Hi Jan,
The toroid is too big (50VA) and if I did the mechanizing the IEC connector, the fuse and the power switch, the toroid was too close to the output RCA and the mosfets (just touch one), and I was very afraid of the bad influence of the mosfet's heat and noise induction on the rca.
Just I put the transformer in a small box and I connect it with a 3 conductor wire and Lemo connectors (I have a bunch of old Lemo).
My DCB1 is still running happily. I put 10R and 8R resistors in to give me ~200ma on each channel, it warms the case quite a bit but I wouldn't describe it as "hot." You can hold your hand on the case or the mosfets directly indefinitely.
Now I'm tempted to put the 3.3R resistors in there to see what I can get away with. The mosfets are bolted directly to the chassis, but I'm using an old ethernet switch as a case. It's made of pretty thin metal, and I think it's steel rather than aluminum. It's basically the same thickness and material as a PC case. Is a proper heatsink a necessity for 600ma, or can I wing it? If it gets 3 times as hot as it does with 200ma, it'll get pretty darn hot but I don't think I'll be in egg-frying territory.
Now I'm tempted to put the 3.3R resistors in there to see what I can get away with. The mosfets are bolted directly to the chassis, but I'm using an old ethernet switch as a case. It's made of pretty thin metal, and I think it's steel rather than aluminum. It's basically the same thickness and material as a PC case. Is a proper heatsink a necessity for 600ma, or can I wing it? If it gets 3 times as hot as it does with 200ma, it'll get pretty darn hot but I don't think I'll be in egg-frying territory.
Popped the 3R3 resistors in, powered it up, and let it sit for about 15 minutes. It's running much hotter now, but I can still hold my hand on the case directly next to the mosfets for 5 seconds. I can handle 8 seconds tops. I'll let it sit for an hour or so and see if it still passes the 5 seconds test.
I don't have a variac or any way of measuring the temperature of the mosfets, so I decided to just plug it in to my system and see what happens. It sounds much better than going straight from my PC to the amp, of course, and I think it sounds better than it did with less current. Wider sound stage, better detail, all that good stuff. More detail comes through at low volume, which is really nice.
However, after being on for 20 minutes or so, it's not passing the 5 second test anymore. I can do 3 or 4 seconds tops. I might have to throttle back a little or find a larger heat sink.
However, after being on for 20 minutes or so, it's not passing the 5 second test anymore. I can do 3 or 4 seconds tops. I might have to throttle back a little or find a larger heat sink.
Hi
I've finally populated and wired up my pre amp and stuck it on my test board (a bit of MDF
). Here are the measurements I'm getting:
V+ = 9.17
V- = 9.58
Measurements across the two parallel 68R's are 1.9V and 1.7V (is that the CCS measurement?).
So far it all looks good, however I'm very suspiscious about my offset measurements as I'm getting some strange results. If I measure the offset just after I've powered on the pre amp then I get 1.7mV on the right channel and 0.0mV on the left channel. However, as I continue to take readings the right channel starts to drop, and the left channel starts to gain mV. After a minute or so the right channel stabalises at 0.4mV and the left channel at 0.3mV.
Should I be concerned about the jumping around of the DC offset? It doesn't feel right to me, and neither do the figures as they seem impossibly small.
Note: I currently don't have the pot wired to the board. Not sure that would make a big difference.
I've finally populated and wired up my pre amp and stuck it on my test board (a bit of MDF
). Here are the measurements I'm getting:V+ = 9.17
V- = 9.58
Measurements across the two parallel 68R's are 1.9V and 1.7V (is that the CCS measurement?).
So far it all looks good, however I'm very suspiscious about my offset measurements as I'm getting some strange results. If I measure the offset just after I've powered on the pre amp then I get 1.7mV on the right channel and 0.0mV on the left channel. However, as I continue to take readings the right channel starts to drop, and the left channel starts to gain mV. After a minute or so the right channel stabalises at 0.4mV and the left channel at 0.3mV.
Should I be concerned about the jumping around of the DC offset? It doesn't feel right to me, and neither do the figures as they seem impossibly small.
Note: I currently don't have the pot wired to the board. Not sure that would make a big difference.
