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Old 21st March 2014, 08:14 AM   #11
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Andrew, I've made all the changes you suggested. Can you suggest any further improvements? What about diode strings in the power rails?

I've left all the small signal transistors as 2n5xxx for the time being because that's what I have available.
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Old 21st March 2014, 08:32 AM   #12
AndrewT is offline AndrewT  Scotland
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VR in the multiplier is on the wrong leg.

These next three are my preferences.
I would allow for a link between Signal Ground and Power Ground.
Locate in the ground trace between the tappings for C6 & R10.
This link may have to pass some Fault Current from a faulty Source. So allow for Power Diodes in inverse parallel as well as the low value resistor.

I would also add more on board Decoupling.

The input transistors are 2n type.
The lead outs of BCxxx and 2sc/axxxx are different. What about a 4th pad to allow other transistors to be fitted?
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Old 21st March 2014, 08:36 AM   #13
mcd99uk is offline mcd99uk  United Kingdom
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Maybe add some RC filtering on the power rails between the output transistors and the rest of the circuit? And then a second RC filter between the VAS and the input LTP?

I'm a bit of a power rail freak. Whenever I have films and electrolytics paralleled I add a snubber across them. (1R + 1u). Some may disagree with this approach...

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Old 21st March 2014, 10:55 AM   #14
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Quote:
Originally Posted by AndrewT View Post
VR in the multiplier is on the wrong leg.

These next three are my preferences.
I would allow for a link between Signal Ground and Power Ground.
Locate in the ground trace between the tappings for C6 & R10.
This link may have to pass some Fault Current from a faulty Source. So allow for Power Diodes in inverse parallel as well as the low value resistor.

I would also add more on board Decoupling.

The input transistors are 2n type.
The lead outs of BCxxx and 2sc/axxxx are different. What about a 4th pad to allow other transistors to be fitted?
Is this what you had in mind? I can't fit extra (4th) pads because I'm working within the limitations of an existing PCB (DX Blame MkIII)
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Old 21st March 2014, 10:59 AM   #15
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Originally Posted by mcd99uk View Post
Maybe add some RC filtering on the power rails between the output transistors and the rest of the circuit? And then a second RC filter between the VAS and the input LTP?

I'm a bit of a power rail freak. Whenever I have films and electrolytics paralleled I add a snubber across them. (1R + 1u). Some may disagree with this approach...
I could add an RC filter on the rails where the 220u caps are located, between the drivers and the VAS. What corner frequency do you suggest?
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Old 21st March 2014, 11:48 AM   #16
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mcd, is this what you had in mind? Fc = 15hz
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Old 21st March 2014, 12:08 PM   #17
mcd99uk is offline mcd99uk  United Kingdom
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Yes, but maybe move C15 and C16 to the other side of the resistors R38 and R39 unless C15 and C16 are for the driver decoupling.

Corner frequency looks fine to me.

Can you add decoupling for each of the output transistors? So it can connect as close as possible to the output transistor collectors.
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Old 21st March 2014, 01:19 PM   #18
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R10 and R17 should connect to signal GND.

R17, R18 are on the large side. R17 is usually 100R-220R, R18 usually 470R.
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Old 21st March 2014, 05:10 PM   #19
AndrewT is offline AndrewT  Scotland
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That looks to me to be a workable schematic.

You could play around with component values in LTspice.
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Old 25th March 2014, 12:22 AM   #20
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Originally Posted by Stormrider View Post
R10 and R17 should connect to signal GND.

R17, R18 are on the large side. R17 is usually 100R-220R, R18 usually 470R.
Thanks Stormrider.

Is someone able to explain how to determine the proper values for R7, R8, R17 and R18?
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