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2520 Op Amp Utility Plugins
Old 7th May 2006
Gear maniac
Nerdyrocker's Avatar

Thread Starter
2520 Op Amp

Is there a way to test one of these to see if it is in good condition without putting it in the mic pre circuit?

I want to test it for my Seventh Circle Audio A12 pre.

Old 7th May 2006
Lives for gear
ulysses's Avatar
Originally Posted by Nerdyrocker
Is there a way to test one of these to see if it is in good condition without putting it in the mic pre circuit?

I want to test it for my Seventh Circle Audio A12 pre.

You'll have to put it in some kind of circuit if you want to test it. Since you can't measure internal voltages in it, the only way you can test it is to power it up, apply a signal, and see what you get out the other end. If you don't want to use an existing circuit you've got on hand (presumably the circuit that will eventually be home to the amp) then you would have to build a new test circuit. That seems like a lot of work, basically building a new preamp just to test the amplifier. If you've got a known good preamp on hand, then slapping the 2520 in there will be the best way to test the amp.

What's your reasoning for wanting to test it without putting it in the preamp circuit? Are you having trouble with your preamp and trying to determine whether the circuit or the amplifier is to blame?
Old 8th May 2006
Lives for gear

You can create a fairly simple inverting amp test circuit with an oscillator or audio source. Since the pins on the 2520 are spread out, it's not terribly difficult if you have some basic tech skills.

Connect a 10k resistor between the - input and out.
Connect a 10k resistor between the - input and hi of your source.
Using a bipolar power supply, or power from some other piece of audio gear, or just a pair of 9v batteries, connect positive voltage to V+, negative voltage to V-.
Connect the output to an amp/speaker combo, or directly to headphones.
Connect grounds of the audio source, power supply, 2520 + input, and 2520 output, and monitor amp (or one side of the headphone cable) together.

I hope you can follow this without a wiring diagram or schematic.

Listen (starting a low level, to protect your amp and speakers) and see what you get.
Old 8th May 2006
Gear maniac
Nerdyrocker's Avatar

Thread Starter
The preamps work fine with the stock Seventh Circle Audio 2520 clone in there. I got my hands on some API 2520s but I do not know if they are in good condition or not. I just want to make sure that I am not going to hurt my pre amp by putting the 2520 in there if it is potientially bad.

Thanks again!
Old 9th May 2006
Gear Nut
avedis's Avatar

I think the SC circuit has a regulator w/protective diodes for each rail so I don't think you'll hurt the preamp by plugging in a bad opamp... just don't leave it there.

The only test you can do without plugging in a opamp is to put your meter on diode test and check the voltage drop across the V+/V- pins, which would be about 1.6v - but this won't tell you much. Like Justin and David said, you'll need to apply power to it to do a proper test.

To see if it's potentially bad when plugged in, check to see if there's any DC on the output and/or on the non-inverting and inverting inputs (+, -) referenced to common. You should read something less than a tenth of a volt. Then you can check it with a sine wave or just listen to it.

David, I hope you don't mind me using a quote of yours in my signature. I couldn't say it better myself and thought it was brilliant.

Old 10th May 2006
Gear Maniac
Helsing's Avatar

I wouldnt worry about hurting anything. Theres not much you can hurt in that circuit. Id just plug in the amp and see if it works. In my experience these amps either work, are dead or have intermittent problems that are pretty easy to hear.

If you are still concerned, just have your test rig setup so you can turn the power off quickly if the opamp doesnt work. Its more likely that would burn up the 2520 by incorrectly cobbling together a test rig. The components in the surrounding circuit that might (unlikely) be damaged by some misplaced DC are a whole lot less valuable that that 2520.

Jon Erickson
Old 10th May 2006
Lives for gear
ulysses's Avatar
I guess the only thing I would watch out for would be DC on the output. If there's a serious offset being dumped into a DC-coupled output transformer, you wouldn't want to leave it powered up in that condition for any longer than necessary. If there's a capacitor between the output and the transformer, then you have nothing to worry about.
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