Hissing and whistling in the STe audio output

[exxos]

That's something I can't reproduce. As you can see below, there deosn't seem to be a 2600 Hz spike on the Filter In pin.

Thats why I think its possible it could be generated internally.

Looking at your first FFT, you can see the harmonics spikes, so the tallest one is around 7,000Khz.. So that could actually be the "master" frequency, and 2,600 could actually be a harmonic.

[sandord]

That's something I can't reproduce. As you can see below, there deosn't seem to be a 2600 Hz spike on the Filter In pin.

Thats why I think its possible it could be generated internally.

That could very well be the case indeed.

Looking at your first FFT, you can see the harmonics spikes, so the tallest one is around 7,000Khz.. So that could actually be the "master" frequency, and 2,600 could actually be a harmonic.

As far as I know, harmonics are always of a higher frequency than their fundamental frequency so 2.6 KHz can't be a harmonic of 7 KHz.

Interestingly, it appears that there are still MF4 compatible chips for sale (Farnell has a small stock for example). Perhaps, later on, if we're sure the MF4s are the culprit, we can try replace them with the (hopefully improved but still compatible) TLC14/MF4A-100 (see http://www.ti.com/lit/ds/symlink/tlc04.pdf).

Okay, so at some point I will bypass the MF4 in my STE, perhaps if my new soon-to-arrive solder socker works really well, I can do this safely. Last time I pulled up a resistor, I destroyed a via :shock:

[sandord]

Yeah, though you may find some which physically fit by the pin pitch.. You probably don't need the full value either.. Looks like there is 47uF for the coupling caps, so even 1uF may work... There are some larger SMT caps like 2220 size which can go up to 100uF.. bodge some wires on those... actually as it looks like I will have to send you a new simm, I have some 33uF ones coming for my PSUs, so I could just send you 4 of those caps as well to try.

Now that I have received these SMT caps from you, what's the plan how to use them? I don't feel confident enough to select the caps to replace by the SMT ones.

[exxos]

Its those electrolytics in the audio path..

[sandord]

I picked up another STE today. I think I'm going to try the cap fix on this STE since it doesn't have the DAC patch yet. That should provide us with better data.

[sandord]

I've got 8 of those large SMT ceramics and there are 10 electrolytics on the schematic. Which two caps would I skip best?

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[exxos]

I've got 8 of those large SMT ceramics and there are 10 electrolytics on the schematic. Which two caps would I skip best?

Its the 47uFs to replace with the SMT ones ( so looks like 2 caps )

[sandord]

Its the 47uFs to replace with the SMT ones ( so looks like 2 caps )

Well, I didn't know that :D I have very little experience reading schematics so I'm walking this path guessing left and right :)

[exxos]

Well, I didn't know that :D I have very little experience reading schematics so I'm walking this path guessing left and right :)

It's the electrolytic's which go bad over time, a smaller ceramic type ones generally do not go wrong.

Of course, my DAC FIX board also needs to be fitted to the machine you are changing those capacitors on..

[sandord]

Of course, my DAC FIX board also needs to be fitted to the machine you are changing those capacitors on..

Good thing you mention that because I was about to do it in my other STE.