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The "Lovely Cube" Headphone Amp (Lehmann Black Cube Linear Clone) - Page 86

post #1276 of 1289

Obviously not the most gorgously headphone amp. There are now aluminum plates for shielding between the parts, connected to the chassis. Also used a glue gun for isolating some wiring and solderings.

 

Left to do now; assembling the black plastic volume knob with some epoxy glue and fix some soft feet underneath. Any suggestions?

post #1277 of 1289

Maybe a wooded box on the outside should be nice.

 

About the feet, the original LBC SE has SSC-feet. How important are those, ase the amp not having any movable parts, lika a CD-player? Maybe some soft rubber foam will be an alternative (as used for packing hard discs)? Already using some for my CD-player and home cinema amp.

 

post #1278 of 1289
Mikael,

Which power supply capacitors do you have in there?

I was also looking at those SSC feet. Same as the original Lehmann but so expensive for no benefit other than for beauty.
Beautiful girls are expensive but with more benefits wink.gif

I decided to purchase the UNI-T UT61A from Amazon for $36 shipped.
http://thebrightsideforums.com/viewtopic.php?f=15&t=1334
I could use an extra DMM.

It comes with a special plug for measuring transistors which ONLY works with model UT61A.
The higher level models, UT61B,C,D,... do not have the hFE transistor measuring function.

sku_114340_8.jpg
Edited by Tribbs - 3/29/15 at 10:07am
post #1279 of 1289
Dose anyone here have experience with Lehman Clone as a preamp ?

Is there anything that should be altered to improve upon ?
post #1280 of 1289
Quote:
Originally Posted by laughingbuddha View Post

Dose anyone here have experience with Lehman Clone as a preamp ?

Is there anything that should be altered to improve upon ?

For a while I used it to connect with my active speakers, the Hivi Swans A30. It worked really well since the speakers' volume control lags a lot. The preamp out allows you to adjust the line out volume.

post #1281 of 1289

I was thinking of gettting this as my ss amp, can anyone comment on how it sounds compared to the Gustard H10 and other amps. im looking for a warm sound. 


 

post #1282 of 1289

Oh noo, what have I done?:confused_face:

 

Just touched the heat sink for LM337 to with a metal tool to chassi, so it sparkle and banged. When I measured afterwards, the heat sink has +14,6VDC and not ground.

 

But everything seems to work fine. May anything in the amp or the connected headphones (HD800) been damaged?

 

And because the chassi is grill ventilated, the temp for the transistors, voltage regulators and the two big filter caps has140 Fahrenheit/60 Celsius and other parts 86Fahrenheit/30 Celsius. Is this too low? Should´nt the transistors be about 185 Fahrenheit/85 Celsius? Maybe I should make less ventilated?

post #1283 of 1289

Maybe I´ts the wrong way to use ventilated chassi or separate the parts with aluminum shielding plates or use bigger heat sinks to lower the temperature!?

 

Above is from LC homepage mod´s/findings:

 

My Advices :

  1. Don't try to cool down the transistors by changing large heat sink or remove and mount on the case . No worries about burn out the transistor , the transistors' (BD139/140) max. junction temp is 150°C (http://www.datasheetcatalog.org/datasheet/fairchild/BD139.pdf)
  2. Don't try to make holes on the case for ventilation. This doing will destroy the heat traps.
  3. Use similar case. It is recommended not to use large case, large case cannot trap heat well.. If cannot find suitable case , buy from me :) .
post #1284 of 1289
I have always wondered about the LC temperature argument. You can use the argument that the transistors performance is optimized at a high temperature. But, at what cost to other components, especially capacitors?

You will notice the latest version of the Matrix M-Stage (another Lehmann clone) has vents for cooling:
post #1285 of 1289

thats really stupid. Semiconductors hate heat.you get odd distortions if you heat them up.

 

why did kress and other companies put huge heatsinks (more than 50% of the case)

inside their highend amps ???

 

 

Transistors:

pair them and you will be happy.

 

I use this schematic to pair my transistors:

 

http://www.fantasyjackpalance.com/fjp/sound/synth/synthdata/16-minimoog/002/905-matching-transistor.gif

it is from bob moog. A synth genius from the seventies.

 

the bc550/560 are the parts who define the sound of this amp. different parts sounds different here.

 

 

A good (!) 4 digits Fluke DVM is enough for pairing without the moog schematic. This cheap china crap like the one in this thread is not accurate enough for me.

 

for power supply I use 2 lead seal batteries. Wonderful warm sound.

 

At the moment I try a shunt regulator design for line supply. the lm3xx is real crap.

 

cheers

 

Shaman


Edited by shaman11 - 4/4/15 at 11:30am
post #1286 of 1289
You don't need accuracy to "match" transisters.

"The 4 output transistors (BD139/140) have BEST performance at about temp 70°C"
"The 4 Capacitors (470uF) have BEST performance at about 50°C"
Edited by Tribbs - 4/4/15 at 6:59pm
post #1287 of 1289

I have now burned in everhing, and made a deeper listening session. I used my HD600 with Cardas cable, a $350 RCA-cable connected to a modded AK4399 DAC.

 

First I was listening to some songs from Spotify, and the impression was intermediate. When I then swapped to 16 bit 44,1 khz (CD-quality) everything was changed - the music was floating all around me and I could spot every note and instrument with high precision with a huge sound stage. Really impressing. When the LC was connected to a speaker amp, the sound were also nice, but just not as good as with the headphones. I have now to try my HD800 and also with higher quality songs, like 24 bit/ 192 khz.

post #1288 of 1289

Will the amp work fine if I remove all the three LED´s?

 

What´s the purpose for the two LED´s after the 4K7 resistor inside the chassi?

 

I know the one after the 15K resistor is for the power, but the other two will not bee seen as the are inside the chassi. Should it be safe to remove all of them?

post #1289 of 1289

When I have no DC coupling caps at the signal path input for LC and measure DC offset at headphone out, it seem´s there is almost 200 mV. But after a few seconds, it drop to about 0 mV.

 

Is there anything to worry about, so I should maybe use coupling caps?

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