Mole Booster need help please

[mph]

Hello

I've just finished the build of a Mole bass booster, I used this schematic:
http://www.muzique.com/schem/mole.gif

I also add the mod from Moosapotamus which lifts a resistor from ground using a switch.

the transistor I used is a BC549C, and I had not the good values for some resistors so I put some in series to get the good value (it takes a bit more place than it should)...
My problem is that the effect is "on" as soon as the batterie is plugged, when I plug the input jack it cuts everything.
I is ridiculous I know, but I have build some tiny circuits already, and to my very little experience I don't understand where is the bad connection.



Can someone help me to wire this effect correctly please?
Many thanks.

Regis

[GREEN FUZ]

Check your input jack wiring. It sounds like you may have reversed a couple of connections.

[mph]

Thank you

yes, I have checked the input connections; in fact the pot was acting like a hum boost when the output jack was connected with the battery, so that made me think the problem was a kind of reverse connection (in fact that was just a huge "hum" that disappeared when I plugged the input jack). sorry fro this mistake.
Anyway I have a very very little signal on the output when everything is connected (like -90dB pad)... I have changed one capa I thought it was dead but with no result.
Do you think my layout is correct?

here's my dirty work:




I have checked the voltage on the tranny:
c: 9,52V
b: 3,23V
e: 2,60V
(for a 9,55V battery).

Do you have any idea of my mistake?

thanks for your help.

Regis

[GREEN FUZ]

I can`t tell from your photo but did you use electrolytics for C3 and C2 and if so are they correctly oriented?

[mph]

No I used non-polarised capa (poly film )... is it mandatory to use electrolytics for C2 & C3?

[The French connection]

Hi! Those 3.3 µF caps look a bit small for me...are you sure they are 3.3 µF? What's the number on it?

Dan

[GREEN FUZ]

No I used non-polarised capa (poly film )... is it mandatory to use electrolytics for C2 & C3?

I`m not sure about C3 but I believe C2 is the decoupling cap and needs to be polarised in order to block DC.

[mph]

Dan, the capas are marked 332G, you're right that mean they are 3,3nF !!!
thanks for pointing this mistake!!!

Green Fuz, I didn't know the decoupling cap should be polarized (!) it's a shame! I will change them C2 and C3 asap!
many thanks

[Gila_Crisis]

stupid question, but did you check if the circuit doesn't touch the box on the trace side?

[mph]

stupid question, but did you check if the circuit doesn't touch the box on the trace side?

thanks; but for testing I am sure there's no shortcut with the box as the circuit is hanged in the air by the cables... if it's working one day and I finally put the circuit in its enclosure, I will put some cardboard as insulation to prevent this problem.

I have changed the 3,3nF caps for the good values, but I used 3,3uF tantalums (I didn't have "normal" electrolytics in my stock)... C3 has the + connected to R2, and C2 has the + connected to R1/C1.
I have a bit more signal, but it's really weak, I have to push my little test amp to the max to hear something.
Interesting thing: when I remove the battery with the "in" and "out" connected, I have a good volume boost (it is still a lot weaker than the dry signal however)... strange, this sounds better without battery???
Now on the tranny there's:
c: 9,55V
b: 0,82V
e: 0,21V

Any idea of what's wrong now?

[GREEN FUZ]

It could be a number of things. I have a couple of minor reservations about your layout that may or may not be responsible. I notice on your layout you have the input and output jacks connected with a ground wire. As the circuit is now in a metal enclosure this is not necessary and might well be creating a ground loop. If you haven`t done so already I would recommend removing that wire.

[Ripthorn]

Did you make sure your pinout is correct?  A lot of times a transistor is wired so that when power goes to it, it blocks the signal.  that sounds like it might be happening here.  Make sure your transistor is NPN and not PNP and make sure that the pinout is right.

[GREEN FUZ]

Judging from the photos it appears to be oriented correctly.

[The French connection]

I got the feeling you have inverted the ground sleeve and the battery switch lug on the input jack but i can't see all the lugs on the photo (the big black wire that come from the DPDT...take macro shot of your input in the way we can see all three lugs. Is your DPDT is a on-on switch BTW or On-OFF-On?

