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The "Lovely Cube" Headphone Amp (Lehmann Black Cube Linear Clone) - Page 61

post #901 of 1168
Thread Starter 

That's way too voltage between 4 and 7 should be closer to 15v. So the problem is further back along. 

 

 

First make sure your transformer is outputting +-15v AC into the board

 
Next check the Vin and Vout of the two regulators you replaced.

 

 

 

 

 

 

post #902 of 1168

IS it too low?

 

Could it be because the MM lead accidently slipped and touched two leads on the LM337?

post #903 of 1168
Thread Starter 

With one of the leds not lit, either the neg or the pos power supply side is not working right (maybe the led is fried?)

 

Anyway the regulators are pretty robust. A short slip is unlikely to kill them, it will send them into protection mode where they shut down completely for a while, as you saw.

 

First are you 100% sure your transformer is wired correctly?

 

Which led isn't working? Follow the traces back to the regulator and check the output. They are pretty easy to follow from the back of the board.

 

 

lovelycubepcb02.jpg

 

Try cross posting this to the M-Stage thread too.


Edited by francisdemarte - 12/6/11 at 7:15pm
post #904 of 1168

The MM should be on AC right?

 

For some reason, the transformer leads are coming up at 19.2V. What in the world??? Shouldn't it be 15V?

 

THe LED that is toward the big 4700uf caps is not lighting up. The other one (towards the edge) does light up.

 

I was following traces and there is a weird find. The four eletrolytic caps..two of them that connect to the LM337 (the one that made the spark when I was checking the voltage) stop as a certain resistance when I do a resistance test. The other two connected to the LM317 keep rising up in resistance as a working cap should be.

 

The voltages on the regulators are:

 

LM317 - Vin is 24.4V and Vout is 3.65V

LM337 - Vin is -24.4V Vout is -1.2V


Edited by JiggaD369 - 12/6/11 at 11:20pm
post #905 of 1168
Quote:
Originally Posted by BlaBlaBla View Post

 

This is real thing...

 

http://gilmore2.chem.northwestern.edu/projects/showfile.php?file=ahammer2_prj.htm

 



Wow - that looks awesome!

post #906 of 1168
Quote:
Originally Posted by francisdemarte View Post

Post up a high res picture of your board, top and bottom and indicate the parts you changed. I think part of the problem is your opamp is fried.


Opamp is not fried. Short circuit was before opamp. Regulators are down.

Opamp is very robust and only thing that can kill it is potential spike or electrostatic spike.

 

post #907 of 1168
Quote:
Originally Posted by JiggaD369 View Post

The MM should be on AC right?

 

For some reason, the transformer leads are coming up at 19.2V. What in the world??? Shouldn't it be 15V?

 

THe LED that is toward the big 4700uf caps is not lighting up. The other one (towards the edge) does light up.

 

I was following traces and there is a weird find. The four eletrolytic caps..two of them that connect to the LM337 (the one that made the spark when I was checking the voltage) stop as a certain resistance when I do a resistance test. The other two connected to the LM317 keep rising up in resistance as a working cap should be.

 

The voltages on the regulators are:

 

LM317 - Vin is 24.4V and Vout is 3.65V

LM337 - Vin is -24.4V Vout is -1.2V


19V after bridge rectifier if you have 2x15V AC transformer

22,5V after bridge rectifier if you have 2x18V AC transformer

 

15V AC RMS goes to 1.41x(15-Vd). It is between 18V and 20V (depends on diode Vdrop and depends if it is double bridge or single bridge)

 

 

post #908 of 1168
Quote:
Originally Posted by JiggaD369 View Post

The MM should be on AC right?

 

For some reason, the transformer leads are coming up at 19.2V. What in the world??? Shouldn't it be 15V?

 

THe LED that is toward the big 4700uf caps is not lighting up. The other one (towards the edge) does light up.

 

I was following traces and there is a weird find. The four eletrolytic caps..two of them that connect to the LM337 (the one that made the spark when I was checking the voltage) stop as a certain resistance when I do a resistance test. The other two connected to the LM317 keep rising up in resistance as a working cap should be.

