Highland Dynamics Dual Delta 4-7

Highland Dynamics Dual Delta 4-7 is a two-channel tube microphone preamp with a DI section, drawn from a 1960s British circuit. The path is transformer balanced at both ends and every unit is wired by hand, point to point.

Gain set by feedback, not by a pad

The four gain modes, Low, Medium, High and Open, differ in how much negative feedback the circuit applies. Less feedback means more gain and more pronounced character. In Open mode there is no feedback at all, so the preamp runs at maximum gain and maximum tone. That makes the gain switch a tonal decision rather than only a level setting.

Parts chosen for character, not for cost

An EF86 handles the gain stage and a 6DJ8 drives the output. The signal path carries West-Cap, Vitamin Q and NYT paper-in-oil capacitors alongside 2-watt carbon composition resistors, with solid-core copper wiring throughout. Gain and bass cut are set on Grayhill rotary switches, so both channels can be matched exactly and a setting can be recalled for an overdub.

KEY FEATURES

• Two channels of microphone preamplification with a DI section
• Transformer-balanced input and output
• Four feedback-controlled gain modes: Low, Medium, High, Open
• EF86 gain tube with a 6DJ8 output tube
• Grayhill rotary switches for gain and bass cut
• West-Cap, Vitamin Q and NYT paper-in-oil capacitors
• 2-watt carbon composition resistors and solid-core copper wiring
• Hand-built with point-to-point wiring

TECHNICAL SPECIFICATIONS

• Type: tube microphone preamp and DI
• Channels: 2
• Balancing: transformer coupled at input and output
• Gain tube: EF86
• Output tube: 6DJ8
• Gain modes: Low, Medium, High, Open
• Gain and bass cut control: Grayhill rotary switches
• Signal path capacitors: West-Cap, Vitamin Q, NYT paper in oil
• Resistors: carbon composition, 2 W
• Wiring: solid-core copper, point-to-point construction