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Folsom EC7293: Battery/Solarcell Powered Feedback, 60/120w

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Hello!

I'm happy to say Folsom has a second amp design to get into the world of DIY. Firstly we're talking more power! Nextly is this is an advanced design for people whom are ready to jump into a more complicated project. But there are rewards for your work!

Here is what it looks like. The final rendition you'll get will be slightly different, as it is getting a few tweaks.

EC7293clear.png


Now let's talk some features:


"Feedback": It uses 4 transistors to compare, and correct - EC, error correction. It actually helps improve phase in higher frequencies - a problem for class AB, and anything with feedback. It isn't an act so much of getting an average (feedback you're use to), as it is an act of fixing. Because of how this work it has an extremely pleasant sound that may remind people of tubes, perhaps related to a function of improving linearity. This is something you don't see. I'm unaware of any other DIY PCB that features feedback like this one. So if you're thinking it's just another TDA7293, you'd be very wrong. It's an opportunity to build something never offered on DIYA as far as I know, and get a damn nice amp in return.


Feedback power
: In order to help keep distortion low & phase accurate, it needs an independent source for power. It has provisions for a 9v battery that will last 2 weeks. But it also has provisions for solarcells. If you want to use the solarcells this is unexplored with what light sources specifically to use, and how to attach them to the enclosure etc, but I will help. I myself want to know the exact setup that'll work. The solarcells will work, I just have tried mounting a variety of LED's etc in a dark box. There is a fair chance of another PCB coming out that will work with the PCB, providing a light source (it'll be cheap, not big).

Distortion: I don't have the equipment to check really low distortion, but can tell you it is somewhere 5-100x better than the standard TDA7293. (It does NOT sound like an average chipamp at all)

Dual Chip Power:
These are running in "modular" mode so that they can handle a 4 ohm load with some dips, while providing substantial power. I'm using a 330VA 25VACx2 transformer, available at Parts Express. At 35vDC +/- it can put out up to 60/120w 8/4ohm. That is the max.

Terminals: Happy to say I've found some that are based on a copper metallurgy, that accept decent sized wire, and don't strip too easily (I can torque them pretty good with screwdriver).

Input Capacitor: This one is less sensitive compared to the DIY7297. It has provisions for the same PHE426 and other caps. There is a hole next to it, to zip tie on larger caps and it has extra pads on the bottom to connect external caps.

CFC, PCB layout, & Copper Pours:
Like all other Folsom projects, it has capacitor field cancellation built in, and copper pours for lower inductance. The layouts are always optimized for grounding correctly, using star points when they should be, optimized parallel traces, etc. We work hard to make them as best as we can, and don't just willy-nilly run traces to make something work.

Input impedance & output impedance:
27k in, and out is much lower than stock, maybe even lower than the wires going to binding posts.

Gain: 32db


*There is not a mirrored channel because it would screw up the relationship to feedback.


Recommended PSU: You'll want 18-24kuf per + and - supply. I believe due to size I'll have to come up with a new one that is like the Antipole in that it'll have CMC's, TO-220 diodes, and some big old snap caps.

Heatsink:
You're going to need more heatsink capability than the DIY7297! It dissipates a lot more idle heat. Any amplifier enclosure with finned side walls should work great if you can fit everything in it.

Cost to build: It's about $200-250 worth of Mouser parts (80v and 50v caps are necessary with the transformer voltage for full power). $70 transformer. And this enclosure should be sufficient if the PSU isn't too large. And whatever for binding posts, RCA's, jacks, and such. (mine right now is on my test piece of plywood, which I guess is an option too)

And it will come with BOM's & Build documentation just like the DIY7297



Price & Amount needed to Print:


In order to print these up so I don't run out the day after, I need a commitment of 12x, two EC7293 boards and one PSU board. What I'd like to see is around hopefully 30-50 orders right away, because, well, it's awesome.

EC7293 $40ea (you'll need 2, to make a stereo amp)
DualPole PSU $40ea
****+$60 if I can get commitments from 25 people, for the specific capacitors that are high voltage. See below.
Shipping USA $8
Shipping International $15

*These will not be printed on el-cheapo PCB with dodgy silk screens. They'll be very nice. It is common for people building amps to need to rework stuff. The 7297 was printed on good PCB and I don't think anyone ever needed a replacement PCB due to lifted tracing, vias pulled out, or anything like that. I plan to keep these more elaborate projects at this quality level, so people aren't having to re-buy a bunch of stuff from reworking or swapping caps.


