My new gainclone page

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Good info. After reading your page I have no choice, but to build one myself.;)

From a review by Herb Reichert (Listener): " The 25-watt Gaincard amplifier will outplay the Krells and Levinsons, it will reveal more of the poetry and structure of musical art than any silicon-based amplifier I have experienced, and it has plenty of cool factor. It seems able to drive a wide range of loudspeakers, and at $2750 complete (with one Power Humpty) this must be considered an excellent value. "

If this is true, maybe I should put more effort towards that little LM chip and not the Alephs?;)
 
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Joined 2002
Nice site Fedde:cool:

Have you tried the Evox Rifa 5% MMKs yet? They work really well for the .1uf cap, almost as good as no cap at all!

My inverted gainclones are still in iteration, I am playing with components, and have found I can actually get shorter connections in some places by using a pcb, but this all may change...

Peter, I am not sure where the expensive prices charged for the Lab47 product comes from, but even in testing, the LM3875 is very special indeed, and for a very small outlay it's got to be worth a try. I belive the Gaincard itself uses a non inverting circuit, and even before optimising, the inverted configuration from Thorsten is just so much better.

If I can build these, then everyone else should have no problems at all, so give it a go!
 
Thor-amp

I do not know how the Thor-amp compares to the 47 labs gaincard. I will try that later this year...
Also, I do not know how it compares to the more expensive ss designs on this planet. At least, I think you could say that when you build such an amp yourself you have a very good quality/price ratio.

Pinkmouse: thanks for the capacitor tip. Probably, it will be hard to get them here in the Netherlands. I will try to find them.

I do not really have problems with the 47 labs pricing strategy. I think that if they are as good as some reviews say, they are worth the money. I mean, you also pay $150 for Windows, and that's even a somewhat crappy product IMHO (but it's getting better). And you get a cd, that's not very expensive is it ?. Most of the costs come from the development. Please don't start a thread about Windows, it was just an example
:)

A more interesting topic would be to discuss what the exact advantages are of a low capacitance supply. Still beats me, more or less...

Fedde
 
Lower supply

Was that with the LM3875? When you have speakers with an impedance under 8 ohm, lower supplies probably work better. It's a pity that transformers are a little too expensive to experiment with. I would also like to try 225 VA toroids or more. I think that the gaincard also has a lower supply. Maybe I will try once...

Fedde
 
frugal-phile™
Joined 2001
Paid Member
fedde,

Good work...

Peter Daniel said:
Reading through previous threads I remember that Dave (planet10) mentioned that LM chip works better with lower rails (18-0-18 transformer). Why would it be?

If you look at the power vrs rail voltage vrs load impedance you will notice that above 25V rails the 4 ohm output goes flat. The statement is based on my belief that all speaker loads are ugly when compared to a resistor and that the ability to deliver current into those loads is important. Now i actually haven't built mine yet so that is theoretical (and based on feedback from some others).

As to the cost of these things, if you are a good scavenger they can be built for well into Frugal-phile(tm) territory. I got free 1875 & 3875 samples from Nat Semi. Toroids are kind of hard to find salvage (ApexJr has surplus 120 VA 18-0-18 toroids fairly cheap) so that will be your biggest cost. Once when i was flush i ordered 10 surplus 225 VA 18-0-18 Plitrons. They shipped 18 so the end cost was very low. Heat sinks can be salvaged from dead computer monitors (you'll have to live with aluminum) and cases too can be salvaged or made cheaply. A trip to value village may even find you a matched pr of aluminum cooking pots or pans that could be used as case & heatsink! Then a handful of passive parts & some bridges. I suspect that $40-$80 USD is very doable.

And if 25 W isn't enuff, just bi-amp :) Or build more efficient speakers.

dave
 
Definitely Fugal-phile (tm) catergory.
Tonight I just got a biamp creation up and going. It uses the lm3876, and its smaller cousin lm2876. I got a module for apex jr. (cheap and easy, but no inverting). The woofer is powered by the 3876 and the tweeter is run by the 2876. I am planning to build the amp into the speaker and so I do not need a totally seperate enclosure for it. Got it running on the workbench, taped it down to a board and carried it in to meet my preamp. Sound was great (at least for one of my projects). It seems to have much more power than my 50W rotel power amp. Here is the cost, perhaps the two speaker boxes together will put it out of frugal-phile(tm) territory. But as far as the spirit of doing it on the cheap this is first class.



