That would depend on your goal. Vereker believed heavily in the speed of the transistors. If you're trying to be true to his vision then I'd stick to the 8MHz comment.
If you're just trying to build a good-sounding amp, then I wouldn't start with anything near the Naim topology. The Blameless or Hitachi topologies would be far better for a "modern" sounding amp.
If you're just trying to build a good-sounding amp, then I wouldn't start with anything near the Naim topology. The Blameless or Hitachi topologies would be far better for a "modern" sounding amp.
Agree.
"If you want to amplify 20kHz signals you need at least 20kHz transistors." - Confucius
But if you want to apply effective, stable GNFB you are going to need a lot more speed. The difference between 2MHz and 8MHz is, in and of itself, more a matter of how much global, negative feedback you can apply.
"If you want to amplify 20kHz signals you need at least 20kHz transistors." - Confucius
But if you want to apply effective, stable GNFB you are going to need a lot more speed. The difference between 2MHz and 8MHz is, in and of itself, more a matter of how much global, negative feedback you can apply.
As said earlier, Naim used standard, high current switching transistors in both NAP and NAIT models before they "switched" to the premium audio grade Sanken LAPTs (70MHz Ft), with the so-called Chrome Bumper series NAP models. NAIT models continued with standard, then house-branded NA00X TO220 and TO3 switching transistors (probably Semelab sourced, like the more recent Naim branded power transistors)
Avondale have not been trying to clone Naim products. They have simply copied the only available Naim schematic from the period and adapted it to suit DIY practice, using industry standard components like the Onsemi, TO3 general purpose power transistors. The result is something quite different in performance to Naim's, so when you add the variable problems of DIY parts sourcing, build quality and that Avondale's source schematic was was frozen back in the 1970s-80s, it's probably only the concept circuit that could be considered as similar up to 2000 or so.
In other words, I wouldn't try to use Avondale's DIY approach to audio as a guide to cloning Naim's amplifiers. You may be happy with the audio result as long as you don't directly compare it with original Naim gear but there are many simpler, cheaper and easier ways to be happy without chasing legends that may not perform in 2022 like you probably hope, when based on a 1970's design that requires obsolete parts.
Avondale have not been trying to clone Naim products. They have simply copied the only available Naim schematic from the period and adapted it to suit DIY practice, using industry standard components like the Onsemi, TO3 general purpose power transistors. The result is something quite different in performance to Naim's, so when you add the variable problems of DIY parts sourcing, build quality and that Avondale's source schematic was was frozen back in the 1970s-80s, it's probably only the concept circuit that could be considered as similar up to 2000 or so.
In other words, I wouldn't try to use Avondale's DIY approach to audio as a guide to cloning Naim's amplifiers. You may be happy with the audio result as long as you don't directly compare it with original Naim gear but there are many simpler, cheaper and easier ways to be happy without chasing legends that may not perform in 2022 like you probably hope, when based on a 1970's design that requires obsolete parts.
They (or anyone else) may have been intending to clone, without really understanding WHY the original transistor types were selected. You do get a working amplifier with MJ15003’s. When you do that it may or may not be true to the original. EF output stages really aren’t that sensitive to fT, but CFP’s (and therefore QC’s) are. The whole idea was to minimize the switch-off problems associated with that CFP in the bottom half, and fast outputs are a solution. CFPs using slower devices are also more prone to local oscillations (remember those Phase Linears?). Using 15003’s won’t cause the amp to explode should cross-conduction occur because of their ruggedness, but there is more of it at high frequency with the slow CFP. And it will cause the crossover distortion spectrum to be different. It may very well be low enough not to bother you, but not necessarily true to the original.
There's an interesting 2020 thread at the Pinkfishmedia forum, titled "Avondale NCC200 mod". Unusual for PFM, it gets a bit technical and even shows the original schematic and distortion measurements + spectra. https://pinkfishmedia.net/forum/threads/avondale-ncc200-mod.235972/page-3
I'm uncertain whether this schematic is still current for Avondale because it appears from the watermark, to have been copied first by the Chinese "hifidiy.net" group. Yes, they're the guys who produced the first Ebay NAP 140 clone kits back in 2007.
I'm assuming you can read the linked pages but if you haven't signed up to the forum, you may not be able to access all pages and features, as we now find with a lot of social networks, who are usually just trying to avoid breaches of privacy and security for their members, due to so many internet undesirables.
I'm uncertain whether this schematic is still current for Avondale because it appears from the watermark, to have been copied first by the Chinese "hifidiy.net" group. Yes, they're the guys who produced the first Ebay NAP 140 clone kits back in 2007.
I'm assuming you can read the linked pages but if you haven't signed up to the forum, you may not be able to access all pages and features, as we now find with a lot of social networks, who are usually just trying to avoid breaches of privacy and security for their members, due to so many internet undesirables.
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Good day
Please replace bdy58 of mjl21194 this a very same devices also you need build amp and power reg after that you listen power transistors and change it if sound is not like
Good day Dear Drorkmeister I still build headphones amps with little alcohol way
)) some times you need listen ready devices with little alcohol time )Attachments
This RC circuits are needs for phase correction of output satage if you change output transistors you need change this RC networks
FWIW, There are several posts and references to this feature, even Julian Vereker's own reasons for including it can be found among his interviews. This is one of the interviews (but not the full details, as I recall) where its mentioned: https://thetomtomclub.ning.com/m/blogpost?id=6506457:BlogPost:922
Perhaps a better description would be in an old post here with comments by mikek, aka Michael Kiwanuka. https://www.diyaudio.com/community/threads/schematic-for-naim-amp.5372/post-53940
Perhaps a better description would be in an old post here with comments by mikek, aka Michael Kiwanuka. https://www.diyaudio.com/community/threads/schematic-for-naim-amp.5372/post-53940
Hi everybody ! I enjoyed the thread and would like to share a few thoughts with you.
