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/

For Sale: $400 shipped in the US

Here we have a passive Motown or Detroit style DI box. This one features a UTC A-14 transformer wired 50k to 30 ohms. Has a nice sweet sound. Input and thru on 1/4” jacks, switchable attenuation, XLR output and ground lift.

Built into a grey hammer tone bud box.

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: $900 plus shipping

Here we have the second and final Dept of Commerce preamp. This unit has a model number of CA-1785. Unlike the previous unit, this one has a solid state power supply. Tube complement is a 6AQ5 and a 6AU6 per channel.

We made some tweaks to the circuit and power supply, replaced all electrolytic capacitors, and added a new film capacitors.

On the front panel, you have a gain control, a switchable 20 DB input pad and a variable input pad that comes after the input transformer. This offers a range of color and harmonic dynamics.

New old stock, Sylvania and GE Jan tubes.

2 channel Gates SA-70 heading to France. Building a 2 channel version has been a nice change, but it’ll be much easier once I get the PCBs tested.

NOS tubes and input transformers. UTM output transformers — new fav!

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…

Two channel Gates SA-70 commission for a client. A little bit different feature set with the gain and feedback controls combined with a JLM Go-Between for the pad, phase and 48V phantom power. We got NYT transformers on the input and UTM on the output.

Went with the International power modules on this build which are great and help keep noise low.

Love the faceplate color with the pop of the red k***s.

FOR SALE: $1000 shipped in US

Here we have another Gates SA-70 with all the usual controls: rotary input pad (-40/-30/-20/0), gain control, switchable bass adjust and negative feedback control. Has a DI and switchable backlit VU meter.

Inside we’ve got a favorite combo of mine; the UTC / RCA N-6565 input transformer with an Edcor output transformer. NOS Soviet oil in paper output cap. High quality caps in the signal path.

RCA 6SJ7, RCA 6C5 and KEN-RAD 6X5

Faceplate painted in a grey hammer tone with sparkle and gold specs. The pictures don’t do it justice.

NOS daka-ware k***s and new style Fairchild k***s.

First time building a guitar amp. Put together this little Fender Champ and am really enjoying the sound. I’m falling for these Hammond enclosures and am debating building a preamp or DI into a similar one.

Got new transformers from Tubes and More. Tubes are NOS RCA from the stock pile.

For Sale: $1000 shipped in USA

We got another Gates SA-70 preamp with a slew features packed into a 2U enclosure. The faceplate is finished in a hammered grey with gold luminescent finish.

Across the front we have controls for switchable input pad (-40/-30/-20/0), variable gain control, stepped bass control and variable feedback control. DI input. Switchable input impedance and switchable VU meter.

We have a Soviet paper in oil cap on the output. Tubes are NOS 6X5 for power rectifier, RCA 6C5 and RCA 5693/6SJ7. UTC A-10 on the input and Triad A-65J on the output. Great sounding transformers.

Please message us with any questions or if you are interested in purchasing.

This one was a beast. You’re looking at a UA 175b tube compressor. I stayed faithful to the original design with a few additional features.

Leverages original UTC O-1 input transformer, UTC A-18 interstage transformer and a UTM 3580 output transformer. Combination of RCA and Sylvania tubes. for the power tube with power transformer and choke.

My two favorite features are the giant VU meter and the purple sparkle faceplate finish.

Additional features are “test” switch for setting balance, Hi/Lo input switch and 150/600 ohm output impedance switch.

Front panel k***s control VU meter input, GR meter zero, input, attack, release and output.