FS: Mini2496 Volume Controlled, Super-balanced Output PCB

[Tenson]

Hi Guys,

I've got some PCBs that may be of interest to you.


(Featured without volume pot and output buffer.)

A lot of pages back, I posted my results from replacing the standard op-amp output of the Mini2496 with a super-balanced output stage, as originally published by Dave Brit of the BBC. There is a clear reduction in distortion and common-mode noise from the Mini2496.

For those that don't know, the super-balanced stage provides exactly the same impedances to each phase of the differential signal, allowing the DAC to operate ideally and providing far superior cancellation of any common-mode (same on both signal phases) noise and distortion than any design that uses a single op-amp to load the DAC.

The PCB features a super-balanced input stage to load the DAC, followed by a volume pot and single op-amp output buffer. The volume pot and output buffer are optional, you can just take the signal from the output of the super-bal stage. The PCB is star-grounded, has RF filtering on the input and DC blocking caps on the output. It is designed to operate around any NE5532 pin compatible op-amps. Best to use high tolerance resistors, 0.1%.

I actually had the PCBs made for another project but stupidly didn't think about the physical size of them not fitting in the space available, doh! So, I'm happy to sell these at a loss, only £2 each PCB + P&P. I'm in London, UK. Please contact me if you want one. Simon

[lesherons]

Could you provide a link to your previous posts you refer to? I searched by title and by your user name and am not sure I am finding what you have referred to. Thank you in advance. Lesherons

[Tenson]

Here is the circuit, and also a BOM.

Originally Posted by SuperBal BOM

SuperBalanced PCB BOM

Resistors:

R7, R8, R15, R16 = 1K
R1, R2, R3, R4, R5, R6, R9, R10 R11, R12, R13, R14 = 2K2
R17, R18 = 47K
R19, R20 = 100R
R21, R22 = 22K

Capacitors:

C1, C2, C6, C7, C11, C12 = 220pF (NP0 ceramic or polyprop film)
C4, C5, C9, C10 = 100pF (NP0 ceramic or polyprop film)
C3, C8 = 10pF (NP0 ceramic or polyprop film)
C13, C14 = 47uF (Non-Polar electrolytic or polyprop film)
C15, C16 = 22uF (standard electrolytic)
C17, C18 = 100nF (X5R or X7R ceramic)

Notes:

Remove remove the 4x 1K resistors right beside the AKM DAC chip on the Mini2496 and connect the SuperBal PCB directly to the DAC outputs.

Take care with ground connections. A good rule is that the star-ground point of the SuperBal PCB should connect to the Mini2496 where 'real' earth connects, possibly at the SPDIF GND input. Ignore the pads 'OUT~GND1' and 'OUT~GND2' on the SuperBal PCB, take signal output ground from the Mini2496 at the above mentioned point.Experimention might be needed to find the best ground arrangement in your setup.

All IC = NE5532 or pin compatible (e.g. LM4562)

Resistors around superbal stage should be 0.1% or better as this directly effects CMRR.
Adjust R5, R6, R13, R14 to change gain.

To bypass volume control and output buffer, jumper 'To~POT~L' to IC3 pin 6, and 'To~POT~R' to IC3 pin 1.

DC blocking components C13, C14, R21, R22 should still be used for equipment fault protection, although the super-bal stage should cancel the common-mode DC bias from the DAC output.

[atupi]

Can be used with DAC's like PCM1794/1798 (current output)?