Ferrites have a property called "magnetostriction". When subjected to a strong magnetic fields, they shrink (just a tiny little bit). So when you run an audio frequency current through them, they vibrate and produce sound. It's the same thing that makes the line coil in a TV whistle.
Ferrites formulated to exhibit this effect to an extreme degree are sometimes used as acoustic exciters in ultrasonic welders.
(You might have found that some linear amplifiers also manage to produce acoustic output. There, the output transistors themselves are the culprits. Silicon devices are piezoelectric and many transistors "sing" audibly with the voltage, not with the current.)
Ferrites formulated to exhibit this effect to an extreme degree are sometimes used as acoustic exciters in ultrasonic welders.
(You might have found that some linear amplifiers also manage to produce acoustic output. There, the output transistors themselves are the culprits. Silicon devices are piezoelectric and many transistors "sing" audibly with the voltage, not with the current.)
Ground/earth between the 4 caps. is a valid way of doing the earthing/grounding and there is absolutely no humm. You'll have to use it with floating input RCA plugs than. No earthing at the mains input, that will cause groundloops.What noise/humm? RFI problems....absolutely not.
Bruno Putzeys said:
ah ok. so this is just something that happens with this type of amp? its not a big deal, it only happens when its cranked up louder, so you would never actually hear it anyways.
Bgt said:
well, its working without hum now, so ill leave it alone. i DID have it hooked up how you mention though, and it didnt work right. so, ill leave it as is.
mac said:
i just got back from the store picking up the last bits and pieces so i can finally bring them up into my main system and test them out. i will now be using twisted shielded cable for the input, and actually have rubber feet on the bottom of the case so it doesnt scratch my rack all up 🙂
it will be interesting to see how a 1.7kva transformer feeds these things. my speakers arent exactly easy to drive (84db efficient, large room, and 4 ohm).
Hi,
I"ll have more to say about the grounding later /questions whatever, once I've reviewed all material..
Great to see you back here Bruno.
Cowanrg, if you want a real kick try the amps with different speakers and see how much it makes them all sound the same, effortlessly.
I"ll have more to say about the grounding later /questions whatever, once I've reviewed all material..
Great to see you back here Bruno.
Cowanrg, if you want a real kick try the amps with different speakers and see how much it makes them all sound the same, effortlessly.
classd4sure said:
im going to try a few different combinations of grounding now that i know what works, just to learn a bit more about grounding for these amps.
im not sure what you mean about it making all speakers sound the same. i think thats a bad thing... i have a few pairs of speakers in my house, and they all have their good qualities. im not sure if any of them would sound at all similar with ANY amp. my magnepan tympani 1D's are pretty unique-sounding and i would hate for them to sound like my B&W 803D's, and vice versa.
maybe you mean it just universally makes speakers sound their best. thursday is when ill get a chance to hopefully listen to them on my own speakers and form an impression.
I'm sure thats what he means... maximizing virtually any speakers performance.
I'm very interested in the 803D performance compared to your other amps...
My modules also needed a little bit of time to "settle in", it could be psychological, but I left them on for a day or 2 at normal volume levels and they got better, more coherent.
I'm very interested in the 803D performance compared to your other amps...
My modules also needed a little bit of time to "settle in", it could be psychological, but I left them on for a day or 2 at normal volume levels and they got better, more coherent.
cowanrg said:
No what I mean is that they'll sound the "same" (within reason). The amp is frightningly independant of load, and so the load attached doesnt' seem to affect the sound much, not like you'd normally expect it to. You'll see what I mean if you try it.
BTW you may have great hearing but my speakers are 102dB efficient and you _need_ to be no less than a foot away from the tweeter to hear the hiss. If you hear it from further away I trust it's imagined. Anyway I'll let you discover it for yourself, but that's what you can expect if you've got it working right.
Regards,
Chris
Yeah it's really low noise, it's amazing at that...
My B&W's aren't efficient speakers, but with the Yamaha DSP-A2 there was noise from the tweeter, audible about 30cm away.
The noise is still there, it's being generated by the noisy opamps/volume control of the A2...
However if I turn it off, it all but disappears... ear against the nautilus tweeter reveals a little noise, when very quiet... and even then it's not like broad-spectrum noise, it's different than your usual amp noise.
