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DIY Stompboxes => Building your own stompbox => Topic started by: Khas Evets on February 03, 2005, 02:21:42 AM

Title: Brian May Boost Pull Down Resistor
Post by: Khas Evets on February 03, 2005, 02:21:42 AM
I'm thinking I should add input & output pull down resistors to avoid pops in the Brian May Treble Boost. On the input side I would increase R1 from 120K to 1M (or higher?) and on the output side I would add one (not sure what value) after C5 to ground.

Besides having a high enough resistance to avoid tone loss, what other issues should I consider? I'm very satisfied with the sound of this circuit, and I don't want to affect the tone in any way.

(http://server6.uploadit.org/files/Torchy-BMTB.jpg)
Title: Brian May Boost Pull Down Resistor
Post by: MartyMart on February 03, 2005, 03:55:19 AM
Someone "step in" if I'm wrong, but if you changed R1 to 1M and also put a 1M after C5, that should do the trick( no pops ) with no "change" in tone.
Perhaps even 2M2's would be fine......? depends on "loading" within your pedal layout/system as far as I understand.

Marty.
Title: Brian May Boost Pull Down Resistor
Post by: mlabbee on February 03, 2005, 11:48:56 AM
I've done it - 1M  on both ends (R1 and after C5) - side by side with one just like the schem and they sound identical.  

FYI - I also buitl one with a switch to pop between a BC182 and a 2n222 - couldn't hear much of a diff.
Title: Brian May Boost Pull Down Resistor
Post by: Khas Evets on February 03, 2005, 02:53:36 PM
That's interesting. I was going to try a 2N2222 (hfe 375) and a higher gain BC183 (hfe 900). They're in the mail as we speak.
Title: Brian May Boost Pull Down Resistor
Post by: mlabbee on February 03, 2005, 04:17:33 PM
I'll be curioous to hear what you think - I'll admit I have a bit of a tin ear, so I may be missing something.  Be sure to post your impressions when you get a chance to compare.
Title: Brian May Boost Pull Down Resistor
Post by: Khas Evets on February 03, 2005, 06:35:29 PM
Just tried the BC183. It's sounds little louder and more saturated as I had hoped it would. I'm going add this one to a switch.

Has anyone tried higher gain 2N5088 (hfe 1400) or 2N5089 (hfe 1800)? The pins are different, so it's not an easy swap. I may try these at some point.