My Pearl One. Some questions

[blackdod]

What is the voltage at the base of Q5. It should be 1/2 voltage of that at the emitter of Q3 (~24v), so close to 12v. If it's not then it could be that your resistors are not both 10k ohm, or there is a solder joint that is not solid, or maybe damage to the transistor Q5.

Thanks John

L. Board:

26,1 volt on Emitter of Q3
20,2 volt on Base of Q5

R18-R21 are 10K

I think that the Q3 is "dead" because yesterday I checked 24,6 on Emitter and 17 volt on Base of Q5

R. Board:

24,6 volt on Emitter of Q3
18 volt on Base of Q5

R18-R21 are 10K

You can measure the resistance of R18 and R21 to ensure they are both 10k.

Yes, I used 10k on R18 and R21

Regards

 

[Johnloudb]

Okay, well, the voltages you get at the base of Q5 on both boards doesn't make sense because it should be very close to 1/2 the voltage of the emitter voltage of Q3. The voltages you measure are much higher than 1/2 that voltage.

So, that's why I suggested you actually measure the resistances R18 & R21 with an ohmmeter, cause there maybe be a problem with a solder connection there or a problem with the Q3 transistors.

Anyway, that's very strange. Hope you can get that solved.

I agree, it looks like Q5 on the left board is damaged.

 

[Johnloudb]

cause there maybe be a problem with a solder connection there or a problem with the Q3 transistors.

I meant to say Q5 here.

I agree, it looks like Q5 on the left board is damaged.

I meant to say Q3 here.

Sorry.

 

[blackdod]

Hello

Thanks John, I checked the soldering and it´s correct. I think that the problem are the ZXT450. I´m waiting more unit and I hope solve the problem.

Regards

 

[blackdod]

Hello guys

I changed the old ZXT450 and finally now I have 11.8 volts on both channels on Q5!!!

Regards

 

[blackdod]

An externally hosted image should be here but it was not working when we last tested it.

Well now I would like add a Led on board. Can I used the Pad 4?

Thanks to all for your patience

Regards

 

[nar]

all's well that ends well 🙂

 

[blackdod]

all's well that ends well 🙂

Thanks Nar 🙂

 

[nar]

An externally hosted image should be here but it was not working when we last tested it.

Well now I would like add a Led on board. Can I used the Pad 4?

Thanks to all for your patience

Regards

No ! Pad4 is intended to use a 9V battery in place of the zener if you want ... It's a reference place for the regulation. Don't use that spot or you would add problems !

If you experience too much noise (hiss) in case of low gain cart, you can remove the zener and try to use 9V battery instead. It should be a tad quieter in high gain cases.

-----------------

I would use a Led + series resistor between V+ and Ground pads. You can use unreg DC if you're suspicious about adding a Led on regulated audio V+. It can be done too, as you wish.

Best,

nAr

 

[blackdod]

Thanks Nar

Ok I'm clear that I should not use the Pad 4.

I take your advice and bring out a led + resistance from the V+ and Ground pads on the PSU.

For about 45 volts. Should I use a very large resistance?

Thanks

 

[nar]

Thanks Nar

Ok I'm clear that I should not use the Pad 4.

I take your advice and bring out a led + resistance from the V+ and Ground pads on the PSU.

For about 45 volts. Should I use a very large resistance?

Thanks

Depends if you use a high efficency one or standard.
Range between 10k and 68k should be ok. For my high eff white ones I use about 137k 0,25W on 48V

Best,

nAr

 

[blackdod]

Nice Nar !!!.

OK, I have some LED High Efficiency. I will test with that value of resistance.

Regards

 

[blackdod]

Hello guys!

I added a 10K resistor to the LED and the result is very good, but when I turn off the LED takes a long time off. I guess adding greater resistance than take off.

I've been testing the masses and how best to go is as I have now (safety Earth).

On the other hand, wanted to ask if the voltage on Q8-12 zone is crucial. I have a voltage of 0.1 V in this area.

Regards

 

[Zen Mod]

nope

when LED is lit for long time , that means its connected across big cap
if you put bigger resistor , it will stay lit for even longer time
either live with it , or feed LED from AC - put diode and resistor in series

 

[blackdod]

Thanks Zen,

Yes, in fact I'll have to live with it or use a diode more resistance (AC).
I am seriously thinking to change it to AC, and add a small capacitor



Regards

 

[Zen Mod]

you don't need capacitor

tell me AC voltage you have , which LED you want to use and I'll do calc for you

 

[blackdod]

you don't need capacitor

tell me AC voltage you have , which LED you want to use and I'll do calc for you

Thanks Zen

I can use +-37 or +-18 volt DC and the LED is a WP7104QBC/G (3.3 volt/20mA)

I would like the LED turns off slowly fod this I was think on a cap

Regards

 

[Zen Mod]

LED resistor calc

say that you're going to use +/-18 ; that's 36Vac ;

say that you're going for max 3mA (plenty for any signal LED)

say that you're going for just one diode in series - that's half rectifier , so you'll have (roughly , but precise enough for purpose ) 36/2 x 1.41 volts DC after diode , with modest cap ; say that 10uF/50V is sufficient

so - we have around 25Vdc

R=U/I
R=(25-3,3)/0,003
R=21,7/0,003
R=7233 Ohms

use first standard value - say 7K5

without recalc of current with altered value , we assume that we still have near 3mA

so - dissipation in resistor is :
P=I^2 x R = 0,003^2 x 7500 = 67mW , so any small metal film resistor is good enough ( factor 3 is always min in my book)

so - secondary - just one diode - cap for smoothing - resistor - LED

easypeasy

if LED is still blinding ya from listening position , you can solve that in 3 ways :

1- turn case for 90 degs , so you can't see LED
2- glue something diffuse across LED (foil or something)
3 - increase value of resitor

 

[blackdod]

😛 😛 😛

Thanks for your good reply Zen.

I keep your post, since it is very interesting and helpful.

I used the 18 volt (DC) and added thanks to your recommendation a cap 10 uF but I used a 10K resistor.

According to my calculations, the result would be: (18-3.3)/0.003= 4900 Ohm; 5K

The result is very good, turning off with a slow.

An externally hosted image should be here but it was not working when we last tested it.