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Folsom EC7293: Battery/Solarcell Powered Feedback, 60/120w
Folsom EC7293: Battery/Solarcell Powered Feedback, 60/120w
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Old 26th February 2018, 09:22 AM   #1
Destroyer OS is offline Destroyer OS  United States
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Folsom EC7293: Battery/Solarcell Powered Feedback, 60/120w
Default Folsom EC7293: Battery/Solarcell Powered Feedback, 60/120w

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.

Click the image to open in full size.

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.

Quote:
Originally Posted by Commitments
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)

Last edited by Destroyer OS; 21st March 2018 at 06:27 AM.
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Old 26th February 2018, 09:28 AM   #2
Destroyer OS is offline Destroyer OS  United States
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Folsom EC7293: Battery/Solarcell Powered Feedback, 60/120w
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.
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Old 26th February 2018, 12:33 PM   #3
lucylu is offline lucylu  England
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Can I put my name down for a stereo set plus whatever parts ,cheers jon
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Old 26th February 2018, 06:00 PM   #4
mlundy57 is offline mlundy57  United States
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Just to clarify, the two boards will make a monoblock, correct?
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Old 26th February 2018, 06:10 PM   #5
Destroyer OS is offline Destroyer OS  United States
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Folsom EC7293: Battery/Solarcell Powered Feedback, 60/120w
Quote:
Originally Posted by mlundy57 View Post
Just to clarify, the two boards will make a monoblock, correct?
Each board is a channel. Two boards and 1 PSU = Stereo amplifier.

It's possible to make monoblocks is you want. Just get two of each, and use two transformers that can be somewhere around half the size of a 330-400va.
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Old 26th February 2018, 06:30 PM   #6
mlundy57 is offline mlundy57  United States
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You can put me down for enough to make two stereo amps. That would be 4 boards and 2 PSUs.

Mike
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Old 27th February 2018, 07:37 PM   #7
Destroyer OS is offline Destroyer OS  United States
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Folsom EC7293: Battery/Solarcell Powered Feedback, 60/120w
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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Old 27th February 2018, 08:23 PM   #8
matt_garman is offline matt_garman  United States
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Folsom EC7293: Battery/Solarcell Powered Feedback, 60/120w
Quote:
Originally Posted by Destroyer OS View Post
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)?
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Old 27th February 2018, 09:11 PM   #9
Destroyer OS is offline Destroyer OS  United States
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Folsom EC7293: Battery/Solarcell Powered Feedback, 60/120w
A separate PSU with a different transformer can work.

But why not use a more simply LED array?
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Old 28th February 2018, 08:39 AM   #10
lucylu is offline lucylu  England
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Quote:
Originally Posted by Destroyer OS View Post
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 ? 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
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