Tuning amps for different pickups

[titser_marco]

Hi guys! I know that some amps were voiced specifically for certain guitars and pickups, and I was wondering about:

1) How is this done? Is this a matter of changing the coupling caps in the gain stages?

2) If this were to be made switchable, i.e. between single coils and pickups, would there be any danger in terms of voltages etc?

[10thTx]

There are numerous ways to voice an amp for a specific guitar or pickup.

One way is coupling caps. Look at a schematic of a Dumble amp and note how they do a mid-boost and PAB (pre-amp boost) both are relay switchable.

You can parallel caps or put caps in series using a switch.

You can also have switchable cathode caps. You can switch cathode resistors and caps both.

You can have bright caps.

You can also have switchable features in tone stacks for voicing.

And the tone stack itself can help voice between single & humbucking pickups by increasing mids for single coils as an example.

Speakers, # of gain stages, boosts, etc ..... Lots of ways to do this.

with respect, 10thtx

[pdf64]

I find that a switch for different values of bright cap is very beneficial to quickly dial in the tone after a guitar swapover (LP to Strat).

[M Fowler]

Change the input impedance or have a switch to go from 150k, 470k, 1m, 5m, etc.

[Structo]

On my dumble clone I have two cathode bypass caps on a switch.
The switch is on the back near the footswitch jack.

.68uF and 4.7uF

With the switch closed the total capacitance is 5.4uF which can help single coils sound fuller.
When the switch is open, it is .68uF which is good for humbuckers.

The resistor helps avoid pops.

[10thTx]

Structo,

Did you mean to draw it the way you did? It would seem like the way you drew it would have the 4.7uf always in the circuit (at some level).

I always thought it was done like the schematic I've attached? Maybe that's not correct? I'm not saying that the way I thought is correct. Just asking an honest question because I don't know the answer?

Please advise.

With respect, 10thtx

[Firestorm]

Mike Holland built in the '90s and several of his had a variable slope resistor billed as a pickup matching tool. Big cap to block DC, then a pot as the slope resistor. Useful because it shifts the tone stack frequencies.

[JazzGuitarGimp]

The way structo drew it is correct in terms of being silent when switching the cap in and out of the circuit. The goal is to keep the switched end of the cap referenced to ground at all times, otherwise, the cap would need to charge (or discharge) when the switch changes states, thus causing a pop in the audio. But I question the value of the resister: at only 4.7K, that 4.7uF cap will always be partially in-circuit, adding some additional gain to the stage when switched out. A much higher value, say 1Meg, will allow the cap to effectively be completely switched out of the circuit, and will still give the cap its needed ground reference for silent switching.

[Reeltarded]

Mike Holland built in the '90s and several of his had a variable slope resistor billed as a pickup matching tool. Big cap to block DC, then a pot as the slope resistor. Useful because it shifts the tone stack frequencies.

Very neutral tone stack, slope, and selectable peaking values over a second stage mixer.

Slope is the key to happiness. It just is.

[titser_marco]

Mike Holland built in the '90s and several of his had a variable slope resistor billed as a pickup matching tool. Big cap to block DC, then a pot as the slope resistor. Useful because it shifts the tone stack frequencies.

Very interesting! What values did he use? And curious, how does a bigger/smaller slope resistor affect the tone stack? I currently have 100K on mine.

[pdf64]

The slope resistor controls the level of the bass and middle shelves relative to the treble shelf; have a play with it in TSC http://www.duncanamps.com/tsc/download.html

[Colossal]

Try 33k as a fixed resistor and add a 100kB pot in series for a variable slope control. This depends on the preamp topology of course, so for example, if working with a hot rodded Marshall preamp, the sweet spot can often lie in the 39-47k region to get the midrange content really singing and the low end tight.

[Reeltarded]

All my amps get 33k with a 50k pot and all my guitars sound best between 40ish and 60ish. strats, teles, les pauls, pointy metal things.. every guitar.

[Smokebreak]

The way structo drew it is correct in terms of being silent when switching the cap in and out of the circuit. The goal is to keep the switched end of the cap referenced to ground at all times, otherwise, the cap would need to charge (or discharge) when the switch changes states, thus causing a pop in the audio. But I question the value of the resister: at only 4.7K, that 4.7uF cap will always be partially in-circuit, adding some additional gain to the stage when switched out. A much higher value, say 1Meg, will allow the cap to effectively be completely switched out of the circuit, and will still give the cap its needed ground reference for silent switching.

Yep, I find that 100K is big enough for a leg to ground. I just did one with a 100KB pot wired as variable resistor and called it grind. Here's also 1 way to do 3 way silent cathode switching with on/off/on spdt.

[Andy Le Blanc]

slope control in the tone stack works good.

A guitar 5way switch as a selector works for say brite and tone shift, and bypass caps.

the real approach is to vary the input impedance to match or mismatch the pickup