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Old 10th May 2013, 07:38 AM   #11
sajti is offline sajti  Hungary
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Hi,

2 of my friends try to build this amp, with many many problems. I don't know what was the problem, but as I remember, there was no success.
This amplifier has NO any relation to Marant MA9. The owner of this design removed all features, what makes MA9 excellent amplifier....

Sajti
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Old 11th May 2013, 12:18 PM   #12
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Default I have a set running

Hi,

I have a pair of these with the MJL4281A + MJL4302A running on 63v rails as my garage workshop amp, I think from that vendor. I just assembled them and fired them up carefully with light bulbs. It was a while back and I think setting the bias was a bit tricky/a slow careful process possibly due to the servo. It was a while back and I don't actually remember what I set the bias to, I really need to check again.

They are hooked up to really old Celestion Ditton speakers with a passive (cheap!) 10K or 20K volume control with a Denon DAB radio. I think they sound bright and missing bass at the moment, the speakers usually sound too bassy and a little soggy on any amp (which I may be a little accustomed to..)

I need to have another look at them and see if I can get the bass better. The servo is perhaps a bit crude with a time constant of .47s, removing it on the SPICE sim improves the response, perhaps I can just lift the opamp and check what offset I get and have a listen.

What input cap do you have on yours? I have a small looking Ero 3.3uf
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Old 11th May 2013, 10:55 PM   #13
clm811 is offline clm811  United States
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Default Check.

Check.

Anyone else?

I will continue to post test results after the second set of boards arrive.

-Chas
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Old 12th May 2013, 07:33 AM   #14
clm811 is offline clm811  United States
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Quote:
What input cap do you have on yours? I have a small looking Ero 3.3uf
Mine came with a pair of (green) 2.2uf Ero MKT1812, but I substituted two 4uf Auricaps. -

-Chas
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Old 12th May 2013, 11:36 PM   #15
clm811 is offline clm811  United States
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Default Pics

Here are pics showing the right channel pcb before- and after, stuffing and attachment to output devices on heatsink using spreader bar.

More pics to follow
Attached Images
File Type: jpg MA9 boards.jpg (482.0 KB, 172 views)
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Old 13th May 2013, 01:50 AM   #16
clm811 is offline clm811  United States
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Taking a week off for Heart procedure Angioplasty and stent(s), so will post again once I recover.

Wish me luck.

-Chas
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Old 13th May 2013, 06:57 AM   #17
sajti is offline sajti  Hungary
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Quote:
Originally Posted by clm811 View Post
Taking a week off for Heart procedure Angioplasty and stent(s), so will post again once I recover.

Wish me luck.

-Chas

I wish!
Check the 1k trimpot, before startup. It must be on the maximum resistance setting!

Sajti
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Old 13th May 2013, 04:26 PM   #18
pchw is offline pchw  United States
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Good luck, Chas!!
__________________
- Fred -
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Old 15th May 2013, 07:51 AM   #19
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Hi all !

I recently assemled this kit without any problems, is stable.
Some measurements, power supply is +-40V

SQR 10kHz into 4.5Ohm
http://i.imgbox.com/actdYwnr.jpg

SIN 10kHz lim into 4.5Ohm
http://i.imgbox.com/acgFTX8t.jpg

SlewRate=28V/us C4=220pF ( with C4=68pF SR=45V/us)
http://i.imgbox.com/acoi6BWW.jpg

SQR 10kHz into 4.5Ohm + 470nF ( R+C parallel)
http://i.imgbox.com/abmeghe5.jpg

Laci

Last edited by maci.laci; 15th May 2013 at 08:11 AM.
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Old 18th May 2013, 12:59 AM   #20
clm811 is offline clm811  United States
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Taking another week off for Heart procedure: Angioplasty and one more stent, so I will post again once I recover.

might have time to post a few more pics of the amp.

-Chas
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