 

The voltages on the regulators are:

 

LM317 - Vin is 24.4V and Vout is 3.65V

LM337 - Vin is -24.4V Vout is -1.2V

 

Wait for two hours, I will check my setup and we will see...

 

post #909 of 1168
Quote:
Originally Posted by BlaBlaBla View Post


Opamp is not fried. Short circuit was before opamp. Regulators are down.

Opamp is very robust and only thing that can kill it is potential spike or electrostatic spike.

 


HI bla,

 

I have ordered new regulators.

 

Quote:
Originally Posted by BlaBlaBla View Post


19V after bridge rectifier if you have 2x15V AC transformer

22,5V after bridge rectifier if you have 2x18V AC transformer

 

15V AC RMS goes to 1.41x(15-Vd). It is between 18V and 20V (depends on diode Vdrop and depends if it is double bridge or single bridge)

 

 


But I'm getting 19.2V AC straight from the transformer leads..they're weren't even attached to the board.

 

Quote:
Originally Posted by BlaBlaBla View Post

 

Wait for two hours, I will check my setup and we will see...

 


Thanks for your help!

 

post #910 of 1168
Thread Starter 

I've killed a couple of opamps before with too much voltage, but I've never *so far* been able to kill a regulator.

Hopefully we'll get to the bottom of this when Bla comes back with his readings. 

 

 

 

 

post #911 of 1168

Is a dual 18v overkill? I'll be driving both low and high impedence headphones, so any chance to get some overhead I'd like to take. Or should I just play it safe and go with the stock 15v

 

http://www.ebay.com/itm/Toroidal-Transformer-15VA-P-115-230V-S-Dual-18V-/400244739603?pt=LH_DefaultDomain_0&hash=item5d30720e13
 

http://www.ebay.com/itm/Toroidal-Power-Transformer-15VA-Secondary-2x15V-Primary-115V-230V-/130612139500?pt=Vintage_Electronics_R2&hash=item1e691715ec

Quote:
Originally Posted by francisdemarte View Post

You want a transformer that has 2 15v secondaries. If your using the stock metal case you have to make sure your transformer fits. I think a 30VA Toroidal is cutting it pretty close. Anything bigger may be too tall to fit. 

 

 

 

 



 

post #912 of 1168
Thread Starter 

 

I use a transformer that outputs 18V and it is fine. Although I don't hear any improvement going from 15V to 18V. Keep in mind that I have a custom enclosure and my transformer is in separate box. If your using the stock enclosure makes sure the larger tranny fits.

 

 

post #913 of 1168

I have Talema 2x15V toroidal transformer (30 VA) that has 17.1V on output. Also have custom made EI transformer (80VA) that has 15.5V on output. It seems that custom made transformers might be more precise because they are hand made and turn ratio is strictly controlled by maker. But that does not have any effect on results.

 

Lets start with voltages.

 

I admit I have made mistake. After rectifier there is 21V. It is 1.25xVac. With rectifier that has 8 diodes it is less...

 

Regulator

Vin=21V

Vadj(below LM)= 13V (because I have 13V zener there)

Vout=14.2V - (because Vout voltage is calculated like Vzener+Vreference. Regulator reference voltage is between 1.2 and 1.3V for almost every good working LM 317 and 337. If you use zener instead R2 you can calculate voltage Vout=Vzener+1.2V)

 

After resistors (47ohm) and before opamp voltages depend on current that is needed for opamp. There I have 14.2V (and -14.3V-but id doesn't matter because this depends on regulator Vout that is not equal without trimpot tuning (instead fixed R2) on Vadj.).

 

DC offset on headphone out is the same through entire volume range (about 6 mV).

 

Try to measure Vadj. It has to be Vout-1.25V. If Vadj is very small and resistor R2 is not burned then something is wrong with tantalum. Tantalum capacitors are very sensitive. Sometimes tantalum may act as diode. My friend had four cases like that (but in 25 years of work with electronics in TV and VCR stuff).

