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Old 22nd July 2012, 12:40 PM   #1
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Default MCA son of ZCA

The ZCA has this strange cult following. I think its great. If people are building DIY audio-Yes its great. The ZCA has proved very, very popular but the pressure was applied to come-up with something else. To have a new ZCA or something very similar.

As far as I am concerned a Zero Component Amplifier has one active component. That is ground Zero. Though not an improved ZCA I do offer for your enjoyment the MCA. The Minimum Component Amplifier can have more than one active component but must strive to keep active component count down. In the MCA the PS and bias networks are unchanged but the power Fet (2SK1058) is replaced by a bipolar.

Part of the ZCA/MAC philosophy is to strive to keep component count to a minimum but also to use "off-the-shelf" parts. The bipolar, which is the heart of the MCA is a 2N3055. But the soul of the MCA is a jFet, 2SK170. Keeping the PS and biasing ccts. the same we replace one power Fet with a Darlington pair of jFet and bipolar. This allows me to bias the 2N3055 correctly and give the amp the benefit of a bipolar output. I like the sound.


The transistor runs quiet cool and and so does the jFet. The load Rs get hot. The power is down to 1.2W RMS but the frequency range is <10hz -3db >125kHz. Strictly using the schematic below with a dead quiet 24V PS will produce a lightning fast, simple SS amp with as much punch and slam as 1.2W will incur. The 100hz, 1Khz and 10Khz SQR wave signals into 8.2 ohms (resistive) are excellent particularly the 1Khz SQR wave. This amp out performs the ZCA many times. Still only two caps in the signal path.


Be the first to build a fully fleshed-out MCA.
Attached Images
File Type: jpg MCA_I.jpg (452.2 KB, 409 views)
File Type: jpg MCA_II.jpg (376.4 KB, 363 views)
File Type: jpg MCA_PS.jpg (326.3 KB, 337 views)
File Type: jpg MCAI.jpg (51.9 KB, 377 views)

Last edited by mhouston; 22nd July 2012 at 12:43 PM.
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Old 3rd October 2013, 04:58 PM   #2
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Hello Mr Houston!
I am interested in building the MCA however I have trouble obtaining the 2sk170 or lsk170 .
Will it be possible for me to substitute another device in its place. ( I have BD 139,BD140,IRF 611,IRF 510 in my parts box).
Along with that, I will like to replace the 15R load resistor with a halogen bulb. Will a 24V 40W bulb suffice?
Thanks in advance.
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Old 3rd October 2013, 10:10 PM   #3
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Quote:
Originally Posted by Quartz19208 View Post
Hello Mr Houston!
I am interested in building the MCA however I have trouble obtaining the 2sk170 or lsk170 .
Will it be possible for me to substitute another device in its place. ( I have BD 139,BD140,IRF 611,IRF 510 in my parts box).
Along with that, I will like to replace the 15R load resistor with a halogen bulb. Will a 24V 40W bulb suffice?
Thanks in advance.
Sorry I can't comment on the use of other driver components or loads. I have only built a rough prototype. I would try yo source the 2SK170 at least. Be aware the Drain and the source are incorrectly marked on the schematic.
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Old 4th October 2013, 03:55 AM   #4
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Thank you.
Do you mean to say that the schematic symbol for the jfet is wrong or the indication is wrong.
Thanks again!
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Old 4th October 2013, 06:02 AM   #5
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Originally Posted by Quartz19208 View Post
Thank you.
Do you mean to say that the schematic symbol for the jfet is wrong or the indication is wrong.
Thanks again!
Just swap the letter "D" and the "S". The jFET is drawn correctly I just labeled the two legs incorrectly.
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Old 4th October 2013, 07:10 AM   #6
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Why not amend the schematic, also emphasizing the 4-way junction at the output node, to avoid confusion since many newbs are attracted to such simple circuits with low parts count and being absolutely clear across language problems helps everyone.

I'm afraid the 2SK170 is also obsolete now but DIYAudio store has made LSK170 available. The problem remains for all the guys who try to use cheap fakes as an unavoidable part of their hobby. Many just don't want to know that their projects won't work properly without genuine parts or even what junk they are actually buying, which is sad, really.

If you experiment with the use of BJTs or at least affordable JFETs with some future, you'll have a lot more happy followers and a better reputation, so keep up the development work.
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Last edited by Ian Finch; 4th October 2013 at 07:12 AM.
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Old 4th October 2013, 07:28 AM   #7
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Originally Posted by mhouston View Post
Just swap the letter "D" and the "S". The jFET is drawn correctly I just labeled the two legs incorrectly.
Sorry this makes me look foolish but the drawing of the schematic and and lettering maybe correct. Proceed with caution. I feel like a dill but I would rather say something than not.

Can anyone confirm which is correct?
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Old 4th October 2013, 07:53 AM   #8
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The fet appears to be correct in the schematic, source=emitter drain=collector.
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Old 4th October 2013, 08:08 AM   #9
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An N-Channel source-follower has the Drain to +ve rail and Source (output) to -ve, as per your schematic, actually and not (as I just assumed it to be) incorrect.

Interestingly, small signal JFETs are electrically the same either way around, so it's likely you can't tell the difference anyway
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Old 4th October 2013, 08:31 AM   #10
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Quote:
Originally Posted by Ian Finch View Post
An N-Channel source-follower has the Drain to +ve rail and Source (output) to -ve, as per your schematic, actually and not (as I just assumed it to be) incorrect.

Interestingly, small signal JFETs are electrically the same either way around, so it's likely you can't tell the difference anyway
From the close-up image of the jFET and transistor it looked correct in the schematic. Not sure why I got confused and second guessed myself. There has been none (MCA) built in the wild yet. I'm still waiting to here from some one who will build one. The ZCA is still getting new followers.
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