Hello! I have a ua733HC differential video ic and would like to build a circuit with it to amplify a vcr read head up to a level that will be viewable and usable in the good ole analog video gear of yesteryear. Found the datasheet for the IC, but anything resembling a basic circuit with the beast is not found using the world wyde webb search. Basically what would be great to know is 1) can one use a simple DC 5volt power source with this...the earth from the 5v going to the V- leg of the 733...? 2) in effect would the input and output earth connections also go to ground..meaning the In 1 = signal and In 2 = ground.... ? and 3) do i need to couple in1, in2, out1 and out2? would love to hear from those who could enlighten me as to what a differential video amp does...how it works...and a simple circuit to hook up and get a video vcr read head up to signal strength for a video mixer. Thank You! datasheet of the 733 attached 8o)

 

Hi r359,
Welcome to AAC
These two PDF's may provide some background information for video OPA's
E

 

The 733 is a simple differential amp with a bandwidth of 120MHz and selectable gain from 10 to 400.
Here's the data sheet for the same device built by National Semi with some example circuits.

 

thank you ericgibbs and crutschow for the datasheets. looking for information specifically with a) the power supply and if one could power a video chip like an audio op amp...+5 and ground....as opposed to a +5 and -5 supply. also looking for information on coupling at the input and output sides of the chip...and lastly ..whether the input and output are freely floating with respect to ground or if they are(or can) in fact be tied to the ground of the +5 volt supply and then be soldered into the second leg of the input and output sides of the chip. the datasheets don't seem to answer those questions ... at least not in a way i can understand...currently my knowledge us more with analog sound amplification with transistors and op amps....

 

this is what i have...is this going to work and give a 400x gain on the signal?

 

one could power a video chip like an audio op amp...+5 and ground....as opposed to a +5 and -5 supply.

The chip is specified for ±6V supplies, so probably would work with ±5V, but likely will not work well (or at all) with a single 5V supply.

information on coupling at the input and output sides of the chip.

The input signals can be referenced to ground level for equal plus and minus supply voltages.
The outputs appear to have an offset so should be capacitively coupled as shown in the data sheet test circuits (example below):



±

 

The IC requires bipolar supplies. Otherwise you will exceed its input common mode range and clip both the sync pulses and half of the color burst, which swing negative.

 

If you really need to operate from a single 5V supply, then you need to use a high-speed op amp that will operate from that single voltage.

 

Or if you must use the 733, employ a charge pump like the ICL7660 to generate your negative supply.

 

thank you schmittrigger & crutschow. just found an icl7600 and with two 200nf caps will give it a whirl..plus the 51 and 1k resistors..the two outputs are a bit confusing i must say...would one simply treat the two outputs as signal and ground for the video signal? like the two inputs i suppose...?

 

I hope you meant 200 microfarads and not 200 nanofarads.
The former however, it is too large and the voltage will take too long to settle. Try instead 10 to 22 microfarads.
EDIT; I can see there is a part number confusion…..my message above may not apply.

 

just found an icl7600

I hope you meant the ICL7660.

The ICL7600 is a combination opamp and auto-zero component. It is not nearly fast enough for video, let alone the 10 MHz bandwidth required for a VHS video carrier. It is intended for low frequency applications that require extremely low input offset voltage errors. The recommended commutating capacitor value is 1 uF.

https://datasheet4u.com/download/625833/ICL7600.html

ak

 

twas a typo. (7660S) 8o) isn't a nano between a micro and a pico? the drawing calls for 2 x .2micros..200 nano isn't it? i reckon i will put it all together and see if i get a black screen, smoke, or video. thank you for all the assistance. great that human forums are still alive and well.

 

the drawing calls for 2 x .2micros..200 nano isn't it?

Yes, there are two 200nF caps at the 733 output.
AK thought you were referring to the 10µF caps the 7660 requires.

 

I have used the LM733 as a video amp, it works. BUT if it is driving a low resistance load it gets rather warm.For normal composit video it does need both supply voltages. OR tricky biasing and series capacitors on the inputs and outputs.

 

you mention a vcr head as the source
these are typicaly transformer coupled to the amp, i.e. AC coupled .
the circuits i see above seem to be for dc coupled
if i remember , the vcr vdeo signal was also modulated, so the phase / frequency of the signal is critical

 

The 733 differential amplifier does require base resistors for base current return.

 

thank you schmittrigger & crutschow. just found an icl7600 and with two 200nf caps will give it a whirl..plus the 51 and 1k resistors..the two outputs are a bit confusing i must say...would one simply treat the two outputs as signal and ground for the video signal? like the two inputs i suppose...?

Differential signals are used in small voltage , low noise systems because the differential signal is more immune to noise pickup than single ended , ground referenced systems.
The circuit needs to be differential up till you have a big enough signal that the noise pickup is no longer relevant compared to the signal .
Are you wanting to use the VCR as a VCR or for something else ?

 

Another concern:The video playback head in all of the VCRs that I have seen is a spinning head, usually one of two or four that is moving around a loop of tape. How are you going to synchronize that with the tracks?? The stationary head on a VCR is just for the sound and the synchronizing signals. OR is that all that you are interested in??

 

Another concern:The video playback head in all of the VCRs that I have seen is a spinning head,

In the early 50's, anybody who was anybody was developing a video recorder, and all of them tried a stationary-head design. Literally miles of tape for minutes of video.

Visualize a big audio tape deck with the tape moving 50 miles per hour . . .

ak