Voltage Drop Mod not really having any effect? Please help!

steveyraff · January 16, 2015, 01:19:10 PM

Hey guys,

Built this simple AMZ booster circuit and it sounds really cool : http://tagboardeffects.blogspot.co.uk/2013/01/amz-mini-booster.html

Now I wanted to add this Fat/Fatter mod: http://www.muzique.com/news/mini-booster-fat-and-fatter/

...which I wired up like this:

Well,

The LED's are operating correctly - they are a little dim, but I guess that is to be expected. However, I am not hearing the drop in headroom that I thought this is supposed to do. Have I done something wrong? I've experimented with many different types of LED as I can see from charts they have different voltages. Have a look at my pic below and maybe you'll notice if I've done something stupid?

If not, is there any way I can make this mod a little more effective ??

All help very appreciated - thank you!

peterg · January 16, 2015, 04:00:24 PM

You could try this...
http://www.beavisaudio.com/projects/DBS/

steveyraff · January 17, 2015, 07:51:52 AM

Quote from: peterg on January 16, 2015, 04:00:24 PM
You could try this...
http://www.beavisaudio.com/projects/DBS/

Thanks man. Just really hoping I can make this switch I've already started a little more effective. I have no idea why it doesn't seem to be doing anything. The LED's take a few seconds to light up too - but I guess that makes sense since the power has to run through the whole circuit for them.

Damn, frustrating when things don't work out

steveyraff · January 17, 2015, 08:16:57 AM

Can I replace the LED's with some other kinds of diodes perhaps? Is there something else I can use in their place to drop the voltage more or something?

induction · January 17, 2015, 08:34:18 AM

You can replace each individual led with two or more leds in series.

steveyraff · January 17, 2015, 08:55:50 AM

Quote from: induction on January 17, 2015, 08:34:18 AM
You can replace each individual led with two or more leds in series.

That's cool! I'll try that today and see what happens

steveyraff · January 17, 2015, 01:19:43 PM

Quote from: induction on January 17, 2015, 08:34:18 AM
You can replace each individual led with two or more leds in series.

Hmm, when I try this, only 2 light up. The extra two on the outsides do not. I'm just joining them as + - + - + - + -

steveyraff · January 18, 2015, 02:51:04 PM

Nope, LED's in series didn't help either.

This is weird. How is this not effecting the headroom at all!?

At one stage, I have 4 LED's between the power and the PCB. For some reason only one of the sets of two works now. But even when all 4 were on, no difference at all!

I'm very confused, but I guess I will just have to give up at leave this as a one knob boost. Really wanted that fat/fatter switch to work!

steveyraff · January 18, 2015, 07:28:08 PM

Anyone any ideas why this is not working for me?

induction · January 19, 2015, 03:55:45 AM

4 led's in series should drop you down to maybe 1 or 2 volts. (You are using a 9V adapter, right? Have you measured it?) If that's not having any effect, then I suspect the switch. Try removing the switch entirely. Let the led's hang from the 9V connection on the board, then alligator clip the 9V wire from the adapter to different places in the led chain, and see if you can hear the difference.

samhay · January 19, 2015, 04:31:21 AM

This is a spot where a pinch of science can be helpful. Can you measure the voltage at the the V+ point on your circuit - where you would normally connect the battery and/or DC jack input - with the switch in various positions?

steveyraff · January 19, 2015, 06:28:33 AM

Ok,

So here's what happens when I remove the switch completely. I simply placed one LED between the board and the power, (the two loose wire ends seen in the above posts photo). I tried this with a few different LED's. Same thing happens every time, upon initial connection the LED lights up for a split second but then goes out again.

Whats going on ? ?

P.S
I've found the only LED that stays on here, is a Ultra bright blue one - although for a split second its very bright, it quickly fades to very dim.

samhay · January 19, 2015, 07:53:35 AM

Assuming the layout you posted is based on this schematic: http://www.muzique.com/amz/mini.htm
then when you first power it up, C4 is a short to ground. It charges via R4 (and the LED) with a 1/16 time constant, so won't take long before it can't pass DC, but for those first few 10's ms while it is charging, you see the LED with about 75 mA passing through it.
Once C4 is charged, relatively little current will flow through the LEDs as the FETS are biased mostly-off, and will thus have a fairly high D-S resistance.

duck_arse · January 19, 2015, 08:58:51 AM

maybe a series pass transistor, with the led string used as a voltage ref to the base would be a more reliable and repeatable (and complicated) method.

steveyraff · January 19, 2015, 06:11:11 PM

Thanks for all the info guys. I'll keep trying. I like it without the mod - so it was just frustrating. But maybe I am just being greedy

pinkjimiphoton · January 19, 2015, 08:10:29 PM

two things come to mind immediately...

well three, but the cap thing has been addressed..

first, are the led's getting blown? they sound like it from your description, you may wanna try a smallish resistor in series with them to limit the current they see...

second, if ya wanna phat/phatter switch, why not just switch the input /and/or output caps instead?
switching the input cap will make it phatter, but increas the distortion somewhat... switching the output cap will let more bass thru and make it phatter and louder. if ya use a dpdt on/off/on switch, you could have the original output cap in the center.... just run two wires from the two points where the cap is on the board to the middle lugs of the switch, and put two more on the outside lugs... then you can have phat/normal/phatter.

may be easier than using led's

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Voltage Drop Mod not really having any effect? Please help!