Hi All, The default opamps of the FireStone Audio Bobby Class A fully balanced headphone amplifier are a quartet of OPA604s. In this year of its 10th anniversary I wanted to see what potential is still in this decade old design by swapping the opamps with a discrete alternative by Sparkos. I did several listening tests and would like to share my findings with Bobby owners and other readers. My audio-chain consisted of: Qobuz (Hi-res streaming service) Roon (running on Synology NAS) HQPlayer (running on Intel Nuc12i5) for upsampling and EQ...

Several years ago I built myself a HP amplifier based on the Texas Instruments TPA6120A2 headphone amplifier chip. This is a compact powerfull device that combines very well with a variety of headphones. I experimented with different opamps in this design and for those interested I would like to share some of my experiences. Recently I replaced the current OPA1611 opamps with Sparkos ss3601 which improved the sonic performance in several key areas. I did several listening tests and would like to share my findings with other owners of TPA6120A2...

Recently I upgraded my Zishan Z1 Digital Audio Player (DAP) with the Sparkos ss3602 discrete opamp. In this short overview I would like to share my opinions and experiences with this upgrade. Used headphones where AKG K712 Pro and Philips Fidelio X2 NE5532 is the default opamp of the Z1 DAP. A few years ago after several tests and opamp swaps (including Muses8920, Muses8820, Burson V5i and LT1028) I settled on the Linear Technology LT1028. As these are single channel in a soic package you had to mount two on a dual 8 pin SOIC to 8 pin DIP PCB...

Recently I upgraded my Zishan Z3 Digital Audio Player (DAP) with the Sparkos ss3602 discrete opamp. In this short overview I would like to share my opinions and experiences with this upgrade. Used headphones where AKG K712 Pro and Philips Fidelio X2 LM4562 is the default opamp of the Z3 DAP. Over time I have tested and swapped numerous opamps in the Z3 with mixed results: Opa1641, Lt1028 and Muses8820 each have their strengths and weaknesses but are overall not better than the default LM4562. The opamps that I valued better than the default opamp...