Salut cousin!
P-)
Dan

[The French connection]

Interesting thing: when I remove the battery with the "in" and "out" connected, I have a good volume boost (it is still a lot weaker than the dry signal however)... strange, this sounds better without battery???

So, not really a boost if it's weaker ...I think it's your dry signal that you ear, try switching your DPDT and see if you lost the signal.

Now on the tranny there's:
c: 9,55V
b: 0,82V
e: 0,21V

Any idea of what's wrong now?

Given 9.55(43K)/(430K+43K)= 0.86V i got the feeling that your voltage on the base is ok! Not sure for the other one...

Bonne chance!
Dan

[GREEN FUZ]

I`ve had some niggling doubts about your layout, principally the placement of R1. I`m not convinced it`s doing what it`s meant to which is contributing to the biasing and dictating the output voltage. Please forgive the vague explanation but I have been trying to educate myself about impedances and still have only a feeble understanding of it.

It`s more of a sneaking suspicion than a confirmed idea and I`m hoping someone more qualified than I will explain whether or not R1 might have a bearing on your issue. In any case, it can`t do any harm to move the resistor.

[CynicalMan]

No I used non-polarised capa (poly film )... is it mandatory to use electrolytics for C2 & C3?

I`m not sure about C3 but I believe C2 is the decoupling cap and needs to be polarised in order to block DC.

Decoupling caps don't need to be polarized. Any capacitor with the right value will do.

[GREEN FUZ]

Decoupling caps don't need to be polarized. Any capacitor with the right value will do.

Thanks. I stand corrected. I thought the polarization was a function of the DC blocking. Obviously not. I`m learning a lot today  .

[mph]

I got the feeling you have inverted the ground sleeve and the battery switch lug on the input jack but i can't see all the lugs on the photo (the big black wire that come from the DPDT...take macro shot of your input in the way we can see all three lugs. Is your DPDT is a on-on switch BTW or On-OFF-On?

Salut cousin!
P-)
Dan

Merci Dan!
here's a pic of the input jack:

The star ground is on the main ground lug of the jack, and the -V is on the ring lug... I think it's correct isn't it?
the big black wire is the signal input, it's shielded but shield is not connected to the DPDT switch.
Yes, this switch is a ON/ON and seems to work correctly, I have my full dry signal passing thru when bypassed.

Decoupling caps don't need to be polarized. Any capacitor with the right value will do.

Thanks. I stand corrected. I thought the polarization was a function of the DC blocking. Obviously not. I`m learning a lot today  .

Thanks I am learning too!!!

I`ve had some niggling doubts about your layout, principally the placement of R1. I`m not convinced it`s doing what it`s meant to which is contributing to the biasing and dictating the output voltage. Please forgive the vague explanation but I have been trying to educate myself about impedances and still have only a feeble understanding of it.

It`s more of a sneaking suspicion than a confirmed idea and I`m hoping someone more qualified than I will explain whether or not R1 might have a bearing on your issue. In any case, it can`t do any harm to move the resistor.

well, on the schem R1 is in parallel with C1... do you suggest to remove this resistor and replace the connection with a simple jumper?

It could be a number of things. I have a couple of minor reservations about your layout that may or may not be responsible. I notice on your layout you have the input and output jacks connected with a ground wire. As the circuit is now in a metal enclosure this is not necessary and might well be creating a ground loop. If you haven`t done so already I would recommend removing that wire.

I have done another test with all the jacks out from the enclosure so they don't touch the metal anywhere: it is exacltly the same, near no signal passing thru the circuit.

Thanks a lot for all your support!

[GREEN FUZ]

... on the schem R1 is in parallel with C1...

Yes but on your layout R1 is effectively bypassed and is now in the audio signal path. That, at least, is my understanding and as you may have noted I am no expert. I believe it is there to limit the current and has a relation to the output voltage. It also, as I read in another post, stops the output signal leaking into the power supply (or vice versa?). Not sure about this but I`ve been reading a lot on boosters in an attempt to understand this one and I`m starting to feel like Mr Knox from Fox in Socks.

Have a look at this.

http://www.beavisaudio.com/techpages/HIW/hiw1.gif

It`s very similar to the Mole/Hog`s foot booster where R3 corresponds to R1 on the schem you posted.

do you suggest to remove this resistor and replace the connection with a simple jumper?

No, just move it so it is directlyin the path between power supply and collector.