| Mayday |
I'm going to build a "boombox" for my brothers doughter, using two LM3886, two fullrange elements, and a volumepot in the same box.
I'll be using a pair of RCA inlets, and a 3,5mm jack for her mp3 player.
This won't need a whole lot of power, my question is, is a 150VA 2x15V~ a big enough transformer? |
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| AndrewT |
Hi,
150VA can support upto 100W of output.
15Vac will give about 20 to 22Vdc.
This results in about 15W to 20W into 8ohms or about 25W to 35W into 4ohms.
Seems like plenty of noise for an MP3 player. ;)
It will sound a lot louder than those advertised as 1000W of pmpo power. :xeye:
Have a look at that other thread on hum in a two channel chipamp. He has a solution that works. |
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| Mayday |
Thanks for the answer!
I've gotten rid of my hum simply by going dual-mono all the way incl trafos. |
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| Mayday |
| BTW, just hit me, I will be using a single trafo for the two LM3886 in the boombox, but only one psu-board, so I should be fine right? When it comes to hum that is. |
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| ppcblaster |
AVEL Y236652 250VA 25V+25V TOROIDAL TRANSFORMER
this would give me 35Vcc, Please give me your opinions and
advise to power a BrianGT stereo kit. |
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| Mayday |
If it's a stereo kit, just hook the secondarys with a dot in the datasheet to the underlined AC on the psu card, and the others to the not underlined AC on PSU, just remember to keep them paired.
One pair of secondarys goes to underlined AC1 and AC1, the other pari goes to underlined AC2 and AC2.
Did I make any sence? |
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| AndrewT |
| quote: | Originally posted by AndrewT
Have a look at that other thread on hum in a two channel chipamp. He has a solution that works. |
| quote: | Originally posted by Mayday
I've gotten rid of my hum simply by going dual-mono all the way incl trafos. |
My memory is like a sieve, I could have checked to find that it was you who found the silence. :o |
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| Mayday |
| That's like me, memory like a goldfish...one lap around the bowl, and "hey! what's this?":D |
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| ppcblaster |
I need to order a tranformer
Is the AVEL Y236652 250VA 25V+25V TOROIDAL a good choice?
Thank You |
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| Mayday |
| BTW, I think someone else said it first, about dual trafos i meen. |
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| Mayday |
| Yes it is. I've gone for higher VA, but that's more or less overkill. |
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| ppcblaster |
Thank you.
The datasheet states 35V at about max.
Is 35V rail the safe max or can I go higher?
First time build for me.... |
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| AndrewT |
| quote: | Originally posted by ppcblaster
Is the AVEL Y236652 250VA 25V+25V TOROIDAL a good choice? |
yes, that will support three channels @ 60W into 8ohms.
You might just be able to stretch to 4channels out of it. But hum reduction on multi channel from one trafo seems to be a problem with the PCBs as supplied.
Do not go any higher with 8ohm speakers.
If you allow for max mains voltage and max transformer regulation and minimum quiescent current in the chipamp you will have a lot more than +-35Vdc in the worst case (fortunately not too often).
If you have 4 to 8 ohm speakers then 25Vac is already too high. |
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| ppcblaster |
| quote: | Originally posted by AndrewT
yes, that will support three channels @ 60W into 8ohms.
You might just be able to stretch to 4channels out of it. But hum reduction on multi channel from one trafo seems to be a problem with the PCBs as supplied. |
AndrewT,
Please explain, |
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| Mayday |
| I missed something...are you going for more than two channels? |
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| ppcblaster |
| quote: | Originally posted by Mayday
I missed something...are you going for more than two channels? |
No, just two channels at this time. |
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| Mayday |
| I'm rather sure that I read that if you use only one psu board, then there'll be no problem with humming when using only one transformer, there's not even enough ac inputs in a stereo kit to use dual transformers. |
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| AndrewT |
Hi Ppc,
how far do you want me to go back?
25Vac gives about 34 to 37Vdc.
This results in about 60W into 8ohms.
