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Constant Current Source (CCS) For Audio Applications
Constant Current Source (CCS) For Audio Applications
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Old 27th July 2016, 11:40 PM   #1
jkuetemann is offline jkuetemann  Canada
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Question Constant Current Source (CCS) For Audio Applications

Disclaimer: I'm just a lowly technician, not an engineer. Many here are well above me in areas related to the knowledge of electronics and more creative as well. However, given the prior statement, please do qualify any statements / assertions made. Don't state something as a fact without some verifiable reference, preferably a link to a professional paper / resource, or at least the name of the resource and author. To simply say 'because it sounds better' will be considered inadequate for the purposes of this thread.

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I'd like to open a discussion on the humble 'Constant Current Source', or CCS, as this fundamental building block relates to its uses in audio amplification.

We often see the CCS used as a source or sink for current where we want a relatively stable and defined current to flow in the face of variable conditions in adjacent areas of the circuit. Some people feel a specific arrangement offers better performance over other circuits in an amplifier, while different folks feel that even basic CCS is more than adequate for almost all needs. The idea here is not to settle any sort of dispute but rather to discuss and perhaps demonstrate, at least in simulation, what might be preferable with the where and when qualified.

Perhaps the application dictates how 'good' the CCS needs to be? Is there a point of 'good enough'? Is a better CCS always better in audio?

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If possible it would be nice to lay down a few guidelines. For starters:

1) Avoid exotic components. The best design is useless if the parts are made of Unobtanium. Parts should be easily available from main stream distributors. Components found in DIY-friendly SMD package sizes are fine.
2) Limit complexity. A CCS that takes more PCB real estate than the amplifier is not practical, especially if the gain in performance of the circuit as a whole is minimal. Let's target not more than two active devices plus required supporting passives unless the increase in performance is dramatic enough to warrant an extra active device.
3) Let's have some fun. Please no poo-flinging, flaming, trolling. Keep things friendly, courteous and civil.

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As a starter for resources:

http://waltjung.org/PDFs/Sources_101_P1.pdf
http://waltjung.org/PDFs/Sources_101_P2.pdf

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And attached are a few basic CCS circuits and a little of their performances. Please do point out any fundamental errors or ways to improve the simulations. Comments, ideas and suggestions?
Attached Images
File Type: png CCS Comparison Sch.png (71.3 KB, 1603 views)
File Type: png CCS Comparison Current.png (78.7 KB, 1556 views)
File Type: png Current Variation v Freq.png (77.8 KB, 1522 views)
Attached Files
File Type: asc CCS Comparison.asc (2.7 KB, 124 views)
File Type: txt Cordell-Models.txt (19.6 KB, 77 views)
File Type: txt Fairchild Models.txt (933 Bytes, 63 views)
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Old 28th July 2016, 02:03 AM   #2
xrk971 is online now xrk971  United States
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Constant Current Source (CCS) For Audio Applications
Nice thread!

We can add the shunt voltage reference CCS. So either a Zener diode or a programmable reference like the TL431. I hear that the TL431 is supposedly quieter than a Zener as it doesn't have the Zener switch noise. The shunted voltage the controls then base of the CCS transistor.
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Old 28th July 2016, 03:19 AM   #3
bimo is offline bimo  Indonesia
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You can try ideal current source for LTP (Long Tail Pair) input and then change it with a resistor in simulator. Please see the THD, harmonic profile, and PSRR result.
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Old 28th July 2016, 03:42 AM   #4
triplej is offline triplej
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I'm interested in this as well. If for power amp applications this would eliminate jfet options for VAS etc.
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Old 28th July 2016, 06:52 AM   #5
erikovsky is offline erikovsky
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Old 28th July 2016, 07:30 AM   #6
erikovsky is offline erikovsky
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Just found a paper:
Low noise constant current source for bias dependent noise measurements
D. Talukdar et al.

A low noise constant current source used for measuring the 1/f noise in disordered systems in ohmic as well as non-ohmic regime is described. The source can supply low noise constant current starting from as low as 1 μA to a few tens of mA with a high voltage compliance limit of around 20 Volts. The constant current source has several stages which can work in a standalone manner or together to supply the desired value of load current. The noise contributed by the current source is very low in the entire current range. The fabrication of a low noise voltage preamplifier modified for bias dependent noise measurements and based on the existing design available in the MAT04 data sheet is also described.
Attached Images
File Type: gif CCS.gif (48.6 KB, 2373 views)
File Type: gif CCS2.gif (46.6 KB, 2313 views)
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Old 28th July 2016, 07:48 AM   #7
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by jkuetemann View Post
Comments, ideas and suggestions?
I did more or less the same thing some time ago:
Improved current source/sink
Improved 2W current sources (II)
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Old 28th July 2016, 09:56 AM   #8
jerluwoo is offline jerluwoo  United States
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The op's sim is flawed since R4/5 are fed ac as well. They should be connected to a dc source with no ac signal.
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Old 28th July 2016, 10:18 AM   #9
astx is offline astx  Austria
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Constant Current Source (CCS) For Audio Applications
Quote:
Originally Posted by jkuetemann View Post

...

I'd like to open a discussion on the humble 'Constant Current Source', or CCS, as this fundamental building block relates to its uses in audio amplification.
...
Comments, ideas and suggestions?
Thx for this summary! What about temperature behavior of the various CCS'es?

BR, Toni
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Old 28th July 2016, 11:25 AM   #10
xrk971 is online now xrk971  United States
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Constant Current Source (CCS) For Audio Applications
Quote:
Originally Posted by erikovsky View Post
Just found a paper:
Low noise constant current source for bias dependent noise measurements
D. Talukdar et al.

A low noise constant current source used for measuring the 1/f noise in disordered systems in ohmic as well as non-ohmic regime is described. The source can supply low noise constant current starting from as low as 1 μA to a few tens of mA with a high voltage compliance limit of around 20 Volts. The constant current source has several stages which can work in a standalone manner or together to supply the desired value of load current. The noise contributed by the current source is very low in the entire current range. The fabrication of a low noise voltage preamplifier modified for bias dependent noise measurements and based on the existing design available in the MAT04 data sheet is also described.
Nice find! I love 2sk170's and was hoping there would be a way to use them for a high performance CCS.
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