The "Lovely Cube" Headphone Amp (Lehmann Black Cube Linear Clone) - Page 55

I don't think it's possible. I've read comparisions between LC and Matrix M-Stage and they said that LC is more power efficient, don't know why would it since it's a clone, but I know a couple of people who confirmed it.

Quote:

Originally Posted by nsk1 

I don't think it's possible. I've read comparisions between LC and Matrix M-Stage and they said that LC is more power efficient, don't know why would it since it's a clone, but I know a couple of people who confirmed it.

LC has stronger transformer (30VA) and more biased BC550/560C transistors. It is 1.2K resistor in LC, instead of 1.5K resistor in Matrix M Stage. (More current is allowed to pass through BC-s.) 

But that has impact only on low impedance headphones. I think, high impedance one will have advantage with higher voltage PSU.

Quote:

Originally Posted by BlaBlaBla 

Cool!

 

The best gain for k701 would be to make better cooling first, and then to check DC offset - because stock BC550/560 are crap. Now I know that those PH transistors are not made by Philips and nothing but low cost fakes that like to burn very often.

 

I would like to se someone who will be able to listen to music more than 4 hours when outside temperature is >30C. "Do not drill/remove top plate, because it has to keep components warm. They sound better." - So big pile of **** I have never seen. Maybe someone likes the sound of barbecue! :)
 

http://www.head-fi.org/t/501046/the-lovely-cube-headphone-amp-lehmann-black-cube-linear-clone/315#post_7236719

Does it have anything to do with this post here^? I want to make the same changes but I have zero experience. If someone can give me some very clear, detailed and hand-holding instructions, I'll go for it! I think I can google for the parts on my own.

Quote:

Originally Posted by francisdemarte 

You'll have to open up the box and resolder the wires in the correct plug. Really easier if you know how to solder or know someone who does.
 

Quote:

Originally Posted by Mad Max 

Use gain of 10 for K701.

Thanks thanks thanks
 

Yes it has. You can replace a few parts, but the crucial is to buy genuine parts available on the market..  Flukell is extremely experienced old school DIY-er but you can't find genuine Philips any more. Also, he mentioned that in the post. Transistors that are supplied in Lovely Cube kit are Philips copy. So when you know that searching for genuine parts is like Don Quijote story, the best that you can do is to buy genuine Fairchild/On Semi/NXP or similar. Do not search for Philips or Toshiba because they do not exist any more (as far as I know - the type that can be implemented in Lovely Cube). Matching transistors (especially BC550/560) will give you great advance in the sound and lower your DC offset. In this case it is better to have matched On Semi transistors than to have non matched NXP.

Next that you can do, is to find better capacitors. Stock Elna are good enough if they are new. That means that 5 years old electrolytic capacitor (from old stock) is worse than a new one. Because electrolytic capacitors are prone to dry out. I think that in Lovely Cube you should try Panasonic FC or Philips BC. Both are excellent. Panasonic FC have deeper sound stage, Philips BC have better dynamic. Do not use Panasonic FM because those capacitors have TOO LOW RESISTANCE and regulators will start to oscillate. They are not recommended after LM317/337 regulators. If you want something more audiophile you can try Elna Cerafine or Tonerex. Elna Silmic won't fit into Lovely Cube because it is too big. But be aware because Lovely Cube goes very hot and Elna won't last too long.

Also, you can replace (in LM317/337 circuit) resistor 1.2K with zener diode (13V, 1.3W). On some sites I heard that this can reduce noises from regulators. I did that and it is ok. But when you do that, be shure to put two zener diodes (parallel) because of safety reasons.  You can play with ADJ and OUT capacitors on LM 317/337 circuit and find capacity that suits you the best. Personally, I found that tantalum alone (by the book for LM regulators) as ADJ capacitors give the best punch and response. Be aware that tantalum capacitors must have voltage twice as much than voltage across them.

Good resistors are not important if there are only a few in a circuit. But if you change resistors on lots of places then you will see improvement. Here I think on cheap but good resistors like PRP, Holco, Kiwame or Vishay Dale (which is one step below first two and represents industrial long life resistor). Using high class (Takman, Shinkoh, AMRG etc...) is total nonsense because circuit alone is not capable to give enough to make those resistors worth. I tried cheap Riken OHM (carbon film) as output resistors (10 Ohm, 2W) and found out that they are excellent. Allen Bradley is excellent too, if you can find them cheap. They have clarity and sound is more relaxed (not too aggressive). In signal path I always use metal film because I don't want any coloration in the sound.

Quote:

Originally Posted by taiyoyuden 

 

http://www.head-fi.org/t/501046/the-lovely-cube-headphone-amp-lehmann-black-cube-linear-clone/315#post_7236719

 

Does it have anything to do with this post here^? I want to make the same changes but I have zero experience. If someone can give me some very clear, detailed and hand-holding instructions, I'll go for it! I think I can google for the parts on my own.

 

Quote:

 

Thanks thanks thanks
 

 

Quote:

Originally Posted by nsk1 

Does anyone know how much power Lovely Cube puts out at 600 Ohm?

And anyone know how much power it puts into 50 ohms?

I finally received the double opamp adapter a couple of weeks ago and have not really heard too much difference between 627,637 and others.  

However am now driving a pair of Hifiman HE-6 from it.... and it seems to have enough power for the job, but quite dark sounding, not too bright treble at all. 

Maybe you should try OPA2111 (v shape - bright high, hard middle high, weaker middle low and good low) or OPA2604 (mellow high, excellent middle, weak low). They are opposite to OPA2107 and OPA627...

Quote:

Originally Posted by alanbeeb 

And anyone know how much power it puts into 50 ohms?

I finally received the double opamp adapter a couple of weeks ago and have not really heard too much difference between 627,637 and others.  

