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Old 16th April 2013, 10:16 PM   #1
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Default B1 buffer DC offset at power up and power down

Hello DIY'ers

I have build me a B1preamp... and it works, so far so good.

I use two 12v batteries for power in series and I noticed that when switching on theres an initial output/offset of about 400mv that drops over a couple of minutes to 0, and when I switch it off theres a brief output of about 1200mv

My question is, is this normal or have I messed something up?, the reason im asking is because my power amp, a Charlize 2 from diyparadise
cannot handle this initial offset as she has no caps to protect her.

If this is not normal, can anyone give me a pointer to what I should have a closer look at?

I thought I could simply put a relay with a delay in there somewhere to activate the output after a couple of minutes, but if I could avoid that it would be best of course.

Thanks

Last edited by seemtorecall; 17th April 2013 at 03:57 PM.
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Old 17th April 2013, 03:59 PM   #2
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Any help is greatly appreciated, I've already burned one chip in the power amp so I'd like to have a safer solution before messing around more with it
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Old 17th April 2013, 04:09 PM   #3
Joschl is offline Joschl  Germany
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Hi,

if you have the B1 as Mr. Pass intended, there is a big cap at the output to block DC from the following amp. I guess the offsets you measure on switch on/off are because the cap in the output charges/discharges slowly. You can look how this is solved in the DCB1 Hypnotize/Mezmerize implementation. There is a simple solution to enable the output with a delay and disable it the moment the preamp is switched off.

Br
Josch
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Old 17th April 2013, 05:12 PM   #4
AndrewT is offline AndrewT  Scotland
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use an AC coupled amplifier until you learn how to protect when adopting DC coupling.
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Old 17th April 2013, 05:29 PM   #5
flg is offline flg  United States
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Isn't the DCB1 a system that does not charge an output cap? It has a nominal 0.0V output? Were as the original pass B1 would have to charge an output cap to 9V through a 10k an huge cap... A minute or so RC?
treats worth
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Old 17th April 2013, 05:58 PM   #6
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Quote:
Originally Posted by Joschl View Post
Hi,

if you have the B1 as Mr. Pass intended, there is a big cap at the output to block DC from the following amp. I guess the offsets you measure on switch on/off are because the cap in the output charges/discharges slowly. You can look how this is solved in the DCB1 Hypnotize/Mezmerize implementation. There is a simple solution to enable the output with a delay and disable it the moment the preamp is switched off.

Br
Josch
Hi Joschl, thanks for your reply, I think I'll try this solution incorporating a relay with a delay.

Last edited by seemtorecall; 17th April 2013 at 06:03 PM.
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Old 17th April 2013, 06:00 PM   #7
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Quote:
Originally Posted by AndrewT View Post
use an AC coupled amplifier until you learn how to protect when adopting DC coupling.
I would have, but since everything is new to me this is how I learned about this issue, next step is learning how to deal with it and that's what I'm trying to do with your help
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