Never ending tweaks and mods? Yes I think so. Actually, my Aikido Pre-Amp already sounds good. But as a DIY, I think the journey never ends. Tomorrow always comes with another mods. After completing the PSU mods with Mundorf MCap Supreme 3.3 uF/800VDC and ASC X386S 40 uF/440 VAC here, I decide to go further with some other components.
First, I still hear small hum. This is mainly caused by the Filament/Heater Center Tap of my DIY transformer is not exactly on the center. So the 1/4 B+ isn’t injected on the correct Center Tap position. The only solution is to create a Virtual Center Tap with a pair of 100 Ohm resistor. I use 100 Ohm 5W Kiwame. Some people may say that you can use any cheap resistor for this purpose, but I always choose the best price/performance. At US$ 2 each, Kiwame fits this job perfectly. Make sure you use an accurate resistor (metal film should fit best, carbon film also ok).
I fire up my Aikido and ta-da… no more hum, even when my ear next to the speaker! But I need to confirm later with high-gain amplifier. With a normal/standard gain amplifier, the hum is usually less noticeable.
Then we go into a deeper stage. As perhaps you have known that I use Duelund CAST PIO 1 uF/630VDC as output coupling capacitor. So I won’t put much detail here. Some interesting entries to read are here, here, and here.
I’m focusing on last bypass capacitor on the B+ line. It should be the C5 on schematic below (I blur the rest schematic on purpose). Upgrading this section surely will improve the sonic quality.
Currently, I’m using WIMA MKP10 0.33 uF/630 VDC. Not a bad capacitor, but it’s just too standard for my taste.
I dig my shelves and find an Obbligato Oil Capacitor 2 uF/630 VDC. Surely this one is better than the WIMA in every aspect. So below is the final appearance of my Aikido.
How about the sound? First off all, the bass is improved very significant. There are two reason. First, the Obbligato is 2 uF vs the 0.33 uF WIMA. The higher value should produce more low frequency. Second, the Obbligato is an oil capacitor, tends to emphasize in the mid-low band, rather than plastic/film capacitor like WIMA.
The overall tonal frequency also improved a lot. The high frequency sounds more extend, the staging also more focused, and especially the vocal is “sweeter”, both for female or male. I notice some of the high frequency instruments are not pronunciated quite well (a little bit “shy”?). Perhaps because some of them are completely new (the Mundorf, ASC, and Obbligato). Will see the improvement after several hours.