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

[Tribbs]

Thank´s for your teply, Tribbs!

It´s a shame I can´t found those gold Neutrik here in West europe, shipping from Mouser is about $25.

It seem´s the shiny connectors that´s not gold plated is made of bronze with tin and selenium(?) plating:

http://www.ebay.com/itm/2x-GENUINE-JACK-PHONE-CONNECTOR-NEUTRIK-NYS216-1-4-6-35mm-STEREO-/280870616292?pt=LH_DefaultDomain_186&hash=item4165317ce4


/ Mikael Markstrom

$25 shipping from Mouser auf Deutschland? - OMG!

Is this jack for the Lovely Cube's PCB?
The part you linked to on eBay is too large.

You need a "Slim Jack" to fit on the Lovely Cube PCB.
http://www.neutrik.com/zoolu-website/media/download/2842/Drawing+NRJ6HF-1

Is this the correct part for you?
http://www.mouser.de/ProductDetail/Neutrik/NRJ6HF-1-AU/?qs=R5cXQUTKuHUV%2FlSznFp3HA%3D%3D

How many do you need?

 

[mikaelmark]

$25 shipping from Mouser auf Deutschland? - OMG!

Is this jack for the Lovely Cube's PCB?
The part you linked to on eBay is too large.

You need a "Slim Jack" to fit on the Lovely Cube PCB.
http://www.neutrik.com/zoolu-website/media/download/2842/Drawing+NRJ6HF-1

Is this the correct part for you?
http://www.mouser.de/ProductDetail/Neutrik/NRJ6HF-1-AU/?qs=R5cXQUTKuHUV%2FlSznFp3HA%3D%3D

How many do you need?

Yes, that is the correct part!
 
For me, the size/ height is not a big deal, as I will build my own case after I has finished the amp.
 
It´s enough for me if I can get four pcs of these headphone/ sockets. Is it possible to buy from you maybe? I can pay with Paypal, if you have an account.
 
 
Grateful regards: Mikael Markstrom

 

[Tribbs]

Yes, that is the correct part!

For me, the size/ height is not a big deal, as I will build my own case after I has finished the amp.

It´s enough for me if I can get four pcs of these headphone/ sockets. Is it possible to buy from you maybe? I can pay with Paypal, if you have an account.

Grateful regards: Mikael Markstrom

PM sent!

 

[mikaelmark]

I think gold plated jacks are cheap - no brainer.

The gold plated jacks that came with my LC "deluxe' kit (deluxe kit no longer available) look like these:

Neutrik NRJ6HF-1-AU http://www.neutrik.us/en-us/plugs-jacks/slim-jacks/nrj6hf-1-au

In stock at Mouser:
http://www.mouser.com/ProductDetail/Neutrik/NRJ6HF-1-AU/?qs=sGAEpiMZZMv0W4pxf2HiV218T9lEUjXAMEGr3NewsmE%3d

Mounting hardware must be ordered separately:
NRJ-NUT-B (black plastic)
http://www.mouser.com/ProductDetail/REAN-Neutrik/NRJ-NUT-B/?qs=sGAEpiMZZMt%2fyfy0dIxWU3AAL6z7x4Ur
NRJ-NUT-MK (metal knurled)
http://www.mouser.com/ProductDetail/Neutrik/NRJ-NUT-MK/?qs=%2fha2pyFadujZed****6FBPxlzcU%2fmwJCCmOJKMSfQcc%3d
NRJ-NUT-MS (metal)
http://www.mouser.com/ProductDetail/Neutrik/NRJ-NUT-MS/?qs=%2fha2pyFadujZed****6FBEfQiNgjNWY4S3DlgOz5xpIxeFS12gEZHQ%3d%3d
NRJ-NUT-R (red plastic)
http://www.mouser.com/ProductDetail/Neutrik/NRJ-NUT-R/?qs=%2fha2pyFadujZed****6FBDcoj1wQT3%252b0eSZ3usZUCC4%3d
NRJ-WB (black washer)
http://www.mouser.com/ProductDetail/REAN-Neutrik/NRJ-WB/?qs=sGAEpiMZZMuur7c7MCGU2IptMe4770rm

I realized those gold plated connectors from Neutrik are made of bronze.
 
As gold is one of the best metals to use as plating (due to it´s resistance to oxidation and quite good conductor behavior - only rhodium will be better against oxidation), it should be better then connectors using nickel or tin/ selenium plating. But as those tin plated connectors are made of copper, I think those will be much better suited as copper is a way better conductor then bronze. And for the conduction of the tin/ selenium, I don´t think it will be so much a grading down as the plating is so thin.
 