I am not an electronics engineer but a pure hobbyist. Therefore when I wanted to build my amplifier I tried to copy as closely as possible what NAIM had done at the time on these old NAP250s. Unfortunately there is not enough information available to build recent versions of the NAP250.
I based myself on the diagrams of neil macbridge. I quickly realized that the schematic of the amplification stage had many errors (or differences with other NAPs). Not having an original to make the direct comparison I had to find photos on the net to read all the values of the resistors. By cross-checking different photos, I confirm theses values of 470 and 150 ohms as mentioned. But other values also differ I could give you the link on the corrections made. I confirm the error on the regulation of the bias also it takes a 1000 ohms. There is also a polarity error on a capacitor I believe.
On the other hand, on the diagram of the regulation card provided by neil macbridge, I had no problem.
I have built two of these amplifiers, they have been working very well for three years, one at my house and the other at my brother's (and my father has an NAP250 original chrome at his house, which allows me to have a point of comparison).
Being an amateur I still made some mistakes. I used MJ15003 which is probably not the best choice. I also wired these transistors which gives too long tracks despite everything I was lucky that the amplifier remained stable. I even did a stress test on a 2ohm load with a capacitance of 1uF in parallel and it held up ^^
If I have time one day I would like to resume my work and make an improved version by correcting these errors and pairing the drivers in particular.
The best would be to have an original in hands to check all the values and find the errors that slip into all the kits and diagrams available on the net. In fact I did not find any diagram which is correct on the net on the amplification part of the NAP 250 whether it is the KITs avondale the DIY or others ... none respect the original diagram.
My brother's version:
I am not an electronics engineer but a pure hobbyist. Therefore when I wanted to build my amplifier I tried to copy as closely as possible what NAIM had done at the time on these old NAP250s. Unfortunately there is not enough information available to build recent versions of the NAP250.
I based myself on the diagrams of neil macbridge. I quickly realized that the schematic of the amplification stage had many errors (or differences with other NAPs). Not having an original to make the direct comparison I had to find photos on the net to read all the values of the resistors. By cross-checking different photos, I confirm theses values of 470 and 150 ohms as mentioned. But other values also differ I could give you the link on the corrections made. I confirm the error on the regulation of the bias also it takes a 1000 ohms. There is also a polarity error on a capacitor I believe.
On the other hand, on the diagram of the regulation card provided by neil macbridge, I had no problem.
I have built two of these amplifiers, they have been working very well for three years, one at my house and the other at my brother's (and my father has an NAP250 original chrome at his house, which allows me to have a point of comparison).
Being an amateur I still made some mistakes. I used MJ15003 which is probably not the best choice. I also wired these transistors which gives too long tracks despite everything I was lucky that the amplifier remained stable. I even did a stress test on a 2ohm load with a capacitance of 1uF in parallel and it held up ^^
If I have time one day I would like to resume my work and make an improved version by correcting these errors and pairing the drivers in particular.
The best would be to have an original in hands to check all the values and find the errors that slip into all the kits and diagrams available on the net. In fact I did not find any diagram which is correct on the net on the amplification part of the NAP 250 whether it is the KITs avondale the DIY or others ... none respect the original diagram.
My brother's version:
Have a nice day dear I haven't seen this PCB design before Please attach your schematic and the gentlemen on this forum will correct it if they find any errors.
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Of course, that is why your project doesn't sound like a NAP250. The MJ15003 has a low fT at 2MHz the frequency point where gain is unity =1. The break point where gain starts to decline to -3db where level at 2MHz falls at 20 dB/Octave, you can draw a line from that point at an angle of 45 degrees on a chart.
Consider then the angle of phase starts to move a decade in frequency below the - 3dB point and will reach -180 degrees before gain has reduced to unity =1 unless some means of reducing the gain is used to prevent this. Compensation then hasto take effect at a relatively low frequency and above this there would be a declining level of nfb.
The muddled sound mentioned by your wife in the Youtube video is due to inter-modulation distortion.
As pointed out by Ian Finch and by me earlier in this thread, to get close to the original circuit switching output transistors are necessary.
If one looks at a plot of collector current on the vertical scale and base -emitter current on the horizontal this followsa pronounced curve from about 0.53V to 0.7V. Collector current increases rapidly in this range and with that the angle of the slope.
A switching transistor will occupy less length along a curve relative to the horizontal scale than such asMJ15003. If you take a plane flight at 30,000 feet the curvature of the earth is noticeable . Down on terra firma it looks flat as it did to ancient seafarers worried about sailing over the edge.
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"The muddled sound mentioned by your wife in the Youtube video is due to inter-modulation distortion."
I don't understand what you are talking about here?
Yes the 15003 is not the best, but it still works very well. If i choose other output transistor i wonder that if i have to change drivers too ? or change other components values to optimize the design ?
From what I understood there could be to modify the phase compensation system.
I don't understand what you are talking about here?
Yes the 15003 is not the best, but it still works very well. If i choose other output transistor i wonder that if i have to change drivers too ? or change other components values to optimize the design ?
From what I understood there could be to modify the phase compensation system.
Of course the box is open only to present the amp on video, rest assured they have been working closed since then.
Regarding the layout of the PCBs and the wiring, I would precisely like to resume my work to redo another better version under Kicad when I have the time, I can also optimize the output transistors, it would be even better.
Regarding the layout of the PCBs and the wiring, I would precisely like to resume my work to redo another better version under Kicad when I have the time, I can also optimize the output transistors, it would be even better.