The goal is to find out how large the ballast resistors must be to prevent current runaway and to control "current hogging" to a given limit. Current hogging is a phenomenon with bipolar transistors when operated in parallel in which the hotter of the set draws more current than the cooler one(s) and so heats up even further. The fix is to put series resistors ("ballasts") in the emitter circuits (see the drawing), but I've not been able to find anything published that says how to calculate the value of the resistors.
The model is for two BJT transistors, with their collectors and bases commoned and their emitters summed through individual ballast resistors. You need to know what the process-variation-caused...
In a search to replace a modified SMSL headphone amp that I use at work, I decided to build a DOA SeNNator, a variant of the filtering headphone amp for the Sennheiser HD 650, published by Solderdude over at - diyaudioheaven along with measurements of the HD650's responses.
It's based on the "HD 650 SeNNator" and "SeNNator build tips" pdfs. In adapting the design, DOAs were used. An upgrade to the filtering caps from polyster to polypropylene. To the original circuit, circuits and design ideas from:
Sam Groner - +/-30mv DC offset adjust and DC bypass cap.
Layout idea lifted from Jeff Steiger's CAPI-2 Line Stage Amp, from Capi-gear.
DC filter from Collective Cases, reducing the numerous different electrolytic caps and upgrading the linear regs. from LM217/337 to LT1963/3015.
Minimized mechanical assembly, using the default PWBs available in Kicad, each channel and the DC filter/regulator boards are in a Euro card form factor...
Posted 29th December 2016 at 11:52 AM byHumbleDeer
I think I'll be painting my small subwoofer in some shade of cherry or wine red. I just need to sand it down once more and give it one final layer of MDF Primer. Hopefully, all dents and small damaged points will be gone. I won't get my hopes up though.
Posted 27th December 2016 at 11:48 AM byjan.didden Updated 27th December 2016 at 11:51 AM byjan.didden
This blog is not about audio. Or at least not in the sense of a design or equipment discussion. It's about how we as humans tick, and possible (probable?) implications for how we form opinions and views about what we hear, about a particular design or sound.
My long-standing interest in this area was recently triggered again by a couple of posts from Mark4w, and a book he recommended (Thinking, Fast and Slow, by Daniel Kahneman). At about the time I received the book I also fell into a scientific discussion on the TV about the process our brain goes through to form an opinion and serve that up to our conscience as 'this is how it is'.
I thought back about all the discussions I've had on diyaudio about sighted versus blind listening. Without opening up Pandora's box yet again, in a nutshell: The brain uses every input it can get its hand on to form an opinion. So when you listen to, say, a new amp, the brain not only uses the sound coming in through your ears,...
Posted 23rd December 2016 at 05:02 AM byrjm (RJM Audio Blog)
Updated 27th December 2016 at 11:46 PM byrjm
Following on from this post and this post, we arrive in time for the holidays with Project Unity. Merry Christmas everyone.
Four circuits: Unity, Unity H, Unity B, Unity BH. line preamp, Headphone amp, line Buffer, Headphone Buffer respectively, all derived from a common base circuit called Unity Root. Unity Root is conceptual, it exists only as a reference so you can see more clearly how the four working variants relate to each other.
It's the "all for one, and one for all" approach to diyaudio, a single research and development line applied to a range of applications, feedback from any of the applications brought back to apply to the line in general.
This simplifies not just the circuit development, similar efficiency is also brought to the documentation, board layout design, and BOM... about which I'll have more to say in a bit.
Posted 20th December 2016 at 04:47 AM byrjm (RJM Audio Blog)
Updated 7th March 2017 at 07:09 AM byrjm(BOM 16b2 uploaded)
I've come this far so I might as well complete the trifecta.
This is the X-Reg circuit, with a new layout and component numbering to match the new S-Reg and Z-Reg boards. Each is a drop in replacement for the other.
Like its siblings, the X-Reg is a low current voltage regulator for line level audio. The output is about 9 V (adjustable up to 12 V) and the maximum load current is 50 mA without heatsinks, 100~150 mA with small heatsinks on Q1,2.
It is not a true regulator as there is no fixed reference and instead the output voltage is defined relative to the input voltage. The high open loop gain of the op amp is harnessed for very low noise and very high ripple rejection. It is necessarily a high feedback approach.
So, there you are: three mix-and-match power supply options for all your low voltage, low current audio needs.
Posted 19th December 2016 at 12:55 PM byrjm (RJM Audio Blog)
Updated 7th March 2017 at 07:11 AM byrjm(BOM 11b2 uploaded)
Companion regulator to the S-Reg. Same board dimensions and connection layout. For line level audio.
Same idea as before rectified 2x12 VAC input, +/- 11 V output. 50 mA max output current unless the transistors are heatsinked.
There is a small amount of over-current protection afforded by R3,4 but do not short the output for all but the shortest of transients.
Eagle/Gerber files attached, so you can go get this made yourself, optinally with whatever modifications you need.
I've use this regulator circuit in my Sapphire headphone amplifier. It's a simple and modest circuit but I feel it works really well in practice as long as the audio circuitry it powers has reasonable PSRR. No feedback means no out-of-band noise or instability, even as the output impedance remains low.