Effect of series resistance

[David Schwab]

Hi Mike,

thanks for the detailed answer.
So, if I understand right, your advice is to put a resistor in parallel to Silent Circuit output, to obtain a lower resistance to ground (about 200 ohm) path for the negative wire from the pickup....?

The normal current consumption from the circuit is 0.5 mA: maybe I can try a progressive lowering of the output load resistance monitoring variations on the circuit current absorption.

What are you trying to achieve by all this?

What is the humbucking quality you obtained? The Silent Circuit I'm testing is mounted on a P90 equipped guitar: the result is good, but the hum rejection from the RWRP combination from both pickups in parallel is largely better.

Keep in mind that the silent circuit must be in an unshielded part of the guitar. On the guitar I removed that from, they had a brass shielding plate under the controls, that was cut away from the dummy coil. Does yours have the trim pot? You adjust that to balance the hum.

The silent circuit is for being able to use a single pickup without hum. Sure, two pickups will reject hum, but do you want to use two pickups all the time?

[Marco Pancaldi]

Hi David,

I'm trying to obtain two things:

1 - a good, flexible method to use the Silent Circuit only when strictly necessary: from schematics on Music Man forum, I noted that in some cases the circuit is "put off" grounding the "input" wire to the circuit (this wire is connected to the coil-preamp connection, and when grounded, no hum is output from the circuit). But the circuit is never bypassed. Obviously, this scheme is simpler (needs only a switch closing "to ground") than a bypass. If I can obtain less "to ground" resistance for the pickup wire, maybe the "off" position can sound more transparent, without necessity to use a more complicate scheme to true bypass the circuit.

2 - I worked a lot with the trimmer, noting that the "best possible" setting (with a single pickup) is never good as two SC pickups in RWRP combo. Putting the trimmer at max., the added noise have lot of hi frequencies (more then the pickup), maybe due to the dummy coil geometry. Maybe I can try to put a cap in parallel to the active input (using the "input" wire) to "equalize" the hum from the dummy coil before working on the trimmer in search of perfect nulling.

And yes, the coil is not shielded from the brass plate.
Tomorrow I will mount an external true bypass switch, I promise a definitive report and opinion.

m.

[David Schwab]

Interesting. I haven't tried the thing out. Sounds like it doesn't work as well as one would think. Probably the coil geometry, and maybe the core. I wonder what they are using.

As Mike pointed out, he made his to me more sensitive to hum. Mike's circuit is also simpler and more elegant.

[Marco Pancaldi]

Hello,

my tests so far:

I used
- Peavey Classic 30 with Jansen speaker, mid-low volume, clean and distorted;
- Tannoy little studio monitors, bypassed Tech21 pedal (for 1M buffering) and a little mixer, using extreme EQ filtering to expose hi, mid, lo frequencies to specific analysis in a full range system;

I tested the guitar (MM Axis Sport, two MM90 PUs, perfectly setup, new 10-46 strings) in all PU positions, with volume @ max. and @ 6-7.

Hard bypass made with DPDT, putting the negative wires from PUs alternatively to ground OR in contact with the Silent circuit output.

Results: I was not able to detect differences between ON and BYPASS, apart hum reduction. Maybe, with Silent Circuit ON, a very little "active" flavor (more string separation, compression, air) emerges, but I'm not sure I can track this in a blind test.

So, the only things to note is a little microphonicity from the dummy (not important in this rear routed guitar, maybe in a pickguard mounted) and a little hiss (noticeable only with full distortion). The hum reduction is useful; not so exciting.
I think the Mike's circuit is a possible simpler (and better) solution.

Now I'd like to investigate more on a simple, little, versatile dummy coil geometry (half P-bass pickup?) and a simple method to emulate different PUs responses (an RC network before the JFET?) for the best nulling.

Any comments and expanations about relation between coil caracteristics (geometry, turns, gauge, core) and produced hum (intensity, harmonics and spectral content) is welcome. Let me know if starting a new topic is more appropriate.

Thanks all.

m.