Mute problem with K4005B

Kits Audio Hi Fi Projects
1

Hello,

I have build 2 K4005B kits and the sound is very good. But, the problem with both is that if i turn on the power,
there is little sound. If i measure the voltage on pin 5 of IC2, TDA7250 the sound directly swith on and is normal.
I measure -23v on pin 5.

It like that if the power switch on, the TDA7250 are in mute and if i touch pin 5, the mute is off.
So i say, the problem is with both kits. I have theck all components and the positions and its ok.

The power on the boards are +/- 25 v DC. I use the K4006 for each amplifier.
Maybe a modification in the mute circuit?

Hopely you can help me.

kind regarts
Wim

2

Hi,

Not sure I understand the question:
Please clarify

1- Are you using the mute function to turn on/off the amplifiers?

this is OK, but turn off using mains power switch for longer periods

2- Are you using a mains (230Vac switch) to turn on/off the amplifiers?

in this cas a small speaker “plop” can be normal

3

I build the kit conform manual and i don’t use the mute. I use powerswitch
Thermic not used.

If power turn on, the sound level is verry low. If i touche pin 5 off IC2 with measure probe, the sound is normal.

Wim

[quote=“VEL436”]Hi,

Not sure I understand the question:
Please clarify

1- Are you using the mute function to turn on/off the amplifiers?

this is OK, but turn off using mains power switch for longer periods

2- Are you using a mains (230Vac switch) to turn on/off the amplifiers?

in this cas a small speaker “plop” can be normal[/quote]

4

OK,

Please check if R14 and R23 have the correct value
Please check if C36 is not mounted in reverse polarity

5

checked. R14 = 68K, R23 = 470K

C 36 correct polarity, + left side.

I have try change R23 from 470K to 220K and it works fine. Now if power on, the sound level is normal.
Good solution?

So jou say, there is al little plop after power off. Not fine. Can i change this?

Wim

6

Hmm,

We have been selling this kit since 1995, without modifications
So it is strange

The voltage at pin 5 must be >3V for the unit to work
If the voltage is negative then the unit will mute

Please check if your supply voltage is perfectly symetrical