Attenuate means bumababa na ang db output from 100hz. Thus kung makinig ka ng music na may double bass or yung mga mababa ang tunog ng instrumento, mahina na ang output ng amp with respect to 100hz and frequencies below that. The sonic t-amp is down 10db at 20hz. Ang "bass" na nadidinig mo from stock unit is not as "low" and impactful as that after tweaking the input cap. Maynard PMed me on what tweaks I did and what parts i used. Basically, they are as follows (in order of preference, ie, biggest difference sonically):
1) Increase the power filter caps from the stock. It's that capacitor stacked in between the 4 inductor filters. Nilagyan ko ata ng 1800uf 35 volt panasonic caps. (effect of bigger filter cap is bigger reserve pag biglang nangaylangan ng lakas yung amp from the PSU, generally, the bigger the better, pero if its too big, bass will seem to slow down a bit ... daw)
2) Changed R4 and R5 to 20kohms (or 22kohms) para ang gain is set to 12v, but what I did was solder the resistor directly to legs #10&11 and #14&15 of the amp, the shortest connection to the chip the better ( I used 1% metallized resistors here, 1/4 watt ata)
3) Changed input caps from default value of .33uf to 2.2uf and soldered this directly from output of volume pot to R1 and R2 (walang pambili ng auricaps, used polypropelene's instead, still better sounding than the stock, highs are not as matinis, mas malambing tumunog and details are mas litaw)
- explanation lang kung bakit kailangan yung tweaks #2 and #3, the capacitor together with the resistors form a high pass filter, and the cutoff frequency is measured as follows: F=1(2*pi*R*C). Thus, Cutoff=1(2*3.14*20000*.0000022), which results to 3.619hz ang cutoff (ideally cutoff freq is at least 2 octaves lower than the lowest frequency expected, thus kung 20hz and lowest expected na tumunog out of the amp, 20hz-10hz is the 1st octave, 10hz to 5hz is the 2nd octave, so yung 3.619 natin is more than 2 octaves lower pa nga). But with the stock .33uf na input cap, cutoff is around 24.154hz, so ang attenuation (reduction) ng output ng bass is 100hz (db reduction) kasi 2 octaves above 24.154 is around 96-100hz. Hope you get the idea. Caveat pala, after increasing input cap, you will definitely hear a turn-on thump na di mo madidinig before with the small .33uf caps, wag lang mabibigla.
- regarding the Rfeedback, ginawa kong 22kohm (or 20kohm), basta same measurement as RIn (R1 and R2) para ma set yung gain ng amp to 12v ata. Effect: Parang mas mahina yung output kaya the need to increase the volume output via volume pot, pero ang maganda dito, hindi sya madaling ma over-drive ng input mo.
4) Changed all the wirings inside using cat5, read somewhere the lower resistance the better for the t-amp or digital amp in general
5) Changed volume pot to Alps
6) Used gold plated speaker binding posts and rca inputs
7) Nilagay sa maliit na lalagyan
Pagnagsawa, bumili ng Amp3 or Amp6 from 41hz.com. Way way better than a tweaked sonic impact t-amp. Kala ko malinaw na yung t-amp, pero nung pinatugtog ko yung amp6, meron akong nadinig na di ko nadinig sa t-amp.
