Like it or not. LM6172 DIP packages are marked as last time to buy. I just spent an obscene amount buying a batch of 120 from Digikey before they became totally unavailable from official distributors and we have to face a horrible mark up from scalpers, fakes etc. They are expensive enough as it is! I’ve learned from having half made modules relying on Teensy boards that are out of production, just bite the bullet and buy while you can.
LZX Cadet and Castle modules rely on them @creatorlars , as do designs by Foxing Hour @Fox , Martin Devices @phosphenes , Reverse Landfill @reverselandfill , Syntonie @syntonie , Visible Signals @VisibleSignals , and no doubt a few others I am not aware of. I tend to buy/hoard pcb and panel sets rather than buy complete kits. Maybe some of the people mentioned will also be buying in bulk so that they can at least send out kits for a while longer.
So what’s the plan when these are no longer available? Here are a few options I can think of.
Adapter boards for the surface mount LM6172 chip that remains in production, at least for now. I had a quick go at this and I have a dual sided PCB design that is a little wider than a DIP-8 package so that is can be manufactured (I suppose castellated edges would be an option to fix this), but at least it was within the same height of a DIP-8. May be a clearance issue with very dense designs and eg decoupling caps close to power pins (a solution would be to mount any parts that might collide on the other side of the PCB) . May have a little problem with capacitance in some circuits (I know it was advised to not use sockets for video circuits in the build instructions for Castle and Cadet modules).
Ive seen Lars’ reference designs with the ADA4851 family of chips. These are low cost, high speed rail to rail but need a -+5v supply and probably 4 layer pcbs as well as being surface mount only. Makes a surface mount to DIP adapter board less simple so probably need a PCB redesign. Then either the designer needs to get the surface mount parts pre-soldered or the customer needs good soldering skills, maybe a hot plate and hot air and potentially a microscope or magnifying glass.
Chroma Cauldron Mainbow (great module BTW) uses TL974 op amps, which is a quad opamp. There are also dual and single versions. They are available as DIP but are not suitable for -+12v so would need -+5v. They have a 12MHz bandwidth (which I think is fine for composite video) but significantly lower slew rate of 5V/uS. I am not sure if the higher slew rates of the other chips is necessary for composite video but Mainbow seems to work well with them. From one article I have read the slew rate is too low for component video. Again not really a “drop in” replacement and likely a PCB redesign but they are through hole and cheap.
I might just get a batch of 5 pcbs made up and test if I can spot any downside to an SOIC to DIP adapter for the LM6172.
I’m not really an expert on op amps for video. I can study a datasheet and compare values but I don’t know what specs are neccesary for what formats. Input from people with better knowledge than I would be greatly appreciated! Want to keep the DIY video synth stuff alive for as long as possible.
I’m about to fire off a V2.2 of the Soft Key which has a combined SOIC and DIP footprint, which should allow the use of remaining LM6172 stock or the other SMD packages.
I’ve ordered some AD8034 to test as a replacement. But I’m absolutely happy for the big DIY players to lead by example on Video ICs, works a lot better for everyone if we use the same op amps!
The ADA4851 family itself doesn’t need a 4-layer PCB, if that’s what you meant.
I wish the ADA4851 family were available at some of the common PCBA facilities so I could just have the board house solder them on. I’ve been holding off on some modules designs I’ve been working on because I don’t want to try soldering them myself. I’m no good with anything smaller than SOIC. I’ve tried looking into what high speed op amps are available at jlcpcb and others, but I’m not sure what’s best of what’s available.
I was taking Lars’ advice from the reference designs post
A 4 layer PCB isn’t significantly more expensive, just an extra consideration.
Ive not done a PCBA order with JLCPCB yet, but it doesn’t have to be parts that are in stock. They just have to be able to order them from a distributor that will ship to mainland China. Did a quick search for the ADA4851 using their global parts sourcing and they have distrubtors with the chips in stock. Then you consign a quanty to them (need a few extra for wastage) and they will hold any excess in stock for you for free, that only you can use. I have even been able to get them to add a part that wasn’t in their database, they just need to check they can get them and read the datasheet to make sure they can assemble them.
