Transformer voltage for lm3886 kit

[davym]

Hi, i'm wondering if this 115/230v 300va 0 25v 0 25v transformer would be ok for this kit when running 6 ohm speakers, or is it to high a voltage?

Toroidal Transformer 300va 0 25v 0 25v

The next down is quite a drop to dual 18v which I feel may be too low a voltage.

I'm also wondering about a suitable volume pot value, would 20k do?

The source will be Musical Fidelity's V-DAC & V-LPS which have low output impedance, the v-dac measures max 78 ohms and 2.08v max output according to a Stereophile review.

Cheers

Davy

 

[lanchile]

I would use that 25vac transformer with not problem. and for the pot I would use a 10K TKD potentiometer http://www.partsconnexion.com/tkd_73334.html

 

[Mooly]

The big problem with any chip amp is getting the heat away from the device. 25/0/25 sounds OK on the face of it but if the speakers are demanding current wise then the 18V may be a safer option. The voltages will be a bit higher anyway when the regulation figure of the tranny is factored in.

There's no right and wrong answer for this one. If you really need the higher voltage swing then use the 25V, if you don't then use the 18V

Try this first,
http://www.diyaudio.com/forums/mult...much-voltage-power-do-your-speakers-need.html

A 10K or 20K pot is fine in practice.

 

[davym]

Cheers Mooly! The speakers are Rega R3's mini floorstanders which are quite easy to drive to a high volume without a lot of power. My main concern is that the amp gets enough voltage to produce a decent bass, I hate soggy bass and one of the reasons I chose this kit was I read it had a nice tight bass. If an 18v transformer will make no difference to a 25v one in this regard, then i'd be as well with the 18v one. I'd value your opinion on this because i'm about to buy the lm3886 kit.

Davy

 

[davym]

An interesting test! I once tried the Rega's on an Icon Audio valve headphone amp with a 3 wpc speaker output. I was amazed how loud it went but it had no bass power or control. Nice mid and highs though if a little bit veiled.

The transformers i'm looking at are rated for 230v, I get 245v as a norm so I suppose the 2x18v might reach 2x20v at times.

Think i'll go for the 2x18 to be safe.

 

[lanchile]

http://chipamp.com/docs/lm3886-manual.pdf

 

[lanchile]

if I "had" to build a chip amp for me, I would build an LM3875 chip amp!

 

[lanchile]

An interesting test! I once tried the Rega's on an Icon Audio valve headphone amp with a 3 wpc speaker output. I was amazed how loud it went but it had no bass power or control. Nice mid and highs though if a little bit veiled.

The transformers i'm looking at are rated for 230v, I get 245v as a norm so I suppose the 2x18v might reach 2x20v at times.

Think i'll go for the 2x18 to be safe.

2x18vac will be 2x25.2vdc after rectifier

 

[Mooly]

An interesting test! I once tried the Rega's on an Icon Audio valve headphone amp with a 3 wpc speaker output. I was amazed how loud it went but it had no bass power or control. Nice mid and highs though if a little bit veiled.

The transformers i'm looking at are rated for 230v, I get 245v as a norm so I suppose the 2x18v might reach 2x20v at times.

Think i'll go for the 2x18 to be safe.

Yes, the secondary voltage will be higher by that primary voltage percentage difference and you must also add the regulation figure percentage to the secondary voltage as well. That will be in the data sheet and probably around 6%. That's the rise in voltage at light loading.

The chip amp voltage shouldn't really affect the bass as such provided the output isn't near clipping. I would do that test, its a real eye (ear ) opener and you might be surprised at the result.

 

[davym]

Cheers folks that's settled it, 2x18v should do fine.

 

[Mooly]

OK

 

[davym]

What a difference a day makes! I ordered the kit today, and I found a 2x22v transformer, it's more expensive but probably better quality and has options for banding or copper wrap.

Standard Range Toroidal Transformers: CM0300222: 300VA 230v to 2x22v

 

[davym]

I would like to build a passive pre in a separate box, would this drive the lm3886 ok (I will use short cables) or does the pot have to be fitted in the same box as the amp boards?

Davy

 

[Mooly]

As long as the gain of the amp is sufficient then passive preamp is a good option. It doesn't have to be in the same box as the power amp. Remember its the source component that drives the amp in such a case, CD players, DACs etc have high output levels, other sources may not.

 

[davym]

Good news thanks. I recently built a headphone amp (cmoy) into one of these cases and it would be nice to have a matching case for the pre.

Silver Extruded Aluminium Enclosures and Accessories

 

[lanchile]

it is better to build it in the same chassis. (the shorter...the better) 10K/25K will be a good choice.

 

[davym]

I had read that somewhere, I take it I need to build more in the style of a gain card with the power supply boards close to the amp boards and the transformer in a separate box? I want to get this right first time because I cant afford to make mistakes with case size and layout.

 

[Mooly]

The success or otherwise will come down to the wiring and actual implementation of the grounding. You don't need separate boxes as long as there is reasonable space to work.