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Old 28th March 2010, 04:22 PM   #521
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Hi Ruwe,

meanwhile i desoldered the mains and measured them, the C-B is about 560Ohm in one direction and closed in the other while C-E is closed in both directions. Those are defenitly gone. Desoldered and measured the TIPs the 0.22Ohm resistor and and the other transistors and they seem to be ok. I ordered the 2SC5200 , the TIPs and the 0.22 resistor now to be on the safe side. Lets see next week.

Regards haggyhug
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Old 28th March 2010, 04:48 PM   #522
Ruwe is offline Ruwe  Europe
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Originally Posted by haggyhug View Post
Hi Ruwe,

meanwhile i desoldered the mains and measured them, the C-B is about 560Ohm in one direction and closed in the other while C-E is closed in both directions. Those are defenitly gone. Desoldered and measured the TIPs the 0.22Ohm resistor and and the other transistors and they seem to be ok. I ordered the 2SC5200 , the TIPs and the 0.22 resistor now to be on the safe side. Lets see next week.

Regards haggyhug
Hi,
When you say "closed", does it mean "short" or "open"? It's normal to have open between C-E in both directions. B-E and B-C should measure something in one direction and open in the other (like diodes)... but again, for power transistors it doesn't always mean 100% good.
Replacing them all is the easiest troubleshooting
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Old 18th April 2010, 08:13 AM   #523
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Default Naim NAP140 clone - re-design

Sorry to open this threadie up again ....but ....I bought a couple of NAP140 Boards in curiousity; and something claiming to be a Mark Levinson design - but firstly with these so called NAIMs

The circuit that came from China I checked with the board and I immediately asked - "why so many compensations in the design, what were they fighting against?". Is it phase correction to reduce X-over distortion? - Why so much HF filtering to prevent HF instability? Why all that spare capacitance to slug the amplifier down? We all know that using capacitors as "frequency dependent resistors" introduces phase angles and reactive impedances

So I sat down and did some maths - examining Xc = 1 over 2π FC - then doing the Rect/Pol conversion to find reactive impedance
Then began loading the circuit into into Spice to play with it.

I have to say the findings are a bit quirky and all these strange compensations doesnt enhance things very much
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File Type: jpg naim-nap.jpg (125.2 KB, 1069 views)
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Last edited by PhaseLockLoopy; 18th April 2010 at 08:17 AM.
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Old 18th April 2010, 08:20 AM   #524
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Default aaargh it's horrible

I dont have all of the Q models in spice - but that isnt going to do much compared to all that passive

This is all looking like a bit of a duffer tbh

yeeeuch
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Old 18th April 2010, 11:55 AM   #525
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Default cleaned it up

What a minger

Now it's more efficient and i've thrown an enhancement idea in there if anyone (like me) who is running complex and demanding loads. Also took out all the phase compromises and claptrap outta there causing a wild load of phase shift for no apparent purpose other can causing unwanted harmonic and phase effects. Put my signature signal conditioning in at the front.

Given the input the proper reference current - took a different view of the feedback path along with it's DC quantity to deck via R21 for the bases of Q3-Q4 and lifted it above chassis with ground return.

Cleaned out the unnecessary. Put some thermal tracking via bias chain with a single diode D5 of which there are a range that could take that space -
the 1N4148 is all I had close as a model -

Improved the component list to modern day and some Motorola and Toshiba favorites/reliables. Cleaned out all the anti RF stability crud and kept it simple with c6.

Less components - more music - better thermal - less phase distortion - better dynamic range -- less sluggish in the bass - less colapse of range in the treble through all that unnecessary filtering, and as long as the PSU has enough uumph ... more capable on difficult loads (Cambridge Audio R50's - KEF 102/4 Reference - Linn Ice Bricks (Isobarik) etc.

Oh I made it more efficient too -- it was burning off energy for no purpose
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Old 18th April 2010, 12:56 PM   #526
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What you end up with is basically a self blameless, the nap was designed like that because apparently it has a particular sound and from what I see a lot of people liked it.

I was reading a review of current naim amps the other day and in one review it was stated that naim still uses the same old nap250 circuit in one of their current amps and this was testemony for the quality and sound of their amps. I was highly susrprised and have been trying to verify this but now Ive lost the link to the review as well as I accidently cleaned the browsing history. The nap250 is basically this nap140 with more output trannies. Interesting if the writer of that review is correct..........
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Old 18th April 2010, 03:59 PM   #527
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There is an error in your last drawing re the constant current stage for the diff pair and vas stage
Found your comments rather interesting I am not sure if I agree with all of them !

regards Trev
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Old 18th April 2010, 06:12 PM   #528
Ruwe is offline Ruwe  Europe
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Quote:
Originally Posted by PhaseLockLoopy View Post

Less components - more music - better thermal - less phase distortion - better dynamic range -- less sluggish in the bass - less colapse of range in the treble through all that unnecessary filtering, and as long as the PSU has enough uumph ... more capable on difficult loads (Cambridge Audio R50's - KEF 102/4 Reference - Linn Ice Bricks (Isobarik) etc.
Hi,

Interesting thoughts and ideas! I just didn't understand are you listening to this amp, or your design is a result of simulation only? ... In my experience the simulation rarely represent the reality ... The original design is not overcompensated. I could easily make it oscillate with slightly capacitive speaker cables. So, I guess the R/C groups are a necessity.
Why such a big inductance at the output? Is there any specific reason? ... The original schematics doesn't have any, the revised kit versions are using no more than 1uH//10-15 ohms.

Regards
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Old 18th April 2010, 06:50 PM   #529
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Quote:
Originally Posted by Ruwe View Post
Hi,

Interesting thoughts and ideas! I just didn't understand are you listening to this amp, or your design is a result of simulation only? ... In my experience the simulation rarely represent the reality ... The original design is not overcompensated. I could easily make it oscillate with slightly capacitive speaker cables. So, I guess the R/C groups are a necessity.
Why such a big inductance at the output? Is there any specific reason? ... The original schematics doesn't have any, the revised kit versions are using no more than 1uH//10-15 ohms.

Regards
I have two boards -- I've decided for the interest of my curiousity to build the old variant on one - and the proposed simplified version on the other. Simulation can only show an indicative model - a lot could come out of final experimentation by physically testing and researching through the differences. Those R/C groups may have been a necessity in the day it was designed. With a phisical examination - we'll see what's what.

But like Bruce Lee and his "Tao of Jeet Kune Do" - get rid of the waste and strip back to essentials
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Last edited by PhaseLockLoopy; 18th April 2010 at 06:59 PM.
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Old 18th April 2010, 07:05 PM   #530
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Default Speaker protection

Hello

I built my Naim clone after the Avondale NCC200 schematic .
All I can say is a great amp , I had before the Ebay kit but these has far better sound .
I have only one big problem !
When I turn off the amplifier and the power goes done at the PS capacitors when it reach around 10V the power stage open up and 6-7VDC goes out on the speaker terminal .
I would like to avoid to the DC voltage destroy my speakers .
Can someone suggest a good quality speaker (DC) protection ?
I need something simple so I do not need to break the bank .
Also have to be reliable and minimal or no effect (downgrade) on the amplifier sound .
Thank you
Cheers
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