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 Post subject: Re: MCA - Son of ZCA
PostPosted: 21 Jul 2012, 19:02 
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redsky wrote:
mwhouston wrote:
Its good to see you all like the ZCA so much. It's so simple and works so well. I can't comment on the other Fets I have only used the 2SK170 BL - dead quiet and good gain. You can match the Fets too. In fact you should. I have only built one channel and mixed the two channel to give mono. But from what I heard I think it is a better performer than the ZCA. It tests much, much better than the ZCA.


Hi Mark,

For my interpretation on the ZCA concept. The simplicity is to avoid any noise from the component. To get the purest sounds. Is that right ?

So, I think we can start to make a fairly comparable about the ZCA.I don't know how. But I think, you all is had an good experience with high end system.

On MCA you are using 2N3055, why not using SK1058 ? I think each Fets has a specific sounds charateristic. Why not using different transistor in the same configuration ? With the same configuration, the same cable, and the same speaker it is fairly comparable if you make a conclusion about the final results.

I'm not a big fan of Fets. After saying that I think they are perfect in low current, low signal devices like preamps, phono preamps and front ends to power amps. After quite a number of conversations with very experienced designers and amp builders I feel bipolars, particularly where high current is required (back-end of a power for example) will produce a "better" sound than a Fet in the same position. "Fet mist" is a term I have heard to put a handle on how Fets can sound.

There is no question I could have done more fine tuning with the original ZCA but I really wanted to try something with bipolars. Part of the ZCA philosophy is to use simple, readily available "off-the-shelf" parts in a dead simple, minimum component amp. The ZCA does this, the MCA does this. The MCA is true to the original goal but improves on the original design and this is born-out in the CRO results. If I could have driven the 2N3055 without the jFet I would have. But maybe I'm getting the best of both worlds here with a Fet up front in the low power part of the cct. and a big hefty bipolar handling current. Not only that I have eliminated any sort of connecting component between the two. No inter-stage cap, direct connection. Component count is down and de-focusing caps (all caps do this) in the signal path are kept to absolute minimum. Of course the problem of low power exists so very efficient speakers are required.

The MCA tests over 500% better than the ZCA, the active devices run cool no need for a big heat sink, the parts are very cheap, there is only one additional component compared to the ZCA and it sounds better. The upper frequency range of the ZCA (my ZCA anyhow) was 30KHz the MCA goes flat to 125Khz!! I think this is due to the lower capacitive characteristics of the 2N3055 compared to the power Fet. Build one and tell me which you think is better.

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 Post subject: Re: MCA - Son of ZCA
PostPosted: 21 Jul 2012, 19:23 
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Here is a better looking schematic for the MCA. I may do a PS schematic but the original one from the ZCA can be used.
Attachment:
MCAI.jpg


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 28 Jul 2012, 09:51 
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I was really hoping some one would build a complete MCA but it appears it is not going to happen. I can remember Sarich http://www.powerhousemuseum.com/australia_innovates/?behaviour=view_article&Section_id=1020&article_id=10041 who invented the orbital engine saying "Just because you invented it doesn't mean people will beat a path to your door".

I'm hoping to build mine in a 1U 19" rack enclosure with two 24V low profile toroidal trannies. I may make the amp a true dual construction and integrated with a BoZ preamp included. Only heat issues are around the load resistors. I have thought about a battery powered unit but that would make it bulky and heavy. The 1U case excites me and could make a really smart looking, very sleek compact build.

I have another design yet to try called "MCAD" - Daughter of ZCA. The MCAS first.

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 Post subject: Re: MCA - Son of ZCA
PostPosted: 30 Jul 2012, 01:43 
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Mark, prior to the ZCA, I did build a bipolar single ended power amp using a 2N3055 being driven by a BD139 and possibly a small T092 input transistor for gain(I think?).

I still have the circuit diagram at home somewhere.
There were a LOT more components to make it work and it was only 2 watts or so .........apparently.

What did it sound like?..............................I built a ZCA and never looked back.

I'll try to dig up the circuit if you'd like?


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 30 Jul 2012, 02:00 
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ziggy wrote:
Mark, prior to the ZCA, I did build a bipolar single ended power amp using a 2N3055 being driven by a BD139 and possibly a small T092 input transistor for gain(I think?).

I still have the circuit diagram at home somewhere.
There were a LOT more components to make it work and it was only 2 watts or so .........apparently.

What did it sound like?..............................I built a ZCA and never looked back.

I'll try to dig up the circuit if you'd like?

Its easy to make a darlington pair out of any power and driver transistor. I'm glad you like your ZCA.

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 Post subject: Re: MCA - Son of ZCA
PostPosted: 19 Aug 2012, 19:19 
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Mark, I have found the circuit and yes, ..............it was a 2N3055 driven by a BD139 and a small T092 bipolar for gain.
Not as many components as I thought, but simple enough to be of interest.
I forget how it actually sounded and may have dismantled it prematurely when the ZCA came along.

I think I'll give it a go again.......................you never know what kind of sound it will produce?


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 19 Aug 2012, 20:16 
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ziggy wrote:
Mark, I have found the circuit and yes, ..............it was a 2N3055 driven by a BD139 and a small T092 bipolar for gain.
Not as many components as I thought, but simple enough to be of interest.
I forget how it actually sounded and may have dismantled it prematurely when the ZCA came along.

I think I'll give it a go again.......................you never know what kind of sound it will produce?

Do you have the schematic?

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 Post subject: Re: MCA - Son of ZCA
PostPosted: 19 Aug 2012, 23:01 
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Yes, I have it at home.
I'll bring it in to work with me tomorrow and scan it then post.

Will be interesting to see what comments/thoughts arise from this circuit? ;)


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 20 Aug 2012, 02:02 
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Here is the Schematic :
Attachment:
rudyproto1.gif


Good for two watts only.


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 20 Aug 2012, 02:18 
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ziggy wrote:
Here is the Schematic :
Attachment:
rudyproto1.gif


Good for two watts only.

Hey I have the cct. and intend to build it. I like it 'cause it is a cathode follower and though low power also have very low output impedance. My "Woody" series use cathode follower for headphone driver/ preamp. I like the sound but some don't when used as a preamp.

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