transformer 120va 18-0-18 $15
diode bridge 10A $2
Voltage regulators 7815/7915 $1
filter caps 1600uf x2 $1 (army surplus store)
fuse + holder x3 2pcb 1panel $4
filter caps 47uf x4 $1.50
IEC power connector w/ filter $2.50
Heatsink aluminium plate $2
amp module lm3876/lm2876 $5
also active x-over
connectors for module $2.50 (hey I was lazy)
cat5 wire scrap
RCA jack $.60
PCB scrap
power switch $2
power cable scrap
----------------------------------------------------------
1 Biamp setup $39.10 USD

Now im saving change to buy that blue led:)
For the record I am totally pleased.
I also got some extra 3876s to replace the 2876 but after listening I really dont need it.
 
first the heatsink... I dont think it takes much of one, right now my setup just uses the band of metal around the module (2.54cm x 30cm x .5cm) both amps sit on the band. When it first got it working I thought i would be able to play it to maybe a watt or two. With the lm3876's internal temperature sensing I was not too worried ( not because I really believed it would work, but because I have a few in reserve and wanted to see what it would do). I was very surprised one I got it to the preamp, When playing it gets warm and I will be the first to admit it needs a better heat sink. It did however get ear splittingly loud without overheating. Im just not sure how much more heatsink its gonna need. I would try whatever is handy, this amp (even two) isn't that picky.

onto the speakers. This is where we depart from Frugal-phile(tm) territory. My current set of speakers (MB Quartz 4in and seperate tweeter for cars) would fit the cheap mold, got them off my brother as payment for boxing up the set he was using in back of his car. He was using these in the front. They cost me about $2 for the PVC pipe for port. The new speakers (and amps)are not going to be mine. Both drivers are Focals the tweeter is
http://www.focal.tm.fr/gb/compo/archives/tweeter/tc90tdx.htm
and the midbass (5in) is
http://www.focal.tm.fr/gb/compo/archives/midbass/5k4211.htm
Im sure together thse knock the speaker out of the frugal-phile(tm) territory at about $130 for both.
 
frugal-phile™
Joined 2001
Paid Member
Lligior said:
Im sure together thse knock the speaker out of the frugal-phile(tm) territory at about $130 for both. [/B]

Still seems reasonable to me, that this is still frugal-phile(tm). Not the lowest levels of frugal-dom at just over $200 for a bi-amped powered speaker. Add a used CD player & a passive-pre and you've still got a system for under $300.

It's not the exact cost but the attitude...

dave
 
Hi,
I can only encourage anybody to build some amp with the overture series chips.
This was my first and actually only finished project and I´m really happy with it.
I used 2*LM3886,220VA 2*18V transformer, dual mono power supply and 20000uF per channel in total.
I only still got problems to get all the induced hum from the power supply away. But that´s hard to hear anyway.
The only thing is I use 8Ohm speakers and so can´t get the full power out. So definitely think about which speakers you´ll be using to get the most out. Bridge or parallel configuration would be another solution. There exists a nice documentation about bridge/parallel operation of the LM3886.
For those who are interested:It´s called BPA-200 from National Semiconductors.
There are many sites about these amps including a specific gaincard forum : Amp Chip Diy
Another project suggestion is by Tim Harrison and can be seen on Headwize .
......
Another interesting chip is the TDA7293.
Probably you´ve read a review of the Linn Klimax Twin.
It uses SMPS and 3*TDA7293 per channel and has quite a bit of power. But you should rather build it yourself. The Linn cost about 9000€($) :bigeyes:

Jens
 
This is quite supprising... glad i ran across this thread.

Ive had a fair bit of experience with the LM3886 and the LM3875 and have buit quite a few amps with them.
I have never had the chance to compare my amps to others though, so its always left me wondering how good they were.

The best one i made used LM3886s bridged running on a +-40V power supply. It was for a home theatre setup, with active crossovers on the L&R.
I managed to fit 2x500VA torids and 8 channels (16 LM3886s all up) into a 3U case.
On measurment it was able to do 220Wrms into 8ohms at 1Khz with <0.08% THD+N. The measument equptiment was quite old so 0.08% was the least amount of distortion it would measure.
Scheamtics are around here somewhere if anyone wants a look.

For those who are interested:It´s called BPA-200 from National Semiconductors.

