AliExpress / eBay JL Hood 1969 Class A Amp

I wonder about the big relay in the unit in the link to the "latest version" posted above by Decomo.
Does it protect the speakers/ears/headphones from the current impuls (that is typical for AC coupled amps when turned on, when the output capacitor is "filled up"), or is it intended to protect the amp itself from by overload? (shorted output leads and such).

Personally I would feel more comfortable in the first case, since I probably would like to try it driving SRD-7 and E-9 transformer boxes (and do not want a transformed up impuls to reach the stat membranes), and also perhaps try it with dynamic headphones. In the last case I would likely use a voltage divider on the output to keep noise down etc, but even then I would not like the expected impulse to reach the drivers, as these may be too fragile to take it, who knows.

 

It could be. The relay is on the logical spot for one, but I don't see much sensing-timing-driving circuitry. Must be tucked away in the bottom.
It's probably only a simple timing circuit that will wait like 2..5 seconds before connecting outputs. I wouldn't hope for an active dc sensing circuitry.

Not a bad idea to have it there, as the big lytic cap will cause a momentary dc into the speakers on startup.
Wouldn't be a problem for a 3 way speaker, I can see my 12'' bass move like 3 mm, 2. order crossovers will protect mid and tweeter from that.
To a puny widebander or a mid running 1. order xo it might cause some excursion damage.

 

I'm sure the high shipping is part of the product cost. Where else are you getting a Class A power amplifier for $250?

 

With all the different versions around and possibly dubious speaker-burning build quality + some DIY enhancements required anyway, seems more like a lottery to just win an expensive case with stuff. I think I'll consider going full-DIY-retard instead.. or pre-assembled boards that are cheap to ship,, or maybe even something like this

EDIT: I noticed atomicbob has a Nobsound HD1969/NS-02G one... ordered the same, $140+51 with coupon, not bad.

 

Heatsinks + case + transformer is practically the price.
Unless you have something already laying around, I wouldn't bother.
I happened to have heatsinks laying about, I wound my own transformer, used desoldered caps, had a stash of 2SC5200s ,welded case from old metal door.
I mean it cost me practically nothing in cash, but it was way-way too much work for such a thing.
My only redemption is that I was going to make more powerful version of it, which I eventually will.
Or maybe try the dc coupled design to drive bass.
DIY-ing the same exact thing from scratch that eBay sells is dumb.

 

Well that was fast, I got my Nobsound already. It actually shipped with DPD directly from Germany, so no customs, $191 total.

Bad news is that it does not have safety ground connected. I will not plug in an amp that is basically illegal. I'll drop it to a local amplifier shop to fix officially and give a test run at the same time anyway. Then I'm not liable if selling it either..

https://i.imgur.com/Kjx7UWK.jpg

 

Safely grounded now. The amp guy tested it 6W@8ohm and was quite impressed with the chinese quality.

Can't find much to fault. Dead quiet, I can barely hear a faint buzz sticking ear inside my horns. Runs quite hot, I can keep my hands on it for 5-10 secs, good space heater during the Winter. Maybe I'll slap an extra heat sink on top of the case just to help it a bit. Those two red leds though, glowing like demon eyes in the dark - need black sharpie asap.

So now I have amps from three classes. Compared to my Mod86 and Lyngdorf, maybe slightly lacking in bass and softer unoffensive treble. Not sure if I get any "Class-A hardon" here, it sounds fine, but I'll probably prefer my marginally cleaner amps. Sometimes I wonder if I had better things to do than trying to listen for some plankton shit differences. I'll still try the cap bypass mentioned here.

edit: Ok it's "dead quiet" only below half pot. But I don't really need much more.

 

If you already warm up your iron, try some proper input caps as well.
Arguably more to be gained here, as quality ones can be used for modest investment (around 1uF is fine).
I'm not encouraging cap rolling, simply the ones in the chinese kits are often awful.

 

Interesting, mine is dead quiet even with the input level all the way up and I would hear it if it wasn't with the huge horns on my Cornscalas.

