Hi francisdemarte,
Laser Collection's clones are not bad, I compared their PCB with the original Lehmann Black Cube Linear PCB and you would think the PCB’s have come from the same Gerber (CAD) files.
Two things though to watch with the clone, I was suspicious of the semiconductors shipped with the kit, we ended up replacing the diodes in the power supply with genuine PHILIPS (NXP) BYV27-200 as per the original, similarly, the LM337 and LM317 replaced with genuine NSC parts.
(When I visited China last year there was a lot of talk in the industry of local backyard companies making inferior clone components and then trying to pass them off as genuine name brand parts - several large companies got stung buying nasty clone decoupling caps that cost a lot to recall product and rectify the situation....it's a real wild west there...)
Again, replace the OPA2134 with the genuine thing from TI/BB. But the real catch is in the diamond buffer output stage: The clone comes with BC560 and BC550, replacing these with Fairchild’s BC560C and BC550C (hFE selection: C) and then replacing the output transistors also with FAIRCHILD BD139-16 and BD140-16 (hFE Selection: Group 16) this amp really comes to life!!! (The current gain of the transistors hFE is important here and what makes the difference between the Lehmann and the clone knock-off's from an audio point of view)
The original Lehmann uses these high beta devices in the output stage - I wouldn't be surprised at all if they hand S.O.T. these parts before they stick them in the PCB: When you look at the genuine Lehmann PCB, the passive components, diodes and regulators look as though they've been wave soldered (e.g. Machine Soldered) while the BD139/140s and especially the BC550C/560C look as if they've been hand soldered - tell tail signs these parts have been Selected on Test (S.O.T.) before being mounted on the PCB, or they were faulty and the board was re-worked - doubt it some how! After all they're Germans, and it's inherent in their culture to measure and calculate everything! No doubt Lehmann will be matching for beta and may be VBE in the NPN and PNP driver stage in each channel - matching NPN and PNP devices is time consuming and expensive, especially with German labour rates...Or, as they sit so high off the PCB, it's just too hard to support them during Wave Soldering - this is going to be one of those unknowns...they'll probably read this and then proclaim that they measure eveything...
(If you can get the original PHILIPS (NXP) versions of the BD139-16 and BD140-16 – this amp kicks arse. PHILIPS produced a superior fT rating of better than 150MHz (the ones I have measure better than the data sheet: ft=150MHz for the NPN and ft=220MHz for the PNP!!!) compared to around 50MHz for the ST parts –haven’t bothered to measure the ON SEMI parts; for some reason, probably embarrassed, neither ST nor FAIRCHILD will disclose the fT switching characteristics, we ended up measuring it on a test rig at work – things you do on a Friday afternoon waiting for the weekend!
Also, the PHILIPS BD139-16 and BD140-16 seem to have hFE that measure on the high side and are very consistent amongst a production batch, so it is easier to get the left and right channels matched)
( I don’t know why NXP killed the BD139 and BD140 product line – unbeknown only to a bloody Dutchman! Their BC550C and BC560C were the best in the industry! The beta variation in batches of these devices was so small you could stick them into a differential stage of an amp without a care in the world as to their beta variation; on the other hand IMO On Semi devices are a nightmare – you have to measure every part for hFE and VBE variation to find two that come close (2%) when using them for a differential pair stage, but they are cheap, price wise! )
We didn’t trust the input caps supplied with the clone kit either, 1,5uF Polyester and not sure about the 22nF. We ended putting in 1,5uF EPCOS Metallised PP B32654 and the BC KP462 (2222 462 .....) Polypropylene 22nF and things really got better.
Also the 100pF (correction) cap across the non-inverting inputs of the OPAMP needs to be replaced with the genuine McCoy BC KP464 (2222 464 .....) F 630V PP 100pF.
Lastly, we replaced the 4.700uF Electrolytics with genuine NICHICON parts from MOUSER, actually the FM Series PANASONIC turned out to be a better bet.
IMO: The biggest issue with the knock-off’s from CHINA, such as the Lovely Cube, is that the people doing the cloning don’t pay enough attention to the subtleties in component selection used in the original circuit / product– they tend to build the stuff with whatever they can get their hands on without any real thought to the quality of what they are producing – shame really!
Either way, I could never afford to buy the genuine Lehmann - just too pricy by the time it gets down to NZ! I saw it in a shop locally, listened to it and thought nice sound, but no way was it worth the money they were asking (NZD$1900) - I just had to walk away from it. When the kit came up on eBay I jumped at it.
Then I got the chance to pull the lid off a friend's Lehmann and spotted all of the above...
Stayed tuned for the next instalment...more to come,,,,
