[time-nuts] Distribution amps for Thunderbolt

Charles P. Steinmetz charles_steinmetz at lavabit.com
Sun May 19 04:58:45 EDT 2013

Chris wrote:

>I have been offered one of these:
>ADA 6 300MX HV HDTV RGBHV 1 x 6 Analog Video Distribution Amplifier
>I *THINK* it should meet my needs except the HV bit worries me. It
>seems this means it has not got unity gain, but a gain of 0.7 or 1
>volt, switch selectable. Could anyone comment if it's suitable to use
>my Trimble Thunderbolt with several pieces of test gear at the same
>time? Thanks. Here in the UK the ADA-3-80 seems a rare find.

"HV" just means that it has an additional sync channel ("Horizontal 
and Vertical").  I think "MX" means selectable gain.  I have two 
plain ADA 6's (no MX, no HV) that I used before I built my own 
iso/DAs.  The gain switching components are present, but the switch 
itself is not populated, so it runs at unity gain overall (the 
amplifier runs at x2 and each output is back-terminated).

My ADA 6's use 6, CLC409 amplifiers and, when modified with 50 ohm 
input and output terminations, each section (3 jacks) can drive 3, 50 
ohm outputs to +13dBm with ~1dB of headroom (I generally only fed 2, 
50 ohm loads from any one section).  Like any video DA, it should 
have much smaller coupling caps installed to restrict its 
low-frequency response to HF.

You need 21, size 1206 (SMD) 50 ohm resistors and some 100 nF 
capacitors to do the mod (I used NP0 ceramics).  You also need a deep 
socket (9/16", I think) to get the PC card dismounted from the back 
panel (it is mounted by the BNC connectors).

As supplied, there are 3, 1x6 DAs in the box.  You can parallel 
inputs internally as desired (deleting duplicate input terminations) 
to make one, 1x18 DA or one each 1x12 and 1x6 DAs.  You really 
shouldn't have more than one HF reference frequency running around 
inside a DA, so the 1x18 configuration is probably the most useful.

I was quite happy with mine for routine distribution of 1/5/10 MHz.

Best regards,


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