[musicarr]

Hi,

I've just finished building my second MP573. Both of them seem to be working well, from the tests I've done according to the Setup Guide. All tests were good. But on the first one, when changing the dB level on the rotary switch, there are little pops, not terrible, but present. On the second one, the pops are quite pronounced, especially when going from 20 to 30 dB. So much so that it puts the meters into the red within Pro Tools.

So main question: Is this normal, or should there be no pop at all when change dB positions on the rotary switch?

I searched for "pop" in the support forums and found the following two threads:

• Low output and distortion at lower gain levels (https://www.soundskulptor.com/forum/index.php?topic=232.0)
• MP573 Having issues after plugging in (https://www.soundskulptor.com/forum/index.php?topic=260.0)

As I'm quite new to DIY, I didn't fully understand all that was said in the above threads, hence this new thread. Sounds like the pops should not be happing. What would be my starting point to test for what might be wrong?

Thanks

[JPK]

Pops are often caused by a reversed electrolytic or tantalum capacitor.
So the first thing to check is the direction of these caps: The + sign on the layout must match the + side of the capacitor. 

[musicarr]

I was consciously, and verbally, careful to the direction of all caps set correctly. But it doesn't mean I missed one somewhere. I'll check every cap and let you know what I find. 

[musicarr]

With the electrolytic caps, it's easier to see where the negative and positive wires are. And on the tantalum caps, the "+" sign to the right of the labeling points to the positive lead. Is it possible, sometimes, that the "longer" lead of might not be the positive lead? I was going off of the longest lead on the tantalum caps. Is that reliable, or should you always look for the "+" marking to know which lead is the positive?

[musicarr]

I checked all the electrolytic and tantalum caps. There was one tantalum cap that was backwards. I switched it to the correct polarity and the "bib pop" is gone. So that must have been the issue. There still is a slight "pop" going from 20 dB to 30 dB. It registers at about -30 db on the Pro Tools meter. The other positions don't seem to have that large a "pop", as they register about -45 dB on the Pro Tools meter. Is there something else I should look at, or is that "pop" going from 20 dB to 30 dB "normal"?

[JPK]

is that "pop" going from 20 dB to 30 dB "normal"?
Some pop at this position is normal because the 30 position adds a preamplifier stage to the audio path.
If it is feels too loud it could be that the reversed tantalum as suffered from the reversed polarity (not unlikely).

[musicarr]

Go it. Thanks for the clarification. Just to see if that might be the case, I'll replace it. As a reference, it was C20 that I had backwards. Just to be sure I'm ordering the correct replacement, I'm looking for a 22uf 16v tantalum capacitor to replace C20. Is this what I'm looking for (amazon)?

https://www.amazon.com/Uxcell-a14042900ux0341-Yellow-Tantalum-Capacitors/dp/B00PZLX93O/

Thanks