However am now driving a pair of Hifiman HE-6 from it.... and it seems to have enough power for the job, but quite dark sounding, not too bright treble at all. 

 

The lazy way to correct for voltage offset independently in L or R channel.(there are other ways, of course!)

(In my case the offset was rather high in one channel, 17mV, while very acceptable in the other. A little trying and failing, and I ended up with less than 1mV offset by reducing the resistance in (what I call) R3 in the drawing to ca. 1.4k by  (from 1.5k) by adding an Rx=18k in parallel. The Idle current was accordingly increased by less than 2mA (of 57mA originally), a totally insignificant change IMO. I don't know if this could be of interest to any of you. You can see the added resistor in the photo).

I must not forget to say thanks to all for an interesting thread, Olaf

(this is also a kind of test posting, since it is my first)

.

You could use trimpot (50K or 20K).
 

Quote:

Originally Posted by chetlanin 

The lazy way to correct for voltage offset independently in L or R channel.(there are other ways, of course!)

 

(In my case the offset was rather high in one channel, 17mV, while very acceptable in the other. A little trying and failing, and I ended up with less than 1mV offset by reducing the resistance in (what I call) R3 in the drawing to ca. 1.4k by  (from 1.5k) by adding an Rx=18k in parallel. The Idle current was accordingly increased by less than 2mA (of 57mA originally), a totally insignificant change IMO. I don't know if this could be of interest to any of you. You can see the added resistor in the photo).

 

I must not forget to say thanks to all for an interesting thread, Olaf

 

(this is also a kind of test posting, since it is my first)

.

 

Quote:

Originally Posted by BlaBlaBla 

You could use trimpot (50K or 20K). 

 

I think you are right, esp in principle (so to speak): It would make it much easier to find the right setting. Personally i think that a resistor has advantages in this case, however. I will be easier to solder on, after that legs have been bended and cut to a suiteable form. Also it is less bulky, cheaper, more often at hand I suppose, and (in principle) more stable...

(I made only three attempts with higher values, by holding a resistor against the legs of "R3" on the component side of the board , before I landed on the right value. But one needs a steady hand for that, true).

The main point was -in any case-  that this was a convenient place in the cirquit to make such an individual adjustment, since you don't need to de-solder any component (or come close to the rather tiny solder joints by the BC transistors and surrounding resistors. Cheers, Olaf
 

You should try transformer with EI core (if you can find one very cheap) because toroidal transformers are very sensitive to noise in the power grid. Also they tend to pass through high frequency noise that are sometimes in power grid, and saturate very fast. EI core transformers are not prone to noises from grid and with them in a circuit you do not need capacitors over recitfier. Furthermore you do not need ultra fast rectifier at all because high noises will not pass through.

If you are able to separate transformer from rest of the circuit or you can make faradays cage for transformer, you should pick up as big transformer as you can put into your case. 60VA > will be enough. When you want to choose transformer, always have on your mind that real power is 80% of its max power. In the case for the 60VA transformer, it would have 40-50W real power (and sometime less). Because this is stereo and push pull topology it will give you 25VA per channel (1,5 A). This is not important when you want to drive high impedance headphones, but for low one - it is.

Originally Posted by miky2011 

Interesting. What about R-Core BlaBla?

Excellent choice, but hard to get a good one with good crafted core and windings. Personally, I think that difference is not as much as price is. Because we talk about power transformers, you actually need a transformer that primary goal is to suppress noises from power grid, and have enough power (current). Superior transformers (like toroidal - better efficiency, less weight, less magnetic field, etc. etc) are better in most departments - especially magnetic field and efficiency, but the last in suppressing noises. They pass through entire spectrum (garbage from grid). EI transformers don't. Actually, if you can isolate magnetic field of EI core, you do not need toroidal transformer at all. But if you want to save space in your enclosure (metal box) then toroidal is way to go.

Keep in mind, if you use toroidal transformer, you will have to use fery fast diodes in rectifier, and capacitors over diodes. Input caps must not be too big because toroidal transformer has huge starting current so with too big capacitor current will be even bigger - and fuse will blow. This is case when 200 VA > transformer is used...

When you use EI core, noises will be lower frequency but not from grid, but from transformer itself. Very good EI transformers have very low hum that is easy to handle and suppress, but they always have low hum. Some people do not want that, some do not care. I do not care too much, because it is audibile when you trying to listen to silence and not music. Also you can use bigger input capacitors because cold start current is much lower. EI transformers do not need ultra fast diodes in rectifier because less garbage passes through (high frequency). With slow diodes you do not have problems with noises made from rectifier itself. Fast recitfiers do not have any sense when they are used for 50/60 HZ frequency.

Quote:

Originally Posted by nsk1 

Interesting. What about R-Core BlaBla?

Great thread !!! Thanks for your answers ...

  I bought the "LovelyCube" for the fun of being able a "exact" copy of Lehmann BCL. That's my goal. 

  That is the reason why I like to know what type of components is mounted in the Lehmann Original. Some are named along the wire. It would be useful put them together in one post.

  It may be interesting that we all make a list. There are not many components and can be very useful for those who want to change this or that component.

  For example, I would like to know what type of resistance used in the original Lehmann (tolerance, VA, brand, etc ...). what kind of resistance are 10R (four) in output? 

  About transformer. In the previous post Chetlanin say that is more than enough with 30VA. Flukell http://www.head-fi.org/t/501046/the-lovely-cube-headphone-amp-lehmann-black-cube-linear-clone/390#post_7247740  claims that with more (VA) the sound is GREATLY improved. 

  its true? not its true? can anyone clarify this?

  more "¿unnnecesary?" power = better sound    why??????

Sorry again for my english.