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Chip Amps Amplifiers based on integrated circuits

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Old 6th June 2014, 05:10 PM   #11
JMFahey is offline JMFahey  Argentina
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Quote:
I wanted something a little stronger since I have higher voltage already available in the circuit (about +40V and -40V off the supply circuit) and didn't want to add another transformer.
And how will you power the tube preamp ? <scratching head smiley>
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Old 6th June 2014, 05:32 PM   #12
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Originally Posted by JMFahey View Post
And how will you power the tube preamp ? <scratching head smiley>
Another transformer. This is where scrounging can come in real handy.

You could also build a messy voltage doubler/tripler too. Don's scrimp on the capacitors either because they'll blow up if you skimp here. Nakamichi employed a voltage doubler in their TA series recievers, and every one I've opened up has the 470 uF, 50 volt capacitor on the power supply board bulging and leaking. There are some high ripple current capacitors offered today that excel for this application, but they cost twice as much as a general purpose capacitor. Nichicon makes some super beefy power supply capacitors.

Another possibility is to use a lower voltage tube. I don't think this will work as well. All the good guitar amps and hi-fi amps of yesteryear use the 12AX7.

Another consideration is protecting the input of the chip amp from overvoltage. A tube amp can swing some large voltages. You can put a zener array clamp on the input to protect it.
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Old 8th June 2014, 09:11 PM   #13
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Eddie,
Thanks for the insight. I'm still new to all this so some of your audio-speak is going over my head but I get most of it. I understand the chipamp isn't the best solution but this is more of a practice amp and not one I'd use for gigging with. I have plans to build a larger amp to drive a 4x12 cab I have but for now this little one is my main focus as I can't practice right now without it. Also the 12AX7 kits I've seen need more voltage than I've got in the case right now. Like I said, I'd love to use the power supply I've got in there with 80VDC (40-0-40). A smaller tube would probably work fine.

Thanks again for all of the info. I've been scrolling craigslist for old consoles too :-)
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Old 8th June 2014, 09:12 PM   #14
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Also, I view power circuits like I view money, best not to spend it if you don't have it... So I'm not looking to use voltage doubler/triplers. :-p
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Old 8th June 2014, 10:51 PM   #15
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Estate sales turn up consoles too. I got a couple of consoles out of the alley and boxed up the electronics for a project some day. I have four projects right now, so it's not on my short list.

Look for old integrated amps too. They used to be easy to find but not so much any more. Brands to look out for are Knight, Marantz, and Sansui. You probably won't find anybody giving away Crown or McIntosh amplifiers. Even some cheaper brands can supply components for a great tube amp.

Plus you can find any tube amp transformer your heart desires right here.
https://www.edcorusa.com/class-x I know there are vendors for some of these, including Mouser and/or Digikey. If Edcor doesn't stock it, they'll make it. If no local vendor offers one of their products, they'll ship it to you.

As far as tubes, there are lower voltage tubes available today. Car radios used tubes until Motorola produced "modern" germanium transistors and now there are compact, low voltage tubes that solder directly to a circuit board. I have seen DIY circuits employing these devices running off as little as 12 volts. I doubt they're anywhere near as linear as a 12AX7. I have no experience with low voltage tube circuits, but I'm sure there are people here that do. You might try the instrument amp section, or the tubes section, of this forum.
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Old 9th June 2014, 07:36 PM   #16
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You could clip the LM3886's input pair with some rather quiet tube-like fuzz, just prior to the spike system's threshold, thus avoiding a nasty screech.

The purple color is for the LTP soft clipper components (ignore R26, which is not part of the soft clip circuit).
You don't need to add any transistors because they're already inside your chip (so, ignore Q4, Q3).
Q4 is +in (LM3886 datasheet, Pin 10)
Q3 is -in (LM3886 datasheet, Pin 9)
C5 is +in coupling cap (LM3886 datasheet, part "C").
C3 is -in coupling cap (LM3886 datasheet, part "Ci").
R16a+R16b use a 500R trimmer for convenience (this replaces LM3886 datasheet's part "Ri"), or different resistor values can be used as needed.
Click the image to open in full size.
In this photo, it is applied to a discrete parts solid state amplifier, but it can be applied to a chip amp easily.
The 470R||1n5819\\1n5819 section is tone management that is not required for basic function.
An alternative use is to dial it in to prevent X-max bangs from the speaker.


P.S.
If I was building a chip amplifier for bass amp, I'd try TWO of ebay item #261061267950 to make One bridge amp with a considerable kick, probably modded a lot like my TDA7293 parallel thread and with a small signal op-amp serving as bridge adapter (demonstrated with TL072 on Rod Elliot's site).
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Last edited by danielwritesbac; 9th June 2014 at 07:39 PM.
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Old 10th June 2014, 05:33 PM   #17
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Thanks for the info guys. This is a lot of information so I'm trying to digest it. I also in my researching found this link for a 60W transistor based amp. Do you think the preamp stage of that would be useful going to a chipamp? The reason I ask is because it looks like the design also has tone control, which would be nice.
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Old 10th June 2014, 11:18 PM   #18
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Here are some projects that you might find interesting.

ESP Projects Pages - DIY Audio and Electronics
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Old 13th June 2014, 01:06 AM   #19
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Very nice collection of projects! thanks for the link!!! So, from more reading it seems that most chip amps are best suited for input from cd/mp3/"program" signals and not so much analog instruments. Unless the instrument is going through some pedals... such as an electric guitar. The box of components I got with all these chipamps came from a guy building guitar amps, that sound flipping amazing. I've only seen some "headphone" amps for raw guitar input for practice amps such as the Altoids tin headphone amp (which I built and just have to debug... love the idea though). I think I may have temporarily solved my immediate need as I found a fellow selling a 350W tube/solidstate hybrid amp for $150, which is about what I'd spend building a 40-60W tube amp... so... I'll keep reading and would love more suggestions. Thanks again Fast Eddie for all your input.
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Old 13th June 2014, 05:09 AM   #20
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Sounds like you scored. You have something more versatile than you bargained for, at a bargain. I suspect that with "350W" it has a solid state output.

You might still consider some of the circuits presented. There is some kind of compressor circuit tweaked for bass, and a couple of sustain circuits, as well as an explanation of how to build a custom equalizer. You could design a custom effects box that runs off a 20 volt wall wart or a couple of 9 volt batteries.

And don't give up on looking for a way to cobble together an all tube practice amp. Nothing sounds like a well sorted ultralinear pentode amp. I'm going to build another one some day myself.
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