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.
Try resistors and go up to a comfortable heat level in the specific box step by step, provided you hear some appreciable subjective gain, I would say.
It's not just the Tj of the FETs you need to consider.
If you heat up the floor of the chassis then you are cooking all the components in the frying pan you have created.
If you heat up the floor of the chassis then you are cooking all the components in the frying pan you have created.
Okay, I'll give it a try. If it runs too hot, I'll just use it as a preamp for my Phase Linear 400 and let them race to see which one turns into a slag heap first 😉
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.
Try turning the mains input voltage up to max tolerance (Variac)
and test temperature of your capacitors.
Then short your output and check the temperature of the CCS FET.
and test temperature of your capacitors.
Then short your output and check the temperature of the CCS FET.
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.
Your measurements look fine. JFETs do warm up, so offset takes a while. Its not impossible small by the way, we got many such low references in the building threads. 1.9 & 1.7 are the CCS, yes. It got quite near in your case. Hook it up and let us know.
Thanks Salas, that's reasurred me.
Tomorrow I will connect the pot and RCA's and then take her on her maiden voyage.
Tomorrow I will connect the pot and RCA's and then take her on her maiden voyage.
strange measurement
hi all,
at last i finished to assemble my mesmerize, supplied with a 2x15 30va trafo...
...warmed it up and took the measurement from the three pads in the middle of pbc:
20 v-
10 v+
very disappointed....
later i'll post some picture...
hi all,
at last i finished to assemble my mesmerize, supplied with a 2x15 30va trafo...
...warmed it up and took the measurement from the three pads in the middle of pbc:
20 v-
10 v+
very disappointed....
later i'll post some picture...
Troubleshoot it. -20Vout is obviously wrong. A picture will help, maybe we can spot something too.
Its nice nothing else went too. Check DC offset on audio outputs and voltage drops across the 68R resistors also.