Ruby amp lm1875

[scaesic]

Hi! i've been looking around for alternative chips for use with the ruby. Has anyone tried using alternative - higher wattage/voltage chips?

i found a couple of threads on hifi forums with favourable low noise reviews of the 1875, if it was voiced for guitar with a decent buffer/pre-amp would it be a good alternative for a louder ruby?

it could be powered with two 9v batteries? it should be able to deliver 15watts at 18v, although it draws around 100mA, reckon thats reasonable for battery operation?

hifi forum - http://www.diyaudio.com/forums/showthread/t-57468.html

spec sheet - http://home.eunet.cz/rysanek/pdf/lm1875.pdf

[Mark Hammer]

An LM1875 is going to want a 2A transformer for most reasonable applications.  A pair of 9v batteries will likely get very hot and then suddenly very dead.

Note that when any chip has a heat sink built into it (as the LM1875 does), that heat sink is there because the amount of current it is pulling from the supply through those little iddy-biddy transistors on board the chip are sufficient to fry them pretty quickly unless something is tugging the heat away every bit as quickly.  If the heat sink has a hole through it, implying that it needs to be fastened to something ELSE to insure sufficient redirection of heat so as to permit survival of the chip, then you can be pretty sure that nothing less than a VERY large battery would be sufficient to power the device to spec.

Apart from that, though, the 1875 IS a pretty decent chip and has been used in a number of low-to-medium power commercial amps.  I've got a couple of 1875s sitting around waiting for an amp to live in.

[scaesic]

bah, i did abit more raking and found the TDA7052, but its only 1 w and fixed gain.

there must be some other power amp chip out there to deliver more than 1 watt with batteries?

[Mark Hammer]

1) Keep in mind that, using the same speaker/cab and input signal and gain structure, you need to bump up the power factor by x10 to achieve x2 the perceived loudness.  So, 15W is not going to be THAT much louder than 1W. and not appreciably louder than 2-4W.  Many folks think that each watt of power matters.  Often, they don't.

2) There are plenty of chips in 14 or 16-pin DIP form that can be easily reconfigured for bridged mode, and can deliver a couple of nice plump watts with very little component overhead, and nothing more than a sextet or octet of C-cells.  For example, the humble TEA2025, found in SO many older sound cards (the ones that would power speakers directly from the output jack) is a 16-pin DIP that can be run in stereo or bridged mode.  The spec sheets indicate that in BTL or bridged mode, it can provide 4.7W to an 8-ohm load, using a 9V power supply.  As anyone who has one of the single-ended 6V6GT or EL84-based tube amps can attest to, 5 watts can be plenty loud, given the right speaker and cab.

Now, whether it can continue to pump that out for very long on even a sextet of D-cells, is another matter, and something you will have to consider with respect to just exactly how battery operated you want this to be.  BUT, if being battery-operable for even a little while at those volume levels is okay by you, then consider checking out one of the many comparable chips.  I would imagine that there are many more choices nowadays (and with much lower current requirements) than there were in 1992, or whenever these powered Soundblaster cards were produced.

Alternatively the L'il Gem MKII, powered right, into the right load, can probably be plenty powerful.  I'm running an LM380-powered amp into a 6" speaker in a reasonable-sized cab with an octet of C-cells, and it is plenty loud.

[Steben]

I'm running an LM380-powered amp into a 6" speaker in a reasonable-sized cab with an octet of C-cells, and it is plenty loud.

yep, LM380 is the right choice. Still cooleable, not too much useless watts and most of all: same range as the 386, meaning compatible tone and character.

[christobean]

to get more volume, wouldnt it be much easier and practical to use multiple speakers than bump up the amount of power?

[scaesic]

could do, but im thinking of portability/feasability of taking apart a working amp. ie i want something thats going to be just as useable.

[scaesic]

anyone know anythign about the LM4562 ?

[Steben]

Or you could build a bridge amp with two LM386.

Do remember that what the 386 really sets aside is its gentle overload, giving it overdrive qualities.
The LM380 is the same family, hence...

[Mark Hammer]

The appnotes/datasheet for the 380 illustrates how to bridge a pair of them.

One thing I've never understood is whether the supposed quadrupling of power that comes from the push-pull action of a bridged pair necessitates a quadrupling of power supply cpacity as well, or whether double is sufficient.  I still don't understand how these things are calculated.

[Ben N]

Does the answer to that question have anything to do with the class of amplifier resulting, and thus its efficiency?

Ben