Bench Monitor Amplifier. Part 2. Based on Naim NAP250 clone kits.

[@gamiwv]

I'm an engineer in electronics (retired a year ago) and it is the first time i'm seeing on a youtube video the adjustment of cross-over distortion. Excellently done for educational of the youngsters in Hi-Fi / Hi-End. I propose that you add this to the headers of the video.

[@lars6627]

Hi! I am going to build the exact same amplifier and are watching your videos with great interest, Just wondering if you in part 3 could in detail show the adjustment for bias and crossover distortion one more time for this amp with the right transformer. If possible also show how you connect everything to the oscilloscope, dummy load and so on. Looking forward to part 3! Regards, Lars

[@MichaelBeeny]

Thank you Lars, I'm expecting the transformer today Saturday or more likely Monday. I will get to work on it ASAP.

[@moon1985bc]

your opinions are honest indeed. thank you very much for your videos.

[@AllboroLCD]

I came across this whole clone amp board market on ebay just recently and was ASTOUNDED by whats available. I was personally attracted to the Nelson Pass amps myself, but the HUGE question was how do these shameless clones sound!?!? So really sir, THANK YOU for documenting your experience and sharing. I look forward to bullding one of these, Id like to fabricate a nice wood/metal enclosure with Vu meters and do a dual mono amp for my Altec speakers!

[@MichaelBeeny]

I think the short answer is some are quite close. Many change the transistors to more modern ones. Some of the original are either not available or way to expensive. The circuits are mainly just the basic amplifier without protection. Obviously even in the original version the power board is quite low cost. The cost in a ready made amplifiers, case, heatsinks and power supply, dealer mark up etc. So if you do all the work, the cost is much lower. Most of the amplifiers that are cloned tend to be old stuff, the original manufacture has probably gone bust or does not care about obsolete products. It's also very expensive to take these Chinese, clones to court. If not impossible. Also the home market is really quite small these day, so who is hurt, who really cares?

[@AllboroLCD]

@@MichaelBeeny In the case of Mr Nelson Pass, he actually promotes DIY clones, even provides PERSONAL support via forums on his website. It really breaks down to the quality of your wiring, filter caps, and transformer that will get you closest (possibly better) sound from the original.

[@nigelpearson6664]

From memory the real NAP 250 has 22K and 1 K in the long tail pair input stage (LTP) collectors. This gives single transistor style distortion. It also gives enough DC feedback to work like other similar types ( Sinclair Z30 ). The reducion of second harmonic using current mirror might not be everyones prefered route. The compensation netwworks to the outputs ( was BDY56) might be to suit Quad ESL57s. Rumour says Quad had thought of a similar design. 405 was the baby of the boss so it was rejected. The singleton distortion needs full voltage really.

[@MichaelBeeny]

See Part 3 here kzbin.info/www/bejne/aaW0qGaZeaqnm6c

[@jamesw5584]

If ur buying an amp for a particular sound then the fact it starts rolling off halfway through the audio spectrum is part of it but if you want a reference that is linear in response then I guess this is not a kit you want to buy. I'd be looking at any capacitors in the audio path and adjusting them for a more linear response personally as I doubt that its intentional. I bought the L15 mosfet amplifier kit and the response on that is completely linear and the sound quality is stunning. I run that at 75volts +/- and easily achieve 510 watts per channel before clipping in to 4 ohms. Another issue with a lot of these kits is they do take some driving from my experience and often line level is not enough to drive it in to clipping.

[@MichaelBeeny]

Hi James, This was the first kit I have ever built with a roll off in the HF. Without exception all modern amplifiers are flat way past 50Khz but saying that it was only 0.5dB down. Small by any standards. I have not tested the original Naim amplifier in comparison, maybe that had a similar response. Still, it was cheap and is fine for what I am using it for. I found the sensitivity fine, about average really. Might not be enough for some phone use however!

[@ford1546]

very nice built amplifier. I have built myself an amplifier with the same naim nap250 clone. you can expect with optimal power supply to get 80w to 100watt 4 ohm. Do not remember 100% must find paper with measurements on. the best amplifier i have tried when it comes to sound qualities is l20 classs-ab amp from LJM

[@MichaelBeeny]

I do find some of the larger, small transistors do run quite hot. Probably not too hot but I like all components to be kept cool. They do last longer, no real way to heat sink them however. Regarding power, If I recall, the next part gives power output.

[@ford1546]

@@MichaelBeeny L15D gets a little hot! but the naim NAP250 does not get particularly hot until you adjust the current to the transistor too high. but you can easily get thermal runaway. Before on many amplifiers you had a small PCB. screwed to the heat sink that adjusted this so you did not get thermal runaway.

[@MichaelBeeny]

@@ford1546 I think I did show how I worked out the best bias current, basically up until no cross over was visible. The output transistors do not get hot and the current is very stable. I think the small drivers really need to be bigger and on sinks. Probably a cost issue.