 

Also try to measure DC offset without opamp pluged in (NEVER LEAVE YOUR HEADPHONES CONNECTED TO AMPLIFIER WITHOUT OPAMP because if circuit is on the edge of stability headphones load might it make unstable. In this way I killed AKG K701.). It must be close to DC offset with opamp. If it is not, that means that your circuit is oscillating. It may happen if LM regulators are oscillating. LM regulators can oscillate if electrolytic capacitors have too big resistance or even worse - to little. Tantalum in Vadj is crucial for stable operation because it allows you to put (after regulator) capacitor with less resistance. If someone tries to force 4 panasonic FM (1000+ uF) on output, regulator will start to ring and it may happen that you have 3-5 volts DC on headphone output with and without opamp.

 

If you have multimeter you can try to measure current that flows through supply. Measure on both lines (+ and -). It has to be equal. If the current is close to 1A or more, that means that something is wrong with transistors (in 95%) or that something has happened after regulators circuit (I guess that regulators are working fine so it might be that capacitor is broken).

Strong distortion on high volume levels might be connected with type of opamp. AD opamps are not good for this type of supply. They are too fast. Sometimes people say that in Lovely Cube AD opamps are "bright", "fast", "aggressive", etc... That is because they are on the edge of oscillation. Slow opamps are safe bet. For example OPA2107. OPA2107 has the same DC offset through entire range and gain (0, 10, 18, 20dB). Just opposite, LME has offest that goes up within volume band raises slowly with gain (8mV to 18mV). This means that LME does not like changes in input resistance and needs steady resistance, OR FEEDBACK (that LC does not have). Furthermore, AD797 (the best, the fastest, etc...) opamp starts with 10mV and in high gain has huge amount of DC offset (100mV and more) which means that is not good for this kind of setup, at all.

 

Without oscilloscope I would say that entire setup works fine if DC offset, with and without opamp, is the same. Try to measure that. Do not buy other stuff and change parts, maybe error is trivial and can be solved easy. If you have plans to change regulators do not pull out entire regulator. Just cut out the body of the regulator and leave legs in PCB. Cut out legs on new regulator just enough to be able to connect new body on old legs. Then solder that connection. Solder can withstand 170 C (WBT), or 190 C (Cardas) or 210 C (Mundorf, and other stock products). If something goes hot that much, melt down of a connection would be the smallest problem.

 

 

post #914 of 1168
Quote:
Originally Posted by francisdemarte View Post

 

I use a transformer that outputs 18V and it is fine. Although I don't hear any improvement going from 15V to 18V. Keep in mind that I have a custom enclosure and my transformer is in separate box. If your using the stock enclosure makes sure the larger tranny fits.

 

 


Usually benefit of bigger voltage is so small that it is limited with other parts of a circuit. It only matters if opamp is made for bigger voltage. For example OPA604 has sweet spot between +/-15 and +/-18V (it depends on power supply). There it has the best characteristic. OPA2134 works the best under +/-14V. Etc... If someone goes to bigger voltage he has to take care about resistors near transistors. Current through BC550/560 will be bigger and BC is the weakest part. I put 1k resistors, but voltage is +/-13.5V. I wouldn't let higher voltage through without making bigger distance between BC and BD (heat dissipation) or placing bigger heatsink on BD (to cool down them).

 

post #915 of 1168


 

Quote:
Originally Posted by BlaBlaBla View Post

I have Talema 2x15V toroidal transformer (30 VA) that has 17.1V on output. Also have custom made EI transformer (80VA) that has 15.5V on output. It seems that custom made transformers might be more precise because they are hand made and turn ratio is strictly controlled by maker. But that does not have any effect on results.

 

Lets start with voltages.

 

I admit I have made mistake. After rectifier there is 21V. It is 1.25xVac. With rectifier that has 8 diodes it is less...