Also, when I take a deep look at a Neutrik connector in my Corda Swing amp, it´s gold plated - but not all of the three connector´s seems to be gold. Strange!
 
So Tribbs; Thank you very much for your kindly offer for those Neutrik´s, but I think I will stay with the copper one´s I already have.
 
 
/ Mikael Markstrom

 

[Tribbs]

I realized those gold plated connectors from Neutrik are made of bronze.

As gold is one of the best metals to use as plating (due to it´s resistance to oxidation and quite good conductor behavior - only rhodium will be better against oxidation), it should be better then connectors using nickel or tin/ selenium plating. But as those tin plated connectors are made of copper, I think those will be much better suited as copper is a way better conductor then bronze. And for the conduction of the tin/ selenium, I don´t think it will be so much a grading down as the plating is so thin.

Also, when I take a deep look at a Neutrik connector in my Corda Swing amp, it´s gold plated - but not all of the three connector´s seems to be gold. Strange!

So Tribbs; Thank you very much for your kindly offer for those Neutrik´s, but I think I will stay with the copper one´s I already have.


/ Mikael Markstrom

Silver is the best conductor even better than copper or gold. Of course solid silver and solid gold is not economical. Additionally, they are not strong enough in a pure form to resist metal fatigue in mechanical contacts such as jacks. Which is the reason for the use of bronze (88% copper and 12% tin) and other metals (plated steel) for mechanical strength. But in audio frequency, a relatively low frequency, the electrical current doesn't flow primarily on the conductors surface (skin effect) as it does with much higher (radio/microwave) frequencies. So, gold plating in audio applications is primarily a benefit as a non-oxidizing contact surface. In addition to gold plating, silver plating is also available. But, silver will tarnish over time, as will exposed copper and bronze, so conductivity may suffer. This is why gold is favored as a plated contact surface.

In any case, I don't think it is of great consequence except for your own satisfaction - I understand this

It's my pleasure - all the best!

 

[mikaelmark]

 
+/-21V is OK.
 
You will always have 14V on output because zener diode doesn't allow anything over 13V and LM regulation voltage is 1.25V. (13V+1.25V=14.25V). You can put there 2x36V transformer and voltage on output will be still around 14V. Zener diode replaced R2. Since you have 18VAC RMS transformer and output (after regulators) is less than 18V DC, you have big reserves. Probably regulators will heat more, but voltage will be stable (up to LM spec) because it is far above safety margin (Vtrans*1.25 - Vout(reg) = 2V).
 
I am glad that you are satisfied. Sometimes there will be good results and sometimes bad. When you do something on your own, you always learn something new.
 

What resistor could be replaced with Zener diodes? You wrote R2 near LM317 and LM337, but I can´t found any resistor named that.
 
So, what value do the replacable R2 -resistor has, and is it only one resistor to replace with Zener? And should it be one or two Zener in parallell?
 
 
Best regards: Mikael Markstrom

 

[Tribbs]

All lies! I need picture proof!

Replaced the 500mA slow blow fuse with a 1A. Reading up on the web about toroidal transformers (mine is 80VA!) it turns out that on power-up the initial surge to the toroid was causing my fuse to blow. After much trouble-shooting and voltage measurements I realized nothing was amiss. So, I simply increased the fuse rating. Dozens of power cycles later no more blown fuses - all is well.

Currently employing a pair of single channel LME49990MA opamps on a Brown Dog adapter - Swwwweet!

 

[sunneebear]

You've inspired me to get off my butt and revive my LC...tomorrow...maybe.  I'm a member of Procrastinators of America.

 

[Tribbs]

 


+/-21V is OK.

You will always have 14V on output because zener diode doesn't allow anything over 13V and LM regulation voltage is 1.25V. (13V+1.25V=14.25V). You can put there 2x36V transformer and voltage on output will be still around 14V. Zener diode replaced R2. Since you have 18VAC RMS transformer and output (after regulators) is less than 18V DC, you have big reserves. Probably regulators will heat more, but voltage will be stable (up to LM spec) because it is far above safety margin (Vtrans*1.25 - Vout(reg) = 2V).

I am glad that you are satisfied. Sometimes there will be good results and sometimes bad. When you do something on your own, you always learn something new.

What resistor could be replaced with Zener diodes? You wrote R2 near LM317 and LM337, but I can´t found any resistor named that.

So, what value do the replacable R2 -resistor has, and is it only one resistor to replace with Zener? And should it be one or two Zener in parallell?

