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Voltage readings:
(Link AGC ON / GAIN 0dB)
Pin 1 : 5v
Pin 2,4,6 : 1.5v(varies with R7)
Pin 3,5,7 : 0v
Pin 8 : 0.14v



Double sided board size: 40mm x 35mm (approx 1.5" x 1.75").
DC input is 10v-12v @40mA.
There is no real setup to make, the preset R7 should be set to midway initially (about 1.8 v on the slider),
with the links set to AGC ON, GAIN 0dB

















Please note that the four mounting holes are not directly connected to ground. Specific earth connections should be made as required.

I recommend simply fitting a 75 ohm resistor in series with the input video, e.g. R3 =75R, R4=0R and R5 O/C.

Use a 47uF for C5 initially
and connect a monitor straight to full output (pin 7 of J1). You may find that this is all you need, if so other attenuator components can be left off. Set preset R7 to mid-way. C5 is optional, if being used in a 'd.c. safe' environment it should be replaced by a 75 ohm resistor, there will be about 1.5v DC sitting on it, but there would be better clamping than using a capacitor. Due to unique internal circuitry a lower value capacitor than usual will generally be sufficient,so I suggest trying a 47uF initially but go up to 100uF if there is poor lf response..







R3&R4 / R5
1dB 1304 / 8.6 1200 / 8.2 1300 / 9.1
2dB 654 / 17.4 680 / 18 680 / 18
3dB 438 / 26.4 470 / 27 430 / 27
4dB 331.4 / 35.7 330 / 33 330 / 36
5dB 267 / 45.5 270 / 47 270 / 47
6dB 225 / 56 220 / 56 220 / 56
8dB 174.2 / 79.2 180 / 82 180 / 82
10dB 144.3 / 106.2 150 / 100 150 / 110
12dB 125.3 / 139.8 120 / 150 130 / 130
18dB 96.6 / 29.3 100 / 270 100 / 300
20dB 91.6 / 371 100 / 390 91 / 360



Some useful attenuator values for 75 ohm circuits...


If you get no video out after building the
project board run the following checks:
Is 5v DC @ 40mA reaching IC1 pin 1.
Are Links 1 & 2 connected to 0v or 5v. Bypass the input attenuator.
Check voltages and resistance on pins. Do Pin 8 volts change when video is connected?
Low volts on pin 4 check R7 and R2.
Resolder all IC pins while pressing down on IC body..
If problem remains please let me know..


Resistance Readings
to GND: (R7 set midway)
(Link AGC ON / GAIN 0dB)
Pin 1 : >600 ohm (ht line)
Pin 2,8 : 4Mohm
Pin 3,5,7 : 0 ohm



UPDATES:  It may be necessary to lower the value of C5 to e.g. 47uF. (Depending on loading). Using a larger value can cause slight video distortion. A 75 ohm resistor can be tried instead of C5, but a s/c on the line might exceed current rating of the IC. If using a 75 R check that the MAX chip is still running cool with about 1.5v on the resistor.
You may not need input or output attenuators at all. Provision has been made in case they are required.
I found that using 3dB input attenuator was best for all my different video feeds. If you have equipment that might give more than 2v pk output I recommend trying 3dB initially. R3,R4=27R and R3= 470R.
The output attenuator can be set to suit whatever circuit it runs into, bearing in mind there is a 0/6dB option link as well. If using 6dB gain setting the attenuators may be of assistance in reducing the level to between 0 and 6dB.
Careful choice of input attenuators will reduce the settling time of the agc. If you are running it from a 5v source via the input pin P1-2 it may be necessary to add some extra decoupling (100uF) at pin 2 (i.e. across C3) if the 5v wire is longer than a few inches to avoid ringing or similar effects due to L1 impedance.














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TOP Views of the PCB.

Overall dimensions are 40mm x 35mm.(= roughly 1.3" x 1.5"). The boards are the same size as the audio processor boards.

Professionally manufactured double-sided printed circuit boards are now available from this website.


The unpopulated pcb is as shown in the image (left).
Boards are available on the STORE page.

An updated pdf with build details and a full description of the circuit is here, original was published by the CQTV 244 magazine in June.

PayPal me as a 'gift' from a friend

or email for more details

If you experience problems getting it running let me know, I will try to help you going.

The MAX7452 IC is no longer in production. I will be carrying a supply, see STORE.
Max. 1 per customer.

Sorry, I cannot supply other components or kits.

Please see the UPDATES column for changes and advice..

Constructors based in the USA will find this
Video AGC USA parts list
from John O'Loughlin useful.