Which 'Nobsound' amp is this?

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chumingo

chumingo

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Joined 2020
#1
Can anybody decipher what circuit topology or amp clone is being sold here, if any know?

https://doukaudio.com/collections/a...power-amplifier-stereo-single-ended-audio-amp

The build seems convenient for me to drive some old Braun 2-way boxes but would like to know more about it, as it is being sold for 200€ and I have no time to build one atm.

Weird that they mention electronic active filtering, but I only see some inductors in the pics which makes me think it’s passive.

Probably a JLH1969? Anyone heard experiences with this particular brand model?




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#4
There are three TO-3 transistors per channel, two MJ2955 (PNP) and one 2N3055 (NPN). Obviously not the classic JLH which has only two TO-3 transistors, at least the 10W version. Besides there are a couple of small TO-92 transistors per channel... No idea which amp is it.

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Are you sure about this @Turbowatch2 ? You would save me a lot of money.
The reason behind is that in my experience and it is a well known fact that discrete amplifiers introduce less noise than opamps and ICs in general, mostly because components (resistors mainly) are bigger and therefore less thermal noise. I have experienced this amplifying electret microphones. Also, I use a discrete JLH headphone amplifier I built myself and it sounds more clear, clean and powerful (soundstage) that any IC based amp I tried before (laptops, cellphones, interfaces, etc.) Maybe distinctions should be made between different ICs of course, since you find everything from AB to digital amp chips. Also, I'm very inexperienced in amplifying for speakers myself, if this is a world where other premises or priorities rule please let me know.
 
#6
The transistors used in this build were old and not suited for audio any more when I was a kid, about 50 years ago. It is a single ended amp, so anything you hear has to pass through this large electrolitic capacitor.
It doesn't matter that this may have been a very good amp in 1965 or has been build by a famous builder. It is old and out of date. The Chinese copy culture has resurected a lot of old stuff that better would have been left in the museum of audio electronics.

I know that people out there talk all kinds of interesting things, like Class D is too analytic and cold, Class A warm and smooth or the like. This is in most cases a result of sales talk. If you combine the amp I linked with a good laptop power supply of 19-24 Volt, you have a great amp. Just connect a good signal source, like a CD player, listen and trust your ears. Do not make your self a fool by listening to the usual noise from the internet. You will have a hard time to find any A/B amp that has a better sound than this little chip.
 
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#7
Those black capacitors appear to be DC smoothing capacitors, for the flat-pack diode bridges located right next to the RCA input connectors. Two 2n3055 transistors (one on each side) located closest to the black capacitors might be part of a very nice, low-noise power rail regulation. The other two capacitors located in the middle of the AMP PCBs, are: one is the current source, and the other one is a single-ended class A current gain/amplifier. The two orange capacitors are most likely connected in parallel and are used to block the halfway DC point from reaching the speakers (i.e. they are used to AC couple amplifier output to speakers binding posts).

The amp may sound pretty good in fact. The only thing I'd be concerned about is overheating flat-pack bridge rectifies. Same as Sugden 21a amplifiers... which I fixed bucket-loads due to the same flatpack bridge rectifiers used, in the same way - i.e. -> no heatsink.
 
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#9
#12
If you want to buy a pre 1970 amp new in 2023, this is sure an option. If you want an amp that represents the state of the art sound possible from a modern amp, with all kind protection for your speakers, this is not for you.
Have a look at TPA3116, TPA3255 or MA12070 for example.
 
#13
Thanks a lot you all, I'm left then with the idea this is a JLH 1969 amp circuit, the third TO-3 transistor on the heatsink being part of the supply filter (a capacitor multiplier probably). I ordered in a bid for 200EUR, arriving from Germany since it is in some local warehouse.

I appreciate also your concerns @Turbowatch2, I'm taking note of the chips you mention and will probably give them a try in the future. For my current purpose I need something very physical and simple, avoiding all kind of resampling (extra ADC/DAC), switching PS modulations, even mosfets in general unless strictly necessary, since this is meant for a mostly analog sound editing system where even the DAC plugged to my PC goes to the bare minimum (TDA1387). I'm sure I'm sacrificing here the analytical mid-range detail and resolution that usually delta-sigma DACs and class-D amps bring up, in exchange for the soundstage, clearance and extreme transparency that only proximity to the source can give 😉
 
#15
My response to hearing a Euro 200 price would be rude, and break forum rules.

