Building an amp

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bs1777

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Minion

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Joined 2006
Seems like you are asking a lot ..... only you would know how to wire it up , I"m sure the instructions came with the kit which should show how to wire it up .......

As for a case there are places that sell cases like "Par Metal" .....

Par-Metal

I generally either make a case out of wood and use a metal paceplate (from a metal supply house or steel/sheet metal shop ) or I salvage a case from an old amp and re-use it ......

To power the Power amp you are going to need a Power transformer that is 35v-0v-35v AC and 500vA and a Power supply board (rectifier and large caps) and for the preamp you need a Transformer that puts out 6v-0v-6v AC , the Preamp has it"s own rectifier and caps ......

Generally the case and Power supply is going to cost you more than the amps and preamp boards , a lot more .....

Good luck ......
 
ianpengelly

ianpengelly

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Joined 2006
freewebs.com/ianpengelly
When you rectify the output from the transformer your effective voltage is the output of the transformer multiplied by 1.414 (square root of two). You can read up about why this happens here:

Rectifier - Wikipedia, the free encyclopedia

I am sure there is also some good info in the power supply section in this forum.

You can easily create your own power supply, have a look at the 4xPA150 Amp thread and you can see one I knocked together with a couple of bridge rectifiers, some caps and a couple of resistors.
 
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Minion

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Joined 2006
Like Ian said , The AC voltage gets multiplied by 1.4 when rectified to DC , And because each channel of the amp is 125w or 250w total you need about double that amount of power in the power transformer as most amps of this type are at best 50% effecient .....

You can make a DC PSU board quite easilly , just a 20a bridge rectifier , and say 4 10,000uF 63v capacitors and that is about it ...... might cost $20 max , The power transformer on the other hand is going to run you upwards of $50 -$100 , for this reason I usually try to salvage transformers from dead amps ......


Cheers
 
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bs1777

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Joined 2010
And because each channel of the amp is 125w or 250w total you need about double that amount of power in the power transformer as most amps of this type are at best 50% efficient
Click to expand...

Im a little confused on what your mean. Could i not just run the wires from the transformer to the PSU then double the wires on the PSU output to have one going to each amp?

-Thanks:)
 
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Minion

Member
Joined 2006
Yes that will work well , it also has a dual primary so you will have to wire the primaries in Paralell and because it has a dual secondary and wire it in series and use the connecting point between the secondaries as your ground ....

hopefully your transformer will have instructions on how to do this , if not post back and someone will help you ....

Cheers

PS: you also going to need a 6v-0v-6v transformer for your preamp , maybe you can find a transformer that is 6v-0v-6v and 35v-0v-35v so you don"t have to buy 2 seperate ones ....
 
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AndrewT

R.I.P.
Joined 2004
Minion said:
.............. And because each channel of the amp is 125w or 250w total you need about double that amount of power in the power transformer as most amps of this type are at best 50% effecient .....
Click to expand...
where did this come from?

It seems like you have drawn a conclusion on transformer power based on a completely erroneous efficiency statement that is simply untrue.

A 125W amplifier will run well from a 125VA to 250VA transformer.
Two channels will run well from a 250VA to 500VA transformer.

These 125W amplifiers will also work with transformer ratings outside that restricted range, only less well. Above the 500VA the transformer provides less performance value for the monetary value expended.
Below 125VA the performance deteriorates much more than what could be saved in transformer cost.
One has to apply a cost benefit analysis. How much performance do I need? How much can I afford to spend?
Do not believe a fixed figure of 250VA for a 125W amplifier.
 
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bs1777

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Joined 2010
So if i have a 240 watt RMS amp. What will power it to its full potential?

And i also need help with a case, cause right now, im am not sure that with all the things i have, it will meet my budget. So anything cheap for a case, or a used or burned out amp case will work.

-Thanks
 
digits

digits

Member
Joined 2011
That depends, is it class A, then a small nuclear substation is in order, class B 500VA is more than enough, and less is fine depending on the load and volume at which it is driven to. Class D, takes what it puts out and sips a little bit extra.

A 250VA transformer is more than enough for a stereo pair of LM3875 driven into 8R at 35VDC supply, and will only get mildly hot when driven hard.
 
M

muddobber

Member
Joined 2010
Read Audio Sector's, Chipamp.com, and Decibel Dungeon's sites for tons of basic info on building amps and power supplies. Lots of ideas and common practices as well as safety issues addressed. These sites were invalueble to me when I first got started in DIY Audio. Good luck!
 
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