Beginner's Gainclone, HiFi LM1875, The Amplifier Board

[danielwritesbac]

Originally Posted by lausar

Thanks, I'm a Nichicon KZ and Elna Silmic II believer.

Nichicon KZ, Nichicon FW and Panasonic FC are suitable for your solid state and chip amplifiers. The "ideal" varies per each amplifier, so I'm sure you'd want caps that are known good with LM1875 and LM4702. When researching this, do beware that caps were re-formulated after the ROHS initiative and contain a new environmentally friendly goo, and; therefore, old performance data does not apply to new production capacitor.

The K50 kit uses 220u amplifier board power caps, actual center-point figure is 330u, and for "laid back" we could use 470u.
I would guess to use the 270u Panasonic FC if the speakers need a clarity boost or the 470u if the speakers are forwards when driven by solid state amplifiers. Aligning for system symmetry means making choices that suit the given models of speakers. To avoid excess shipping charge I'd buy 2 pair 270u and 2 pair 470u and several different models of 100u and some 150u examples too; and, that way the money goes towards useful parts instead of the postman.

Originally Posted by lausar

What's the 4.7uf used for?

Component selection for this is touchy. It is an audiophile power filtering to "uncongest" the midrange (by removing noise) so that loud playback can be more pleasant, with slightly higher resolution and slightly decreased blare. The Mallory Cornell SEK 250v 4.7u is good for this. Other alternatives include polyester speaker crossover caps in the range of 2u2 to 4u7, and RCR filters as well. I would suggest the known good model from Cornell because it is easy, it works and it is just a few cents. Because of publishing the measurements for proof, Cornell is the industry leader when it comes to power purpose caps, especially smoothing caps used for getting rid of noise.

Originally Posted by JMFahey

Just arrived (no, didn't read the 12 pages of posts) but curious: Why do you add unnecessary output capacitors in series with the speaker?. Besides showing them as polarized in post #111. Wiring them in antiparallel will not turn them into bipolars. In post #114 you attribute no polarity to them, maybe hinting you'll use bipolars there. I wonder where you will find 1000uF bipolars but even more what's the perceived advantage of adding them there. Plus, as I said before, you don't need them, that split supply amp has 0V DC at the output. And a polarized electrolytic is not happy at all (as in exploding with a loud bang) with AC across its terminals.

Lausar has plans to use a quickly made chip amplifier to rock the house with costly, rare, classic speakers that were made for current drive, and he also has rails fuses and twin-smps split rail power, both of which may cause rail asymmetry hazards. Output caps prevent destruction of the irreplaceable speakers. Perfect.
And when the size is chosen well, the caps also facilitate some current drive slightly before roll-off and bass/headroom management suited to small amplifiers, so that rocking the house succeeds. A live test with my circa 1962 Pioneer coaxials worked nicely.

Single rail amplifiers commonly use polar caps at output and their output is the same AC audio as a split rail amp. Any cap durable enough for power supply use will also withstand output cap use. For the past several years, all of my amplifiers have output caps, no failures and no exceptions. THANK YOU for causing me to look at Mouser for the big bipolars. Antiparallel (for undistorted signal symmetry and zero treble distortion) will work just fine with radial Bi-polar caps too by using the pin length as an indicator. Bi-polar is more likely to survive a worst case accident. The Nichicon ES has a reputation for low loss and bass slam. I like this idea!
Aluminum Electrolytic Capacitors | Mouser
Really cool! Those big green Nichicon ES should work perfectly for his output caps. Thanks again!

Originally Posted by JMFahey

AFAIK the Gainclone idea is to build a very simple very flat and clean "piece of wire with amplification" , and big electrolytics in series with the speaker do not exactly fulfill that task, at all.

A "gainclone" actually refers to a 47 labs "gaincard" clone with a National Semiconductor Overture chip. My apologies for having misused the term back in 2008. There's no gainclone on this thread. LM1875 isn't an Overture, doesn't have the spike system and doesn't have adequate protection. This thread has a chip amplifier, just like a discrete amp except for the rather flimsy miniature output devices of a chip. The failure mode is to output one full rail's worth of DC offset, so personally I find it quite responsible to use output caps as protection. . . or at the very least, that's an excellent excuse to install really rockin bass extension.

[danielwritesbac]

Another way to do output caps is series 2200u's (makes 1100u bipolar) or series 3300u's (makes 1650u bipolar). And then parallel those things for lower loss and the bigger capacitance value you want. You can do higher voltage large value bipolar caps this way. The method can usually survive worst case accidents. It is also popular for increasing bass slam of subwoofers.

