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Voltage Regulators for Line Level Audio. Part 10 : Simple Shunts

Posted 11th April 2014 at 07:59 AM by rjm
Updated 16th April 2014 at 12:52 AM by rjm

Part of a series.

I've been meaning to take up shunt regulators for some time. I've never got around to building one myself to try, so I'll have to make do by playing in simulation.

Today's circuit is the shunt analog of the Z-reg series regulator: no feedback, Zener reference, single transistor regulation. The output impedance and ripple rejection-characteristics are similar too, with about 40 dB of RR and an output impedance of just a few ohms. It can be built equivalently from either an pnp or pnp transistor. (See attached LTSpice .asc files.)

The difference between shunt and series regulation can best be explained by considering the upstream power supply: In a series regulator an increase in current demand by the load causes the regulator to increase the current to compensate. In a shunt regulator an increase in current demand by the load causes the regulator to decrease the shunt current to balance, so there is no net change in current flowing...
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File Type: asc voltageregulator8-pnp.asc (1.5 KB, 118 views)
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Old

One Farad capacitor array

Posted 3rd April 2014 at 04:08 AM by abraxalito
Updated 4th May 2014 at 05:53 AM by abraxalito

This array of 127 10,000uF caps measures -j2.9mohms at 50Hz which I reckon makes it comfortably over 1F in capacitance. ESR is 1mohm @ 50Hz.

The individual caps were measuring on average 8,500uF. Although they're marked 10V (the brand is ChengX a slightly shady Chinese one) they're not good for anywhere near this voltage. I reckon they're in reality 6.3V and they seem to have decently low leakage at this working voltage. I shall be using them at 5V or below.

Update1 - seems I wasn't using enough copper in the wiring. I've now built a second one with 2.5mm2 wiring around the loops and 1.5mm diameter cross links and ESR is down to 0.5mohm @ 50Hz now, decreasing at higher freqs. I have enough caps left for a third one...

Update2 - now the first array has a basement level giving 2.1F total with ESR below 0.4mohms @ 50Hz. There are six paralleled TDA1387s atop the combined hexagons giving unprecedented LF dynamics. Amp long, long overdue for an upgrade.......
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Old

The case of the crazy Sapphire amp.

Posted 3rd April 2014 at 02:24 AM by rjm
Updated 3rd April 2014 at 12:07 PM by rjm

Case report:

A set of Sapphire boards gave the proper V+, V- voltages out of the Z-reg, providing about 10.5 and -10.5 to op amp power pins. The output offsets were unusually high however, apparently at about 2 V in one board, and somewhat less in the other. Typically the offsets are in the order of +/-15 mV.

Changing out transistors and op amps did not help, and to all inspection the passive components were installed correctly and working properly. The offset voltages were extremely temperature sensitive. Measurements for the various circuit voltages were just screwy enough to be inconclusive.

I could ask for no more tests, so requested the boards be sent back to me. I found the circuit basically worked as expected, but the offsets were indeed high on both boards, though I measured 0.6 V max rather than 2 V.

***** stop here and make a guess *****

Blowing on the board through a soda straw, the offset shot up when I blew on...
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Old

Screen Capture

Posted 23rd March 2014 at 05:24 AM by SyncTronX
Updated 8th October 2014 at 04:58 PM by SyncTronX (spell check and clarify)

Here is one method to capture your computer measurements
from your computer screen.

To capture only a window that is selected:

Press ALT and Print Screen
keys at the same time.

OR

To capture the whole computer screen image:
Press the Print Screen key.

Then open your paint program and paste
the capture:

Press CTRL and V keys.

Your window/screen is now in your paint program.
Save it in a JPEG format.

Note, the generic paint program is listed
under the Start Menu:All Programs:Accessories:Paint

When saving, look and see where Windows
puts the file...it can get real tricky to find again.

IMG or BMG files are huge.
JPG (Joint Photographic Expert Group)
has algorithms that compress the file size
down to make it easier to send and receive.

Here is my screen capture:

http://origin.dastatic.com/forums/ga...rintScreen.jpg
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Old

Hexacap-based Ozone DAC

Posted 20th March 2014 at 04:18 AM by abraxalito
Updated 31st March 2014 at 02:07 AM by abraxalito

Here's my current bench lash-up DAC based on three hexacaps. Total capacitance of the order of 1.3F.

32fs EIAJ is fed in, balanced, from the left, the central hexacap feeds two TDA1545ATs. Filters are TDK inductor based, six stage balanced with X7R caps (gasp!). Caps in the centre provide the mid-rail power (2.5V) which the I/V resistors are fed from. The two hexacaps on the right power the post amps based on AD815ARBs, gain set roughly to 26dB with a little NOS droop correction. They're the postage-stamp sized boards roughly in the middle. Output is differential and fed to ferrite-cored transformers to convert to SE.

