12v tx for 1875

[wicked1]

I want to run my lm1875 amp on about 12v for some computer speakers.
The only 12v tx at parts xpress is 30va.

Does anyone know where I can find a larger one?

thanks!

 

[Minion]

Do You mean a single Rail 12v Xformer ?? If you do then I don"t think you can run a LM1875 on 12v , I believe the LM1875 needs a Minimum of 16v DC , even 12v ac would give you 16v DC but it would drop to 14v or 15v under a load .....

If you mean a 12v ,0v ,12v Xformer then I know were I live I can get a 12v ,0v ,12v 4A Transformer at Radio shack for about $10 ......


cheers

 

[wicked1]

I mean 12,0,12. And I think I need something a lot bigger. Like 250VA which is, I think, about 20 amps. That sounds like a lot, so I could be completely wrong w/ my math, there.

 

[wicked1]

So, after a lot more reading, 250va is overkill, but still, I can't find any available over 30va. I think I need something around 180va.

I suppose I could go w. 15v, but I really don't need much power (And can't find any 15v large enough, either)

 

[Minion]

30 Va per chip should be OK but 50Va would be better ...... You don"t need 180Va , At +/-15v DC you will only get about 8-10w into 8 ohms so you really only don"t need a huge transformer.......


Cheers

 

[kaos]

Avel Transformers work ok and they take credit card phone orders. Check out the Y23 standard range listings.

http://www.avellindberg.com/transformers/y23_range.htm

 

[AndrewT]

I mean 12,0,12. And I think I need something a lot bigger. Like 250VA which is, I think, about 20 amps. That sounds like a lot, so I could be completely wrong w/ my math, there.

110Vac:12-0,12-0Vac, 250VA is a 10.4Aac transformer.

Output { VA / Vac } = output Amperes

The 1875 will give about 10 to 12W into 8r0 from a +-16Vdc PSU.
It will approach 20W into 4r0 if the PSU can hold up.

Both of these, 8ohm or 4ohm, could be powered by a 30VA transformer.

If you require two channels then roughly double the transformer VA rating.

 

[wicked1]

Avel Transformers work ok and they take credit card phone orders. Check out the Y23 standard range listings.

http://www.avellindberg.com/transformers/y23_range.htm

Thanks! I had written them, and they hadn't gotten back to me. They just did, and the price is GREAT! I asked for a quote on the 250va 12v + 12v, and the price is just barely more than the 30va 12v at parts express!!
Now that I know I can use an even smaller tx, it should be even better!

 

[sandyhooker]

Try MPJA.com for usable trans. at reasonable prices. You really dont need toroidal stuff always. I've used iron units without a problem . Take a look..

 

[wicked1]

I have no issues w/ a good old iron xfrmr, and started looking into that.

Is there a difference in the power supply if I go w/ a 12,0,12, vs something that has 12,0 + 12,0?
Would I just share that common ground?

(ive ordered pcb's from chipamp.com, but have not seen a schematic)

 

[sandyhooker]

Either way is acceptable. I found my little amp to be just right for computer operation.

 

[AndrewT]

I have no issues w/ a good old iron xfrmr, and started looking into that.

Is there a difference in the power supply if I go w/ a 12,0,12, vs something that has 12,0 + 12,0?
Would I just share that common ground?

Hi,
there are at least two big differences between Toroid and EI.
The Toroid has lower regulation.
The Toroid has less attenuation of the HF.

Operationally there is a big difference between 12-0-12 and 12-0 + 12-0.
The 12-0 + 12-0 can be easily converted to Centre tap and both versions suit a single single rectifier with the centre tap connected to Audio Ground.

The 12-0-12 cannot be converted to dual secondary.
Only the dual secondary can use the dual bridge rectifiers, with the zero volts line connected to the Audio Ground.
In a monoblock this makes absolutely no difference.
In a multi-channel amplifier, this can make a big difference in the flexibility of organising your separated audio grounds.

If you plan to build any multi-channel amplifiers and want the flexibility to experiment with the grounding, then buy the dual or quadruple secondary transformer.

 

[sandyhooker]

Hi,
there are at least two big differences between Toroid and EI.
The Toroid has lower regulation.
The Toroid has less attenuation of the HF.


The 12-0-12 cannot be converted to dual secondary.
Only the dual secondary can use the dual bridge rectifiers, with the zero volts line connected to the Audio Ground.

In this particular case dual secondaries are'nt necessary. It is doubtful that dual 12 volt secondaries would be used to power multiple amps.Get a Marlon Jones iron job for little money and enjoy the sound.

 

[wicked1]

I just got my PCB's and it looks like in this case, it doesn't matter (as the previous poster said)
There is no provisioning on the board for 2x full bridge rectifiers.
Same goes for the mini-a PS pcb, but I'll ask my questions about that one in the correct forum. (I haven't seen a single aleph PS schematic that doesn't use dual rectifiers)

 

[wicked1]

Well, I got them built last night.
I found an old audiosource SS3 surround sound processor w/ a 14-0-14, 100va tx inside. ALSO, a nice double heatsink. The SS3 was a little chip amp, w/ the other brand (not lm) chip of about the same power as the 1875. (sorry, parts aren't near me and I forget what chips it had)
So, finding that ss3 in a stack of old stuff in my basement was a huge help on this, and saved me a lot of money!

It sounds great on my 'big' speakers (little 6" full rangers) and I'm sure it will be perfect for its intended use as a computer/desktop speaker amp.