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
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
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
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.
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
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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:
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:
Communication seems fine; definitely explaining it wrong.
The circuit has two rails (+/- supplies), you're just measuring incorrectly. You need to measure from GROUND to each supply pin, not from the negative supply to the positive supply.
Anyway, I guess the newer Bursons don't have the ground wire. I wasn't just making that up though....
Burson Audio opamp modules and buffer review - [English]
help:ground pin for opamp?
Ok, thanks for telling me the proper way to measure the voltage. I measured from ground to the rails and it comes up as 13.4 volts. So I should be good there. What I have done though is shorten the wires which i used to connect the burson. It has made things better. Now once the volume gets past the fourth click the noise goes away 100%. Dead quiet. I just need to improve it even further so there is no noise at any level. Why would it matter how long the wires are? I mean we're talking inches here..
Someone mention wires... wires to opamps are not good. Inches... even a few millimeters or less can cause issues.
I would ditch these Burson things (not for the first time problems have been reported with these on here) and try a different quality opamp.
As we don't know what is fitted I would suggest something sensible like an OPA2134 and see how you get on.
I would ditch these Burson things (not for the first time problems have been reported with these on here) and try a different quality opamp.
As we don't know what is fitted I would suggest something sensible like an OPA2134 and see how you get on.
Assuming the unmarked IC he pulled out was actually a dual op-amp to start with. According to the Blue Circle website:
If that was actually true, then they wouldn't be using a dual opamp for stereo. They also claim "minimal circuit design", so I wouldn't expect more than one opamp per channel unless it caters for balanced inputs or outputs.
I was going off the diagram in post #10 and the fact it does still work with the Burson. The supplies seem to be where they should be too on pin 8 and 4.
I wish I had a better camera but the pictures from the cell phone are horrific and won't help. I guess since it has two stepped attenuators they figure they can call it a dual mono. It is a minimal circuit. All the case has is a 1 small toroid, 4 diodes, 8 filter caps, 1 opamp, 1 selector switch, and two attenuators with a low/high gain switch on each of them. That's it. I don't see what asides from a dual opamp it could be. If it was anything else where the pinout was different it wouldn't work at all. And it does work perfectly.. past the forth click :/
Managed to find a description on Google for it. Bing didn't turn anything up.
It says it's DC coupled from input to output. That limits you to a FET opamp to minimise DC offset.
Not sure where the "the same high speed polypropylene caps as the BC103 and BC3000MKII come into it.
They can't be in the signal path or else it's not DC coupled. PSU maybe ?
It would be really interesting to see pics. Can you tell if there are coupling caps at input and/or output ?
I would still go with the OPA2134 or maybe an OPA2604 is you want to try something more "coloured" (but coloured in a good way... particularly on less than perfect digital sources).
Voltage gain of 13.5db or around "5" in real money.
It says it's DC coupled from input to output. That limits you to a FET opamp to minimise DC offset.
Not sure where the "the same high speed polypropylene caps as the BC103 and BC3000MKII come into it.
They can't be in the signal path or else it's not DC coupled. PSU maybe ?
It would be really interesting to see pics. Can you tell if there are coupling caps at input and/or output ?
I would still go with the OPA2134 or maybe an OPA2604 is you want to try something more "coloured" (but coloured in a good way... particularly on less than perfect digital sources).
Voltage gain of 13.5db or around "5" in real money.
Hi Mooly, thanks for looking that up. I'm trying to find whether the burson is a fet opamp or not. It's too bad if i can't make it work cuz it actually sounds real nice. I'll borrow a good camera and take a pic for you to see. Either way, i'm not sure if i can find any opa2604s laying around but i do have an adaptor with two opa627bp's in it..From the good ol days when they sent out free samples!
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