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Old 13th June 2017, 10:26 AM   #2561
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Yes indeed, same with all NAP clones built as per the original models. Note that this is not an instantaneous adjustment. The current will certainly change when you adjust the control but as the amplifier temperature then changes accordingly, it will slowly drift and settle to the new current. Before powering up, set the controls fully anticlockwise so that current is not set to maximum with the output transistors overheating. The process can take ages until you realise what goes on when you set bias current. To be more accurate and save time, lay the case cover in position with the meter leads still attached and after briefly raising the cover for each adjustment, continue to monitor the current as it stabilises to the new setting. Don't forget to read other reference(s) to Naim bias current setting method as per my earlier post and already detailed many times in this thread.

Also note that the Vbe multiplier transistors (next to the pots.) should actually be mounted on the bottom (copper side) of the PCB. This allows them to be close to the bottom plate which is also the heat sink and can give much faster settling. This is shown in pics and instructions attached to other seller's offers over the last year or so. Look around on the sites offering the CAOWEI boards.
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Old 16th June 2017, 04:59 AM   #2562
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Anyone else feel like the NAP200 sounds a bit bass anemic? I don't know if it's my room or setup, but it sounds bass light.

**Add
also a big shout out to Ian Finch, thank you very much for being one of the biggest help in this thread if not the whole section. He kept repeating the same thing over and over again and linking the http://www.acoustica.org.uk/t/naim/power_amps.html for information. At first I didn't quite understand what the page meant but I scrolled down and found the Minor Mods/Servicing section and it all just clicked and made sense. (Almost) everything is already in there; suggestions, measurements, general circuit layout, parts name, Adjusting the output DC offset, Adjusting the bias (standing current), TR11 & TR12 OUTPUT TRANSISTORS, TR1 & TR2 INPUT PAIR etc.
I am truly humbled.

Last edited by penmarker; 16th June 2017 at 05:14 AM. Reason: Added extra info.
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Old 16th June 2017, 09:48 AM   #2563
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Good that you found the information and suggestions about the original NAP models helpful. Comments about the sound quality of kits is still all here in this thread, if you search it among the other concurrent topics.

Read back over the last year so in this thread to where the NAP200 builds began - following #1752. You will find comments on perceived bass as builders completed the work over the next few months. I had no problem after I fitted the specified type of transformer with dual CT windings, making it a virtual dual mono design as per the original. When I began testing with a standard type 28-0 + 28-0 wound toroid supply, common to both channels, it did seem a little thin in comparison. Another possibility is undersized tantalum feedback caps in Zerozone kits, if that's what you bought - I saw only 47uF caps at the input as well, in their kit pic. The feedback caps should be at least 68uF. 100uF is shown in the original but the voltage rating should be ≥ 6V or they will probably fail. Otherwise, you can use NP (non-polarized) radial electrolytics of 16V or more, for preference.
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Old 16th June 2017, 09:52 AM   #2564
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Yes mine is the zerozone kit with all the standard parts.
With this better understanding I am more confident in checking and possibly replacing the parts to better ones.
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Old 18th June 2017, 12:34 PM   #2565
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Quote:
Originally Posted by Ian Finch View Post
Good that you found the information and suggestions about the original NAP models helpful. Comments about the sound quality of kits is still all here in this thread, if you search it among the other concurrent topics.

Read back over the last year so in this thread to where the NAP200 builds began - following #1752. You will find comments on perceived bass as builders completed the work over the next few months. I had no problem after I fitted the specified type of transformer with dual CT windings, making it a virtual dual mono design as per the original. When I began testing with a standard type 28-0 + 28-0 wound toroid supply, common to both channels, it did seem a little thin in comparison. Another possibility is undersized tantalum feedback caps in Zerozone kits, if that's what you bought - I saw only 47uF caps at the input as well, in their kit pic. The feedback caps should be at least 68uF. 100uF is shown in the original but the voltage rating should be ≥ 6V or they will probably fail. Otherwise, you can use NP (non-polarized) radial electrolytics of 16V or more, for preference.
Should I follow the value from the Naim amps mod page?

Quote:
upgrade C1 form blue 10uf tant to a 1uf-3.3uf Evox SMR polyphynl sulphide capacitor.
Other caps are also viable- see preamp coupling caps section.
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Old Today, 12:48 PM   #2566
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Quote:
Originally Posted by rensli View Post
For a whole day original naim design has been playing, laboratory +/- 30V. MONO(one channel).

It is very stable with TIP42/41's as drivers, 2sc5200 outputs, VAS stage 2N5401 and 5551, bias sense transistor 5551, VI limiter transistors MPSA06 and 56.
CSS and LPT diff. BC182B and 2xBC550C(matched) accordingly.

Miller is 56pF, everything else is as in Original Design except outputs inductor ~ 0.5uH 15R parallel. Forgot, i had no 620R resistor... so 560R is placed on CSS emitter.

It sounds dam good... even on laboratory supply (unusual long PSU wires).
All capacitors are tantalum except input(tant is good too here) and COG TYPE

I decoupled 2SC5200 outputs with small electrolytic (10uf) and 47nF ceramic/MKP for better EMI protection...thats all what is needed.....

Why ppl even bother to modify naim amplifiers ??? I don't even use LPT and VAS stage separate PSU's... still, the sound, especially rhythm(timing) sooooo nice. !!!!

Soon Ebay H-140 china kits will be replaced by clone originals, lets hope they won't fight each-other with 1 shared filter-bank PSU.
Hi
Can you tell me more about those tantalum caps U using. V rating and uF rating.
Are they 47uF or 68uF? I want to order some..
Interesting I did not like the TIP drivers with the MJL4281A power devices I prefer the MJE15030/31.
I want to test the MJE 243/253 with the 2SC2922 Sanken power devices. May be with your Toshiba-s the TIP drivers are better.
Thanks
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