Help:Brian May treble Booster

[burningman]

I've quickly prototyped the hand-drawn 'official' schematic for Brian May's treble booster. I was wondering if anyone knew how to cut down the extraneous noise without loosing tone or volume? Also does anyone know what kind of potentiometer I should use and how to adapt it to this project? Thanks,
Ian.

[DougH]

I was wondering if anyone knew how to cut down the extraneous noise without loosing tone or volume?

Use metal film or carbon film resistors.

Also does anyone know what kind of potentiometer I should use and how to adapt it to this project?

Sub the collector resistor with a log-taper pot, same value. Wire it like a Rangemaster gain control.

[burningman]

Thank you for the advice Doug, I'll try that out right now.
Cheers,
Ian

[Renegadrian]

Built it the past night - doesn't work...
No sound at all...

I used Andy's layout HERE - I checked it with the schem and it seems correct, but one thing...It misses the 1k res., so after the input I have the 100k res as pull down (I had no 120k, but I believe it should be the same?) and the 4,7 nF cap to B of the 2n5088. The other layout I found has that resistor and the signal goes thru it before reaching the B.

Some voltages.
battery 8.86V
after the 100 ohm res 8.85V

2n5088
C 0.43V
B 1V
E 0.42V

[Renegadrian]

[Timmay!]

Hi Renegadrian,

I've no experience with this circuit but I'm planning to have a go soon.

Omitting the 1k resistor to base will change the base biased.  Maybe the 2N5088 it's outside it's working range?  Also, is it possible the transistor is bad/got fried with static?  Maybe you can test it with your meter, or sub a fresh transistor.  Also, while the transistor pinouts look fine in the layouts you posted, I guess it's an easy thing to mix-up:  BC182L = ECB; 2N5088 = EBC.

Good luck!
Tim

[Renegadrian]

Tim, thx for the reply...
I tried several 2n5088 and a 2n3904 as well (I read it should work too...)
Altough the pinout is different, C B E are tied to the right components as per the schem (B receive signal, E is to ground thru the 47µF, ecc)
Dunno why this thing doesn't work...Grrrr

[Renegadrian]

I have bought some BC182L - I hate when simple circuits don't work and can't find errors...GRRRRRRRRRRR

[Gus]

Using the schematic I found at GEOFEX.
http://www.geofex.com/images/BrianMayboost.jpg
Lets use Ohms law and 9VDC as the supply voltage You can sub in what ever supply voltage you have for the 9VDC and redo the math.

The bias resistors are a 100k a 1K and a 22K for a total series resistance of 123K
9VDC / 123k = about .073ma

.073ma x 22k = about 1.609VDC at the base

should have about 1VDC at the emitter (about .6Vbe (1.6- .6))

1VDC/2.4ma = about .416ma

emitter current close to collector current with Si higher gain BJT and a circuit like this.

6.8VDC x .416ma  =about 2.8VDC across the collector resistor, 9 -2.8 =about 6.2VDC at the collector.

First thing to try remove the transistor and measure if you have about 1.6VDC at the base node.

[Renegadrian]

Gus, THX for your precious reply - tranny taken out,  got 1,57V...now what?  
----------
Also I have 8.90V (the same reading of the battery) at C

[Gus]

Your C and E readings being about the same voltage is not right.

I would check the C and E legs of the circuit with the transistor out of circuit and no battery and using a meter set to Ohms you should read about 6.8 K from +9VDC node to the collector and open from +9VDC node to emitter.

Transistor still out of circuit you should read 2.4K from ground to emitter and open from ground to collector the meter might take some time to stop at 2.4k because of the bypass cap

Check you transistor pinouts.  Look at the fairchild semiconductor site you should find PDFs of the transistors

[Renegadrian]

No battery connected and no tranny, black probe to ground, here are the readings...
C 183k
B 21k
E 2.6k

No battery connected and no tranny, red probe to the 9V in, here are the readings...
C 65.5k
B 97.5k
E 122k

The tranny is a 2n5088, it has the standard CBE pinout (flat side on the right) - I can read its hfe of 500 putting it in my DMM NPN socket. I already used some of its "brothers" from the same batch for other (working) projects and their pinout is correct.

THX again Gus

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Funny note - with the circuit engaged, strumming the strings gives no sound - If I disconnect the battery just after that strum, some effected sound can be heard for some seconds and then fade out...

[Gus]

What value is the collector resistor?  The schematic has a 6.8K.  Your reading of +9 to collector node no transistor installed is 65.5K

[Renegadrian]

 

Gus, as you alredy understood and correctly pointed out, the problem was that wrong value resistor...my bad...
I shouldn't build late at night...
Now it works like a charm...THANK YOU so much for your precious help!!!