Upgraded opamp in preamp and now there is a hum/buzz

sardonx · 2nd February 2012, 03:51 AM

I know i shouldn't have blindly done this but i took a chance. I have a blue circle bc101 preamp which is based around a basic dual opamp (don't know which one, they covered the top with a black substance). Because the layout is point to point it was easy to replace it with something else. So I did - with a burson audio "descrete opamp module" that i had sitting around doing nothing. The problem is that when the preamp is running and the dual stepped attenuators are anywhere from the zero position to the fourth or fifth click there is a bad hum/buzz coming from the speakers. It is bad enough to trip the protect circuit on my amplifier when switching on with the volume on the preamp at zero. The noise however decreases incrementally as the volume is turned up, to eventually disappear completely when the attenuators are nearing their last steps.
I am guessing these opamps are maybe made to work at unity gain only? They are designed to replace cd players output opamps and such. My electronics knowledge is limited so that probably makes no sense and is way off. Does anyone know if this is a simple fix (adding a resistor somewhere) or should i just put the old IC back in and forget it. Mladen

Bonsai · 2nd February 2012, 09:00 AM

can you photograph you installation and post it up - maybe we can give you some advice once we take a look.

I assume your Burson op-amp was just plugged into the original socket, yes?

Mark Hedges · 2nd February 2012, 02:52 PM

Quote:

Originally Posted by sardonx

I know i shouldn't have blindly done this but i took a chance. I have a blue circle bc101 preamp which is based around a basic dual opamp (don't know which one, they covered the top with a black substance).

Its of topic but remind me to never buy anything from blue Circle. I can't stand it when companies do this. It is basically them saying "Sure we may be a tiny two bit company, but trust us - we will always be here to service your gear".

Anyhow as to your problem - did you make sure you put the leads in the right way (not backwards)? Do you know the max voltage of the Burson?

Mark

Wavebourn · 2nd February 2012, 07:33 PM

One possible explanation why it may hum, because it may oscillate in layout that was fine for an old one. When it oscillates power supply ripples modulate oscillations by amplitude that when demodulated cause hum.

sardonx · 2nd February 2012, 11:29 PM

Unfortunately I only have a cell phone camera right now and it's not so good. I will try though and see how it comes out. Yes it was wired the original way. I checked and double checked. There is no socket, the IC is being held up above the capacitor banks by stiff copper wires which are directly soldered. Like I said it's point to point. I did not wire it incorrectly. It follows a regular dual opamp number scheme. There are two things i can think of. I'm using quite long wires to connect the burson as it was convenient this way. It wouldn't have fit otherwise, it's about 20 times bigger than a regular opamp. And like Mark said it could be the voltage. When i measured the power rail feeding the original opamp it measured 29.5 volts on my voltmeter. The burson website states operating voltage at +/-12-25 V DC. This always confuses me as I don't know if that means a total of 24-50 or what. I will take some pics as soon as i can and see how they turn out.

Bonsai · 3rd February 2012, 04:52 AM

Wavebourn,

yes, this absolutely can be one of the reasons sardonx has a problem. I wonder if the Burson spec'd for unity gain?

QSerraTico_Tico · 3rd February 2012, 05:10 AM

Maybe the voltage regulators run out of regulation as the Bursons draw a lot of current.

Mark Hedges · 01:12 PM

Quote:

Originally Posted by sardonx

And like Mark said it could be the voltage. When i measured the power rail feeding the original opamp it measured 29.5 volts on my voltmeter. The burson website states operating voltage at +/-12-25 V DC. This always confuses me as I don't know if that means a total of 24-50 or what. I will take some pics as soon as i can and see how they turn out.

I think if each rail feeding the Burson is 29.5 volts than the voltage is probably too high. If the measurement is between the two rails then you should be OK.

Mark

theAnonymous1 · 3rd February 2012, 01:29 PM

Doesn't the Burson have a ground wire that needs to be connected?

sardonx · 3rd February 2012, 06:47 PM

Well i can see this has more possible answers than I thought! I think i will put the old opamp back in, or perhaps just wire it to use the attenuators as a passive preamp. It is a nice looking unit.

To explain it in my electronically uneducated manner, when i hooked up my volt meter to pins 4 and 8 the readout was 29.5 volts. It's a dual opamp, so it only has one rail. I hope i'm explaining this correctly and not miscommunicating.

