New projects coming: balanced preamp with stepped attenuator and modular headphone amp

Right after getting things up and running and promising more frequent updates, it has been quiet for some time. However, it has not been quiet in my home lab. I’ve had two major projects under development: balanced preamplifier with relay stepped attenuator and modular headphone amplifier where amplifier boards can be swapped. The preamp is not completely my own design but is based on work by Bruno Putzeys and Hans … Continue reading

OnePlus 3 volume control step size and output level measurements

OnePlus 3’s 16-step volume control has too coarse steps – 5 dB in the middle volume range. Maximum output level is -1.5 dBV (around 95 dB THD+N ratio), providing over 20 mW into a typical 32-ohm headphones – more than enough for any portable headphones. I’ve had my OnePlus 3 phone since last October. Generally I have been very happy with it, excellent value for money. I’ve had some battery … Continue reading

Win an oscilloscope in Keysight Scope Month – like I did last year!

It is March again, meaning Keysight are having their Scope Month where they give away impressive number of free oscilloscopes. You still have plenty of time to win as they draw names every day in March to give away their new 1000-series entry level scopes. While the scopes are significantly cheaper models than last year, they give away a whopping five scopes each day in March. In addition, two 4000-series … Continue reading reopened

After over 2 years of silence I have updated and reopened this site. I have spent huge amount of time documenting all the projects I have designed, built, and measured within the last year. With this big personal investment I will honestly do my best to keep updating the site this time. This will mean new projects and also blog posts related to these projects and interests. I am slowly building … Continue reading

Bit-perfect ASIO drivers to solve issues with Windows audio quality

By default, Windows audio quality can be technically not superb. ASIO drivers or similar can improve audio output significantly by bypassing Windows resampling and other audio processing stages. This post is a consequence of testing the USB-input of H-DAC. Its PCM2707C-circuit is capable of “only” 48 kHz / 16-bit audio so I was not expecting superb measurement results but was still amazed how bad they actually are. This is purely technical … Continue reading

LME49724 vs. OPA1632 in Addon BalOut

Following performance figures have been measured in Addon BalOut module: Both opamps are so good that it is difficult to measure differences directly. LME49724: Noise level: -117 dBV (A-weighted), THD+N ratio: at least -109 dB (1 kHz, 2 Vrms), around measurement instrument limits. OPA1632: Noise level: -118 dBV (A-weighted), THD+N level: at least -109 dB (1 kHz, 2 Vrms), around measurement instrument limits. Measurements Originally the balanced addon board Addon BalOut for H-DAC have LME49724 fully … Continue reading

PCM1794A left/right channel distortion difference

Basically in all of my PCM1794A measurements I have seen something strange going on in the distortion figures between left and right channels. Right channel is constantly weaker but the results are very consistent between measurements, parts, and even different opamp models, while left channel shows better performance but the results are very inconsistent. I will show few examples from different measurements. To be honest, I still do not know what … Continue reading

Understanding audio measurements: Crosstalk

Expresses “leaking” between channels; it is measured by driving a stimulus signal in one channel while listening the other. Crosstalk is expressed as a ratio between the quiet undriven channel and the stimulus in the driven channel, and given in decibels. In stereo system, crosstalk is measured by driving a stimulus signal in one channel while listening the other. As the signal level is very small, sharp bandpass filter is … Continue reading

PCM1794A output stage opamp measurements: LM4562, NE5532, and OPA2134

LM4562 and NE5532 show almost identical performance in I/V stage, while OPA2134 is 2 dB weaker. LM4562 is the best performer in differential amplifier. The best solution is to use NE5532 in I/V-stage and LM4562 in differential amplifier as it gives almost identical performance to all-LM4562 implementation Differences in distortion are mostly due to odd left/right channel differences of PCM1794A. Introduction PCM1794A has differential current outputs and therefore requires some analog … Continue reading

Understanding audio measurements: THD+N vs. amplitude and frequency

Presents the unwanted part of the signal – something that was not put there and should not be there. THD+N vs. amplitude graph is important as it reveals SNR, dynamic range, and THD+N ratio; all are expressed as ratio compared to a specified signal level. Signal level, signal frequency, and measurement bandwidth must be known (or guessed) when analysing results. THD+N, Total Harmonic Distortion plus Noise, is one of the best audio … Continue reading