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.



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.


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.

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YES- A target date and ability to Pre order.

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Your best estimate on 404 Avail-?
And ability to pre order?
And how this will be announced, so that I don’t have to sort thru this forum?
IE : A wait list for the 403/404…and you will email for pre order?

That is good news - I will just stick to the QA403 as it will be out sooner in that case… I am currently working on a Class A amplifier design (that I hope to have manufactured here in Australia) and this equipment is vital for me. If there could be a preorder list come out - that would be great! I am just very worried that because I live in Australia, I will miss out.

Do the QA403 and QA404 use the same ADC?
Which one?
Thank you.

Great news here, i´m 100% positive to pay that 50 bucks more for that 1-2dB and SPIF :slight_smile: Looking forward to replace my QA401 ! :innocent:

Hi @Sparky, yes the ADC is ES9822QPRO and the DAC is ES9038Q2M. Same converters for both Q403 and QA404

Hi Matt, will the DAC of the QA404 be able to work at 384k sample rate?

Hi @clane, no, with isolation being added back into the QA404 there will be same timing issue from the isolators. In the QA403 (and QA404) I think you can use the -384K command line option and enable 384K for the ADC, but this is more of an experimental setting and it might not work on every unit. The DAC in 384K mode will definitely not work.

It would be great if the isolation could be switched on and off.
Best of both worlds… for the job at hand.

Hi @Sparky, You can always connect the BNC shell to earth ground if you want to bypass isolation. For example, on the QA403, if you are wondering if isolation is helping, grab a USB cable that is plugged into your desktop PC (laptop won’t work) and touch the metal shield of the USB connector it to the BNC shell. That will bring the isolated ground to the same potential as the PC. And you can see how your spectrum noise floor changes. Sometimes it doesn’t matter much, and other times it does.

Oh… okay, I see…