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Voltage Regulators for Line Level Audio. Part VII : The k-multiplier

Posted 17th February 2014 at 11:55 PM by rjm
Updated 18th February 2014 at 12:08 AM by rjm

Part of a series.

This circuit is from this page by Kean Token, also referenced in his recent blog post.

Two versions are presented, one with all the protection diodes and a simplified version with extraneous components removed.

LTSpice simulation shows so-so performance into a light load, with about 70 dB of ripple rejection and a fairly high output impedance, but the drop out voltage is respectably low and we must factor in - coming directly from the Jung Super Regulator - that this is just a two transistor circuit, with no error amplifier to provide feedback.

As a frame of reference, it is quite similar in performance to the Z-reg we looked at back in part III.

The k-multipler is of a class of voltage regulators where the output is referred to the input voltage, rather than to ground. It provides "X volts less than the input", rather than the traditional regulator which provides "X volts above zero"....
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File Type: asc voltageregulator-kmult.asc (2.9 KB, 173 views)
File Type: asc voltageregulator-kmult-simple.asc (2.1 KB, 178 views)
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Old

Voltage Regulators for Line Level Audio. Part VI : The Jung Super Regulator

Posted 13th February 2014 at 04:21 AM by rjm
Updated 14th February 2014 at 10:52 AM by rjm (clean up)

In the next part of the series, I'll be presenting various published regulator circuits.

Today we have the "Jung Super Regulator" (2000 version) on deck, thanks to Tangentsoft's excellent write-up.

In translating the circuit to LTSpice, I've made some concessions. While I have kept the protection diodes so as to be consistent with the original - even if they do nothing in this simulation - the op amp, transistors, voltage regulator and reference have been substituted with working equivalents from the LTSpice libraries. I've been approximate in the resistance and capacitance values, and tuned the circuit to output 10 V at 10 mA to keep in line with the previous circuits I've uploaded.

It works though, and, under simulation at least, it works extremely well. Putting it together in LTSpice gave me a new appreciation for just how much work and refinement went into its design. Now, its an open question whether such over-the-top performance...
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Old

Voltage Regulators for Line Level Audio. Part V : Graduation Day

Posted 20th January 2014 at 03:32 AM by rjm
Updated 20th January 2014 at 10:21 PM by rjm

Part five of a series.

Last time, we'd got to a functional voltage regulator, with a pass transistor and op amp error amplifier but I cheated and used ideal voltages for the reference and op amp power supply.

This time I've sketched out a functional circuit using real parts found in the LTSpice library. I've chosen a rail-to-rail op amp to avoid problems with low voltage references. The LT1009 reference puts out 2.5 V, the op amp gain is 4, for an output of 10 V into 1 kohms.

Two versions of the circuit are included below. Voltageregulator5 has some additional RC filter stages to remove noise from the reference and op amp power supply Voltageregulator5b just takes everything straight from the input voltage. As you can see there's a fairly substantial advantage gained from judicial use of RC filtering.

So that's the end of Term 1. The basics have been covered, however briefly. I encourage you to download the LTSpice files and play...
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File Type: asc voltageregulator5b.asc (1.9 KB, 157 views)
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Old

Voltage Regulators for Line Level Audio. Part IV : The Error Amplifier

Posted 18th January 2014 at 06:05 AM by rjm
Updated 20th January 2014 at 10:21 PM by rjm

Part 4 for a series.

At the end of Part 3 I promised to introduce feedback, and I will, but what we are really talking about here is the addition of the error amplifier, the heart of all modern series pass regulators. The error amplifier is a non-inverting DC signal amplifier, and its function is simple: amplify and buffer the reference voltage. The twist is that the amplifier output is connected to the base of the pass transistor, while the feedback connection is taken from it’s emitter. The pass element is thus placed inside the feedback loop of the error amplifier, improving the ripple rejection and output impedance of the regulator dramatically.

So here we are, the three building blocks of a voltage regulator are in place: the reference voltage, the error amplifier, and the pass device. In the LTSpice circuit I’ve cheated, deliberately, in order to make the operation easier to follow. Instead of building a practical voltage reference I’ve...
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Old

Voltage Regulators for Line Level Audio. Part III : The Z-reg

Posted 17th January 2014 at 04:35 AM by rjm
Updated 20th January 2014 at 10:21 PM by rjm

Part 3 of a series.

I’m going to have to make a detour to point out what we are doing here is learning how these circuits work, and get a very rough idea of their relative merits. We’re not trying to minimize the output impedance, or maximize the ripple rejection. Three reasons immediately come to mind for why it would be bad practice to try and do that:

1. Any such contest will be easily won by the largest capacitor placed on the regulator output.

2. There are clear limits on these parameters after which further “improvement” is unlikely to serve any useful purpose.

3. There are other considerations such as the output noise of the regulator and the stability under dynamic loads, which are equally if not more important.

