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Post by sumgai on Oct 28, 2022 16:44:26 GMT -5
frets, Yes, that's a winner of a circuit. And fortunately for you, the LM1875 can accept up to 30VDC for a power supply, so no need to attempt a reduction from your battery down to 9VDC. However, I see that the parts diagram shows polarized capacitors, yet provides no voltage rating, something that is quite important for this type of cap. I recommend using caps rated at no less than 30VWDC. (That's Working Volts Direct Current.) Make sure that the positive leg gets hooked up as shown, or the cap may self-destruct. Probably won't be catastrophic, but it will certainly bring your MojoTone to a screeching halt. Notice the very low parts count. This is the result of years of refinements in engineering practices, and comes directly from field experiences. It means that this portion of your TailGate'r will cost less than the pre-amp portion, provided that you (or any interested viewer) were to go out and buy all of the parts and pieces. I must applaud your getting your hands dirty like this, as there is a metric ton of battery powered amplifiers out there for sale. But who knows, absolutely every bo-teek amp maker started by doing exactly what you're doing here - no formal knowledge, just an overpowering desire to be different from the mass of society. My hat's off to ya! HTH sumgai
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Post by MattB on Oct 28, 2022 17:26:16 GMT -5
This circuit has the input at 0V DC. The example circuit given in the datasheet for a single supply has the non-inverting input biased to VCC/2.
I would trust the datasheet over a random website that looks a lot like a link farm.
Also, the minimum supply voltage given in the LM1875 datasheet is 16V. I don't know enough to say if it would work at 12V, but you can probably find something that's actually designed to run at 12V.
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Post by sumgai on Oct 28, 2022 17:51:49 GMT -5
matt,
While like you I generally believe the DataSheet to be the Holy Word From On High, I do know that a slew of pocket-sized amps are out there with this chip, and indeed some of them are running a 9volt battery (commonly known as a PP3). I've seen them in Pignose clones, but I wasn't impressed with either the tone or the battery life. (Though a rechargeable setup might've mitigated the latter concern.). Better units actually use a pair of PP3's to provide a plus/minus 9 volts, which does sound better, at the cost of twice as much for the same runtime.
HTH
sumgai
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Post by frets on Oct 28, 2022 18:34:57 GMT -5
Sumgai,
Thank you for your input on the circuit. I feel like Iām ready to build it. I have all the components so I should be able to breadboard it rather quickly.
I could have bought a portable amp system but I want the experience of building circuits. I build a lot of pedal circuits and want to extend my skills into preamps and amps.
Therefore, it was a good thing Tragās diagram was for a preamp.
I had one last question, if the preamp has a volume, is there any need for the amp to have a volume?
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Post by frets on Oct 28, 2022 18:36:33 GMT -5
MattBšø
Thank you so much for finding the better circuit. I have the 1875 and think Iāll try that out first.
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Post by thetragichero on Oct 28, 2022 18:43:32 GMT -5
you can get a power amp boards shipped to your door for only a few bucks on eBay. i will search around for what I've had success with next time i open up laptop. these days with power amp chips it's generally cheaper to buy a working board than the chip itself
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Post by sumgai on Oct 28, 2022 19:11:19 GMT -5
these days with power amp chips it's generally cheaper to buy a working board than the chip itself That's true, but as frets herself said, it's all the about the learning experience. I daresay, probably everyone who's ever posted this forum, we all started out the same way - curiosity that just couldn't be satisfied with an open check book and an eBay account. (Or in my day, it was Lafayette or Allied Radio.) A sawbuck says that frets comes through in the clutch. Any takers? sumgai
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Post by thetragichero on Oct 28, 2022 21:30:22 GMT -5
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Post by frets on Oct 29, 2022 15:17:39 GMT -5
Trag,
Thanks for the link. I actually bought two (I always buy a backup with stuff like this) but still plan to build and use the combination of your preamp and the 1875 amp. I almost have it done breadboarding it. If it works well and lasts for a while, I will use the home built one. If not, I will use one of these Chinese ones. Iām sure at 12v that little Chinese amp is not pushing 30 watts of actual sound though. But even if itās a third of that it should be loud enough.
However, I am truly enthusiastic that the one we came up with will work, and function for the purpose I proposed. As you well know, there is an intangible of building something by scratch and having it fill the unique need one desires.
Of course, itās longevity on the battery will be a large determining factor. I donāt need it for that long, on and off, for a few hours before a game. At the most, Iād probably use it 45 minutes. And thatās the high end. Most get tired or complain regarding my Stevie Ray impersonation within about 20 minutes given they are drunk and their attention spans are pressed by all the activity around them.
What is the most fun is to learn the fight song or other song associated with the opposing team and playing a horrific heavy metal version of it with many flashy flourishes. I get to meet a lot of people that way.
Again, thanks for all your help. Thanks to Sumgai and MattB as well.
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Post by newey on Oct 29, 2022 17:06:10 GMT -5
a horrific heavy metal version of it with many flashy flourishes. I'm visualizing Ozzie covering "Mr. Touchdown". This may keep me up late tonight . . .
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Post by ashcatlt on Oct 30, 2022 10:53:14 GMT -5
Any amp a 12V amp if you have an inverter. If the vehicle has an āaux holeā, you could just use an amp sim pedal. I know thatās not what you asked for, but it looks like youāve got that under control.
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Post by newey on Oct 30, 2022 13:12:59 GMT -5
I've played a lot of battery-powered amps, always looking for the portable solution. For the most part, they have such low power and tiny speakers they don't sound like much. But you don't have to have a guitar amp, necessarily, a portable PA will work just fine, put a couple of pedals in front of it
First battery-powered amp I ever played through was an Electro-Harmonix Mike Matthews Freedom Amp, and it sounded great, I thought it one of the best solid-state amps I had used up to that point (the first solid state guitar amps in the late '60s and early '70's were mostly atrociously bad, with some exceptions). But it was "battery-powered" as more of a gimmick than anything else. It took the big "D" cell batteries, as I recall, 40 of the suckers. . . for which one got about an hour of playing time. SO everyone just kept them plugged in.
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