[mortron]

My local has the LM1875 chips in stock for about $5 a pop... I am tempted to throw one of these together. Can the circuit at the beginning of the thread be made to run on batteries? Say a 12v? is there a circuit you would suggest?

As well, your input cap comment, I am assuming the value will dictate the bass roll off? If so, what cap value would net a 40hz roll off?

Is it safe to try this on a 6ohm speaker? I have a few, but one I know is 6ohms.

[tommy_o]

6 ohm is fine. I havent heard of someone running one off of batteries, but it would be possible. It'd be a very hungry battery, though. This is a good alternative circuit that I've built: Squelette, the Bare-Bones Amplifier It uses a cheap $12 Radioshack transformer, which would probably be cheaper than a battery.

[JMFahey]

Dear mortron.
*If* you are forced to run on batteries, the "simple 5 pin chip" solution is the original one, which gave birth to all others, specifically designed for car radios and such: TDA2003
Download its datasheet and build the example shown there.
They even suggest a PCB.
With just 12V it will beat more modern, fancier amps, simply because it was optimized that way.
And it happily runs down to 2 ohms loads, all day long
Not too loud but, hey, you only have 12V available anyway.

[danielwritesbac]

Originally Posted by mortron

My local has the LM1875 chips in stock for about $5 a pop... I am tempted to throw one of these together. Can the circuit at the beginning of the thread be made to run on batteries? Say a 12v? is there a circuit you would suggest? As well, your input cap comment, I am assuming the value will dictate the bass roll off? If so, what cap value would net a 40hz roll off? Is it safe to try this on a 6ohm speaker? I have a few, but one I know is 6ohms.

You might want to try the LM1875 datasheet's single rail schematic example. Or maybe not? Considering the low 12vdc power would have LM1875 at 4 watts max and clipping madly, let me suggest these alternatives: 12V DC gainclone?

[mortron]

Originally Posted by danielwritesbac

You might want to try the LM1875 datasheet's single rail schematic example. Or maybe not? Considering the low 12vdc power would have LM1875 at 4 watts max and clipping madly, let me suggest these alternatives: 12V DC gainclone?

Thanks Daniel... I am looking over this list and its overwhelming. Is there one you would recommend to me that would sound nice? I am looking to keep it efficient, but am hoping to get about 15-25W per channel at least if possible.

Do you suggest simply building the circuit on the datasheet for whichever chip selected? Part of the reason I liked this one, was its simplicity and low cost. Thanks again.

[JMFahey]

am hoping to get about 15-25W per channel at least if possible.

Not enough voltage available, no matter what you use.
You *may* use a bridged power amp for 16W RMS into 4 ohms.
I commercially make portable Guitar amps, using either 2xTDA2003 bridged (in fact I have one of them on my bench right now, fed from a small 12V Alarm battery) or bridged TDA2005 which is the same, inside a single chip.
There are more modern ones, I mention these because I have built tons of them in the last 30 years (or more) and have all the extra stuff (PCBs, front panel sikscreens, transformers, etc.) already well worked out.
Plus, as the Brazilians say: "Não se mexe com time ganhador" = "You don't mess with a winning Team"
We're talking Football here ("Soccer" in USA)

[danielwritesbac]

Originally Posted by mortron

Thanks Daniel... I am looking over this list and its overwhelming. Is there one you would recommend to me that would sound nice? I am looking to keep it efficient, but am hoping to get about 15-25W per channel at least if possible.

That voltage is too low, so that makes a complication.
12v power and 15 or more watts to 8 ohm speaker?
Maybe these:
TDA1560Q
TDA1562Q
About 8 watts to 8 ohms Class AB, but instead of clipping, they proceed to make Much more power in Class H mode.
That's about as easy as it gets, considering the lack of voltage.

[mortron]

Originally Posted by danielwritesbac

That voltage is too low, so that makes a complication.
12v power and 15 or more watts to 8 ohm speaker?
Maybe these:
TDA1560Q
TDA1562Q
About 8 watts to 8 ohms Class AB, but instead of clipping, they proceed to make Much more power in Class H mode.
That's about as easy as it gets, considering the lack of voltage.

Ok, I actually take it back... I forget that there isn't full use of the watts in my amps now, as I pad the inputs... I'm a dummy. I guess most music is only using a few watts constant, the rest is for peaks?

So at 12v, is it reasonable to expect 5-10 watts? If so, is there a chip that is well suited? I will go through the list and start reading more.

As for circuits, is the one on the data sheet the recommended build?