Clear? No cookies for the “most bestest” circuit in LTSpice. The great utility of LTSpice is it allows you, the designer, to easily check if you’ve left performance...
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Old

Voltage Regulators for Line Level Audio. Part II : The Pass Transistor

Posted 16th January 2014 at 04:14 AM by rjm
Updated 20th January 2014 at 10:21 PM by rjm

Part 2 of a series.

Instead of pulling the output current through R1, we add an npn pass transistor, Q1. The output current now "passes" through the transistor, while the Zener diode still regulates the output voltage by being connected to the transistor base.

The output impedance falls to a few ohms, but the ripple rejection improves only slightly.

This is a useful basic circuit block for audio, but the ripple rejection can easily improved by the addition of a couple of additional components, as we'll see shortly.
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Old

Voltage Regulators for Line Level Audio. Part I : Zeners

Posted 15th January 2014 at 11:34 PM by rjm
Updated 16th January 2014 at 04:40 AM by rjm

This is the first of a series, where I will be investigating the output impedance and ripple rejection of various voltage regulator circuits using LTSpice.


Today, for the first "lesson" (I'm teaching myself, as much as anything) we will look at the very simple zener voltage regulator.

The load is 1 kohm, and the Zener breakdown voltage is 12 V. The load current is about 10 mA, and to avoid gross inefficiency we will limit the current flowing through the Zener to about 5 mA, by adjusting R1 accordingly. The input voltage is fixed at 18 V.

To measure the ripple rejection, we perform an AC analysis with the voltage source AC set to 1 and the current source AC set to zero. The ripple rejection is the negative value of the signal at Vout: so -20 dB means 20 dB ripple rejection (1 V ripple at Vin generates 0.1 V ripple at Vout at a given frequency.).

To measure the output impedance, again the AC analysis function is used but...
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Old

Hakko FX-888 : ebay unhappiness

Posted 29th May 2013 at 12:12 PM by rjm
Updated 29th May 2013 at 11:59 PM by rjm

Oh, for Heaven's sake...

Just got the FX-888 soldering station I bought on ebay.

It does not power up.

Do you know why it doesn't power up?

So glad you asked...

It does not power up because - pause for effect - the fuse board that fits on the power transformer is inserted the wrong way round. That's right, the full "rotated 180 degrees" deal.

Fortunately I have another soldering iron. You know, so I can fix my soldering iron...

*****

I would just return it, but the shipping would cost me half again what I paid for it. Perhaps ebay will refund me anyway. We'll see.

I think I know what happened: The people selling these are modding them by changing the voltage and power cord. The soldering stations are officially bound for the Chinese domestic market, 220 VAC. The box, when it came, had "110V" hand-written on it, though the instructions...
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Old

A catalog of headphone amplifier circuits.

Posted 19th May 2013 at 10:45 AM by rjm
Updated 21st May 2013 at 12:12 AM by rjm

Lots of circuits out there, but most are variations of a small set of archetypes. Let's see if I can put together a list:

1. Dedicated headphone amplifier IC. e.g.(lme49860)

2. Battery powered, single stage, generic audio op amp. The ever-popular mint tin cmoy.

3. Op amp + buffer (complementary transistor pair, diamond buffer, unity gain op amp, etc, in either integrated or discrete package.)
a. closed loop connection or "compound amplifier" configuration as developed by Walt Jung.
b. open loop, two stage circuit, e.g. nwavguy o2 and my sapphire amp.

4. simple 2 or 3 transistor "introduction to electronics"-style amplifier

5. The "little big amp", a scaled back version of a transistor or vacuum tube power amplifier design. (Zen, DoZ, transformer coupled SET amps)

6. The power follower. Single-ended MOSFET or BJT, with or without CCS load, voltage...
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Old

Audacity sucks.

Posted 9th May 2013 at 02:50 PM by rjm
Updated 10th May 2013 at 03:35 AM by rjm

Under windows at least, Audacity is unable to record audio at bitrates above 16 bit.

It will seem to, all right, but the data is quantized at 16 bit (30 microvolt LSB), regardless of the settings chosen.

The attached images show the same source, the first recording is made in Audacity, supposedly 24 bit, but actually only 16 bit, while the second is recorded with a program than actually supports 24 bit, exported, and imported into Audacity. The data is amplified +70dB in both cases to make the difference visible.

Audacity will happily manipulate and save high bit rate data, but as a result of licensing restrictions and on account of it being freeware, it does not support the actual recording of this data.

***

Any internet search will confirm that the Windows version of Audacity is limited to 16 bit recording. And yes, it's more of a limitation of Windows than it is of Audacity. My irritation, however, is chiefly with Audacity...
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