Downbeat Studio

Downbeat Gates SA-70 PCBs are in and available for sale!! $25+shipping gets you the foundation for a great DIY Build. Message if you’re interested and checkout the Downbeat Blog for more details.

https://downbeatstudio.com/2025/06/08/db-70-gates-inspired-diy-preamp/

The ‘DB-70’ is our version of the Gates SA‑70 preamp. The DB-70 is a classic tube-based microphone preamplifier from the mid-20th century, valued for its rich tonal character, transformer-coupled signal path, and flexible tone-shaping capabilities. These will be available for sale soon as partially assembled kits or just PCBs . Historical Context & Lineage Originating from vintage broadcast and studio gear, the SA‑70 shares its heritage with designs from…...

‘DB-70’ Gates Inspired DIY Preamp The ‘DB-70’ is our version of the Gates SA‑70 preamp. The DB-70 is a classic tube-based microphone preamplifier from the mid-20th century, valued for its rich tonal character, transformer-coupled s…

For sale: $1500 shipped in US

You’re looking at a 2 channel Dept of Commerce CA-1588 tube mic preamp. This was put into commission in June 1957.

This preamp definitely has vibe. I’ve gone through the unit and rebuilt the power supply, updated the circuit, added capacitors, resistors and replaced all faulty components. Added a proper IEC power connector, star ground and hum control. Got NOS military grade and JAN Sylvania tubes. One 6AU6 and 6AQ5 per channel. RCA 5Y3 tube rectifier.

Controls on the front are a pre input transformer pad, post input transformer input control and a gain control between the 1st and 2nd tube stage. Lots of control for variation of drive and harmonic saturation.

Old mil-spec connectors are converted to XLR. Plug n play ready.

This preamp is quite old, so I did my best to lower the noise floor, but it’s still higher than current production preamps.

It has roughly 60db of gain on tap. Transformers are rated for small band frequency response, but pass audio 20-20k. I’ve got it at 5db down at 20hz and 5db up at 20khz.

Great piece of history ready to use in your studio.

I have a second similar unit I’ll post this week.

Hi allI'm back with the final installment on how our Gates SA-70 preamps are crafted. Today, we'll focus on the enclosure, layout, and metalwork. We're moving a bit in reverse, as this is usually the first step in building a preamp. Lets start with parts we are going to need for a single channel preamp enclosure: Chassis Box - Hammond, Aluminum, 17" x 8" x 3"...

Gates SA-70 Part 3 – Enclosure Hi allI’m back with the final installment on how our Gates SA-70 preamps are crafted. Today, we’ll focus on the enclosure, layout, and metalwork. We’re moving a bit in reverse, as…