The burson does not have a ground wire. It's pins are numbered in the same physical order as any small dual IC. Like here:
opamp-pinout-dual.png

2nd February 2012, 03:51 AM	#1
sardonx diyAudio Member Join Date: Jun 2003 Location: Canada	Upgraded opamp in preamp and now there is a hum/buzz I know i shouldn't have blindly done this but i took a chance. I have a blue circle bc101 preamp which is based around a basic dual opamp (don't know which one, they covered the top with a black substance). Because the layout is point to point it was easy to replace it with something else. So I did - with a burson audio "descrete opamp module" that i had sitting around doing nothing. The problem is that when the preamp is running and the dual stepped attenuators are anywhere from the zero position to the fourth or fifth click there is a bad hum/buzz coming from the speakers. It is bad enough to trip the protect circuit on my amplifier when switching on with the volume on the preamp at zero. The noise however decreases incrementally as the volume is turned up, to eventually disappear completely when the attenuators are nearing their last steps. I am guessing these opamps are maybe made to work at unity gain only? They are designed to replace cd players output opamps and such. My electronics knowledge is limited so that probably makes no sense and is way off. Does anyone know if this is a simple fix (adding a resistor somewhere) or should i just put the old IC back in and forget it. Mladen __________________ The End

2nd February 2012, 09:00 AM	#2
Bonsai diyAudio Member Join Date: Aug 2006 Location: Taipei, Taiwan	can you photograph you installation and post it up - maybe we can give you some advice once we take a look. I assume your Burson op-amp was just plugged into the original socket, yes? __________________ bonsai http://www.hifisonix.com/

2nd February 2012, 07:33 PM	#4
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	One possible explanation why it may hum, because it may oscillate in layout that was fine for an old one. When it oscillates power supply ripples modulate oscillations by amplitude that when demodulated cause hum. __________________ The devil is not so terrible as his mathematical model! Wavebourn: We Create Creativity!

2nd February 2012, 11:29 PM	#5
sardonx diyAudio Member Join Date: Jun 2003 Location: Canada	Unfortunately I only have a cell phone camera right now and it's not so good. I will try though and see how it comes out. Yes it was wired the original way. I checked and double checked. There is no socket, the IC is being held up above the capacitor banks by stiff copper wires which are directly soldered. Like I said it's point to point. I did not wire it incorrectly. It follows a regular dual opamp number scheme. There are two things i can think of. I'm using quite long wires to connect the burson as it was convenient this way. It wouldn't have fit otherwise, it's about 20 times bigger than a regular opamp. And like Mark said it could be the voltage. When i measured the power rail feeding the original opamp it measured 29.5 volts on my voltmeter. The burson website states operating voltage at +/-12-25 V DC. This always confuses me as I don't know if that means a total of 24-50 or what. I will take some pics as soon as i can and see how they turn out. __________________ The End

3rd February 2012, 04:52 AM	#6
Bonsai diyAudio Member Join Date: Aug 2006 Location: Taipei, Taiwan	Wavebourn, yes, this absolutely can be one of the reasons sardonx has a problem. I wonder if the Burson spec'd for unity gain? __________________ bonsai http://www.hifisonix.com/


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3rd February 2012, 05:10 AM	#7
QSerraTico_Tico diyAudio Member Join Date: Oct 2004	Maybe the voltage regulators run out of regulation as the Bursons draw a lot of current.

3rd February 2012, 01:29 PM	#9
theAnonymous1 diyAudio Member Join Date: Feb 2004 Location: Anonymityville	Doesn't the Burson have a ground wire that needs to be connected? __________________ "If you don't like funerals don't kick sand in Ninja's face." - Ninja

3rd February 2012, 06:47 PM	#10
sardonx diyAudio Member Join Date: Jun 2003 Location: Canada	Well i can see this has more possible answers than I thought! I think i will put the old opamp back in, or perhaps just wire it to use the attenuators as a passive preamp. It is a nice looking unit. To explain it in my electronically uneducated manner, when i hooked up my volt meter to pins 4 and 8 the readout was 29.5 volts. It's a dual opamp, so it only has one rail. I hope i'm explaining this correctly and not miscommunicating. The burson does not have a ground wire. It's pins are numbered in the same physical order as any small dual IC. Like here: opamp-pinout-dual.png __________________ The End

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