Well what a great forum this is. I have learned a lot from browsing on here and decided to implement a first project - an LM3886 amp. Boards were acquired already populated and are marked BrianGT. Chips are all verified genuine from legitimate suppliers. I read the "Done Right" material and tweaked a little by adding the Theile components. Since the photo I have also added RF filtering to the inputs.
The amp is built into a Cambridge Audio A3 (V3.0) case and uses the original transformer and mains switching. This case is Class 2 (rated double insulated and so the transformer must be compliant). and so there was no PE. Since I haven't altered the mains wiring arrangements and have only modified to add more insulation I have kept it that way. OK there is one error as is -- the IEC socket I added is 3 pin as I am awaiting the arrival of the rarer 2 pin variant.
The "preamp" is an Alps 20k pot - nothing added. The strange white things on input are actually the DC blocking caps in shrink tube.
All worked first time. I did a few rudimentary checks before switching on. DC offset was minimal (in spite of the boards omitting Ci), noise (measured on a Levell microvoltmeter) was truly minimal, and it reproduced sine and square waves as well or better than my NAD C320 (I only have a low spec Picoscope so this is very subjective really - eyeballing the traces).
Anyway ... great fun.
The amp is built into a Cambridge Audio A3 (V3.0) case and uses the original transformer and mains switching. This case is Class 2 (rated double insulated and so the transformer must be compliant). and so there was no PE. Since I haven't altered the mains wiring arrangements and have only modified to add more insulation I have kept it that way. OK there is one error as is -- the IEC socket I added is 3 pin as I am awaiting the arrival of the rarer 2 pin variant.
The "preamp" is an Alps 20k pot - nothing added. The strange white things on input are actually the DC blocking caps in shrink tube.
All worked first time. I did a few rudimentary checks before switching on. DC offset was minimal (in spite of the boards omitting Ci), noise (measured on a Levell microvoltmeter) was truly minimal, and it reproduced sine and square waves as well or better than my NAD C320 (I only have a low spec Picoscope so this is very subjective really - eyeballing the traces).
Anyway ... great fun.
Thanks @tomchr ! As you have I think commented before chassis costs end up being one of the largest elements of a build. The problem here was that the chassis and hence front panel are from an integrated amp and thus there are cutouts for controls that are simply not going to be there. I have now probably spent about as long adapting the front panel as I did building up the amp! I went for a car repair approach to fill the unwanted cutouts (backed them with mesh then car filler paste, and then flattened and sprayed. The pictures tell the story I guess. ....
Pretty impressive. I reused the chassis from a Parasound A23 at one point. I kept the power supply, connectors, and chassis. I chose to integrate the various functions already in the chassis into my own design, so the amp looks like an A23 and functions like an A23 but contains an LME49811 + ThermalTrak amp. 🙂
Tom
Tom