My B&W's aren't efficient speakers, but with the Yamaha DSP-A2 there was noise from the tweeter, audible about 30cm away.
The noise is still there, it's being generated by the noisy opamps/volume control of the A2...
However if I turn it off, it all but disappears... ear against the nautilus tweeter reveals a little noise, when very quiet... and even then it's not like broad-spectrum noise, it's different than your usual amp noise.
right now im getting NOTHING from the tweeter, even with ear touching the driver almost, it sounds the same as when it's off, so thats good.
i bought shielded cable yestertday that i still havent installed, so that will be just extra caution so that there is NO noise going on.
i bought shielded cable yestertday that i still havent installed, so that will be just extra caution so that there is NO noise going on.
Yves Smolders said:
me too!
i need to build the second monoblock tonight and then they will both be running. it will only take about 2 hours or so to get the second one fully working. so, hopefully tonight ill have some listening time, but tomorrow until i start forming an opinion.
something just came to me...
im building TWO of these things, and i only have a lightbulb for one. i was using the light bulb as the softstart, but i only have one. i could easily just buy another bulb and base, but is there something else i could do for a quick soft start?
i plan on getting the LC audio ones for the real amps when i build them, but i dont have them yet. can i just put a resistor or something in series with the transformer for a down and dirty soft start?
im building TWO of these things, and i only have a lightbulb for one. i was using the light bulb as the softstart, but i only have one. i could easily just buy another bulb and base, but is there something else i could do for a quick soft start?
i plan on getting the LC audio ones for the real amps when i build them, but i dont have them yet. can i just put a resistor or something in series with the transformer for a down and dirty soft start?
40 ohms of resistors (25w or higher) and a momentary switch- press the momentary switch for a few seconds before switching on the PSU, then release the switch.
oh, just to be clear- have the momentary switch/resistors bypass the main power switch/ running parallel to the switch.
oh, just to be clear- have the momentary switch/resistors bypass the main power switch/ running parallel to the switch.
Yves Smolders said:
I'm trying to get some details on that, because I would like to build some UCD400 amps using off-the shelf Plitron audio transformers, and those come with 30V, 45V and 60V secondaries. They are so expensive, I don't even want to ask them for a custom wound 42V unit (at that point I'll go with the 60V and build some UCD700s instead, spending the extra $ on the modules and not the custom winding of a toroid).
So if I do want to go with the 45V I will have at least 63.5V DC on the rails (my wall voltage is actually 124 some nights, so I am going to be above that value by a bit). Has anyone built UCD400s with such a transformer?
I've never built a big power amp, only preamps and other low voltage stuff, so this may be a dumb question related to this: is there a way to lose a few volts in a PSU without a) vaporizing some resistors, or b) screwing up the sound of the thing? I guess anything that could drop the voltage in such an application would be a component that is bound to generate a lot of heat.
I'm kinda torn between UCD400 and UCD700 right now, and the 42V transformer secondaries requirement makes the decision rather difficult (and no, I don't want to use the 40V Avel transformers from partsexpress if I can avoid it)
Peter
Hi,
Don't try to get it so close that you run into that situation in the first place. You need to allow for a 10% mains overvoltage condition while the supply is unloaded, at that VA rating that's another 5% for 15 total worst case. Just by using a dual bridge rectifier supply you can drop another volt or so,
Don't try to get it so close that you run into that situation in the first place. You need to allow for a 10% mains overvoltage condition while the supply is unloaded, at that VA rating that's another 5% for 15 total worst case. Just by using a dual bridge rectifier supply you can drop another volt or so,
What about running it through 3 or 4 adequately sized diodes in series on each rail. Should drop it a few volts without too many negatives.
classd4sure said:
I think I wasn't clear about my reasons - I don't "want to get it close" - I want to use off the shelf Plitron transformers and that limits me to 30V (too low), 45V (probably too high for UCD400), or 60V (great for UCD700, but that costs me more $$$ in other areas, such as capacitors, module cost and larger transformers), and since I plan to biamp and use 4 channels, that adds up.
I suppose I gotta go and ask them for their custom pricing before I give up in the 400s and start saving for four UCD700s. I'd rather spend the extra cash on the modlues than custom transformer winding.
Peter
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