DIY AU-D11 II bias adjustment

[rayner06]

Guys, my D11II (actually D707X) is not playing very well, especialy the left channel. The sound is very "dead", it has no life and not much power. My D7 is playing way better...

I think it needs some adjustments. I'm trying to adjust the bias but i'm not a eletronic expert. Here is what the service manual says:

I got the right values for balance, but the "Center DC" is impossible to set between 0~5mV. It keeps drifting +-100mV (if I set a value "x", it goes to x+100 and x-100, never stop).

Also I dont know what "Emitter of power transistor is" to adjust the bias current. Of course I know what the output transistor is. I think the adjust is made between one of those "legs" of the transistor. Here is a picture of them with the "legs" numbered:

The value mensured must be between 20mV to 2mV?

Thanks.

 

[Hyperion]

Guys, my D11II (actually D707X) is not playing very well, especialy the left channel. The sound is very "dead", it has no life and not much power. My D7 is playing way better...

I think it needs some adjustments. I'm trying to adjust the bias but i'm not a eletronic expert. Here is what the service manual says:

I got the right values for balance, but the "Center DC" is impossible to set between 0~5mV. It keeps drifting +-100mV (if I set a value "x", it goes to x+100 and x-100, never stop).

That is quite normal for that adjustment, even though it seems to say otherwise in the manual, just get it as close as you can and leave it - don't spend any time on it. Just to clairify this is the measurement from speaker terminal to ground. The other DC offset measurement is across the speaker terminals "+ and -" you should easily be able to get this below 5mV and steady.

Also I dont know what "Emitter of power transistor is" to adjust the bias current. Of course I know what the output transistor is. I think the adjust is made between one of those "legs" of the transistor. Here is a picture of them with the "legs" numbered:

The value mensured must be between 20mV to 2mV?

Thanks.

Sorry can't see pic at the moment (blocked at work).

What they are asking you to do is measure between the emitters of 2 power transistors. In other words across the 2 emitter resistors that connect them. I believe the correct setting is 20mV, +/- 2mV

Just make sure you are connected to the correct 2 transistors for each of the 4 measurements and setting operations required. You have 4 trimmers - each one will adjust the bias current for ONE pair of transistors. BE CAREFUL with your probes...

 

[stopkidding]

oooh Time my revive my own restoration. Been idle for 4 weeks now

 

[rayner06]

Thanks for the help Hyperion. The emitters that I used to mensure were: 1- 6+, 7- 12+, 18+ 13-, 24+ 19-. There's an "E" on the board. It was about 32mV before the adjustment and now the amp is a little better with 11mV for all.

The Center DC keeps drifting.... Strange that when it's too high the protection enters.

Can you say how these adjustments can affect the sound?

 

[Ronito6]

It took my noobie brain forever to figure out what "emitter of power transistor" meant.

These documents were written in Japan and then translated. The translators are rarely technical specialists and will defer to the most direct translation when it comes to the deeper technical details and procedural instructions.

So, "DC voltage between Emitter of power transistor"
should actually have been written as (for example)
The DC voltage between the emitters of the power transistors kQ61 and kQ63.

 

[Ronito6]

Maybe more clearly:
Measure the DC voltage from the emitter of transistor kQ61 to the emitter of transistor kQ63.

The hilarious English of owners manuals of electronics from Japan back in the eighties comes to mind considering this.

 

[Hyperion]

Thanks for the help Hyperion. The emitters that I used to mensure were: 1- 6+, 7- 12+, 18+ 13-, 24+ 19-. There's an "E" on the board. It was about 32mV before the adjustment and now the amp is a little better with 11mV for all.

The Center DC keeps drifting.... Strange that when it's too high the protection enters.

Can you say how these adjustments can affect the sound?

Ah, that is a problem - you must be talking here about the DC voltage between the speaker terminals (adjustment 1 & 2), because the DC reading that drifts seemingly uncontrollably is the measurement of DC voltage from Speaker terminal to ground (adjustment 3 & 4).

Having too much DC voltage across the speaker terminals will significantly affect the sound, and despite the protection circuitry could damage your speakers as well, so, if you are thinking of ignoring it, you cannot. Please clarify which adjustment you are referring to that causes 'protection' to activate?

Many thanks Ronito6 for clarifying the adjustment text from the manual, most helpful.

 

[rayner06]

Ah, that is a problem - you must be talking here about the DC voltage between the speaker terminals (adjustment 1 & 2), because the DC reading that drifts seemingly uncontrollably is the measurement of DC voltage from Speaker terminal to ground (adjustment 3 & 4) - which does not trigger the protection circuitry.

Having too much DC voltage across the speaker terminals will significantly affect the sound, and despite the protection circuitry could damage your speakers as well, so, if you are thinking of ignoring it, you cannot. Please clarify which adjustment you are referring to that causes 'protection' to activate?

Many thanks Ronito6 for clarifying the adjustment text from the manual, most helpful.

Hyperion, it's the DC voltage from speaker terminal to ground that makes the amp enter in protection mode if too high. Adjustments made by kvr2 on F-4266 board.

The DC voltage between hot and cold speakers terminal are fine.

 

[Hyperion]

Well whatever, you can't get it stable, nobody can - so get it as near as possible and leave it. However if it is so unstable that it triggers protection, you might have a mains supply problem.

Clearly I was wrong when I suggested this adjustment would not trigger the protection circuitry - my apologies. For me the kVr2 adjustment is a 'set and forget' adjustment, as the more important one is the measurement between the speaker terminals.

(my post #7 edited to avoid misleading others)

Please explain a bit more about the stability of the kVr2 adjustment, you seem to say you set it, but it drifts so much that it triggers protection - is that correct?