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Old 2nd August 2003, 01:24 PM   #1
sobazz is offline sobazz  Denmark
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Default P3A mono blocks finally finished (picture post)

Well, finally I've finished my P3A mono blocks. They are only rated 30w into an 8 ohms load, but this amount of power suits the cabinet as the top of it is used as heat sink. The xformer used is a 120VA 18-0-18. The output devices are MJL21193/94 - fairly overrated, one must add. The electrolytics are some cheap Rubycon 4700uF from Farnell. I chose them because of their small size.

There are two minor issues. A little bit of hum is present, but I have to put my ear all the up the midbass driver in order to hear it. I suspect that this is the result of placing the transformer this close to the amp circuitry or unshielded input wires. The input wires will be changed soon, but the hum is no problem.

The other issue is under dimensioned input caps. I used some Icel 1.5uF 1% polyprolene. They are definetly too small. I've ordered some 10uF polypropylenes from Elfa, but I'm sure if the space is too tight. I guess I'll find out.

Anyway, here's the pictures.

Click the image to open in full size.

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Old 2nd August 2003, 08:52 PM   #2
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It looks nice... but it doesn't sound nice (you say)... If an amp doesn't soend nice, the project is not yet finished i think.

Why monoblocks? That is more expensive.
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Old 3rd August 2003, 11:19 AM   #3
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realy cool !!!!!!!!!!!
!!

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Old 3rd August 2003, 12:18 PM   #4
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I'm in the process of making a P3A in quad configuration - i.e. two boards, one for each speaker.

It'll be used in as a passive bi-amped design - I would go active, but I don't want to risk my speakers warranty.

I'll post pics if it's finished any time soon !!
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Old 4th August 2003, 03:26 PM   #5
sobazz is offline sobazz  Denmark
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Thank you, Douchekop and Dj BASS AMP.

Well, when it comes to music reproduction these amps seems to do it rather well. Their power resources are of course limited, but still enough for my Mirage FRX-3.

When compared to my Harman/Kardon HK680 the bass roll off issue is very clear. I did sense the problem from the very first second these amps played. The HK680 has exellent bass reproduction and I doubt that these amps will ever get near, but at least they should be able reproduce bass below 20hz.... I'm shooting for a roll off at around 8hz by using a 10uF input cap.

The FRX-3 speakers are very laid back. But with these amp they seems much more "neutral". I'm looking forward to letting the P3A amps power my fathers Dynaudio MSP200.

They will definetly be much easier to judge with these speakers. And they will probably be pushed to the border.

The overall impression is definetly possive. But I cannot give them a fair critique as long as the input cap issue has not been corrected.

So yes, they are actually not finished yet..
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Old 7th August 2003, 05:59 PM   #6
sobazz is offline sobazz  Denmark
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I got the SCR capacitors from Elfa yesterday and installed the 10uF right away. Changing these certainly cleared up the bass issue. The space is _very_ tight, but they fit.
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Old 7th August 2003, 06:26 PM   #7
jleaman is offline jleaman  Belgium
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Very nice. Very nice. i wish i could get some of those cases as i have seen the a lot and want them. can you send me a link to where i can get them or maybe pass on some money to you to get me a few.. i would like to use them for my active x-overs as i need 4 cases. good job on the amps. : O)
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Old 8th August 2003, 07:59 AM   #8
Freddie is offline Freddie  Sweden
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JasonL,

You can get SCR caps from Elfa.

http://www.elfa.se/elfa/produkter/en/2012665.htm

/Freddie
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Old 8th August 2003, 08:44 AM   #9
UrSv is offline UrSv  Sweden
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Really nice amps. I really like those cases but so I should...this was one of my GC mono blocks:
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Old 8th August 2003, 02:06 PM   #10
sobazz is offline sobazz  Denmark
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That is certainly some nice clones, you've got there, UrSv. Is heat buildup a serious issue in your amps - at what rail voltage are you running the amps?

JasonL, the cases are - afaik - only available from Conrad in germany (www.conrad.com). The cases are not very expensive, but transport may very well change that. Isn't possible to get those cases or some like them in USA/Canada, anyone?
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