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.
(http://img17.imageshack.us/img17/1984/molebooster.th.gif) (http://img17.imageshack.us/my.php?image=molebooster.gif)
Can someone help me to wire this effect correctly please?
Many thanks.
Regis
Check your input jack wiring. It sounds like you may have reversed a couple of connections.
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:
(http://img7.imageshack.us/img7/4572/imga0779.th.jpg) (http://img7.imageshack.us/my.php?image=imga0779.jpg)
(http://img17.imageshack.us/img17/8764/imga0781.th.jpg) (http://img17.imageshack.us/my.php?image=imga0781.jpg)
(http://img17.imageshack.us/img17/9428/imga0786.th.jpg) (http://img17.imageshack.us/my.php?image=imga0786.jpg)
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
I can`t tell from your photo but did you use electrolytics for C3 and C2 and if so are they correctly oriented?
No I used non-polarised capa (poly film )... is it mandatory to use electrolytics for C2 & C3?
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
Quote from: mph on March 18, 2009, 10:44:26 AM
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.
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
stupid question, but did you check if the circuit doesn't touch the box on the trace side?
Quote from: Gila_Crisis on March 18, 2009, 04:54:03 PM
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?
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.
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.
Judging from the photos it appears to be oriented correctly.
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
Quote from: mph on March 19, 2009, 04:33:28 AM
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 :P...I think it's your dry signal that you ear, try switching your DPDT and see if you lost the signal.
Quote from: mph on March 19, 2009, 04:33:28 AM
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
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.
Quote from: GREEN FUZ on March 18, 2009, 11:49:00 AM
Quote from: mph on March 18, 2009, 10:44:26 AM
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.
Quote from: CynicalMan on March 19, 2009, 06:19:09 PM
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 :).
Quote from: The French connection on March 19, 2009, 11:18:41 AM
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:
(http://img18.imageshack.us/img18/7825/imga0789.th.jpg) (http://img18.imageshack.us/my.php?image=imga0789.jpg)
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.
Quote from: GREEN FUZ on March 19, 2009, 06:53:34 PM
Quote from: CynicalMan on March 19, 2009, 06:19:09 PM
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!!!
Quote from: GREEN FUZ on March 19, 2009, 02:08:21 PM
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?
Quote from: GREEN FUZ on March 19, 2009, 06:11:10 AM
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!
Quote from: mph on March 20, 2009, 03:05:58 AM
... 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 (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.
Quote
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.
Quote from: mph on March 20, 2009, 03:05:58 AM
Merci Dan!
here's a pic of the input jack:
(http://img18.imageshack.us/img18/7825/imga0789.th.jpg) (http://img18.imageshack.us/my.php?image=imga0789.jpg)
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?
Correct!
Quote from: mph on March 20, 2009, 03:05:58 AM
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.
So why use a shielded wire if you don't ground it? Maybe your input is touching the ground of your shield that goes to your star ground. Change this wire for an ordinary one. You don't need shield wire for that application...just for high gain pedal i think. Moreover, you've soldered the pot directly through the pad instead of using the lug, check if it does'nt short with the box when in position. The layout looks fine for me but i'm learning to, so you can swap the caps and R1 and see if it change something. But try changing your shielded wire before and check your pot for short with the box. Just for the kick, try it outside the box first.
8-P
Bonne journée!
Dan
Quote from: GREEN FUZ on March 20, 2009, 07:21:56 AM
Have a look at this.
http://www.beavisaudio.com/techpages/HIW/hiw1.gif (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.
Quote
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.
Thanks for this very useful link and your sharp observation; I've placed R1 correctly and that works now!!!
You were right, I have made a stupid mistake on my layout.
I have also followed the advices from Dan (thanks a lot too): I use a normal wire for the input and I'm sure there is no shortcut with the box.
But now, there's a new problem:
the mod from Moosapotamus isn't working; when the (R6+R7+R8) combination is grounded everything is normal, but when it's lifted from ground that cuts the signal...
Any idea? It is supposed to let pass a bit more the high frequencies...
Have I understood this mod correctly?
Quote from: mph on March 21, 2009, 05:22:15 PM
Thanks for this very useful link and your sharp observation; I've placed R1 correctly and that works now!!!
You were right, I have made a stupid mistake on my layout.
I have also followed the advices from Dan (thanks a lot too): I use a normal wire for the input and I'm sure there is no shortcut with the box.
But now, there's a new problem:
the mod from Moosapotamus isn't working; when the (R6+R7+R8) combination is grounded everything is normal, but when it's lifted from ground that cuts the signal...
Any idea? It is supposed to let pass a bit more the high frequencies...
Have I understood this mod correctly?
You lifted it from ground but i think you have to
take it out from the path and still ground the 430k...I think you must switch between ''with or without the 43k resistor'' not between ''with or without ground''...I don't know if i'm clear. :icon_confused:
Bonne soirée!
Dan
Merci Dan,
I was a bit confused with that ground stuff and resistor switching. Now that's working perfect ;)
Thanks again for all your help
Bonne soirée également.
Regis
Génial! Does it sound good? Do you use it with bass or guitar?
Dan