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 Post subject: ZCA project completed !
PostPosted: 12 Jul 2010, 06:47 
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Posts: 788
Location: Christchurch, NZ
Hi All,

I have recently built Mark's ZCA amp - http://diyaudioprojects.com/Solid/ZCA/ZCA.htm. This is the clearest amp I have ever heard which does not induce listening fatigue. Also one of the rare amps which does not make bass sound dry or with overhang. It sounds neither like a valve nor an SS amp. The tiniest nuances are heard and the overall presentation is ultra light and clear. None of the valve sweet warmth or lushness. This is pure neutrality at its best ! It even outclasses my reference Aussie Amplifier NXV200 solid state amp in the midrange which costs 10 times more. The only issue with this amp is your matching with suitable speakers. They need to be 90dB or more, preferably with a high dispersion silk dome tweeter. I am listening from 3m away and it has no problems powering my 90dB homemade Scanspeak TMM 2 way speakers. I am enjoying this amp so much that I will build custom 97dB speakers if I need more output in a larger room. (or try Ziggy's higher voltage version ZCA).

Please note that special care must be considered for chassis cooling. I have 2 external CPU fans
blowing on the external heatsinks. Here in Malaysia it gets very hot even with the AC on.
I drilled some ventilation holes directly above the tranny and a horizontal section above the load
resistors. The power tranny gets hot as it is an EI type. After powering everything, I touched the side
panels and felt the tranny's mechanical hum. Miraculously, this did not go through to the speakers.
The amp is dead quiet even with the Oatley K272 pre-amp kit connected. The power supply is critical in reducing hum. So don't skimp on the 10mH inductor used.

Total cost of parts: USD 130
Carbon film resistors, cheap electro caps and polyester snubbers.
160VA EI 18-0V tranny
Mundorf 10mH Iron Core inductor. 200 watt power handling. 0.4Ohm

Enjoy...
Attachment:
ZCA-whole-assembly.JPG

Attachment:
ZCA_top_panel.JPG

Attachment:
ZCA_Side_Heatsink.JPG

Attachment:
ZCA_front view.JPG

Attachment:
ZCA_SideBack.JPG

Kind Regards,
Dinesh


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Dinesh

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PostPosted: 12 Jul 2010, 11:04 
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Joined: 31 Dec 2008, 15:34
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Hi Dinesh

Congratulation, it's a nice build you've got there :up:

Everyone who builds Mark's ZCA construction are satisfied, so it really must be good 8-)

I've got all the parts except a choke ( or two ), i must get that, so i can make a ZCA to. It will be used in my shop, it's just a little room, so it's not required to have much power, but good sound is a must ( a couple of watt's is enough ). Maybe i could use two 6,8 mH inductors for loudspeakers in a serial coupling, maybe i'll try that first. I would also go for double powersupply, one for each channel. :idea:


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PostPosted: 12 Jul 2010, 11:34 
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Location: Christchurch, NZ
Hi Kramme,

Thanks for the kind words. The inductors need to be rated to handle 4 Amps and have low DCR. The indcutor I used is an audio grade Mundorf Iron Core, 16AWG which can handle about 200W of power. I do not know the max current it can handle but so far I have had no problems. They don't get warm at all when the amp is running.

So for your double power supply you need 4 chokes right?
ALso, what speakers are you going to use?

Regards,
DInesh

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PostPosted: 12 Jul 2010, 13:31 
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Hi Dinesh

Yes, four chokes, but i only got two of them. I guess they are able to handle high power, they are named Corobar, data in following link: http://www.intertechnik.de/Lautsprecher ... ,3742.html . I've also got two transformators with an output of 21,4 VAC, 6,5 A , i think they are great for the PSU ( 30 VDC output ).

The goal for me, will be usage of what i already have got in stock :xfingers: and not what i'll have to buy. :$:

Maybe it's possible to get it runing with only one choke pr. channel, as Dual PSU
Image

If not it should be possible with two 6,8 mH for a Single PSU
Image


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PostPosted: 12 Jul 2010, 18:47 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
Nothing wrong with a double Pi filter but not sure it is required. Only on my most efficient speakers do I hear a slight hum with one choke. The choke also helps make the sound. I'm a big believer in choked PS(s).

Dual supplies is a good way to go. The original ZCA is specced for 24V so if you go higher you may need to increase the load R. It's best to keep the load R low if you can. It will matched better with 8 ohm speakers.

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PostPosted: 12 Jul 2010, 19:15 
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mwhouston wrote:
Nothing wrong with a double Pi filter but not sure it is required. Only on my most efficient speakers do I hear a slight hum with one choke. The choke also helps make the sound. I'm a big believer in choked PS(s).

Dual supplies is a good way to go. The original ZCA is specced for 24V so if you go higher you may need to increase the load R. It's best to keep the load R low if you can. It will matched better with 8 ohm speakers.

Hi Mark

Do you think the shown Intertechnik inductors will be usable for chokes ?

It will be a dual PS then and i have a lot of 10 Ohm's 10W resistors, so the load can be 10 Ohm, by coupling 2 x 2 in serial/parallel or 15 Ohm load will also be possible with 2 x 3 of them in serial/parallel. I think 30 VDC PS are no problem or should i say ...i hope so. :xfingers: :horseshoe: :clover:


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PostPosted: 12 Jul 2010, 19:29 
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Location: Australia
As long as the chokes have the tuned air gap they should be fine. I have even used a 9mh Xover, iron core choke in a PS and it worked quite well. I think if you push for 30V you will have to increase the load R. The ZCA is very finely tuned and it doesn't take much to push it over the edge. Lucky FETs have a negative temp. coefficient.

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PostPosted: 12 Jul 2010, 19:33 
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Location: Winnipeg, CANADA
Congrats Dinesh, enjoy the amp! With the right speakers a SE FET can sound great!
Cheers

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PostPosted: 13 Jul 2010, 04:22 
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Location: Christchurch, NZ
KrammeAcoustics wrote:
It will be a dual PS then and i have a lot of 10 Ohm's 10W resistors, so the load can be 10 Ohm, by coupling 2 x 2 in serial/parallel or 15 Ohm load will also be possible with 2 x 3 of them in serial/parallel.

Use as many resistors as you can to reduce internal heat of the enclosure =)
Also keep the heat away from the electro caps/FET. I dropped some red ants on the 4 series-parallel resistors and they didn't survive for more than 1 second...

Gio wrote:
Congrats Dinesh, enjoy the amp! With the right speakers a SE FET can sound great!

Thx Gio. Am enjoying the amp now but will try building a more efficient speaker system to better match the amp.

Does anyone know the distortion levels of the ZCA, into 4 watts and total bandwidth?
It sounds so clean that im guessing it is below 0.1%.

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PostPosted: 13 Jul 2010, 05:31 
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dtsup1 wrote:
Use as many resistors as you can to reduce internal heat of the enclosure =)
Also keep the heat away from the electro caps/FET. I dropped some red ants on the 4 series-parallel resistors and they didn't survive for more than 1 second...

I knew it was a killer-amp :mrgreen: ...Let the ants, commands !!! :lildevil:


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