You must consider that rectifiers have an internal resistance that cause a drop and being the resistance almost costant, the higher the current the higher the voltage drop. Consider also that different rectifiers have different internal resistance. Hi speed dicrete diodes have better efficency (read: lower internal resistance)
Secondly, not all transformers behave the same. The best ones are "stiff" enough not to drop the voltage when the load is absorbing huge currents (and Class A amps are very demanding).
In other words, the lower the transformer regulation (%), the lower the difference between the voltage with no load and when delivering the rated (max) current (and Class A amps are absorbing the max current all the time).
Secondly, not all transformers behave the same. The best ones are "stiff" enough not to drop the voltage when the load is absorbing huge currents (and Class A amps are very demanding).
In other words, the lower the transformer regulation (%), the lower the difference between the voltage with no load and when delivering the rated (max) current (and Class A amps are absorbing the max current all the time).
Actually, the voltage drop in the rectifier is not resistive in nature--it's built-in to the nature of a PN junction; about .65V or so, regardless of current drawn through the diode.
Grey
Grey
I could have used this design 25 years ago when I was first getting into x-overs. I used to split the pre signal into several power amps and then feed the x-over. How interesting to feed the passive x-over before the power amp! I wish I would have known that, then.
🙂
🙂
jleaman said:
I have that exact toroid in my F4 and 122V out of my wall as well. I posted a few pages back that I was measuring 26.5V after rectification, but that number dropped to about 23V after the amps were connected.
I thought about getting more anteks, but Plitron is local for me, so even though I have to pay 2 taxes, I would get 2 300VA 18V toroids instead. After shipping, duty and exchange, the price works out to be close and the plitrons are potted, so they are a bit easier to mount (and they're not as tall).
Member
Joined 2002
twitchie said:
Plitrons are really expensive, i can't afford thos. If i could id order potted ones also or just one but 800va one for a stereo F4. i'm going the single psu per channel tho.
as to carpender's post im doing this exactly 🙂
Already started last week on the active xovers boards that were designed are etched and on there way.
J'
jleaman said:
My idea is to configure a "passive"--not active--x-over before the power amps. I already have an active x-over manufactured by TDM. It sounds like you're doing the active route. Yes?
If you're doing the passive thing, tell me how it's treating you. Thanks.
🙂
Member
Joined 2002
I'm actually running active x-overs with a passive pre-amp at the moment.
Is there a difference between the 2 you think, in sound ?
Is there a difference between the 2 you think, in sound ?
simpler is better, I think--within reason. My TDM x-over must have two dozen op-amps; that's several hundred transistors above my preference.
jleaman said:
800VA for non balanced stereo amp ?? isn't that a little overkill
some postings before
Or are you planning to biasing the hell out of them ?
And for the losses in your PS of course the forward voltage of your diodes but on bad toroids the internal copper losses are also a little factor.
Member
Joined 2002
Jaac said:
thats 400 va per channel or one single 800va for 2 channels.
Any one know where to get matched fet's ?
This guy http://tech-diy.com/hexfets.htm isn't replying to any of my emails or others so i'm looking elsewhere.
Match them yourself. It's not difficult. You'll find uses for the others soon enough.
I keep having to buy more. I think mice are eating them. Or maybe it's the Palmetto bugs (Periplaneta americana). Worst case scenario: fire ants (Solenopsis invicta--them's some baaaad boys). Just bought 100 N-ch and 25 P-ch. My fingers are crossed that gets me through the summer, but I've got a thick stack of scribbled ideas and an itchy solder finger.
Grey
I keep having to buy more. I think mice are eating them. Or maybe it's the Palmetto bugs (Periplaneta americana). Worst case scenario: fire ants (Solenopsis invicta--them's some baaaad boys). Just bought 100 N-ch and 25 P-ch. My fingers are crossed that gets me through the summer, but I've got a thick stack of scribbled ideas and an itchy solder finger.
Grey
jleaman said:
Has anybody heard from JackinNJ recently? My order for F-4 bits arrived but there was a small mix-up. I haven't had any replies to my e-mails.
Perhaps he's on vacation.
JLeaman ... if you google "matching fets" you'll find plenty of references.
Ryan
Member
Joined 2002
RKH said:
Im not just doing this for my self i'm doing this to help others locate parts sources, I don't have the funds to buy lots of fets to match them. i'm building 4 channels 2 for me and 2 for a friend.
I've always had great results from Tech-DIY. So if you can wait a bit, I'm sure he'll get back to you ... er ... us. My IRFP240s arrived, nicely matched to 0.01 V. I can't remember what Mr. Pass says how closely the First Watt F-4 devices are match.
Good luck.
Ryan
Good luck.
Ryan