DC Blocking on Pre-Amp

Puffin · 19th January 2009, 06:51 PM

I have copied this from the SOAP thread as it might grab a wider audience.

Can any of you geniuses out there (a few regular posters spring to mind) give me a definitive answer as to whether this board (SOAP) has any DC blocking on it.

I had a problem with mine at the weekend and when testing/playing with it, it blew an old speaker! A strange noise and then....phut!

__________________

AndrewT · 20th January 2009, 01:13 PM

Hi,
provide a link to a schematic

Puffin · 20th January 2009, 01:33 PM

Andrew. I did try to get one from the SOAP thread, but it does not seem to want to work. Zei who made the boards says there is DC blocking on the output. If you look at the last few posts on that thread you will see that the problem may have been the way I had it wired to the pot.

Tripmaster · 20th January 2009, 07:37 PM

Quote:

Originally posted by AndrewT
Hi,
provide a link to a schematic

Puffin, what would you do without me?

Puffin · 20th January 2009, 07:43 PM

Why thank you. I have tried wiring the SOAP the other way as suggested by Zei and it is still playing up!

pacificblue · 20th January 2009, 09:22 PM

Quote:

Originally posted by Puffin
give me a definitive answer as to whether this board (SOAP) has any DC blocking on it.

Yes, it has DC blocking at the non-inverting input and at the output. That is, if you built it according to the schematic Tripmaster attached.

DC is not the only reason, why a speaker would blow. Did you actually measure DC at the SOAP's output?

Your power amp obviously has no DC protection of its own. Did you measure, if the DC is coming from the power amp?

Could it be that the voltage regulators offset the ground, because they are slightly disadjusted? Then you could indeed get DC at the output through the 100k resistors.

Was the attenuator full open, and the signal too strong for the speaker, because the SOAP adds a gain of two?

Puffin · 21st January 2009, 08:06 AM

pacificblue. I will do as you suggest and report back.

mjf · 22nd January 2009, 05:42 PM

hello.
perhaps oscillations? (wiring,missing decoupling cap,......).
greetings.............

Puffin · 22nd January 2009, 08:08 PM

mjf. I haven't had time to go over the board yet, but you may be right.

19th January 2009, 06:51 PM	#1
Puffin diyAudio Member Join Date: Feb 2006 Location: U.K	DC Blocking on Pre-Amp I have copied this from the SOAP thread as it might grab a wider audience. Can any of you geniuses out there (a few regular posters spring to mind) give me a definitive answer as to whether this board (SOAP) has any DC blocking on it. I had a problem with mine at the weekend and when testing/playing with it, it blew an old speaker! A strange noise and then....phut! __________________

20th January 2009, 01:13 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, provide a link to a schematic __________________ regards Andrew T.

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20th January 2009, 01:33 PM	#3
Puffin diyAudio Member Join Date: Feb 2006 Location: U.K	Andrew. I did try to get one from the SOAP thread, but it does not seem to want to work. Zei who made the boards says there is DC blocking on the output. If you look at the last few posts on that thread you will see that the problem may have been the way I had it wired to the pot.

20th January 2009, 07:43 PM	#5
Puffin diyAudio Member Join Date: Feb 2006 Location: U.K	Why thank you. I have tried wiring the SOAP the other way as suggested by Zei and it is still playing up!

21st January 2009, 08:06 AM	#7
Puffin diyAudio Member Join Date: Feb 2006 Location: U.K	pacificblue. I will do as you suggest and report back.

22nd January 2009, 05:42 PM	#8
mjf diyAudio Member Join Date: Jan 2009 Location: upper austria/near linz	hello. perhaps oscillations? (wiring,missing decoupling cap,......). greetings.............

22nd January 2009, 08:08 PM	#9
Puffin diyAudio Member Join Date: Feb 2006 Location: U.K	mjf. I haven't had time to go over the board yet, but you may be right.

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