The transistors are probably TO-220 in fake TO-3 packages.

And I get transistor amp populated boards for less than 20 Euros here, a 80W / channel amp, assembled, with FM / USB Stick / Bluetooth is about 50 Euros. Plug and play, even has a remote.
 
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#18
chumingo said:
There are three TO-3 transistors per channel, two MJ2955 (PNP) and one 2N3055 (NPN). Obviously not the classic JLH which has only two TO-3 transistors, at least the 10W version. Besides there are a couple of small TO-92 transistors per channel... No idea which amp is it.
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Are you sure about this @Turbowatch2 ? You would save me a lot of money...............
Click to expand...
I bought one of these versions for a friend, some years ago and I did it that way to check it out for him while saving on local freight charges. It was fine and like an increasing number of Chinese built clones, it had reversed power polarity due to the PNP output stage. Maybe it was cheaper that way but it certainly attracted some interest by offering something different.

Well, it sounded only a little different but a tad quieter than my own DIY builds of the amp. It does run hotter, due to regulation losses and only just enough cooling from the heatsinks to prevent discomfort when you touch the case. At 30-40C ambient temperature though, you'll be wishing you'd gone for class D but class A is an attitude as well as an experience and there are diehards out there who will endure any discomfort for just a few tracks with full class A amplification.

A real PITA with these and other commercially built clones and kits now, is in the number of stupid specification errors in the seller's listings. Think about it - there is no such transistor as 2N3955 (its a dual JFET) and 2N2955 is (or was) a Germanium TO3 power type. Unisonic also hijacks the 2N2955 ID for a TO247 version of MJ2955. Therefore, these cannot be 'pulls"of genuine, used semis. The confusing mess of fake semi IDs is best ignored completely and I suspect that new products probably just contain TIP 2955/3055 or similar chips in a TO3 package. That's fine but the VAS transistor, Tr3, is critical to the sound and it needs to have the Ft, capacitance and power rating of the recommended parts. Don't waste your time trying out TO92 semis intended for small-signal applications.
 
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#19
Turbowatch2 said:
The transistors used in this build were old and not suited for audio any more when I was a kid, about 50 years ago. It is a single ended amp, so anything you hear has to pass through this large electrolitic capacitor.
It doesn't matter that this may have been a very good amp in 1965 or has been build by a famous builder. It is old and out of date. The Chinese copy culture has resurected a lot of old stuff that better would have been left in the museum of audio electronics.
Click to expand...
I've been listening to class D amplifiers for many years now too. It's true, I think, that the audio processor chips they are usually built on have reached a stage of development where the output is not only clean but doesn't kill off the musical qualities like, for example, MP3 digital processing does.
'Still nothing like a good class A amplifier, though.

Otherwise, there are good reasons why this thread is so popular and the DIY design covered here is still around when its commercial competitors bit the dust long ago. It has little to do with the availability of Chinese clone kits, finished products or using particular discrete semiconductors that have a long history dating back decades. A discrete semiconductor produced today in Japan, China or wherever will not be the same as the original product because chips, semis and their processes, packages etc. are revised and updated like anything else that proves to be popular and has a permanent place in catalogues. In truth, they will often now be different chips inside the package and any "out of date" tag is irrelevant.

JLH'69 makes a great introduction to class A and costs little if you build it yourself without trying to make a work of art out of it. With class A there are no crossover artefacts that plague class AB and D amps. Typically, it will sound just wonderful and music lovers really gravitate toward class A once they are over their 250W power trip, barn size listening room or dreaming of ceiling height loudspeakers. Enthusiasm for those audio icons seems to fade when you look at the price tickets just for the materials and you realise that you only need about 5W of that power and the rest is just along for the ride.


 
#20
chumingo said:
Thanks a lot you all, I'm left then with the idea this is a JLH 1969 amp circuit, the third TO-3 transistor on the heatsink being part of the supply filter (a capacitor multiplier probably).
Click to expand...
I think it is a variation of JLH 1969 with a third transistor for a capacitance multiplier. For some inexplicable reason, PNP transistors were used. The two trimpots give away the need for careful adjustment. 😉
Ed
 
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