I'm blown away by the dynamics of this, given the right recording. Next up is an amp based on paralleling 8 or 10 AD815s. Each fed from its own hexacap, of course....

Update1 - the DAC supply has now been upgraded to two tiers of the 4700uFs, interconnected by six 1.5mm diameter solid copper wires. Capacitive reactance measures 2.5mohm...
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Old

Bugle 2

Posted 17th March 2014 at 02:38 PM by MagnumOpus

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Built the Bugle 2 to replace my Boozehound J-fet riaa. I had som headache trying to sort out a mistake I made, mixing up som resistors, but it works! And it sings beautifully

I do rank the Boozehound above this one, but the Bugle 2 most assuredly kicks the Gram Amp 2 SE's butt, bigtime.
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Old

Simple DSP Crossover implemented using PIC32MX450

Posted 17th March 2014 at 11:49 AM by googlyone
Updated 17th March 2014 at 11:58 AM by googlyone (incomplete)

It must be close to 12 months ago that I saw the PIC32MX450. I was convinced that a chip that included two I2S audio interfaces, and ran at 100MHz implementing 32bit arithmetic in pretty snappy time would surely be able to do some fun audio stuff.

I started with getting a board designed, and porting the code that I use to control my Analog Devices audio DSP. Then I generated the code to implement a direct digital synthesiser. These worked fine.

Over the last couple of weeks I have completed the "core code" for a digital crossover all implemented in the PIC32 itself.

The basic implementation is:
- An analogue to digital converter
- The PIC
- A digital to analogue converter
(Oh and an interface PCB done on veroboard to route the MCLK and power to the A/D and D/As. I am kind of tempted to re-spin the PIC32 board to do this for me...)

The PIC drives the I2S interface as master, generating...
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Old

Radio Shack Linaeum measurements

Posted 14th March 2014 at 11:40 PM by hbc

I bought a pair of these in about '95 and modified them a bit. I blocked up the ports, stuffed them with fluff, replaced the inductor with an air cored type, and rewired with CAT5. I also removed the top cages and grills which subsequently got lost, and also removed the rubber from the woofer voice coil, and put in a phase plug fashioned from some dowel.

I lived happily with these for about 10 years, ending up with an 18" subwoofer which used an equalised bass guitar speaker. The advantage of this equalisation was a degree of cancellation between the sub and the little woofers, resulting in a very smooth lump free transition in the listening position.

I found them to be an excellent tool in the development of audio stuff, it was quite easy to discern the difference between different types of cables, for me and friends, etc etc.

I bought another pair but I was wondering if the tweeters were fried as they sounded a bit dull compared to my modded...
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Old

Adventures in low impedance power supplies

Posted 10th March 2014 at 09:01 AM by abraxalito
Updated 17th May 2014 at 04:52 AM by abraxalito

Here's my latest crazy project, intended to answer the question 'How low can you go?' in power supply impedance. No listening tests yet, I've just finished assembling this stack of hexagon capacitor arrays out of cheap electrolytics. Total capacitance of the top 4 tiers is comfortably above 1F. The top tier is designed for lowest ESR at HF using Nichicon 1500uFs, the next tier is a trade between ESR and uF. The last two are the highest capacitance density I could find (a total of 182 4700uFs). I've yet to connect the bottom two hexagons to the upper tiers but the top two are connected by wires running through the gaps between caps.

The whole is intended to push the limits of low frequency noise in powering a couple of TDA1545s which will sit on a small PCB supported on thick wires from the centre of the top tier. I am aiming to get a capacitive reactance (at 50Hz) at the DAC supply pins below 3mohm and ESR below 1.5mohm.

Update1 : connected the bottom two tiers...
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Old

Goodmans Magnum SL woofer distortion

Posted 5th March 2014 at 04:17 PM by hbc

I have a pair of tired Goodmans Magnum SLs. They are in reasonable condition, but one mid is blown, and they have no front covers. I tried grafting a new mid on to the broken one, expecting I would need to do some crossover work, but it really did not sound good. A very unpleasant sound that I found quite fatiguing and unpleasant to listen to coming from the upper bass lower mid area, quite a relief to turn it off actually. I put bigger and bigger choke on the woofer to try and filter it away, but that didn't work. I took of the dust cap in case that was causing it but no.


I am thinking of re-purposing the boxes now, but first did just check the woofer to make sure it has a problem. Below are some distortion plots, for a good one, the bad one and also for a Wharfedale Dovedale 3 woofer, with fixed rubber (Note the different scale). These plots were done at quite low level, like normal neighbour friendly listening levels.
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