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 Post subject: Re: MCA - Son of ZCA
PostPosted: 05 Dec 2014, 16:38 
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max130 wrote:

I though I need bigger/more capacities but the Output looks not too bad.
What do you think, should I try bigger caps or not?

best regards
Stefan


Hi max130

About bigger capacity = I have to say yes ...i have a totally humfree amplifier running. I use 30 VDC 66000 uF caps in a CLC filtered PS. This setup ( 66000 uF - 10 mH - 66000 uF ) has a voltagedrop of 2 VDC.



I took a picture where you can see a couple of other chokes i've made. If you have an old transformer it an be changed to a nice choke ( actually two ). Note the left one in the foreground is a 1 H choke ( made from the primary coil = 220 V / 87 V scraped toroidal transformator ) where i've cut a slice/gap into the toroidal core with a saw, which makes it perfect for choke use. The blue one in the background is used in the shown amp's setup and has a inductance of 10 mH and the coil is the secondary coil, coming from the one in the forground ( wounded up on some plastic spools i've found in a scrap-dump ). The last grey one is also a diy and has an inductance of 6 mH and with big caps it actually also does a humfree PS ...but with a lower voltagedrop. The cores in the blue and grey one comes from loudspeaker coils.

On my scope i see a straight DC line ...AC is almost not noticeable !

Go for it 8-) ...get a good bank of caps ...the more the better. You can couple more of those 4700 uF in parallel as you already got, it will do the job ( try adding more caps like the edited schematic below, you've made ) ...and remove the resistor. The combination with a good choke you'll get much better sound than a resistor can offer in a CRC filter.


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 05 Dec 2014, 17:51 
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Location: Australia
How big is your choke and what is its current carrying capacity?

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 Post subject: Re: MCA - Son of ZCA
PostPosted: 05 Dec 2014, 19:12 
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Location: Germany
Me?
it is the Hammond 10mH 5A Choke we have seen with the ZCA

Stefan

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 Post subject: Re: MCA - Son of ZCA
PostPosted: 05 Dec 2014, 19:19 
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Kramme
when I remove one of the 2R2 I have 28V Output, without it (as you suggested) it's 32V and the AC is 5 times bigger.

I think i will stay with CLCRC as it smothens the Output well and reduces the voltage to the value we want to have (28V).
I use 3-3-4 caps now, so 47000 uF in total.

Having those huge chokes and caps you are using may be an upgrade for the future.
Impressive what you do there

Best regards
Stefan

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 Post subject: Re: MCA - Son of ZCA
PostPosted: 05 Dec 2014, 19:53 
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All sounds good. That must be a huge choke.

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 Post subject: Re: MCA - Son of ZCA
PostPosted: 06 Dec 2014, 16:16 
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max130 wrote:
Kramme
when I remove one of the 2R2 I have 28V Output, without it (as you suggested) it's 32V and the AC is 5 times bigger.

I think i will stay with CLCRC as it smothens the Output well and reduces the voltage to the value we want to have (28V).
I use 3-3-4 caps now, so 47000 uF in total.

Having those huge chokes and caps you are using may be an upgrade for the future.
Impressive what you do there

Best regards
Stefan


Hi max130 - Stefan

28 VDC is just fine ...no problem, in my test configuration the MCA were running for several days as far as up to 35 VDC ....later i turned it down to under 30 VDC ( no problem with heat ...because i'm running the load with 3 x 12 V 20W bulb's in a serialcoupling, instead of 15 Ohm resistors per section ). The important matter for you is a hum/ripple free PS ..so if this is 28 VDC then just run it there. The rule is still half voltage measured between drain and the 15 Ohm resistor = then 14 V in your case :-)

Yep, have your eyes open ...look around at electronic scrap yards for frequency converters and computer supplys ( ex. backup power supply's ), they often contains big heatsinks and big electrolytic capacitors, even good MosFet's to. I think the employers at your place are just the same as here in Denmark = a six pack of beer, in exchange does the job. Remember to have some tools like a wrench, screwdrivers and cutters with you. To be safe look for high voltage electrolytic capacitors ...dont touch the leads :!: , if they not are empty and still contains high voltage. For even better security a pocket multimeter can become handy beside your tools.