****If I can get 25 orders to start with commitment to buy caps, I can provide the caps you need for $60, price from mouser is $70. The beauty here is I'll have stock for the entire lot of PCB's, where as if I don't get these then you may have to order from different places and pay extra shipping too. I'm getting a quote on the 7293 as well, I may be able to provide it too, a little cheaper.


I think this is going to be a very popular board. The DIY7297 is still really popular, and still a great amp that crushes anything near it's price point up into the thousands of dollars... It's a really great starter project. But the EC7293 is a big upgrade in many ways - one thing I still like about the 7297 is that the texture is perhaps the best available among any amplifier on the planet. I haven't got to compare the new EC7293 head to head with as many high dollar items as I did the 7297, but I can assure you, the value is going to be absurd. Think like you could replace VAC statement amps without batting an eye.

Commitments said:
lucylu 2,1 (1x)
mlundy57 4, 2 (2x)
paul hirst 2,1 (1x)
RJ (gm) 2,0 (0.5x)
pinnocchio 2,0 (1x)
flavo cadillac 2,1 (1x)
soldersmoker 2, 1 (1x)
Luthierguy 2, 1 (1x)
 
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Because the capacitors at 80v and 50v are expensive, I'm looking into sourcing them to sell with the PCB boards. If I can get them for a decent price, I will. Whether or not it'll save a lot of $ is somewhat irrelevant to the fact that you won't be having to order from multiple locations if one distributor runs out.

I'll update the main post when & if this can be possible.
 
I'm surprised there has not been a flood of people interested. This is probably the most interesting amplifier on the DIYaudio forum atm. And not only is it interesting, it sounds damn good. It certainly will spank at least the vast majority of commercial offerings I've heard. (Pass, Para, Spectral, DartZeel, ModWright, VAC, ARC, Bryston, AVA, Jeff Rowland, McIntosh, Crown, NAD, etc etc)
 
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Feedback power[/U]: In order to help keep distortion low, it needs an independent source for power. It has provisions for a 9v battery that will last a long time (months). But it also has provisions for solarcells. If you want to use the solarcells it will be up to you to figure out how to power them, and get enough juice into them. I will help some, but the default supported feature is a 9v battery.

For feedback circuit power, how independent is "independent enough"?

Is it not enough to have a second power supply (transformer + regulator), but powered from the same mains (as the power amp circuit)? Or some other ground isolation circuit or similar scheme? Or maybe a rechargeable battery with a hard-switched charging circuit on-board (i.e. open the charger circuit during playblack, close it to charge when not playing)?
 
I'm surprised there has not been a flood of people interested. This is probably the most interesting amplifier on the DIYaudio forum atm. And not only is it interesting, it sounds damn good. It certainly will spank at least the vast majority of commercial offerings I've heard. (Pass, Para, Spectral, DartZeel, ModWright, VAC, ARC, Bryston, AVA, Jeff Rowland, McIntosh, Crown, NAD, etc etc)

It sounds that good ? :lickface: well I am in no rush as moving house save it for later in year
Perhaps a quite time of year am sure it will take off
 
Oh yes! It's a silly a good amplifier.

I was irritated when I hit probably the extreme of how good the 7297 just happens to be (I know, that's funny, it's just a little chimpamp that doesn't allow any feedback changes etc, but it's a magical little chipamp). I view all amplifiers as competition. There is no reason to be making stuff unless I can try and offer new/better/super-value things, especially innovative ones.

When it comes to DIY, I want people to really feel the value of their labor. If the project doesn't at least pronounce to be easily as good as a commercial one that cost 5x what their build cost + labor, then I think it isn't doing that well. So far that is a non-issue.
 
Can these be made into multi channel amp powered by smps? Like 4 channel in one box?

Yes.

Yes you can put all of them you want in a box. They would pretty easily fit in a HT style setup where you have multiple heatsinks in a row, with multiple amp boards. They would need some airflow top to bottom or active.