2 channels is 60+60=120W and a 120 to 180VA transformer can meet this demand.
Your selection has a capacity of about 50% to 100% more than that, indicating that 3 or 4 channels could be powered from this transformer (if you had that need).
If one were building a 5.1 system, the simultaneous demand from all the channels rarely matches the sum of the channels and if the sub were run from a separate transformer (or separate windings off the same transformer) then the 5channels may/will run successfully from a smaller transformer than normally recommended.
hum.
mayday and a few others are finding a problem silencing stereo and multi-channel chipamps. There are solutions, but they seem to vary from build to build. Be prepared for experimentation - bolted ground connections are a lot easier than soldered! |
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| Mayday |
| Don't forget proper fusing, lot less expensive to have a fuse blow than say a 10000uF cap. |
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| ppcblaster |
The maunal sucks.
What type and size fuse do I need?
Also my avil transformer has dual pirmary and dual secondaries.
I am confused how to connect the wires and where to mount the
two, on board terminal blocks and on what boards.
Boards assembled, only 3 bandaids on my fingers,
Thank You.. |
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| ! |
| Fuse depends on multiple factors, I'm not familiar with that kit but in general unless you have gobs of PSU capacitance or are doing a 3+ chip paralled or bridged amp, a 2A slow-blow should suffice, but 3A slow would be a more conservative choice. This assumes it is a mains-side fuse, not after the transformer. If after the transformer, just apply the figures in a in/out ratio multiplier fashion to the above amperage figures, fudging a bit since such low single digit numbers leave some margain for error. |
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| AndrewT |
Hi Ppc,
please think about your questions and make them less ambiguous.
What fuse? What equipment are you feeding? What mains voltage? Is there soft start? Are there timed relays? What rail voltage? What smoothing capacitance? What speaker impedance?
Help us to help you. |
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| ppcblaster |
| BrianGT suggests a 3A slow blow. |
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| desert_rainbow |
| suggest AC+-25~+-28V :) |
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| Jackson Audio |
Hello all.
Fusing is dependant on power draw. If, for example, a 150VA transformer is being used, then you don't want the transformer to draw more than its continuous power rating from the mains. In the example above, which assumes that the transformer is properly sized to the application, 150VA / 120VAC would yield a current draw of 1.25 Amps. Size your fuse for that rating, or just a wee bit more, and you'll be in the clear. The use of a slow blow will help combat inrush current concerns, but again, if the transformer is sized properly to the job and is not crazily oversized (read 750VA when 150VA will do fine) then a standard fast blow as above should suffice.
Hope this helps. |
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| AndrewT |
Hi Jackson,
Ppc has not told us what he wants to fuse yet. |
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| ! |
Unless the amp has current inrush limiting (which it should, really), the fuse rating will need be either slow-blow or significantly higher current rating than would seem necessary from the transformer VA rating.
IOW, an example might be a 300VA transformer and a few tens of thousands uF capacitance, it may blow a fast-blow 3A fuse (on primary winding @ 110VAC) at turn on, eventually, even if not the first few times the amp is turned on. |
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| ppcblaster |
I have the amp working, a
BrianGT Stereo Chip Amp, about 35vdc rail voltage,
I (solved the fuse problem), The directions state a 3A SB.
I am using a Pentium 2 slot 1 heatsink, The amp sounds great!
my consern is, I had to try it out to see if it worked with 4ohm
Automotive speakers. The heatsink was very warm after
about three songs on a CD. I used a portable CD player as
the input until I find a volume control. I also turned up the sound
to hear what it would do, I am impressed!
I have searched all over, Where can I get one heatsink for
both channels?
Thanks |
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| ianpengelly |
| quote: | Originally posted by Mayday
BTW, I think someone else said it first, about dual trafos i meen. |
I did start a thread about using a single transformer and more than one psu board and that it resulted in thread, solutions were 1 psu or 2 transformers (assuming a 2 channel setup). For your boom box a single transformer and single psu board to feed both channels will be just fine.
Hope this helps. |
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