Always a problem: finding the right amp to fit the available transformer.pinkmouse said:
I would be interested to hear your findings, I have a couple of 50-0-50 toroids lying around, that have an undefined future
I'll post results and a schematic (assuming Rod's approval) once I get it working.
pinkmouse said:
Ok, will do this as soon as I get back from holidays..
I think.... Or perhaps I'll just turn ont eh amp next to me now, and see how much noise there is... ok.. lets see...FIRST!!! close MSN so no-one can send me a message while the amp is connected to the soundcard with the volume up full..
Now, play an mp3 to make sure I am actually listening to teh computer..
STOP!!!!!!
Now, turn up the volume..
Ok.. on 10!!!! I hear hiss and slight motorboating..... Now, to see if the noise is there without the computer connected..
Nope..... totally silent.... no, wait...
Yeah, nothing...
BUT!!!! what about the project on Rod Elliots site to make a switchmode car amplifier powersupply??
Found HERE
It operates at about 50Khz.... isn't that going to introduce noise??
Rod is an audio designer, and is aware of problems and how to work round them.
PC guys are paid to reduce form factor, increase power output and decrease cost of manufacture.
I am not knowledgeable enough to give you the full details of noise production in switching psus, but basically the faster the switching, the less noise in the audio band.
And let's face it, how much background noise are you actually going to hear doing 70mph!
PC guys are paid to reduce form factor, increase power output and decrease cost of manufacture.
I am not knowledgeable enough to give you the full details of noise production in switching psus, but basically the faster the switching, the less noise in the audio band.
And let's face it, how much background noise are you actually going to hear doing 70mph!
pinkmouse said:Rod is an audio designer, and is aware of problems and how to work round them.
PC guys are paid to reduce form factor, increase power output and decrease cost of manufacture.
I am not knowledgeable enough to give you the full details of noise production in switching psus, but basically the faster the switching, the less noise in the audio band.
And let's face it, how much background noise are you actually going to hear doing 70mph!
1. Thats all well and good, but Rod didn't design the circuit..
someone else did, and he did a slightly modified version...2. So, why can't I add more filtering to teh output, or adjust teh switching frequency... shouldn't be too hard.
3. So, make it faster..
4. true..
lol
I'm not sure where you're getting your numbers from. 4 x 60W amps, even if they were 100% efficient, would need 240W of DC. Add efficiency of, say 60% (optimistic), and the fact that you need more VA from a transformer than DC watts (say double), and you're up to an 800VA transformer.Redeye said:
Or did you mean for a single channel? You'd still need 150 - 200 VA.
i'm been working on a 2 way active crossover with 2 3886 amps running off +/-40V rails for powered speakers for the last few weeks. this is all running perfectly happily off a 30VA transformer - absolutely no problems at all.
the reason i was told you can use such a low rating is to do with duty cycles of the music you play through it and various other things that i can't remember off the top of my head. the person who helped me decide what transformer to use is pretty well qualified given the number of well regarded pro-audio amps and various bits of analogue kit to his name, so i trust him. i was pretty grateful for his advice 'cos this saved me quite a bit of expense and problems in mounting an unnecessarily large transformer.
i'm sure there are people going to disagree with me but the bottom line is that it works fine. i've had no problems with the supply crapping out on transients or anything.
the reason i was told you can use such a low rating is to do with duty cycles of the music you play through it and various other things that i can't remember off the top of my head. the person who helped me decide what transformer to use is pretty well qualified given the number of well regarded pro-audio amps and various bits of analogue kit to his name, so i trust him. i was pretty grateful for his advice 'cos this saved me quite a bit of expense and problems in mounting an unnecessarily large transformer.
i'm sure there are people going to disagree with me but the bottom line is that it works fine. i've had no problems with the supply crapping out on transients or anything.
Redeye said:
Sure for a Class AB amp I would not design for 2*4*60 W if I am on strict budget. My recommendation for 300 VA is exactly what you describe but a bit more on the safe side. Normally in DIY some people would like twice the rated power for a single channel, which is nowhere near as it is for 4 channels, but as you said, the music is not really pulling the power constantly and and simultaneously for all channels so the rated power and then some would probably do just fine for most systems. Hence the 300 VA (i.e. 75 VA per channel). If you also look at many amps in the normal range many have transformers that are rated at the maximum output in 8 Ohms and maybe a little more. They still do pretty good in 4 Ohms and lower. Music is transient events...
For Class A we enter a whole new world...
/UrSv
for class a, absolutely a different ballgame. but for class ab is there really any significant audible benefit to using a bigger transformer? instinct tells me that the size of the caps (ie. the ability to provide high transient currents) would be far more significant than the transformer rating? i'd be interested to try this for myself now i've asked the question - i might see if i can find any 250VA transformers that we've got lying around here and see if it sounds any different.
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