Ok, I knew that was too little. Should I aim for 200VA? And what caps? How much power will this (and the www.generalguitargadgets.com board, lm3886) deliver?
you should get a transformer that has atleast 150VA...with the lm3886, you should get about 55W for each channel using the transformer they use in their project (18-0-18V). Using the lm3876, you should get about 45W per channel using their project's transformer.
i'm assuming your load is 4 ohms...is that correct?
i'm assuming your load is 4 ohms...is that correct?
Before ten years I was made fourty 75 W RMS combos for guitar and bassguitar. There was 100 VA toroid, so by nominal output power was little bit overloaded. To this time I have any complaint. These combos was made by the same principle like Gallien - Krueeger and you can bring them on only by one finger 
. Remember, that musicians ( on the beggining ) must take own apparatus by own arms .
. Remember, that musicians ( on the beggining ) must take own apparatus by own arms .
Yeah, but here we're talking about 120W peak power...
Yes, my load should be 4 ohm, but I want to build an amp that's capable of delivering some watts either in 8ohm. 2 and 16 ohms aren't used.
So, 200/220VA toroid at 20-0-20 (that's all I've found) - 25A bridge rectifier - 2200/4700 uF per side - generalguitargadget PCB - lm3886 - 55W per channel?
But what termal resistance of the (isolated) heatsink I'm looking for?
Yes, my load should be 4 ohm, but I want to build an amp that's capable of delivering some watts either in 8ohm. 2 and 16 ohms aren't used.
So, 200/220VA toroid at 20-0-20 (that's all I've found) - 25A bridge rectifier - 2200/4700 uF per side - generalguitargadget PCB - lm3886 - 55W per channel?
But what termal resistance of the (isolated) heatsink I'm looking for?
a 20-0-20V transformer will give you about 28V DC which make the lm3886 68W into 4ohms or 38W into 8ohms. so, that PSU should be fine with the caps and 25A bridge rectifier. for my PSU, i only use 220uF caps...its quite a bit cheaper and works well enough for my purposes.
as for thermal resistances, i'm not sure...i've never built one but you can find the equations for thermal resistances on National's datasheet.
http://cache.national.com/ds/LM/LM3886.pdf
as for thermal resistances, i'm not sure...i've never built one but you can find the equations for thermal resistances on National's datasheet.
http://cache.national.com/ds/LM/LM3886.pdf
you could either order off the internet or you could get two 100VA toriods and connect them in parallel
a cheap place is www.parstexpress.com but they have high shipping costs espescially outside the U.S.
a cheap place is www.parstexpress.com but they have high shipping costs espescially outside the U.S.
What about
having a funktion so that you can choose between a 2X50W stereo amp and a bridged 100W mono amp?
would,nt that be a nice thing? just a small switch in the front or something..
i know i would like that. anyone here good and kind to make a small scematic on how to make that work? Proberly very simple.
regards
Z
having a funktion so that you can choose between a 2X50W stereo amp and a bridged 100W mono amp?
would,nt that be a nice thing? just a small switch in the front or something..
i know i would like that. anyone here good and kind to make a small scematic on how to make that work? Proberly very simple.
regards
Z
Hello zei! I want to do precisely what you want to do. I also have a Pod (the xt version ) and would like a pwr amp to drive a 2X12 cab or 4X12... but I am doing nothing at the moment because I haven't got the money yet, and I've got to decide what can I do.
Here in Italy things are difficult to do: you can't buy a chassis, for instance, you've got to recicle something (
) or build something from scratch. The only useful thing I have seen is on this site www.audiokit.it, they list some heatsinked chassis at not too high prices.
Transformers here are hard do find in the shops: my favourite one (30 minutes by car from my home) doesn't carry anything over 10VA, and you could order models up to 150VA, not more.
Also I haven't found a place where I can get the LM3886, I've seen a website that lists them for 20 euro (quite expensive for DIY, I need two... but what happens if I burn one
)
I think I won't do anything yet... My hope is to find an old hi-fi integrated amp or poweramp to cannibalize... or if it's powerful enought I will just use it...
Sorry but I can't help you. I suggest you to ask at www.generalguitargadgets.com for some info on that, they might have some feedback from someone that has built one...
) and would like a pwr amp to drive a 2X12 cab or 4X12... but I am doing nothing at the moment because I haven't got the money yet, and I've got to decide what can I do. Here in Italy things are difficult to do: you can't buy a chassis, for instance, you've got to recicle something (
) or build something from scratch. The only useful thing I have seen is on this site www.audiokit.it, they list some heatsinked chassis at not too high prices.Transformers here are hard do find in the shops: my favourite one (30 minutes by car from my home) doesn't carry anything over 10VA, and you could order models up to 150VA, not more.
Also I haven't found a place where I can get the LM3886, I've seen a website that lists them for 20 euro (quite expensive for DIY, I need two... but what happens if I burn one
)I think I won't do anything yet... My hope is to find an old hi-fi integrated amp or poweramp to cannibalize... or if it's powerful enought I will just use it...
Sorry but I can't help you. I suggest you to ask at www.generalguitargadgets.com for some info on that, they might have some feedback from someone that has built one...
"Make 1 channel inverting, and the other non-inverting.
For bridged use a ' Y ' cord into the inputs.
For stereo connect one of the speakers out of phase."
Good that! But in the "bridged" mode, how will I connect the speakers? I don't understand real well.. if the outputs are out of phase won't they cancel? or all the current would flow from a chip to another, avoiding the speaker? Sorry I am not an expert!
We will keep it as an option, but we would try to make the two channels with the same PCB on www.generalguitargadgets.com
For bridged use a ' Y ' cord into the inputs.
For stereo connect one of the speakers out of phase."
Good that! But in the "bridged" mode, how will I connect the speakers? I don't understand real well.. if the outputs are out of phase won't they cancel? or all the current would flow from a chip to another, avoiding the speaker? Sorry I am not an expert!
We will keep it as an option, but we would try to make the two channels with the same PCB on www.generalguitargadgets.com
its kinda hard to see but for the bridged config, the output of one amp is connected to the input of the other amp and the speaker. the output of the second amp is connected to the other side of the speaker. both of the amplifiers are inverting. since the amps are out of phase, while one amp is pushing current through the speaker the other amp is pulling current through it which is why bridge mode is a.k.a. push-pull.
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