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 Analogue TV video modulator Silicon chip March 2018, what spec op amp do I use
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 Return to top of page · Post #: 1 · Written at 7:25:22 PM on 25 May 2018.
Gordon's Gravatar
 Location: Melbourne, VIC
 Member since 17 March 2015
 Member #: 1714
 Postcount: 19

I hope someone give me some advice, I am in the process of building the Analogue TV modulator from the Silicon chip March 2018 issue. I was wondering with the LMH6642 op amp there are various types to choose there is LMH6642MF, LMH6642QMF and LMH6642XMF. What would be the best one to go for? This part seems a little hard to get but Mouser have some, any help would be greatly appreciated. This is the last part I need to finish the project.

 Return to top of page · Post #: 2 · Written at 10:12:15 PM on 25 May 2018.
GTC's avatar
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5342

That article's author is a member here, so I'm sure he'll be able to advise you.

 Return to top of page · Post #: 3 · Written at 12:17:17 AM on 27 May 2018.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1353

Hi Gordon

They are all basically the same part, as long as it has the SOT-23-5 package, i.e. to match the PCB footprint, you'll be OK. Other than that it isn't critical because it's only running on 5 volts. The 6642 is a "video-rated" op-amp with the ability to drive a low impedance load.

That is the hardest part to hand solder onto the pcb, btw. You'll probably need some solder wick if you don't have it.

Turns out my little project has been quite popular by all accounts.

 Return to top of page · Post #: 4 · Written at 11:59:04 AM on 27 May 2018.
Gordon's Gravatar
 Location: Melbourne, VIC
 Member since 17 March 2015
 Member #: 1714
 Postcount: 19

Hi Ian,

Thanks for your reply and advice, I'm lucky that I work with SMD as part of my work including hand built prototyping so building the modulator was quick and easy. I checked all the caps with a Peak LCR meter prior to installing them, I found flux is also your best friend when working with SMD parts, mainly the IC's. I built a audio video transmitter from Silicon chip many years ago and I'm interested to see if I can feed the RF output from the vintage TV modulator into the RF amplifier stage of the earlier transmitter which uses 2 cascaded upc1688 IC's so I can transmit to my portable TV's.
Thanks for designing such a great project.

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