Miscellaneous
Everything that didn’t fit elsewhere…
Discrete Class A DI-Box
DI-Box_r1.pdf
DI-Box_r1_PCB.pdf
DI-Box_r1_thdn.pdf
A phantom-powered DI-box with transformer-balanced output. Carefully designed for low noise, excellent PSRR and high input headroom (almost +23 dBu at 1 kHz). With ground-lift switch. Above 80 Hz and below +20 dBu the THD+N plots show the noise floor rather than actual distortion. The output noise has been measured as −116 dBu for a shorted input—which is simply the residuum of the meter used. Check the pictures.
Notes:
- To get the desired output stage quiescent current it is needed to add a 120 Ω resistor in series with D8 or D9.
- Charging C6 takes a few minutes. At the beginning of the charging process D7 conducts and injects common mode noise into the output. No problem with that as after start-up this will stop completely.
OPA2134 based DI-Box
A simple IC based and battery powered DI-box.
IC Headphone Amplifier
A relatively simple headphone amplifier with volume control. The input should be driven from a low impedance and DC-free source. Note that the amplifier has inverting polarity—a balanced input buffer (which is AC-coupled to the amplifer or got a decent DC servo) might be a good addition. So far untested.
LL5402 Single Supply Output Buffer
LL5402_single_supply_buffer_r1.pdf
Using the LL5402 output transformer with a +48 V single supply. Untested.
HLMP-6000 Red LED Forward Voltage And Impedance Distribution
HLMP-6000_forward_voltage_batch_2.pdf
HLMP-6000_impedance_batch_2.pdf
Measurements of the HLMP-6000 forward voltage and impedance distribution at 5 mA DC current (feed trough 11 kΩ resistor). For the impedance measurement the DC current was modulated with a 1 kHz/0.5 mA sine wave. The impedance was checked and found to be consistent over a frequency range of 100 Hz—100 kHz. The results show that this part is very well suited as biasing element for BJT current sources. The forward voltage of all samples is well within 1 % of the average reading and the impedance consistently low.
Batch two was purchased about two years later. It was measured at slightely lower temperature which contributes to the voltage difference to the first batch. The effective difference appears to be about 17 mV. More information on current source biasing can be found in the Parts & Components section.
Terms Of Use
The designs described on these pages are not commercial in any way. This means that I do not sell PCBs, kits, or anything like that. It also means that any for-profit use of the information on these pages is strictly prohibited—you may not sell PCBs, kits (neither partial, nor complete) or finished (or unfinished) units of the designs on this site, without the express written consent of Samuel Groner/SG-Acoustics.
Disclaimer
Notice that all information, schematics, layouts etc. are supplied as is, and that I can in no way be held responsible for its accurateness, functionality or even safety. Samuel Groner/SG-Acoustics shall not be responsible and disclaims all liability for any loss, liability, damage (whether direct or consequential) or expense of any nature whatsoever, which may be suffered as a result of, or which may be attributable, directly or indirectly, to the use of or reliance upon any information, links or service provided through this website.