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Setting Bias and DC Offset on Concept 16.5

7

71R/T

Member
Does anyone know what the bias and DC offset settings are for a Concept 16.5? I have the schematics and I have looked at the posted links here on AK but I cannot find any information on setting bias and DC offset. Thanks!!!!
 
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Adjust the bias for 10mv across one of the large ceramic emitter resistors.
The pot closest to the edge is the DC offset adjustment.
DC offset is adjusted via VR501, bias via VR502.
 
fandersen said:
Adjust the bias for 10mv across one of the large ceramic emitter resistors.
The pot closest to the edge is the DC offset adjustment.
DC offset is adjusted via VR501, bias via VR502.
Click to expand...

Cool, where did you get this info? As far as I know there is no SM available for pretty much any Concept. There is a former tech from other audio forum which obviously knows a thing or two about Concept.
But when I asked him about bias values, measuring points and such for model 2.0 he was not keen for sharing any details.
 
Mico said:
Cool, where did you get this info? As far as I know there is no SM available for pretty much any Concept. There is a former tech from other audio forum which obviously knows a thing or two about Concept.
But when I asked him about bias values, measuring points and such for model 2.0 he was not keen for sharing any details.
Click to expand...

Same here. I emailed him several days ago with no answer. I guess he feels that he should have the exclusive world market share on Concept 16.5 units.
 
Mico said:
Cool, where did you get this info? As far as I know there is no SM available for pretty much any Concept. There is a former tech from other audio forum which obviously knows a thing or two about Concept.
But when I asked him about bias values, measuring points and such for model 2.0 he was not keen for sharing any details.
Click to expand...

Thanks!!!
 
71R/T said:
Same here. I emailed him several days ago with no answer. I guess he feels that he should have the exclusive world market share on Concept 16.5 units.
Click to expand...

Ditto! And not only on 16.5 but all other Concept receiver models. I sold otherwise mint Concept 2.0 for not being able to adjust it. :thumbsdown:
 
fandersen said:
Adjust the bias for 10mv across one of the large ceramic emitter resistors.
The pot closest to the edge is the DC offset adjustment.
DC offset is adjusted via VR501, bias via VR502.
Click to expand...

I tried this and at idle with no drive signal I only get around 1mv regardless of the pot setting and the only way I ever see 10mv across one of the emitter resistors is to apply a drive signal to the inputs. I am confused as to the results I am obtaining. The bias pot is working as I see a change in voltage on the base of the output transistors. Any ideas?
 
71R/T said:
I tried this and at idle with no drive signal I only get around 1mv regardless of the pot setting and the only way I ever see 10mv across one of the emitter resistors is to apply a drive signal to the inputs. I am confused as to the results I am obtaining. The bias pot is working as I see a change in voltage on the base of the output transistors. Any ideas?
Click to expand...
Complete guessing without SM - but did you positively confirm that VR502 is Bias and VR501 DC offset adjustment pot?
 
VR502 is the Bias 1K ohm trimmer.
VR501 is the DC Balance (Offset) 5K ohm trimmer.
The amp boards are mirror images and not swappable. One Bias trimmer is zero ohms full clockwise, where the other is zero at full counter clockwise.
I set them at half and will be using a DBT and two meters for the initial fire up.
We'll see shortly.
 
Last edited:
The Left amp is adjusted for bias CCW
The Right amp is adjusted for bias CW
To achieve the 10mv setting across one emitter requires 3/4 full turn on VR502.
 
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