[Whitebread]

Hello guys, I'm making 2 small speakers and a small amp for my GF to use with her Ipod as a grad/going off to college gift. I'd know this is a headphone forum, but I don't know any forums that has such a developed DIY sub forum.

The amp needs to provide 15-40 watts per channel into 8 ohmns continously and it needs to have a preamp built in with at leaset 2 pairs of inputs with a low enough input sensitivity that an Ipod will drive it.
The amp must be solid state.

The GF can't and won't enjoy the merits of a tube amp whatsoever.

Money isn't much of a problem.

Thanks guys!

 

[mrdon]

First of all at your amp wattage ratings I would recommend very efficient speakers. However, it is very hard to find an efficient small speaker.

Now to give an amp recommendation. I would suggest the Amp6. Here's a review. The Amp6 tends to be on the analytical side so I would suggest paper in oil caps for the input caps and adding a 10,000uf/16V cap in parallel to the 1800 uF closeup cap for tighter and more pronounced bass. You can easily make this an integrated amp by adding an Alps27 pot and an input selector switch. Again, the Amp6 sounds much better with high efficient speakers. Below 90db they sound a little thin.

 

[Whitebread]

Well, these small speakers are made using CSS WR125S speakers. They exibit power compression around 35 watts full range so I figure 20-40 watts will work fine.

I will look at that design, thanks for the recomendation.

 

[Whitebread]

The amp6 is more than small enough and cheep,but I'm afraid my gf might blow the amp as it doesn't quite provide the power that the speakers need. The amp 1 seems to get teh job done very well, but I will still look around and see what others cna provide.

 

[Garbz]

I'd suggest a very basic Gainclone. A single chip handles 2 stereo channels. It's as easy to build as a CMoy, and works in much the same way. Add an input volume control and a switch and you got yourself a passive pre/selector.

Just google gainclone. There's a few different chips used but most are of the National Semiconductor Overture series of chip amps around 46watts. But I've seen higher and you can always bridge them for +70watts.

Oh and they sound very nice too!

 

[Whitebread]

Wonderful! I will check that too.

 

[MASantos]

Since the ipod line out signal is not very strong, what about a buffered gainclone?
There is a schematic for one using opa 627 at decibeldungeon. Search decibeldungeon on google. It's the equivalent to tangent's website if you want to build a gain clone.

There are other buffers schematics available there but I think that one is the simplest.

Manuel

 

[Garbz]

What's the point of buffering? You're not talking about buffering the output are you? If it's the input you're talking about buffering again would defeat the purpose. An active pre-stage if the ipod is too quiet could be used, but the Gainclone could always be setup to a higher gain.

The analogy I see in my head from what you said would be like buffering a high current high gain amp like the dynalo and doesn't make sense to me. If you're talking about input impedance a Gainclone can easily have a very high impedance, ok fair enough no 10Mohm like a FET opamp, but either way the iPod shouldn't have trouble with even a 10k load.

 

[mono]

Quote:

Originally Posted by Garbz What's the point of buffering? You're not talking about buffering the output are you? If it's the input you're talking about buffering again would defeat the purpose. An active pre-stage if the ipod is too quiet could be used, but the Gainclone could always be setup to a higher gain. The analogy I see in my head from what you said would be like buffering a high current high gain amp like the dynalo and doesn't make sense to me. If you're talking about input impedance a Gainclone can easily have a very high impedance, ok fair enough no 10Mohm like a FET opamp, but either way the iPod shouldn't have trouble with even a 10k load.

Are you thinking "what will work" or "what sounds better"? Many have compared their GC with and w/o a buffer and the buffer sounded better.

Given the requirements a good candidate would be a LM3875 kit like this and a discrete or JFET opamp buffer but I think OPA627 is an unnecessary expense for this use.

 

[Whitebread]

Thanks guys. School is finally out so I'm gonna take tomorrow and go through everything and see what suits me the best.

 

[Whitebread]

Guys, using a higher gain to accomidate for the lower power of the Ipod headphone out is a possibility, but what if teh GF connects a hotter source? Adjustable gain isn't really a posibility because she'll have no clue how to calibrate it.

 

[patricklang]

Check out the most recent Parts Express speaker building project from their flyer:
http://www.partsexpress.com/webpage....WebPage_ID=341

It's a iPod jambox, could be adapted for indoor use. They chose a T-Amp powered off a 12v sealed lead-acid for several hours of power outdoors.

 

[DaKi][er]

You’re complicating things far too much here, Garbz has it right for just using a straight gain clone. The ipod isn’t a weak source, just use the line out/headphone out set to full volume and be done with it, a pot on the input does a wonderful thing called 'volume control'

Fair enough to go all out if you want to build an audiophile amp but this is just for running some average speakers for the girlfriend, keep it simple

 

[mono]

Quote:

Originally Posted by Whitebread Guys, using a higher gain to accomidate for the lower power of the Ipod headphone out is a possibility,

or necessity, unless you want a lower volume ceiling or to add the gain at the preamp which will incurr same issues of readjustment.

Quote:

but what if the GF connects a hotter source? Adjustable gain isn't really a posibility because she'll have no clue how to calibrate it.

We can assume she will use the volume knob like anyone else would... that is, you should have one, and to at least make the gain high enough that it's reasonable for the iPod.

Having built a GC myself, I think you are overthinking this. Try setting the gain to about 30 and put a volume pot on the input. Get extra pairs of different resistor values so you can raise the gain a little higher later (permanently) if it seems necessary. A GC can play pretty loud though, given a reasonable load, so a little lower gain may not be such a problem particularly in a smaller room.

 

[00940]

The amplifiers chips don't have a wonderfull bandwith. I wouldn't use very high gain with them. So, if your source is really weak, adding a gain stage makes sense.