I bought this little guy off the forum a couple of months back. I wanted a compact stereo amp to use in the sitting room for e-z listening (as in easy to listen to, not to listen to easy listening music 
).
On paper it seemed to fit the bill niceley. It is mysteriously branded "Olevia", although it's manufactured by AudioSource and marketed as such everywhere else. So 2 channels into 8 ohms, 50wpc. Can be bridged. It has "auto sensing power on" which I liked as it means I can stick it on a shelf out the way, and just leave it on, and it'll kick in when music source starts. It does auto-select of input, so I can leave music streamer as primary, and an iPod as alternative.
There's a quite long review and some measurements here https://www.kenrockwell.com/audio/audiosource/amp-100.htm
So far so good. Hooked it up, and wasn't too blown away. Sound quality was a bit meh (lows a bit muddy, not terribly crisp). The volume pot was scratchy as hell. The auto-sense was erratic, especially with classical music (quiet passages in the music would sometimes by misunderstood).
It seems to be a popular little amp to tweak though ... it's a bit weird, it's a mix of very decent quality stuff (big torroidal txformer, good solid case with proper fastenings, etc) , and some quite cheapo stuff (pots, IC supply caps, relay). There also appear to be some basic errors in engineering... multiple sets of blocking capacitors.
There was a cook-book tweak thread here http://techtalk.parts-express.com/forum/tech-talk-forum/56976-how-to-turn-your-audiosource-amp-100-into-a-real-amp-paying-it-forward which I finally got around to completing last night. No thanks to Electrocomp which completely stuffed up my parts order.
Most of this is removing unnecessary caps, replacing supply caps with better ones, replacing the pots with quality ones, replacing cheapo op amps with LM 4562.
I followed the guide, just skipping the changing the feedback resistors which would add a little gain -- I don't need more gain and accessing the resistors without removing the heatsink would have been a bloody pain. Also did not change the bootstrap capacitors as the parts were not included in my order :cr@p: :cr@p:
So - question -- what the hell are bootstrap capacitors and is this important? I did a little reading on it and am no the wiser. It seems like a bit of belt and braces, it seems bootstrapping does a similar thing to negative feedback?
Schematics available here https://elektrotanya.com/audiosource_amp100_preamp_schematic.pdf/download.html and https://elektrotanya.com/audiosource_amp100_poweramp_schematic.pdf/download.html
Conclusion?
The changes made a significant improvement. In the obvious things (scratchy pot!) -- but more importantly made this little amp sound pretty decent. A lot more presence and crispness, auto-switching better (although is still a wee bit erratic). Substantially more gain (even though I didn't do the main gain tweak), which I may need to dial back.
).On paper it seemed to fit the bill niceley. It is mysteriously branded "Olevia", although it's manufactured by AudioSource and marketed as such everywhere else. So 2 channels into 8 ohms, 50wpc. Can be bridged. It has "auto sensing power on" which I liked as it means I can stick it on a shelf out the way, and just leave it on, and it'll kick in when music source starts. It does auto-select of input, so I can leave music streamer as primary, and an iPod as alternative.
There's a quite long review and some measurements here https://www.kenrockwell.com/audio/audiosource/amp-100.htm
So far so good. Hooked it up, and wasn't too blown away. Sound quality was a bit meh (lows a bit muddy, not terribly crisp). The volume pot was scratchy as hell. The auto-sense was erratic, especially with classical music (quiet passages in the music would sometimes by misunderstood).
It seems to be a popular little amp to tweak though ... it's a bit weird, it's a mix of very decent quality stuff (big torroidal txformer, good solid case with proper fastenings, etc) , and some quite cheapo stuff (pots, IC supply caps, relay). There also appear to be some basic errors in engineering... multiple sets of blocking capacitors.
There was a cook-book tweak thread here http://techtalk.parts-express.com/forum/tech-talk-forum/56976-how-to-turn-your-audiosource-amp-100-into-a-real-amp-paying-it-forward which I finally got around to completing last night. No thanks to Electrocomp which completely stuffed up my parts order.
Most of this is removing unnecessary caps, replacing supply caps with better ones, replacing the pots with quality ones, replacing cheapo op amps with LM 4562.
I followed the guide, just skipping the changing the feedback resistors which would add a little gain -- I don't need more gain and accessing the resistors without removing the heatsink would have been a bloody pain. Also did not change the bootstrap capacitors as the parts were not included in my order :cr@p: :cr@p:
So - question -- what the hell are bootstrap capacitors and is this important? I did a little reading on it and am no the wiser. It seems like a bit of belt and braces, it seems bootstrapping does a similar thing to negative feedback?
Schematics available here https://elektrotanya.com/audiosource_amp100_preamp_schematic.pdf/download.html and https://elektrotanya.com/audiosource_amp100_poweramp_schematic.pdf/download.html
Conclusion?
The changes made a significant improvement. In the obvious things (scratchy pot!) -- but more importantly made this little amp sound pretty decent. A lot more presence and crispness, auto-switching better (although is still a wee bit erratic). Substantially more gain (even though I didn't do the main gain tweak), which I may need to dial back.