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 10 Dec 2014, 14:39 
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Location: Germany
Yes Kramme, I will have a look for components but here in Germany it is difficult to go in touch with old equipment.
When old devices reached the recycling area there is no chance to get them out again.

My update:

Attachment:
DSC_1534.jpg


I did not increased the capacity yet but took better care for proper grounding. The hum is now nearly gone, just noticable directly in front of the speakers.

The two ceramic 4.7 R in parallal in the psu are running very hot. I have measured 125°C.
How long do they last at this temperature?

The big 15R and the transistors on the heatsink are staying under 40°C.

The Sound is impressive although not far ahead of the ZCA in my opinion.
The MCA is sounding a bit more detailed, somehow "faster" and more "direct".
Bass seems even more precise than ZCA.
The ZCA on the other hand is sounding very relaxed for listening for a long long time without getting rid of the musik and just a little little less detailed. Maybe a bit less 3D.
This is what I have noticed after listening to just a few tracks (Yello).

Next step will be a bit more capacity, even better grounding and a nice enclosure.

BR
Stefan


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 10 Dec 2014, 16:30 
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About ceramic power resistors ...they are able to handle lot of heat. Just remember the limitation is what they are rated for in Watt !

An example:

For simplicity, lets say you've got a voltagedrop of 5 VDC, the formular is following:
Voltage (E) = 5 V
Current (I) = 2 A
Resistance (R) = 2,5 Ohm
Power (P) = 10 W

Another example:

If you've got 4,7 Ohm 10 W resistors in parallel with a 5 V voltagedrop the formular is following:
Voltage (E) = 5 V
Current (I) = 2.12766 A
Resistance (R) = 2.35 Ohm
Power (P) = 10.6383 W
which is a bit over the edge ....but very close !

Measurements should be done by testing the voltage over the resistors ! :wizard:

Now is the time for you to tell what the resistors are rated for in Watt and what the voltagedrop measurements in VDC is over the resistors !

Next step= yep, bigger capacity, but also try removing these resistors in the PS and maybe place a better/bigger choke. One choke + big capacity in a CLC filter will do the job.

By the way i love to see your amplifier mounted on a wood plate :up: ...that's the same way i made several of my amplifiers, instead of building into metal enclosures. It's all about listening to music ...it's not a beauty contest. Image


Last edited by KrammeAcoustics on 10 Dec 2014, 17:33, edited 1 time in total.

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 Post subject: Re: MCA - Son of ZCA
PostPosted: 10 Dec 2014, 17:12 
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Location: Germany
It is 4.4 V over 4.7 Ohm so a Little less than 1A for each resistor in my calculation.
The resistors are 17W types so theoratically no danger.
But I would have not expected the Rs getting that hot with that underrated load.

My concern when changing to CLC (getting rid of the Rs) is that the voltage would be at 32 to 33 V then which might be too high (see my post last page).
So the reason for having those Rs is dropping the voltage rather than filtering in my case.

Regards
Stefan

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 Post subject: Re: MCA - Son of ZCA
PostPosted: 10 Dec 2014, 17:14 
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About sound:

Have you tried different caps for both input and output, related to best performance ?

If i'm not wrong it looks like you're using SCR paralleled on the output electrolytic ( not necessary, often it brings a hiss and distorted sound ) and the small yellow-thingys as input caps (?). These yellow ones can be done better, i promise you. I've also added those caps in the illustration, just to know for sure if it's the same caps !

In the attached illustration, you can see the orange Philips ( i'm using them as input cap ) ...they do a very nice job when it comes to detailed sound. I'm using only Nippon electrolytics for the output, stand alone ( without paralleled small caps ). After tons of listening tests with a lot of different caps, i finally found a nice combination. If you have some, try it !


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