Chinese JL Hood 1969 Class A amplifier off Aliexpress

[mdkanakakis]

Hi there as well. New to forum, I wanted to ask something.
So I have decided for my New desktop setup to go with emotiva airmotiv b1+ with emotiva se8 subwoofer (space limitations).
From what I read here, I decided to go with
LJM Finished Hifi L12-2 Power amplifier Ultra low distortion amp 120W+120W L23-9 from ebay. The one without the volume control. For a dac I am thinking of using the topping e30, as highly suggested for the price. Do you think the Audiophonics pre tc10 which is a tonal eq with volume control would work for this setup? I am thinking of putting the subwoofer level on max and then adjusting the bass level from the audiophonics module as per my preferences for convenience. Also should I put the dac before or after the eq? I pressume I will set the topping e30 to max gain, right?
Thank you

 

[Plesuvius]

Just a quick note to say I picked up the amp in the OP (available on ebay, JLH 1969 18+18w 4 transistors per channel high output version. Sells as 2020 newest version. I picked up the boards first and had a go at making an amp but couldn't source heatsinks large enough cheaply enough so just went ahead and bought the finished version - currently £174 del to UK but I had to pay £16 import duty also.

I've not had it long and not checked the bias currents but it does run a little hot (just the hot side of warm). I would say the sound is very good, better than 3116 based cheap amp and as good as the best valve amps I've heard. Class A is really something, vocal performance is very clear and I am super happy with the amp. I was using Elac F6 floorstanders but the amp didn't really get on all that well with them - a little distortion was apparent. I switched to standmount Triangle speakers and the amp was much happier. They are more sensitive too.

I was very pleased with the sound of the boards and the build quality and the amp has not let me down in the short time I've had it. It might even be starting to sound a bit sweeter. I fully disagree the sound is mellow or boring it's great and smooth. Recommended for the price if you can get away with using it around 10w or less (which you likely can).

wolf6911 on ebay sold me mine and there is currently just one left of 5 worldwide. It's cheaper than the Nobsound NS02g and the boards are a little better I think (at least the output is specced higher - fwiw).

Any questions or photo requests please let me know.

 

[puggles1973]

Thanks for the picture. It is really puzzling to see three TO-3 power transistors there for each channel. There should be two and then a less beefy one for driver.

It is cute and clean nevertheless.

One of the T0-3 transistors (MJ15024G) is a Capacitance Multiplier in the PSU circuit. This is a necessity in Class A amps as the quiescent current is so high (in this circuit about 1A to 2A) that without the CM, ripple in the supply rail would be very prominent as to cause intolerably loud hum.
I would also like to point out that this particular amp uses a PNP output stage (MJ15025G) which is a variation from the original JLH design ((NPN), so constructors need to bear this in mind (and also all corresponding transistors will be reversed). Constructors will find that the MJ15025Gs get significantly hot and though neat as the layout of the PCB is, it does not cater for longevity of these output transistors. They are best mounted as far apart from each other (off board) as the heatsink allows in order that heat distribution/dissipation is effective. The brackets supplied in these kits also look woefully inadequate at 3mm thick, in my construction, I have chosen 1/4" X 2" X 2" 300mm brackets. Heatsinks are 2 pieces of MF35-151.5 (350mm) from Conrad Heatsinks (Australia).
If anyone is interested, I will attach some pics at a later stage. I have to say at this point that my circuits are of the original JLH (NPN) design with slight circuit and components alterations.

 

[Lorenzo]

Hi Plesuvius ,
You said : " Just a quick note to say I picked up the amp in the OP (available on ebay, JLH 1969 18+18w 4 transistors per channel high output version."
My question is if it the same you can find here ?
https://fr.aliexpress.com/item/32831028577.html?spm=a2g0s.8937460.0.0.5b642e0eTf65lh

Thank you

 

[alnasique]

Hello, who has this Chinese jlh1969 Version ? (See the attachment). Please help identify which of those three black capacitors Is responsible for feedback? I want to replace it with a elna 2 of greater capacity like 470uf. I read this hack on a Russian JLH forum. Thanks

 

[Plesuvius]

Hi Plesuvius ,
You said : " Just a quick note to say I picked up the amp in the OP (available on ebay, JLH 1969 18+18w 4 transistors per channel high output version."
My question is if it the same you can find here ?
https://fr.aliexpress.com/item/32831028577.html?spm=a2g0s.8937460.0.0.5b642e0eTf65lh

Thank you

Sorry for late reply. I believe it's the same one (and that's a good price in euros if you don't want to use ebay). I am not 100% sure but maybe 95% sure. Transistors are same, same count, back front and chassis look the same, price is similar, etc.

