# Depth mod cap values?



## rpurdue (Nov 9, 2011)

I want to do a depth mod on my 5153. I've been reading on the appropriate caps to use. Soldano recommends a 0.0047u cap but i've also read that you can use anywhere from 0.002u to 0.01uf. Can someone please explain the relationship of cap value to the bass response? If it goes higher does the bass response of the mod diminish and lower the bass increases?


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## LydianGuitars (Apr 18, 2013)

The depth mod is basically part of the negative feedback loop of the amp. The presence and depth (aka resonance) circuits basically feed back part of the signal into the power amp's input to control the amp's output. The presence circuit is a low pass filter that only feeds back the everything under a certain frequency while the resonance circuit is the opposite (high pass filter). The more negative feedback you have, the more the amp is "controlled". 

You can calculate the cutoff frequency with this forumula: f = 1 / (2π RC)

The cap you mention is relative to the R value (resistance) it is associated with. The cap value will determine how much low end you let through without going through the feedback loop, thus, emphasizing those frequencies. You have to watch out though because if you go too low, your tone will lose definition and the amp will work harder.

Another thing to consider is which tap you select for the feedback loop: the 4, 8 or 16 tap. The effect gets more noticeable as you move from the 4 ohm tap to the 16 ohm tap.

The 0.0047uf cap is typically used with a 1M pot.


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## rpurdue (Nov 9, 2011)

Thanks for the great info. Mine is from a selector switch so is that still relevant? I think I used the 16 ohm tap though. So for instance the 0.0047u will be a broader range and a 0.01uf will be a lower frequency that's more narrow? Does the value of the pot also affect tone or just the sweep to bring on the effect?


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## dcole (Oct 8, 2008)

The smaller the capacitor value, the more mids that will be increased along with the bass. Basically if you goo to large in value, it won't have any effect on the bass, just sub bass regions and if you go to small in value it will start having an effect on the mids region of the frequency spectrum so there is a certain range of values that will be effective. 

The pot value helps swamp the capacitor to allow the effect to be brought in gradually and also helps not disconnect the feedback network entirely at low frequencies.

If you were bringing this amp into me, we could try a few different values while you play to see what cap value you like best. Send me a PM or text if you would like to do so.


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