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Beefcake: a beefed-up BA-2
Beefcake: a beefed-up BA-2
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Old 31st January 2019, 08:29 PM   #1
JeffYoung is offline JeffYoung  Ireland
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Beefcake: a beefed-up BA-2
Default Beefcake: a beefed-up BA-2

I've been working on something to drive my Maggies. It's essentially a BA-2 beefed up to dump 60 clean watts (and a couple hundred dirty ones) into 4 ohms.

The LTP's CCS uses BJTs to handle the higher rail voltage. They're a bit noisier than a JFET CCS, so the LTP is paralleled a la the J2 in an attempt to claw some of that back. The LTP is also cascoded for the higher rail voltage.

The VAS bootstrap CCS is also replaced with a BJT version. No particular reason, it just looks more symmetrical that way.

The power supply is split with a 49V shunt reg for the front-end and a 46V CRC for the output stage.

Schematics in the PDFs; a somewhat simplified LTSpice one is also attached.
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File Type: jpeg beefcake.jpeg (544.8 KB, 567 views)
Attached Files
File Type: pdf beefcake frontend.pdf (114.0 KB, 60 views)
File Type: pdf beefcake output.pdf (41.4 KB, 45 views)
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Old 31st January 2019, 08:46 PM   #2
JeffYoung is offline JeffYoung  Ireland
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Beefcake: a beefed-up BA-2
Draft of PCBs. Dissipation is on the order 350W/channel, so a monoblock design is used.

The first board contains a front end with + and - shunt regs; the second is one-half of an output stage. The OS board has output connections at each end so a single design can be used on both sides of the case.
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File Type: jpg fe_front.jpg (187.9 KB, 595 views)
File Type: jpg os_front.jpg (77.7 KB, 556 views)
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Old 31st January 2019, 10:45 PM   #3
Itsmee is offline Itsmee  England
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Beefcake: a beefed-up BA-2
I'm reading the F4 Beast thread again, I'm thinking of swaping my BA2 O/P for pucks - my Apogee Stage are 3 ohm
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Old 31st January 2019, 11:05 PM   #4
Itsmee is offline Itsmee  England
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Beefcake: a beefed-up BA-2
I prefer this arrangement.
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Old 31st January 2019, 11:11 PM   #5
Itsmee is offline Itsmee  England
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Beefcake: a beefed-up BA-2
I prefer this arrangement.
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Old 31st January 2019, 11:15 PM   #6
JeffYoung is offline JeffYoung  Ireland
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Beefcake: a beefed-up BA-2
At 3 ohms you've got a lot more options as you probably don't need more voltage than a stock F4/BA1/2/3. I like the idea of a puck-ed BA2.

That CCS has too many parts.
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Old 4th February 2019, 01:48 AM   #7
JeffYoung is offline JeffYoung  Ireland
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Beefcake: a beefed-up BA-2
I found a more suitable opamp for the FE shunt regulator (LTC6090). It does require soldering a thermal pad on the bottom to the board.

I put a pair of large vias in the pad to flow some solder through. The datasheet recommends 7 smaller vias, but I think the larger ones will allow me to use the solder as a heat-wick and therefore (hopefully) avoid the whole toaster-oven-reflow thing.

In service the solder filling should more than compensate for the reduce via wall surface.
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File Type: jpeg opamp_front.jpeg (50.9 KB, 417 views)
File Type: jpeg opamp_back.jpeg (22.6 KB, 50 views)
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Old 4th February 2019, 01:57 AM   #8
JeffYoung is offline JeffYoung  Ireland
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Beefcake: a beefed-up BA-2
Oh, and I also dropped to a lower voltage Zener for less noise. There's no bypass cap in the Spice sim (because Spice doesn't appear to model Zener noise anyway), but there is in the Kicad schematic and board file.

I've attached the Spice sim of the shunt reg. If anyone wants the Spice sims of the rest just holler.
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File Type: asc beefcake_fe_opamp.asc (7.4 KB, 12 views)
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Old 4th February 2019, 02:58 AM   #9
metalman is offline metalman  Canada
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Watching this thread intently. I’ve been planning a BA-2 Turbo for several years and have most of what I need gathered. This is inspiring me to get back on this project.

Cheers,
Terry
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Old 4th February 2019, 06:39 PM   #10
Itsmee is offline Itsmee  England
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Beefcake: a beefed-up BA-2
Swap the current limmiting resistors for a cc, it will probably sim better, I know it will perform better

These arrived today, I hope the 40N60C is a good match to the 40P50P
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