[BlaBlaBla]

My second LC is finished. Pictures of the board - tomorrow.
 
It took ten hours until everything settled in, and until it started to sing like I expect...

 

[ringer]

This is the best mode I have made for LC.
 

 
I don't know why they put 1.5uF in the input. If you put more capacitance you will fill the difference. The frequency response will not change, but bass will be better. And there will be less noise when attenuator on height position. I've used 8.2uF, but I think 22uF will be even better.
 

 

[BlaBlaBla]

Quote:

This is the best mode I have made for LC.
 

 
I don't know why they put 1.5uF in the input. If you put more capacitance you will fill the difference. The frequency response will not change, but bass will be better. And there will be less noise when attenuator on height position. I've used 8.2uF, but I think 22uF will be even better.
 

Nice work!
 
Mine looks like this...
 

 
 
I agree that bigger capacitors in input, are better. Bass is much better.
 
I made something unusual. All resistors are PRP, except those in output. I do not know but I think that output resistors are something like Riken Ohm RM or Allen Bradley. I bought 50 pcs and all of them have exactly 10.1 Ohm resistance, which is impressive for such an old product.
 
There are two ERO KP 1837 (0.1uF) after regulators, four Panasonic FC (680uF) on output, two Nichicon Muse (22uF) and two polystyrene as coupling (10 nF).
 
In input there are two ERO MKC 1862 (4,7uF) and two AEL polystyrene (31 nF),  as input filter I use two FSC Styroflex (100pF).
 
 
Transistors are stock BC550/560 and matched BD139/140 (believe me I do not see any improvement over unmatched trensistors).
 
 
First few hours amplifier was mellow and restricted on highs. But now things are different. It is unforgiving for bad recordings.

 

[ringer]

Thanks

Yours looking good to
 
I'm not sure, but I think unmatched transistors could be cause of rising DC in the output and some increase of distortion, but it might be not noticeable because it less then headphones distortion.
 
Why you use 31nF caps in the input? I think it will be batter to use only one as good as possible then two (IMHO).
 
Also try to move transformer as far as possible from signal wires and board. Even half centimeter will reduce noise significantly.

 

[gwikse]

Looks very nice. You should try to change all the fixings and screws to brass. Start with the transformer mounting. This little tweak has so far allways led to better sq in all my components. I am waiting for larger trannies as well (80VA).  I still have a lot of work to do before I mount it all in its final chassis.

 

[BlaBlaBla]

Quote:

Thanks

Yours looking good to
 
I'm not sure, but I think unmatched transistors could be cause of rising DC in the output and some increase of distortion, but it might be not noticeable because it less then headphones distortion.
 
Why you use 31nF caps in the input? I think it will be batter to use only one as good as possible then two (IMHO).
 
Also try to move transformer as far as possible from signal wires and board. Even half centimeter will reduce noise significantly.

 
Thanks!

I will try that when I find better (bigger) box for amp. (I think that I have a few metal boxes somewhere in the house...) Bigger transformer is my next goal. 80 - 100VA is way to go. This enclosure is too small, tight, and heats too much. That is not good for polystyrene-s and MKP-s.
 
I tuned DC offset with Radj on LM regulators. I always use Radj because it is hard to find good regulators which have the same heating "offset". Also it is hard to find PNP and NPN that have the same hFE. On this setup (550/560C) I achieved 2-3 mV offset when I tuned LM317 on + 14.8V, and LME337 on - 14.1V.
 
I have another LC amplifier with different transistors 139/109C. And there, offset is smaller (1-2 mV) when voltage is - 14.3V and + 14.25V. I have feeling that those old metal transistors have better temperature characteristic than this new, made of plastic... Well, who knows...
 
It is true. Less capacitors in a circuit is better. I will try two big MKP-s when I get them. I put polystyrene caps because I tried to make sound more colored in a way that I like. Without polystyrene sound was, slightly, too bassy and mids too dark. Polystyrene caps brightened up sound stage. I like trying different components (capacitors, opamps, transistors). It is interesting how they change final picture of the sound. But it takes time because every component needs burn in time (that is usually 10 hours of playing).
 
I connected cable coatings directly to ground. On Grado and ATH headphones, at max volume, I barely hear transformer hum. But that would blow my ears anyway. Grounding is very interesting and important in audio circuits. I was reading something about different resistor values in the ground loop and how they can direct parasitic current to bypass crucial circuits and components... I am interested in grounding technique, but do not have time to study it. Too much to do, and too little time.
 

 

[ringer]

Quote:

 
Thanks!

I will try that when I find better (bigger) box for amp. (I think that I have a few metal boxes somewhere in the house...) Bigger transformer is my next goal. 80 - 100VA is way to go. This enclosure is too small, tight, and heats too much. That is not good for polystyrene-s and MKP-s.
 
