From Brian Willoughby Sent Tue, Jun 19th 2018, 06:56
From Brian Willoughby Sent Tue, Jun 19th 2018, 06:56
Thanks for the information! I recently repaired a TR-808 where the noise was so quiet that full = volume on the trimpot didn=E2=80=99t reach service manual = specifications. I accidentally bumped the capacitor that connects the = noise transistor to the op-amp gain section, and noticed that it got = louder. Turns out that cap was flaky, and replacing it brought the noise = back up to normal levels. I don=E2=80=99t believe in the re-capping = myth, but when testing shows a known bad cap it=E2=80=99s worth the risk = of lifting a trace to solder a good cap in its place. On Jun 18, 2018, at 2:50 AM, Oakley Sound via analogue wrote: > Noise in reverse biased transistor junctions can be surprisingly = variable in quality. One of my designs, the 5U Oakley Noise/Filter = module, requires selection of the noise transistor which is a BC547. >=20 > Originally I had thought that the process of selecting the best noise = transistor was to find the loudest one. But oddly, the loudest ones = actually didn't sound as good as the quieter ones. The loud ones were = often prone to random bursts of noise while the quieter ones produced a = more even and wide band noise. The BC547 sounded better than the BC550 = too. >=20 > On another note, I have found that noise transistors and noise diodes = often become quieter with age. The amount of Pro Ones I saw in my later = years as a repair engineer that had really quiet noise. I'm pretty sure = they weren't that quiet when they were new. I wonder too if the noise = spectrum changes over time. >=20 > Tony >=20 > www.oakleysound.com >=20