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Old 28th November 2012, 03:52 PM   #611
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by jprco View Post
.................... When I assemble the amp as per the guide and do the bias adjustment with only 1 MJE4281 and 4302, I set it to 24m between MP!/MP2 no problem. But when I insert the second pair of MJE's, the value measured jumps to about 48mV - do I need to readjust the pot back to read 24 mV or leave it at aROUND 48 mV.
The other question was if it easier to adjust the bias measuring the voltage across say a 100R resistor instead of the fuses (after everything with the board as checked out okay) as was done with the DX type amps................
MJEs, not for output devices.
If you havean output bias that changes from 24mVre to 48mVre by adding and extra pair of output then you have a broken amplifier.

Revert to single output pair and check what you post and edit the data if necessary.


DO NOT set and measure the amplifier quiescent current by measuring across 100r resistors in the fuse location. This is very bad practice. DX has been told this repeatedly but he refuses to listen and keeps posting the same wrong information.
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Last edited by AndrewT; 28th November 2012 at 03:54 PM.
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Old 29th December 2012, 09:48 AM   #612
Junie is offline Junie  Philippines
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Finished Amp.

Click the image to open in full size.
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Junie
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Old 29th December 2012, 09:59 AM   #613
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Junie: your build looks absolutey nice and attests you great craftsmanship!

I hope that you like the sound of the SYMASYM as well.

Best regards - Rudi
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Old 29th December 2012, 10:07 AM   #614
Junie is offline Junie  Philippines
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Thank you Rudi,

The sound is fantastic, though I made a bias conservatively due to small heatsink. I'm happy that katie melua voice is really good on this amp :-)
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Old 29th December 2012, 06:05 PM   #615
evette is offline evette  Canada
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Hey Mr. Junie Can I have 1 For christmas past Pleaseeeeeeeeeeeee. Evette
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Old 30th December 2012, 08:44 AM   #616
Junie is offline Junie  Philippines
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Hi Joe,

How I wish Canada is only a kilometer away from my place so i can bring my amp and try in your speakers then we can have a tea and listen to your favorite tunes. HAPPY NEW YEAR !!

With warm regards,
Junie
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Old 30th December 2012, 05:19 PM   #617
atupi is offline atupi  Romania
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@Junie congratulations for your build. I love your case, and how you organized everything inside.
Regards,
Adrian
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Old 30th December 2012, 06:06 PM   #618
brianco is offline brianco  Ireland
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Being new to this business of DIY solid state power amps I have little idea of heatsink requirements. [Juni's remarks that his heatsinks are small has reminded me of this fact.]

I have a pair of sinks which are 200mm long, with 40mm fins [including 10mm backplate] and fins on 8mm centres, and 160mm high. Are these adequate for this amp? Or can I reduce the heigth to a more ideal size [as I suspect that too much radiating surface can be detrimental]?

The rest of the case will be made from 7.5mm alloy plate. I intend plenty of ventilation and to place the heatsinks on the external sides. Having plenty of alloy I am considering building the heavy end of a dual mono PS in a seperate chassis.

Lastly, what size transformers will adequately cover the needs for such a supply?

Thank you for any advice you may be able to offer.
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Old 31st December 2012, 01:55 AM   #619
evette is offline evette  Canada
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Junie You,ll always be able to visit me with the most warm welcome You always have a great pleastant thing to say Thank You MY FRiend. Joe
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Old 31st December 2012, 07:25 AM   #620
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Brian, your heatsinks are more than adequate. Any 1 C/W heatsink will do it.
Concerning the transformer: if you plan to build a dual-mono design (like Junie did) I recommend you to use 2 x 25 VAC / 160W.
Else take 1 transformer, 2 x 25 VAC / 250W - 300W. This is what I am using myself.

Best regards - Rudi_Ratlos
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