 

Regulator

Vin=21V

Vadj(below LM)= 13V (because I have 13V zener there)

Vout=14.2V - (because Vout voltage is calculated like Vzener+Vreference. Regulator reference voltage is between 1.2 and 1.3V for almost every good working LM 317 and 337. If you use zener instead R2 you can calculate voltage Vout=Vzener+1.2V)

 

After resistors (47ohm) and before opamp voltages depend on current that is needed for opamp. There I have 14.2V (and -14.3V-but id doesn't matter because this depends on regulator Vout that is not equal without trimpot tuning (instead fixed R2) on Vadj.).

 

DC offset on headphone out is the same through entire volume range (about 6 mV).

 

Try to measure Vadj. It has to be Vout-1.25V. If Vadj is very small and resistor R2 is not burned then something is wrong with tantalum. Tantalum capacitors are very sensitive. Sometimes tantalum may act as diode. My friend had four cases like that (but in 25 years of work with electronics in TV and VCR stuff).

 

Also try to measure DC offset without opamp pluged in (NEVER LEAVE YOUR HEADPHONES CONNECTED TO AMPLIFIER WITHOUT OPAMP because if circuit is on the edge of stability headphones load might it make unstable. In this way I killed AKG K701.). It must be close to DC offset with opamp. If it is not, that means that your circuit is oscillating. It may happen if LM regulators are oscillating. LM regulators can oscillate if electrolytic capacitors have too big resistance or even worse - to little. Tantalum in Vadj is crucial for stable operation because it allows you to put (after regulator) capacitor with less resistance. If someone tries to force 4 panasonic FM (1000+ uF) on output, regulator will start to ring and it may happen that you have 3-5 volts DC on headphone output with and without opamp.

 

If you have multimeter you can try to measure current that flows through supply. Measure on both lines (+ and -). It has to be equal. If the current is close to 1A or more, that means that something is wrong with transistors (in 95%) or that something has happened after regulators circuit (I guess that regulators are working fine so it might be that capacitor is broken).

Strong distortion on high volume levels might be connected with type of opamp. AD opamps are not good for this type of supply. They are too fast. Sometimes people say that in Lovely Cube AD opamps are "bright", "fast", "aggressive", etc... That is because they are on the edge of oscillation. Slow opamps are safe bet. For example OPA2107. OPA2107 has the same DC offset through entire range and gain (0, 10, 18, 20dB). Just opposite, LME has offest that goes up within volume band raises slowly with gain (8mV to 18mV). This means that LME does not like changes in input resistance and needs steady resistance, OR FEEDBACK (that LC does not have). Furthermore, AD797 (the best, the fastest, etc...) opamp starts with 10mV and in high gain has huge amount of DC offset (100mV and more) which means that is not good for this kind of setup, at all.

 

Without oscilloscope I would say that entire setup works fine if DC offset, with and without opamp, is the same. Try to measure that. Do not buy other stuff and change parts, maybe error is trivial and can be solved easy. If you have plans to change regulators do not pull out entire regulator. Just cut out the body of the regulator and leave legs in PCB. Cut out legs on new regulator just enough to be able to connect new body on old legs. Then solder that connection. Solder can withstand 170 C (WBT), or 190 C (Cardas) or 210 C (Mundorf, and other stock products). If something goes hot that much, melt down of a connection would be the smallest problem.

 

 

 

Hi Bla,

 

 

A. I checked the volatges on the regulators again and they are:
 
LM317 - Vadj is 2.4V, Vin is 23.7V, and Vout is 3.6V
LM337 - Vadj is 0.0V, Vin is -23.7V, and Vout is -1.27V
 
According to your measurements, it looks like they're blown?
 
B. At the 47ohm resistors before the opamp, I'm getting two different reading on both resistors. It's 3.6V on the Left and -1.2V on the Right.
 
C. R2's seem fine. Should I swap them out for the 13V zeners I ordered?
 
D. But the Tantalum that was connected to LM337 ADJ pin is ringing when I do a continuity test so thats blown, right?
 
E. DC offset on the headphone jack is 160mv. :(
 
 

Edited by JiggaD369 - 12/7/11 at 9:31pm
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