As you might have read in my previous installment I started playing with a relatively inexpensive Chinese Bluetooth receiver by doing some modifications to it.
The balanced current outputs of its PCM1794 DAC chip were terminated to ground via resistors for a passive Current-to-Voltage (I/V) conversion, all operational amplifiers were removed and the outputs were wired directly to the RCA sockets. Then via interconnect cables the tiny signals were fed through a pair of coupling capacitors into a discrete low-pass filter before they finally hit the grids of the vacuum tubes located in the analogue output stage. Sonically the outcome of that setup was revelatory. As a result in the following months my listening habits completely oriented towards streaming over Bluetooth instead of playing CDs or records. It was that good. At the end I decided to put all the components together into a single enclosure and that’s how this project was born.
But let me tell you first how I reached that point where I was so familiar with all my records that I didn’t want to listen to any. It happened gradually, all I wanted then was something new. I wanted to be taken on a journey of discovery instead of treading the old beaten tracks. At the same time I was trying to avoid complications imposed by adoption of a typical streamer/DAC combo which requires internet connection, installing third party applications, dealing with authentication and so on in order to work. Bluetooth in contrast is not tied to a specific streaming service like Tidal or Qobuz for example but allows any content in the smartphone to be replayed on the audio system through simple pairing. And this includes audio/video content in the web browser which has a great deal on offer.
At the end Bluetooth gave me the freedom and user friendliness I was longing for, it liberated me from the tyranny of the physical media once and for all. Yes, it might sound absurd but being reliant on physical media to enjoy music has become a form of tyranny for me lately, mostly because of the constraints a home record library imposes on one’s listening behavior. I couldn’t afford enough variety which was limited due to a lack of storage room from one side and the heavy burden on my wallet from another. Finally with the introduction of a high performance Bluetooth receiver in my audio system all that changed.
As I have previously mentioned the largest part of the effort and expenses went into building the output stage and its dedicated power supply which are hand wired. The analog output stage is based on ECC88/6922 tubes in an SRPP configuration descending from classic Audio Note DAC circuits utilizing the Burr-Brown PCM63 chip. The high tension power supply relies on EI type power transformer feeding a diode bridge rectifier integrated circuit followed by a choke input filter. The low voltage digital power supply utilizes R-core transformer and a high quality regulated power supply based on TL072 dual operational amplifier as voltage reference processor. The Bluetooth receiver itself employs the Qualcomm QCC3095 chip supporting streaming of up to 24-bit/48kHz resolution.
The parts selection for this project has undergone a rigorous process. I have spent countless hours trying different parts in the key positions because everything matters – wires, resistors, capacitors, transformers, everything – each has its imprint over the final sonic product. At the end I settled with a balanced mixture of parts which does not break the bank but at the same time maintains the quality: Audio Note tantalum resistors and SCR/Solen Fast film capacitors in the signal path, Mills wire-wound resistors and Audio Note standard electrolytic capacitors in the power supply, Nichicon Muse electrolytic capacitors and Takman carbon film resistors on different places.
All I can say is that the sound of this device is very balanced and extremely involving. I use it mostly to stream music through YouTube Music app from my smartphone having the Bluetooth audio codec set to Qualcomm aptX HD. To my ears this setup feels in now way inferior in terms of sheer resolution to CD or record player and most importantly my attention is immediately drawn towards the music and the performance instead. I have two friends visiting me regularly both having iPhones, one is streaming lossless audio from Tidal, the other likes to play self made recordings of concerts he has visited and I must say they both sound very decent and we always have a great deal of joy listening. Especially unprocessed, amateur made recordings of live concerts, available on YouTube Music or elsewhere, strike with their immediacy and life-like character when streamed through this receiver being very effective in transporting me at the concert venue. All in all I am very satisfied with the sound.
Thank you for stopping by and always happy listening!