I tuned DC offset with Radj on LM regulators. I always use Radj because it is hard to find good regulators which have the same heating "offset". Also it is hard to find PNP and NPN that have the same hFE. On this setup (550/560C) I achieved 2-3 mV offset when I tuned LM317 on + 14.8V, and LME337 on - 14.1V.
 
I have another LC amplifier with different transistors 139/109C. And there, offset is smaller (1-2 mV) when voltage is - 14.3V and + 14.25V. I have feeling that those old metal transistors have better temperature characteristic than this new, made of plastic... Well, who knows...
 
It is true. Less capacitors in a circuit is better. I will try two big MKP-s when I get them. I put polystyrene caps because I tried to make sound more colored in a way that I like. Without polystyrene sound was, slightly, too bassy and mids too dark. Polystyrene caps brightened up sound stage. I like trying different components (capacitors, opamps, transistors). It is interesting how they change final picture of the sound. But it takes time because every component needs burn in time (that is usually 10 hours of playing).
 
I connected cable coatings directly to ground. On Grado and ATH headphones, at max volume, I barely hear transformer hum. But that would blow my ears anyway. Grounding is very interesting and important in audio circuits. I was reading something about different resistor values in the ground loop and how they can direct parasitic current to bypass crucial circuits and components... I am interested in grounding technique, but do not have time to study it. Too much to do, and too little time.
 

Try to move transformer in this box. It's not necessary to screw it symmetrically. Take a look on my photo.
 
2-3mV is an excellent result! Even ten times more is OK
 
Look at my addition for LC

This is heavy duty 5W single ended class A amp. With 200W transformer on board. The circuit by Mark Houston http://diyaudioprojects.com/Solid/ZCA/ZCA.htm
I'm using LC as preamp for listening MBQuart 450 headphones. The sound starts to be more natural and balanced. Sound signature no more bright. The mid-low and low range are very good and precise. It seams that MBQuart 450 likes to be driving by height power. Compare to this thing LC is cold as snow in winter ))


 
Trying to make some dinner

 

[francisdemarte]

Quote:

This is the best mode I have made for LC.
 

 
I don't know why they put 1.5uF in the input. If you put more capacitance you will fill the difference. The frequency response will not change, but bass will be better. And there will be less noise when attenuator on height position. I've used 8.2uF, but I think 22uF will be even better.
 

Nice! Reminds me that I have a couple of old Vitamin Q Oil and Paper caps I want to try in this position! Will report back with pictures  

 

[T.IIZUKA]

Quote:

 
Mine looks like this...
 

 
 

What does the output resistance use?
 

 
I switched to DALE CW-2B.
 
 
A former pic.
 

 

[francisdemarte]

 
I heard it was bad to use the center screw of your torodial transformer as a ground point.

 

[gwikse]

My "stock" lovely cube has been running for a long time now. Used two in a balanced config but screw up one when trying to remove some parts. So next step (if I deside to stay with the lc) is to max out two with better parts (matched and so on) or just tweak a little on the one I allready have (change the input caps). I used mundorf supreme solder, fairchild voltage regulators and 139/140 as well as BYV27-150`s and a 80VA transformer on the one I`m using now. Audio-GD opa earth is also great in my system. I`m using a hifi2000 [size=x-small]1NGXA288N case [/size]so space is not an issue. Have not drilled out the front plate yet though so it all looks a little diy`ish atm...
 
Been running it with a TPA Buffalo II - legato 2 DAC the last few days and I am as close to audio nirvana as I have been for quite some time (must go back to during my crazy Burmester + Audiophysic days).
Bought a set of T1`s and the last few days the system has stopped being a system, and started to do its job well enough to make me fokus on the music, movie, sports or whatever. Lovely cube indeed

 

[gwikse]

After this experience I pulled the trigger on a fully balanced beta22 with sigma22 psu. Should be ready sometime this summer. The lovely cube will be mated with my Matrix mini-i on the rear of my computer screen (I`m making a chassis to be mounted to the screen`s vesa holes).
 
I have to do something with my dc offset though. the 10mV - 3mV I have now is "ok" with my 600ohm T1`s but will be too much on my DT770-80. Oh well trimpots on the way I guess

 

[hifienthusiast]

The headphone output of my Blackcube Linear clone is silent but when I use the line output to my Quad 306 power amp, there is a constant hum through the speakers. What is the cause of this hum through the line output? Could it be the body of the Alps pot not being grounded properly?

 

[gwikse]

Cable to the pre-out too close to the transformer will cause hum. If it were the alps pot you would also hear it when using headphones.

 

[BlaBlaBla]

I have three ground poins. First is metal case, second is ground on PCB, and third is central screw of transformer. No problems at all. With ATH and Grado, there is no hum.
 
Quote:

 
I heard it was bad to use the center screw of your torodial transformer as a ground point.