[@Unker_Spunkanathan]

Saw your upload this morning but I need to work today so only got to view it now. Always been interested in the ljm nap250 kit... Was deciding on this vs mx50se n eventually bought the latter coz I read comments on its clean sound. So how many ljm kits have you completed? Keenly waiting for your final review with the farnell txf

[@p_mouse8676]

A class-ab amplifier has an efficiency of around 60-70%. So 10-15W unclipped is not so far off actually. Nice project 👍🏻😎

[@MichaelBeeny]

Wow, you were quick to view. It's always good for my viewers to agree with me!!

[@zighunt]

The HIFI magazines worship NAIM amps because of this I grew up thinking i had faulty hearing because i dont like NAIM sound.My brother has a naim integrated around 1000gbp

[@CoquiAudio]

hi I have a schematic and I would like to know the actual proper bias adjustment

[@Eucal]

Thanks for documenting everything Michael, there is little information on these clones and you're onto something here. Im building the same kit. Do you think it would be possible to tell us what the trimmer pot value ended up being to eliminate the crossover distortion? Since many people dont have a scope , the alternative is to guess at it.

[@MichaelBeeny]

You should set the QI to about 20/22mA total for each channel, no input or speaker connected. Giving a pot value is not a good idea because this not only sets the QI but compensated for component tolerances. This is covered on part 3, link below.

[@Eucal]

@@MichaelBeeny My bad, i didnt see the part 3. Yeah it is indeed explained there, thanks for your thoughts on it

[@MichaelBeeny]

@@Eucal It's OK, I had to re watch it myself, thought I covered it but not 100% sure!! senior moment.

[@nigelpearson6664]

Also from memory. Quad 303 is about - 80 dB second harmonic 1 watt ( a critical test ). This reduces like a suspension bridge curve. Jean Hiraga argues this is ideal. 303 is not a muscle amp so might not suit everyone. NAP250 has slight 3rd harmonic bias and 2nd and 4th in displaced singleton curve. This is the Naim sound. Hiraga says we hear harmonics as in a musical structure. We don't like wrong steps. That is percentage between haronics. Thus 1% THD can sound perfect. A Quad valve amp doesn't. Nor a Radford. Leek TL12+ might. Our ears are not perfect, even the best. Oxford University speculated 30% THD which the brain can sort out.

[@joshaas]

Hello sir, first i do not now about amps, but i now about speakers, i do build them and ad first i did build speakers that are flat the hole spectrum and they did not sound very good, so i did go and look for the optimal spectrum for the human ear and i did find a youtuber that did say that the optimal spectrum is not flat but it drops of a bit in the highs, he did say something about a person that did investigate about that, i forgot the name, so i did try this in my new speaker design build, and there was where i was looking for, a warm and clear musical sound what a pair of speakers 10 times as expensive sound like, so that 0,5 db of this amp i do not think that it makes it a bad amp, distortion makes a amp bad not a 0,5 db role of in the high frequency thats what i think, i am a electrical engineer so i do like to build my own amp, i never did build my own amp so i did stumble to this channel, thx for what you do it helps me al lot

[@joshaas]

o ja i did find it again, the Harman Target Curve, i did find the page again, look here for more info: www.audioheritage.org/vbulletin/showthread.php?39134-Harman-Target-Curve

[@MichaelBeeny]

It's very true that the human ear is far from having a flat frequency range but the perfect amplifier or speaker should reproduce the sound exactly the same as the live performance. This way your ears will receive the sound exactly as it was if you heard the sound live. Everyone's ears are very different but the equipment you have should present the recorded sound to YOUR ears exactly as live, not minus some frequency's or frequency's at different levels. Many people like EXTRA this, extra bass, it's a preference of the sound but it's not a true replica of the original sound. True HiFi should not add or subtract anything from the original sound. Sadly no microphones or any part of the system is perfect, they all add or subtract something. Then the recording engineer adds compression, limits frequency's so the recording medium can cope with it. These day's much music is presented in MP3 or other nasty lossy formats, plus few people today have EVER heard real live music so really have no idea how to judge HiFi.

[@joshaas]

@@MichaelBeeny yes but i think when you measure the real sound what you get from your speakers and your room conditions there will be some comprise in sound, and when you have a true amp and speakers you find the sound to be not nice for you, you feel that its lifeless and cold, i did have a (almost) perfect amp and a (almost) perfect speakers and the sound was beautiful on my meters and so perfect in specs on my laptop, but i did not like it at all, nobody did, so what i like to say is that you can build a perfect violin but nobody likes the sound, sound needs tot take you away, that u get emotional, when i am listening to my diy speakers they take me away in to the music get me emotional, and thats not only my opinion, i see people get emotional if they here that sound and thats what i am looking for, sound thats is a live and give u the feel that you are there, not emotional dead, u did say from the 4 amps u have you realy only like 1 amp, maybe when you measure the sound what that amp makes with you speakers u see maybe thats not perfect on the meters but perfect for you, sound needs tot have colour a feel to it so that it can thake your hart and let you fly, thats what i think sound needs to do