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Active Pickup circuit problem
Active Pickup circuit problem
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Old 10th January 2018, 01:33 AM   #1
argonrepublic is offline argonrepublic  Canada
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Default Active Pickup circuit problem

This circuit is acting up. It is functioning almost like a gate. There is no signal unless I hit the strings hard. Then it switches on. If I supply power to only the active pickups, it works fine so I am assuming the problem is in the preamp mid boost) circuit. My circuit is the Active 612A circuit.

Thanks
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Old 10th January 2018, 01:58 AM   #2
rayma is online now rayma  United States
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Quote:
Originally Posted by argonrepublic View Post
This circuit is acting up. It is functioning almost like a gate. There is no signal
\unless I hit the strings hard. Then it switches on.
One stage could be saturated, coming out of saturation temporarily,
when there is a large input signal. Check the DC levels at each stage's output,
before any coupling capacitors. The values should be roughly halfway between
the power supply rails.

Last edited by rayma; 10th January 2018 at 02:00 AM.
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Old 10th January 2018, 03:08 AM   #3
leadbelly is offline leadbelly  Canada
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Wrong forum, this belongs in I&A.

I looked at the manual, quite infuriating as the wiring diagram, wiring schematic, and circuit board schematic do not match each other.

In any case my tip would be to check all mechanical elements first: switches, jack, battery connector, wire solder joints. Hitting the strings hard also imparts a mechanical force to the guitar. If you think this sounds stupid i can show you a guitar with a pickup switch that has a mind of its own.
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Old 10th January 2018, 03:42 AM   #4
argonrepublic is offline argonrepublic  Canada
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Thanks for replies. I figured it belonged in the instruments forum except that active pickups and circuitry have more in common with preamps than 9 out of 10 electric guitars.
It is definately not mechanical although it has been on more than one occasion. The wiring was a non functioning rats nest when I got it. I worked my way through and had it working beautifully for about a week.
I double checked today thinking battery voltage was sagging but it is still over 9 while under load. The schematic is accurate it is just displayed terribly in the manual.
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Old 10th January 2018, 05:04 AM   #5
Enzo is offline Enzo  United States
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The schematic shows a single IC. It runs on a single 9v supply. Make sure your battery is alive first. But then the IC must have a voltage reference. Over on the left are two 47k in series across the 9v and ground. the center point between them is your 4.5v reference. Note the 10k resistor to each IC input from that 4.5v.

DO you indeed have 9v and ground at the IC and about 4.5v on the other six pins? If the reference is missing so will most of your sound. otherwise, if one or both output pins of the IC are at some DC other than 4.5v, then swap the IC.
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Old 10th January 2018, 12:38 PM   #6
Tubelab_com is offline Tubelab_com  United States
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Are you trying to fix a broken Yamaha built guitar, or did you DIY the circuit from the schematic which has at least one ugly error. In fact some of it makes no sense at all.

Follow the positive (right most) end of the battery. It is connected to the positive end of C4 which it the audio input to the opamp circuitry. These can not be connected. R3 and the other 47K resistor above it create the mid supply (4.5 volt) reference for the opamps, which is connected to the input through a 470K resistor (correct). Then there is a 10K resistor to ground that messes the DC reference all up. There is something drawn wrong with that whole area of the schematic since the 10K is actually wired directly across the battery and performs no function other than to drain the battery, or possibly perform an orderly discharge to avoid a thump.
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Old 10th January 2018, 12:41 PM   #7
Kay Pirinha is offline Kay Pirinha  Germany
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If your 4558 dual opamp IC reveals to be dead, replace it by a TL062 (same pin-out). This will increase battery life dramatically.


Best regards!
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Old 10th January 2018, 02:40 PM   #8
argonrepublic is offline argonrepublic  Canada
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The 10K resistorto the left of C4 is open. Haha! There is also a K30A N-FET.
The Drain is connected to 9V source is connected to input and the Gate is connected to positive of C4. Providing I am correct with pins 123 ( GSD )
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Old 10th January 2018, 07:49 PM   #9
Tubelab_com is offline Tubelab_com  United States
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For an N-fet to work there the gate would go to the input, the drain to the battery, and the source to the 10K - C4 connection.
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Old 14th January 2018, 02:52 PM   #10
argonrepublic is offline argonrepublic  Canada
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It is just like this. All stock. Does not match original schematic
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