I bought two NOS ALC0300 recently to make a stereo amp. One worked perfectly -- it sounds great and the DC offset is only 18mv at the output. The other not so much -- DC offset is a constant ~400mv, there is a high-pitched sound coming out of some components (i.e., from the amp itself, not the speaker), and the there is no sound output, all regardless of whether the signal inputs are open, shorted, or connected to a source. It feels like that the amp is in protection mode or standby mode after being turned on.
I checked all wirings and could not find anything -- all continuity/impedance readings between the two amps are consistent with each other, and the two amps are housed in the same project box with similar grounding arrangement. I disconnected the working amp, and nothing changed with respect to the non-working one.
Any thoughts? Thanks!
I checked all wirings and could not find anything -- all continuity/impedance readings between the two amps are consistent with each other, and the two amps are housed in the same project box with similar grounding arrangement. I disconnected the working amp, and nothing changed with respect to the non-working one.
Any thoughts? Thanks!
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Just wanted to add that per the post below, it appears that my amp is in standby mode: i.e., high-pitched sound, no output. Still don't know why though. I could try to ground the Disable pin to forcefully pull the amp out of standby, but before I try that (and potentially cause damage to the amp), I would prefer to get more advice. Currently, the disable pin is left open, and I am not connecting any of the standby, V+/V- pins. Thanks!
https://www.diyaudio.com/forums/class-d/190182-abletec-alc1000-experience-6.html#post3484115
https://www.diyaudio.com/forums/class-d/190182-abletec-alc1000-experience-6.html#post3484115
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Issue resolved. The surface-mount fuse (F200) blew/was not working. I thought, based on my reading of the manual, that this fuse was for the +/-15V aux power supply that I was not using/never used, but apparently once the fuse was blown, power to the input op amp (+/- 12v) was also cut. I found out the cause when I measured no power at the op amp. And yes, per the voltage reading at the standby pin, once the fuse was blown, my amp went straight into the standby mode and could not be pulled out from the mode by grounding the Disable pin. As soon as I soldered a wire to short the fuse (I know it's bad), everything was back to normal, and the high-pitched noise is completely gone -- I think the other comment was right, that the noise is from a standby device.
Anyways, now both amps have been working perfectly for hours, with no distortion, overheating, etc. DC offset at the output is 9mv and 18mv (both within range).
I also changed the op amps to OPA2211s (one in each amp), which immediately lifted the veil I previously sensed. Now the amps are super transparent but still sweet sounding (i.e., not metallic, harsh, or bright). I highly recommend upgrading the op amp on the underside of board to better ones. The MC op amp (forgot the model) was very veiled (but one could say it was "musical"?) The improvement from upgrading to OPA2211 was about 20% -- you will notice it immediately, and it would move the amp to a different league in terms of overall sound quality. I did not roll any op amps as soldering SMD is too much a hassle. Note that the voltage to the op amp is +/-12v, so you could try many of the nicer AD op amps that are only up to +/-13v (AD8620 could be a good candidate. I like it more than any other AD dual SMD op amps, but my hands are too shaky for SMD op amp rolling).
Anyways, now both amps have been working perfectly for hours, with no distortion, overheating, etc. DC offset at the output is 9mv and 18mv (both within range).
I also changed the op amps to OPA2211s (one in each amp), which immediately lifted the veil I previously sensed. Now the amps are super transparent but still sweet sounding (i.e., not metallic, harsh, or bright). I highly recommend upgrading the op amp on the underside of board to better ones. The MC op amp (forgot the model) was very veiled (but one could say it was "musical"?) The improvement from upgrading to OPA2211 was about 20% -- you will notice it immediately, and it would move the amp to a different league in terms of overall sound quality. I did not roll any op amps as soldering SMD is too much a hassle. Note that the voltage to the op amp is +/-12v, so you could try many of the nicer AD op amps that are only up to +/-13v (AD8620 could be a good candidate. I like it more than any other AD dual SMD op amps, but my hands are too shaky for SMD op amp rolling).
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It has been a long time -- I no longer recall which/where is the fuse. I would recommend that you search the internet for the amp's manual, which should indicate how to find the fuse.