'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 (click on it). The final rendition you'll get will be slightly different, as it is getting a few tweaks.
Now let's talk some features:
"Feedback": It uses 4 transistors to compare, and correct. It actually helps improve phase in higher frequencies. It isn't an act so much of getting an average, as it is an act of fixing - as a crude way to compare it to traditional feedback. 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.
Feedback power: 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.
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.
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.
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 & Copper Pours: Like all other Folsom projects, it has capacitor field cancellation built in, and copper pours for lower inductance.
*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.
Please See here for pricing and joining the GB.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.