Transformer questions

[synthius]

Hello All,

I am designing a 45 +45 watt stereo amplifier using the lm4780 and I trying to decide what transformer to use. I will need +-35V rails so this is what I came up with.

1. Will a 24-0-24 150VA toroid transformer be sufficient for my project or shall I increase the VA rating?

2. Are there any major differences between the toriod and "box(not sure what they are really called)" transformers configs? I would like to go with the box configs since they seem smaller in size.

2. Does anyone know of any good websites that sell transformers?(its seems that there are few out there.)

Thanks guys

[tangmonster]

Make sure you use 8 ohm speakers with that voltage.

Many people seem to choose minimum 160VA for 50W x 2.

But I have seen MANY kits proclaiming 100W and only having a 100VA toroidal included( no way)


make sure you have between 10000uF to 20000 uF of filtering caps per rail.


(this is my opinion about what i have read on these forums and simple maths and common sence, others may differ)

Tang

[Nuuk]

make sure you have between 10000uF to 20000 uF of filtering caps per rail.

No! Start with the 1000uF per rail and then try adding 10,000uF and see which you prefer!

[tangmonster]

Like i said

Everyone feels a bit different

1000uF rectification for 3.5A peak currents into 8 ohms , just doesn't compute correctly with me.

But it's all about the diy builders choice.

[AndrewT]

Hi,
low values of combined smoothing and decoupling located at the chipamp seem to do very well for good sound quality. This is particularly applicable to high sensitivity speakers.

I suspect the overriding reason for this, is very good mid and treble performance, where much of the current demand is very transient.

I know that sustained bass power will draw down the voltage (with it's attendant high ripple) on small caps more than on big caps.

If one wants good bass response and good power delivery then I suggest that a separate chipamp be used for the bass driver, and leave the relatively light loading of mid and treble to a chipamp tuned to give it's best for that range of frequencies.
Then that gives the flexibility/option to tune the bass chipamp and driver to give best performance for the low frequencies in the signal.

That way you get the best of both worlds.

[Nuuk]

Or go regulated!

[defect9]

from everything I've read around these parts, it seems that builders such as Peter Daniel recommend at least 220 VA, and usually choose more in the range of 300 VA. naturally, choose what works best for you. 150 VA will power it, but adding a more powerful transformer will add to the sonics.

recommended transformers, again, are a matter of opinion, but i see a lot of recommendations for Plitron, followed by Avel if you're on a tighter budget.

sites to buy stuff:

plitron power transformers: http://www.plitron.com/shopping/shop...l+Transformers

partsexpress.com is one place to get avel transformers

additionally, you can also get Hammond transformers from parts express, which are boxy. google may provide better results, not sure.

-Jared

[synthius]

Thanks guys,

Make sure you use 8 ohm speakers with that voltage.

Yes I will be using 8 ohm speakers

[

make sure you have between 10000uF to 20000 uF of filtering caps per rail.

I have seen many designs that use a 10000uF cap per rail, i think i might go that direction.

rom everything I've read around these parts, it seems that builders such as Peter Daniel recommend at least 220 VA, and usually choose more in the range of 300 VA.

I have heard there is such a thing of having a transformer that is too powerful therefore affecting the sound. Is this true ?

[tangmonster]

Originally posted by synthius

I have heard there is such a thing of having a transformer that is too powerful therefore affecting the sound. Is this true ?

nope , But getting a huge one is overkill and isn't cost effective.

[synthius]

Ok guys This is what I have ordered so far through your help.

• 400V 25A Bridge Rectifier
• Littlefuse 4A 3AG Slow Blow Fuse
• AVEL Y236652 250VA 25V+25V Toroid

All I have left to order is the two 10,000uF capacitors. I have been looking for them online all day and can't seem to find good ones.

Does anyone have any suggestions on brand or specific types and where I could purchase one?

Thanks