dîaz’s insights, particularly when it came to his guitar and, more importantly, his amps. The collaboration between the two was pivotal in shaping Vaughan’s sound.
Dîaz first encountered Vaughan at a club in Bethesda, Maryland, in 1979. Impressed by Vaughan’s playing but unimpressed by his sound, Dîaz approached him with a suggestion. Vaughan’s primary guitar at the time was a ’59 Stratocaster, known as “Number One,” though it wasn’t yet worn down and the “SRV” initials were still intact. It lacked a left-handed whammy bar, a modification Vaughan had yet to make. Dîaz suggested that he emulate Jimi Hendrix’s setup by adding a whammy bar positioned at the top for better vibrato control. Vaughan agreed, and the modification was made.
At this stage, Vaughan was not particularly concerned with the technicalities of his equipment. He played intuitively, without much technical knowledge. However, over time, Vaughan became more focused on improving his gear and sound, which led to him becoming increasingly particular about his setup.
In his early career, Vaughan used a black-panel Vibroverb amplifier, specifically the rare version with a single 15-inch speaker. Dîaz recalls that the Vibroverb was slightly loose in the low-end range, but it still worked well for Vaughan’s needs. When Vaughan acquired a second Vibroverb, the two amps were from the same production year, 1964, which was the only year the particular model was produced.
Vaughan was always open to suggestions about improving his sound, often seeking Dîaz’s advice in the middle of the night while on the road. Dîaz became known as “Stevie’s pacifier” due to his ability to calm Vaughan when he became uptight about his sound. Vaughan appreciated having Dîaz around because he could make adjustments to the equipment on the spot.
Vaughan’s first significant gear modification involved replacing the output transformers in his amps. The original transformers were worn out, causing an imbalance between the tubes. Dîaz explained that with push/pull amplifier designs, it was crucial for the transformer taps to match closely to ensure the tubes heated up properly. Dîaz’s work on the transformers was one of the first steps in optimizing Vaughan’s tone.
Vaughan’s use of heavy strings—ranging from .013 to .052—and his half-step-down tuning had a considerable impact on his amp performance. Dîaz noted that the nonstandard frequencies created by Vaughan’s tuning generated different spikes in the amp’s signal. As a result, Vaughan’s input sensitivity had to be adjusted to account for the changes in pitch. Additionally, Vaughan’s aggressive playing style, particularly his heavy attack on the low strings, often caused the tubes to overheat, leading to dramatic visual effects like smoke rising from his amps. Despite these issues, Vaughan remained committed to the Vibroverb as his go-to amp.
Stevie Ray Vaughan had a superstition about numbers and preferred to keep his amp controls at specific levels regardless of the sound they produced. For example, he would set the volume at 6, the treble at 5 1/2, and the bass at 4. To avoid any issues with the amp not sounding right at those settings, Dîaz would adjust the volume control without Vaughan noticing, ensuring that the amp appeared to be set at the same level Vaughan was accustomed to.
While Vaughan’s guitars were mostly stock, one of his instruments was modified with an extra coil inside to cancel out hum. Although Dîaz was knowledgeable about rewinding pickups with reverse wraps and reverse polarity, he was not the guitar tech—Rene Martinez handled those modifications. Vaughan, however, was very particular about his tone and often discussed the sounds of other guitarists, including Mike Bloomfield, Hubert Sumlin, Otis Rush, Pee Wee Crayton, and Guitar Slim. These players, who favored a bright, cutting tone similar to that of a Telecaster, influenced Vaughan’s tonal preferences.
Vaughan’s commitment to his sound extended to his studio work. During the recording sessions for In Step, Vaughan played as loudly in the studio as he did on stage. When rehearsing in New York, Vaughan’s extreme attention to detail sometimes frustrated the other participants. However, he brought 32 amplifiers to the session to ensure he had the perfect sound. Vaughan’s acute hearing allowed him to identify issues with the amps that others would miss. During the session, he once complained that a small Gibson amp upstairs was malfunctioning, and Dîaz confirmed that there was indeed a problem with the amp.
Despite his incredible success and signature tone, Vaughan was always in search of a better sound. He was never fully satisfied with his achievements, always striving to improve. His sobriety allowed him to focus more clearly on his musical future, and there was still much more that he wanted to explore in terms of his sound and playing style.
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