Best regards: Mikael Markstrom

You are right. There is no "R2" resistor on the LC schematic or PCB.
The "R2" resistor to which Bla Bla was referring is relative to the LM voltage regulator notes at the following site:
http://www.acoustica.org.uk/t/3pin_reg_notes1.html
Quote in middle of the page, "replace R2 with something like a zener diode"

If you follow Bla Bla's method you will need four Zeners. Two parallel (piggy-backed) Zeners per each replaced 1K ohm resistor.
See photo in my next post. You can simply measure their resistance to be certain you have the correct resistors.

The cathodes of the Zener diodes should be oriented towards the higher voltage potential.
Zener pair one towards +15V, and Zener pair two towards 0V (ground),

This end, the anode, should be oriented towards the lower voltage potential, 0V and -15V, respectively.

See Bla Bla's diagram in my next post.

Fairchild Part No.: BZX85C13
Mouser Part No.: 512-BZX85C13
Newark Part No.: 18C6023
Digi-Key Part No.: BZX85C13-ND

:basshead:

 

[Tribbs]

Note each Zener diode pair's cathode orientation...


Look at Bla Bla's diagram #1 below...


So, the R2's would be R306 and R308 on the LC's PCB shown below.

The cathodes of the two parallel Zener diodes replacing R306 should be oriented towards C307.
The cathodes of the other two parallel Zener diodes replacing R308 should be oriented towards R304.

:atsmile:

 

[Tribbs]

You've inspired me to get off my butt and revive my LC...tomorrow...maybe.  I'm a member of Procrastinators of America.

 

[mikaelmark]

You are right. There is no "R2" resistor on the LC schematic or PCB.
The "R2" resistor to which Bla Bla was referring is relative to the LM voltage regulator notes at the following site:
http://www.acoustica.org.uk/t/3pin_reg_notes1.html
Quote in middle of the page, "replace R2 with something like a zener diode"

If you follow Bla Bla's method you will need four Zeners. Two parallel (piggy-backed) Zeners per each replaced 1K ohm resistor.
See photo in my next post. You can simply measure their resistance to be certain you have the correct resistors.

The cathodes of the Zener diodes should be oriented towards the higher voltage potential.
Zener pair one towards +15V, and Zener pair two towards 0V (ground),

This end, the anode, should be oriented towards the lower voltage potential, 0V and -15V, respectively.

See Bla Bla's diagram in my next post.

Fairchild Part No.: BZX85C13
Mouser Part No.: 512-BZX85C13
Newark Part No.: 18C6023
Digi-Key Part No.: BZX85C13-ND

Thank you very much for this explanation!

So, I guess the idea of using paralell Zeners are because of the low wattage they can handle. But if using a higher wattage Zener, do you think it´s enough with only 2 pcs (just single 1+1, not paralell 2+2), such as this 13 Volt 5 Watt 1N5350B:

http://uk.farnell.com/multicomp/1n5350b/diode-zener-5w-13v-5-do-201ae/dp/17980031N5350B%20DIODE,%20ZENER,%205W,%2013V,%205%,%20DO-201AE

As for the 1 A fuse instead of 500 mA, I also had a problem when I used a high Wattage toroidal transformer, so the fuse blowed up when powered on. When I replaced it with higher value (slow, of course), everything was fine. But where is the fuse in this amp? The only fuse I can see is the two yellow heat fuses PPTC at the incoming 15, 0, 15 VAC? I guess there should be a glass (or even better a AHP) fuse in the case, at one cable of the incoming 115/ 250 VAC after the IEC? But how high value dare the fuse have, is 2 A Slow too much?
 
 
Best regards: Mikael Markstrom

 

[mikaelmark]

Note each Zener diode pair's cathode orientation...


Look at Bla Bla's diagram #1 below...


So, the R2's would be R306 and R308 on the LC's PCB shown below.

The cathodes of the two parallel Zener diodes replacing R306 should be oriented towards C307.
The cathodes of the other two parallel Zener diodes replacing R308 should be oriented towards R304.

I assume the 200 Ohm resistor for R306 and R308 is only a mod when stay with the 1K1 resistors, and should not be used if replaced with Zener diodes, right? Is it two different mod´s?
 
/ Mikael Markstrom

 

[Tribbs]

Forgot to share this in previous post:
I have reworked the schematic with correct part naming (much easier to work with)

It's still wrong!

R307 should be labled "R308" (=1.1K ohm)
R308 should be labled "R307" (=100 ohm)

 

[Tribbs]

I assume the 200 Ohm resistor for R306 and R308 is only a mod when stay with the 1K1 resistors, and should not be used if replaced with Zener diodes, right? Is it two different mod´s?

/ Mikael Markstrom

WHAT 200 Ohm resistor???

The two resistors to be replaced with zener diodes are 1.1K ohm resistors: R306 and R308 as designated on the PCB of the Lovely Cube amplifier.