Oh thanks for letting me know. I guess I'll have to see how much I notice it/it bothers me.

Tiido wrote on 2022-10-09, 12:32:

This card has few issues :
* no way to bypass the speaker amp so it will be too loud and also quite noisy because of it
* no proper voltage regulator for analog side, only a zener based shunt so expect digital noises etc. in the output. There is a spot for a 7805 and this can fix at least this problem.

The amp chip could be bypassed with circuit bending.

I did mean without modifications, with soldering iron, a lot of things become possible 🤣

So the card has arrived now and I'm really happy with it. I am running it through my main PC via audio-out to line-in, but I'm not hearing any noise whatsoever interestingly enough. I don't know, maybe at higher volumes or something it might cause problems, or maybe I've just got tinnitus I'm ignoring that's covering it up, but for now it sounds great.

gdjacobs wrote on 2022-10-10, 02:39:

Tiido wrote on 2022-10-09, 12:32:

This card has few issues :
* no way to bypass the speaker amp so it will be too loud and also quite noisy because of it
* no proper voltage regulator for analog side, only a zener based shunt so expect digital noises etc. in the output. There is a spot for a 7805 and this can fix at least this problem.

The amp chip could be bypassed with circuit bending.

wouldn't it be possible to just desolder the amp and bridge the traces.

Of course, definitely an option and something I have done on a few random low-end cards I have.

Bridge the traces as in bridge Left In to Left Out? etc.?

ya isn't that basically what those jumpers on cards that have them do. a socket in place of the amp might be more elegant.

Warlord wrote on 2022-12-07, 19:26:

ya isn't that basically what those jumpers on cards that have them do. a socket in place of the amp might be more elegant.

Yeah but removin the amp ic from the socket would result in no output then..

When you have those jumpers then that is what you will use, but lowest end stuff doesn't give you that option and other methods will have to be devised 🤣. If the amp chip is socketed and you take it out, yes, you will no longer have any output at all.

Idea is to get Line level output from the card and to bypass the amp. But since on lowend cards you cannot use a jumper to bypass the amp, you re options are remove the amp and route the line level output from the pads that the amp used to be sitting on. I'm not sure what other components you would have to remove or modify but it's entirely feasible.

I'm pretty sure on those cards when you jumper them to bypass the amp you're still getting output no? All you need is 1v. For line level.

For example here is a card that has pads for a TEA2025 but is not using it, but it still works.

https://retronn.de/hwpics/Yamaha_Xwave.jpg

That particular card has two little resistors at the jumper block that does the connection of "line out". All cards without populated amp from factory have a similar thing done on them. To know what to bridge one has to look at the datasheet of the amp chip and see where its inputs and outputs are and go from there, there usually are few more parts to omit or bridge that way too i.e input capacitors are not necessary anymore as there already are the ones that were on output that do this job and there may be few misc resistors etc. to remove too.

Warlord wrote on 2022-12-07, 14:36:

gdjacobs wrote on 2022-10-10, 02:39:

Tiido wrote on 2022-10-09, 12:32:

This card has few issues :
* no way to bypass the speaker amp so it will be too loud and also quite noisy because of it
* no proper voltage regulator for analog side, only a zener based shunt so expect digital noises etc. in the output. There is a spot for a 7805 and this can fix at least this problem.

The amp chip could be bypassed with circuit bending.

wouldn't it be possible to just desolder the amp and bridge the traces.

Yes. That's what I was getting at which Tiido definitely noted. It might even be easier to unpower the chip and bridge the pins, although I'm not certain if that route would be as clean in terms of audio output. The amp chip still might have some parasitic effects even while powered down.

Tiido wrote on 2022-10-10, 05:11:

I did mean without modifications, with soldering iron, a lot of things become possible 🤣

So, the option was raised, but Tiido's choice was to keep the card unmolested. Fair play to him.

Warlord wrote on 2022-12-07, 19:26:

ya isn't that basically what those jumpers on cards that have them do. a socket in place of the amp might be more elegant.

The jumpers usually change the feed point of the output jack from a low Z output after the amp chip to a somewhat impedance matched output after the mixer chip. The amp chip remains connected and powered with perhaps some shunt resistance and capacitance to keep it happy, but limited or no bleed through onto the output jack.

Unpowering a chip never works, it will then start powering itself up through all the other connected pins and this will lead to excess distortion etc. You really do need to remove a chip or utilize some actual disable feature when present.

Tiido wrote on 2022-12-10, 08:29:

Unpowering a chip never works, it will then start powering itself up through all the other connected pins and this will lead to excess distortion etc. You really do need to remove a chip or utilize some actual disable feature when present.

Even worse, I bet the behaviour is quite difficult to predict.