Originally posted by MoreBass
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Yes there is a simple way to increase the bass with the way that you have a CT on each end of the low impedance string loop. Simply hook the microphone wire with the XLR connector to only one CT. Then listen to the sound, then alligator clip or tack solder a short across the second CT. This will have the effect of changing the impedance of the low impedance string loop to make it look like a thicker wire. The bass response should increase. A few years ago I tried putting a 1K ohms pot across the second CT (not connected to the XLR wire) and found that by varying the pot as a variable resistor, I could achieve a tonal change. In my lab notebook I labeled this a "RITE control" standing for Reflected Impedance Tone Equalization.
Just so you and everyone else reading this knows, the output impedance of the CT is governed by the primary string loop resistance multiplied by the square of the turns ratio. Just a CSE187L with the AWG 12, 250 microohm primary bent to form a shorted loop has 79 ohms impedance, 8.4mH at 1KHz measured on the secondary (20 ohms side). When you add AWG 8 wire with 52.3 microohms per inch you can see how each inch adds .0000523 X 250000 = 13.075 ohms per inch of wire plus the impedance of the second CT. Remember, the resistane of everything in the primary loop is in series and good soldering and low resistance connections are required. Try using silver solder for a little lower resistane connection on the primary string loop. You want to keep the output of the CSE187L below about 250 ohms converting 1000 microohms (or 1 milliohm) on the primary side as measured on the secondary. This is a good match for a mic matching transformer or XLR microphone preamp impedance typically around 2000 ohms. The lower the string loop impedance the higher the output will be and the better the low frequencies will be. Shorting out the second CT will be the quickest fix for your bass pickup design. Another quick fix is to put a short between the magnets so each CT sees its own string loop, However, there will be some interaction between the CTs if you were thinking of having a balance control for each string pair.
If hum is a problem, make two short 2-string loops and wire them like a humbucker. You can switch them between series and parallel for some tonal variation. You can put a balance control/independent volume pots (try 1K) to control the balance of each string pair with no interaction between them as the primary string loops are now totally independent.
For more bass, try using AWG 6 wire that is .1620" in diameter. Simply use a drill press and make two vertical holes .078" diameter (to match the CSE187L primary turn diameter) in the vertically-held wire end about .187" deep to insert into the ends of the CTs. Use silver solder to secure.
I applaud your effort and hope these tips will make it sound better. Let us know how it works out and which alternative identified above you tried?
Joseph Rogowski
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