[namaiki]

  Do You know how sounds Lovely Cube with dac unit? It is with usb CM6631A and base on ES9023 dac. 

I have a Lovely Cube Premium AD (the one with the built in DAC) on the way in the near future. However, I only have a Apex Glacier and Leckerton UHA760 that I would be able to compare it with. I have no idea at all what to expect.

 

[truly194]

I hope that Lovely Cube has very nice applicate sabre dac - it can sound very nice

 

[shaman11]

Maybe I´m wrong, but when I read the reviews from the Le*mann site they talk about an Class A amp.
When I look the pictures from this Lovely Cube I wonder why they use bipolar NPN and PNP transistors. when everyone knows that mosfets are less noisy than the old bipolar ones.
For Class A you don´t need a (matched?) pnp and npn transistor, usually one transistor (pnp or npn) do the job but you can use more parallel to enhance the power output.
So for me it seems that LC is a class AB Amp rather an Class A design and this is not exactly the same , Mr. Le*mann said ?
 
How do you guys know, if the hongkong fab matched every bd139/bd140 per hand to find the right couple ? did someone of you take the LC in a audiolab and do some measurements (bode, thd etc etc.) ?
Years ago, when I repair my minimoog Synth I waste hours of matching a bulk of transistors ...
Maybe one of you can shed more light on this topic ?
 
( I found this thread after looking google images in search of a clear picture of the Le*mann pcb where I can see which transistors
he used .. )
 
cheers
 
M

 

[namaiki]

I'm not really a technical person, but from what I recall it is possible to "bias into Class A" so I guess it may not be in Class A in stock configuration?
 
Received my Lovely Cube Premium AD with built in DAC this morning. Postage to Australia was only 4-5 days.
 
Just got home from work so I haven't had a good listen yet, but I can confirm that there is not any channel imbalance at low volume which is the thing that I was really most worried about. (You might notice that my last two amps have stepped volume. I nearly went for a stepped attenuator which is an option, I believe, instead of the stock volume pot) Still, there is no channel imbalance in the pot at any point that I can detect so I am extremely happy about that!
 
edit: The PRaT coming from this thing is great. It has a pleasant delicate treble which is great for acoustic instruments and especially drums. Snappy and decent amount of space.  Vocals are sweet sounding and bass is good. I almost hate to say it because I don't usually care about this kind of thing, but the volume knob really has a really nice feel.

 

[shaman11]

so everybody seems happy with this project regarding biasing, matching or nothing at all.
so its worth to try this LC and it doesn´t matter if its a Le*mann or not
 
all right
 
I will try this for myself.
First I was curious about hongkong tec. but all folks here are happy with the result.
and if not they upgrade it with more and more expensive parts.
 
I wonder why they build the transformer so near to the Line Inputs. Normally you avoid this with carefully audio design.
The magnetic fluxlines induce hum to this lines.
Its better to leave the ac/dc parts outside of the amp or shield it with nonferrous materials (like the multimediaboxes in the 90ies)
 
M.

 

[Laybar]

how do I post pictures?

 

[namaiki]

Click the following icon and upload your pictures, or upload your pictures elsewhere and paste the link in your post.
 

 

[penmarker]

You need to have more posts to be allowed to post pictures sorry.

 

[Tribbs]

I wonder why they build the transformer so near to the Line Inputs. Normally you avoid this with carefully audio design.

The magnetic fluxlines induce hum to this lines.

Its better to leave the ac/dc parts outside of the amp or shield it with nonferrous materials (like the multimediaboxes in the 90ies)

 

M.

 

I am under the impression the toroidal transformer alleviates stray magnetic flux with an 8:1 reduction of radiated magnetic field over an equivalent rated EI transformer.

"The advantage of the toroidal shape is that due to its symmetry the amount of magnetic flux that escapes outside the core (leakage flux) is minimum, therefore it radiates less electromagnetic interference (EMI) to nearby circuits or equipment."

http://en.wikipedia.org/wiki/Toroidal_inductors_and_transformers

From elsewhere:

"Due to their physical structure, toroidal transformers tend to be quieter (especially in terms of 60 Hz noise) and they are more efficient.

"The efficiency part means that a smaller tranny can do the job of a larger one, making them useful for rack gear and things that need to be packed into smaller spaces.

