Voice Coil DC PWR Rating

[rjg]

Hi Guys,
I am making making (made?) an amp to be used for SE spkr dsn and am trying to figure out if it is worth filtering a quiescent DC offset of about 200mV. To me, that is not much for a 20W tweeter, but I am being advised being DC will not have a benefit of movement cooling: bad. While I can't disagree, I am not sure it is worth ripping apart "completed" amp. Thanks for any inputs. -bg

[Ludo]

Hi Guys,
I am making making (made?) an amp to be used for SE spkr dsn and am trying to figure out if it is worth filtering a quiescent DC offset of about 200mV. To me, that is not much for a 20W tweeter, but I am being advised being DC will not have a benefit of movement cooling: bad. While I can't disagree, I am not sure it is worth ripping apart "completed" amp. Thanks for any inputs. -bg

200mV into 8 ohms is 1.6W so the driver heating should be minimal, but this will cause an offset in the cone's steady state position which could lead to higher distortion. Won't the tweeter have a series cap as part of its x-over (high pass filter) thus blocking any DC output from the AMP?

Louis

[rjg]

Thanks, Ludo. When used in typical system, yes you are right with series cap to twe, however when used with Sound Easy, the twe filter is a digital one, with the filter output to the amp and twe connected to amp as the load. I am toying with the idea of a very large cap(220uF), just as standard practice, on the twe terminal when I set up for this. BTW, how do you get 1.6W? I get .2^2/8 = 5mW. thx. -bg

[Ludo]

Thanks, Ludo. When used in typical system, yes you are right with series cap to twe, however when used with Sound Easy, the twe filter is a digital one, with the filter output to the amp and twe connected to amp as the load. I am toying with the idea of a very large cap(220uF), just as standard practice, on the twe terminal when I set up for this. BTW, how do you get 1.6W? I get .2^2/8 = 5mW. thx. -bg

Duh, correction; you are absolutely correct, 5mW.
Personal note.... don't post any threads before having coffee in the morning!

The series cap for removing any residual DC sounds like a good idea. Not sure why you would use such a large one which would give you a 3dB corner of 90Hz (hope I did the math right this time)?

Louis

[rjg]

Not sure why you would use such a large one

Well, to keep it away from influencing the DF, but ya that is pretty large. What I would probably do is cut it in 1/2 and use an NPE and poly bypass. You have given me more confidence in moving forward, though, so thanks. -bg

[bmaupin]

I'm no amp designer, but seems you should look upstream to see if a dc offset can be removed before amplified by a gain stage. ?

- Brad

[rjg]

I'm no amp designer, but seems you should look upstream to see if a dc offset can be removed before amplified by a gain stage. ?

It can. I am trying to determine if it is worth ripping these boards apart for this addition. thx. -bg

[philiparcario]

a cap of 25uf to 40 uf right at the tweeter pos lead is the easy way. I would try that for 20 hours or more of music/movies. Then decide if tearing the amp apart is worthwhile.