QA404 and QA403 Update

A short update on what is happening with material shortages and QA404 and QA403. First, a graph over time of the % of TI’s portfolio that Digikey has in stock. This is focused on DCDC converters because throughout the shortage there hasn’t really been an issue getting TI’s analog parts. But their DCDC converter segment hasn’t been so lucky. From the graph, we can see that early June 2022 looked to be the low water mark. That is, less than 25% of TI’s catalogue DCDC converter parts were in stock in June of 2022.

Recently, there’s been a lot of improvement. And coincidentally, we’ve had three different sources (Digikey, Mouser and Arrow) send thousands of SN6505B parts with more coming. This wasn’t the only shortage, but the other areas are hopefully manageable via substitutes. The SN6505B had no substitute.

In the last few weeks, a decision has also been made to add isolation into the QA404. Part of this was due to the SN6505B arriving (meaning an isolation solution can be built). Another reason is that there are measurements where the isolation isn’t just nice to have–it’s important to have. The QA404 will use a more streamlined isolation solution that needs a single SN6505B, while the QA403 will continue to use 3 SN6505B.

And so, what this all means is that there will be QA403’s available again, hopefully in March. And the QA404 will follow that shortly in April or May. A comparison of the differences is below, along with target pricing.


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When can we place pre-orders/orders for the QA404? Do you have any UK dealers that orders can be placed with, or can I order directly? Thanks.

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Matt, this is good news indeed.

Just curious, how are you able to use just one SN6505B in the QA404? Any downside with fewer SN6505Bs?

Hi @djsb, currently there is not way to pre-order, but we are trying to get a shopify tool working that will allow US$10 to place the order, and then the balance is collected right before shipping.

Hi @aaa, it’s done by using a larger transformer. The SN6505B can do 1 amp in the primary (5W), so it’s got plenty of capability. So, you send 5V across the iso barrier and then do the voltage conversions in the iso domain.

Thanks for the explanation Matt.

Any chance of offering existing QA 403 owners an upgrade board, internal or external, for SPDIF output?

Greetings Matt-

The 404 will test a DAC, I presume? Feed it digital, measure the analog coming back?


Hi Matt,

Is there a blog entry showing the QA404 features (SPDIF etc)?



Thanks for the update. Apart from the table you have provided - will there be any other changes (for example, the max input voltage or anything like that?). I am really excited for the QA403 or QA404 as I am trying to design a Class A amplifier and really need one of these to check the SNR and THD. But I am trying to decide whether to go for the QA403 or are there any additional features that make the QA404 worth the wait (apart from the 1-2 dB better and S/PDIF which I do not need).

Hi @Bartosz, those are the big differences between the QA403 and QA404. The QA404 might have a bit more protection if you subject it to 100V DC (or ACpk) with the attenuator off, but that is still being evaluated.