EDIT: Any upgrades suggested for this design? There is always the possibility of improving the sound with such cheap a start I feel. It does sound great already though, if not really 18w in loudness seeming out of the box (bit less).

 

[Lorenzo]

Sorry for late reply. I believe it's the same one (and that's a good price in euros if you don't want to use ebay). I am not 100% sure but maybe 95% sure. Transistors are same, same count, back front and chassis look the same, price is similar, etc.

EDIT: Any upgrades suggested for this design? There is always the possibility of improving the sound with such cheap a start I feel. It does sound great already though, if not really 18w in loudness seeming out of the box (bit less).

No worry for late reply , and thank you for answering , I don't know if it is and upgrade, but I am very curious about this model :
https://fr.aliexpress.com/item/4000196334238.html?spm=a2g0o.cart.0.0.50873c00A5WyQ1&mp=1
Any advices , observations welcome .
I have the Nobsound NS02 G and wondering if as you say . " There is always the possibility of improving the sound with such cheap a start I feel "
May be not in terms of power, but in quality sound .
I have now a pair of Magnat 757 https://www.magnat.de/en/HIFI-Speaker/Quantum-750/Quantum-757/Quantum-757
with sensivity 93 dB (2,8 W /1M ) and plenty volume reserve, with very clear and stage sound .

 

[DavidMcRoy]

I wanted to experiment with something to replace an Aiyima A07 driving the GRS PT1618-8 dipole planar tweeters in my DIY dipole speakers, above 1500Hz. (Another A07 drives the dual MarkAudio Alpair 12P "full-range" drivers. All the drivers are rated at 94dB efficiency; see my profile pic.) This thread inspired me to give this amp a shot. It was advertised as an "improved" version and cost $178 US plus shipping. What can I say? It sounds quiet and clean and it's

just right for my application. It's just loafing along at modest volume most of the time so it stays only slightly warm. It's a keeper.

 

[restorer-john]

Pardon me, but were you given to understand that this was a Class A amplifier? A true Class A is hot at low output. Very hot. Per your description, this is not a Class A amplifier. I am confused.

Jim

Jim

Looks a lot like this:

John Linsley-Hood 1969 Class A Amplifier aka Nobsound NS-02g

jelabs.blogspot.com

 

[DavidMcRoy]

It is advertised as a Class A design. Elsewhere on the web a user who also noticed not-crazy-hot chassis temperatures noted that some internal parts were rather hot and speculated that this particular implementation might have better heat dissipation than most, but who knows?

 

[notsodeadlizard]

currently US$134. I paid $38 extra for shipping to Manila.

For the money, you should be happy this misunderstanding works at all.
Oh, these Chinese fake builders with their penny profanation of everything in the world...

 

[restorer-john]

@DavidMcRoy Might not be a bad idea to check whether the amplifier is correctly chassis earthed...

 

[Lorenzo]

I just want to testify about my experience with the Nobsound NS-02G HiFi Pure Class A Single-ended Amplifier Home Stereo Audio Amp Power Amplifier 15W x 2.

https://fr.aliexpress.com/item/4001193297443.html?spm=a2g0o.order_list.order_list_main.30.21ef5e5bH0hGjc&gatewayAdapt=glo2fra

Purchased in October 2020, it continues to please me with its very beautiful musicality. Its operating constant temperature is 40º centigrade .
Lately I bought the Topping L30 II, for use as a preamp and therefore to be able to benefit from a power gain.
Very happy with this combination. The Topping L30 II is an excellent device!

Topping L30 II Review (Headphone Amp)

This is a review, detailed measurements and listening test of Topping L30 II. It was sent to me by the company and costs US $149. It comes in a number of colors. Usability could not be better with positive clicking switches for power/pre and gains. Three gains are provided with the low gain...

www.audiosciencereview.com

Here is my little contribution.

 

[JohnnyAudio]

I have the BRZHiFi PMOS-1969 and I like it. Very quiet.

 

[Lorenzo]

As for me I upgraded with this 30w*2 Reference PASS A30 Class A Power Amplifier FET

https://www.aliexpress.com/item/1005004924657560.html?spm=a2g0o.detail.pcDetailTopMoreOtherSeller.3.3e9fhvDihvDikQ&gps-id=pcDetailTopMoreOtherSeller&scm=1007.40000.327270.0&scm_id=1007.40000.327270.0&scm-url=1

More power and much more clear and wide soundstage may because of the double tranfo alimentation .
Still using the Topping L30 II as a pream in medium position .
With DSD source albums it's heaven !

 

[maty]

JLH 1969 + аудиофильские штучки

For now with mix at 2%

 

[maty]

JLH 1969 - WZMACNIACZ KLASYK W KLASIE "A" !!!