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50w Single-Ended BAF2015 Schade Enabled
50w Single-Ended BAF2015 Schade Enabled
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Old 4th May 2016, 01:31 PM   #1
vdi_nenna is offline vdi_nenna  United States
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Default 50w Single-Ended BAF2015 Schade Enabled

Hi Everyone,

I've been interested in how a high powered, single-ended amp might sound for some time. I suppose a large Aleph could solve that mystery. The BAF2015 SE 50w has a couple of nice twists, one being it uses Schade feedback to give the MOSFET triode like curves. It's also a really simple circuit.

I suppose it's worth while thread to start, unless one was started already.
I searched and went back a few pages, but didn't see anything, so here it is.

Attached is a screenshot of the schematic with its creator. In the shadows...

I'll crate a wiki once things get rolling so that FAQ can be answered.

Hope to hear from interested people.

Vince

Notes:

Dave Hill at Jensen, the JT-112-L (what's on the schematic in the video) is an obsolete part number, the part still exists as the JT-123-FL, and the various mounting permutations of that transformer.

Power transformer: 500va minimum, 600 to 800va recommended.

10k resistor adjustment. See post #49.

To adjust CCS, change .2 Ohm resistors. For example, to lower current by half, increase resistors to .4 Ohm.

NP: "If your source is cap coupled, then you will need some resistance to ground.
Try a value like 10K and watch for motorboat (with load). Decrease the
resistance until the motor stops."
Example preamps: BA3- Pre and B1 are cap coupled.
Set input to ground on SE amp input before Jensen input transformer.

NP:
1) The amplifier must be driven by something with a resistive component
to its output impedance. That means that the source cannot be capacitively
coupled, or if it is, there is a resistor to ground after it. Otherwise the
amplifier will motor-boat.

2) The DC Drain voltage of the circuit's gain transistor is temperature
dependent, but it generally should be fairly stable if the heat sinking is
adequate - If it's not stable enough you can put a 5 or 10 watt 220 ohm
resistor from Drain to Source to stabilize it better. I don't think you need
the complexity of a servo.

For more on stabilizing see page 40 of this thread.
Attached Images
File Type: png Screenshot_2016-05-02-22-24-33[1].png (438.9 KB, 3227 views)
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Last edited by vdi_nenna; 15th August 2017 at 06:06 PM. Reason: Add note
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Old 4th May 2016, 01:34 PM   #2
MASantos is offline MASantos  Portugal
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There were some discussions regarding heatsink size and dissipation values.
I remember this would need quite a large heatsink for each device, making it a no o fo many around here.
Will you be producing boards or making a prototipe of it?
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Old 4th May 2016, 01:37 PM   #3
vdi_nenna is offline vdi_nenna  United States
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First big question is heat sink size. Doesn't look like a 5U case will handle 300w.

What are the options? Lower power? Takes the fun out of it.
Huge heat sinks? A combination of large heat sinks and fans?
Mono blocks?

3.2A x 60v = 192W Does this tell the whole story?
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Old 4th May 2016, 01:59 PM   #4
2 picoDumbs is offline 2 picoDumbs  Australia
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You will need 2 x 4U cases

Or build your own chassis using 4 x Conrad MF35-151.5 heatsinks.
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Old 4th May 2016, 02:02 PM   #5
vdi_nenna is offline vdi_nenna  United States
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Quote:
Will you be producing boards or making a prototipe of it?
I can easily see a point-to-point board with this one.

What's the efficiency on this circuit? 20% at best?

If the voltage is dropped to 50v, that's about 30w, correct?
For me 25w to 30w SE with triode curves is still intriguing to me.

Can the circuit scale that way without change any values?
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Old 4th May 2016, 02:03 PM   #6
2 picoDumbs is offline 2 picoDumbs  Australia
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My Jensen transformers arrived. Still need to order a few other things.

You will need 2 x 400VA transformers putting out about 8V to 10V higher unregulated dc, cause it's adviseable to use a regulated supply.
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Old 4th May 2016, 02:06 PM   #7
vdi_nenna is offline vdi_nenna  United States
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Thanks pico.
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File Type: jpg ConradHeatsink.JPG (40.8 KB, 3007 views)
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Old 4th May 2016, 02:15 PM   #8
2 picoDumbs is offline 2 picoDumbs  Australia
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I'm tossing up between mono blocks or a super long case (700mm) with 2 of those heatsinks on each side.
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Old 4th May 2016, 02:25 PM   #9
vdi_nenna is offline vdi_nenna  United States
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I was thinking of lining up a pair of these HS for one channel.

SIT Amp - Empty hassis - My Photo Gallery
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Old 4th May 2016, 02:30 PM   #10
2 picoDumbs is offline 2 picoDumbs  Australia
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They are certainly capable for one channel
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