Mod no. 1: I had replaced WIMA MKS 4 (Metallized Polyester) with JB JFX Premium Film Cap (Polypropylene Film) bought recently from TME.
I might be inclined to tell that trebles are a bit more upfront and detailed now, but to be honest without proper A/B testing it's quite hard to tell if any real difference occurred. Anyway, according to audiophile forums & resources Polypropylene is better than Polyester, so I'm pleased that I swapped WIMA MKS with JB MKP (I was tempted to use MIFLEX MKP10 or MKP11, but they were too big to fit properly). Caps links: 1, 2, 3, 4, 5, 6.
WIMA MKS input caps replaced with JB JFX Premium Filter MKP (however, I had them replaced all 4 of them later 4.7uF later)
Mod no. 2: I had installed G.O.S.S. (Grain Oriented Silicon Steel) to shield the toroidal transformer.
Initially, with my sensitive AKG K550 and without any source connected to XLR inputs, when using +20dB gain setting I was able to hear a bit of a hum noise when volume pot was at 3 o'clock or more, especially on the right channel. Now after partially shielding the transformer that noise is COMPLETELY gone!
G.O.S.S. shield installed
Mod no. 3: I got installed as well an EMI/RFI noise suppression filter, but this mod added a bit of hum noise again, because the AC lines from the EMI/RFI filter were too close to XLR inputs (also, PCB traces from XLR were right besides the noise suppression filter). So, I moved the filter from right to the left side, just above the 120/230V selector, as the red arrow shows (sorry for not providing a picture of the actual noise suppression filter positioning, but I was quite struggling with fitting the filter inside the case and I totally forgot to get another picture). Also, please ignore the big red wire, it was connected to the 2 Y-capacitors, but it's not really needed, so I removed it from lack of space (it also did a quite nice short-circuit with flame, so next time I'll be more careful).
G.O.S.S. sheet and the EMI/RFI filter
EMI/RFI filter on top of right of the PCB, just on top of the XLR input traces (had it moved on the left side later to remove the hum induced to the input traces)
Mod no. 1. is recommended and this will improve the sub-bass a bit. This is easy to be seen with square-waves on the scope more than listen to the ears.
Mod no. 2 is recommended only if with sensitive cans you can hear mains hum, otherwise there's risk of short-circuit, so needs care.
Mod. no. 3 is not recommended; instead an external EMI/RFI filter could be added later...perhaps one included in the power strip or something similar. There's too much risk with this filter to get installed inside the metallic case.
I might be inclined to tell that trebles are a bit more upfront and detailed now, but to be honest without proper A/B testing it's quite hard to tell if any real difference occurred. Anyway, according to audiophile forums & resources Polypropylene is better than Polyester, so I'm pleased that I swapped WIMA MKS with JB MKP (I was tempted to use MIFLEX MKP10 or MKP11, but they were too big to fit properly). Caps links: 1, 2, 3, 4, 5, 6.
WIMA MKS input caps replaced with JB JFX Premium Filter MKP (however, I had them replaced all 4 of them later 4.7uF later)
Mod no. 2: I had installed G.O.S.S. (Grain Oriented Silicon Steel) to shield the toroidal transformer.
Initially, with my sensitive AKG K550 and without any source connected to XLR inputs, when using +20dB gain setting I was able to hear a bit of a hum noise when volume pot was at 3 o'clock or more, especially on the right channel. Now after partially shielding the transformer that noise is COMPLETELY gone!
G.O.S.S. shield installed
Mod no. 3: I got installed as well an EMI/RFI noise suppression filter, but this mod added a bit of hum noise again, because the AC lines from the EMI/RFI filter were too close to XLR inputs (also, PCB traces from XLR were right besides the noise suppression filter). So, I moved the filter from right to the left side, just above the 120/230V selector, as the red arrow shows (sorry for not providing a picture of the actual noise suppression filter positioning, but I was quite struggling with fitting the filter inside the case and I totally forgot to get another picture). Also, please ignore the big red wire, it was connected to the 2 Y-capacitors, but it's not really needed, so I removed it from lack of space (it also did a quite nice short-circuit with flame, so next time I'll be more careful).
G.O.S.S. sheet and the EMI/RFI filter
EMI/RFI filter on top of right of the PCB, just on top of the XLR input traces (had it moved on the left side later to remove the hum induced to the input traces)
Mod no. 1. is recommended and this will improve the sub-bass a bit. This is easy to be seen with square-waves on the scope more than listen to the ears.
Mod no. 2 is recommended only if with sensitive cans you can hear mains hum, otherwise there's risk of short-circuit, so needs care.
Mod. no. 3 is not recommended; instead an external EMI/RFI filter could be added later...perhaps one included in the power strip or something similar. There's too much risk with this filter to get installed inside the metallic case.
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