op-amp based inductor

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Hi.

I have an Acoustic Model 126 Bass AMP with one control of the EQ not having any effect on the sound. After checking the amp, I found a damaged 375MHY (= mili-Henrys) inductor on the EQ board.
After doing some research online, I found a picture of a very simple op-amp based inductor consisting 3 resistors, a poliester cap and an uA741 op-amp. Unfortunately there was schematic or picture of the back of the circuit.

I found the value of this inductor on a dedicated Acoustic Amp forum.
The inductor is coated with a brown varnish and appears to have a screw in its center. Overall size is approx. 1.5x1.5cm by 1cm thick. The op-amp based circuit is slightly larger.

Does anyone out there has an idea on how this is made? And maybe someone knows the formula to calculate this circuit to a specific value?
 
Hi Phantombox, search and post the Ampeg 126 schematic , tell us which band is not working, and I may suggest a simple 1 transistor gyrator to replace it.

You have single supply there, not +/- 15 V for an Op Amp so this will be easier.

You will also probably replace the inductor and the associated cap with this new one.

No big deal.

That said, first pull the original inductor from the board and look at it under good light (or the Sun) and a jeweller's loupe, maybe the wire is cut close to the mounting leg and you can scrape and resolder it.
 
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I craped the resign from the inductor, hoping to find the broke-away wire in order to solder it back on. No luck at all.
It must be a really tiny wire that goes away easiely each time I get my blade over it. But being extremely tiny it would be very hard to solder back on.
I've done this kind of jobs before (with headphone and speaker coils, and really small wires on PCBs). But unless there is a small lenght of wire exposed, it is virtually imposible.
 
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