ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hey I'm trying to set the bass voltage of my Beolab 8000 to 4.8V with a signal of 100mv at 1Khz. However I can't get it any higher than 4.32V so I'm assuming that age got the best of some parts could anybody suggest some parts that might need replacing? I can get the tweeter to 2.95V just fine btw.
I am wondering if 4.8V is even correct. Does anybody know what voltage the bass drivers need to be set at?
I've not heard of setting a particular number to amplifier output other than on BL1 & 9 which is to match individual driver sensitivity. b&o mark each driver according to some testing procedure.
Perhaps b&o are referring to VAC peak rather than RMS? Is your meter capable reading VAC "true" RMS? Most cheap meters on AC only are reliable a low mains frequencies 50-60hz. Audio amplifiers (apart from real PA ones) actually output relatively low total power.
I am not sure to be honest the beolab 8000 service manual says the output should be 4.8v when the input is 100mv at 1kHz when both woofers have been replaced. Which is what I tried to do. I was able to calibrate my beolab 6000 properly so I assume the multimeter should be fine. I am thinking that the service manual is for the really old type of beolab 8000 which was a 3 way speaker. And that the specifications changed. I think the original value was 3.2V before I ajusted the pot. But I am not sure...
Could be. Earlier 8000 had an additional analogue 'passive' xover rather than the later ones both drivers being wired in parallel.
Also are you testing with or without a load (driver) connected? It's pretty standard to test AC outputs loaded, audio or otherwise. This is due to the tiny resistance that DMM places on circuit under test, leading to inaccurate readings. Tiny components are one thing, 'power' sources are another.
I tried them with and without drivers but that doesn't change very much. The tweeter pot ranges from 2V to around 5.4V on both my Beolabs and the default value was around 2.9V which is correct according to the service manual on this site. But the woofer rangers from around 2.8V to 4.3V on both speakers. I just don't know what the correct value should be.
Okay.
Did you twiddle with the other unit as well?
I did because I thought that both of the values were wrong when I read the service manual. Then I thought one of the amplifiers was wrong. But now I am assuming that the manual has an old value. So yes I did. And I feel really stupid about it.
No load needed. Servicemanuals mentions this clearly.
The output voltage depends on the serialnumber and therfore on the used woofer. Earlier 8000's had a different impedance than the successor.
When you replace the woofer with a new one, a sheet is provided with the correct voltages.
This difference can be found at the input of the amplifer for the woofer. (afaik different values for R42)