So this topic partly comes from me intending to redo the Cadet series, maybe even the sync generator if I can sort out the clock issues. For the PCBs that require sync I intend to have both sync options - a rear phono sync input using an LMH1980 and the ribbon cable from the C1 sync gen, selectable via a jumper.
I am leaning toward making it all -+5v anyway, making the video op amps with a combined DIP8/SOIC8 footprint. Protect any inputs with diodes. Then if I want to do a sub assembly with eg a TSSOP to DIP8 in the future the circuit is ready. Doing it this way is probably the most versatile as it means it will be easier to use alternative parts. I will probably prototype with both the LM6172 and the TL972 since it is so much cheaper and being DIP easy to work with.
I don’t like diptrace so I am in the process of redrawing PCBs. Probably starting with ramp generator first as I think its the least complex board that requires sync - want to test out the dual sync jumper idea.
That’s general video electronics advice, not ADA4851-specific advice. It’s definitely a good idea to do it, but it applies to all op amps and isn’t a requirement. That what I was trying to point out.
True, but in-stock is cheaper, as I understand it. And less complex to some degree, I’d imagine. I’ve never done PCBA so I’d like it as cheap and easy as possible as I figure it out.
I get the impression at least JLCPCB are moving away from having non passive parts in stock. They have only 20 different ICs in stock under their amplifier heading. I think I am going to do a small run of adapter boards for LM6172IM/NOPB, which are already in their global parts sourcing database - also going out of production but replaced with LM6172IMX/NOPB. I will do a castellated edge and then it is at least a drop in replacement option for others who can’t bulk buy like I just did. I will let you know how it goes
If this was something you’d want to do as a community I’d be interested in tackling a few. Would be great to get them all on four layer boards! I’ve already benefited so much from them now being open source so I’m very interested in keeping it that way for the next generation.
JLCPCB has a “global parts sourcing” feature where they can order from the likes of Digikey/Mouser etc in the event they dont have something in stock.
You can even send in your own parts for your parts inventory now, it used to only be available to Mainland China but they recently opened it to out of the country. We just sent them a few hundred LDO’s we had in one of our parts drawers and it went without issue. Very straight forward.
Jlcpcb’s parametric search constantly gives BS results, you’re much better off just typing in known part numbers or browsing on LCSC. It might show 20 amps when there are tens of thousands. There was some github project that offered a better parametric search for JLCPCB but even that often wouldnt bring parts up that couls be found by just typing the part #
Yeah I am in the process of doing a PCBA order with JLCPCB. I had exactly what you were saying about expecting to find a part number in the search that wasnt there. Found it on LCSC and I am waiting for approval but they were pretty quick last time.
Gave up on castellated edges. JLCPCB need the board to be bigger to do this process. PCBway will do it, but only as part of an “advanced” PCB order, which would leave the board cost too high unless I did an order of 50+. So just sticking to small as possible and hoping there will be no clearance issues. I just want people to have a relatively low cost drop in replacement for existing designs when the dip LM6172 goes out of stock.
Working on an updated ramps generator too but I am doing this in my spare time and I am a little busy so progress is slow.
PCBA order for LM6172 SOIC to DIP adapter now sent for assembly. Only having 5 made as a test. At this scale, the price is about 40% higher than just getting 1x LM6172IN/NOPB from an official distributor like Mouser, but once the main distributors run out this will likely be the most cost effective way to get an LM6172 in DIP form.
Provided this is a working solution I intend to open source the gerbers, but I hope to have some PCBs for sale too - both populated and unpopulated.
Hope to have some time to work on ramps generator later in the week.
Yeah that is my suspicion too. Thankfully the AD8034AR is SOIC8 with the same pinout and looks like it might be a suitable substitute. Lower slew rate of 80 V/μs vs 3000V/μs and slightly lower bandwidth of 80MHz vs 100MHz but that should be fine for most video designs. At least its SOIC so just about solderable by hand