Do you still have the PDF?
It was on NSCs web site for about 1 month before it was retracted. I lost the PDF but i still have a print of it somewhere. I asked NSC about getting a copy of the PDF, but they said it couldnt be given out for some strange reasons.
The amp i mentioned above (a another i made) are based on this app note.
 
gainclones...

whaddayaknow, people are still talking about these little things... :p

i'm actually about to build a gainclone myself. but first, a couple notes on the commercial versions...

i heard the 47Labs gaincard at the stereophile show this past June. i thought the sound was wimpy and anemic but the system was so weird i couldn't tell how much of it was the amp. personally i think it probably sounds quite good in the right circumstances but is overhyped.

my magazine editor had reviewed the Andy Bartha mono amps, which use LM3886. he said the sound was quite good in many respects but only with the right speaker (i think he liked a small 2-way Kirksaeter with it, which seems to be a fairly benign load). even then it wasn't really his cup of tea, lacking air in the high frequencies and overall dynamics i believe. note however that the bartha amp has a few different design touches (e.g. a 600 ohm input transformer).

i'm currently reviewing the Blue Circle Music Pumps (IC amp in a woman's pump show), which was inspired by the gaincard. the designer doesn't reveal what chip he's using but i suspect it's a LM1875. these amps were the talk of the stereophile show, interestingly with the same Kirksaeter speakers my editor liked with the Bartha amps. i admit they sounded quite excellent - full, musical, detailed, very natural and enjoyable. the bass was quite something too. in my system, they sounded downright awful with my Merlin TSM's, which generally need tubes to sound good. however, with another small 2-way i have (Role Audio Windjammer), they sound very nice indeed, though with restricted dynamics (theyr'e rated at just 20 watts). i believe the load impedance of these speakers never drops below 7 ohms.

i was all set to build a LM1875 amp, which i like because the output and inverting input pins are next to each other so i could stick a SMT chip resistor right on the pins for the feedback. however i'm definitely desiring more power so i decided to go with the LM3875, which doesn't have the same optimal pin layout but i believe it's the device used in the gaincard.

i am seriously considering using the chip in inverting configuration a la Thor (hence my inverting amp thread a few weeks ago) but i have some concerns with the compromise between feedback and input impedance. i don't want input impedance any lower than 20k or so (i'm using a shunt attenuator before it) but that necessitates a very high impedance feedback path, which to me has its drawbacks. i'm also unsure of the need for all the extra capacitors shown in the Thor schematic. i've heard good things about AC coupling the input but i for one prefer as few parts in the signal path as possible. i think to properly use this chip in inverting configuration, you will need some sort of preamp or buffer before it or dynamics/noise/distortion performance may suffer.

i'm not so sure about the low capacitance supply thing. you'll notice they offer a higher power gaincard with twice the capacitance. does that make it somehow inferior? personally i think using a little more capacitance is fine. i'm thinking of using 1000uF by the chip as in the gaincard, but with another 1000uF or so close to the rectifiers. or maybe a bank of multiple 470uF caps. in any case, they will be Nichicon Muse types.

other design touches... resistors will probably be IRC tantalum chip if they prove to be good-sounding (doing a resistor comparison test soon). attenuator will be 15k fixed series, 50k Noble pot for shunt. i will use a zobel on the output (10ohm + .1uF), along with a little bit of series inductance (a few turns of 16 gauge OFC magnet wire). i'm hoping to get an R-core power transformer, around 200VA or so. not sure what rail voltage to use but probably a 20VCT transformer is about right. soft recovery diodes of course. one thing i'd like to try out is putting a small capacitor on the secondaries, before the rectifiers, to reduce RF noise... a form of AC conditioning you could say. a good 0.1uF polypropylene would do the trick.

the biggest obstacle at this point is getting a nice chassis for it. the whole thing would fit nicely into an aluminum box 6" x 6" x 5" or so... it would be about the size of a Nintendo Gamecube. i have the construction details in my head but getting it custom machined will be expensive... need my own machine shop. (damn you Peter!)

another idea i've had is use multiple LM3885's as amps for an active loudspeaker. e.g. the speaker i'm using now uses very simple 1st order crossovers... would be a piece of cake to incorporate the filters using either input or feedback caps on the amp chip. i think this could be a killer app... the ICs would probably perform extremely well since they're seeing a much less complex load now. you get more total power due to using multiple amps and no power loss from the xover. you could tailor the circuits to the different drivers, e.g the tweeter amp could use very small capacitors for maximum "speed" while woofers could use more capacitance for better dynamics and bass impact. due to the small size of the amps, you could easily build them into the speaker, very close to the drivers. i think with a nice speaker, the sound could be excellent.

ok enough babbling for now... just throwing out all the random things going through my head the last several weeks. :D
 
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