Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Guitars => Topic started by: dude on May 30, 2020, 04:45:44 pm
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I just put a set of Strat pickups in, plug a dummy guitar cord with meter hooked to it. Wanted to make sure all pickup reading were good before stringing up. Every ohm reading looks good, N- 6.4K, M- 6.3K, B- 7.1k. Set is suppose to be a 62 strat copy with a slightly hotter bridge.
The strange thing is when l turn the volume down, even just a little, my ohm meter starts jumping around like 32K, a little more 50K, goes up then halfway Ohms starts going down. This way on all pickups..? I checked the wiring, all correct, is this normal..? Waiting till l get an answer before stringing up. Only difference is l have a push/pull in bottom tone pot, just a on/off switch to turn on the bridge, off Strat acts normal, pull it turns on the bridge with switch in any position. All 250K pots, normal cap .022, what gives. I think this is normal but can't figure out why...?
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I check my American Standard Strat ; it is same funny readings, your guitar is ok
Why ? I have to look on a Strat wiring, for now I don't understand :BangHead:
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That’s completely normal and expected. The pot puts series and shunt resistance into the guitar’s circuit. The value of those resistances is varied according to the pot setting, their sum = total track resistance.
With the vol full CW, the series resistance is 0, shunt is the full track. We choose track resistances to achieve a reasonable impedance bridge, ie that don’t load down the pickup’s voltage output much. But not so high that a mid way setting will result in an output impedance that, combined with the capacitance of the connecting cable, rolls off too much treble.
At full CCW, the series resistance = track resistance, the shunt resistance = 0.
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Another perspective. The meter is reading DC, so treble roll off though otherwise important is not a factor here. The pot is wired as a variable voltage divider with a series & a shunt resistance. The shunt R is in parallel with the PU. Per the Rule of Tens, if the pot's shunt resistance = 10X or more of the PU resistane, then the net shunt resistance = the PU resistance. As the pot's shunt resistance falls below 10X, then the net shunt resistance decreases below the PU resistane and approaches -0-.
If there is also a tone pot, the system is more complex, but follos the same them.
Meanwhile, as the pot's shunt R decreases, it's series R increases proportionately.
This accounts for the seemingly screwy meter readings.
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Pdf64, that makes sense. I checked all my guitars they do the same. I know a cap or cap and resistor in series or parallel across the volume pot will bleed high frequency signals threw and not to ground to keep more highs when turning the volume down, a nice mod. I hear a suggestion of a 150k/.001 cap, in parallel across the middle and feed pot will let more highs threw when turned down. On some of my strats this works well, other no so much, they seem to get more muddy faster, would l increase the resistance or decrease it to fix this, (250k pot). Any other suggestions to keep more highs when turning down a bit welcomed.
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Muddy tone ; look for pickups out of phase.
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A lower resistance would be better. I seem to remember that the Kinman site suggests a method for optimising the values; need to register for full access, but it’s worth it as there a lot of good info there.
Muddy tone ; look for pickups out of phase.
:w2:
Pickups connected in opposing polarity tend to produce a hollow, nasally tone. I think of Albert Collins’ typical tone, and the Bohemian Rhapsody solo, as examples.
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Thanks pdf64, l'll check that site out. Nice to be able change the volume a bit