Sony ECM-HST1 Modifications for External Microphone Connection

I really wanted the ability to connect my external wireless and shotgun microphones to my Sony HDR-HC3 camcorder. Shame on Sony for not providing a microphone input on this camera, but it was the right camera at the right price for me when I needed to go to High Definition in mid 2006. I didn’t want to be limited to Sony’s small collection of Active Interface Shoe microphones. After googling around and finding a photo that William Zaggle posted about modifying the Sony ECM-HST1 stereo microphone, I decided to try it myself. It was a delicate operation to cut the traces and solder such tiny components, but it seems to have succeeded. Here are some pictures I took along the way. Click any photo for a larger version.

** Alternative solution: Sony Part #183064611, circled in this photo, is a hotshoe plug with wire leads. It sells for about $65. You'll need to solder an 1/8" stereo jack to the wire leads and that's it, although you might consider putting capacitors in series and a backwards diode to prevent a blowout. See schematics below.

First twist off the front cover.

Then twist off the back cover. For those unfamiliar with this kind of mic, there is a forward-facing mic that feeds both Left and Right output channels, and a sideways-facing mic that picks up sound from the left and right sides at the same time. One output channel gets the forward signal plus the sideways signal, and the other output channel gets the center signal minus the sideways signal. There is a 90-degree/120-degree switch on the back of the HST1. The sideways signal is multiplied by a larger factor in the 120-degree position than in the 90-degree position, creating more stereo separation.

Slide off the plastic shield. Unsolder the ground connection to the metal screen. Remove the holding screw and separate the HST in two. The photo below shows the two 1/8” mini jacks that I added. Each jack is stereo because I already had them in my junk box, but I only used the connections for the tip and left the ring connections alone. You could use just one stereo jack if you want, but I wanted to be able to use the HST1 for one channel and an external source for another channel, and two jacks gave me the flexibility to do this.

Carefully remove the microphone from the housing by unhooking the rubber supports. Here is one side the circuit board.

Here is the other side. You don’t need to remove the black insulator from the left as shown below.

Here is a composite photo of the front and back. I zoomed into this on my computer to figure out the connections. The IC in the middle with the yellow marks is the dual op-amp used in the output stage. Click here for a datasheet for the op amp.

Here is the same photo with some marks to show connectivity.

Here is a schematic of the output stage.

Here is the photo that William Zaggle posted showing where to cut traces and how to wire the jacks. As mentioned earlier, I used two separate jacks as shown in the schematic instead of just one.

Here comes the tricky part. If you have a friend who is an experienced electronics technician who has a good magnifier on his workbench and tiny soldering iron, it would be worth paying him or her to do the actual soldering. The next part was difficult with my old eyes and a generic soldering iron. As shown in the last photo of this page, I used a piece of wire wrapped around my soldering iron to create an extra-fine tip, but it didn’t work so well. Maybe I should have filed down the regular tip instead. Anyway, I found very thin stranded wire inside some lightweight headphone cable, stripped and tinned the ends, cut the traces as indicated by the Xs, and somehow soldered my wires in place. Be sure to make a good connection, but also be careful not to apply too much heat. When I was finished, I used hot glue to hold the wires in place (avoiding the 90/120 degree slide switch). The solder connection alone is barely strong enough.

The wires and hot glue bumped into the microphone when I tried to reassemble everything, but cutting off some plastic from the white mic assembly gave me clearance.

Here is the gadget re-assembled halfway.

For anchoring the external microphone jacks, I found a plastic bottle in my medicine cabinet (expired syrup of Ipecac) which was the perfect diameter. I cleaned it thoroughly (with paint thinner to get the label off), cut it to size, drilled holes in the end, and attached the plugs.

I cut a small opening in the bottom to still have access to the 90/120-degree switch with a pen or other object. Looking back, it might have been better to put this hole on top for easier access when the HST1 is attached to the camera, but most of the time I will probably leave it in the 90-degree position, putting more of the center mic into the Left and Right outputs, since I usually film things that are far in front of me and I don’t get much stereo separation at the camera anyway.

The brown bottle fit snugly on the back of the HST, but to keep it from getting pulled off when plugs are removed from the jacks, I used my tiny soldering tip to melt a hole through the bottle and the HST shell and put a very small screw through both to secure them together.

See the picture at the top of the page to see the finished product. Good luck if you attempt this procedure. I hope I was able to help. Thanks to William Zaggle for getting me started.

--Tony