sub for 3.3uF NP cap in AMZ mini-booster?

[Wounded Paw]

I can't find a 3.3uF non-polarized capacitor locally, is it safe to sub in a 1uF non-polarized cap?  What effect will that have.

I have a 3.3uF tan cap that appears to have a - marking on one side, I take it that means it's polarized?

[R.G.]

Use the 1uF. The cap is driving an impedance of about 500K. With a 1uf, the rolloff at bass is F = 1/(2*pi*500K*1E-6) = 0.318 Hz. With a 3.3uF cap that goes to 0.096Hz. The lowest note on a guitar in standard tuning is 82Hz.

By the way, putting a 1K resistor between the Q1 source and the Q2 drain and taking the signal off the source of Q1 improves the circuit's performance a lot. See "Modding your Mu-Amp" at GEO.

[MikeH]

By the way, putting a 1K resistor between the Q1 source and the Q2 drain and taking the signal off the source of Q1 improves the circuit's performance a lot. See "Modding your Mu-Amp" at GEO.

So you mean put a 1K resistor between the Drain of Q2 and the junction of C2, C3 and the source of Q1?

[R.G.]

No. Leave C3 attached to the drain of Q2; call this point 1. Leave C2 attached to the source of Q1; call this point 2. In the schematic as it is now, these two points are attached by a wire. Break that wire. Now point 1 is still the junction of C3 and Q2.  Point 2 is still the junction of C2 and source of Q1. But the two points are not connected. OK so far?

Now put a 1K resistor between point 1 and point 2. C3 is still attached to drain of Q2. C2 is still attached to source of Q1. But now there is a 1K resistor between the source of Q1 and the drain of Q2.

C3 stays with Q2. C2 stays with Q1. In between there's a resistor.

[mnordbye]

How does that improve the circuit? I'm already "over the top" pleased with my mini-booster.

Magnus Nordbye

[R.G.]

It improves the circuit by providing it a low impedance output. It will drive other circuits without treble loss, and with higher gain.

[DuoJet]

I'm having the same issue! Would a 563k cap also be a suitable substitute? I have one on hand and would like to get this project started.

[Mark Hammer]

If a 1uf cap provides for a rolloff around 0.3hz, then a 560nf cap is going to move you up to that dangerous dangerous territory of rolling off around 0.6hz. 

Bottom line?  Don't sweat it.  Use 560nf.

[DuoJet]

If a 1uf cap provides for a rolloff around 0.3hz, then a 560nf cap is going to move you up to that dangerous dangerous territory of rolling off around 0.6hz. 

Bottom line?  Don't sweat it.  Use 560nf.

OK, maybe I'll risk it. I'll be sure to wear a full body crash suit and the requisite eye protection when I test it. 

[WGTP]

.1uf is used in many designs with the Mu.  Stick a .22uf greenie in there for max bass and resonable size.   

[kbibs]

RG,
I've read your explanation several times and compared it to your "Modding the Mu-Amp" article, (thanks for that by the way), and I keep concluding that you have your cap #'s reversed. C3 should still go to source of Q1 and C2 should go with Drain of Q2, right? ... if not I'm totally confused!

[soggybag]

I seem to recall a quote from Jack Orman saying the 3.3µf cap was chosen because it was what found on his bench at the time.

[slacker]

C3 should still go to source of Q1 and C2 should go with Drain of Q2, right? ... if not I'm totally confused!

Yeah that's right, or it matches the "mod your mu amp" example anyway.

[rosssurf]

Viewing this layout,http://www.aronnelson.com/gallery/main.php/v/French+connection/Vero+Layout/AMZMosfetBoost.jpg.html how would I acomplish what you wrote below.? I am not real good at truly understanding the signal chain of a circuit, I am just a paint by numbers kind of guy. Would I simply cut the traces somewhere and add the 1K resistor? Is it even  possible to do this mod with this vero layout ?

No. Leave C3 attached to the drain of Q2; call this point 1. Leave C2 attached to the source of Q1; call this point 2. In the schematic as it is now, these two points are attached by a wire. Break that wire. Now point 1 is still the junction of C3 and Q2.  Point 2 is still the junction of C2 and source of Q1. But the two points are not connected. OK so far?

Now put a 1K resistor between point 1 and point 2. C3 is still attached to drain of Q2. C2 is still attached to source of Q1. But now there is a 1K resistor between the source of Q1 and the drain of Q2.

C3 stays with Q2. C2 stays with Q1. In between there's a resistor.

[R.G.]

Viewing this layout, (AMZMosfetBoost) how would I acomplish what you wrote below.? I am not real good at truly understanding the signal chain of a circuit, I am just a paint by numbers kind of guy. Would I simply cut the traces somewhere and add the 1K resistor? Is it even  possible to do this mod with this vero layout ?

It's not possible. That's the "MOSFET Booster", not the same animal as the "Mini-Booster", which has two stacked FETs. The names are confusingly similar though.