For an SMPS, one of these could power 4x boards at +-30v.
 
EC7293 $40ea (you'll need 2, to make a stereo amp)
DualPole PSU $40ea
****+$60 if I can get commitments from 25 people, for the specific capacitors that are high voltage. See below.
Shipping USA $8
Shipping International $15



^^What is the ****+ for $60?

Roughly how much internal space (inside the amp case) will be needed to make this amp?
Would it be possible to put the heat sink inside and just have the sides of the amp with slots for breathability?
If I understand correctly, this will either be powered by a 9v battery or a solar cell? Just a standard $5 battery? And the PS in reference will be in a different case?
And all in, the build will cost in the neighborhood of $600 and up depending on case, connectors and so forth?
Either way, I'm in for one. I think that's 3 boards in total?
 
The $60 is for the specific capacitors that go on the board. If I get 25 commitments I can buy them in bulk, and sell them cheaper than you can buy them from Mouser.

If you don't want to use them, you would have to go with significantly lower voltage. 4 of the caps per board need to be more than double the voltage of the V+ rail. I believe I've chosen wisely for caps that are common enough, high performance, and not so tall it requires a different type of enclosure (or too fat for that matter).

I believe you might have thermal problems if you don't use heatsinks externally. My thick aluminum blocks are insufficient to maintain output power at louder volumes. When I play Dire Straits and get those massive drums and guitar, it heats up. My heatsink needs fins, and convection would help with any fins (air flow above and below fins). I would highly advise against internal heatsinks without an active system (fan). If you had a fan that blew through a tunnel of fins, it would work. (an old design you see sometimes)

The feedback only is powered by the 9v or solarcell. The rest of the amplifier needs a regular V+/- & PG PSU. I'm not done with the PSU PCB board to show pics, but will be before ordering. It'll be like the Antipole, in that it'll have CMC's, TO-220 diodes, and snap caps. You could also use an SMPS like I linked to.

The powersupply can be in a separate enclosure if you wish. That would be one way to use two smaller enclosures, instead of a larger one. The EC7293 amp PCB is only 2x6.5 inches. You'd need two. SO it it is possible to fit them into an enclosure that is only a little over 4 inches width, and 6.5 depth internally.

I'm very realistic about costs, and don't claim you can make anything cheaper due to possibly unavailable/non-existent parts. If you find a way to make it cost less, great, please share. But be advised about things like buying 7293 chips off eBay or such, they are almost always relabeled 7294s. I think $600-800 is a good approximate largely dependent on connectors and enclosure costs. The good thing is you can buy as you go/have cash, which keeps it very accessible. But compared to commercial offerings you'll be saving the cost of a nice used car, so I certainly don't get too wrapped up in looking at it as expensive. After all I do still sell 7297 boards and that project can come in hundreds cheaper. And if you are comfortable with a scrap piece of wood you can always shave up to $200 on price :)

The new PSU should be close to size of the transformer, maybe a little bit bigger. About 6 inches wide, and less deep, maybe 4.5 inches.
 
I'm surprised there has not been a flood of people interested. This is probably the most interesting amplifier on the DIYaudio forum atm. And not only is it interesting, it sounds damn good. It certainly will spank at least the vast majority of commercial offerings I've heard. (Pass, Para, Spectral, DartZeel, ModWright, VAC, ARC, Bryston, AVA, Jeff Rowland, McIntosh, Crown, NAD, etc etc)

I could give you a few hints as to why:

- You are claiming that this amp "will spank at least the vats majority of commercial offerings", yet we only have your word to take for it; no measurements, no pictures of populated board, no link to another thread showing the amp. I am not doubting your capabilities as an amp designer nor your trustworthiness, I am just giving my outlook as someone who is looking for his next amp build and happened to check out this thread.

- Given all of the above the price seems a bit steep when compared to other offerings e.g. I have just bought a class AB board that has been proven to measure down to great distortion levels at full power, and not require any fancy parts or complex setup. It might not be as good as your amp, but I had access to charts, data and builder reviews to make an educated decision before buying.

In any case, I am interested in this amp, but will remain on the fence until I have enough information to decide whether to pull the trigger or not.

Best of luck on your GB!
 
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