"Due to the shape of toroidal transformers, there is some inherent common-mode cancellation of radiated EMI. In fact, once installed, they can be rotated in place (while listening to the circuit) until the noise is minimized. There's sort of a 'notch' where self-cancellation is maximized.

http://www.electricalaudio.com/phpBB/viewtopic.php?f=5&t=48683#p1093089

 

[penmarker]

The Lovely Cube circuitry is well built. Recently I lost my laptop charger (again) and had to resort with an aftermarket adapter. It's probably a little faulty or not well made, so I can feel some current leakage on the aluminium keyboard surface when I run my finger across it. If its plugged into the Lovely Cube, the leakage disappears. It doesn't matter if it's connected via the 3.5mm jack or through the Aune T1 as a DAC, it helps with the leakage.
 
Or maybe its a really simple fix, I don't know, I'm no electrician lol.

 

[Tribbs]

I've read much discussion earlier in this thread, and elsewhere, regarding replacing the LM317T/LM337T voltage regulators. But no one has mentioned using the Belleson Superpower regulators SPJ17/SPJ79 www.Belleson.com

Datasheet http://www.belleson.com/download/Superpower_datasheet.pdf

Anyone tried these regulators in the LC or other amp circuits?

 

[nippon]

Quote from the website of the "superpower":
 
SPJ78, specify voltage [note that standard LM78xx can be used]... as also for SPJ79...
 
Moneyburner detected! You can easily DIY a really nice power supply for less!

 

[ervstil]

I have a "original" Lovely cube with a strange problem. It has rather loud 50 hz hum and buz. It is intermittent, some times it is there an some times not. It is always the same level and goes from 0 to 100%, never in between. It is not affected by the pot position, not related to the input (shorted input makes no difference). The regulators are functional genuine ones, the main PS caps are ok. Does anyone have the same problem or does anyone have any ideas?

 

[shaman11]

check the diodes (wrong direction ?)
cold solder points ?
check this with an ohm meter and check the diodes off the pcb with the meter.
move the headphone cable, the audiocables and look if the problem is gone ? if yes take a look to this solder joints.
check the line in cables around the toroid transformer .. is the hum comming and going ?
 
cheers.

 

[ervstil]

Thanks for the reply!
 
Last night i solved the puzzle at last. I have checked all the usual suspects, including the suggestions above every thing was OK. I changed my 627 op amps for another pair. Same thing. Then i changed to a genuine opa2134 in dil package. Dead silent! As it turns out the opamp adapter functioning as an antenna and my  R-core transformer induced hum right in the feedback loop. I verified this by adding a "class a bias socket" and thing got really hummy. I have ruled out this before because i tried different shields and positions of the transformer with absolutely no difference. 
 
So last night i re-winded a 60 va 2x12v toroid to 2x16v. I also added a electrostatic screen and connected it to the star ground. It was a really tight fit and i have to isolate the center bolt because it tushes the top of the case. I did not expect a good result because of the size of the transformer, now  the input and output cables are really close.
 
The result was near perfect! 99% of the hum is gone! I did not expect this kind of difference between r-core and toroid.  Strange because the hum problem was not so severe a couple of moths ago. The most surprising thing was the audible quality difference between my old 30va (probably closer to 20 va in reality) and the new 60 va.
 
The sound is better in the whole register especially the bass. I have seen comment of this earlier in the forum but thought it was bs. Why would a class a regulated circuit sound better with a massively over sized transformer over a sufficient one? Well this one does.....
 
I was also surprised how much better  the amp sounds with my assumed fake 627 compared with my genuine 2134. maybe they are genuine....
 
After this success  i decided to to competently remove my good quality 2.5 uf input cap. another huge step up! even better bass and another "veil" removed. I do not understand why the original value is so low. Going from 1.8 uf to 2.5 was big difference, removing it completely was a greater step up. If you have a offset problem it is better to solve the problem instead of adding a cap.
 
One last observation, disconnecting the audio ground from the chassis and mains ground really improved the hum situation, so i vill leave it out or try to find space for a diode bridge ground isolator, Nelson Pass style.
 
That would be the last mod i will do to it as at soon will be retired. I only use my electrostatic headphones now, and when my dac is finished i have no use for a pre amp. And if i fire up my dynamic phones again i have my balanced "aleph h" that blows this amp away competently. Highly recommended, dirt cheap to build on a breadboard and no opamps. Look it up on diyaudio if you are interested. 
 
B.R Christian