YBA DT INTEGRE - problem bias

[kalinkata]

Hi. Sorry for my english.
I have Yba Integre. When i rotate trimmer potentiomer for left channel to set bias, values for other channel also change? If i set 2-3mv for left channel, other channel automatic is 130mv. If i set 40mv for left channel, other channel is 105mv. When i set two trimmer potentiomet to min , on both channel i have 60mv.
Can you tell me how the transistors are located (TIP35/TIPC)
With RED dots, which are transistors? Tip 35 or tip 36?

 

[analog_sa]

Are the power supply rails stable? Such behaviour is very strange.

 

[analog_sa]

Doesn't the Integre have a dual mono power supply? In that case such behaviour is just impossible.

 

[Mark Tillotson]

There are at least 4 versions I think, a quick search spotted an alpha and a delta version, so its probably a shared supply in most of those, perhaps dud supply, loose shared grounding point, dead caps, something to track down starting with multimeter on the DC rails checking voltage stability and ripple, checking emitter resistors if appropriate. But always remove speakers and check DC offset on the output before anything else, fried speakers spoil your week!


[ edit I should have looked more carefully, DT seems to mean dual transformer, so probably separate supplies, but perhaps there's shared protection circuitry, thermistor, dodgy mains connection etc that's common to the channels. Or it might just be very flaky on both channels so they appear to interfere when are actually both wandering around? ]

 

[kalinkata]

Now i set 2.5mv on left and right channel. On output terminal i have 70mv, after 2 minuts they are /left channel is (minus)-3mv, right channel is +5mv/. On collector TIP 35C/ TIP36C I HAVE +/-35V. Is it normal?
Do you know how many milivolts i need to set YBA Integre DT ALpha. This amplifier is with two transformers, and 6 big capacitors.

 

[petrnyc]

YBA Integre a single transformer

My YBA Integre a developed a distortion, and from what I was able to find on the web, it looks like the bias has drifted out of proper adjustment.
Does anyone know how to set the bias on this amp? I can not find any information about this anywhere.

A- where do on the board you read the mv?
B- what should the voltage be for proper operation?

Thank you
Petr

 

[Michel]

Here is the answer to which output transistor goes where and how to adjust the biases.

In the DT version, the transformers are not one for each channel.
Their secondaries are paralleled and wired as one transformer for each polarity.
This way the output stage has access to more current.

The biases going down with time is a known issue.
You can recognize the issue as soon as you hear a slight fuzz in the sound.
When the bias goes too low, you enter the crossover distortion zone.
The last time I had to deal with this issue, I replaced the original Piher PT-10 bias trimmers by PTC10LV10-103A1010, which should prove more stable with time.

I am at your disposal if you have more questions.

Michel

 

[petrnyc]

Here is the answer to which output transistor goes where and how to adjust the biases.

In the DT version, the transformers are not one for each channel.
Their secondaries are paralleled and wired as one transformer for each polarity.
This way the output stage has access to more current.

The biases going down with time is a known issue.
You can recognize the issue as soon as you hear a slight fuzz in the sound.
When the bias goes too low, you enter the crossover distortion zone.
The last time I had to deal with this issue, I replaced the original Piher PT-10 bias trimmers by PTC10LV10-103A1010, which should prove more stable with time.

I am at your disposal if you have more questions.

Michel

Michel,
Thank you, very helpful.
Petr