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Folsom EC7293: PVI Powered Frontend, 60/120w 8/4ohm
Folsom EC7293: PVI Powered Frontend, 60/120w 8/4ohm
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Old 23rd May 2019, 06:17 PM   #1
Destroyer OS is offline Destroyer OS  United States
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Location: PNW
Folsom EC7293: PVI Powered Frontend, 60/120w 8/4ohm
Default Folsom EC7293: PVI Powered Frontend Amplifier, 60/120w 8/4ohm, 0.0005% THD

**Updated: Lower distortion with a slightly different board.

Alright everyone! We’ve got the redesign done.

Click the image to open in full size.
(Image of prototype)

The EC7293 uses 2 chip amps in parallel for high power with a discrete error correction frontend which reduces distortion; and has very low memory distortion. High sensitivity makes it perfect for a variety of sources with 8ohm and 4ohm speakers.

Input impedance: 27k
Gain: 32db
Distortion 1K; 8ohm; full power w/Antek AS-3225: <0.0005%

At 8ohms:
Click the image to open in full size.

At 4ohms:
Click the image to open in full size.

Click the image to open in full size.

Board size: 6.25x2.25"

*****There is not a mirrored left/right set because it would screw up the feedback layout*****

Discrete front end: 4 transistors

PVI: The frontend uses a photovoltaic power supply for galvanic isolation of the signal path. It uses a G4 LED bulb with a current source to disable the onboard driver of the G4.

Distortion: <0.0005%

High power: These are running in "modular" mode so that they can handle a 4 ohm load with some dips, while providing substantial power with a max output current of 20A. The Antek AS-3225 is a great fit for 60/120w. More power may be possible if you follow the guidelines of the TDA7293 datasheet and make provisions with higher voltage capacitors, and larger heatsinks.

Terminals: Happy to say we'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) that the boards are made to fit, and I recommend in the BOM.

Input Capacitor
: This one is less sensitive to capacitors compared to the DIY7297. It has provisions for the same PHE426 and other caps. There is a slot-hole next to the pads so you can zip tie on larger caps and it has extra pads on the bottom to connect off board/long input capacitors.

CFC, smart PCB layout, & Copper Pours: Trace routing is optimized to improve performance and the power capacitors are placed for field cancellation (CFC); and copper pours are used for lower inductance.


Click the image to open in full size.

Dualpole PSU PCB

Board Size: 4.25x3"

TO220 Diodes

CFC, smart PCB layout, & Copper Pours

Via holes for snap caps

RC and bypass: dampen the transformer & reduce noise


Suggested implementation with EC7293:
  • 18000uF to 24000uF per rail
  • Antek AS-3225 transformer
  • Keratherm insulators from DIYAudio store. (Chip tabs are 1.1” apart).
  • Heatsinks need to be larger than used on the 7297, nearly any enclosure with heatsinks for sides should work
  • 3U enclosure from DIYAudio store is a good fit. **
  • 2x Duapole's for dual mono with 2x transformers (Antek AS-2225)

**2U may work in dual mono with two smaller (shorter) transformers

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. I'm hoping to see a lot more than 12x. To anyone that liked the DIY7297, this one is better, simply better.

EC7293+G4LEDR PCB $45ea (you'll need 2, to make a stereo amp)
DualPole PSU PCB $40ea

Shipping USA $8
Shipping International $16

And it will come with a BOM and some build details.

Quote:
Paul Hirst 2,1 (1x)
s610adam 2,2 (1x)
Pi DE 2,1 (1x)
Roundtoit 2,1 (1x)
pistollero 2,2 (1x)
jmc207 2,1 (1x)
Danny23 2,2 (1x)
Domino99 2,1 (1x)
annamarykahn 2,1 (1x)

Last edited by Destroyer OS; 11th June 2019 at 02:34 AM.
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Old 23rd May 2019, 06:35 PM   #2
Paul Hirst is offline Paul Hirst  Canada
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Put me down for one please and thank you!

Paul
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Old 23rd May 2019, 06:46 PM   #3
s610adam is offline s610adam  United States
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Join Date: May 2013
Hey I'm interested in a dual mono setup to try
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Old 23rd May 2019, 09:45 PM   #4
flavo cadillac is offline flavo cadillac  United States
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What's the time frame for the boards to be ready?
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Old 23rd May 2019, 10:06 PM   #5
Destroyer OS is offline Destroyer OS  United States
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Join Date: Nov 2005
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Folsom EC7293: PVI Powered Frontend, 60/120w 8/4ohm
Once the GB goes through 2-3 weeks is normal for printing.
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Old 24th May 2019, 05:42 PM   #6
danielwritesbac is offline danielwritesbac  United States
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Oh my gosh! The documentation quality is so much better.
But, you really could have bragged up the output linearity instead of understating it.
Per each channel, four made-for-audio output fets in addition to an EC circuit!
Sure has clear and evident means-to-work.

Also, it is at fairly big scale, but if you wanted to know when you have enough, this will do it.
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Old 24th May 2019, 05:50 PM   #7
Roundtoit is offline Roundtoit  United States
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Join Date: Feb 2016
Location: By a creek in Missouri
Paul Hirst 2,1 (1x)
s610adam 2,2 (1x)
Pi DE 4,2 (2x)
Roundtoit 2,1 (1x)
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Old 24th May 2019, 05:58 PM   #8
Destroyer OS is offline Destroyer OS  United States
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Folsom EC7293: PVI Powered Frontend, 60/120w 8/4ohm
Quote:
Originally Posted by danielwritesbac View Post
Oh my gosh! The documentation quality is so much better.
But, you really could have bragged up the output linearity instead of understating it.
Per each channel, four made-for-audio output fets in addition to an EC circuit!
Sure has clear and evident means-to-work.

Also, it is at fairly big scale, but if you wanted to know when you have enough, this will do it.
Well, I was trying not to use so much hyperbole this time... But it's true, it's a very good amplifier. I think people under estimate the value of memory distortion as well. The transistors are BC550's. I consider them to be extra special and near magical compared to other transistors I've used for things like phono.

I updated the graph to the 8ohm, I accidentally put up 4ohm. This one isn't as hard to read, either.
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Old 25th May 2019, 06:55 AM   #9
pistollero is offline pistollero  Portugal
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Join Date: Apr 2016
Location: portugal
Paul Hirst 2,1 (1x)

s610adam 2,2 (1x)

Pi DE 4,2 (2x)

Roundtoit 2,1 (1x)

Pistollero 2,2 (1x)
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Old 26th May 2019, 04:59 AM   #10
jmc207 is offline jmc207  United States
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Join Date: Feb 2008
Paul Hirst 2,1 (1x)

s610adam 2,2 (1x)

Pi DE 4,2 (2x)

Roundtoit 2,1 (1x)

Pistollero 2,2 (1x)

jmc207 2,1 (1x)
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