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MJR7-Mk5 by Renardson
MJR7-Mk5 by Renardson
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Old 10th January 2017, 07:59 PM   #21
MikeRenardson is offline MikeRenardson  United Kingdom
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Join Date: Oct 2004
The wide ranges specified for the mosfet parameters may not be a serious problem in practice, all the recent samples I bought are fairly well matched, with close to 0.6V Vgs at 100mA quiescent current. Of course that could just be luck, but I found a description by Exicon for their lateral mosfets as 'Well matched on Vgs' even though they still use the 0.15 to 1.5V range in their data sheets.

Exicon Lateral MOSFETS - Why use Exicon?

Regarding quiescent current the maximum adjustment is limited by the LED in parallel with the 220R preset, which limits the gate to gate voltage to about 1.7V, which could be too low if the specified maximum Vgs at 100mA was ever needed for both n and p-channel devices, then adding one or two forward biased 1N914 or similar diodes in series with the LED is a solution, but I am not aware of anyone having that problem.

I expected to find lower distortion with higher quiescent current than the recommended 100mA, but found some higher order harmonics increased a little. Using less than 100mA increases open-loop output impedance and may adversely affect stability with reactive loads, so 100mA is both the minimum and recommended level. The exact value is not critical, I usually set my own amplifiers to 120mA total current per channel.
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Old 15th March 2017, 10:03 PM   #22
Livius is offline Livius  Sweden
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Join Date: Feb 2012
Location: Mölndal
Hi

Finaly I finished the power amplifier. It sound realy good. I'm impressed with the sound quality.
Here is some picures off the amplifier and case. It's a 300VA transformer. Supply voltage is 66.6V and the quiescent current is set to 150 mA.
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File Type: jpg eff1.jpg (258.9 KB, 373 views)
File Type: jpg eff2.jpg (184.0 KB, 364 views)
File Type: jpg eff3.jpg (137.3 KB, 352 views)
File Type: jpg MJR7-Mk5.jpg (212.4 KB, 354 views)
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Old 31st March 2017, 05:09 PM   #23
J.M.K is offline J.M.K  France
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Join Date: Jan 2009
Location: France
Default Blowing fuses ..........

Hi,

I have a MJR7-MK5 that's always been working fine until today.
Built exactly as it should ..........
I get 62V DC from my supply, source voltage set to 31V, and quiescent current to 120mA.
The sound is great.
I used to have it working previously with other speakers than the one I'm having now - and these new speakers are needing more current.
Just for the fun, I tried to push the volume very high, and blew the 2A fuse.
Is it ok the have a 2.5A or 3A fuse with this board ? Or not ?

Thanks in advance .......

JMK
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Old 31st March 2017, 05:25 PM   #24
J.M.K is offline J.M.K  France
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Join Date: Jan 2009
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Default And a picture !

And here is a (not that good) picture of my amplifier !

JMK
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Old 31st March 2017, 06:51 PM   #25
latala is offline latala  United Kingdom
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Join Date: Feb 2006
Location: staffordshire
MJR7-Mk5 by Renardson
Mike Renardson
I have been trying to contact you for nearly 20 years ever since your improved class b amplifier
Please send me a pm
TREV
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Old 31st March 2017, 07:04 PM   #26
MikeRenardson is offline MikeRenardson  United Kingdom
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Join Date: Oct 2004
Hi J.K.M.

The 2A-T fuse was originally specified for an earlier version with a single channel on each board, so the single fuse for two channels on the Mk5 board could be rated for a higher current. I mentioned that somewhere in the design notes. According to some sources T-type anti surge fuses, can typically survive at 10 times their rated current for about 100 msec, and at 5 times the rated current for 1 sec, so a 2A supply line fuse is not necessarily a serious limit to output power. With low impedance speakers driven at continuous high power, then provided the heatsink is not getting too hot , a 3A-T fuse should be ok.

Mike
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Old 31st March 2017, 08:52 PM   #27
J.M.K is offline J.M.K  France
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Join Date: Jan 2009
Location: France
Hi Mike !

Thanks a lot. I'm going to try a 2.5A-T first and see what happens.

And give you more decent pictures of your baby ........

J-M

PS: and if everything is fine, I intend to change its power supply for a 60V SMPS

Last edited by J.M.K; 31st March 2017 at 08:55 PM.
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Old 4th April 2017, 08:28 AM   #28
boyet0173 is offline boyet0173  Philippines
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Join Date: Jun 2011
Hi Livius ,

Can you share your pdf layout. Interested to build.

Thanks,
Boyet
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Old 5th April 2017, 06:43 PM   #29
Livius is offline Livius  Sweden
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Join Date: Feb 2012
Location: Mölndal
Default Board

Hi
Off course you kan get a pdf. I like this amplifier very much so I am happy if more people builds this small wellsounding amplifier made by Mike Renardson.
Read his komments how you adjust the amplifier. Here is the link Audio Amplifier Design
If someone are interested in the Eagle-file I can post that too.


Livio
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File Type: png MJR7-mk5 komponentside.png (60.2 KB, 123 views)
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File Type: pdf MJR7-mk5 sch.pdf (202.3 KB, 62 views)
File Type: pdf MJR7-mk5 board.pdf (101.1 KB, 49 views)
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Old 6th April 2017, 08:26 AM   #30
boyet0173 is offline boyet0173  Philippines
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Hi Livio, Thank you very much!

Regards,
Boyet
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