I left the ground as it is, I have tons of amplifiers and receivers around without three prong plugs.

 

You are right, without input connected it's dead quiet. Gungnir Multibit's RCA creates a ground loop, at max it's quite loud mix of buzz/hiss. If I use my non-grounded Dac Box S2 with USB, it's dead quiet. I could do some chassis-connecting trickery or whatever, but I'm thinking pairing nobby with S2 anyway since it's a bit brighter/harsher dac. Gotta love balanced connections.

Not using safety ground is not an option. I know electricity is different there and we actually have safety regulations.. I'm not going to trust some chinese trafo not crapping itself and leaving 230v floating on the case.

 

I've had this amp in my main 2-channel system for three and half weeks now. Everything @Marvey says about this amp is true, both positive and negative. It really does the Class A thing great. The only reason I'm not going with it permanently is the Sherwood S-6040CP has greater synergy in my system. It has a bigger soundstage, is a little less veiled and is a more laid back, smooth sounding amplifier that really pairs well with my Cornscalas. I'm keeping the JLH 1969 around a while though because it might ultimately win out. It's an outstanding bargain at the $194 I paid. It cost me more to restore the Sherwood than the cost of this amp.

Just remember that it needs very sensitive speakrers. My KLF-20s, Cornscals and Monoprice Stage Right worked great but even my Focal Aria 906, which I consider to be fairly sensitive ran up against the 6.5W of power when cranked. Normal listening levels were fine though.

 

Has anyone had experience using this power amp to drive the inefficient Hifimans (e.g. HE-6)? I’m getting conflicting reports: some say that since HE-6 loves power, going for moar power is almost always better and recommend amps that output at least 50W per channel, sometimes as high as 100W+.

On the other hand, some say that’s not necessary true, what’s really important is the quality of the first watt (a la Nelson Pass) and reported great results with high quality FirstWatt amps that only output 10W into 8 ohms (which would result in much less watt into HE-6’s 50 ohm load).

IIRC, this JH 1696 amp only has a relatively low output of about 10W, as much as the FirstWatt amps do, albeit with incredible sound quality. I wonder if it will be an excellent match with HE-6, because if it is, then it’s apparently a goddamn steal.

 

The JL original scheme (27V supply) will give HE-6 about 1.5W of power, 111dB SPL peak (before clipping).
Do you think it's enough?

The amp could easily be built into the same chassis with higher voltage psu and lower quiescent current to have some serious overhead in terms of power into HE-6.

 

Would this be good alternative for Sugden a21? I recently got ProAc Tablette 8 Sig bookshelf speakers and read online that Sugden is great match.

The speaker is 85db sensitivity at 8 ohm and I normally listen avg 83dB to max 90db loudness in nearfield setting.

I guess that 10w is enough and just want to check before ordering if possible

Thank you..

 

Generally not recommended to use 85db/W/m speakers with 10W of power.
You'll get these 90dB with JLHood and your speakers, if your source is hot enough.
Perhaps a Vidar is better idea?

 

@Hekeli gave me some guidance on grounding the JLH69's power cord connector (which, from the factory, has the grounding lug just hanging there unconnected to anything) to the amp's power transformer mounting bolt.

Doing this got rid of most of the horrible high-frequency noise I was hearing with this amp hooked up to my very sensitive Edgarhorns. It's still not dead silent, but it's much improved.

Usual caveats about deadly voltages apply, but it's an easy enough mod that if you also have noise problems with this amp it might be worth trying.

 

Some pics of 'viscera' )). Using this baby to drive my Audiozenith PMx2 v.2 from Schiit Yggdrasil.

 

Maybe I'll pick one of these up once I complete my 511b horn system. Seemed to work well for Marv. Need to upgrade my vintage onkyo receiver.

 

Hi Guys,
How do you bias these amplifiers?The Ebay sellers instructions does not make sense.thank you in advance.

 

I just realized I can get one of these for about $120 shipped here, maybe less if I do some local legwork. May give it a go in the future.