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SymAsym - The Sequel, AAK's PCB GB

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A

AAK

Member
Joined 2004
Order Update.

Hi All,

I've sent boards only (option 1) already, but I'm still working on orders that include matched parts and components. Without any major distractions popping in, Option 2,3 orders should go out by the end of the week, Option 5 orders the following week.

I still have boards available for those interested.

Best regards,

Al
 
A

AAK

Member
Joined 2004
Order update.

Hi All,

lpm76, your order shipped on Saturday along with all Option 3 and a few Option 5 orders. According to USPS international orders should take 6 to 10 days to arrive.

I'm still working on packaging orders for CeeVee, Johngalt42, ncc, JohnN, and psymo. Your orders should ship this week.

psymo your order is ready to ship but I need you to email me your shipping address.

I'll start a new builders thread tomorrow that will include all the latest information for building and testing the boards.

BTW, for those interested in this GB I still have some boards available.

Best regards,

Al
 
A

AAK

Member
Joined 2004
Hi All,

I just realized while cleaning up the mess I created to get all the orders completed that I didn't include the BD139 (Mouser part # 512-BD13916S) in any of the Option 3, and Option 5 orders that shipped on Saturday. I'll make sure to include them in the orders that have not yet shipped.

My apologies for the inconvenience. Hopefully I've made it a little easier for everybody to build their amps and ultimately enjoy them as much as I have.

Attached are the latest BOM, and schematics. Those that ordered Option 3 and have not yet placed orders for the remaining components make sure to include the BD139, you'll need one per board.

Best regards,

Al
 

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A

AAK

Member
Joined 2004
A

AndrewT

R.I.P.
Joined 2004
Hi,
is bd139 important to the performance of the amplifier?
I would use any low current, medium gain, medium fT, To126 NPN for the Vbe multiplier.
I would even consider and have used a To92 glued to the output transistor or the heatsink.

R34=499r may be a bit high. You might have to reduce slightly to 390r, or 430r to allow output bias to be set.

I think the 35mV bias voltage is the sum across both emitter resistors, i.e. 17.5mVre.
 
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A

AAK

Member
Joined 2004
Andrew, I see your point on R34. Since R28 is also 499 I decided to make R34 the same value so that I would have one less part to keep track of. It also provides a small margin of safety incase bias pot R36 is not turned to it's lowest setting when initially powering up the board.
 
A

AndrewT

R.I.P.
Joined 2004
AAK said:
Andrew, I see your point on R34. Since R28 is also 499 I decided to make R34 the same value so that I would have one less part to keep track of. It also provides a small margin of safety incase bias pot R36 is not turned to it's lowest setting when initially powering up the board.
Click to expand...
R36 to it's maximum resistance for initial setting up.
This ensures least or nil output bias current.

The ratio of R35:R34 is ~4:1. I tend to use from 5:1 to 6:1 to ensure sufficient range of adjustability to suit a wide range of different transistor Vbe.
eg if Q17 has Vbe ~0.55V then the maximum bias voltage is ~2.75V
If the output transistors have Vbe ~0.65V then one needs ~2.65V to get a Vre=25mV. That leaves only 100mV spare for tolerances. But this is worst case design, not for a fully specified design. 499r should work, but will nearest E24 value of 510r work?
 
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